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RV-A skid plate design

vlittle

vlittle

Well Known Member
The other thread is so big that's it tough to find new postings. Here is a link to my design for an RV-A nose gear skid plate design. You can see a photo of my implementation below, and details are on my site.

Vern Little -9A

Tips Page



nose_skid.jpg


126_2677_1.jpg
 
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I see what you're doing, and I understand the philosophy.
I'd just like to suggest a consideration.

While resins in many respects are quite strong in many applications, impact resistance is not usually one of their strong suits. And we're talking BIG IMPACT here, not just a scuffing.
A properly bracketed, curved piece of steel might be better (if anything) because while steel may bend, it should still work as intended while a piece of catalysed resin will very possibly shatter. Even if the resin didn't shatter, I can imagine it being dislodged by the impact.
(To test my theory, mix up a big ball of material and let it cure. Then set it on the ground and whack it as hard as you can with the heaviest sledge hammer you can find. That will be only a fraction of the impact a nose gear might see if it drops into a hole.)

If that happens, you could then have either one big chunk, or a bunch of loose material (inside the fairing), jamming and deflecting the wheel itself and perhaps causing accelerated damage and subsequent flip where the standard arrangement might have been ok with just fairing damage.

Just thinkin' it through to a logical "conclusion". :eek:

This is one where I would definitely ask for Van's blessing before going with a chunk of resin in that area.
 
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Highflight said:
I see what you're doing, and I understand the philosophy.
I'd just like to suggest a consideration.

While resins in many respects are quite strong in many applications, impact resistance is not usually one of their strong suits. And we're talking BIG IMPACT here, not just a scuffing.
A properly bracketed, curved piece of steel might be better (if anything) because while steel may bend, it should still work as intended while a piece of catalysed resin will very possibly shatter. Even if the resin didn't shatter, I can imagine it being dislodged by the impact.
(To test my theory, mix up a big ball of material and let it cure. Then set it on the ground and whack it as hard as you can with the heaviest sledge hammer you can find. That will be only a fraction of the impact a nose gear might see if it drops into a hole.)

If that happens, you could then have either one big chunk, or a bunch of loose material (inside the fairing), jamming and deflecting the wheel itself and perhaps causing accelerated damage and subsequent flip where the standard arrangement might have been ok with just fairing damage.

Just thinkin' it through to a logical "conclusion". :eek:

This is one where I would definitely ask for Van's blessing before going with a chunk of resin in that area.
Click to expand...

Yes, I did consider this. the problem with a steel or aluminum skid plate is getting it to fit good enough to transfer any impact load to the front of the nose fork (and not the back part that would tend to roll the fork) before the nose cone collapsed. Another consideration is that I used flox, not glass fibers for the skid plate.

Flox is more flexible than glass fibers and when combined with epoxy resin, can resist impact quite well.

I did contact Van's on an earlier design, and they denied that there was an inherent design problem, so that was a dead end.

Finally, any impact strong enough to shatter the skid plate would probably blow the tire and shatter the rest of the wheel fairing as well due to the impact. This skid plate is much stronger than the nose cone itself, and is designed to improve the margin of safety, not function under unlimited extreme circumstances.

No skid plate design can solve the inherent problems with the nose gear design. My 'fix' is simply to provide a theoretical increase in the design margin that was relatively easy to implement.

That being said, I'm confident that others can improve on the design. Testing any of the designs is difficult, but the debate on line is healthy.

Thanks for the feedback.

Vern Little
 
Can't hurt

Cant hurt and might help ride out a pot hole vs. dig in. It comes under no technical objection, no harm and might help. Hard to test and hope you never find out if it does not work if you know what I mean. Good idea George
 
vlittle said:
No skid plate design can solve the inherent problems with the nose gear design. My 'fix' is simply to provide a theoretical increase in the design margin that was relatively easy to implement.Vern Little
Click to expand...

There is a very effective design mod for eliminating this problem. Like most good solutions, it is the obvious answer... Build a 9 instead of a 9A!!! :D ;)

Sorry, that was just too easy to pass up!
 
As long as this was brought up again, one thing I thought of earlier was that perhaps someone who works with metal castings of some sort could make a mold and cast a solid piece out of aluminum.

A piece like that wouldn't add any more weight than a chunk of resin (maybe lighter even), and my mechanical intuition says that it might work more as intended if ever needed.
 
