PAGES

• Intro To FAQ
• General Info
• Welding Related
• Fuselage Construction
• Tail & Controls
• Fuselage Assembly
• Engine & Prop
• Wing Construction
• Cover Finish & Rig

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01/10/03 ALUMINUM FIN FAIRING, SHEETMETAL

I am working on the aluminum fairing panels under the fin which close out the horizontal and vertical stab. I have the Kimball sheet metal kit. My concern is how to end the sheet metal at the vertical tailpost. The sheet metal extends past the post about an inch. Any help would be great. Thanks, Al
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The panels can be fitted 2 ways. One without tail gap seal rubber, the other with gap seal rubber. I would assume you will use the gap seals as we did.

With gap seals, mark the point top and bottom where the skin touches the peak of the vert fin spar. Add another 1/4" to the aft of that mark and that is where to cut the panel. Bend the panel to have a hug up wrapping around the fin spar. Now your rubber gap seal will fit.

Without gap seals, mark the contact point to the spar as above. Mark approx 1/8" points from the contact point marks aft top and bottom. Make a series of very shallow bends in order to form a smooth curve in the metal that wraps around the vert fin spar tube. Then skins should nearly meet at the center.

In both cases, match drill the fin attach bolt hole through the skins as this bolt is used to attach the aft edge of the skins. The alum will have to bridge the size step down from the fuse tail post to fin spar tube. Take care to make this a smooth change in size for a nice look. KK

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Here's a picture of my fairing fitted, also you can jump to the entry for 9/24/03 of my build log which shows the process I used. Darin

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01/09/03 BOTTOM SHEETMETAL INSTALLATION, BELLY FORMER INSTALLATION

Kevin, I would like to know how the bottom fuselage tunnel sheetmetal fits with the firewall and lower side panels. I don't have any pictures of this stuff to look at. Darin
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Darin, The tunnel area metal is assembled as follows: First install the rear belly and mid belly panels with screw hole in the belly formers without holes in the longeron strips. Fit the 2 small bulkheads from sta0 to sta 24.9 on the lower longerons. Fit the left and right tunnel skin such that the 3/4" flange fit into tunnel cut out nicely to accept the tunnel piece. Cleco front and rear to hold in place. Insert tunnel skin such that all of it is closer to the outside than the firewall flanges and side skin flanges. In drops in place when the fuse in inverted without tucking under anything. Note is should allow the curved strip on the firewall cut out to have a radius and not square out the corner. KK
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My problem is that I don't have my belly formers installed yet. What angles do they go at? I thought they simply bisect the angles formed by the bottom longerons where they bend, but I'm not sure now. After reading your instructions for putting the sheetmetal on the belly I just realized that if I don't set them at the proper angles, the sheetmetal overlap may not work out. After I saw this picture of the belly former at FS 24.9 (1st former station) obviously leaning aft, I started to wonder and thought I should ask.

Also the formers at the 3rd station look like they are leaning aft too in this picture, maybe my camera is catching wierd angles! Darin
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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".
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All the panels are designed to overlap 3/4". Same at the rear ends of the aides 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
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Click here to jump to the approriate page from my build log

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12/16/02 STRINGER STOCK AND TAPERING METHOD

Kevin, what stock do you use for the fuselage stringers? Also you told me how you go about marking and cutting the taper in them to get a nice contour?
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Use 2" x 3/8" spruce stock, I think the blanks need to be 7ft long for the longest stringers. You need 6 pieces in all.

Install the stringer blanks on the airplane so they are up to the fabric surface at the sta 86 formers and then are in contact with the vertical tube on the fuselage. Drill the holes matching those in the tabs and attach with screws. Mark on the bottom of each stringer where the end of the tabs are. Remove the stringers, mark a point such that you have 1/4" more overhang of wood past the end of each tab. Draw a smooth arc from the flush point at the fwd end thru the 1/4" offset marks. Cut on this line, use a router to make the edge a full radius varnish and reinstall. The tail end is rounded off just aft of the rear most side diag.

Belly stringers are the same basic proceedure except they will not fit against all the belly tubes due to the depth. You will have to notch the belly stringers around a belly diag as well. KK
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For more detail see my drawing Tail Stringers.

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11/09/02 FREEPLAY OF CANOPY IN LATCHED POSITION

After tack welding the little 1/4" square canopy stop blocks I noticed that when the canopy is latched for flight, it seems like the canopy could go a bit more forward. Question: how much free play forward / aft should it have between the stop block aft and the pins bottoming into the delrin bushings going forward?

It seems like I could move the block forward about .060 and still not have a problem after installing the delrin bushings. I'm just wondering how much slop to allow.
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The delrin bushings have a flange on them about .060 thick. The latch swings up and aft as it rotates so it needs a bit of room to be able to swing up past the front corner of the fwd stop block. Ususally, when the canopy is full forward, there is .050-.060 gap between the end of the latch and the fwd stop block. All this should work out about right with the way the jig is set up. KK

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11/08/02 TEFLON STRIPS IN CANOPY KIT

What are those teflon strips (see picture) included in the canopy kit for and where do they go? Thanks! Darin
Darin, the teflon strips are to be used if needed and where needed. If the canopy works and slides good except for the fact that it drops down a bit when the pins are not in the sockets, you can use the teflon strips at the point needed to hold the canopy up a bit for pin engagement. On 360KC the pic you posted, the canopy frame is not as straight as the kit frames. It was the first one and we used several strips to keep the pins aligned when closing. I have used only 1 or 2 strips on the canopies we have installed since then. Use flush pop rivets to install the strips. Don't install them until you have fully rigged the canopy and it is working perfectly except for a sag at a pin that cannot be adjusted by hinge bearings etc. KK

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06/14/02 CANOPY & TURTLEDECK FIT

When I centered the turtle deck in the aft end of my canopy, the edges of the turtle are not centered on the longerons, enough off to the left that I think the fabric will drag over the longeron on the right side.

