Fuselage Construction

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01/09/03 PLANS vs. HP BELLY FORMERS, INSTALLATION
01/09/03 PAINT INSTEAD OF POWDERCOAT, SANDBLAST, TORGINOL
12/21/02 TAILSPRING TUBE
12/16/02 GAP IN LOWER FAIRING ANGLES, J-STRIPS, RUDDER PEDAL PINS
10/31/02 BELLY FORMERS STOCK vs. HP
10/27/02 CANOPY JIG, CANOPY BUSHING INSTALLATION
08/23/02 FUSELAGE TABS
06/03/02 FLYING WIRE FITTING ANGLE
11/03/01 STABILIZER BRACE ATTACH FITTINGS
11/02/01 STABILIZER INCIDENCE
10/08/01 ANTI-STAGGER HOLE IN AFT CABANE FITTINGS
10/07/01 PRE-BENT CABANE FITTINGS, CABANE FITTINGS INSTALLATION
08/12/01 TAIL SPRING HOLES
05/10/01 TAILSPRING TUBE
05/10/01 GEAR BUSHINGS
05/01/01 TAILPOST
04/15/01 WING FITTINGS, WIRE FITTINGS, WING INCIDENCE
04/14/01 LASER CUTTING STEEL, WATERJET
01/09/01 BELLY & SIDEWALL FORMERS, STANDOFFS, 4130A
01/08/01 CONTROL RODS, HARDWARE, QUADRANT, PLATING
12/22/00 LASER CUTTING, PLASMA CUTTING, EDGE PREP, BEFORE BENDING
12/20/00 ROLL BAR
12/19/00 HARNESS, SECONDARY SEATBELTS, BUSHINGS
12/19/00 AIR TANK MOUNT TABS
12/17/00 BENDING LONGERONS, CONSTRUCTION METHODS, TABLE, CROSSMEMBERS
12/03/00 TABLE, LONGERONS, CROSSMEMBERS, DIAGONALS, LADDERS, TAILPOST
11/11/00 TUBE TUCK AFTER WELDING, POLYESTER FILLER ON LONGERON JOINTS
11/07/00 BUNG LOCATION, LONGERONS, LAYOUT
11/06/00 ENGINE MOUNT, JIGGING
11/05/00 REAMERS
10/18/00 DARINS FUSELAGE MODS
10/18/00 FUSELAGE MODS, KEVIN'S OPTIMIZATIONS
10/18/00 BUNGS, REAMER, TAP
10/17/00 LINSEED OIL
10/13/00 LAYOUT, TABLE, SHIMS, STAINLESS LASER BEAM
10/05/00 CORROSION, RUSTLICK
09/02/00 CONSTRUCTION METHODS, TABLE, SHIMS, TUBE BENDING, LONGERONS, ROSETTES
09/02/00 CONSTRUCTION METHODS, TABLE
08/23/00 METAL PAINT PREP, POWDERCOAT, SANDBLASTING
08/03/00 TOP & BOTTOM VS.SIDES
07/18/00 LAYOUT
06/13/00 SQUARING WINGS, LOWER WING FITTINGS
06/07/00 FUSELAGE MODS, FUSELAGE CONSTRUCTION METHODS, JIGGING, TUBE SIZES
06/05/00 REAR SEAT MODS
05/11/00 TURTLEDECK CONSIDERATIONS FOR SHORT FUSELAGE
05/04/00 FUSELAGE MODS, CANOPY CONSIDERATIONS
05/04/00 FUSELAGE MODS, SHORT ENGINE MOUNT
04/27/00 FUSELAGE MODS, SPORT AVIATION ARTICLE, HISTORY

   

01/09/03 PLANS vs. HP BELLY FORMERS, INSTALLATION

Kevin, I have the belly formers I bought from you, but they don't look long enough to work to the dimensions in the plans. Are they different than specified?
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Monty, part of our restyle of the HP fuselage was to take the pot belly out of the bottom profile. The stock former shapes will work also. We resized the belly formers both in depth and spacing of the points. On ours, sta 24.9 is 6" deep with 18" wide flat to match the firewall so the cooling air tunnel can be square. Sta 48 on ours is 5" deep with a 17" wide flat. The 3rd sta on the belly is 2.75" deep with a 14" wide flat. All these measurements are made from the bottom of each station tube to the surface of the flat angle that touches metal or fabric.

I think all these changes are noted on Darin's site as he and I have chated about it before. Also, there you will find that the idler brackets mounted to the rear seat are rotated up a bit to allow the pushrod to clear the new belly former shape under the rear seat.

By the way, all our side formers are the same basic shape as the plans except that the rear ones at the rear seat station are longer that plans to account for the added length of that tube after the seat was angle more. KK
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Kevin, What angle do the belly formers go at?

I thought they simply bisect the angles formed by the bottom longerons where they bend, but I'm not sure now. I just realized that if I don't set them at the proper angles, the sheetmetal overlap may not work out with the lasercut panels I bought from you. After I saw this picture of the belly former at FS 24.9 (1st former sta) obviously leaning aft, I started to wonder and thought I should ask.

Also the formers at the 3rd sta look like they are leaning aft too, maybe my camera is catching wierd angles! Thanks, Darin
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Darin, you are correct in that all 3 belly formers and the left and right rear most side formers lean aft slightly on the fuselages we build. The belly formers are tilted just enough to split the angle change from panel to panel. This allows best fit. The rear most side formers are tilted back too to allow best transition between fabric and metal side panel. Just another one of those little detail items that comes from years of building airplanes. Many such details are built right into our parts. For you, you need to match the sheet metal you bought from us when installing your formers on your shortened fuselage frame. For others building from plans to plans length fuselage dimensions, installing the formers as shown in the plans may be the best fit for them. KK
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Thanks Kevin, I appreciate not having to build hundreds of airplanes to learn the finer points of doing a quality job. I think I'll mark the centerlines of the panels, then tape them together to see where to put the formers so they break in the right spots. About how much overlap should I set up in the panels? It looks like I could set up anywhere from 1/2" to 3/4".

Note added January 2003: From my 1st quarter 2003 build log, here's a picture of what I ended up doing to set my formers properly.
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Darin, all the panels are designed to overlap 3/4". Same at the rear ends of the sides and belly. The formers are 3/4" wide and the panels should cover the former completely.

The underlapping edge of the side and belly panels may be longer than the above 3/4" overlap. It is done that way by design to allow for variations. Trim the underlap after all are fitted and drilled. KK


01/09/03 PAINT INSTEAD OF POWDERCOAT, SANDBLAST, TORGINOL

Monty, I understand you are planning to paint your fuselage frame instead of powdercoating it. Why, and what are you planning to use?
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One reason I didn't want to powdercoat is I'm sure I've got some small holes here and there that will have to be touched up. I have a small pressure feed sand blaster. You have to remember that I live 90 miles out in the country from facilities that could powdercoat plus I don't want them to scrub off very much tubing thickness which means I would have to be standing right there, then haul it home. Easier and just as effective to do a good paint job.

I'm planning to use an epoxy primer such as DuPont Corlar or PPG DP-40, then the top coat that Aviat uses, which is called Torginol Epoxy. I got the name and source from Danny Hiner at the Pitts factory. Danny says this is what they use on the factory airplanes and Poly-tac or Super Seam will not soften it. I have NOT used it so I'm taking Danny's word, which is usually good. It supposedly requires an undercoat.

Torginol, Inc.
710 Forrest Ave.
Sheboygan Falls,Wisconsin 53095-0102
800-558-7596

The color I will use is #9460 Light Grey. I purchased 1 gallon of Part A and 1 Gallon of Part B plus gallon of thinner per mixed gallon. Coverage is 300 sq.ft. at 6 mil thickness wet, which dries to 3 mil. - Monty


12/21/02 TAILSPRING TUBE

I just welded my tailspring tube onto the tailpost, and now I need to clean out the weld penetration so the tailspring will slide in. Anyone have a good method?
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I ground most of the burrs and dingle berries out with a long shanked stone but the socket was still a little rough and tight. So, I then purchased one of those brake cylinder hones, one with a spring that can be adjusted for stone pressure. Cost about 8 bucks at a NAPA store. Put it in an air drill, criscoed up real good and honed up the inside of the tube. Spring fits nice, smooth, a light push fit. Took about 15 mintes. - Monty B.


12/16/02 GAP IN LOWER FAIRING ANGLES, J-STRIPS, RUDDER PEDAL PINS

Kevin, I was sorting through the fairing angles (j-strips) I bought from you, trying to figure out where they go with the help of some measurements I made off Jimmy's fuselage. I discovered there is a gap between them of about 1.5 inches between FS 24.9 and FS 48.0. What is this gap for, or why didn't you make it one strip? See  Picture #1  and   Picture #2

Also, I measured out Jimmys strips at 9 and 10 inches, while mine here are 9.5 and 10.5 inches long. Should I trim mine to get that same 1.5" gap or go with what I have? I'll probably trim them anyway, a gram here a gram there...Thanks, Darin
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Darin, the gap needs to be wide enough to allow the pedal pivot shaft to pass thru the gap. That is the reason for the gap. It also allows you to get a drill and reamer in to clean the bushings prior to installing the pedal shaft. Your strips are longer because we made this gap smaller in later fuselages. You have the later strips, Jimmy's is the earlier version. The smaller gap increases the chances of you hitting the strips when you drill for attach screws. Don't trim them and be sure to to note the strip locations BEFORE you drill holes in the skins! KK
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For more detail see my drawing Fuselage Fairing Angles.   Also, if you change the location of your rudder pedal pivots to fit basketball players or midgets, you will have to adjust the J-strips to put the gap where needed. - Darin


10/31/02 BELLY FORMERS STOCK vs. HP

Kevin, I'm fitting the precut and bent belly formers I got from you on my short fuselage built from Darin's drawings. My rear belly former didn't have enough material on it to make the 4" height shown on the plans at Sta 83, I think it is. The standoffs for that location weren't capable of 4 " either. I'm talking about the transition area from sheet metal to fabric. I am at 3" that location. The first 2 belly formers are on the money or within a 1/16 of plans dimensions of "6 1/2 and 5 3/4 ".

The problem is there is a considerable waterline shift from the middle former to the back. I can reduce the 5 3/4 waterline on the middle former as I only have it clamped but I don't know about possible interference with " stuff " inside the fuselage box if I do that.

Also the 17 " width of the " flat on the belly is actually 18 " on the formers. So is the vent opening in the firewall. I think I can deal with that; just have to brake the vent outlet sheet metal on a bit of an angle.

By waterline shift I mean there is a considerable break in the flat plane of the belly sheet metal. Might look like hell. Would sure be obvious. Any ideas? MB
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Monty, the formers you have are designed to fit our HP fuselages, and will also work on Darin's fuselage too. Part of our restyle of the fuselage was to take the pot belly out of the fuselage. We resized the belly formers both in depth and spacing of the points. On ours, FS 24.9 is 6" deep with 18" wide flat to match the firewall so the cooling air tunnel can be square. FS 48 on ours is 5" deep with a 17" wide flat. The 3rd sta on the belly (FS 75.75 on my fuselage - Darin) is 2.75" deep with a 14" wide flat. All these measurements are made from the bottom of each station tube to the surface of the flat angle that touches metal or fabric.

I think all these changes are noted on Darin's site as he and I have chated about it before. Also, there you will find that the idler brackets mounted to the rear seat are rotated up a bit to allow the pushrod to clear the new belly forer shape under the rear seat.

