I was wondering why, instead of the Fafnir rod ends specified in the plans I couldn't use another brand with the same dimensions. I am talking about the ones for the push-pull tubes in the elevator and aileron control systems. I was looking through the latest edition of my 'Chassis Shop' catalog (they sell race car equipment) and noticed they had Aurora brand 4130 rod ends rated at 5260 lbs radial load for $14.96 each in quantity (10+). The equivalent Fafnir from ACS cost $50. Personally I don't see how I could ever come close to exceeding the load they are rated for. Brad
Here is an image showing information from the Aurora and Fafnir bearing catalogs:
Fafnir vs. Aurora Rod Ends

The question was about substituting an Aurora AM series rod ends for designer-specified Fafnir REP series. Without a bearing catalog to look at, you had little information, mostly just price and a load rating. Might there be more?

As it turns out, the Fafnir REP series and the Aurora AM series are very different bearings. Different doesn't necessarily mean "can't substitute", but it's best to do so in an informed manner.

The major difference is that the REP is a ball bearing rod end, while the AM is a simple PTFE coated race (no rolling elements). That explains the difference in cost, and the lower load rating for the Fafnir. If I understand the tech pages correctly, the Fafnir rating is based on the lower of two different methods, the load that dents the rolling element parts, or 66% of the load that ruptures the outer casing. Aurora doesn't tell you much in their catalog. Apparently it's rupture strength less "appropriate safety factors". Point is that you gotta read the tech pages to find out how they came up with that load rating. In any case, the Aurora plane bearing will have a higher static load rating just because the only moving part (the big ball) has much more contact area than the little bearing balls in the Fafnir.

Ok, the Aurora is stronger. Here's the downside. Given a proper clamped installation in double shear, it will have more friction, perhaps a LOT more. I suspect the designer specified the Fafnir for a reason, that being control feel (frictionless) and better hands-off return-to-center performance after a control input away from trim speed. We all value buttery smooth, frictionless, low-breakout control forces in a sports biplane. So what are you willing to pay for it? When considering the overall cost of the airplane, most people opt for the Fafnir.

There is another important detail. Note the allowable misalignment angles. The Fafnir allows 20 degrees total. The Aurora is 16 degrees. This is often an issue on elevator control systems, usually at the aft end of the control stick mechanism. If you use the Aurora, you much check carefully to be sure you have enough angle without hitting the limits at full control deflection. Dan


Kevin, what hardware (bolts/nuts) do you use for the elevator stops on the torque tube?

Do I need to grind flat or round the end of the bolt for hitting the stick lower 510-14 plates?

See Front Stick Picture

Also I just discovered that I put the -14 plates a little too high about .15 -.20. When I look through the stop hole, it doesn't appear to hit the stick lower much, maybe just the edge. Same in the back. Should I just cut a couple little pieces from some sheet and weld them in for the stops to hit?

It looks like even if I had put them right at the 3.20 dimension from bearing C/L, there still wouldn't be much there for the stop bolt to hit. Just exactly how much of the -14 plate on the stick lower is the stop bolt supposed to hit? Darin
We use 5/16-24 2" long stainless steel bolts that we thread full length for the elevator stop bolts. If the nuts welded to the torque tube are positioned such that the bolt is as high in the thru hole as possible and the stick is welded up correctly, you should have full bolt contact to the stick face but a 2/3rds minimum bolt dia hitting the stick face is OK. Keep in mind that the stick positioning and travel affect the contact point. Normally, there is quite a bit of bolt sticking into the box area (over an inch).