I should have been suspicious when I saw the little extra gap between the rear left bushing and the longeron. When I installed the canopy jig, it was tight there, not excessively, but had to be squeezed in by hand.

If I center the turtledeck so that fabric will clear all around, it has excess gap on the left side of the canopy and rubs on the right. Not satisfactory. I don't have formers and stringers on it yet so not absolutely sure about the fabric-longeron interference. With the turtledeck centered, the bottom of the turtle overhangs the longerons about 1/8 inch. - Monty B.
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Monty, the intended position of the turtledeck is to be centered over the longerons. The canopy should have about 1/8" wider gap at the lower left than the lower right. The reason is that on our first airplane, N360KC I had this gap equal on each side. We found that in closing the canopy, people were pulling inward on the handle causing the canopy to drag on the turtledeck at the left side about 4" up from the longeron and downward. So, we widened the canopy frame a bit to the left rear to relieve this.

Now, for yours, simulate the right side top stringer with a 2" tall object 7" below the longeron. This is the location and height of the stringer. Use a straightedge from the turtledeck down over this simulated stringer and slide the turtledeck left until all has a min of 1/16" gap to longeron at splice joint. That'll give you all the cheat you can to the left. Also, take a ball peen hammer and smack away at the underside of the turtledeck at the front left corner to make a concave pocket of sorts for the left longeron to nest into. Only about 2" along the left side or as long as the 1" dia longeron tube is. After smackin' it, put the tdeck in place, close the canopy and jam shims between the turtledeck and the rear edge of the canopy on the upper right area to force the canopy to roll left and utilize the smacked in pocket. Locate the canopy left to right as discussed above and center it at the rear, then drill mounting holes thru the tabs. Oh yeah, the turtledeck is designed to be about 1/8" wide like you have found. KK

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05/20/02 INSTALLING P-K SCREWS & SHEETMETAL, SCREW SPACING

What spacing should I use for the screws into the sheetmetal? Also how do I make the threads in the steel formers for the P-K screws?
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We use 3" screw spacing on most everything. Adjust for corners etc. Also, on our pre-welded fuselages, we fit the lower skins first, rear to front, then the sides rear to front. Note: When fitting the formers to the fuselage and sheetmetal to the formers together at the same time when scratch building my fuselage, I found it easier to fit everything from forward to aft instead, but I did do the bottom panels first like Kevin suggests- Darin

Use #8 x 3/8" long stainless steel sheet metal screws in most all the alum skins. These are only used where the steel formers or longeron strips are located. Instrument panels, firewall, small bulkhead at lower longeron aft of FW, etc are aluminum, so we use 8-32 nutplates in these places. (cowl uses 10-32 nutplates)

The trick is to drill all the attach holes #40 for use of sliver clecos. Do not open the holes up in the steel strips. Typically, people have trouble getting a stainless screw to thread into the steel. So, they open up the holes and quickly find the screws stripping out. Buy a few #8 CAD or Zink plated steel sheetmetal screws from the local hardware store. These should be 1" long min. Make sure they have the same thread pitch as the stainless screws you plan on using. Cut the heads off the screws and chuck one up in your variable speed battery drill. With firm pressure, thread the screw into the #40 holes in the strips and formers. Reverse the drill to remove the screw and then repeat this process for all the #40 holes.

Then open the holes in the alum skins to 3/16". This will allow for primer, paint etc and give you some freedom to adjust the skins here and there.KK

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03/09/02 FUEL TANK VENTING

Can you explain the basic fuel tank venting method used on the Model 12?
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The standard pitts tank has a single 1/4" vent line rounted from the forward bulkhead at center top to out the bottom of the fuse and down the gear leg to near the pant. This one vent is adequate to vent the tank when inverted as the air will still bubble into the tank as needed.

In the model 12, the system is just about like the standard pitts, except we have a header tank too. So, the header tank is tee'd into the same vent point on the center top front of the main tank. This allows the header and main to equalize and vent to atmosphere. Simple like all Curtis' ideas. No need to over complicate the issue with check valves, dual vent lines etc. There are lots of reasons to pick the right hand gear leg too. KK

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01/06/02 P-K SCREWS VS. NUTPLATES FOR SHEETMETAL

Kevin, I've noticed you used P-K screws to hold the sheetmetal on 360KC, why didn't you use nutplates and machine screws? Don't you cut yourself on them working inside the plane? Denis
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Yes, we did use sheet metal screws into the steel formers rather than nut plates. Faster, lighter and so far, still working great. We have some nifty tricks to get them to hold and stay in for many years. We use 3/8" long screws. You say that you would hate to get your hand into them. Me too. But if I had my hand way the hell over there in that position, I deserve it. They are not in a place were you would get into them in normal use. So that is not a real problem.. You are more likely to bleed on a tie wrap than one of these screws. Why did we do it this way? It is light. Pick up a bag 200 of 8-32x1/2" long screws, 200 nutplates, and 400 rivets. Comepare that to a bag of 200 #8x3/8" long SM screws. Ounces>> pounds>> tons>> etc. The yellow and purple model 12 weighed 1472 empty with full smoke system, canopy, and all the other features. That is 7lb lighter than the green culp that had no canopy, pants, cowl, smoke system, etc when weighed. So at 1472, that M12 was only 200lb heavier than the average skybolt and has 2 times the thrust!!!

Heres the scoop on the sheet metal screws. I know there are 'experts' out there that say not to use sheet metal screws on acro airplanes or any airplanes for that matter but the greatest expert of them all, Curtis Pitts, uses and recommends them on his designs. BTW, an 'expert' is someone more than 50 miles away from home..........

Most people like to use stainless steel screws. If you try to thread a SS sheet metal screw into something thick or very hard like 4130, the screw usually rings off the threads. So, most folks will make the hole larger so the screw will go in. Unfortunately, that makes the hole too large and the screws have very little thread engagement resulting in frequent loss of screws.

When CAD plated steel sheet metal screws are used, they will thread into the 4130 without ringing off the threads and usually stay better. The down side is the steel screws get rusty etc.

