N395V

N395V

Well Known Member
This thread is to split from a prior merged thread. The thread

Group effort for a new Nose gear design
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was merged with nose gear theory, There does not appear to be a tool to unmerge the threads so if you wish to continue this thread please go to the nosegear theory thread and cut and paste your responses here.
 
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Since this thread seemed to have been orphaned, I thought it might be useful to use it to compile a collection of pictures of other nose wheel leg designs. Whether or not these can be adapted to the RV-?A, people have been interested in what other aircraft designs have done. If anyone has any pictures, especially without the pants and cowling, please, share. I think the Grumman, Cirrus, and C-162 would be interesting.

RV-10:
rv-10.jpg


Just Escape:
Just%20Escape.JPG


V-Plane Concept:
v-plane.jpg
 
How is the nose gear mounted on the various Pipers? They all seem to have a nearly vertical oleo strut from what I remember.
 
Picture of RV-7A or 9A...

I'd love to see a picture of a 7A or 9A similar to the RV-10 in this thread, just to compare the pictures side-by-side.
 
I will try to locate a picture of side by side two seater RV-xA with modified nose gear mount. RV-10 style. Was so much work involved that Russians decided it's not worth.
 
The Jabiru looks nice - ridged, light weight and not likely to stick a non-moving piece into the ground. But it would put the the wheel in an entirely different location. Then the RV-10 looks pretty good too. Am I correct in assuming it's made of tubing? Presumably the design is intended not to flex and would hopefully completely fold up on failure rather than snapping back and causing the airplane to pivot on it. From what I can see of it a new builder (me) would do well to utilize a design similar to the 10.
 
The -10 design looks so similar to the -7A design that it might be pretty easy to change. The pivot on the -10 sits below the lowest bolts though, and on the -7 there isn't any extra room there. So there are still challenges, but it doesn't look insurmountable.
 
The Grumman photo gives rise to an idea....

The photo of the Grumman gave rise to an idea. In the 60's, Chrysler cars used torsion bars instead of coil springs for front suspension. No matter how hard we teenagers tried to wreck these cars, we never broke a torsion bar even after a series of wheelies!

If the front RV gear leg was attached to a horizontal torsion rod that flexed, might that provide an element of spring versus burdening the gear leg with all of the flex? I circled the location of the proposed horizontal torsion bar on this Grumman.

My .02

Barry

grummannose2.jpg
 
Does anybody have a pic of the RV-7 like the one shown above that is directly from the front? I have an idea, but it would make it a lot easier to illustrate with a direct shot instead of the 3/4 view like above.

thanks
 
Well, this is the best I can do with MSPaint. Kind of pathetic, but hopefully you will get the idea.
The Red is parts to remove, The Blue is parts to add for structural strength, and the Green is the torsion bars.

There would need to be a bearing block of some sort for the central tube to rotate around at the blue area right next to the gear mount tube. The supports on the sides would only be to spread the loads across the complete firewall.



Well, dang, now I can't post my image. I don't have a website I can post images to. Is there another way to get pics up here?
 
Well, dang, now I can't post my image. I don't have a website I can post images to. Is there another way to get pics up here?
Click to expand...

See "insert pics" ..... top left corner of this page.

L.Adamson --- RV6A
 
Several new cars offer RUN FLAT tires - Good idea!!

Rivethead said:
On some vehicles the military uses tires that are designed to run flat in case of being shot through.
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Agreed, anything that keeps the nut off the ground will be helpful. Your idea solves the problem of tires that go flat after departure. Fortunately, the technology already exists meaning it simply needs to be applied to GA.

What would be VERY helpful is a cooperative effort that includes a testing facility to safely test each of the three major theories for rollover reduction. Those theories are:

1) the distance of the front nut from the ground
2) the rolling resistance of the front wheel
3) and the capability of the front gear leg

I believe we have one or two volunteers who would perform the engineering. We can probably gather parts easily. What we do not have is the test facility to assemble & evaluate each solution.

A letter writing campaign was launched yesterday (10-5-2010) that politely asks Vans to consider spending some more time and energy on the rollover issue.
 
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I was about ready to start design work on the -10 style nosegear for the RV-7a and -9a (the 6a doesn't appear to have the problem because of superior geometry).

Then I realized the problem with it, every one I've worked on is different, and would interfere with current engine installations. The airbox is a major problem on the O-360 powered crafts. Anyone in socal with a -7a interested? I could outline what I've figured out, but I was planning originally to bring a product to market.