Think back to the mid 90's... The nut on my nose wheel was hitting the fairing so I cut the Van's fairing and glassed in a bubble over the nut area. Seeing the danger of digging the nut into the ground I laid up five or six layers of heavy marine cloth to a finished thickness of about 1/4". Well, while flying off my time and learning how to land my shiney new RV I porpoised pretty bad and did not catch it in time and I bonked the nosewheel. I did not think anything of it at the time but taxied back to the hangar to cool my jets. A close look revealed that I had ground a flat spot on my reinforced area. It appears as though the gear leg flexed enough to allow the nose wheel to rotate back & up until the nut hit the pavement. Without the fiberglass ski I am certain it would have dug in and been much worse.

My ski was nothing more than a thick area in the bottom of the nose fairing. There is nothing backing it up. The fiberglass flexed until it was backed up by the nut, and it was enough to save my bacon.

Live and learn and keep the nose up...
 
A bit of Trigonometry.

It is admirable that a number of ?A? fliers are putting a lot of effort into reducing the risk of rollover in the aircraft.
Sitting here with my bum on the ground (Tail-dragger) I can?t help thinking they are overlooking a bit of year 11 Trigonometry and that their efforts may be in vain.

If the Nose STRUT bends back two things will happen.
1. The Wheel Base is reduced and therefore placing an increased load on the nose Strut.
2. The Strut will effectively lengthen; relative too the main gear, loading the Strut even more.

If the Nose STRUT bends back it must be because something besides the wheel is in contact with the ground. Whatever it is that is dragging on the ground, smoothing it or strengthening it is not going to reduce the friction and the more it bends the more it is loaded and the more it will continue to bend. We are not talking about snow skiing here.

I doubt that any mods other than making the nose fork rigid with a trailing link will solve the problem.
Meanwhile, I think it would be best to avoid rough fields.

If you are interested here are my calculations:
1. IF the Nose Strut bends back and remains Straight (Not Curved) it will protrude nearly 1? below the main gear. Of course it will bend in a curve, but it gives you an idea of how your aircraft comes to be poised over the nose wheel.
2. From a spreadsheet I knocked up.
Nose wheel Load Load /Main Wheel
Normal Position 300lb 400lb
Bend Back 5? 330lb 385lb
10? 360lb 367lb
15? 413lb 344lb
20? 471lb 314lb
Note that a 10? rear deflection puts as much weight on the Nose wheel as is on the mains.
Pete.
PS.
I am happy to send anyone the Spreadsheet and I welcome all to check my Trig.
P
 
fodrv7 said:
If the Nose STRUT bends back it must be because something besides the wheel is in contact with the ground. Whatever it is that is dragging on the ground, smoothing it or strengthening it is not going to reduce the friction and the more it bends the more it is loaded and the more it will continue to bend. We are not talking about snow skiing here.
Click to expand...

I'll take issue with that statement because it really is about skiing of some sort. Try snow skiing with just the boots and see how far you get.

While Pilot Dane's observation about how his "solution" avoided a more serious event is anecdotal at best, there is an obvious difference between what would happen if a sharp edged object digs into the ground (the nut) and what would happen if what hits the ground were a smooth transitional piece that would allow some "skiing" action.
In fact, to take this to an extreme example, imagine if you put a ski on the nose gear instead of a wheel and you can see that the darn thing would NEVER dig into anything. Of course, taxiing would be problematic... :rolleyes:

Anything that would present the ground with some kind of skid plate rather than a ski pole (again, the nut) would have to offer a better chance of avoiding more severe bending.
 
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Correction

Vern, You are quite right. Reducing the friction (Resistance) of any fixed part of the nose wheel is going to improve things.
If however, the resistance is still sufficient- a largish hole for example- to bend the strut back, then as I have pointed out, the load on the Nose Gear and therefore the resistance will only increase.

After all that is the whole point of trailing arm suspension. Deflection decreases the load.

Pete.
 
fodrv7 said:
Vern, You are quite right. Reducing the friction (Resistance) of any fixed part of the nose wheel is going to improve things.
If however, the resistance is still sufficient- a largish hole for example- to bend the strut back, then as I have pointed out, the load on the Nose Gear and therefore the resistance will only increase.

After all that is the whole point of trailing arm suspension. Deflection decreases the load.

Pete.
Click to expand...
I have been reading all of the threads that have started due to the most recent nose over. The trailing arm suspension nose wheel has always seemed to be the most logical design for ANY nose wheel airplane. I have never understood how the leading link could be anywhere near as strong.