So, how do you get stainless screws to stay in like steel ones? You use a steel screw to 'prethread' the 4130 so the stainless one can screw right into the preformed threads. Simple if you think about it. This works for .025 4130 formers, .035 tubing, etc. Here is the proceedure for #8 sheet metal screws, modify sizes as needed for #6, or #10 screws:

Drill skins and formers #40 drill and use silver clecos to hold in place. When all skins are fitted, remove skins and open skin holes to 5/32". Use a 1" long #8 sheet metal screw chucked into a variable speed screw gun or drill (makita battery drill) and force thread the screw thru the .025" thick 4`30 strips/formers. As soon as the screw turns easily, stop, reverse motor and remove. Repeat for all screw holes. This will form a thread in the strip that is more than one full thread and actually extrudes the steel a bit making it locally thicker. You end up with 100% thread engagement. Add to this a thin nylon washer under the screw head and you have a set up that will stay in as good as a nut plated screw and will stand many, many in/out cycles without getting loose. If you get a screw hole that gets loose after a while, you can use a rivet squeezer on the hole in the former to flatten the metal again closing up the hole a bit and re-thread it.

Now, this is only done on steel formers/strips etc. This proceedure will not last on aluminum. On all alum formers, we flush rivet in nutplates.

As for the pointy screws you worried about before, you can use "B" point screws that have a tip that is just about as blunt as a machine screw of that size.

We use 3" screw spacing on the skins and cowl for the Pitts Model 12. Yes, 4" will work and save you a dozen or so screws but the metal, even .032" will "pooch up" between the screws with 4" and not with 3". We use a 7 degree hug up break 1/4" wide on all skins too.

BTW, we fit the lower skins first, rear to front, then the sides rear to front. KK
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Kevin & Group, I think sheet metal screws in 4130 sheet is probably OK. However, if you look at any Wichita Whizzer (Cessna) airplane that has had more than 2 annuals (real ones) you will find MOST of the sheet metal (P-K, for Parker-Kaylon) screws loose in the substrate, which is usually aluminum.

P-K screws come in more than one type, i.e. Type A (pointed) and Type B (blunt tip). There is a difference in thread pitch. Type A screws should not be used in a Tinnerman clip or riveted on "speed nut".

I agree that Curtis Pitts is the most capable designer of Biplanes world wide, but Curtis does not usually keep an airplane long enough to do an annual inspection. MY point is that Curtis may not be concerned with the " maintainablility " down the road..... Monty
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Monty, yeah I undestand your point about service down the road. But we used the technique I described on the 2 original clipwing monocoupes we restored, one 10yrs ago, the other 8yrs ago and they still have the same sizes screws at when they started. One key is to not have a gorilla operating the screwdriver! Also, our yellow/purple model 12 has screws this way and has been flying since 1999, again same size screws still in it. I was in ATL recently to do some demo flights with n360KC and looked it over real good before and after the flights. All screws there. I asked the owner about screw loss, and he responded, "what screw loss?" KK
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What about using locktite on the threads of the P-K screws? Bart
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Bart, I wouldn't say locktite is a no-no for p-k screws but it is an unusual place for it. The thing about locktite is its color and that it is thin or thinnner than thin depending on which one you use. A better choice for P-K screws IF you have one or 2 that try to back out is to place a small dab of clear RTV silicone on the threads just under the head. It won't show up like the red locktite. The screw will easily wind out when needed. KK
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I decided to use nutplates. For a list of what hardware I used see my sheet metal hardware list - Darin

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10/31/01 MASTER SWITCH, BATTERY SIZE, CIRCUIT BREAKER SIZES

Should I install a master breaker in my electrical system, or can I just use a master switch? What size battery should I use? Also can you list some circuit breaker sizes you use for various equipment? I'm planning to use the Becker remote radios. Thanks, Charles
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Charles, here are some answers to your questions on Model 12 and M14P electrical requirements. No need for a master breaker. Use a DPST with both sides parallel for the master switch. Use another identical DPST switch for the Radio master.

A 17 ah battery is a bit larger than what we use. We use the B&C 7.2AH battery. Using it, we can get both the battery and the ELT on the batt tray leaving the left half of the tray frame for the smoke pump, ELG ant etc. Mount the Becker remote boxes under the Batt tray stacked flat. Make your own straps to hold it. The stock clip brackets are not so good for many g's.

Breaker sizes:

5A Aux fuel pump
3A (all 3 on 1 breaker) Prime solenoid, air solenoid,air compressor dump solenoid
3A scavenge pump
5A smoke pump and solenoid
(Use mfg info) Radios / Transponder / intercom
(use mfg info) EIS

You can put the breakers, switches etc on a side panel. but, it adds extra wiring work. KK

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09/15/01 INNER COWL DESIGN

I recently pulled up a copy of NACA Report #662 "Design of NACA Cowlings For Radial Air-Cooled Engines." Good stuff, well worth reading.It is available at
http://naca.larc.nasa.gov/reports/

Anyway, one of the interesting details found in the report is the statement that the shape INSIDE the inlet leading edge lip (ie nose section) is unimportant, as velocity is very low.

I have noted some lovely diverging ramps inside entry lips on cowls.  Kevin's cowl on the recently completed black M12 is a good example. Anybody have any considered opinions on the subject? Is there some later report or data that suggests the divergent ramp is worth the trouble to fabricate? Dan
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All the cowls we sell for the model 12 have the inner baffle in them. It is there for strength of the nose of the cowl. So, I designed it as a diverging section similar to a venturi like the work I did on 2 wind tunnels in college. If it were aluminum, it would have been a simple cone. Fiberglass is what we use for the cowl. KK

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08/26/01 TIRE SIZE

What size tires does the Model 12 use?
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The model 12 in designed for and uses 6:00-6 tires. This is a step up in size compared to an S2B/C or Extra that all use 5:00-5. KK

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05/07/01 ALUMINUM SHEET EDGE TREATMENT

My Arcoduster is covered with Aluminum(0.025") from the firewall to the rear cockpit. All my Aluminum is cut and shaped.

