UNIVERSAL MAINTENANCE FREE TAIL-WHEEL

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Toobuilder

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This forum is and has always been a harsh "shark tank" for potential manufacturers. If you intend to sell something to us, you need to do your homework first.

OTOH, if he had posted this in the "Members Projects" section and said: ..." look what I made in my garage this weekend"... , then the feedback would have been much softer.

Selling a product is a tough one- You better be wearing your big boy pants.
 

Victor Bravo

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IMHO split the difference.

On one hand Graeme has not done anything whatsoever to upset anyone. He came up with an interesting idea that has a clear potential to solve a tailwheel geometry issue that everyone has just accepted for 100 years. It is obviously not perfect, and like any other product it will need some tweaking. And like every other product it will not solve every problem perfectly. We should definitely not discourage or be overly harsh. On the other hand he walked into a pretty big room with several experienced engineers lurking about, and presented an idea that is very different. He asked for feedback, and aero engineering type people will pretty quickly identify potential flaws or failure points.

So, absent anyone else doing it I will be happy enough to state a couple of things that may not be obvious to everyone.

Graeme, thank you and congratulations for putting the time, thought, energy, and work into this idea. Having clever people put time and energy into airplane hardware is a good thing, regardless of whether the ultimate product does or does not work better than the status quo. It looks like your tailwheel design has clever and potentially important features. DEFINITELY worth pursuing and developing.

As you mentioned in the beginning, this is the development phase, and identifying what is good and bad in the design is what development is all about. Identifying flaws, failure modes, or engineering problems now is a lot better than finding these things out after you have mounted it on an airplane or tooled up for production.

Through this forum and its members, a whole lot of talented and experienced people are willing to provide creative input and engineering experience, at no cost. Considering where some of these people work and what they do for a living, and the overall level of their engineering capabilities, that's a huge benefit that most of us could not ever afford to purchase. So by being brave enough to present the idea here, you will speed up the development, have the brains of several really high-end people focused on your project at no financial cost, and have potentially costly or "deal-breaker" problems identified sooner than otherwise.

All you have to do to get these important benefits is to understand, accept, and manage the fact that airplane people and especially engineers can appear harsh or hostile when they are absolutely not trying to be that way.
 
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Victor Bravo

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A CF leaf spring (especially the one I have in mind) would/should be stiff enough to prevent the bobbing and weaving your talking about, all the spring action would be in Graeme's poly bumpers.
That's an interesting carbon tailwheel mount, with a T cross section. Definitely not a "spring"... very little deflection... more like a solid strut.

May I ask... if you are not wanting that strut to deflect and store energy (traditional tailwheel spring), what is the reason for having the tailwheel unit offset behind the aircraft by way of this strut? Meaning... what is the benefit of this strut if you don't need it to behave like a leaf spring?

Based on your previous comment that the VP rear bulkhead was not intended to take that kind of direct load, then a tail strut that doesn't "soften" the impact/load (because it's not hardly flexible) will just throw those loads back into the fuselage at the same place??? Maybe even worse because there is now a lever arm????
 

FritzW

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...Definitely not a "spring"... very little deflection... more like a solid strut.
That's the plan, ideally all the spring action happens after the pivot axis for all the reasons that have been mentioned.

...what is the benefit of this strut if you don't need it to behave like a leaf spring?
It mounts to the standard VP mounting locations (easy) and transfers the tailwheel loads into the fuselage the way the fuselage was designed to take them (safe)*.

Based on your previous comment that the VP rear bulkhead was not intended to take that kind of direct load, then a tail strut that doesn't "soften" the impact/load (because it's not hardly flexible) will just throw those loads back into the fuselage at the same place??? Maybe even worse because there is now a lever arm????
The rubber (poly) plugs "soften" the impact/load. Instead of having rigid tailwheel arms and a flexible leaf spring, you have flexible arms and a rigid leaf spring. ...you still have deflection (shock absorbing), it just keeps the deflection out of the pivit bolt/bellcrank axis.



*...here's a thought experiment: if you had a super kung fu guy punch a VP stern post it would break exactly where this vertical mount would attach.

*...here's a better thought experiment: if you had to break a VP stern post, and you didn't have access to a super kung fu guy, the easiest way to do it would be to mount a bar exactly where this vertical mount would go and apply the same kind of load that the tailwheel would if it hit a little pot hole in the taxiway.

Like I said in post #31, it's certainly possible to mount a tailwheel like that to a VP, but IMHO it'd be a bad idea (...and my screwy VP ideas even scare Matthew :gig:)
 

proppastie

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I like the wheel, off the shelf or purchased.....anyone know, and what is the load rating of the wheel/tire?
 

Victor Bravo

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Ahhh, OK I see... the carbon arm you want to use mounts somewhere other than the fin post. Got it.

Another option is to glue two plyood cheek plate doublers to the rear fuselage sides, which extend slightly aft of the fin post. This essentially creates a fork, inside which you can mount Graeme's "vertical" tailwheel attachment. All of the loads would then be transmitted into the fuselage side skins, more or less bypassing the (weak spot) VP fin post.
 

Blackhawk

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Graeme,
I really like your design and think out would be a good fit for my plane, but would require some redesign of the bulkheads it would be mounted to. Can you give some dimensions on how it would be mounted? Or is it still too early in the game?
Will; if your aircraft is/was using a spring tailwheel, you would mount the UMF using the same bolt holes as the spring as I've shown in the drawing.

