brianwallis

brianwallis

VAF moderator
Since the flip seems to be related to a resonance in the nosegear, is there anybody out there that would be willing to manufacture a nosegear that is different than the present nosewheel gear on the 6a and 7a? I'm thinking there are some awfully smart guys out there that have seen the resonance video of the nosegear and can calculate and design an aftermarket nosegear for the airplane....? (perhaps like the grumman line?(or adapt a aa-5 nose strut to the vans so we dont have to manufacture it?)
Best
Brian Wallis
 
Just a thought....

I've thought about finding a nose gear from a 172 or 182 and trying to fit it in somehow. But the chances of that happening aren't very good.

But I did wake up at 3AM last night with an idea, and I think it's a pretty good one too.

There are really two different problems.
1) Turf - The nose gear burying and causing the flip.
2) Asphalt - A general collapse from a not-so-graceful nosegear first landing.

The answer to #1 is pretty easy; put a bigger wheel there.

The answer to #2 is more challenging.

Have you ever taken a drinking straw and folded it? It's very easy to kink. But if you take straw #2, and make it a sleeve around straw #1, the support of the structure increases more than 2X.

Here's what I'd like to see:
- Before the landing gear is bent into position, sleeve it with a close fitting pipe. Then bend the entire assembly as one piece.

Weld it up to the engine mount as usual.

On the bottom side, cut it off a tad shorter and make allowances for a larger nose wheel.

There you go, a stronger nose gear assembly (Problem #2 is fixed) and a larger nose wheel (Problem #1 is fixed).

Honestly, I'm far from an expert and I'll admit that I'm very green when it comes to building. But it just sounds like a better way to skin the cat.

I can see some potential corrosion issues between the nosegear and sleeve. I'm sure a few drain holes in the sleeve would help. But not nearly as much as getting the right metals involved. I'd have to leave that to the metals experts.

It's just a thought.

Phil
 
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I'm definitely all for a stronger gear - I'll accept the weight (and perhaps drag) penalty for a more robust gear that will be more forgiving of my Cessna-style crash-and-dash landing technique. :D

It will be a while before I get to that point, but I can say with a good deal of certainty that I won't be fitting the stock nosegear on mine - whether I have to design it myself or buy someone elses design.
 
Carbon fiber

I believe that a wooden stiffener front and rear, matching the current shape, then overlaid with several layers of carbon fiber cloth would sigificantly add to the overall stiffness with a small weight penalty.

As far as corrosion with carbon and steel, not sure how that issue would be resolved.

Regards,
Pierre
 
The easiest solution would be to move the nose wheel slightly aft, maybe 17 feet aft, back near or below the rudder. Oh wait, that design already exists, its called a tail dragger :D
 
Thanks for contributing an original idea, Tobin.

Pierre,

I kinda like the glass idea, but I worry it handling the shock factor. I guess if you can make wings or boats that bounce across a lake at 70mph, it should handle the shock of a bounced landing........

Intresting thought.

Phil
 
Since you want to keep the gear leg from folding back and are looking to increase strength at minimal weight, glass or carbon definitely seems the best choice. But I would think you would not want to wrap it per sea. Why not a longitudinal build-up along the forward face of the gear to strengthen the leg from that bending moment, like a strap if you know what I mean? You could also shape the reinforcement to streamline the gear leg and kill two birds with one stone.

Just a thought.
 
Phil said:
I kinda like the glass idea, but I worry it handling the shock factor. I guess if you can make wings or boats that bounce across a lake at 70mph, it should handle the shock of a bounced landing........

Intresting thought.
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In the "good old days", as when my RV6A kit was produced; it was all wood stiffeners wound with fiberglass. The pre-made leg fairings didn't exist yet.