All our side formers are the same basic shape as the plans except that the rear ones at the rear seat station are longer that plans to account for the added length of that tube after the seat was angle more. KK


10/27/02 CANOPY JIG, CANOPY BUSHING INSTALLATION

Kevin, I spent some time the other day working with the canopy jig, tack welding the bushings in place. Before I proceed further I have some concerns and questions about canopy fit. I'll tell you what I've done so far, and then what has caused me to stop working until hearing from you. Hopefully everything I'm not out of whack.

I assembled and tightened up the jig free on the table. Then I loaded bushings in per instructions. Then I tried to set it on the fuselage with the goal of running it aft till it stopped at the FS 86 top rear seat tube.

My fuselage is a little skinny at the front support part of the jig and it fits tight in there, trying to bow the jig crossmember. Its nots so tight at the middle, but still snug there. Its ok at the rear support. I had to force the jig down on the longerons, and I think it bowed the front cockpit area longerons out just a little bit. Just to make sure I didn't bow the front jig cross angle, I clamped some reinforcememt tube to it to stiffen it against the squeezing of the longerons.

I also had to use clamps to pull the jig aft to the FS 86 tube, with more clamping needed on the right side. I was careful not to clamp the jig downward anywhere except at the points where it rests on the longeron 6 places. After I tack welded the bushings in, I test fit the canopy. It slides in ok, but I have to squeeze the sides of it closer together. I think this is ok, since the width of the jig on the table is less than the width of the pins on the free standing canopy.

However when sliding the canopy forward, the pins on the right side stop first, leaving about 0.2" gap on the left side pins. I did a quick measurement of the pin locations on the jig OFF the fuselage, but they don't appear to be square, so it will be difficult to determine if my fuselage and/or my pulling/clamping is affecting the bushing locations. Maybe the canopy has some rack built into it and the bushings are in the right spot, I don't know.

When I set the jig back on the fuselage, the bushings on the left side appear to be lower than the jig wants them to be. They had a pretty good sized gap when I tack welded them, so I assume that somehow they sucked back down during the welding. I'll probably cut them loose and redo them, but before I do I like to find out if I've got some "rack" in the canopy going on. Thanks in advance for your help. - Darin

See associated pictures:
Canopy Jig On Fuselage
Fwd Left & Right Latch Pins Comparison
Left Side Bushings Sucked Down To Longeron
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Darin, I have looked at your photos and the notes you placed on them. First, it should be noted that your fuse is a slight bit narrow in areas of the jig, and is so snug that it must be forced down into position with clamps. This may affect bushing pin alignment. This same jig on one of our fuselages is not as tight as what you have there. Second, DO NOT FORCE THE JIG AFT AS YOU DID!. This will rack the jig and cause the bushings to be installed out of phase left to right as you have noted on your Fwd Left & Right Latch Pins Comparison photo. The jig fit perfectly against sta 86 on our frames without any clamps whatsoever to hold it aft or down. You are to simply place the jig on the fuselage and let it find a happy spot with the rear blocks as near sta 86 as possible without ANY force being applied. If your 86 cross tube is slightly off, fuse narrow, etc, you may not get the jig fully aft by 1/8" ot so, that is OK, just DON'T force it to get there. The jig is made to match the canopy which is more important on fit up than if your fuse is different than ours.

I don't understand why 2 left side bushings sagged if the tacks were done with the jig in place and the correct 5/16" dia bolts thru them.

I suggect you cut bushings off and reinstall without the pull aft clamps so the left and right bushings stay in proper phase with each other. Let the jig find a naturally happy home, don't force it. Clamp only at the 2 designated locations to hold it down. Be sure to use the 5/16" bolts for the bushing locations. Remember that the canopy jig is designed to place the bushings such that they match the canopy and bending or racking the jig will alter the alignment. KK
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Kevin, Here's the results of my latest attempt:

1) Loosened all jig bolts, wiggled it around on the table a little and tightened it back up again to make sure it it didn't have any stress in it.

2) While jig was still on the table, I made 3 trammel points on jig with a drill bit, then using trammel, located 4th trammel point. Also measured width between forward points and aft points for later comparison to check squeezing of the jig.

3) Removed ALL 6 bushings from fuselage.

4) Put jig on, slid it back as far as possible, then wiggled it and banged on fuselage to allow it to seek happy spot. Gap between jig and FS86 upper rear seat tube was .062 on the left side and .132 on the right.
See Canopy Jig Unclamped In Happy Spot

6) Discovered that anything but VERY light clamping will pull the jig down at the bushings, which must have been my earlier problem. Still I used various thicknesses of feeler gage to keep jig from sucking down on tube while welding.
See Keeping Pins From Getting Sucked Down

7) Before welding, I checked trammel points to make sure jig was still as square as on table. No racking noted when the jig was clamped lightly to fuselage. Also the width measurements showed no detectable change due to longeron squeeze.

8) After tack welding, I discovered that the left side of the canopy still has room to slide forward when the FOWARD and MIDDLE pins on the right side stop against the bushings. The AFT right bushing still has some gap with its pin, just like the 3 pins on the left.
Left & Right Pin Comparison After Tack Welding

Questions:

A) Could the bushings be located properly and its the canopy instead that has a slight rack to it when free? (Kinda like my engine mount isn't right on dimension when free standing) I noticed also that the canopy pins are a little bit wideer apart that the bushings on the fuselage. The canopy must be squeezed in just a tiny bit to mate all the pins.

B) Should I cut them loose and try something different for a 3rd attempt?

C) Can you elaborate on which way those little 1/4" square blocks go? The cutouts on the jig are a little odd shaped. See Canopy Stop Block Orientation
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Darin, I've been reading your threads regarding canopy bushings and jig questions. I had almost identically the same problems, i.e. tight at station 86, gap between longerons and bushings , gap between canopy bushings on left side when right side is butted up. I also trammeled it with about the same results. I ended up cutting mine off three times. I finally got it close, not perfect, but close. Mine sits slightly to the left at the rear. It will close but I had to do a hammer job on the lower left edge of the turtle deck to get the headrest centered. It is still off a little bit. When I first got the jig from Kevin it was tweaked a little bit. I sent it back and he confirmed the tweak and repaired it. I also had to shim between the left rear bushing and the longeron. It had too much gap and wanted to suck down when I finish welded it. I'm not 100% satisfied with my work on my canopy installation but not sure what the fix is.

As I built my fuselage from the dimensions on your website I'm not surprised that Sta. 86 is a little snug on both fuselages. - Monty
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Darin, sounds like you had a good proceedure. So, let's check a few details and make sure the jig is OK. The diag measurements on the bushings are as follows:

Left front to right rear: 47 5/8"
Right front to left rear: 47 5/16"

These are both measured by hooking the tape on the outer rear corner of the rear bushings and then taking the measurement at the center top end of the forward bushing. Check to see if you have the same measurements and more importantly, the same relative difference between the 2 measurements of 5/16" even if you get a slightly different overall number due to how you measure it. If you get different numbers here, the jig has been damaged. The error you are seeing is less than 1/4" total meaning a racking error of half that and even less on a diagonal measurement.

If the above check shows a problem, you should check the jig by either sending it back here for a refit or go visit Jimmy and try it on his Kimball fuse.

It is normal for the canopy to be slightly wider than the fuse. This is done to keep the canopy frame from dragging on the turtle deck during closing as most people tend to pull in on the canopy when seated inside the airplane.

The blocks are installed as your choice A in your pic. Favor the front of the slot. It appears the slots are getting worn a bit from use, maybe inadvertent welding to the jig etc. KK
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Kevin, I did those measurements you suggested and found the jig puts the bushings on my fuse without rack. My measurements both came up 1/16 short, 47 9/16" & 47 1/4" respectively, so the jig appears to be ok.

I think the jig is getting some right yaw when fit on my fuselage. This is evidenced by the left bushings being too far forward. Also when measuring from the windshield stubs to the center of the FS 0.0 crossmember, the left one is further forward by 1/8" than the right one. Using my caliper on the canopy pins / bushings, I figured the left bushings had to come back about .190 somehow compared to the right ones. That would even up the windshield stubs too.

So I cut all the bushings off again (third time's the charm right Monty?) and reinstalled the jig, but this time clamped the left side all the way back to FS 86. I then shimmed the right side to have about .200 gap on the right side with the FS 86 crossmember. It stressed just a tiny bit of rack into the jig, but after tacking the bushings in, the canopy fits pretty even now. See Forward Pins Now Pretty Even

There's a little gap on the aft right bushing/pin, but it was there last night too. I may try to figure out a way to slide that bushing just a tiny bit aft so its pin may engage fully. Also, I test fit the turtledeck, and with it just sitting on the longerons, it has a nice even gap all around the canopy. Hopefully I can keep it that way.

Also Monty, our fuselages are built to plans dimensions back to FS 86 on the top so that shouldn't be the problem. My short fuse changes occur aft of FS 86 on the top and aft of FS 48 on the bottom. Also the jig on my fuselage is tight further forward, at FS 53, its got some wiggle back at FS 86. The jig is designed to make clones of 360KC's fuselage. I'll bet that fuselage has a little variation from plans dimensions in the canopy area, and also all our homebuilder's fuselages will vary a little. Drawing lines on a table, setting blocks, welding method, etc will introduce some variation between fuselages. -Darin

Note: Also you can jump to my Build log for date 02/28/03 where I do my final adjustment to the canopy pins and actually make the canopy a tiny bit narrower to get it sliding in/out of the bushings nice and smoothly. Be careful if you decide to adjust your canopy like I did, it is very possible to crack the canopy! You are now warned.


08/23/02 FUSELAGE TABS

Kevin, I'm trying to figure out where to put all those laser cut tabs, brackets etc. I just discovered that there are two different kinds of tabs. (see illustration)

QUESTION: Where do the three .063 tabs go? I assume they are not for bungy cords to hook onto for holding skiis on the airplane:) Thanks, Darin
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Darin, the .063 tab is the electrical system ground tab that goes on the down tube of the battery rack. You should have a photo showing it. The other two .063 tabs are extras as it is always nice to have spare tabs. You should have extra .040 tabs too. These .040 tabs are for quadrant cover mount, floor boards, turtledeck, etc. KK


06/03/02 FLYING WIRE FITTING ANGLE

I''m setting up those 210-57&58 flying wire fittings on the fuselage, the ones at FS 0.0 at the bottom longeron. Question: should I set them at the plans angle of 27.117 or should I use something a little steeper since I'm using HP wings? I know I could probably tweak them later if needed, but why crack powdercoating if I don't have to?
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We set these fitting at about 28 degrees. Seems to work ok. Sometimes, they have to be 'adjusted' with a large crescent wrench to line up perfectly with the wires. No big deal and the angle change is small enough that the p-coat will not crack. KK


11/03/01 STABILIZER BRACE ATTACH FITTINGS

How do I orient the 210-6 strut fittings? I assume parallel to the longeron, but I'm not sure and plans don't show.
StabBracePic#1    StabBracePic#2

Also, I assume no welding is done on the inside of the strut fittings, just around the perimeter?
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The edge goes parallel to the longeron. The fitting is welded on the bottom of the fuselage only along the triangle portion of the fitting. Do not weld on the top of the fitting between it and the longeron.KK


11/02/01 STABILIZER INCIDENCE

When installing the 210-79 Stabilizer Attach Bushings, what angle of incidence is the horizontal stabilizer set to?
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The horizontal stabilizer as well as both wings are set to 2.0 positive incidence. KK
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See picture of Setting Stabilizer Incidence


10/08/01 ANTI-STAGGER HOLE IN AFT CABANE FITTINGS

The plans have all the holes in the cabane fittings as 1/4", but the aft cabane fittings I got from you have one hole that is 5/16". I assume that it is the anti-stagger wire hole, and that the wire had to be increased in size for some reason. Can you tell me more? Should I note the change on my website?
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Yes, the rear cabane fittings we sell have a 5/16" dia hole in them for the anti-stagger wire. The plans show 1/4" for all holes as you point out. The reason is that the 1/8" cabane fitting -53 as listed in the plans calls for a quantity of 4. Only the rear ones need the larger wire pin hole. SO, we decided to leave the plans with 1/4" hole and have scratch builders (some are making their own fittings) ream out the required hole on each side AFTER the fuselage is welded. The plans indicate which wire goes where and a builder can easily determine to ream out the hole as required to fit the larger pins.