Sounds like you built the sticks with the end plates too high. A simple fix would be to move the nuts that are welded to the torque tube up as needed to give you full bolt contact on the sticks. KK
I ended up moving the nuts higher on the torque tube. Also, after ruining a die trying to cut threads to the bottom of a stainless bolt, I cut a length of SS threaded rod and welded a nut on top to accomplish the same result. See My Elevator Stop Bolt...Darin


How do you prepare the AN490HT threaded rod ends and the pushrod tubes for welding?
All push-pull rods are fishmouthed. Aileron, elev, trim etc. The 2 fuse idlers are not as there is not a large enough load pulling the end out of the tube. The proper angle for a fishmouth joint on a tube is 30 degrees. You can get that in 2 ways. A single angled cut or a V style cut. The V style is shorter overall and is the one that will work with AN490HT ends. The 30deg angle is from centerline of tube in 2 directions so the included angle of the cut should be 60 degrees. On a 3/4 tube, this usually leaves about a 1/4" wide flat on the end of the tube in 2 places so that your cut does not fall off the end of the AN490 insert. The weld is to be 360 deg around tube in the V's and the 1/4" flats. All welded. On the trim rods, this is V cut is done as well but is small and by the time it is all welded and painted, it is hard to see.

One additional note on AN490 HT ends. If you get them from most of the vendors rather than direct from the manufacturer, thay will be CAD and Irridite plated like an AN bolt giving them a gold color, which is clear/silver CAD like the old days plus a coat of gold irridite. CAD plating does not weld very well and causes lots of snapping popping, gas smoke etc. So, remove the plating. Get some Muriatic Acid (swimming pool acid) and and plasitc container and put the ends in the acid. It will quickly eat the Cad off and leave the parts bare steel for welding. Wash them with water to neutralize the acid then quickly rust lick them to prevent rust. Welding will be much nicer. KK


Regarding our earlier discussion about your HP elevators being slightly shorter chord than plans, what length should I make the trim tab push rods, shorter or plan length?

Regarding the hardware, from the pics I have of N360KC
Front End of N360KC Trim Rod     Aft End of N360KC Trim Rod

To verify the hardware used: I know you substitute F34-14M rod ends for the trim rods, and use AN3-10a bolts and AN310-3 castle nuts, but what are those BIG washers? It looks like they're there to keep the rod end on if the bearing fails.
Darin, you are right on target. Shorten the trim rods so that with the elevator and trim tabs in neutral the trim arms that hang out the bottom of the stab are in a vertical position, approx 1"shorter.

Regarding the rod ends, a large area safety washer is required on all bearings that are installed in single shear, where there is structure only on one side. That way if the bearing fails the washer will keep the rod end from coming off entirely. If the bearing is sandwiched in the structure like the elev push rods no washer is required. These trim rods, aileron slave struts at the bottom, torque tube hanger KP4 bearings in the fuselage, etc are places to use a safety washer. An AN970-3 is the one to use. KK


Whats the basic method to making the pushrod ends shown at See Picture? Does the tube just get flattened then welded to the two channels, or is part of the tube cut away? Is any welding done vertical inbetween the two channels?
Making the elevator pushrods is not that difficult. The trick is that you want to end up with a 1/2" gap between the 2 channels so that after paint, etc. the rod end will still slip between the channels.

To flatten the end, mark the tube at the point where the flat spot ends(don't have the dimension in front of me at the moment), stick a piece of 3/8" thick flat stock inside the tube deeper than the line just drawn. This 3/8" thick piece needs to be as wide as you can fit in the tube and can be made of alum, hard plywood etc. Take this set up to the vise and crank the tube flat down to the 3/8" piece inside. We use our hyd press with a set of flattening plates we have but vice will work. The tube will spring open a bit leaving the 3/8" piece loose in the tube. That is about right.

We have a fixture to weld the channels to the tube but you can bolt them together with a 1/2" spacer between them. Line up the angle bend to the line on the tube and tack in place. Form angle tab to match slope of tube and tack. The channels shou ld be welded along the length both sides and around the angled tab but should NOT be welded inside across the end of the tube.