L.Adamson
 
Where is the weak spot

Seems to me that the gear leg itself is not all that weak but when a load is applied the gear leg bends at the transition from approx 45 deg to 90 deg just above the wheel. In all the flips I have seen the nose wheel is bent over where the factory bends the leg. Weak spot I guess. Would a gusset welded on top and/or on the inside radius stop the nose wheel from folding under. Even if it would help, I think a larger wheel would also be an additional improvement
 
[email protected] said:
Seems to me that the gear leg itself is not all that weak but when a load is applied the gear leg bends at the transition from approx 45 deg to 90 deg just above the wheel. In all the flips I have seen the nose wheel is bent over where the factory bends the leg. Weak spot I guess. Would a gusset welded on top and/or on the inside radius stop the nose wheel from folding under. Even if it would help, I think a larger wheel would also be an additional improvement
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I'm no engineer but:

I think that the gear just wants to flex at the bend point, it's quite natural. The solution would therefore be, add a different point of flexture. My idea, modify the current new style nosegear leg by adding a system like the -10 with donuts to absorb the shock, combined with a 5.00x5 nosewheel fork (optional). The question becomes, how much would a person with a -A pay for the components to retrofit this to their airplane? It would most likely run above the $1000 mark to make it all in a marketable kit form like I would want to do. New engine mount, gear leg, fork, and hardware. Also include installation instructions.

Could do it on a exchange basis I suppose (engine mount, old gear leg (new style) provided as a core, to bring the costs down).
 
I hate to be a naysayer but my main concern about being an aftermarket manufacturer would be liability.
Could you even get any kind of insurance to protect against that? And if you could, it would likely raise the cost beyond what most would pay.
The way things are these days I would be afraid of all that liability exposure.

T.
 
Test

L.Adamson said:
In the "good old days", as when my RV6A kit was produced; it was all wood stiffeners wound with fiberglass. The pre-made leg fairings didn't exist yet.

L.Adamson
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To take this thread a step further, we could buy or borrow a nosegear leg, put it in a vise and pull backwards on the nut end with a scale attached. Then fab the stiffener out of S-glass or carbon sandwich and re-test to see how many extra pounds of pull the new gear takes for the same deflection as earlier......pretty simple.

FWIW, Leland Snow at Air Tractor used to test the 1340 cu. in Pratt engines by tying the tail through a scale and running the engine wide open and noting the "pull". :)

Regards,
Pierre
 
Pardon my ignorance, but how do you guys know that the nosegear isn't designed to flex, especially in the case of a rough or nose-first landing? Could you be making the gear more dangerous by trying to stiffen it, adding gussets, etc? Flexing does not necessarily imply a fold-under failure due to an out-of-control harmonic vibration.

Someone may want to try contacting the fellow who machines the gear legs for Van's. He seemed very knowledgable, though I forget his name.
 
Paul Eastham said:
Pardon my ignorance, but how do you guys know that the nosegear isn't designed to flex, especially in the case of a rough or nose-first landing? Could you be making the gear more dangerous by trying to stiffen it, adding gussets, etc? Flexing does not necessarily imply a fold-under failure due to an out-of-control harmonic vibration.
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I second this thought. I do believe the nose gear leg is designed to flex. If that flex is taken out of the gear leg there is going to be some bending and breaking further up the chain (bent firewall, bent engine mounts). The answer to this engineering issue is not the strength of the leg. It is the proximity of the yoke to the ground. Remove that initial contact point and the risks go way down.

Having said that I do believe the -10 model nose gear is a big improvement on the design. I would be very interested in such a nose gear configuration mod myself. If the -10 design could be transferred to the 6-7-9 models I think we could go a long way toward decreasing the nose collapse risk.
 
Paul Eastham said:
Could you be making the gear more dangerous by trying to stiffen it, adding gussets, etc?
Stiffening something draw more load into the part. The load always will follow the stiffest path. That may not be an issue as there is only one load path for the nose landing loads; up the nose gear strut. That being said I think some flexibility is need to disapate some of the enegy in landing. Otherwise you maybe adding extra loads into gear/engine mounts.
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The mount is extremely strong, much more so than the leg or attachment bolt. When I force landed my -6A in a rough plowed field, the leg bent right back under the cowling, the retaining bolt sheared and the leg punched through the firewall to stop against the battery. The mount and firewall were not even tweaked. Main gear was also splayed, again no damage to mounts or structure.

The leg section is necked down below the lower spigot. This could be made a constant section (and bigger if need be) all the way to the bottom at the expense of something like 6-9 more pounds. The stiffness increases as the 4th power of the diameter if memory serves me so this would make a big difference and it could still bolt on to existing mounts.