A bit of history on this item. Originally, N80XP was designed built with 1/4" wires for all the stagger and anti-stagger wires. But prior to the airplane making its first flight, Curtis Pitts changed the antistagger wires to 5/16" dia. The 1/4" wire would mostly likely have worked but the margin of safety was too close to zero at 9 g's to make him happy. The 5/16" wires increased the factor of safety to acceptable levels. Normally, a 5/16" wire comes with 665 ends that use a 3/8" hole but 5/16" pin hole AN665-46 are available and a cabable of a high enough load that the required margins were met. Specifically, a 1/4" wire with AN665-34 ends is rated at 4200lb load. A 5/16" wire with -46 ends is good for 4600lb. A 5/16" wire with -61 ends (3/8"pins) is good for 6900lb. So, in this particular case, the wire would see about 4100lb at 9 g's. Pretty close to full capacity of a 1/4" wire assy. But the 4600lb -46 setup gives a 500lb safety margin.

I would not add a change to the plans because of the high likelyhood that a builder would one up the wrong holes or too many of them. It is best for the hole to get opened when they discover the need when installing the wires during a test rig of the airplane. KK


10/07/01 PRE-BENT CABANE FITTINGS, CABANE FITTINGS INSTALLATION

Note: Much of this topic is moot since I ended up making a set of cabane jigs off a Kimball fuselage to help install my fittings.It is still helpful to read this however.
Goto: Cabane Jig Page

Kevin, I was going through my box of pre-bent fittings, planning ahead and taping them together so I could understand more about how they are installed, when I discovered differences compared to the plans. I have some questions.
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Darin, you are correct. The fittings we sell do have some slight differences from what the plans have drawn. The minor changes are there to make installing the fittings easier. For example, we added a small bump to all the rear cabane parts which is to point forward when the fitting is installed. This ensures the fittings are placed in our installation jig correctly and can be used as a guide for you to install the fittings in the correct locations. As you can see, station 22-24.9 vertical tube is not truly vertical running aft as it runs down to the lower longerons. The fittings as in the plans are drawn to fit on a true vertical tube at this station. If you simply tack heat hammer form the fittings to the vertical tube, the 2 1/8" thick blades will try to run off the front of the vertical tube. As you heat the fittings for forming, you can force them aft to align with the center of the tube but it is not that fun to do. We did this on the first few airplanes we built. As we revised the laser cut fittings , we continued to make slight changes to make installation easier. Frankly, most builders never even notice the minor changes and benefit from our learning curve without being aware of it. More of the little 'bonus stuff' that builders get when buying items from us verses totally scratch building things. So, yes, there are changes to the fittings as I mention to all those who purchase them at the time of purchase. Some differences exist between the plans and the fittings we sell based on us having already cut and used some fittings prior to Randle making changes to the plans. For example, the master cylinder mounts are simple tapered tabs as drawn by Curtis Pitts rather than a U bend part as shown on the plans. We already had it in the laser nest as Curtis created it and found no need for it to be changed to the form that Randle put in the plans.

While some changes make assembly easier and some reflect the original form of the fittings, some eliminate wasted metal or labor. An example of this is the front lower wing attach fittings. In the laser parts, we have 2 types of this fitting instead of 1 type as in the plans. 2 are exactly as the plans show and 2 are trimmed off. Why? Because the part has to be trimmed anyway so why not let the laser do it the right way from the start. Here is an example of the difference in CNC made parts and hand made ones. The CNC machine doesn't really care if the parts vary. A man at a band saw does. KK
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Question 1) What is the general sequence for welding the fittings? I'm curious when the edges get welded. I assume they get tacked together, then the edges get finished when finish welding the fittings on the fuselage.
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We bolt all the cabane fitting parts, the oil tank mounts and main fuel tank mount bushings into a jig and weld them to the fuselage and each other all at one time. For the scratch builder, it may be easier to do as you suggest and tack the various parts together and then fit them to the fuselage. KK
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Question 2) Regarding the FORWARD fittings, it appears that the -102 thin parts are bent to a completely different angle than plans, so the part that rests on the top crossmember is pointed up. Is this done so it can be heated and smithed down onto the crossmember?
See Fwd Cabane Fittings Picture #1
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The -102 is bent to the initial form required to install it. The plans show the final shape after all forming and welding is done. This is why you will find -53 and the other fittings at slightly different angles than shown. The bends are as required for the START of the installation. Not the result. As you can see in the details you put in your email, -53 must be bend to an angle that allows to fitting to run tangent to the longeron above the centerline of the tube. The fitting will run away from the vertical tube being bumped out by the longeron. Once the -53 is tacked at the ben lline to the longeron and the upper blade is held from moving, the lower tail or finger can be heat formed to curve around the longeron perimeter and then down onto the vertical tube. Tack the lower end of the tail and then form the finger to wrap around the vertical tube for a snug fit at the edges.

Same goes for the -102 part, when placed in our jig and then onto the frame, the bend area of -102 lays on the 1.25" over sleeve on the front of the longeron that is NOT shown in your email detail drawings. If -102 was initially bent to 115 degrees, the fitting would be forced up about .2" from the desired location partly caused by the wall thickness of the 1/25" sleeve and partly by the lack of a hump in -102 passing over the sleeve. So, the proper location for the -53/-102 combo is for the -102 to rest on the 1.25" sleeve. KK
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Question 3) Regarding the FORWARD fittings, What is the proper method to postion the -53's on the fuselage so that they are at the right height?
See Fwd Cabane Fittings Picture #2
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Partially answered above. But, as you can see, the bend is just above the C/L of the longeron. KK
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Question 4) Regarding the AFT fittings, it appears that most of the aft cabane fittings don't fit together very well, and there is a noticable difference in how indentical parts are bent between Phil's and mine. The bend lines vary by .060 to .100 between the same part. Its like the guy bending them was just eyeballing them into the brake. How should we proceed?
See Aft Cabane Fittings Picture #3
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Here again, we bolt all theses fittings into a 40lb steel fixture that hold all the parts in proper relation to each other and the frame. The slight variations in the bend angles and bend points are within aceptable limits for our construction. If a fittings needs more bend to make things easier for you, bend it. If less, bend it. What ever you do NEVER TACK WELD THE FINGERS TOGETHER UNTIL YOU HAVE THE FITTING FIRMLY FITTED AND WELDED TO THE FRAME. The fingers need to slide relative to each other as they are formed to the frame. The fingers get the crap smacked out of them while they are heated and formed in place and because of this, the bend angle is not critical. KK
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Question 5) What is the postioning of these fittings with respect to the longeron?
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Basically, the longeron is to be in the radius of the bend so that the sway wire lug rolls around th elongeron without gap. Specifically, you will need to place the rear cabane fittings such that the upper wing become mounted at precisely positive 2 degrees incidence. As you know, the cabane struts are all 22" long center to center. The front ones stand exactly vertical. The rear ones lean aft as they go up to the wing. This leaning is only part of the 2 degree result. The remainder comes from the fact that the rear spar is not as tall as the front one which causes the rear cabane fitting strut bolt hole to be closer to the wing chord line than the front one is. The result is 2 degrees incidence. How did we do this on N360KC? We built the wings, then built the fuse frame. We installed most all the fittings except the aft cabane fittings. The -53/-102's were tacked on the frame and the wings installed and rigged with the rear cabane fittings being clamped to the fuselage frame. We then adjusted the location of these clamped fittings until careful transit reading indicated a 2 degree incidence angle. (BTW, the lower wing should indicate the same angle) Then we tacked the rear cabane fittings in place. Following this, we built a jig from N360KC for locating these fittings on all other frames. Scratch builders have a choice to make here: Build the wings and use them to properly place the fittings on the fuselage like we did, Or build the fuselage as best you can guess without using the wings to locate the fittings. Later build some scaffolding to support the wings in proper relation to the fuselage and measure the required length of each cabane strut so that the errors in placement of the fuse fittings are corrected. If you do this, chances are you will end up with 4 unique length struts rather than the specified 22" C/L to C/L units. This is not a big deal. The idea is to get the wings correct and if the struts have to be custom made, that's fine.

All of the above discussion is a great example of why $8900.00 fuselage frame from us is a great bargin. We went thru all of this already. Likewise on all the other parts we sell. We sell exactly the same pieces we use in building assemblies here. Why? Because we know they work for us and feel they are the best shot for scratch builders to be able to get good parts on their own. Likewise, scratch builders can benefit from our knowledge of how to build the various parts that make up a model 12. Unlike many other plans and kit outfits out there that merely sell plans or parts without a true knowledge of how the parts came to be what they are now.

We do enjoy the Model 12 program we have. We meet lots of great people and have fun helping builders, scratch and kit, make their airplane whole. Airplane building today, homebuilding in specific, has changed so much from what it once was. In the 70's if you wanted to build an S1S Pitts, you got 7 sheets in a FULL SET of plans!!! That's it. You had to 'create' all of the non-primary structure on your own. A kit was simply a box of raw material. Today, it is expected to be a very complete set of finished parts that snap together and have explicit instructions on every move required to assemble the thing. In my opinion, for what it is worth, scratch building and building from sub kits like with the model 12 produces builders with a greater understanding of what building is and more importantly, what his/her airplane is made of. Simply reading instuctions and sticking premade parts together throughout an entire project shows that an "assembler" can follow directions. This builder does learn some about the airplane he is building but in no way does he/she learn as much as someone building from plans or subkits. KK


08/12/01 TAIL SPRING HOLES

Why are there two holes in the tailspring, wouldn't one hold in?
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One 1/4" bolt has adequate shear strength for the loads that would be seen on the tail spring. Same is true for the solid stainless steel spring. But the .058" wall tube that the spring slides into is a different story. One bolt will, to use a southern term, "waller out" the hole in the tube resulting in a spring that can rotate which is bad. So, 2 is better with twice the shear area. 5/16" is better yet with more area. Try for 1/4" bolts. If you have the least bit of slop in the holes, ream them up to 5/16". These bolts should have a perfect fit.