This is only my attachment idea using the KISS system, others might want to build something more complex.

Tailwheel installation.jpg
 
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FritzW

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Just to be clear, there isn't a weak spot on a VP stern post. There's just a predictable failure mode if you bolt a vertical tailwheel mount to the middle of it.

Another thought... I think we're talking about two different things here: 1) Graeme's "vertical" tailwheel and 2) vertically mounted tailwheels in general.

If we're talking about vertically mounted tailwheels in general on a VP, IMHO I think it's a huge pain in the arse solution to a very small problem.

If we're talking about Graeme's "vertical" tailwheel in post #1, and I don't mean this to sound harsh but..., I'm absolutely sure you'd never make it to the runway without it folding up. You have a small diameter 316SS bolt (about the weakest kind of steel bolt you can find) loaded in just about the worst way possible (bending). It wouldn't apply to a VP but if it's mounted like the picture in post #25 (rigid turnbuckles to the rudder bellcrank) it's going to take the rudder with it.

The rubber baby buggy bumpers are a really interesting idea but the rest of the assembly... er... still has a ways to go.


Graeme, build your rbbb tailwheel idea into something like this and the VP world, all 5 of us ;), will beat a path to your door with our checkbooks in hand.

TW1 exp2.jpg ...the computer guesses 3.33 lbs total (it's probably pretty close)
 
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Will Aldridge

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Will; if your aircraft is/was using a spring tailwheel, you would mount the UMF using the same bolt holes as the spring as I've shown in the drawing.

This is only my attachment idea using the KISS system, others might want to build something more complex.

View attachment 61938
I'm building my own design, so the tailwheel can mount however I want it to. I was a little confused when I first saw the components and thought the steel rod would be the pivot and extend into the fuselage and would be mounted to bearings that were attached to a bulkhead somehow.
 

Blackhawk

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I'm building my own design, so the tailwheel can mount however I want it to. I was a little confused when I first saw the components and thought the steel rod would be the pivot and extend into the fuselage and would be mounted to bearings that were attached to a bulkhead somehow.
The pivot of the tailwheel is in the front of the torsion block and pivots on the lower SS rod which is 25mm diameter.
 

Will Aldridge

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The pivot of the tailwheel is in the front of the torsion block and pivots on the lower SS rod which is 25mm diameter.
Yeah I figured that out. Just so you know a little about my plane this is what it looks like with your tailwheel assembly very roughly drawn in:
tailwheel.jpg

in the lower right corner is a cutaway that shows the bulkheads. I was thinking that the steel rod could possibly be bolted to that bulkhead
 

Blackhawk

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Yeah I figured that out. Just so you know a little about my plane this is what it looks like with your tailwheel assembly very roughly drawn in:
View attachment 61963

in the lower right corner is a cutaway that shows the bulkheads. I was thinking that the steel rod could possibly be bolted to that bulkhead
That would be OK, very simple.

Plane looks great; how far along are you
 

Toobuilder

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The pivot of the tailwheel is in the front of the torsion block and pivots on the lower SS rod which is 25mm diameter.
Well, no. The "pivot" is that small diameter bolt - from which the entire assembly is cantelevered. The lower SS rod could be half the diameter you have and would still be far stronger than that bolt.
 
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Will Aldridge

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Well, no. The "pivot" is that small diameter bolt - from which the entire assembly is cantelevered. The lower SS rod could be half the diameter you have and would still be far stronger than that bolt.
This is an idea I had based on your previous post TB and confirmed by the above. What if (at least for my application) we used a 5/8 shaft that went all the way through the block with a washer welded as shown to prevent any upward movement of the tailwheel assembly with bronze bushings (thought bushings might be better than bearings due to size constraints) at the top and bottom of the block and then a bolt that threads into the bottom of the shaft with a washer between it and the shaft and allow say 1/16" or less of play?

tailwheel2.jpg
(spring block omitted for clarity)
 

Toobuilder

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Thats much better, but does eliminate the sealed bearings, which is part of the appeal with the design.

The problem with using a large enough diameter axle is the corresonding large OD of the bearing package. Maybe some small OD roller bearings top and bottom and a delrin or other thrust washer at the top? The main body might not even have to be enlarged to accomodate the roller bearings. Also, the axle shaft could certainly be a tube, vs a solid shaft.


So now that I look more at this, keep in mind that the "rigid" mount is going to drive a LOT of shock into the lower fuselage - something a flexible stinger does not do to nearly that degree. A study of the repairs bush pilots have to do would be a good bit of research. The fuselage may have to be reinforced to such an extent that it might negate the weight savings of the tailwheel. Something to look at closely.
 

Will Aldridge

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So now that I look more at this, keep in mind that the "rigid" mount is going to drive a LOT of shock into the lower fuselage - something a flexible stinger does not do to nearly that degree. A study of the repairs bush pilots have to do would be a good bit of research. The fuselage may have to be reinforced to such an extent that it might negate the weight savings of the tailwheel. Something to look at closely.
Yeah I've been thinking about that. The previous design (a flexible stinger) used the lower fin as a fairing over the for and aft mounts for the spring allowing it to be replaced if necessary. However this aircraft will live most of it's life on pavement, so hopefully those stresses will be minimal, but that bulkead it mounts to is alsodirectly connected to the vertical fin spar and main spar of the horizontal stab. If the tailwheel gets ripped out of it there will be some major damage to repair. If i go with this type of tailwheel maybe need to think about breakaway plates?
 
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