Bush gear topic reopened

[1avidflyer 1983]

I've been getting back to thinking about building bush gear now that my Avid MK IV is back up and flying.  Looked over Bob McCaa's posts about building his gear (from the old yahoo group)  http://www.avidfoxflyers.com/index.php?/topic/2110-build-your-own-avid-spring-gear-document/#comment-15460   Also got to looking at some of the other posts of bent longerons and such with the bush gear.  I remember that Joey went with a gear with shock absorbers and all that looks real nice and seemed to do the trick, but at more $ than I'm wanting to spend.  Has anyone got anything new or different to add to this discussion?  Or even a rehash of the old. :-)  Thanks, JImChuk

[birddog486 21]

Nothing to add but I'd sure like to find a set of gear that was affordable and didn't need to fight wrapping with bungees.....

Travis

[akflyer 1427]

I have drawn up a much better one that will take most of the stress off the lower longerons, I just have not yet sent the patterns and plate off to the water jetter to get it cut out.  I am not too crazy about sending them out the door till I get a little time beating the crap out of them on my plane, not just flying off pavement or a grass strip then saying hey fellers, buy my awesome bush gear..

 

[1avidflyer 1983]

Just thinking about this some more.  Maybe there is a better way.  Joey's gear features shock absorbers, and that is a good thing no doubt.  Having the gear compress on a hard landing is fine, but if all that happens then is the springs (or whatever absorbs the shock) flings you back into the air, something is lost.  If you look at the Just aircraft landing hard in this picture, you see there is no bounce back up. https://www.youtube.com/watch?v=jJUdRE3_XFc   Shock absorbers do work.  Think of your car or truck when the shocks are shot.  Here is a design that incorperated a shock absorber years ago.  They don't have much travel, and they aren't light, but I wonder if this approach might have some merit.  You would have to make a way to attach to the center of the seat truss, but I don't think that would be very much of a problem, and you could use your existing landing gear locations on the longerons.   I'm not saying to use a Champ or Chief landing gear, only the design concept.  The pull down on the seat truss wouldn't be near as much as bungees do, most of the force would go up the gear legs just like it does now.  How the shock absorbing is added in is the biggest question, but I'm wondering if some type of motorcycle spring and shock setup could be used.  That way you have something already designed that works at known weights.  At any rate, it's maybe food for thought.  JImChuk

http://johnpropst.yolasite.com/resources/Aeronca Oleo Strut rev 9.pdf

[1avidflyer 1983]

I had seen this before but forgot about it, and ran across it again today.  It kind of demonstrates what I had in mind in my last post on this thread.  JImChuk

 https://www.youtube.com/watch?v=oodTrBqArhw

[1avidflyer 1983]

Made a bit of a mock up today, to see what kind of travel one would get.  I was surprised how much the wheel would move up and down with way less travel on the shock absorber leg.  You can see the lines I made on the conduit that comes out of the copper tube, moving the axel up 6" only move the shock leg 2 1/2".  10" on the wheel moved the shock leg 4".  In the pictures, the top of the copper tube is screwed on where the gear leg would attach on the longeron, the axel shaft fastens about 1" off center of the fuselage.  I probably wont build such a thing, but maybe some one more gifted than me in the welding department might get an idea and go for it.  What to use for the spring/shock absorber?  Bungees would be nice, for weight, but harder to make than springs I'm guessing.  You're still left with what do you do about the shock absorbshun.  Any ideas?  Remember, you have to be able to hook down low on the shock leg for the rear brace leg, and the spring and shock movement happen below that brace.  Does than make sense?  Look at how the Berlinger gear works in the video in my last post.    Anyway,  any thoughts?  JImChuk

PS  I think the nice thing about this design is it puts the force where it's always been, right up into the gear leg attachment points, and I don't think it stresses anything else really.  The axle leg does pull down on the seat truss where it attaches to it, but only about 1/4 or less of the force on the wheel going up on the other side of the shock leg which becomes  a fulcrum as the axel leg becomes a teter toter in a sense.  