If you want to use a single bolt, you could add some diamond patch doublers around the bolt holes to increse the thickness of the tube for increased capacity. But, my personal take on it is that 2 bolts are better for several reasons. Shear or lose one you still have a spare. 2 bolts place at 90 degrees to each other tend to eliminate slop and free play in attachments, splits up the shear loads, etc. KK


05/10/01 TAILSPRING TUBE

Regarding the Tailspring and where to drill it, could you please explain further, I'm kinda confused.  Maybe my assumption that the spring is inserted into tube 210-22 so that the start of the taper just meets the end of the tube is wrong. As you can see by the attached graphic that I have a bolt going into the tailpost.......Where have I gone wrong?
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I see the problem.  In the drawing you attached, the tail spring mount tube is far too long.  The 10+" length as shown in the Model 12 plans is a rough length and the tube needs to be trimmed to a finished length of 1" aft of the fin post tube.  In other words, 1" of the spring mount tube hangs off the end not several inches as you show it.  This will move the tail spring and its mounting holes forward.  KK
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For a correct drawing of the Tailspring installation TailSpringInstall.gif


05/10/01 GEAR BUSHINGS

I've got a question on the gear bushings. If they hang down below the longeron by 1.25 and the gear spring is 1.25 thick, what about the .090 aluminum sway plate? It would seem the hang down would be:

Hangdown = 1.25 + .090 - Desired Crush

Or is the .090 gap just the way its done?

I don't have any good pictures of the gear (this is the best I could find FrontPedals.jpg) and I am not sure how it really works. Heck I just discovered that the round part of the bar goes up against the spring!   Darin
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The .090 gap is exactly what we like to see there.  Keep in mind that the clamp bars are holding the  gear up and that the majority of the loads are from the gear pushing on the longerons.  The clamp bars keep the gear in the airplane when the tires are not touching the ground and get a little load when you land hard on 1 wheel only, hit a hole in the runway, lock up the brakes, etc.

An undesireable gap would be 2.5" or greater as the contact area between the bushing and the alum gear spring would not be enough to prevent excessive wear over time.

Recall the "haybail airplane"?  It took a direct hit to the right gear leg and wheel at 70mph by a maverick 2000lb round hay bail.  The longerons broke not the bars, bushings or gear. KK
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Should I worry about weld bead size between the bushings, where it might interfere with the gear spring? Darin
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Not unless they are ridiculous. Remember that sway plate sandwiches between the gear and the longerons. Those beads are where the sway plate holes need relieved, so the plate rests on the longeron. (Done it twice).   Jerry


05/01/01 TAILPOST

Kevin,  Since its about time to put the tailpost in, I noticed on the plans that it is 1.00 x .035 tube. The vertical fin tube that slips inside it is .875 x .035.  It seems that it would be a bit wiggly in there. What am I missing? Do the wires provide all the strength? Should the tailpost be .049 wall?     -Darin
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The tube sizes are correct.  It is actually nice to have the clearance on the tail post as it allows room for paint etc.  The ring welded around the fin tube keeps it in place agains the pull of the wires.  We put one bolt thru the joint as you can see from you pics and use that same bolt to hold the tail fairing in place at the rear end.  You can use 049 if you want. KK


04/15/01 WING FITTINGS, WIRE FITTINGS, WING INCIDENCE

Any suggestions on locating / jigging the spar fittings and wire brackets to the fuselage to insure accuracy? I understand you guys use a jig. I would guess the lower wing spar fittings are the most critical?  Darin
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The wire fittings at the lower longeron Sta 0.0 are not that crittical.  The forward edge of them in parallel to Sta 0.0 and the rear edge angle back.  Place them such that the .063 doubler touches the outboard face of the longeron and engine mount bung.  Tack them and blacksmith to fit.  When you do your test fit/rig of the whole airplane, you can bend these for wire alignment if needed.

Now, the rear wing attach fittings are a different story.  I tell ya, since you own lower wings now, I suggest you use them to jig the fittings.  You could set them in place with the wittings bolted on them.  Set and tack the front ones, then check squareness etc and tack rear ones.  We have a welded steel jig to do this that we buiilt from 360KC's fuselage.  KK
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That sounds like a good idea on setting the wing fittings. I don't have any rigging data yet. Does the lower wing have the same angle of incidence as the lower longeron in the area, 2.0 degrees?
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The lower wings are at 2 degrees as are the uppers  KK
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Instead of using my wings, I'm now working on a jig (Click here for Drawing or Here for Picture) to locate the lower wing attach fittings, I've milled the blocks for it to 1.438 and 1.120 wide respectfully per plans. However when I put a caliper on my spars with the plates on both sides, I get 1.380 on the front spar and 1.040 on the rear spar.

It seems that's a pretty sloppy fit between the wing and the fittings. Is this correct or is something in need of adjustment somewhere?

Also, I've noticed that there are two styles of laser cut 210-59's. I assume the one with the most material goes in the aft position. How do you guys do that nice curve around to the fuselage vertical with it?
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Darin, the 1.438 and 1.120 seem correct for the fitting spacing. I checked the wing drawings and found that the front spar, 2 each 1/8" spar plates, 2 each steel fitting plates adds up to 1.406". Rear spar builds up to be 1.063. Plus, glue, varnish, paint or powdercoat on fittings and fuse frame and the spar will just barely slip into the fuse fittings.

Regarding the -59's, yes the long ones are the rear ones. They are as the plans show and the fronts are shorter as they needed to be trimmed from plans length anyway. We bolt these to the jig and weld them on the longeron for the outboard half of the longeron. After that, we use the rose bud and heat the bottom tab and top tab on each and form them into place for welding. Then clean and weld. Our jig for these fittings has steel blocks that hold the fittings in the proper spacing just slightly farther inboard than the wing spars will go. In otherwords, make sure your steel blocks are not too far away from the longeron or too close for that matter. KK


04/14/01 LASER CUTTING STEEL, WATERJET

I visited CF Laser Services, our laser cutting guys, again this year while in Lakeland.  They have both high precision laser cutting and water jet cutting systems there.  The water jet is new since last year and I got to see both in action.  These are VERY expensive machines, ones with very tight tolerences and accuracy.  The laser has a repeatability of .001".  The Waterjet is more like.007" and does not cut a square edge.  The WJ is not accurate enough to cut our parts so that they will cleco in our jigs.  The water cuts on a taper.  So,  with WJ, if you need a hole to pass a 1/4" bolt thru you can cut it 5/16" on one side and it tapers to 1/4" on the other thru 1/4" thick steel or you can re drill the hole to size after cutting it small.  Also, I found out that the WJ absolutely sucks at cutting thin stuff.  The water jet causes it to vibrate and you have to lay heavy steel on thin alum or steel to keep it from flopping all over the place.  The WJ is noisy and messy too.  The laser is quiet and clean. We have found only 3 items out of thousands for the Model 12 that can be cut on the WJ vs. the Laser.  One is a thick alum plate that we redrill the holes on and the other 2 are fiber disks for the throttle quad and wing drag wires. KK
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Kevin,  Be careful with the laser cutting.  I bought my gear brackets, bent up, from Hale and there were small cracks in the bend areas. Hale told me it was a result of the laser hardening the metal at the edge of the cuts.  FYI   Andy
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Careful is not really the issue.  Knowing what to do is.  3 yrs ago, Hale was hard against laser cutting believing the bandsaw was the only way to 'skin' the 4130 fitting 'cat'.  We have been using and knowing how to treat, prep, bend etc. laser cut 4130 since 1995.  It isn't something we just started to do recently in the Model 12 program.  When I send out a set of flat 4130 fittings to a builder, I include a proceedure sheet on how to prep the fittings BEFORE they are to be bent.  The fittings you got apparently were not properly prepared.  Heck, the grain direction may not have been preperly specified either.  When we send out a fully bent set of fittings like we sent to Darin and others, they do not get this info sheet as we have already done all the work for them.

My point in comparing waterjet and laser is accuracy.  While WJ can be more precise than a hacksaw, it is no where near camparable to laser.  The cutting industry has found and shown that WJ is a good choice for 1/2" to 12" thick material while laser is better for materials under that.  BTW, the edge left by a WJ cutting system is very rough and no where near as smooth as laser.  Removing .002" from the edge of a laser cut fitting takes a lot less time than removing .010" roughness from the same fitting cut with WJ.  Both laser and WJ cut the parts in a similar sequence.  Holes first, then the perimeter of each part.  The reduced accuracy of WJ compared to laser in locating these holes properly in the parts would make many fittings unusable by our builders. Now, if you are gonna match drill your spars to whatever the fitting is, then WJ may be good enough.  We CNC cut all the parts, with all holes both in metal and wood.  They have to be perfect to satisfy us.  We have tried both and from these trials, have found what works best for us. Listed in descending order of accuracy: CNC machined, laser, CNC routed, WJ, plasma arc, trace torch, bandsaw, hacksaw.  KK
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I had the same problem with some steel that was bent after laser cutting. No biggie just weld a fresh bead over the area. As to this new debate Laser vs Water what's the faster method?
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For the types of material and thicknesses we are talking about in this forum like 1/4" or less 4130, alum, stainless, laser is faster for a given cut quality.  Water jet cutting can be faster on thicker materials and really has advantages in cutting stone, thick steel 6" or more thick etc.

Laser CNC cutting systems use the laser beam to generate a very fine molten point on the material to be cut.  The amount of power used is based on the type of material and the thickness, generally. The focal point of the laser beam is set to be just below the bottom of the material so that the beam doesn't cut the machine, floor and world in half at the same time as cutting the part.  Oxygen or nitrogen, depending on the material being cut, is used to blow out the molten line of metal creating the cut line.  With laser, this line is about .020" wide in thin material.

CNC Waterjet cutting is basically super high pressure, narrow stream wet sandblasting.  The water is pumped up to anywhere from 50,000PSI to 100,000PSI depending on the machine.  This water stream does not do the cutting.  Garnet dust is fed into the water stream next at the nozzle and is the actual cutting media.  That is why the edges of a WJ cut part look sandblasted.  The nozzles for the WJ are very expensive with diamond units costing about $750 each and Ruby ones costing about $250 each.  The Ruby ones do not last as long as diamond ones but don't hurt your feelings as much as when the material breaks a diamond one.  The stream of water is traveling at about MACH 3.  Because of this, the material being cut is placed in a large tank of water with its upper surface just above water level.  The jet stream shoots thru the material with the garnet cutting it and goes into the water in the tank.  The tank has to be cleaned out too.  The water tank suppresses the majority of the noise yet you have to yell to each other when within 20ft of it.  The laser fairly quiet.

I agree with you that for a do-it-yourself homebuilder, CNC cutting of any type is a luxury that may not fit into the budget.  But if you are building an airplane that has these parts available for a slightly higher price than the raw material, I think it is foolish to not use them.  Keep in mind that you too must consider grain direction when making your fittings.  Improper grain orientation can result in cracks no matter what method of cutting is used.  KK


01/09/01 BELLY & SIDEWALL FORMERS, STANDOFFS, 4130A

Forming the angles is very easy to do.  No real tricks to it.  We make the ones on the Model 12 from  3/4"x3/4"x.025 cond A 4130.  We bend the angle 90 degrees.  Also, we bend a second bend 1/4" from the edge of the 3/4" face that will touch the sheet metal.  This is a very slight bend like 7 to 10 degrees.  This keeps the edge of the former from digging into the back of the sheet metal.  Gives a very professional look to it too.  Once you have the 2 bends in the strip to be formed, shrink the flange that is not to be in contact with the skin to match a template drawing of the curve you want. Trim the ends to fit the longerons and station tubes as needed for a nice weld joint and weld on with ER80S-D2.  We use 2 stand offs per former to support each former.  These are made of .025 4130 too.  Take a look at some of Darin or Bud's pix on Darin's site or maybe in the vault! .  This will explain alot.  Using this type of former lets you use sheet metal screws, nutplates, clip nuts, whatever you want to attach the metal.  It is also nicer to glue the fabric to at that former.  Dillsburg Aeroplane works has Cond A 4130 and can shear it into strips for you.  This is where we get it but we shear it here.  KK


01/08/01 CONTROL RODS, HARDWARE, QUADRANT, PLATING

I'm about to order some hardware and have some questions about the Pitts 12 control quadrant shown in the picture:  ControlRods.jpg

1) What are the clevis fork rod ends that are welded on? Are they AN481, if so what size?