Keep in mind that you have a special fuselage. Plans length pushrods will not fit your airplane. This will require that you install the sticks, torque tube, stab, elevators, make and install the elev idlers and then make the pushrods to fit. KK
See Picture of Jig I made Darin


Any tips or tricks on how to assemble the trim tab hinge rib in there when building the elevators? Does it get laid out at the 4.5 & 3.0 dimensions from the trailing edge? Darin
Yes, the trim tab is the same size as the plans. You can make slight adjustments to the hinge to get proper trailing edge alignment to the tabs. But an easy way to have the trim tabs line up to the elevator is to make or buy the tabs first, screw the attach former to it, align it to the trailing edge of the elev, then tack weld the strip.KK
I already have the trim tabs I got from you on one of my Orlando layovers. It sounds like my next mission is to find a 120 degree countersink and a cherry rivet puller. Darin
You do not need to rivet the nutplates on now. It is better to rivet them on after you sandblast and powdercoat the elevators. So, for now, simply use 3 screws and 3 nuts to hold the trim tab to the strip. This way you can tack the elevator together, then remove the tab, weld, sandblast, powdercoat, then rivet the nutplates in place.KK
I put the 3 screws in, but the channel seems to be much lower than the tab. Is it supposed to be that way? Should I replace half the piano hinge and re-drill it to put them closer together?

Heres a picture of what I'm talking about. Darin
Darin, I have looked at the pic you posted. Try something for me. Put a .040 to.050 shim between the hinge and the strip. See how the tab aligns then. Look for the tab skin to match the rail not the hinge bulb. Also, check and see if the strip is at the correct bend angles. Sometimes we have to tweak them a bit opengin up the lower bend and closing the top bend. If this needs to be done, the hings will lay down more.

If one or both of these gets things lined up for you, good. If not, see how much you need to move the holes in the hinge. If it is less than 1/4" hole, simply elongate them in the direction needed. If over 1/4 hole (I don't think it is), replace the hinge.

Oh yeah, you might be wonderin' what the shim is for...Fabric, dope and paint have measureable thickness. Especially when you end up with 3 to 5 layers of it in a trim attach strip area. When the strip is angled like the model 12, that thickness pushes the tab down as much as aft .....He He, He.....BTW, don't weld the rail into the elevator with the shim in place and align the tab to the elev trailing edge. If you do, the fabric build up on the trailing edge will make the tab look as though it is too far forward. KK
I think those suggestions will take care of it. One more question about the tabs: When I fit the trim tabs in the elevator there seems to be a large gap on each side of the tab. I'm pretty sure I laid out the elevator right, it matches the stab. Do you add some sort of wingtip to the tab, or is the gap supposed to be there? Trim Tab Gaps
Darin, Glad you got the tab lined up. The gap is normal. There will be 4 to 6 layers of fabric wrapped around the elev rib by the time it is covered and taped. Add to that some dope and paint and the gap will tighten up a bit. The gap is about the same as the 1/4" to 5/16" gap called out on the ailerons. It just looks big on the smaller tab. KK


Kevin, I was doing the layout of my elevators today, and the pre-bent HP elevator ribs I got from you don't match the plans, it appears the ribs are almost 1" shorter than plans dimensions, resulting in less elevator area. For example the 320-8 rib in the plans is supposed to go 20" back from C/L of the elevator spar, but mine is only 19".

This discovery is correct I hope. How did you come to change it? I guess I'll just layout the trailing edge to hit all the ribs. Thanks, Darin
Darin, You look too close at everything, man!! We have solds lots of the fuse/tail metal sets and you are the first one to see the difference in the elevator chord length. Most builders simply clamp the spar tube to the table with rib locations marked, put the ribs in place and then stuff the trailing edge up against it. But, if you draw out the elevators to the plans dimensions, you will see the difference as you found.

Basically, it comes down to area. Curtis spec'd the elev area and stock planform. We changed the tip shape to a sharper corner. To correct the area back, we trimmed the chord of the elevator a bit. This allowed us to maintain the spec'd elevator area. Now, if you Cad draw the stock elevator and cad draw our HP elev, you will see an additional slight error in area. This error is very slight, I don't recall the amount but I thin it is lees that 1 square inch. That is, the area of the HP elevator is almost the same as the area of the stock plans elevator but not exactly the same. This small error in area is due to slight differences between the orignial area spec we developed the HP tail from and the final form of the elevator after Mid America did the Cad drawings. The error was small enough that there was no need to bother adjusting the plans.