 

Edited 14 Sep 2017 by 1avidflyer

[Willja67 144]

 

Made a bit of a mock up today, to see what kind of travel one would get.  I was surprised how much the wheel would move up and down with way less travel on the shock absorber leg.  You can see the lines I made on the conduit that comes out of the copper tube, moving the axel up 6" only move the shock leg 2 1/2".  10" on the wheel moved the shock leg 4".  In the pictures, the top of the copper tube is screwed on where the gear leg would attach on the longeron, the axel shaft fastens about 1" off center of the fuselage.  I probably wont build such a thing, but maybe some one more gifted than me in the welding department might get an idea and go for it.  What to use for the spring/shock absorber?  Bungees would be nice, for weight, but harder to make than springs I'm guessing.  You're still left with what do you do about the shock absorbshun.  Any ideas?  Remember, you have to be able to hook down low on the shock leg for the rear brace leg, and the spring and shock movement happen below that brace.  Does than make sense?  Look at how the Berlinger gear works in the video in my last post.    Anyway,  any thoughts?  JImChuk

PS  I think the nice thing about this design is it puts the force where it's always been, right up into the gear leg attachment points, and I don't think it stresses anything else really.  The axle leg does pull down on the seat truss where it attaches to it, but only about 1/4 or less of the force on the wheel going up on the other side of the shock leg which becomes  a fulcrum as the axel leg becomes a teter toter in a sense.  

 

Just came across this. Ive been thinking myself for awhile about improving the landing gear I've got. I really like that Berringer gear idea. After watching Mike Pateys landing gear upgrade on Draco

I looked up King air shocks.  

http://www.filthymotorsports.com/King_Air_Shocks_p/king-air.htm

 

The Bush gear I bought from Stace Schrader has a leg length of 28 inches and King sells a shock that's 28" long that compresses 10".  Given your mockup above that travel length might be excessive (put the prop in the dirt excessive) but you might use a shorter shock and use the axel attachment to make up some of the length.

 

They're $300 ea so a little pricey but probably way better than some Acme aero shocks and if Mike Patey for whom money is no object would use them they must be pretty decent quality. Bush gear generally sells for around $1000 it seems, so if you can fab your own and use these shocks you still  come out cheaper than buying a bungee set. 

 

Edit:

I should add that King isn't afraid of airplanes. I emailed and asked some questions telling them what I wanted it for and they were cool about it. 

They also seem willing to customize as much as is practical. I have very little knowledge of shocks but I wonder if it's possible to use the body of a shock that has the appropriate compression length and the shaft from a longer shock to make the gear leg the right length?

Edited 31 Aug 2019 by Willja67

[Allen Sutphin 705]

Anybody ever see a Funk gear? I had a Funk and it had a wonderful gear. You could drop it in from 10' with no damage. It was similar to what everyone is talking about, using shocks instead of springs, bungees, or some high dollar setup.  Of course like everything else on a Funk, it was surplus Ford parts. Henry Ford knew how to cut cost.

Edited 31 Aug 2019 by Allen Sutphin

[Turbo 162]

I have often wondered why nobody has criss-crossed the space below the fuselage with slightly longitudinally offset gear legs, then use the kind of vertical spring-shock arrangement above the wheels.  The Just Aircraft SuperStol gear pivots about the centerline keel.  Criss-crossing the lower fuselage give even better geometry, with shallower angles, and hence even less squat as the gear compresses.  It puts more stuff out in the propwash, though.  Still, this concentrates virtually all the gear's force at the shock/spring attachment.

[Allen Sutphin 705]

Looks like it would be a easy solution to add damping to a stock gear. On the two tubes where the bungees wrap, come back about 2-3 inches back from the bungees and weld  a tab to the side of each tube and bolt a shock of whatever length depending on the distance between the two tabs. The bungees and shock would still absorb the impact of a rough landing but the shock would inhibit the bungees from retracting quickly to avoid the bounce back into the air. It wouldn't affect the bungees from smoothing out a rough taxi or normal smooth landing that we all make. Most auto shocks are harder to pull one direction than the other so use the stiffer side on the retract action. A UTV shock is usually adjustable from light to firm so one could fine tune it to their liking. Drag would be minimal due to the shock being in front or rear of the bungees. I may be a crazy hillbilly but it seems reasonable. And probably wouldn't cost a small fortune!  In a greaser landing the worst would be is a bent tab or a busted shock, no more damage than without the shock. I may get gutted and hung since its not a high dollar modification but I go with the KISS theory. In the event of a broken bungee, the shock would keep the airframe from smacking the ground for those that removed the safety cable.

Edited 2 Sep 2019 by Allen Sutphin

[Willja67 144]

Had an idea that's interfering with my sleep. Had to draw it out before i forgot it.  

Why keep the cabane at all? Run shocks from the axle to the top of the seat truss. 

Problems i can see is that with a cabane a hard landing pulls the fuselage sides in, aren't structures usually stronger in tension than compression? 

That seat truss obviously isn't anything close to accurate i just drew it to give the idea. 