2) What is the rod used? I can't find it in the plans.

3) What are the pins used to attach the forks?
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1. The forks are AN481-4P or MS27976-4 not so cheap but they sure work great.

2. Rod is 3/8x035 4130 tube.  Forks are designed for it.

3. The clevis pins are AN393-2-11.  These may be listed on the fuse hardware list.  Did you get this list from me yet?  I think we are updating it a bit right now and I can send it to you soon if you don't have it.

Remember to remove the plating from these forks or any other weld in end before you weld it.  Do this with Muriatic Acid(pool acid).  Takes only a few seconds then wash them with water.  KK


12/22/00 LASER CUTTING, PLASMA CUTTING, EDGE PREP, BEFORE BENDING

I understand that laser cutting devices harden the metal around the cut. Good or Bad for the Part???  As to using a metal band saw it's slow but works. Need a saw that will run around 150 feet per min.  Denis
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We have a plasma cutter here too.  It is fine for cutting but not as nice as the laser for cut quality.  Yes, the plasma cutter, laser and the victor cutting torch all harden the metal along the cut edge.  But, if you are gonna weld it along that edge, so what.  If not welded along that edge, you should clean the hard edge off. It the case of the plasma and gas cutting torches, the edge is fairly rough and you sand/file/grind it smooth to get a quality part.  This removes the hard edge.  With Laser, the edge is very smooth and straight so all that is needed is to sand a few thousanths of an inch off the edge to remove the hard spot.  When sanding the laser part, remove the dark edge leaving bright white metal and you have gone far enough.  BTW, with flame, plamsa, or laser cut parts, you should remove the the hard BEFORE YOU BEND the part to prevent cracking at the bends.  KK


12/20/00 ROLL BAR

I got looking at a pic of a fuselage in your shop that Bud sent and cannot see the purpose for two tubes extending upward and forward from FS 113.0. Since you know EVERYTHING, I thought I'd ask. Is it for shoulder harnesses?
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That is a pic of a frame that is in our shop for FWF plumbing.  It is a scratch built one.  It has an added a roll bar and these tubes are the rear legs of that bar.  Note all the tabs on the longerons too.  A removeable turtledeck skin is planned also.  Not needed in our view.  Access is easy thru the rear seat and the tail fairing metal.  The roll bar is useless too.  That is what the top wing is for........OK for monoplane, extra crap for bipe.   KK


12/19/00 HARNESS, SECONDARY SEATBELTS, BUSHINGS

What are the 210-79 bushings under the seat tubes for? Is it for a harness or something?
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The secondary seat belts and the crotch belt.  Use the hooker double belts with one attached to the belt mounts and the other to these bushings. KK


12/19/00 AIR TANK MOUNT TABS

What brackets and locations were added to the front tubes at the firewall? Bud mentioned adding a few.
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These are brackets to mount the air system to the firewall.  We have only done 6 or 8 this way so far.  Before that, we use clamps to mount the air stuff. Clamps work just as good and are most likely needed on scratch built frames.  KK


12/17/00 BENDING LONGERONS, CONSTRUCTION METHODS, TABLE, CROSSMEMBERS

I'm building my fuselage bottom-then-top and I have a question about doing the bends in the longerons, for example at FS48 (FS75.75 too), should I bend them inward right at the FS48.00 with the axis of the bend right on 48.00 THEN put the crossmember in....OR Tack in the crossmember at FS48 then bend the longeron, which would put the fulcrum of the bend probably right near the aft edge of the crossmember?  Thanks!  Darin
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Heat and bend the longerons after the cross tubes are in place and clamped firmly.  Once you make contact to the cross tube with the longeron tack the front side of it.  Then heat it right on station using the cross as the bending fulcrum. After bent to next station tack there and the back of the previous station.  Now, the clue here is to have the cross tubes cut at an angle that represents the longeron being bent on station.  If you do this the cross tubes at these stations will have an angled fishmouth so when you bend the longeron to a station it contacts the forward edge of the cross notch but not the aft.  After you bend it, it will contact the aft edge.   So, tack front, bend on station, tack next front and previous rear, and so on.  KK


12/03/00 TABLE, LONGERONS, CROSSMEMBERS, DIAGONALS, LADDERS, TAILPOST

I'm starting to think about fitting the crossmembers and diagonals in between longerons (which I'm still welding and need to bend) and am curious....does it work better to fit tubes from the front working back to the tail or is it better to work from the tail forward? Also, any advice on how/when to fit the tailpost would be appreciated. I have no idea how that fits into my plans yet. I was thinking I could figure out exactly where and at what angle to put a surrogate section of tube to represent the tailpost, then I could at least cut and fit the longerons to it back there.  Thanks in advance,  Darin
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Here is how I like to assemble the ladders in the conventional side-side method: I like to locate the top longeron in all respects over the drawn location on the table and block it and clamp it in place. Then, locate the station upright tubes and tack the to the top longeron.  Next place the lower longeron at sta 0 to sta 24.9 and clamp then tack to the uprights at those stations.  Then heat the lower longeron at sta 24.9 and bend it to sta 48 and tack it.  Continue for each station working aft.  After the lower longeron is tacked to all uprights.  Fit, place, clamp and tack the diags front to rear.   Repeat for second ladder.  Now, with the top longeron view drawn on the table, place the 2 ladders on the table inverted and continue with the assembly.

Now, for the top-bottom ladder method like I did: Build the bottom ladder first then the upper one and make sure you draw the upper one on the table as viewed from the bottom looking down in the table.  Build the lower ladder by clamping the cross tubes in place on the table.  Then locate the lower longerons at sta 0 and clamp and block in place back to sta 24.9.  Work your way aft until the longerons are clamped fully fore to aft ends.  Check squareness and then tack weld at cross tubes.  Now add the diags and tack them.  Now remove the lower longeron ladder from the table and repeat this process for the upper ladder.  For both of these ladders, you will need to cut a hole in the table at the location of the tail post and place the tail post or a scrap piece the same size in the hole and brace it vertically to fith the longerons to it.

Now that you have the 2 ladders and the top one is still clamped to the table inverted, build some structure to hold the lower ladder up in the air above the upper ladder.  Now fit and place the uprights for the sides squaring the frame and tack in place.  Next add the side diags and tack.  Next add the cross fuse diags.   Tack to the tail post then too.  

I hope this explains how we do it here as well as how I suggest the typical side-side method.   KK
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Thanks for the info. Is there much problem fitting diagonals in after the crossmembers are tacked in? I didn't think you could get them in. For example on the bottom ladder, I can see that diagonals #26 and #28 would slip between tube easily, but the others, especially #34 and #36 look impossible to fit if the longerons are tacked. Maybe I'm not following you correctly.  I wish I knew, right now, what I'm going to know after I'm done!!!   Darin
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Yes some diags are hard to get in.  Even with our Steel jig.  A few of the tubes will need to have one of the extended points left after the fishmouth cuts trimmed enough to let the diag fall into place past the other diag.  An example is the diags under the rear set that converge to a centerline point to the rear.  Put one in place, trim the other until you can push it into place.  The idea is to firmly establish the location of as many of the tubes as possible.  Then add the rest.  Trying to get all the tubes, crosses, diags, longerons in place all at once is not possible with our jig and most definitely not possible on a table as you are using.  So, don't sweat the small stuff.  Get the major portion of the tubes in place and make the rest fit.  Yes, you will have to fill the extra trimmed end point with weld material.  This is acceptable industry wide.  KK


11/11/00 TUBE TUCK AFTER WELDING, POLYESTER FILLER ON LONGERON JOINTS

Just finished the finish welding of my fuse.  Welds look good and I'm pretty happy with it.  Got a question about some minor distortion though.  I had a couple of areas where the top longerons bowed in a bit between stations, I know this is normal and used outside heat to straighten them up some and my mallet to finish them.  However their not perfectly straight and my question is how straight do they need to be.  I really don't want to do any more heating and beating on them.  I should add that visually they don't look bad, it's only when I put a straight edge up to them that the bow stands out. 

So how about your experiences, am I being to picky?  Cheers,  Steve
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Don't worry about the tube tuck.  Straighten them or bow them out a bit after all welding.  We don't use heat to suck them straight.  A block of wood and a mallet works well. The upper longerons are not a problem as the turtle deck will hide any bow in them.  The lower should be pretty straight to look good when covered.  Another trick is to barely bow the lowers out a bit between stations so that when you shrink the fabric, they pull back straight.  Do this on the tail feathers too at the rudder bottom, elevator inboard etc.  I also like to use some polyester filler on the longeron slip joints to smooth them out.  This way when you cover the fuse, you will not have the lumps at the fish mouths.   KK
See TubeTuck.jpg


11/07/00 BUNG LOCATION, LONGERONS, LAYOUT

Note: See build log this date for images and more info
I'm getting set up to locate the lower bungs on the table to start making the longerons. Looking at the plans it looks like the distance from the front face of the bung to the c/l of the 1st LG bushing hole should be .188 + 3.00 = 3.188. However on the bungs I have here it looks like that distance is about 2.93". I assume the bungs will work, and the location of the landing gear isn't critical. What distance in front of STA 0 should the face of the bungs be on? From pictures I have it looks like it should be .188 + .625 (half a 1/25 tube) = .813. Is this one of the little things you do differently?  By the way, I love this project!!!!  Darin
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The parts we sent you are correct.  If you want to set them like we do, set the rear bushing hole at exactly Sta 9.0.  That is a horizontal dimension back from Sta 0.0 NOT as measured along the longeron on its upslope heading forward.  Make sure to measure it at the centerline of the longeron axis and not at the top or bottom of the tube.  Now, with Sta 9.0 set, we measured forward along the lower surface of the longeron 6.75" to locate the front gear bushing because the gear is 6.00" wide.  I then chose to have the bung stick forward of the Sta 0.0 tubes such that at the center line of the longeron, it is .125 ahead of the Sta 0.0 vertical tube.  This is the same as we did on the top bungs, .125 ahead of Sta. 0.0 tubes.

This makes it .625" from sta. 0.0 to the front face of the bungs.   This was not specified by Curtis on the prototype drawings.  I chose .125, Randle .188. !!!