Edit: I considered the Grumman setup, and then ruled it out based on WEIGHT!
 
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That was an interesting report, but it doesn't seem that the FEA included a buckling analysis. If it did, it wasn't mentioned.

Beam-column buckling tends to increase the deflections, given an aft load.

Additionally, it appears that dynamic effects weren't studied, except qualitatively.
 
Nose gear

In my opinion the set-up on the RV10 is not the answer. Those rubber donuts are there to absorb shock from upward deflection of the nose gear. None of the gear failures I've seen on RVXAs has been from an upward failure - instead the leg has folded under and back. I'm also not sure it can be blamed on the gear nut digging-in. It MAY dig-in, but it may also happen AFTER the leg has started to fold backwards, and this may be clouding the issue. The digging-in MAY however cause the airplane to "pole vault" and flip over. Compare the side view of the RV9A to that of the Grumman. The RV9A angle relative to the line of the fuselage is much steeper than the Grumman. Also the Grumman sits much lower to the ground allowing for a nose gear leg that more closely parallels the line of the fuselage.

I still feel that a lot of the problem could be solved with a larger nose wheel. Would you rather ride over a curb in a shopping cart or a bicycle? I have to believe that much of the forces pushing that nose gear backwards is due to a small diameter wheel. More rolling resistance is coming from that small wheel going into and out of ruts than any issues with the wheel axle. I'd like to see Van do some studies with a larger nose wheel and with strain gauges on the gear and compare the forces on the nose gear to that using the supplied wheel. I'll bet the differences will be dramatic. This will also have the added benefit of getting the nose gear nut even further off the ground.

As for pilot technique - there's NO question that proper technique will go a long way towards preventing these accidents, HOWEVER, non of us is perfect, and once in a while we drop the nose a little too fast, or too hard, or land too flat, and anyone who says these accidents are due only to pilot error is being naive. A properly designed nose gear will be a lot more forgiving than the RVXA appears to be. When I think of all the crappy landings I've made over the years in Beechcrafts, Pipers and Cessnas, I'm grateful for their forgiving design. There should be no reason why the RVXA nose gear shouldn't be as reliable as any other castering nose wheel design like the Cirrus or Grummans or Diamonds.

Van needs to step up to the plate here.
 
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I agree that a larger nosewheel is needed, but that is a start. There needs to be some sort of suspension. Right now, by design or not, the thin gear leg provides that, and it is not capable of it. A larger wheel will produce more force on an already too weak leg, so that needs to be buffed up. Now you have a larger tire, with a stronger leg that does not provide any suspension travel, this will result in all the force directing towards the motormount and firewall. By adding some method of intended suspension, the force will be transferred where it should.

The cirrus, grummans, etc. all have a suspension component to their design. The 6A,7A,8A,9A models do not.

There are many engineers on this board that have expressed excitement about working as a group to design something in a more scientific manner.

Maybe we can get the mods to provide a new Forum, maybe under the neverending debate section, where those interested can focus their attention?
 
Not so sure

that a larger wheel will result in more forces on the gear leg. Yes, the moment will be a little longer, but less forces will be transferred to it from rough surfaces - again, would you rather ride your bike over a curb with 12 inch wheels or 27 inch wheels, and I think hitting a curb with a 12 inch wheel will do a lot more damage to the fork than with the full size wheel. The only way to know for sure is to do the study, and this is a VERY easy thing to do. I think the only thing an RV10-like suspension will do is allow a beefier, stiffer gear leg to used (and maybe that was your point). My point is, let's try the easier things first before we completely redesign the nose gear. Don't forget, the solution needs to be retrofitable to existing RVXs lest we risk utterly devaluing the existing fleet out there.
 
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I think you...

Av8torTom said:
In my opinion the set-up on the RV10 is not the answer. Those rubber donuts are there to absorb shock from upward deflection of the nose gear. None of the gear failures I've seen on RVXAs has been from an upward failure - instead the leg has folded under and back. ....
Click to expand...

...missed a bit here.

As I see it, the main difference between the -10 (and the Grumman) nose gear and that on the -6, etc. is what item "springs".

On the -6, etc the spring is in the entire gear leg, including flexing at the curved bit just before the pivot.

On the -10 the leg is much stiffer - heck, it even has a weld in it - and the "spring" is provided by the rubber donuts. It's the same in the Grmman leg - the nose gear leg is a stiff heavy wall tube, that pivots about a cross tube just aft of the firewall.