So here are some questions I have:

Why does Vans look at the leading link design as a good design for his aircraft? If it is because of ease of building vs another design I do not believe that is an adequate reason. If that is the reasoning I will equate that to the construction industry that will use a design because they can put it up cheaply, quickly, easily but once it is up the use of it by the home owner is nothing but trouble for them for the life of the design.

What is involved in the construction of a trailing link design?

Can it be done on the -A model RV's? (I am aware that it can be done. What I am asking is, can it be done effectively, efficiently, and without a great deal of expense in $$$, weight and complexity?)

If this nose gear is a weak link in an otherwise very good airplane, I would like to do something with my plane that will reduce the problems associated with this weak link.

If there are any out there with serious thoughts on the trailing link design I would very much like to hear what you have to say.

Thanks,
 
From a different thread:

"Friends of mine in Lockhart, TX. built what they call their "jock strap", a rounded steel plate covering the big nut holding the nosewheel fork on. Hopefully it will skid along the ground keeping the nut from digging in and prevent a tip over."


Anyone from Lockhart, TX reading this thread and maybe care to elaborate?
 
GrayHawk said:
"Friends of mine in Lockhart, TX. built what they call their "jock strap", a rounded steel plate covering the big nut holding the nosewheel fork on. Hopefully it will skid along the ground keeping the nut from digging in and prevent a tip over."
Click to expand...
I like the name "skid plate" better myself. :D

Seriously, this sounds like just the thing.
 
Highflight said:
I see what you're doing, and I understand the philosophy.
I'd just like to suggest a consideration.

While resins in many respects are quite strong in many applications, impact resistance is not usually one of their strong suits. And we're talking BIG IMPACT here, not just a scuffing.
A properly bracketed, curved piece of steel might be better (if anything) because while steel may bend, it should still work as intended while a piece of catalysed resin will very possibly shatter. Even if the resin didn't shatter, I can imagine it being dislodged by the impact.
(To test my theory, mix up a big ball of material and let it cure. Then set it on the ground and whack it as hard as you can with the heaviest sledge hammer you can find. That will be only a fraction of the impact a nose gear might see if it drops into a hole.)

If that happens, you could then have either one big chunk, or a bunch of loose material (inside the fairing), jamming and deflecting the wheel itself and perhaps causing accelerated damage and subsequent flip where the standard arrangement might have been ok with just fairing damage.

Just thinkin' it through to a logical "conclusion". :eek:

This is one where I would definitely ask for Van's blessing before going with a chunk of resin in that area.
Click to expand...

Maybe a few plies of glass covering the flox blob and lapping onto the nose fairing could give extra strength/shatter resistance??

Fin 9A
 
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Try this on..

The leading arm/trailing arm comment reminded me of an old four wheeling argument about the benefits of a trailing arm type suspension over a leading arm.

As we already know the nose wheel on a A model is a form of leading arm suspension.

Give this little experiment a try (at your own risk). Get a push broom. Place your hands at the very end of the handle. Then hold your hands and the handle against your chin. Using your chin to push the broom walk around a bit. The broom and handle is the leading arm with your face as the pivot point right? Now walk into a step up or a door casing with the broom. You bust your lip and knock your teeth out right? Now walk backwards with the broom in the same location pulling it instead (trailing arm). Now you can go over curbs or anything and the broom just hops up over the obstacles.

With that said, in theory, I think the nose gear would be fine (ok better off) if it didn't have to castor right? That would place the axle at the end of the gear leg not at the end of a trailing fork. I believe it is the fork itself that acts like an arm under a sudden load bending the leg the opposite direction forcing the pivot nut TOWARDS the ground. Having the fork at a right angle to the pivot is the worst possible design. I believe the updated fork is at an angle that reduces the bending moment and increases the ground clearance. Getting rid of the fork would help the pogo problem, but of course we need to steer the plane so that won't work!
 
RVbySDI said:
Why does Vans look at the leading link design as a good design for his aircraft
Click to expand...

I suspect the answer to that question lies in the fact that the design of an aircraft requires an in-depth knowledge of a whole lot of different technologies. If the aircraft is designed by one man then it is reasonable to assume that he may have a stronger grip on some required technologies, and a lesser grip on others. That stands to reason.