I have attached a modified view of the gear drawing you have in your plans. This version is changed to show how I determined the gear locations for you.  I just did this for you.  I found that Randle had the rear gear bushing about .125" aft of exactly on Sta 9.0 as I show it here and we build it.  It may have started as a WAG that he didn't touch up.  That little error would not cause any design or performance issues.  I just wanted you to see how I arived at the #'s I use.    KK


11/06/00 ENGINE MOUNT, JIGGING

EngMountRcvd.jpg   EngMountReceived.gif
I got everything today, and was pleasantly suprised to see the straight tail tubes included with the bent ones and pre-drilled, thanks a lot! That will really make the entire tail just a kit now. I thought I was just getting the bent stuff. I noticed the mount rocks when set on the table. I had to put .09" of feeler gage under one leg to stop it. Also I determined that it is off dimensionally. See the attached files. It sure has nice welds on it.   Sincerely, Darin
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UPS didn't hurt it.  The jig builds a mount that is perfectly dimensioned also.  Fact is the legs do spring a bit and move a bit during the final welding that occurs AFTER the mount is removed from the jig.  There is about 10% of the welding that cannot be accessed while in the jig.  You will see that the legs easily flex in and out to the required position.  This is normal.  Piper, beech, Stearman, Pitts mounts all require a push or pull somewhere to get all the bolts in.  If you put an engine on the mount and plan to set it on the 4 mount legs, be sure and bolt that piece of plywood you mentioned to the 4 legs to keep them from bending outward.   KK
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I'm glad to hear that no action is required and that its ok. I think I can still use it for fuselage jigging too, I'll just get a plate of aluminum (or steel) and drill holes on the proper pattern and then bolt it between the fuse and the mount. That way I can still take advantage of the proper angles the mount provides. Any other advice? Thanks again for the education once more.   Darin
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yeah I think I would layout a guide to sandwich between the mount and the frame.  Should work great.  Keep me posted.  Bud Clark was here today getting some bearings.  He is almost done with the welding and will soon get some wings stuff.  KK


11/05/00 REAMERS

What reamers will I need for this project? Darin
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Darin,  A full set of reamers would include:

.188 or .190, .250, .313, .375, .5, .510, .750.  Not all are required.  I'd wait and see what holes you have trouble getting a bolt through then buy that reamer.  KK
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Straight reamers work just fine for our type of stuff. You can ream by hand, or with a drill press or hand drill. Use light oil for lubrication. Remember that all reamers take only a very small cut, so don't try to enlarge a hole by 1/64th of an inch with a reamer. Half that, at the most. Spiral are more for production work.

Also, I remember someone asking about rod for aligning the front and rear landing gear brackets on a Skybolt. Threaded rod (as recommended by several in the Hangar to me some time ago) worked very well. Use 7/16 threaded rod and just grind/sand the threads off one end down to the root diameter to get the 3/8 diameter for the rear brackets. Worked slick!   Andy


10/18/00 DARINS FUSELAGE MODS

Darin,   I just viewed your building log.  Great job. Would you discuss your reasons for shortening the fuselage, how you did it, and the changes in seat position?   Steve
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This answer has been superceded by a page dedicated entirely to my short fuselage Click Here to see it.


10/18/00 FUSELAGE MODS, KEVIN'S OPTIMIZATIONS

Darin,   Most builders don't realize how many things are affected by a simple change of one item.  We had to make about 150 changes to the fuse systems to make all things work with the short fuselage. There are only a few items that are the same in the fuse kit we sell and the plans versions.  Front stick, pedals (but not location), 1 idler, 1 pushrod, 85% of the tubing sizes.  Other than that, we changed everything all to get the look and safety we wanted to have.  We also add a lot of things to the fuse that are not on the plans that we know are a slick way to do things. 

What I mean is this.  As the tubes changed lengths, the dia. or wall thickness or both can be changed to better match the loads being applied.  In most cases, the tubes in the 12 frame got shorter and or the angles got better.  By doing a full finite element analysis of the  frame, I was able to optimize the tube sizes while trying to maintain the external appearance of the plans frame.  So, some of my tubes are thinner or smaller or both than the ones you are planning to use.  I changed a few to larger dia tubes for reasons of convenience of assmbly or better fit of a fitting etc and reduced the wall thickness to make an equivalent strength member.  But, for the most part, our frame will look like yours and vice versa.  I just have ours tweaked a bit more than you will to save some weight.  KK


10/18/00 BUNGS, REAMER, TAP

Kevin,  I have started machining the engine mount bungs and question the .495 Ream in the front.  Why is this .495 as opposed to say .500? Thanks, Steve
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Yes the bungs are reamed to .495 to get the proper fit to the shank of the engine mount bolts.  A 1/2" AN bolt is slightly under .5 dia.  This gives about .002" interference fit to the shank of the bolt so that there is no play.  The shank must get inside the bung to take the load.  No shear load should be placed on the bolt threads.  KK
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I am ready to finish up the engine bungs and I have a couple of questions.  First, do I use standard taps or something special for the 1/2 AN bolt?  Second, why drill .4375 instead of the usual .4531?  A machinist friend told me I would break my taps in a .4375 hole.  Third,  is this all related to Class of thread fit? Sorry if my ignorance is showing.  Thanks for your help. Steve
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Standard Carbide taps are used.  4130 is kinda tough to tap.  .4531 (29/64") is the standard tap drill size and is fine to use.  This will give a very good thread. There are classes of threads as well as percent of full thread.   Be sure and use the .495" reamer for the front of the bungs as shown.  This will leave some threads in this area.  It is .005"undersize to get tight fit to AN bolts. Keep a buildin'!  KK


10/17/00 LINSEED OIL

Denis,  We do not oil the inside of the Model 12 frames.  Those who buy our kits can oil the longerons if they want.  It is easy on a model 12 as the longerons are open at the front end until the engine mount is bolted on.  The reason we don't oil the inside or even recommend it is simple.  We have restored/rebuilt 80+ airplanes some of which were over 60 yrs old.  We have NEVER found a fuse frame that was rusted from the inside out.  ALWAYS from the outside in.  Usually where the fabric and the tubes comes together and dirt and moisture collects.  We have seen lots of struts, like cub struts rust from the inside out when they get wet inside and the water sits in the bottom end.  This may be why everyone things the HAVE to oil a fuse.  Of all the airplanes we have worked on, Stearmans are the only ones that are internally oiled with linseed oil.  No oil inside of cubs, champs, staggerwings, WACOs, stinsons, etc.  Just look around and count how many of these airplanes are still here with us without oil inside them.

BTW, the linseed oil that was used in the stearman frames was RAW Linseed oil that is as thick as tar!  I has to be heated to lower the viscosity, is pumped into the fuselage, the frame rotated for about an hr as the oil is pumped in and flows out the outlet.  After that, excess oil is pumped out leaving only a thin film inside.  The oil cools and thickens and preforms its main task.......sealing pin holes in welds to make the fuse air tight.  That's right, it is to seal any pin holes rather than 'lube up' the inside of the tubing.  The tube seal sold by polyfiber is a thin oil that lubes the inside of the tube walls but doesn't fill pin holes. To be honest, we have never use the tube seal product but have done the above process to stearman frames we have repaired.    KK


10/13/00 LAYOUT, TABLE, SHIMS, STAINLESS LASER BEAM

Help! I haven't been able to think of a good way to get a good straight centerline on my table before doing the rest of the layout for a fuselage ladder. I thought about snapping a chalk line, but hopefully someone has a better way to do it. Also any other tips, or ways to avoid mistakes doing the layout would be greatly appreciated too.  Darin
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The best thing we have found that doesn't cost an arm and a leg is the good old "Stainless Laser Beam".  On the off chance you haven't heard that term, I'll let ya' in on it now.  The "SLB" is a very tightly stretched piece of .020 Stainless steel safety wire.  Fasten one end at the table's edge ever so slightly elevated off the table and stretch to the other edge that same way.  Mark the table along the wire in several places with a sharp pencil and then use a straight edge to draw the center line.  If you build it to a tolerence of a pencil mark, it'll be straighter than most factory stuff.

Later, as you build the fuse up from the table surface, you can use an elevated SLB to measure L and R of center at your stations.  Center the SLB over the original marks on the table by using plumb bobs.

As I have mentioned to you before, paint the table white then do your layout.  After you build the first layout, repaint the table and draw the next one.  On the subject of layout, don't draw centerlines for the tubes. You can't see them.  Draw out the actual width of each tube so you can use a square to align the tubes to the layout marks.  Mark any slip joint reductions too so you know yo place them properly.

Use shims to maintain a constant centerline of all the tubes.  For example, your 12 fuse has 1.25" tubes at the forward longerons.  Then 1", then 3/4".  Use shime to hold the smaller dia. tubes up off the table so that their centerlines are in the same plane off the table as the 1.25" tube.  1/8" shims under the 1", 1/4" shim onder the 3/4" and so on.  This will maintain the proper alignment of all the tubes as you fit them and join them. We use some contact cement to hold the shims in place and then knock them loose after use.

The table we have here has built a fe airplanes.  I originally built it to construct the GeeBee Z replica fuse and tail.  Did that.  Next we rebuilt 3 stearman frames on it.  After that, built our Model 12, the yellow and purple one, and most recently, have used it to repair some L-3 Aronca struts.   KK


10/05/00 CORROSION, RUSTLICK

We use Rust Lick 631 Moisture Displacing Rust Preventative.  MSC, 1-800-645-7270, has it in several packages and we buy the 1 gal jug at about $16 per gal.  We use it on everything steel before welding, after welding, etc.  We use it on sandblasted parts ONLY if it will be a few days before we can get the parts powdercoated.  Otherwise, we normally try to p-coat the parts the same day they are blasted. It is great to wipe on the weldments after you weld to prevent rust from forming after the oil is burned off the  tubes.  You can weld parts coated with 631 without any ill effects then recoat them to stop the rust.  We use it to keep our machinery from rusting too.

We have used the Rust Lick for several years.  A machinist/radial engine overhaul oldtimer buddy of ours turned us on to it.  It is a very thin juice.  We do weld parts coated with it.  We have made tests and can find zero difference in the quality of the weld between RL parts and clean ones.  It is not like having motor oil on the metal which acts more like an insulator like paint does.  Using RL has reduced our sand blast time by about 25% as we now blast rust free parts.  KK
Goto www.mscdirect.com or see a sample catalog page showing RustLick 631 and OLD prices!


09/02/00 CONSTRUCTION METHODS, TABLE, SHIMS, TUBE BENDING, LONGERONS, ROSETTES

Darin,  You will have to heat the longerons at several of the stations to bend them.  Lowers at the second thru 4th stations.  The uppers at the second and the 4th.  Note the top longerons are striaght lines from sta 22 to 86 do this so the canopy will fit.  Slip a piece of alum between the tube and the table where you are heating it.  Will keep the table from burning up.  Basically, if you can pull the tube into the correct position cold and clamp in place, do it.  If you can't heat it. 

Another note is that you will needs shims of various thicknesses.  Say the largest dia tube in the bottom ladder is 1.25dia.  That makes the centerline .625 off the table.  SO, you will need .125 shims under the 1" tubes, 3/16 shims under the 7/8 tubes etc.  You want the centerlines of all tubes to be .625 off the table.  So figure the shim requirements out first and fasten them to the table.  We used glue to tack them in place.  We used 3" long 3/4"sq blocks with a hole at each end for drywall screws to clamp the tubes down over the shims and to the table.  Hope I am making a good picture here for you.  Use blocks on the sides of the longerons and some tubes to keep them in position.

Also, no rossettes on the splices.  The idea is that the weld line is 30degrees to the load which is the minimum stress line of the assembly.  If you add a rossette, you will change to the load path to a higher stress line. KK


09/02/00 CONSTRUCTION METHODS, TABLE

Darin,  40" is plenty wide enough.  You will use the table for the fuse, and the tail building.  Horses are used for the wings.  I suggest you paint the top of the table white.  Makes it easier to see your marks. Layout the fuse bottom and tack it up.  Then repaint and layout the top and tack it up.  Leave the top there anly having to shim it off the table at the tail post and assemble the fuse.  When fuse is done, repaint the table again and layout the tail feathers.  KK


08/23/00 METAL PAINT PREP, POWDERCOAT, SANDBLASTING

How much sandblasting is required to get good adherence between the primer and base metal? Does the oxide layer (rather black layer) on the tubing have to go? Is working hardening of the metal surface a problem? Or should I just degrease it and go? Thanks, Charlie
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Sandblasting is a good idea.  All rust must go.  We try to get all the metal to bright white removing all the dark mill color of the tubing and sheet steel.  Try to get all you can.  Use 35-65 sand or finer.  The big stuff is too abrasive.  Take care on .025 parts.  The blasting can warp them.  Blast only what you can prime in one day.  We blast a fuse, for example, and powdercoat it all in a few hours.  No time for new rust to form.  Touch it with your skin as little as possible too.  Don't drip sweat on it either.  We inspect all the welds after sandblasting and before powdercoat.  We sometimes find a pin hole or other item  to touch up with the torch.  Then we coat it.