Question.. In order to make a nice interface between metal sheets it is  generally recomended to make a 5-10 degree 1/4 inch downward  flange on the edge of the metal. I bought a flanging tool from Aircraft Spruce to do this and it works well on flat, planar surfaces.

Question is, if the surface is curved ( like a rounded fuselage section) and you flange it 1/4 inch while on a  flat layout , it will buckle when you bend it to take the curve. We are talking about 0.025" 20204T3 .. tough stuff.  The only alternative I see is flanging the material on the same curve while forming. This means patterns, jigs and stuff... work..there must be a better way! Any suggestions? Glenn
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On your curved cowl sheets, bend the 1/4" flange down 5-10 degrees like you described below. To get the flange to lay down on curved sections without any buckles you have to shrink it a little. That can be done by tapping the flange with a small leather hammer while it is supported by a cast iron table. I used the cast iron top of my table saw for support. It takes about 10-15 min. of gentle tapping to get a cowl wrap flange about 20" long to lay right. Nothing hard to do, just takes time. Bill
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If the edges you are adding a hug up to are a straight line, use a bending brake to do them.  If not, the hand former.  If the curve is gentle enough as are most on a fuselage, very little or no shrinking will be needed.

We machined a set of rollers for our bead rolling machine that put a 5 degree (max that I suggest using) edge on sheet metal panels.  It will work on straight edges, curves, zig zags etc with ease. The angle is 7 degrees and results in a 5 degree bend after spring back and tool flex.  We also have one that does a 20 degree hug up for the edges of the 4130 tail ribs in the Model 12. KK

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04/18/01 FUEL TANKS

Bud and I have been discussing the fuselage tanks. I'm curious, why do the plans specify different Aluminum for the header than the main tank?  Also, do you sell the end caps for the tanks?  Do you make them as per plans, or do you do something special here too?  I know for sure I'll be buying a wing tank from you.  Darin
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Let me begin by refering you to the Sport Aerbatics article on the Model 12 that interviews Ben Morphew.  Read the section where he refers to spending $700 to build a $300 tank.  If after that you still wish to build your own, OK by me.

The Smoke tank is not in the plans, it is special from us.  The header tank is built as shown in the plans.  Bud is using standard weld in Bungs which is ok but it is better to use some custom made to the drawings for several reasons like clearance, strength etc.  Also, the ones he plans to buy require that the skin have a flare pressed into the skin for welding.  This is done with a set of special made dies.  If you have no tools for this, you need to re machine the flanges for welding. The main tank we sell in not made to the plans.  It is dimensionally different, includes many added features and improved fillerneck/cap etc.  WE make the main tank and header from 3003. The other material specs are to allow for easier forming of the parts.  We do not sell any parts for the tanks, complete tanks only.  Note the special fittings in the main tank big and small that fit into the tank rather than on the outside, this is a must.  You cannot use store bought fittings here like the 3/4" pipe bung on the bottom of the main tank.  If you use a standard bung here, you will not have room for the elbow and hose above the header tank.

Now, the plans main and header tanks will fit fine.  Ours have more fuel and have added features not shown on the plans.   Our wing tank is special and the smoke tank is not shown in the plans.
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I'll also look into the difficulty of making the 651-6 bungs before I decide. What material are they machined from,  3003?  Darin
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The bungs are machined from 6061 alum.  Easiest to get.  Our main tank has added capacity that makes up for the loss of volume in the wing tank when we redesigned the wing/centersection to remove the external stiffeners. There are several other 'extras' in our main tank the least of which is that the parts are laser cut and hydroformed for a very high quality part. Let me know when you are ready for tanks.  Typical lead time is 2-3 months.  KK

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03/05/01 TRIM HORN

Trim horn bolt holes. How shall I line everything up before drilling the bolt holes attaching the trim horn to the shaft? Neutral elev, neutral trim handle, neutral tabs and drill?
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Line up the trim horn and both output arms even.  Say all 3 vertical.  No need to have the trim tabs linked to the output arms with the rods.  The idea is to have the 3 pieces aligned.  After the 3 are bolted together, adjust the rods so that with trim handle level with top longeron, stab horn assy is vertical, elev in neutral and trim tabs aligned with elevators.  KK

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03/05/01 FUEL PLUMBING

Just got my March Sport Aviation.  Two articles that drew questions. Page 35, Fuel Systems. With regard to the M12 I have mine plumbed almost like the right side of page 36(series feed), except I don't have the return line with the orifice and check valve and I have a tee for a riser as recommend for the fuel flow sensor.    They state that the parallel is better.  I like the simplicity of the series as you aren't pumping against a check in the other pump , but the aux must pump thru the engine pump.
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Simple is always better.  The Model 12 fuel system has hundreds of hrs of flight time with a very simple layout. Tank, valve, boost pump, gasco, engine pump, carb.  IF fuel flow is added, place between valve and boost pump.  If the system has adequate flow rate this way, no need for the extra parts.    KK

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03/05/01 SEATS, PLYWOOD

I want to get the plywood for my seats in the Model 12. Kevin says 1/4" birch ply. But, when I look at the catalogs I see to ply orientations, 90 and 45 degree. In concept I like the idea of 45 degree orientation.  Any ideas?  Also I haven't seen a pic yet of the plywood seats installed. I'm not sure how high up they should go. Top of the frame? Above the frame? Anyone have a pic? Jerry
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Jerry,  90 is what we use.  45 degree is for applications with large loads in the plane of the plywood.  45degree ply will be no better than 90 degree stuff for loads like on a seat. The ply seat boards are cut such that the top edge does not extend above the upper most part of the cross tube they fit against.  The front one has notches in the top of it to clear the shoulder harness straps.  KK

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03/05/01 FIREWALL

I have never tried to form stainless firewall material like the alum bulkheads.  My guess is that it would be very difficult to do without pressing flutes into the flange.  In the case of the Model 12, .018" thick stainless is not strong enough to do the job of the firewall flange.  The flange hold the cowl on the airplane and is .063 alum angle riveted to the FW and then a .050 2" wide strip riveted to that.  KK

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02/05/01 LANDING GEAR INSTALLATION, SWAY PLATE, TAILSPRING HOLES, TAILWHEEL

Here is a run down on how to get all of the gear installed.  First, use a flat file to remove the p-coat from the gear bushings so the main gear spring will fit between them.  Only remove a small flat spot along the length of each bushing where the alum gear will touch it.  It is a SNUG fit.