So, square corner elevator=less chord.     Round corner elevator = 1" more chord.


Regarding the 510-31 stab trim horn and the two 310-22 stab trim arms, are they aligned with each other and perendicular to the stab centerline when rigged properly with the elevators and trim tabs faired?
Yes they are Aligned As Shown Here KK


What is Aileron, Elevator & Rudder travel, and does it vary between plans and HP versions?
Travel is 25 deg up and down ailerons, 25 up and down elevator, and 30 left and right for rudder. Plans and HP are same.KK


Regarding the elevator horn block, what is it's material and dimensions?
The elevator spacer block is basically like the one in all pitts. It is a piece of 1/2" square alum 6061 bar that is as long as it can be and beveled on the front 2 corners as needed to clear the pushrod end and the stab tab. KK
Elevator Spacer Drawing

10/03/01 WELDING STAB RIB 310-10

I'm wondering how you guys weld the little rib inside the big rib shown at:   StabRib310-10.jpg

I know I can get to part of it easy enough, but is that enough? Darin
Yep, just weld the 3/8" long easy edge. the sides are not to be welded. KK


Kevin, I just looked at the pictures of your rudder hinges AFTER tacking mine in place. I noticed my hinges are only free to slide about 1/8" in the spar tube, while yours seem to have about 1/4". Am I ok since I will be setting my fin/rudder/fuselage together at once instead of batch production like you do?

Picture of Yours       Picture of Mine

Hopefully its no big deal, but now I'm wondering since you do everything for a reason.

Also, do you use the 1/4" wide rings or the 1/8" rings?   Darin
Darin, we use the 1/4" rings and set the hinges up with 1/16" gap on each side of the hinge. So, with a hinge slid over tight to one ring, the total gap or side play is 1/8". So your 1/8" is ok. The reason for the gap is to prevent binding at the hinge as it rubs on the rings. The reason we use 1/16" gap on each side is because that is what Curtis Pitts says to do. We just say, "Yes Sir" KK

06/28/01 TAIL STRAP HINGES, DR-109

The DR-109 uses 3 strap hinges per side PLUS the center pitts style double KP4 bearing center mount. This is WAY past over kill unless you plan on 100-150 mph backwards...........

The pitts style set up with one strap hinge per side plus the center bearing mount works great and is exactly what we have on the model 12. Some super abusive acro guys add on extra strap hinge per elevator very near the tip for a total of 2 per elevator plus the center mount. If you don't understand the center mount, get a look as some S1S plans or model 12 plans, or superstinker plans. The reason for the added hinge outboard is that the end of the elevator can get bent in tail sides. Usually a minor bend that is not noticed until sometime later. So the extra hinge. Many people that add a hinge let it kinda float in the reduce binding. It can contain the elevator spar from bending while being allowed to float fore and aft a bit. The strap style hinge goes way back to the late 20's. It is a good, strong way to get the job done. KK
Also as I recall, the DR109 copies the tail hinge design of the Eagle II with a slight modification. The Eagle II uses a 3 piece hinge assembly. The strap and 2 bronze halve sleeves with a shoulder. Kind of a slip bushing. These are installed after the elevator is welded between the 2 1/4" wide rings. The DR109 does basically the same thing but with nylon or delrin instead of bronze. When people have added a tip hinge to the elevator of existing pitts, they use the split eagle hinge assy. The advantages are that you don't have the hinge in the way to cover the part, can polish the bearings surface after all the wetsanding etc. then install the hinge. The disadvantages are you have more pieces to deal with, the support piece on the tab needs to fit the bushing better to support the 2 piece bushing more, and you don't have the actual hinge in place to jig the 1/4" rings in place during welding. Basically, it is a slick way to do it but not needed. To quote my Dad......"It's a lot of sugar for a nickel" KK


I remember at SNF we looked at a biplane that had very stiff controls, and I can't remember what you said caused it, but I remember it was something to do with the bearings or cages. I want to make sure my bearings work smoothly without inappropriate stress on the bearings. Since I am getting close to making some bearing cages (I cut a bunch of tube on the lathe yesterday) could you tell me:

1) What is the basic method to building them? Any techniques, tricks, or things to avoid would be appreciated.