What flexes, and the geometry are major differences, something needs to provide the "front suspension"...:)
 
Well I agree

that if a stiffer, stronger gear leg is the answer, then a suspension of some sort will be needed indeed. I'm just trying to think of solutions that could be "easily" applied to the existing fleet.
 
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The -10 solution...

Av8torTom said:
that if a stiffer, stronger gear leg is the answer, then a suspension of some sort will be needed indeed. I'm just trying to think of solutions that could be "easily" applied to the existing fleet.
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..is actually quite effective, and probably as easy aas any other...:)
 
The Tecnam approach is viable - especially when one considers these airplanes have been designed for use on pretty rugged surfaces, as trainers, etc. Yes, the aircraft is definitely lighter than an RV, with much less weight forward of the firewall. But with the brainpower available here I'm sure some flavor of new nosegear could be brewed up, and bringing other, more radical designs like that of the Tecnam into consideration will no doubt help get the creative juices flowing!
 
No easy answer

Av8torTom said:
In my opinion the set-up on the RV10 is not the answer. Those rubber donuts are there to absorb shock from upward deflection of the nose gear. None of the gear failures I've seen on RVXAs has been from an upward failure - instead the leg has folded under and back. I'm also not sure it can be blamed on the gear nut digging-in. It MAY dig-in, but it may also happen AFTER the leg has started to fold backwards, and this may be clouding the issue. The digging-in MAY however cause the airplane to "pole vault" and flip over. Compare the side view of the RV9A to that of the Grumman. The RV9A angle relative to the line of the fuselage is much steeper than the Grumman. Also the Grumman sits much lower to the ground allowing for a nose gear leg that more closely parallels the line of the fuselage.

I still feel that a lot of the problem could be solved with a larger nose wheel. Would you rather ride over a curb in a shopping cart or a bicycle? I have to believe that much of the forces pushing that nose gear backwards is due to a small diameter wheel. More rolling resistance is coming from that small wheel going into and out of ruts than any issues with the wheel axle. I'd like to see Van do some studies with a larger nose wheel and with strain gauges on the gear and compare the forces on the nose gear to that using the supplied wheel. I'll bet the differences will be dramatic. This will also have the added benefit of getting the nose gear nut even further off the ground.
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The geometry of a castering nose gear is such that both upward and backward forces on the wheel produce a 'tuck under' moment on the front of the gear leg. The RVxA legs are rigidly mounted to the engine mount and are quite flexible (by design) so the deflections are significant. The forces on the gear leg, and therefore the deflections, will be about the same regardless of wheel size. However the higher clearance means more deflection/force will be required before the nut contacts the surface and starts the pole-vault effect. A larger wheel will handle smaller bumps/ruts with less force as well. The newer noswheel fork helped with more clearance. But none of that changes the geometry or flexibility of the gear leg.

The other designs (Grumman, RV10) cited have a MUCH stiffer gear leg and are mounted differently to the fuselage, so there is far less (if any) 'tuck under' deflection and the forces are reacted in a completely different manner - the gear leg moves up, not back.
Reducing the 'tuck under' deflections on the RVxA gear is "easy" - stiffen the gear leg. However that drives different loading into the mount which is likely to be probematic.

A geometry change could help: make the vertical/forward slant of the leg point toward the rear of the wheel and then run longitudinally forward to the point where it bends down for the pivot (kinda like the Grumman). Now vertical loads would bend the gear leg up and forward and counteract the 'tuck under' moment of the reaction at the pivot. It would be ugly IMHO, because the longitudinal part of the leg would have to be far enough away from the wheel/fairing to not touch. It would require a change to the engine mount (new angle for the gear tube) a new leg, and fairing, and it would still be ugly.

I'm just going to stick with what I've got :rolleyes:
 
Reducing the 'tuck under' deflections on the RVxA gear is "easy" - stiffen the gear leg. However that drives different loading into the mount which is likely to be probematic.
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As is......these legs allow for substantial "dropping through the flare" mistakes while landing... without driving them through the airframe. So yes, stiffening them up, could be asking for a different problem.

L.Adamson
 
I mostly agree

Dennis, with the possible exception of your first sentence I totally agree with everything you say. Relying on the flex of the nose gear for suspension purposes requires a gear leg that is just not strong enough especially with that geometry. The FAA FEA report makes this pretty clear to me. I'd still like to see a similar analysis using a larger nose wheel. I like the Tecnam design, but that's not a retrofit.
 