Next, carefully open the 4 holes in the centering plate until the plate will slide over the bushings all the way to the longerons.  Keep these holes as tight as possible.  When you get the plate to slide fully on, you will see that it hits the welds at the bushing/longeron joints.  Carefully chamfer the holes to clear the welds.  NOT all the way around the holes, only at the front are rear of the bushing where the weld touches.  When you get this right, the plate will lay on the longerons.

Now, I find it easier to rotate the fuse right side up and set it down on the gear.  It takes a couple of people but works better.  Hold the centering plate in place with tape.  Lower the fuse onto the gear. Now, note that the front of the gear is straight all the way across and the back tapers to the shoulder.  The gear clamp blocks go on with the round surface touching the gear leg.  Heads down nuts up. With the fuse sitting nice and flat on the gear diag measure from the bottom end or one axle bolt hole to the opposite front gear bushing end. Repeat and adjust the spring left to right until even.  Look at it too.  Believe your eyes.

Now, drill the 1/4" hole from the top down through the centering plate. Mark the centering plate so you can put it back on the same way later.  Like TOP and FORWARD.

Now I would put the tail wheel on.  Bolt the tail wheel unit to the rod spring with 2 3/16 bolts.  Clean out the tube in the fuse so the spring slides in easily.  Find the point on the rod where the 1" straight section meets the start of the taper.  Mark it with a marking pen.  Drill 2ea. 1/4" holes in the spring.  It is as hard as woodpecker lips.  Use liquid dishwashing soap for the cutting fluid.  Drill one hole vertical (same as the 2 that hold on the wheel unit) located about 1" aft of the front end of the rod.  Drill another 90 degrees to it or horizontal about 2 1/2" aft of the first one.  Step drill from small drills to 1/4 to get them thru. (Darin's note: A 1/4" Solid Carbide Straight Flute Drill works well by itself no steps) Now measure from the mark made earlier to each hole and mark the fuse to at the hole locations.  Drill 1/8" holes in fuse tube.  Slip rod into fuse. Level fuse across top longerons at rear seat cross tube.  Shim under gear legs as needed.  Place a level on the side of the TW housing to level it making it vertical when fuse is level.  Use a large c clamp to pinch the end of the fuse tube onto the rod to keep it in place and aligned.  Use a dremel or die grinder bit to open the right side hole and bottom hole in fuse tube to match the holes in the rod.  Drill 1/4" thru to the other side using the rod to align the bit.  Drill the front one first and put a bolt in the hole. Then drill the other one. Take a look at TailSpringInstall.gif. Now, install the pant brackets, axles and torque plates on main gear legs. Then the wheels.  KK

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01/31/01 HEEL TRAYS

We use .050 3003-H14 as it is easy to bend at sharp 90 angles.  We make ours about 6" wide with 3/4" to 1" tall flanges pointing up alonge the sides.  Slippery is good for the heel trays.  Your heel slides fore and aft as you move the rudders.  Nonskid would be a bad thing for these.  We leave ours bare alum, slightly polished.  The shoes do the rest of the polishing.  KK

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01/10/01 TAILWHEEL

Here is the scoop on tailwheels...........Denis, What you have is refered to in the industry as a "Steerable tail wheel".  It is connected to the rudder via chains and springs and is steerable 30 degrees left and right of center.  Beyond 30 deg, the unit casters free to swivel freely.

A second type is full swivel or non- steerable tail wheel.  This one has no steering attached to it nor any other controling mechanism.  It is free to swing a full 360 degrees all the time.

A third type is lockable tailwheel.  This one locks into a straight centered position for take off and landing.  When manually unlocked via a cable control in the cockpit, the unit is free to swing 360 degrees for taxi and parking.  A haigh Locking tailwheel made popular by Pitts S1 pilots lock this way yet does not swivel 360 degrees.  If you want to back the airplane up, you must lift the tail or use a dragging unit to pull it backwards.

A forth version is the steerable non swiveling tailwheel.  This is on many older a/c types like monocoupes, and others.  It steers with the rudder but will not swivel 360 degrees.

There are slight variations on all of these above.  

The scott 3200 is super overkill for a skybolt.  It is good ballast weight if you need it.  The Maule tailwheels and Lang tailwheels aren't that reliable. We use the Aviation Products unit.  It is on Model 12s, DR 107, DR109, G200, G202, Extras of all models, and many more.  It is not expensive and comes in rod type or flat spring type units.
I have watched the action of the tail spring on the Model 12 on landing and it deflects a fair amount.  It may be too great to allow a direct link to work well. Two chains and springs, if set up correctly with zero slack, give very positive response and the springs allow the chains to stretch when the tail bounces.  Much of the trouble with steering chains is from leaving them slack.  Set up correctly, the 2 chain method is as positive as the direct rod yet results in zero bump steer.
BTW, the unit we sell is modified by A/P to our specs.  They make or have made the spring for us too.  But, as with our other vendors for gas tanks, gear, wing wood, laser parts, fiberglass, etc., the drawings we sent them and the parts they make from those drawings are proprietary to us,  So, they are not supposed to sell a spring made from my drawing to anyone but us.  Now, I  don't know if they have other similarly sized rod springs available or not.   I do think they have the standard smaller dia ones available.   KK