2) Which dimensions have to be spot on, and which dimensions are not critical for it to work smoothly?

3) What made the controls stiff on the one we talked about?  Thanks, Darin
Darin, that airplane at SNF had stiff controls due to poor workmanship of assembly.  Here are some answers to your questions:

1) Cut the tubes to the specified lengths and deburr.  Drill rosette holes in outer tube only.  Cut some assembly plugs for each end from 1" solid bar and machine them to have 1/4" of 1" OD and a section turned down to 0.901 that is the exact length of the bearing position in the cage.  Make 2 of these one for each end so it centers the inner tube precisely in the outer one.  I don't have that dimension at this computer, sorry but you can do the math for it.  Drill a 1/4" hole in the center of each and use a 1/4" bolt to hold the entire package together while you rosette weld it.  Also use these plugs to keep the tube round while welding on the various arms etc.  Use anti seize compound on it too (lesson learned here).

2) The length of the inner tube must be dead on to get the proper bearing spacing.  Also the 3/8x058 spacer needs to be dead on length too.  The bearing cages should be cleaned out with a paper roll on a die grinder so that the bearing slips in by hand.  DO NOT PRESS IT IN!!!  This is the big screw up in that other airplane.  They did not clean the powdercoating out of the cages and the forced the bearings in.  This deforms the outer race of the bearings making them stiff and ratchet as the rotate.

3) See above.  They screwed up.  I am quite sure that the bearings in the wings are OK.  It is all in the fuse.  This wings were built here in FL by a friend of mine.  The fuse was done in a real hurry in MO.  All the stiffness could be in the cages on the fuse that the TT hangs from, the sticks themselves, and the idlers for the elev rods.

I just finished the control riggin on the blk/pur 12 here.  They move soooo sweetly.  The difference between sweet movement and the super stiff situation in that airplane is approx 1 or 2 hrs work.  Lets see, that's about 0.08% extra time in the project......KK
For a drawing / pictures of the Bearing Cages see BearingCages.gif   CagePartsWithPlugs.jpg   PlugWeld.jpg   BearingCageAssembled.jpg
Here's the method I devised to get my bearings fitting perfectly in their cages...Darin  BearingCageReamer

02/06/01 TAIL TUBES

Kevin,  I just discovered that in the set of bent tail tubes you sent, the two 310-2 are .875 x .035 tube, while the plans call for .049.  Same with the 210-4 LE.  Is this another Kimball optimization?     Darin
The original plans by curtis call for .035 on the stab LE and TE tubes.  This is what we use in ours and build all our stabs with as we begain doing so prior to Mid America reworking the drawings in CAD.  So, you are good to go with them as they are. 

As for making a dwg change, I don't think it is required.  Those plans building can bend .049 to the same curves as the .035.  There are about a dozen tubes in the airframe that are larger or heavier than Curtis originally specified.  Our Yellow 12 has tubes sizes like curtis spec'd. as does the black prototype.  All the fuseframes we build has tube sizes like the plans show so that a customer who buys a frame from us doesn't think he got short changed.  None of the Mid America changes were needed.   KK


I recommend that on your next trip to Orlando to see Kevin, take along the materials to make all the empennage hinges.  Jim showed me a simple jig they use to center the strap around the tubing. This is sort of hard to get exact without it, and I bet they wouldn't mind letting you use the jig.  If they are off at all, then getting them aligned with the bushings is difficult. All you need to do to prep the straps is to drill the rosette holes before you bend them.  This is one of the things that make the empennage difficult to build.  If you do that, and drill the bushing holes straight, it won't be as difficult.

Also, and you probably already know this, Kevin doesn't make the hinge rests/brackets the same as the plans call for.  His are like Pitts.  They are the 4 pieces of about 1 X 1.25 inch metal. 