Edited 6 Sep 2019 by Willja67

[Allen Sutphin 705]

Sounds reasonable. Guess there is more than one way to jerk the hide off a possum!

[Turbo 162]

Top of seat truss - big compression forces!  Potential for column failure.  Need to maybe reinforce in two dimensions?

Edited 9 Sep 2019 by Turbo

[Willja67 144]

Just eyeball Engineering here since i don't know how to run the numbers anyway, but the tendency of a cabane spring gear to pull the lower longerons together is well known. My drawing of the seat truss might not be dimensionally accurate but the general placement of the tubes is. The tube that angles inward and down from the proposed upper shock mount location seems to my untrained mind to be better for that application that a cabane style landing gear. If that tube started at the bottom of the truss and angled upward instead methinks it would be better for the standard Bush gear as it would offer a little more resistance to pulling the longerons together. 

 

Still not suggesting it's adequate for what i proposed just suggesting the geometry might be a little better. 

[FredStork 453]

Just eyeball Engineering here since i don't know how to run the numbers anyway, but the tendency of a cabane spring gear to pull the lower longerons together is well known. My drawing of the seat truss might not be dimensionally accurate but the general placement of the tubes is. The tube that angles inward and down from the proposed upper shock mount location seems to my untrained mind to be better for that application that a cabane style landing gear. If that tube started at the bottom of the truss and angled upward instead methinks it would be better for the standard Bush gear as it would offer a little more resistance to pulling the longerons together. 

 

Still not suggesting it's adequate for what i proposed just suggesting the geometry might be a little better. 

I think the basic approach is correct but to get the geometry right we should look at Just Aircraft and their Highlander. 

You could even go all the way up to the wing (and add a cross bar...). 

 

[Willja67 144]

Just eyeball Engineering here since i don't know how to run the numbers anyway, but the tendency of a cabane spring gear to pull the lower longerons together is well known. My drawing of the seat truss might not be dimensionally accurate but the general placement of the tubes is. The tube that angles inward and down from the proposed upper shock mount location seems to my untrained mind to be better for that application that a cabane style landing gear. If that tube started at the bottom of the truss and angled upward instead methinks it would be better for the standard Bush gear as it would offer a little more resistance to pulling the longerons together. 

 

Still not suggesting it's adequate for what i proposed just suggesting the geometry might be a little better. 

I think the basic approach is correct but to get the geometry right we should look at Just Aircraft and their Highlander. 

You could even go all the way up to the wing (and add a cross bar...). 

 

That's actually the Super Stol not the Highlander. After i drew that first drawing I went back and got some more precise measurements off my plane and worked out the geometry. If you use a 32" long shock that only compresses 4 inches you can get 20" of vertical travel at the wheel. That would allow the wheel to hang down 8" further than the lowest it can go now with the bungee setup and and still have 12 more inches of deflection past the statically loaded point.  With my engine and prop setup if i came down in a level attitude that still gives me 2" before I smash the prop. I imagine I'd probably come down more tail low than that. 

Aside from the seat truss probably not being up to the task none of the shocks that i could find came in 32" lengths that only compressed 4". If you use a 32" shock the compression stroke is around 12" which means the tire could theoretically hit the bottom of the wing (of course the belly would hit long before that happened).

Given all the stories about collapsed gear that are documented on this site I'm thinking that some kind of suspension system with these kind of capabilities would pay for itself on your first hard landing. 

Edited 9 Sep 2019 by Willja67

[Klmt101 5]

Will instead of redesign completly what about triangulating top of cabane to help with stress on longerons and adding the shocks next to the bungies? 

[Willja67 144]

Will instead of redesign completly what about triangulating top of cabane to help with stress on longerons and adding the shocks next to the bungies? 

The whole point of this thread(as I understand it) is to explore new and different ideas. Try some out of the box thinking that might lead somewhere totally unexpected and perhaps unlikely but we just might find a better way that's never been thought of. If nothing else I think it's fun even if nothing comes of it.

[Klmt101 5]

I understand what your after now, was at Reno today and seen a yellow fox with a cabane added and it finally clicked how they are doing it without modifying fuselage. Front gear mounts have an additional piece sandwiching outside of mount that the cabane is welded too. Plane was equiped with dual springs basically replacing the bungies.

[Willja67 144]

Wouldn't happen to have been this one would it?

[Klmt101 5]

Thats it.