I've recovered factory pitts, cubs, etc that were not blasted and the primer comes off the metal with the fabric in alot of spots. KK
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Good point on the cost of powder coating.  Do you send out all the steel parts for powder coating?   Also, have you tried any of the home powder coating products?  I've seen articles where people get an old oven and use it for powder coating. 

I just took a look at the motor mount you sold me months ago.  It had been sand blasted and "oiled".  It still looks completely free of rust.  How long will the oiling last and how is it preped before powder coating?

You also once mentioned touching up powder coating if you must later add a weldment or the like.  What was it you used? Thanks,  Bud Clark
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We do powdercoat all the steel parts in our kits.  All fuse and tail related stuff is grey.  All wing internal steel parts are black.  We use 2 colors to keep similar looking parts from being mixed up by the builder.

As for the engine mount that is blasted and oiled, the powder coat shop will degrease and surface treat the metal prior to coating.  Part of their process.  If you are priming yourself at home, you will need to clean it with solvent.  As long as you do not see rust, it is ok to coat.

I have not tried the home powdercoat stuff.  The majority of the parts in a model 12 will not if in a home oven.  The fuse takes a 14'x7'x7' oven.

We had the local auto paint store mix some urethane to match the grey powdercoat we use.  We use this for touch up.

By the way, take a look at the rudder pedals of some finished skybolts, pitts, etc.  Painted or primed ones will wear thru the paint on the pedal tubes pretty fast, especially here in sandy Florida.  Our model 12 has about 200hrs on it now, alot of acro and many, many pilots.  The powdercoating is still on the pedals.  I was even asked at oshkosh by a sharp observer as to whether we had repainted them for the show.  I told him nope.   KK
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On sandblasting your steel you need to remove ALL material from the surface. It should be white metal before you apply the epoxy primer. If you do this at home build a good booth so that you don't get sand all over everything and do a little at a time and immediately apply the primer. That clean 4130 will start rusting in two hours or less. If it must sit longer than that coat it with a good preservative, of course the problem then is the complete removal of the preservative before priming. This is a pain in the a$$ and is why I said to blast a little and then prime a little. We did our fuselage in about four foot sections. Of course some of the richer builders will have a shop do the whole job including powder coating but we liike to build our own airplane. I admit that powder coating is very nice but it is definitly not necessary. Epoxy primer works just fine. We used Poly Fibre's epoxy. Keep building Keenflyer
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This may be a true statement for well off homebuilders.  We offer our parts raw or coated.  2 raw ones so far, 30 coated.  We don't allow a commercial sandblaster to do the blasting.  We do it here ourselves.  The commercial guys can do more damage than good on light thin parts.  I agree that powdercoating is not needed.  But a good coating of epoxy primer alone is not enough.  Primers are porous by design so the top coat paint will stick to them.  All primers, including the PolyFiber epoxy are designed to be top coated with a paint.  If you are going to spray your own steel parts, epoxy prime them, then top coat them with a color that must be resistant to the glue.  Like the epoxy and Aero thane from polyfiber.  Other choices exist too. 

So considering that both primer and top coat are required on the steel parts, lets do some math.  Enough epoxy primer to do a fuselage cost about $60.00.  Top coat about $55.00.  Granted that you will buy a gal of each so that comes to over $200.00 for the 2 products.  The look at the time to spray the epoxy and top coat.  On a Skybolt sized frame, it takes about 3 hrs to prime and about 3 hrs to top coat if you do a really good job.  We paint alot of frames here having restored/built 80+ airplanes.  We've got the technique down pretty good.  It cost about $400.00 to powdercoat a skybolt sized frame.  So, subtract the $200.00 material and that $200 labor money left.  That ain't enough money to cover the labor cost here in our shop.  So, for our parts, we can sell them to our builders for $150.00 to $200.00 less by powdercoating them than painting them.  From a homebuilder point of view, powdercoating the fuse only cost $200.00 more than doing it yourself.  KK


08/03/00 TOP & BOTTOM VS.SIDES

I'm planning on building top & bottom trusses instead of sides. The top truss should be pretty easy since its mostly flat to STA135, but I'm thinking a lot on the bottom one since it is only flat from STA75.75 on back. Here's my plan so far:

Make a flat pattern layout of the bottom truss using the intersection to intersection distances taken from the CAD program. This won't take into account bend allowances, but should be pretty darn close since the degree of bend is slight. Next I'll tack together the bottom truss on a flat table, but let the tubes at the tailpost run long a little. When it comes time to put the top and bottom together, I'll have the fuselage upside down, resting on the top truss. I'll bolt the two trusses into the motor mount at front, plumb the attachment points out to achieve thrust line O degrees up/down, then support the bottom truss tail up so that the 4,5,6,7 diagonals can be tacked. Next I'll have to bend the bottom truss down so that diagonals 8,9 can be placed. I'll continue to install diagonals then bend the bottom truss down until I get to the tail post, which I will then trim tubes to correct any short/longness problems to get the tailpost correct. I know it would be nice to build the fuselage to .001" of my plans, but after flying numerous R/C airplanes etc, I know that the airplane doesn't care if its off a little, as long as its straight.

Any better ideas / thoughts on the process?   Thanks,  Darin
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I like building a fuse that way better than the side method.  For the average guy, it is not possible though without cad to help.  KK


07/18/00 LAYOUT

Got a little problem with my fuselage side pattern..... I've recently finished laying out the fuselage side pattern on my unpainted particle board work surface.  I did a very careful job of measuring and felt confident everything was within about 1/64".  Being the paranoid first time builder I am, I went back and measured again before putting down the rest of the tube guide blocks.  It seems that due to the particle board drying out and shrinking some of the tube intersection points are off by up to 1/16". (There's also a gap where the two particle board sheets used to be butted together.)

The Model 12 plans call for 0.010" tolerance when measurements are specified to three decimal places. (Which the fuselage side pattern is...)  Maybe I'm being way too anal, but the 1/16" differences I'm seeing are almost seven times the tolerance allowed.  I'm seriously considering starting over with plywood (and painting it too.)  Anyone think I'm crazy?  Thanks, Jeff, Model 12 S/N 104
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I don't think you have a problem.  The main thing is to make the 2 side ladders as exactly the same as possible.  Building a fuse frame like this and being within a 1/16" is very good.  You will be fine.  As a matter of fact, most pitts and skybolts and the like out there are a lot too short.  This happens because the plans in most cases do not have the flat pattern layout like the 12 does and guys layout the ladder to the lengths of the side view in the plans.  When they bend the sides together to the tail post, the frame ends up about 3/4" short.  Still flies the same..

Start hackin' tubes and burning holes in that new table!!  Its fun!!  KK 


06/13/00 SQUARING WINGS, LOWER WING FITTINGS

Charlie,  a 1/8" tolerence is a perfect airplane.  A tolerence that tight makes a few assumptions.  You must assume the fuse is straight and that the wings are both trammed perfectly.  I'm not saying that it is impossible to have such fine parts, but it ain't the norm. 

SO, when he says 1/8" difference, that means using a tape measure measure from some convenient point on the wing, says the rear I strut bolt hole, to a point on the tail post, say at the lower longerons.  Repeat for the other side of the plane.  If these numbers are within 1/8" of reading the same left to right, that is a PERFECTLY SQUARE lower wing set.

What is good enough?  In our shop, I have seen as much as 1.5" difference in this measurement.  Our personal limit is 1/2" difference.  Keep in mind that we deal with alot of very old, previously wrecked airframes.  In the Model 12 world, we don't give a number for the builders to look for when measuring the squareness of the wings.  We tell them to measure the lower wings and write down  the measurements.  What ever the difference, set the upperwing to the same difference which will set the upper wing directly square with the lowers which is more important than how they square with the tail.

What are some tricks to use for a Skybolt or S2 Pitts type top wing with a center pylon??  First, do this measuring BEFORE you install you leading edges.  IF you can, do this before you weld on the lower wing attach fittings, measure the squareness and clamp perfect then weld on the fittings. Or if your fittings are welded on and leading edges are off, retram the lower wings to get the measurement good enough to suit you.  Then  install the leading edges.

Top wings on a center pylon airplane are tough.  You have to get the pylon on perfect and the fitting perfect of wait and drill the fittings when you install the wing for the first time and measure the squareness to the tail.  Again here, if the LE is not on, you can do the best you can with the fittings, then retram the wings to get them to have a satisfactory measurement.  Here use the EXACT SAME POINT to measure the upper wings as you did the lowers.  You can have some slight lean in the tail post if it is not rigged perfect with the tail wires.  So, eliminate the chance of error when aligning the upper and lower wing by using the same EXACT reference point, say the tail post at the lower longerons.  Keep in mind that the diag measurement for the upper wing will differ from that of the lower wing.  KK


06/07/00 FUSELAGE MODS, FUSELAGE CONSTRUCTION METHODS, JIGGING, TUBE SIZES

Kevin,  Tom Weinberger and I were wondering a few things about our fuselage changes. On the short fuse it appears that the lower longerons are totally straight from the rear seat bottom (STA75.75 or so) all the way back to the tailpost. Does that sound right or is there still a little bend up at the first joint aft of there (STA98.25 or so)?

For figuring out the flat table layout figures for the fuselage sides, did you calculate the moldlines, bend allowances and setback etc just like the tubes were sheet metal? Or is it as simple as taking the 3 dimensional point-to-point distance from each joint and adding them up with some factor for bending?

Also, we have assumed that all the tube dia./wall thicknesses remain unchanged. Are we correct?

I've also been doing some tube welds and had some problems right off the bat. After much head scratching and some key help from some guys on a welding newsgroup, it turns out I had a bad can of argon! I had a contamination problem that would make the tungsten turn blue way up into the cup. It first showed up as foaming metal around the edges of the weld. I switched cylinders and no more problems. Now I just have to improve my puddle and feed as I go round the tubes.   Thanks for helping us rookies!   Darin
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Yes the lower longerons are straight from the rear sear area splice aft.

We cheated on building our fuse.  We built the top and bottom, not the sides. Didn't have to figure our as much and it kept the longerons good and flat.  Harder to jig together though with the lower longerons up in free space.