Elev & Rudder Hinges.JPG    Hinge with arrow.jpg   Hinge Brackets on Weldment Sheet.jpg    -Bud Clark
My hinges are already bent from Kimball's, do I still need a jig?    Darin's Hinges.jpg     -Darin
Maybe a jig won't be needed.  Mine weren't pre-bent like yours.  They came in the flat sheet , and I had to figure out how to center and bend them.  Just make sure that the arms are equal length on each side of the hinge when you are through. You might want to tack them at the rosette,  slide them all on a tube and see that they all line up.    

Again, make sure the bushings that they attach to are straight and aligned with the tubes they go through.  I'm sure there is a good way to do that, but I haven't found it.  After doing it manually, I  bought a tool to help alignment things one plane (see pic), but it still takes some setup and eyeballing in the other.  Give it some thought.  Maybe your friend with the milling machine has a good way to do it.

The rests aren't quite as big a deal since you will have to adjust them when you assemble things.  You want the rests to bottom out as well as touch the sides of the hinges.  Remember that the tubes on the vertical stabilizer are a different size from the top to the bottom.  The bottom is the 1 inch tube that is part of the fusleage, and the top is smaller to fit down inside it.  At first I was thinking I needed to put a something under the top one, but you don't.  The key is the hinges are all the same length, and you alter how far they standoff from the tubes with the rests.  By the way, it would be better to not powder coat the fuselage until you have finished and fitted the empennage in case you need to bend or file things a bit.  I didn't and now will have to touch up afterward.  Have fun, Bud
Kevin,  some time back you sent me a drawing for setting up the tail hinges. I've noticed in my laser cut metal that you use a different piece to act as a spacer instead of the plans combination of 310-18 & 310-20.   Before I start to build a jig to put the hinges together, I want to verify that the spacer in my laser cut set works to the same dimensions as the plans.
HingeJig1.gif     HingeJig2.jpg
The plans way is a change that Randle did when drawing up the plans. This is actually a more difficult way of building a hinge support. We use the original way that Curtis Pitts designed the support which is the 1" wide "V" shaped piece of 4130. It works perfectly.KK


Here is a tip you might need later on.  You have to drill some 3/8" holes for bushings in the horizontal stabilizer and vertical stabilizer spars.  They need to be perpendicular to the stabilizer spar tubes when you are through, and it is hard to free hand the holes exactly as they should be.  What I did was drill the holes as best I could freehand.  You then put the bushing in place, and then run a piece of 1/4" X 36" threaded rod throught it.  The long rod allows you to see if they are in fact straight.  If not, some file work will let you alongate the holes so the bushing can be positioned exactly, and then spot welded.  I use threaded rod because sometimes you want to run some nuts up to keep it in place. Bud Clark


Regarding how to attach the 510-60 outer tube to the 510-59 inner tube on the brake pedal: Does it just get edge welded on the outer side away from the rudder pedal tube 510-54?

I had a long layover in Hawaii with my laptop and spent about 4 hours figuring out how long to make Idler 510-41, don't think I'm completely nuts, I did get a little beach time. I'm pretty sure it needs to be 0.7" shorter, does that sound about right? I know the width of the pushrod is 1.188 but I used 1.4 to give me a little cushion up there. I also plan on leaving the idler mounts set at the same 48 degree angle, is there any reason to tweak that? Maybe you can tell me why they don't align with the 210-14 tubes to begin with. Also, what's up with the tailwheel lock shown on the idler in the plans? Does it engage the lock with full up elevator? I don't recall seeing it in any pictures, do you even install it? Darin
That sounds about right.  I don't recall the final length of the rear idler.   I do recall that I had a length that was shorter and that I thought would work but had to shorten it a slight bit more when the airplane actually got built.  I maintained the 48 deg angle of the mounts.  The prototype 12 had a one of a kind locking tailwheel on it.  It was elevator control system operated.  With the stick at full down, the tail wheel was unlocked.  Just a bit off the down stop relaxed the cable attached to that rear idler arm and lock the tail wheel for straight ahead only.  So, if you wanted to taxi and steer, you had to do it with full forward stick which is spooky with all that power.  That is why we don't have that tab on the rear idler. KK


Darin,   Here's a hint for you on the controls......Keep the torque tube the same length as stock and adjust rear seat to clear curved stick.  A short TT won't work out.  I tried it too.  KK
Thanks for the advice. As I was drawing it I realized that any length adjustment would only be made to the rear stick mount location. Let me guess, the short TT probably is probably limited in down elevator travel by hitting the front seat up higher where the added recline isn't a factor.....