[Good old number 29 158]

I do like the way my modified J3 Cub gear is turning out. I should be able to try it out soon. If anyone is thinking of doing the same, I have a couple suggestions. One is to cut both legs. I removed the back leg, cutting both ends off, changing the angle slightly, so it fit to the lift strut attach point. My old gear legs were 1-1/4 front and 1-1/8 back, at .049” thickness. I used 1-1/4 .058” as an outer sleeve over the 1-1/8 ends. The PA18 gear is 1-3/8 front and 1-1/4 rear, both .058”. You could slide 1-1/4 inside the front, and 1-1/8 inside the hind leg, with either .049 or .058, and adjust the lengths and alignment by sliding each piece inside the existing ends, tack it in place, then take it back off to weld it. The Cub gear also uses 3/8 AN6 bolts instead of the 1/4 AN4 that the Kitfox has. I reamed the holes out to 3/8, but I suggest doing it differently, and keeping the 1/4” mounting holes. First, fit the cabane vee inside the landing gear bracket, around the front gear leg, but inside the attach bracket. Cut a piece of 3/8 .058 tubing to fit tightly inside each attach bracket. The tubing will fit through the cabane mount (with a 3/8 hole) and gear legs, acting as a bushing, then the assembly fits snugly in the mounting bracket, the 1/4” bolts tightened to hold the 3/8 bushing, so the gear pivots on the outside of it, rather than a bolt, and the cabane mount and a washer or two fills the extra space in the bracket. No worry about shear strength of the bolt, because it would have the 3/8 tubing pinched tightly inside the bracket. It would be stronger than having the gear pivot on the bolt, as originally designed, without compromising the bracket, or having to fiddle with its tabs that are in the way if you fit the cabane V mount to the outside of the bracket like I did. I think that doing those two things as I described would make the project fairly easier and a bit lighter. It would also give you slightly more width than I got, extending the fromt leg, too.  I see two different complete PA18 Super Cub landing gear sets for $750 and $800, complete with Hydrosorbs and bungees (you’d want to swap to lighter ones), and another set of just legs for $400, on Craigslist. I got my beat up, thin, old J3 legs for $150. If you get the Hydrosorbs, you have easy rebound damping. Using a simple, proven design, with all the hard welding already done, make this a good and economical answer for bush gear with shock absorption. 

[napierm 2]

For all users of wide "bush" gear on a KF I know from experience that the rear gear mount is very weak in compression.  The front mount is attached to the seat truss and so is pretty stout.  But the rear one attaches at a point where there is a single tube going across under the seat.

What this means is that if the gear catches hard this cross tube can fail and the rear part of the gear leg attachment wants to come through the bottom of the seat.  Think of it as a long lever arm and picture where that rear point wants to go....

If I were designing a wide gear set I would do a Highlander style with the 3 attachments, the rear one with a big diameter tube that attached below the lift strut.  That is a very strong attachment plus it is not under my butt.

FWIW

 

[akflyer 1427]

For all users of wide "bush" gear on a KF I know from experience that the rear gear mount is very weak in compression.  The front mount is attached to the seat truss and so is pretty stout.  But the rear one attaches at a point where there is a single tube going across under the seat.

What this means is that if the gear catches hard this cross tube can fail and the rear part of the gear leg attachment wants to come through the bottom of the seat.  Think of it as a long lever arm and picture where that rear point wants to go....

If I were designing a wide gear set I would do a Highlander style with the 3 attachments, the rear one with a big diameter tube that attached below the lift strut.  That is a very strong attachment plus it is not under my butt.

FWIW

 

the issue with this is that its sometimes tough enough to get two bolt holes to line up on a fuse that may have been tweaked a bit.  If the truss is reinforced with the plywood or plate and the sides boxed in the same way, a properly designed gear wont fold up the fuse.  

The issue is a PROPERLY designed gear and not just a spit ball copy that has thus far been done.  

Unless your mission is to be a youtube sensation the super long travel shocks etc are not needed for rough back country flying.

 

[72chevy 98]

For all users of wide "bush" gear on a KF I know from experience that the rear gear mount is very weak in compression.  The front mount is attached to the seat truss and so is pretty stout.  But the rear one attaches at a point where there is a single tube going across under the seat.

What this means is that if the gear catches hard this cross tube can fail and the rear part of the gear leg attachment wants to come through the bottom of the seat.  Think of it as a long lever arm and picture where that rear point wants to go....

If I were designing a wide gear set I would do a Highlander style with the 3 attachments, the rear one with a big diameter tube that attached below the lift strut.  That is a very strong attachment plus it is not under my butt.

FWIW

I had thought about doing the 

I thought about doing a 3 point attachment  but decided to only use 2 one at the seat truss and one at the rear float fitting.