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01/01/01 RUDDER PEDAL HINGE PIN, BRAKE PEDAL END CAP WASHERS

Well thats about it for the question free period. I couldn't find anywhere in the plans what is used as a hinge pin inside the 210-108's and the 510-53's on the rudder pedals. I assumed it would be 1/2"x.035 like the rest of the pedal, but the pics I have show something that looks solid, with a bolt holding it in position.  So what is the hinge pin made of and what hardware keeps it in?
Another question, I went to find the 510-62 washers to put on the ends or the top brake pedal tubes, but couldn't. Are they supposed to be in the laser cut stuff? I couldn't find them, or the holes they came out of.
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The pins are made of 1/2 x .035 like you thought.  They are held in with a #8 or #10 screw thru the outboard bushing and pin that is drilled horizontally.  I am sure you got a pic of this of the fuse we are readying for cover.  The solid bolt picks may be from the jigs.  We use a 1/2 bolt when welding the bushings on to keep them aligned.
Those washers are standard AN960-10 washers.  This is a washer that is 1/2" OD with a 3/16" hole(sloppy) and it is 1/16" thick.  You can use a washer from an autoparts store or hardware store if you don't have access to AN washers.    KK

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12/26/00 LANDING GEAR, BRAKES, BRAKE LINES, TIRES, WHEELPANTS, GUNDRILLING

Gundrilling of landing gear, in this instance Kimball model 12. It seems to be a very slick way of handling the brake lines, yet Kimballs stock setup has external lines and a fairing. Is there an inherent flaw in gundrilling gear?

Tire ratings. Kimballs call for 6.00x6 tires. Looking at ply ratings 6 ply rated to weights 1750 lbs, 8 ply to 2350 lbs. Model 12 gross 2250 lbs. Should each tire be rated to a/c gross? Half gross? While we're on the subject any experiences good or bad with specific tires?  Thanks in advance, Jerry
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Gun drilling the gear is a very slick and safe way to get the brakes hooked up on most alum spring gear airplanes.  Another technique is to groove the trailing edge to allow the brake line to be bonded in place.  

In the case of the Model 12, the gear is too long to gun drill.  The length of the legs makes them look skinny so I designed a flexable rubber fairing that glues to the trailing edge of the gear.  It adds about 2" to the width of the gear making it look nicer and wider.  Inside this fairing are 2 holes that run the length.  The alum brake line is slid into one of the holes.  The gas tank vent line is placed in the other.  This gets the tank vent down to the pant so that during acro, you do not vent fuel overboard.  If you have a gun drilled gear or skybolt bungee style gear, you can't run the vent down the leg.

The tires are rated at the load per tire.  So, 6 ply rating tires are the recommended tires for the Model 12.  To be specific, 6 ply rated 6:00-6 tires are rated at 6 ply but have only 4 plys in them.  The raintg scheme must be left over from old tire technology.  Purchase 6:00-6 6 ply rated tires.  I suggest you get some old ones from the local maint shop for all the rolling, building fitting etc and then buy some tires a month or so before you fly.  If you take a yr or 2 to build, buying news tires at the start is a waste of $.  KK
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I don't understand the comment about not being able to vent through the Skybolt bungee style gear.   We ran our brake lines and our fuel tank vent lines through the gear vees on our Skybolt with no problems. We used aluminum tubes attached to the inside of the vees with adel clamps. The brake lines are on the front LG tubes and the vent lines are on the rear. Fuel vents face forward and are down at the brake caliper level. On the brakes we used a flex high pressure hose from the master cylinder to the internal aluminum lines and on the vents we just used a plastic line with safety wire fasteners.  Is this wrong???  Keenflyer
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Sorry for the confusion about the vent lines.  I agree you can run them inside the fabric or alum leg cover but not inside the structural members, the equiv to gun drilling an alum leg.  In brake systems, it is best to use as little hose as possible as even the $50 per foot hose will swell with pressure resulting in a softer, less positive brake.  On the bungee type gear, you need a hose from the top of the gear leg unit to allow for movement of the leg and hose at the master cyl.  If the M/C is 18" or less away from the point where the brake line enters the gear leg,  a one piece hose from the m/c to the leg is ok.  If it is over 18", using a short hose at the m/c, another short hose at the leg, and an alum line between them will give better brake action.  On the Model 12, we run the alum line from a bulkhead fitting mounted in a tab welded to the fuse frame down to the caliper as no hose is needed at the top of the leg.  The tab is placed so that only a 12" hose is needed at the m/c.

With both bungee gear and spring gear, the axle does not move relative to the leg (at least it is not supposed to).  The caliper moves only a small amount. So, no hose is required at the lower end of the leg to the caliper.  Just run the alum line right to the fitting on the caliper.

On brake sizing, single piston 6" wheel are perfect for a skybolt of model 12.  A 12 has about double the static thrust and a higher gross weight than the skybolt yet we use and recommend single piston calipers.  In a tail dragger, you don't want brakes that are strong enough to hold a full power run up.  You want them to hold more than a tipical mag/prop check run up but not full power.  That is too much brake.  This is true for our kinds of tail draggers as well as staggerwings, stearmans etc.  We set staggerwing brakes up to just creep forward at full power.  Now for the model 12 with single caliper brakes, the tires slide on grass with the brakes locked at higher power run ups!  Also, the M14P has soooooo much thrust, if you cycle the prop at an rpm higher than 2000 rpm, the tail will lift even with the brakes locked and the stick full aft!  So, it is a good idea to do m14P run ups and mag/prop checks at less than 2000 rpm on skybolt and model 12 sized airplanes. The 2 blade prop may not do this as much as the 3 blader but it is something to watch for.  KK

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12/23/00 INSTRUMENTS

Discussing the cost of instruments for my 12 with my wife she asked why I needed an altimeter, airspeed, tach/MP in the front pit as she really doesn't  want to see them anyway! I couldn't really come up with a good reason why I should invest in them. Your input solicited. Thanks,  Jerry
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We too wondered about what instruments to place in front and why.  First of all, the panel itself has to be there to hold up the sheet metal.  

Here are a few reasons why I can think of for instruments in the front ( and Brakes for that matter).

1)  Good to have backup instruments incase of loss of the rear ones.  In the 12, you can see a fair portion of the front panel from the rear even with a pax onboard.  Nice safety feature.