I ordered a few pieces of hardware like the rod end bearings, and rod ends so I could measure them for my drawing and analysis of the idlers. I'm basically going to figure out the "plans" geometry, then adjust my idler radiuses to keep the pushrods in the same angles as the plans version. After I ordered them from AC Spruce I remembered that you guys sell them too. How's your pricing on the bearings, rod ends etc compare?

Its really cool to draw the fuselage stuff and see how it all fits together, its like getting building experience without touching metal. Plus it keeps me out of the bars on my layovers. I never would have known about the very slight interference fit of the TT in between the bearing cages otherwise. Also I discovered how close the elevator horn comes to rubbing on the stab rear spar, it must just kiss it.

Yep.  The rear stick down travel is the issue on the TT. Keep smilin. Sounds like you are having fun KK


Darin, I finally stumbled onto a good box for the jigs.  They are boxed up, and I will mail them tomorrow. You probably know this, but remember to just tack them while on the jig, and then remove them for final welding. If you don't, you'll end up welding the pedals to the fixtures. On the brake pedals, you will have to make sure the toe portion is straight after tacking as the tube is able to move slightly on the jig if your not careful.  The brake jig is such that you will add the tube that goes inside the rudder pedal after it is off the jig. Add it before you final weld the pedal or you will have to have a hard time reaming it out before the tube will slide in.  If you don't already have one, you might as well go ahead and get a .510 inch straight fluted reamer as you are going to need it. You can get a good carbide tipped one from MSC Supply  They are pricey.    Later, Bud


The radius of bend  that Curtis uses in his tail feather designs  was determined by him experimentally.  In otherwords, Curtis took some 3/4 4130 and kept bending it until he got as tight a turn as possible with out kinking.  That is where the 9.5 to 10 inch radius on the stab leading edges comes from.  Here is how he and now we do it. 

Take a piece of 3/4 thick hard wood, ply will work for 1 or 2 times.  Cut it in about a 8.5" radius and put a strap on it to hold the end of the tub against it.  Clamp it in a  vise and pull the tube down and around it.  It will spring back to about 10" radius.  Recut the radius as needed to get the final shape you want.  Put a mark on the board to tell you where to stop the bend.

For the stab tubes we make here for the model 12, the tube flattens approx .015 but the flattened protion is in an area of the stab, the tip, where it does not matter.  This method is fast too. 

For many other tubes, round and square,  in the Model 12 like sticks, I strut tubes, canopy frames, engine mount rings etc, we use our powered tube roller. We have  roller wheels for it to roll tubes from 3/8" dia up to 1.25" dia.  Max wall thickness for 4130 we can roll is about .095.  Mild steel .190.  This device works great and can produce any desired raduis of bend from infinite to as small as 7" in 1x.095 tube as an example using the same wheels rather than having to have a set of dies for each radius.  We use this tool to create the airfoil curved square tubes on the top and bottom of our I struts.

I do agree that the tools you refer to as well as the one I have mentioned can produce parts to a greater level of accuracy.  But, in the case of the original posters Super Stinker, the tolerances are lax enough to allow for flattened tubes, heated bends etc and still have a high quality part.  It was designed that way, Curtis built it that way.  Heck most homebuilders don't even have the tools to measure .010 squish in a tube.  KK


Darin,   Tail rib bending can be bent on a common brake with some extra mallet work after.  You bend the hug up edges, then the 90 degree bends, but stop short on the 90's and then use a mallet and bench to finish.  We have a special brake for bending the tail ribs and a few other parts.   KK