In other words, aircraft landing gear systems may not be Richard VanG's strong point. That should not be surprising. Aircraft landing gear systems is a science in itself. The larger aircraft corporations probably subcontract out their design requirements to specialist mechanical engineering consultants (or have dedicated specialist in-house engineers).

On the RV12 nose gear Van initially attempted something different. It looked like an oleo strut but in fact it was nothing of the sort. It incorporated a spring and some people who saw it up close at Airventure 2006 described it as amateurish. In the end I believe Vans agreed because he seems to have dumped the new design and gone back to his stock configuration.

Van's nose gear design on the current 2 seat fleet is an over simplification of a complex structural requirement. Does that tend to indicate that the design has stretched Van's expertise in the area. Very possibly.

It may also explain why quantifiable improvements to the system are not forthcoming.
 
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Captain Avgas said:
I suspect the answer to that question lies in the fact that the design of an aircraft requires an in-depth knowledge of a whole lot of different technologies. If the aircraft is designed by one man then it is reasonable to assume that he may have a stronger grip on some required technologies, and a lesser grip on others. That stands to reason.

In other words, aircraft landing gear systems may not be Richard VanG's strong point. That should not be surprising. Aircraft landing gear systems is a science in itself. The larger aircraft corporations probably subcontract out their design requirements to specialist mechanical engineering consultants (or have dedicated specialist in-house engineers).

On the RV12 nose gear Van initially attempted something different. It looked like an oleo strut but in fact it was nothing of the sort. It incorporated a spring and some people who saw it up close at Airventure 2006 described it as amateurish. In the end I believe Vans agreed because he seems to have dumped the new design and gone back to his stock configuration.

Van's nose gear design on the current 2 seat fleet is an over simplification of a complex structural requirement. Does that tend to indicate that the design has stretched Van's expertise in the area. Very possibly.

It may also explain why quantifiable improvement to the system are not forthcoming.
Click to expand...
My only issue is this. Van has sold TONS of kits and a majority are now (sadly) nose-draggers. Hire on some outside help and fix the darn problem!
 
osxuser said:
My only issue is this. Van has sold TONS of kits and a majority are now (sadly) nose-draggers. Hire on some outside help and fix the darn problem!
Click to expand...

I wonder if this problem, is with any more frequency than mechanical failures of retractable landing gear.

It doesn't appear so; and believe this whole issue is getting rediculously overblown!

L.Adamson
 
L.Adamson said:
I wonder if this problem, is with any more frequency than mechanical failures of retractable landing gear.

It doesn't appear so; and believe this whole issue is getting rediculously overblown!

L.Adamson
Click to expand...
It's not, because people buy RV-A's because they are fixed gear, nose draggers. They want the simplicity of FG and the familer wheel in the front. And with startling commonality, a percentage of them are getting bitten in the behind by a corner of the operational envelope that shouldn't be a problem at all.

If any certfied company made the -A models there would be an AD by now, but these are kits, so no AD. I am left to wonder, as word gets out about this little problem, if people won't start either building TW's or maybe just building something else?

Given the frequency we see these landing accidents, and my desire to land on grass, you couldn't pay me to put a nosewheel on my -7 build...
 
osxuser said:
If any certfied company made the -A models there would be an AD by now, but these are kits, so no AD. I am left to wonder, as word gets out about this little problem, if people won't start either building TW's or maybe just building something else?

Given the frequency we see these landing accidents, and my desire to land on grass, you couldn't pay me to put a nosewheel on my -7 build...
Click to expand...

Stephen, you spread doom and gloom unnecessarily. Many fly routinely out of grass with the -A, it is not a big deal. Keep the stick aft as with the TD.

This discussion is about a nose gear that has been raked over the coals numerous times before. Many of the flips would have flipped with any nose gear.

Tail draggers are cool, that's why guys like them. Not many go that route because they fear the -A. They do it because the TD looks better and is more satisfying personally. The configeration is not better aerodynamically, especially during landing.
 
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the_other_dougreeves said:
I like the name "skid plate" better myself. :D

Seriously, this sounds like just the thing.
Click to expand...
I talked via phone with the people at Lockhart who made the "jock strap"; but he actually called it the "knee cap" this time.

Apparently it is a steel skid plate, shaped & welded to fit over the leading edge of the fork, covering the lower edge & nut, held on by bolts. He promised to try to scan & send some photos.

No test data & they are not in any business due to liability. The design would just serve as an example.
 