2)  Is there even a remote possibility that you will have to get checked out in this airplane?  If so, wouldn't your instructor like to have instruments in the front to make decisions?  Brakes too?  

3)  Is there ever a chance that you will need to check someone else out in the airplane.  Kids friends, wife, buyer?  I'd bet instruments would help there too. Brakes also!

4)  What else are you gonna do with the 31" wide by 11" tall panel.  Its a mighty big blank spot to stare at for 3+ hours at a time!

Reasons why not:

A)  Saves weight.  between 1 and 2 pounds for the basic instruments that you mentioned.  That's 0.008% of the gross weight.  Not much savings.  

B)  Saves some $.  About $300 to $500 depending on what you use.  Not much in the big picture of building an airplane.

C)  You never plan on giving or gettingcheck outs or letting someone fly it from the front.

Here is where we are doing and recommeding these days for instruments.  In the rear, an A/S, ALT, G Meter, EIS system for all other functions.  In the front, compass, A/S, Alt, and second EIS slaved to the rear one.  Total cost for instrumenting both holes of a 2 holer this way is about $2200.  Also in the rear, we recommend the Micro Air comm and transponder.  They have a new version of each coming avial in a few days.  Both are 2 1/4" dia panel mount and remote mounted brain boxes.  This means that the comm and transponder can be in the rear panel as well rather than under it or on the back of the front seat.  Very nice stuff.  The comm/xponder package is about $2k.  Add a handheld GPS nicely clipped to the rear panel and you have all that is needed for your airplane.  KK

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12/20/00 RUDDER PEDAL, BRAKE PEDAL

Does the little .38 long piece of 510-60 just free float, held by a cotter pin or something?
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Cotter Pin YEP.   KK

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12/19/00 TAIL BRACE WIRES, HORIZONTAL STAB, VERTICAL STAB

When looking at some pictures, I noticed Ben's red airplane had 2 brace wires from the vert stab to the horiz stab while the plans and pictures of 360KC show only one on top. Was that just added for extra strength?
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He did it just because he wanted to.  Cost extra $400 for the added tail wires.  Curtis says not needed.  KK

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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

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11/20/00 FUSELAGE MODIFICATIONS, PUSHRODS, CONTROL SYSTEM, IDLER, TRIM TAB, RIGGING, ELEVATOR TRAVEL

I did some measurements on the REPB3N2's and have drawn the plans version elevator control system. Now I am considering the necessary changes for my shorter version. Of course, I have a few more questions:

1) What are the neutral rig points for the elevator? Is it faired with the horiz stab?

2) What are the degrees of travel for the elevator up/down?

3) What about the trim tab system, where does it rig, and what are its travels?

4) When considering the pushrod system, I think I will leave the forward idler at the rear seat the same, and the rear idler a little shorter (about .16")  Did you leave the front idler the same as the plans version too?

5) I found the two pushrods from the front idler out to the elevator do not form a straight line, but instead sag down to the rear idler by about .9", is there any reason for this? Is it better for the pushrods to form a straight line along the idlers when at neutral?

Thanks in advance for your answers,  Darin
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1.  Elev centerline is aligned with stab centerline in neutral.

2.  25 deg. up and down for elev

3.  Rig centerline like elev.  Travel is something like 19 one way 7 the other.  Let it go what ever it does.  Don't use it all.  

4.  Yep.  My front idler is same length, and the rear one is shorter to clear the diagonal in the fuse frame.  Consider the width of the bracket end of the pushrod to clear the fuse diag.

5.  Sag OK.  To clear another fuse diag.  No toggle over center problems.

KK

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11/12/00 BEARINGS, PUSHRODS, CONTROL SYSTEM, IDLER, REPB3N2

Here is the list of bearings we sell in our Bearing kit:

22 KP4 all sticks idlers bellcranks
18 REPB3N2 all elev and aileron pushrods except one below
2 F35-14M #1 elev push rod(one under rear seat rear stick to 1st idler)
4 F34-14M (sometimes substituted with Aurora equiv.) Trim tab rods
2 KP3L

Regarding the substitution of HEim bearings for the Fafnir: Basically, you don't want the heim style bearings used as replacements everywhere.  We put them where it is ok but they have more slop than the Fafnir.  The fafnir is a double row ball bearing inside the rod end.  Very slop free (read flutter free).  Saves about $100 to get the stuff from us over catalog price.  KK
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I got my bearings from ACSpruce today and have some questions.

1) As the torque tube is twisted for aileron inputs, is all the twist taken up in the two REPB3N2's on the 510-34 rear stick to idler tube? Or does some of the twist transfer up the line further?

2) Oops, I just realized that you substitute the F35-14M's on that pushrod, is that to allow more twist allowance?

3) What would you consider the minimum thread engagement for the REPB3N2's? I am curious about the adjustment range of them.

4) What hardware is used to attach the REPB3N2's to the pushrods, and the idlers/torque tubes to the bearing cage assy's?

Thanks, Darin
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The 2 F35-14Ms give nearly all the rotation needed for full aileron travel.  The aileorn system is designed to allow 27 degrees max travel to jam each way.  Stops are set for 25 deg each way leaving a 2 degree cushion.  The elev rod front front to rear idler will rotate a bit with the TT swing but not to its limits.  Min thread ingage is to the tail tale hole in the bearing shank.  To be legal, the rod must block the hole when checked with a piece of wire.   When I design rods, I set them so the threads are inserted half way from the tail hole to bottomed into the bearing.  I don't recall that # here but you can measure it.  This will give you max adjustment in and out. KK