Tube sizes did remain the same. KK
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Thats an interesting idea, about doing tops and bottoms, I'll have to think about that...I'm all for cheating like that. Thanks!   Darin


06/05/00 REAR SEAT MODS

We did change the angle of the seat bottom and the height at the front.  I don't know what it was exactly, we just made it feel good and clear the stick.  I suggest you do the same.  Build the frame, stick assy etc, then tack in a seat frame and try it until all works for you.  KK


05/11/00 TURTLEDECK CONSIDERATIONS FOR SHORT FUSELAGE

Kevin, Do you sell both long and short Turtledeck assemblies? If so is it possible to buy the shorter one? I imagine it would be smart to have it around before I get too far into a modified fuselage project.  Darin
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We only sell short T-deck assys.  We do sell t-deck bulkheads that scratchbuilders can use to made a t-deck to fit their fuse.  You could buy a short one we sell but I'd recommend building the fuse first then build a T-deck to fit it. KK
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How feasible would it be to get one of the short turtledecks and make the fuselage fit it? Could it be as simple as matching the distance from the forward vertstab post to the back of the canopy?  Darin
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I really think it would be harder to force the frame to match one of our parts than to made a tdeck to fit your fuse.  We made this T-deck fit the frame that we welded and because we jig build the frames from a jig made from the first fuse, the tdecks all fit on our frames. KK


05/04/00 FUSELAGE MODS, SHORT ENGINE MOUNT

If I somehow figure out a shorter fuselage, will you sell me one of your short engine mounts? I'd feel more comfortable knowing that big radial is pointed in the right direction on a straight motor mount. Does it make sense to have the mount fairly early in the fuselage build, at least when the mating points are established?  Darin
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Yes, we can sell you an engine mount short or long.  If you are scratch building the frame, having the mount there is a good idea.  KK


05/04/00 FUSELAGE MODS, CANOPY CONSIDERATIONS

Would you recommend getting the canopy assembly also before I build a shorter fuse, to make sure I get things situated at the proper station measurements?
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You don't need the canopy before you start your fuse.  Just keep the station spacing the same as the plans from sta 86 forward on top longerons and sta 48 and forward on bottom longerons.  None of that changed on our fuse so the wings and canopy etc will all fit both versions.  Once you have a fuse built, you can order the canopy at which time we can send you a loaner jig to place all the canopy weld on parts on the fuselage.  KK


04/27/00 FUSELAGE MODS, SPORT AVIATION ARTICLE, HISTORY

Kevin,  I will probably be sending a check for a set of plans soon.  At this point I am considering your wing kit, but am undecided about the fuselage. Call me nuts, but I want to build my own fuselage, however I think that I also like your shortened version. Am I correct that you do not make available drawings of your modified fuse?   Also I have more questions that your website couldn't answer regarding the fuselage decision:   1) Where did you shorten the fuselage in your version, and do you use a shorter engine mount?   2) Is there a difference in the fore/aft seating positions between versions?   3) What other differences are there between your fuse and the plans fuse?   4) Are there differences in the tail feathers too?   5) Do you see any problems with this plan: Build the wings while I defer the decision on the fuselage?   Also, your website doesn't have nearly as many pictures as you had at the forum. Could you please post as many of the JPG's as possible on your site, or email them to me. I'm on a fast cable modem internet connection, so file size doesn't matter. As far as I'm concerned, the more and Thanks in advance for your answers,   Darin
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Darin,  It was nice to meet you, Shawn and your Dad.  I'm still recovering from the 10 days at the show.  Sorry I didn't see you on Thursday.  I was on the Runway holding a ribbon pole for Jim Leroy and his Pitts. 

The plans have the long fuse and stock wing info on them.  The plans do not have the short fuse, modified wings/ailerons etc. on them. 

The fuse is shorter all over not just in a particular bay.  The geometry of the wing attach, gear attach etc remained the same.  It is hard to explain how the changes were made but basically, the humans are forward into the wing cell more and the tail moved forward with them.

Yes, our seats have more recline in them.  However, scratch building a fuse would allow you to angle the seats as you like without changing the main fuse structure.

Our fuse has the stringer lines re contoured to smooth the belly and sides a bit.  Our fuse has the canopy mounts welded on.  These are not on the plans but we send you a jig to install them if you scratch build and want the canopy.  We have all the cable fairleads and a few other items welded on that must be installed thru trial and error on a scratch frame.  We have mounts added for the header tank and smoke tank.

The stab and fin are stock.  Elevators are stock except for the sharp corner on the elevator to match the wing tip styling.  The rudder is larger and reshaped.

Good plan.  Build the wings first as you decide what to do on the fuse/tail etc.  The wings fit on both style fuselages.

I'll send some pics to you and post more to the website.  Let me know how we can help you in this project or in the decision process.  KK
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Kevin,  I'm pretty sure I will end up building one of your airplanes, I'll know for sure after seeing the plans, so I'm sending you the $ for the plans tomorrow. I probably would have sent for them earlier, but I just bought one of the Linoln TIG machines that I got to play with at the SNF workshop.

Compared to the Skybolt/Firebolt, I like the fact that you'll still be a young man throughout my projected building time, your plane is a recent design, and more robust than the Skybolt/Firebolt. Plus, its just plain cool!

As you can tell by my welder purchase, I decided that I really want to weld up my own fuselage. But...is there any possibility of making plans available for the short fuse at additional cost? I'd really like to build the short version, but to just get a prewelded fuse would be like taking half my project away. I think that the shorter fuse looks better and would keep the proportions of the shorter wings, plus I think I would like to have the increased manuverability of the shorter tail moments.

I'm sure you have quite a bit of time into engineering the modifications, and desire to sell as many pre-welded fuselages as possible. Think of it this way, here is an opportunity to make some more money off someone who is going to weld their own together anyway....at this point I don't see the difference in looks and performance as worth the added cost of not getting to put my fuse truss together. Of course I'm only basing my opinion on what I've heard so far. What are your thoughts? Is there really that much difference in the fuselages?

I'm really not in any hurry to get anything in the air since I get to fly at work (although straight and level mostly if I do it right) and I really want to put the whole thing together. Maybe I should just stick with my plan to do wings first, while I try to persuade you to make your short fuse plans available! :)  Thanks,  Darin
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Darin,  We are printing up more plans sets now and should be able to get a set off to you quickly.  You may wish to get a fitting set from us for your fuse to save time.  The sets includes all flat 4130 fittings for the fuse, fuse controls, engine mount, tail. 

As for making the short fuse changes available, I'll be upfront with you.  Drawings from us on these changes are not available.  You are not the first to ask.  Many have and have offered to pay for them.  But, we have made the decision to keep the specific changes private.  The engineering time is only part of the investment we have in the changes.  Jigs fixtures, etc, etc, too. That being said, several builders have asked questions to which I gave general answers.  They were than able to create a fuse similar to ours.  One guy did just this building 2 frames at once.  He finished the first from and then with the second tacked sitting there, bought a frame from us for the second plane. 

I would suggest you begin with the wings scratch or from our wing kit.  Then move on to the frame.

The only reason we made the changes to the fuse was to make it look better.  Performance is the same if the large rudder is on both.  The wing  kits improve the performance of the airplane quite a bit.    Look forward to ading you to the plans holder list.   KK
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Kevin,  Thanks for the candid reply, I certainly appreciate it and understand your position. And it sounds like you understand my position, probably more than I do!

From what I could get from The EAA article, the airplane as shown in the plans had a C.G. problem that required the engine mount to be 11" longer. Do you make two different engine mounts, one for your version and one for the plans version?  Are they 11" different? that sounds like a lot.

Your reply about other builders making changes was a little hard to follow, but if I understand correctly, several builders have built shorter frames based on what information they could get from you.

Is it possible to know who they are? I would be interested in finding out their experiences, and what changes they made. If the changes are relatively minor without sacrificing the safety of the structure I would consider making them too. If its possible to make the airplane look better, I'd like to do it.

I agree about getting one of your fitting sets that Scott makes. I think the accuracy as well as the time saved makes it worthwhile.   Also, what is the larger rudder you mentioned?  Sorry for all the questions, Darin
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Darin,   The SA article  is slightly misleading.  Curtis designed the model 12 with a 14" engine mount.  The airplane had a very short Samson like nose in the orig 3 view we first saw in 1995.  Because of a lack of hard CG data on the engine, prop, accessories, etc., Curtis decided to build the airplane complete from the firewall back.  I mean everything, belts, cushions, pants etc.  Then they weighed it.  They assembled the engine, prop, cowl oil tank air system, etc on a temp. engine mount and weighed that.  They determined the CG of the FWF unit.  Curtis then did the math and found out that the engine mount needed to be 23.75" long rather than 14" long.  About 10" difference.  The FWF stuff was lighter than he first planned on.  So, the engine mount drawing was updated and very first engine mount built for a Model 12 was 23.75" long.  As it turns out, a 14" mount would not have been long enough to get all the FWF stuff in place anyway. 

So, the plans we sell have an engine mount and fuse length just like the plane Curtis and the Boys built, 23.75" mount, 169" fuselage. 

When we started the wings for our Model 12, the prototype had not yet flown. Dad and I had a copy of the stub nosed 3 view and when we saw the actual airplane after the engine was on, we were shocked as to how long the nose had gotten.  We saw it with the engine on but without a cowl and it didn't seem too bad.  But when the cowl was added, it had gotten real long.  We were disappointed.  So, we determined how short the engine mount could be and stilll get all the FWF stuff in it.  Next we redesigned the fuse to allow for the shorter mount.  The net result is a plane that is about 10 to 11" shorter than the black prototype.  In making these changes, we adjusted the seating, changed the canopy, made the rudder bigger, partly req'd for shorter wing span, partly because it needed more rudder.  Then Ben Morphew test flew the black on some for Curtis doing all the acro tests.  He loved it and decided he wanted one too but didn't want to build the wings.  He contacted us and because the wings were yet to be built, he asked for some changes to them based on flying the stock wings on the black 12.  He wanted 1ft less span, bigger ailerons, 3 hinges, slave rods to behind the I struts.  SO, with him wanting these things, we decided to add a few wants of our own to the wings.  Smooth C-section, alum ailerons, beefed up spars in spots, tighter rib spacing to help the fabric stay put, and we wanted to keep the same wing area as stock which forced the square-ish tips.  The end result is the wing set we have in kit form now.  Now, this meant the ribs we had built so far from based on the stock wings were not gonna work and we had to start over.

This gives you the basic genesis of the Model 12 as it is today.  The  plans mount is exactly the length of the black 12 prototype.  Our mount is approx, 4.5-5" inches shorter than the stock one.  We have a jig that makes both the stock and our length mounts.  If you build the mount per the plans, it will be the longer stock unit.

So far, one guy has made a shorter frame on his own, the one I refered to in the last email.  He then decided that, long or short, it was too much work for him to do again and bought the next frame even though he had a home made short one underway.  Other guys are building the long frame, using our fittings, and getting the exterior lines to look like ours, smoother sides and belly etc.  Some are reclining the seats and adjusting the control placements to suit them.  I'll ask if it is ok to pass their names to you.  I suspect it will be ok. 

When you get ready for the fittings, let me know early as we add that set to our order which is every 6 months or so on those parts.  If we were to get just a single set for you, the price would be almost doubled compared to the quote I gave you. 

The rudder we build is larger than the plans rudder.  As I stated above, partly req'd by design, partly for acro.  If you get the fuse fitting set from us, the ribs for the larger rudder are included.  You can build it larger, or cut the ribs down and have the stock size rudder.

Keep firin' away with the questions.  All these will help you decide the best plan of attack for you on a Model 12 project.  Every builder is different and has varied ideas of what they wish to do or buy. We're here to help anytime........KK
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Kevin,   Thanks for the history lesson. I've read your email 3-4 times now trying to make sure I understand how you guys have been working the teeter-totter.  From what I can gather there is only about 5.75" or difference between your fuse and the plans aft of the firewall, or about 19" of mount and 163" or so of fuse.

Hopefully I'll be able to find out more about the other guy's experience in shortening it, but its nice to know that both fly the same if built with the bigger rudder. I have quite a bit of autocad experience designing my house, and will at least investigate the process. I am slightly leery of redesigning the whole fuse, as I'm sure changes made in one place necessitate changes in other unexpected places.  Darin