LifeofReiley said:
Hi Bill,

I would like to see these pics too. (Planetalk?)
Click to expand...
Yes, it is the PlaneTalk hangar group. I'll post the photos when I get them, or if I'm down in Texas, may stop over at Lockhart.
 
osxuser said:
If any certfied company made the -A models there would be an AD by now, but these are kits, so no AD. I am left to wonder, as word gets out about this little problem, if people won't start either building TW's or maybe just building something else?

Given the frequency we see these landing accidents, and my desire to land on grass, you couldn't pay me to put a nosewheel on my -7 build...
Click to expand...

:eek: :eek: :eek:

I'd prefer the violins....

I've been around RV nosedraggers for 12 years now. There is no rash of accidents, and an overwhelming and compelling reason for AD's.

Well, after 12 years, I'm still waiting that "big" secret to be exposed to the world!

Yes, as a prior reply stated, your doom and gloom scenario is uncalled for.

L.Adamson
 
osxuser said:
Given the frequency we see these landing accidents, and my desire to land on grass, you couldn't pay me to put a nosewheel on my -7 build...
Click to expand...

Items to ponder. If "grass" is really your thing. Then keep that wheel pant trimmed "high" for clearance, even if it means a loss of top speed. Better yet, take off the wheel pants altogether! So what if it's another loss of 11 kias or so!

It appears that some are still making RV taildraggers sound as "bush" machines, but they are not! It still all comes as a compromise, because ground clearance means loss of airspeed, that is gained with the new pressure recovery wheel pants. Low wheel pants and anything higher than dead rock hard "dry" grass, can result in a nice wheel lockup, and over she goes...

FWIW, my 6A has pressure recovery on the mains, and the old two-piece higher clearance pant on the nose. For rougher fields, the old pants are recommended for the mains too, but at a loss of top speed.
 
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It's not that there are a huge percentage of the fleet flipping over or anything. But this last video and pictures of the -7a accident prove that the guy did have the stick all the way back, and was doing everything right as far as we can tell.

It's not that percentage is high, it's just that these accidents seem very random and unpredictable when the pilot appears to be doing everything right. This leads to the conclusion that there is a design flaw. At least with the tailwheel you know what to expect.

I don't want to cause 'conflict' and spread 'doom and gloom' but there is a real problem here, Van's has addressed it as such, and their solution is inadequate. If these airplanes were certified, I can tell you with absolute certainty there would be an AD and a fix by now. Fortunitly, they aren't, because Van's would probably be backrupt too.

I'm also not saying that the tailwheel is the way to go. I personally see it fitting my operational mission better than the nosewheel. The good looks and personal challege are bonuses if you want to look at it that way. So, I'll be working in the next few months to see if I can come up with a feasible 5.00x5 nosewheel setup for the -A's. Not a perfect solution, but combined with the new nosegear legs from Van's it might be adequate.
 
so..... what do we see in the video?

osxuser said:
But this last video and pictures of the -7a accident prove that the guy did have the stick all the way back, and was doing everything right as far as we can tell.
Click to expand...

Going too fast to have the nose wheel on the ground with full up elevator.
Flaps still down loading the nose wheel. On the brakes??? do to landing too fast???? Fwd cg?? 0360 and c/s prop?? more weight on the nose.....

NOTHING LOOKS RIGHT about this landing. And then the nose wheel hits a hole a bump or??? and folds under (stubs) and over you go, like on a bicycle.

Watch Piper flyers learning, they will three point most of the time. Cessna too. It is hard on the nose, but the a/c was rented so what. Then they think that they can do that in a RV. It just does not work on grass without care.
 
osxuser said:
The good looks and personal challege are bonuses if you want to look at it that way.
Click to expand...

To be honest, it was the "looks" that swayed me to the "A" model after months of indecision. The first time I saw an RV, was two of them sitting side by side. One an A model, and the other just a 6.

From a distance, I thought they were Glasairs, as I had never heard of an RV. Never liked the looks of a 2-place tail dragging Glasair, compared to the retractable and sleek looking nose wheel model.

Well, it's the same with RV side by sides. The "A" looks more substantial, because you don't see the short straight & stubby wings, while the wheel in the back model reminds me of a squatting dog, ready to do it's thing! :D

But.............in the air, the nosewheel seems out of place, and the TD version looks better. But better yet, is retracts, such as the P-51 looking "4" model!