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11/10/00 INSTRUMENT PANEL, TURTLE DECK, ALUMINUM FORMING

Most panels on planes like this are made from .050 aluminim.  In the case of the Model 12 and all pits before it, .050 6061-T6 is used.  Cut a 3/4" thick plywood cut out of the panel as you want is shaped.  Cut another ply piece 1/2" smaller all around and cemnter it on th efirst one and drill 4 3/16" alignment hoes thru both.  Cut out a panel blank 3/4" larger than the panel plywood and sandwich it between the 2 with bolts thru all.  Use the ox torch to anneal the exposed flange and quench with water.  Hammer flange over 90 degrees.  Reheat and anneal as needed a few times.  Makes perfect formed panel with no rivets to hold on the flange. Annealing tips: Scribble a lline from a black sharpie pen on the flange.  carefully heat the alum until the ink disappears that gives proper temp of metal.  Then quench with water.  Practice a few times before you do the panel.  This is how we make the front and rear panels, bulkhead fwd of read panel, and the turtle deck bulkheads.  No flutes or wrinkles.  KK
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Denis,  Your form blocks look good.  One should be the size you want for the panel less the thickness of the material if you want to be extra picky.  This is the actual form block over which you will for the panel.  So, to explain it better, place this block on the table(it is the larger one shaped exactly like the paenl all around.  Next, lay on it the .050 6061-T6 alum.  The alum panel blank should be 5/8 to 3/4 inch larger than the form block on the table.  Next stack on the topp clamping block.  This one is 1/2" smaller all around than the form block and about 1-1/4" smaller than the alum blank with the extra metal to form the flanges.  This one is smaller than the form block to give you room to hit the alum with a  plastic hammer to form the alum over the larger block on the table.  IF the clamp bolck were the same size as the form block, it is hard to form the metal.  Now, bolt all 3 together in say 3 or 4 places.  I like 4.  Clamp it all to the table, mark with the sharpie as I described before, and hammer to shape.  You may only get part way and the material gets too hard to continue.  Sharpie again, anneal, hammer.

This is how we make the panels and bulkherads for the 12 except we have 3/4" thick steel form blocks and 1/4" thick steel clamp blocks.  We also laser cut the alum blanks to shape with bolt holes in them.  We use steel so we can make hundreds of them without the tools getting hurt.  Wood is great for one airplane like you are doing. KK

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10/19/00 FIREWALL

Kevin and Group, do you M12 builders insulate the firewall? If so, what do you use and how is it applied? I get a fair amount of heat through the un-insulated firewall behind my Lycoming and think I might get way too much heat from a m14p in the summer.  Regards, Bill
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Sorry for the delay in writing back to you.  I have been in S. Florida.  I don't know what the other Model 12 guys are doing/planning to do.  We used some of the 3M Sound Dampening Tape, aka, 1/4" thick closed cell foam with alum foil on one side and adhesive on the other.  We installed it in pieces between all the tubes at the FW station on the back side of the FW.  Seemed to work OK.  KK

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08/13/00 RUDDER PEDALS

Pitts style rudder pedals are simple.  The vertical tube of the rudder pedal has 3 bushings.  Top for brake pedal, bottom for pivot on fuse bushings and a 3/8x058 one thru the tube near mid way up.  Thru this bushings we run a 1/4" bolt.  On the outboard side of the pedal, bolt the adjuster plate and the link rod using that one bolt with the adj nearest the pedal.  I'll find a pic of it and show you.  Very simple, light, easy to adjust, etc. Our rudder pedals are adjustable.  We have an adjuster plate at the rear pedals ala Pitts S1 and S2.  Allows for approx 3" of pedal adjustment and takes a few minutes to do.   KK

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08/12/00 RUDDER CABLES

Looking to order rudder cables! I'm thinking 7x19 Flexable 1/8 Dia in Stainless.(yes/No)  with a swaged fork end for rudder bell crank. Looks cleaner. Am I on the right path? What's a tensometer and do you really need it. I thought 2 2x4 and a few clamp's to impend any movement of the rudder blocking it and a good pull on the cable with anouther chap ready with the nicropress is how it.s Done and a good turnbuckle to pick up any future slack. Add Kevin's Adjustable mount plate vola. Or is this wrong? This is a point that could be added to the plans. Denis
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1/8" cable is the one to use.  I agree that swaged ends are neater.  We use them often but have used the plans specified nicopress sleves on the 12 so far.  Galv cable is stronger and far less stretchy than stainless.  It has a higher pull out rating than stainless too.  We made some tests to varify this a while back with a wench and a load cell.  The cable always broke before the nico end or swaged end failed.  The nico ends are rated to have a higher pull out rating than swaged and out tests showed this to be true.  Each time the cable broke before the ends slipped or pulled out.  Keep in mind that you will apply only about 200lb on the cable when the rudder hits the stop and you keep on pushing.  So, you have quite a large margin of safety.  I saw a stearman that crashed that the pilot survived.  He had a broken leg.  The 1/8" rudder cable held and as he slid forward into it, his leg shattered.  Tough cable.  KK

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08/03/00 COWL

We cowl the Model 12 without attaching the cowl to the engine itself.  The cowl is mounted to the firewall only and seals to the engine baffles with rubber rub strips.  The russians use a cowl of many pieces.  The 2 piece nose bowl is mounted hard the the engine clammped to the baffles and with braces to the cyls.  The remaining cowl from the nose bowl aft the the firewall is made of 4 or 5 panels attached with a camloc type fastener.  Full cowl is cleaner than speed ring.   KK

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06/25/00 FUSELAGE CONTROL RODS, SKYBOLT REVERSER BEAM

The Model 12, or any pitts design for that matter, does not use a reverser beam like the skybolt.  Pitts style elevator horns point up not down like a skybolt.  This gets rid of the problem of the longerons getting too close together at the tail post when welding and allows for the rod end bearing without clearance problems.  But the main reason for it is loading on the push rod.  It is best, when you can, to load a control rod in tension for the primary use rather than compression.  In the case of the pitts way of doing things, stearmans too, the elev rods are all being pulled for up elev not pushed like the rear rod in the 'bolt.  The Model 12 has 2 idlers in the elev linkage to keep the pushrods short and stiff.  It is common practice in these type control systems to lilmit a 3/4 pushrod to a max length of about 45" so that it will not bend or buckle under loading.  Also, if it is too long it could vibrate or buzz causing a failure. KK

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