Taper

Why not strengthen the lower part of the leg to prevent tuck? A simple matter of slightly changing the taper or reinforcing the existing leg. If necessary, slightly thin the upper part of the leg. The strain is moved nearer the firewall, just like a donut arrangement. A slightly larger wheel can help minimize rearward force. Done.
 
No simple answer

zav6a said:
Why not strengthen the lower part of the leg to prevent tuck? A simple matter of slightly changing the taper or reinforcing the existing leg. If necessary, slightly thin the upper part of the leg. The strain is moved nearer the firewall, just like a donut arrangement. A slightly larger wheel can help minimize rearward force. Done.
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The slightly larger wheel will slightly minimize the rearward force - some of the time. Not the long pole in the tent IMHO.
Reinforcing the lower part of the leg and/or thinning the upper part are structurally the same concept. Both drive the force to the upper part of the leg which also increases the force (longer moment arm means more moment to react). Thinning the leg has the potential of driving the failure point to the new thinner area. Just stiffening the lower part would drive more force into the mount. Maybe it could take it,maybe not. It's been way too long since I've done structural analysis :eek:
 
I'm curious

Av8torTom said:
Dennis, with the possible exception of your first sentence I totally agree with everything you say. Relying on the flex of the nose gear for suspension purposes requires a gear leg that is just not strong enough especially with that geometry. The FAA FEA report makes this pretty clear to me. I'd still like to see a similar analysis using a larger nose wheel. I like the Tecnam design, but that's not a retrofit.
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about that first sentence... :confused:

Designing a gear leg that is both flexible and strong enough, with that geometry, is not a big problem, given the proper re$ource$. Van's team did a pretty good job, but it's obviously the weak link in the system. The design has to be for the whole system (leg, engine mount, fuselage attach and related structure) not just the leg. The engine mount and fuselage attachments may be capable of just beefing up the gear leg a bit, but without analysis and/or testing, it's a risk. All it takes is time and money to find out :rolleyes:
 
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Comments On Recent Posts

Life?s a series of tradeoffs. So is landing gear design. Recent posts suggest increasing the leg stiffness as a solution to the rollover problem. Concerns are noted on the impact to the system specifically the engine mount frame. Will the frame stand up to the new increased loads?

I have reviewed most of the data, pictures, etc on nose gear failure. There is no mention of damage to the engine mount frame itself. The engine mount frames for the RV10 & RV12 are similar in design to other RV models. The nose gear legs on the RV10 & RV 12 are a stiff design and transmit higher loads to the engine frame. As the RV 6,7,9 engine frames are similar in design they should be capable of similar loads.

Conclusion, if the RV10 & 12 can take a stiff leg design so can the RV 6, 7, 10 frames. A stiff leg design should be considered.

Let?s face it. I would take a bent engine frame over a total write-off from a rollover.

Starbird
 
engine mount bent

Starbird
I know of one RV6A that has landed so hard on the nose that the axle bolt was bent and no tip over. On another hard landing (same RV6A) it bent the nose wheel gear and the engine mount which all had to be replaced and again no tip over. So go figure for the life of me I have no idea what happening with all these tip-over..
Squeak
 
Squeak said:
Starbird
....So go figure for the life of me I have no idea what happening with all these tip-over..
Squeak
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They happen at very low speed. My flip happened at such a low speed, it almost did not go over. I thought the airplane was about stopped when the skinny NG hit soft sand and dug in for the pole-vault. That event was not caused by the strut flexing as in the old video, it was simply a pivot point come to life due to a little tire and very soft river bottom sand.

A hard landing is a different issue. The airplane is moving faster and more than likely will bounce. The bending of the engine mount is the result of a vertical load from the hard landing. With the slow speed pole-vault the only thing that gets bent, and not much, is the NG strut itself. It supports the entire weight of the aircraft remarkably well.

IMHO, the #1 mechanical item that will slow down flips is a larger NG. And that will mean a larger NG fairing, a stiff vertical strut system to hold it, and more weight. Yes, the 10 and 12 NG assemblies are in that direction, but the jack-be-nimble, jack-be-quick cool little airplanes we now have the privilege to fly will be gone.

IMHO, the #1 non-mechanical item that will slow down flips is pilot proficiency.

The approach and landing phase of any flight is the most challenging and must be practiced to keep from becoming complacent, lackadaisical and/or simply incompetent. Unfamiliarity with flight comes from not going there on a regular basis and that leads to poor speed control, poor situational awareness, and a general inclination to accept less than perfect performance, which of course no one ever achieves - but is no excuse not to strive for it.