So, what do I really like, looks wise? How about a Lancair with its high aspect ratio tapered wings; or a Harmon Rocket or F-1 that just looks "mean"!

I'd settle with an "8" taildragger, because it looks good from most angles, but not all. That's why you see the photo's of P-51 look alike "8's" from certain angles! :)

In the meantime, my 6A has it's stars and stripes, along with a black and white band of invasion stripes. I can pretend it's a P-38 with one engine out, or a P-51 if I stand in front of the nose wheel for photo ops, while someone sits on the tail. :D

L.Adamson
 
Video

http://www.youtube.com/v/NfaCGc16jQ0

There seems to be no poor piloting technique here, although it looks like the elevators might not have been full up until AFTER the nosewheel started to dig. Hard to tell. Look at the background at some of the other aircraft that made it into that field with no problem. Bad luck? Maybe. I tried to embed the video, but I guess HTML is off.

I still draw the conclusion that these airplanes should be able to land anywhere a Grumman Tiger can. Just my opinion, and that doesn't seem to be the case.
 
BrickPilot said:
What about a beefier version of this trailing link design.... Sure, it's for an ultralight, but perhaps it could be adapted.
Click to expand...

There is another issue (other than leading/trailing link) that will make integration of your suggestion a challenge. The vertical pivot axis for a castering wheel needs to be well in front of the wheel contact patch. This restriction may result is much of the suggested trailing link mechanism residing in the same general area as the problematic caster nut.

The pictures from your link appear to be from a steerable nosewheel arrangement. Of course.. If we went to a steerable system on the RV, the caster axis goes away completely.. :rolleyes:
 
rzbill said:
There is another issue (other than leading/trailing link) that will make integration of your suggestion a challenge. The vertical pivot axis for a castering wheel needs to be well in front of the wheel contact patch. This restriction may result is much of the suggested trailing link mechanism residing in the same general area as the problematic caster nut.
Click to expand...
I would like to comment on this idea.

I own a Challenger II and am currently flying it. The very interesting thing about flying the Challenger is that I was warned before I purchased it that the nose gear on the Challenger is a weak point in its design (doesn't that sound familiar). Everyone, including the dealer, warned me that when landing I needed to make sure I land on the mains and hold the nose off as long as possible while bleeding off speed on the roll out (again, doesn't that sound familiar). The nose gear is really nothing more than a stubby bicycle front fork design. I cannot say for sure but it looks like it was indeed taken straight off of some kid's bicycle and modified to fit this airplane.

I have been flying for over 3 years now in this airplane with the factory nose gear. Every landing, with the exception of less than a dozen landings on paved strips, has been on grass strips. In fact I have had two unfortunate experiences setting this plane down off field with engine failures. Landing in a very rough terraced pasture did not do any damage to this precarious nose gear because I landed on the mains and held the nose gear off all the way to the point where the speed bled off to a slow enough pace the nose wheel could handle.

I mention this because I feel the RV-A models need to be handled very similar to this Challenger. There indeed is a technique involved in landing these airplanes. I will say that the reality is this though, the Challenger is a peach of an airplane to land once you understand it (hmmm, again, this sounds very familiar). Having said all of this though, I will say that however involved the pilot has to be in learning this technique, I still do not believe the design of these nose gear should allow for such devastating consequences when poor technique is applied.

On another note concerning the free castering nose gear vs the steerable nose gear like the Challenger, I really do not see any downside to the steerable nose gear design. It does work very well in that plane. Just press the rudder pedal in the direction you wish to go and the nose gear turns that way and so does the airplane. It is a very simple design that works very well. In fact I really do not understand why Vans changed his design on the RV12 away from the steerable nose gear when it looked like it was working quite well for that aircraft. In fact I might say, considering the potential use of those who intend to fly the RV12, it might be a much superior design over this problem plagued castering gear on the current RV's.

The pictures from your link appear to be from a steerable nosewheel arrangement. Of course.. If we went to a steerable system on the RV, the caster axis goes away completely.. :rolleyes:
Click to expand...
The pictures posted appear to have some potential for application with castering RV gear. The Challenger gear is simply "stabbed" onto a straight tube running down from the fuselage. It is simply bolted onto that gear leg. The current RV gear leg has a curve pointing down at the end of the leg that would be very similar in design. The attach point for the pictured design would not be very far off. It would be high up from the ground and have much more bulk that would require some new fairing needs but I can see it still functioning in a leading link/trailing wheel arrangement.
 