A titanium leg could save the weight increase- don't Rockets use these?

The leg is at an angle to provide spring but it is a divergent structure. I think a stiffer leg and a solid metal or composite fork skid would avoid many of the current failures.
 
I inquired..

n5lp said:
http://www.langair.com/
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with Langair last week but have not heard back (maybe he doesn't like email). I also inquired at Grove and they said they were not interested in the project.

I think the best "fix" would be '10' design scaled down for us 7/8 drivers but alternatively a stronger leg, larger tire and more fork clearance would probably do the trick.
 
The -10 design unfortunately would require a new engine mount because of the pushrod and donut design. It could be designed to be lighter due to its tubular leg but not be too popular with the mount price and work to change.

Not rocket science to design something stronger but retrofitting to existing mount would be paramount and the fabrication in large numbers with good dimensional and heat treatment process control would be important.
 
Lots of "eyeball engineering" going on around this subject. Reminds me of the old Harley Davidson design philosophy:
"If it breaks, make it bigger. If it sticks out, chrome it."
Tough to get at root cause when you keep neglecting the operator side of the equation - A/C specific experience, currency, recurrent training, etc.
Perhaps Van's should start spec'ing accelerometer/recorders so that we could all know how hard their planes are being banged down. At least then they'd know how strong they needed to make the gear to accomodate a wider range of skill levels and circumstances.
Terry
RV9A
N323TP
 
terry,
like the thread, how much flying did you do while building. I read most of them saying, 10,to 30 hours a year. hardly enough. I think I could dream flying at night and stay current, comparably.
 
I would be primarily interested in how many failures there have been on hard surface runways NOT due to wheelbarrow or hard, level touchdowns. I suspect most failures are on rough surfaces or due to bad landing attitudes. I'd welcome feedback on this issue.
 
Hey, why do they taper that leg down at the end anyway? The Grummans look to be uniform in diameter. Seems like that alone might take care of the apparent weak spot at the bend? And, oooooh, I like the titanium idea though it sounds expensive!

Ditto on the flying experience issue. The prospect of not flying for 3 years is the principle reason I'm still flying the Archer instead of building. I fly every week and I believe that's what it takes to make your landings consistantly good (or at least acceptable).

Steve
 
I know a guy...

Ever hear that before?
He is building a 10 and wants to take it into back country strips. He is putting on bigger tires all around. The main will be 8x6 with dual brakes on each wheel and the front will be the wheel and axle off of a Cherokee 180 nose wheel. That would make it a 6 inch tire. The Cherokee has a better axle design that Vans (he claims). He is getting the fork made by Steve Furjesi (sp?) of Experimental Aircraft Metal Fabricators (360) 245-3478.

These plane are experimental and you can build them any way you want.

Good luck and enjoy.

Kent
 
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Speculation for an answer ...

s_tones said:
Hey, why do they taper that leg down at the end anyway? The Grummans look to be uniform in diameter. Seems like that alone might take care of the apparent weak spot at the bend? And, oooooh, I like the titanium idea though it sounds expensive!

Ditto on the flying experience issue. The prospect of not flying for 3 years is the principle reason I'm still flying the Archer instead of building. I fly every week and I believe that's what it takes to make your landings consistantly good (or at least acceptable).

Steve
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When one analyzes failure modes, often it is best to "design in" the *point* of failure at maximum stress. Somewhere has to be the weakest spot. And it is ebst that you know what, where and how this is and its behavior.

As someone mentioned, if the gearleg was infinitely strong, the load would have to be taken by the firewall. Have you seen what it takes to fix Cessna firewalls as a result of bad landings?

If the gear is weaker at a certain point then it will bend there and not pass on the forces to the firewall as much. In the best case, you just have to replace the gear. Worse, a prop or a prop dressing. Even worse, and engine teardown, repair and prop replace. Clearly there is a point also where it gets even worse (flip over) as recently evidenced.

I know of a person who had a small lapse (mind wander) on landing. <He openly admitted it.> The result was he nicked his prop on the bouncing but was able to taxi in. I think he had the engine inspected and the prop fixed etc. He is glad that the gear "bent" and the designed "bend point". Saved him a lot, we think.

Your mileage and views may vary ...

James
 
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