Whatever comes of this debate, I will not change my airplane if it moves it closer to becoming a run-of-the-mill span can. And whatever does come, do not believe for minute it will prevent forever all flips. Many a span can has been flipped due to poor flying and/or training mishaps and that won't change with these airplanes.

The RV adventure is so popular because it is not in any way a span can experience. Let's not go in that direction, let's learn how to fly these things as they should be flown and keep what we have.
 
David, add a 6.00x6 wheel/tire to the nose. Maybe it loses 2-3 mph. If that is what solves the problem go for it (whoever needs it).
 
wheel weight?

I wouldn't think that changing the nose wheel/yoke for a size 5 will not add so much more weight as to require an upsize to the strut. The increased bending force on the strut due to the larger moment of the longer yoke may require more strength but not much compared to the accompaning better rolling ability thereby reducing the load caused by a bump in the first place.

No engineer here but " if it looks right, it must be..."

Bevan
RV7A not flying yet
 
Dave, I saw nada of concern in the video from Post #43. Did I miss something. If so, at what time hack?
 
not an engineer but,

I think there's a lot of merit to the idea of a larger nosewheel with a modifed fork and gear leg.

Looking at the nosewheel from the left side of the aircraft, the current fork is close to parallel to the ground, with the gear leg meeting the fork at about the 9 o'clock position. What about a simple mod with a more angled fork meeting the gear leg at say 10 or 11 o'clock combined with the larger nosewheel.

It seems to me that you could use the same motor mount-- simply changing the gear leg and the fork and wheel.

With the increased ground clearance of 3 or 4 inches, this should eliminate most all of the ground/fork contact incidents. You would still have the fore and aft movement of the current leg configuration but with much higher ground clearance.
 
I don't get it.

MauiLvrs said:
The transition between the first takeoff (where it seems to stall) and the second takeoff 0:20.
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Looked like a little bubble of air caused him to correct with ailerons. Don't think that there was any stall there.

Kent
 
kentb said:
Looked like a little bubble of air caused him to correct with ailerons. Don't think that there was any stall there.

Kent
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I saw that little maneuver at 20 seconds the first day and agree it was not a stall. The airplane was ready to fly and it did one second later.

It is very difficult to stall these airplanes with full power on. I tried it once at altitude and finally gave up out of a concern the nose was so high, it might end up inverted when it happened. That would prove nothing in my book.
 
Does Size Matter??

I'm in the building stage of my RV-12. This is a nose wheel airplane, with similar design to the troubled models, but it uses a 500 X 5 tire and wheel on the nose wheel, just like the mains. I haven't heard of a single RV-12 rollover!! But, maybe we are premature. I think that there are less than 50 flying. However, could the light loading of the nose wheel, and the larger tire size be playing a major roll here?? Some of the RV-12 guys are, in fact taking advantage of sod runways without incident.

Tom
 
Not to worry . . .

todehnal said:
I'm in the building stage of my RV-12. This is a nose wheel airplane, with similar design to the troubled models, but it uses a 500 X 5 tire and wheel on the nose wheel, just like the mains. I haven't heard of a single RV-12 rollover!! But, maybe we are premature. I think that there are less than 50 flying. However, could the light loading of the nose wheel, and the larger tire size be playing a major roll here?? Some of the RV-12 guys are, in fact taking advantage of sod runways without incident.
Tom
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I did the flight testing on a 12 (the first one completed in Michigan). It is so light it's not even in the same league as the 6/7's with respect to the nosewheel loading.
You may someday hear of a 12 flipping due to strong gusty winds, but I don't think you'll ever hear of a nose gear folding, regardless of the runway surface.
 
I looked another 6 times....

MauiLvrs said:
Just looked like it smacked the ground rather hard to me....
Wouldn't want to do that in ours....
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I am sure that the main didn't contact the ground again. I did see the mains rock back and forth. With take off power and the elevator pulled back, it would take something big to ever cause the main to hit the ground.

That is unless you were not holding back and keeping the plane on the nose for some reason.

When I apply takeoff power to my -9A the stick is full back. When in 50 ft the nose leaves the ground and I ease pressure to just keep it off the ground. The plane does the rest by itself.

There have been a time or two that I eased a little to much and the nose wheel touched the ground, but with the stick having back pressure on it the touch was brief and with very little weight on it.

Kent
 
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