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I is a little hard to second guess what went wrong.

The video is of poor quality and the still pictures are missing one important shot (when the front wheel tucked).

Given that constraint, this is my conclusion:

The landing was flat. The plane looked to be going at a good speed and yet the front tire was not being held up. The elevator was back, so either the CG was way forward or the brakes were being applied.
I think that being the short grass runway the pilot may have been a little to hot and was applying lots of braking. A some point the front hit a little high spot (you can see the tail go down). The braking continued as the front wheel rebounded in to a low spot and then tucked.
I the plane were a tail wheel and the pilot had used as much braking then the plane would have flipped over even sooner. Although a competent tail wheel driver would have known not to over brake and do a go-around.

I don't think that any kind of skid would have saved this plane, because the skid would fold under anyway. The way to land correctly would be to land on the mains (same as a tail wheel) and keep the elevator back (nose wheel off the ground). Apply only as much braking as would allow the nose wheel to be held off the ground, until the speed has reduced.

That said I do see a value to the skid addition to the fairing. At low speed taxi when a hole is encountered the skid could help you out of a unseen hole. Might save rebuilding the fairing or fixing the front gear leg.

Kent
 
One Example

I got permission from the fine people at the "Plane Talk" hangar at Lockhart, TX, to post these photos of their steel "knee cap" design. This is for the old wheel fork.

normal_MVC-001S.JPG


normal_MVC-002S.JPG


normal_MVC-003S.JPG


normal_MVC-004S.JPG


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GrayHawk said:
I got permission from the fine people at the "Plane Talk" hangar at Lockhart, TX, to post these photos of their steel "knee cap" design.
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I like it! I was thinking of something a little larger and with a different curve, but this is exactly the concept.

As far as testing it out ... 3, 2, 1 NOT IT!

Actually, thinking about it, hard packed snow might be a good way to test the design without risking too much injury.... However, it will be a while until we can get some of that. Maybe I'm just thinking about snow because it's 104 here in Fresno.... Guess I need to get back home to Dallas where it's cool :eek:

TODR
 
Does it seem like he was going fast

osxuser said:
http://www.youtube.com/v/NfaCGc16jQ0

There seems to be no poor piloting technique here, although it looks like the elevators might not have been full up until AFTER the nose-wheel started to dig. Hard to tell. Look at the background at some of the other aircraft that made it into that field with no problem. Bad luck? Maybe. I tried to embed the video, but I guess HTML is off.

I still draw the conclusion that these airplanes should be able to land anywhere a Grumman Tiger can. Just my opinion, and that doesn't seem to be the case.
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Don't blame him/her if they let up on the stick when it dug in, but is that to speed? It does look like they where going fast. The video last about 4 seconds before it digs in. My wild guess is 13-20 mph. Not really that fast, but my margin of error is +/- 100%

I know fast taxi speed is a relative term, but there is a min energy (fwd velocity) that is needed to cause the gear to fold back, dig-in and have enough energy to flip, if you get a "snag". Really a pilot should not BE ABLE to do anything wrong, at least wrong enough to cause this, bar driving into parked planes. Also the video is poor and hard to tell anything, but GOSH the internet is amazing.

TAXI SLOW good idea? The one or two last year or so that did not go over but dug in causing varying amounts of damage. Pictures where available and from the description I guess they where probably going slower. Clearly having a gear dig-in does not mean always going over. I have now seen damage from just the nose wheel faring, plus the gear leg and faring itself and in slightly worse incidents, prop and spinner and than wing tip. The worst is the full flip.

Of pilot controlled things, back elevator, surface, taxi speed and CG, I don't think its just one thing, but its a combo of many things. I can see two heavy folks, no bags, heavier engine prop combo being worse than a light plane aft CG. When the RV-6A first came out 320's and fixed wood props where common, ie light.
 
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speed calcs from videos

You only need time and distance for speed.

Try counting fuselage lengths per second. Try it for each second and over the first 3 seconds.

Since the camera is panning, you can use objects in the back ground or fore ground to get the relative movement of the airplane. For example, if the nose of the airplane is aligned with a tree limb in the back ground, by the time the tail passes that tree limb, the airpane has moved about one RV-7 length (20 feet?). The airplane does not have to be square to the camera for this to work.

Don't stick your dividers in the computer screens.

(# fuselage lengths/# seconds) X length of fuselage gets you speed in fps. Divide by 1.466 to get mph or by 1.69 to get knots

Also look for pitch undulations from start to the end. If you can perceive them on a video like this, they are usually significant.
 
I think the knee cap is a great idea. A couple of questions: Can it be made of aluminum instead of steel (weight), and what did you do with the zerk fitting for greasing the pivot?

One observation. My fiberglass design minimizes the collapse of the nose cone by transferring the load to the fork. With the knee cap, nose cone collapse is still possible. We don't want the nose cone jamming the tire.

Perhaps a combination of techniques would be usefull: the knee cap plus some fiberglass packing in the nose cone to give a tight fit.

If you know some handy mechanical types, it's possible to do a test when the gear is off the plane. You'd need a fixture to be able to provide force downward on the gear leg, and force backwards on the wheel axle (representing friction and pitching moment of the airplane during braking).

Finally, I think it's possible that a modified form of knee cap would work even better on the new fork design.

Great work, keep it up!

Vern
 
vlittle said:
I think the knee cap is a great idea. A couple of questions: Can it be made of aluminum instead of steel (weight), and what did you do with the zerk fitting for greasing the pivot?

One observation. My fiberglass design minimizes the collapse of the nose cone by transferring the load to the fork. With the knee cap, nose cone collapse is still possible. We don't want the nose cone jamming the tire.

Perhaps a combination of techniques would be usefull: the knee cap plus some fiberglass packing in the nose cone to give a tight fit.

If you know some handy mechanical types, it's possible to do a test when the gear is off the plane. You'd need a fixture to be able to provide force downward on the gear leg, and force backwards on the wheel axle (representing friction and pitching moment of the airplane during braking).

Finally, I think it's possible that a modified form of knee cap would work even better on the new fork design.

Great work, keep it up!

Vern
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Cannot speak for the Lockhart group; I am only posting the photos.
But my guess is yes, it could be made of aluminum. The grease zerk hole is used for one of the 3 mounting holes.

Maybe someone from Lockhart will join in.
 
RVbySDI said:
BrickPilot said:
What about a beefier version of this trailing link design.... Sure, it's for an ultralight, but perhaps it could be adapted.
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The pictures posted appear to have some potential for application with castering RV gear. The Challenger gear is simply "stabbed" onto a straight tube running down from the fuselage. It is simply bolted onto that gear leg. The current RV gear leg has a curve pointing down at the end of the leg that would be very similar in design. The attach point for the pictured design would not be very far off. It would be high up from the ground and have much more bulk that would require some new fairing needs but I can see it still functioning in a leading link/trailing wheel arrangement.
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Jessica Schmidt from Custom Flight Systems contacted me regarding a query I made to them. She indicated that they would be interested in developing a nose gear mod for the -A model, but she needed some photos of the stock nose gear up close or drawings of it. Can anyone contact me with these pics? I'm sure all the -A builders would be interested in at least another option.
 
GrayHawk said:
Cannot speak for the Lockhart group; I am only posting the photos.
But my guess is yes, it could be made of aluminum. The grease zerk hole is used for one of the 3 mounting holes.

Maybe someone from Lockhart will join in.
Click to expand...
OK, I got another email from Lockhart & I have been giving this skid plate design the wrong name. It is not 'knee cap" and I quote:

"BTW we named it the JOCK STRAP because it protects the NUT."

I'm not sure if they mean the nut holding the fork on, or the one behind the stick. ;)
 
Can someone point me to pictures of the old and new gear?

I am curious which gear design I have, any have pictures comparing new vs old gear?
 
I have a 9a with the old nose gear, and ready to match drill and swap to the new nose gear becasue of these issues.

Trying to estimate speed from the video is unhelpful, as MANY mobile phone videos I have seen tend to play fast when reviewed.

I am very interested in the jockstrap as it is elegant solution much like Verns, but possibly easier to implement. It is vital that with potential impact weight on the the skid plate, that the back of the plate does not push into the front wall of the tyre, or this will cause sudden deceleration of the nose gear (like a wheel lock from overbraking), which will exacerbate the tuck under. I will be looking to install a jock strap shortly!

The incident aircraft filmed did not have the new nosegear (IIRC). I still do not have a feel for how helpful the modern design is. Are there still reports of mishaps with the new design.

Justin
old nosegear 9a
(4months on grass no problems yet)
 
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