Nose gear Theory..

[David-aviator]

There's a bit of mass hysteria going on here caused by a couple videos posted on the internet. To keep things in perspective, everyone should be required to look at 1000 normal landings where the NG did not fail and the airplane did not flip. The ratio of normal landings to flipped landings is probably much higher, but viewing a 1000 would get the point across.

Why is it everyone wants a technical fix when the problem is not knowing how to prevent the event from occurring in the first place?

How many tail draggers have come to grief during a landing? Do we ever hear about getting rid of them or redesigning them, heck no. Everyone knows the cure for many TD mishaps is a NG but that is not on the table - better training and knowing how to avoid the circumstances of TD mishaps is the emphasis.

Attempting to land the A model flying too fast is a recipe for trouble - I know because I've done it. The thing will go into a porpoise bouncing off the NG like a screwed up tail dragger landing. THE AIRPLANE CAN NOT BE SAFELY LANDED 25 KNOTS OVER STALL BECAUSE THE NG WILL TOUCH DOWN FIRST. If you can not flare normal with the nose coming up, you are too fast, period. Go around and get it right.

Landing or taxiing on a poor surface unsuitable for the airplane is asking for trouble. Avoid it. That's true with any airplane. And that doesn't mean you have to avoid turf runways, many are very smooth and a delight to land on. BUT A ROUGH SURFACE THAT CAN SNAG OR LAUNCH THE SKINNY NOSE WHEEL MAY RESULT IN A FLIP.

There is no NG fix that will make the airplane bullet proof to accommodate poor flying habits and/or inadequate landing surfaces. Like any airplane, the RV series A models have limitations - but the limitations are not unrealistic considering the total performance aspects of the airplane. I submit that any modification will compromise a very good flying airplane and make the machine more like a Cessna than an RV.

 

[ferret]

We have had some -A NLG failures, enough to cause concern. What we do not know very much about are the failure modes. There may be several and they may be cumulative in their affect. Many individuals have made numerous proposals, but that approach will probably only yield a satisfactory result by sheer luck. You cannot solve a problem that you do not understand.

We do not know precisely what conditions actually cause the NLG lower nut to contact the surface. A static loads analysis of the NLG structure confirms that the NLG design is adequate for normal operations and expected loads. I have been able to identify some additional loading conditions that were probably not taken into consideration by the original designer. However, even when these are taken into consideration, there is no clear indication of a design deficiency from a static loads analysis standpoint.

Because this NLG is an undamped spring, the effect of resonance must be explored as to how it may contribute to the failure mode. We have seen some movies of a NLG that experienced a resonance event at a relatively low speed. Quit frightening. We know the main gears on the tricycles resonant often.

Before a potential design solution to a known problem can be made, we have to be able to measure the dynamic and static response of this gear to a rather robust spectrum of loading events. In order to do this we need to build a test fixture where we can load the NLG up and dynamically stimulate it to get enough deflection to cause the nut to contact the surface. The dynamic loading to induce resonance is not an easy task. The test fixture would consist of an engine mount, a complete NLG assembly and a dynamic impulse generator to stimulate the gear with loads and frequencies of loads.
This is what I am proposing that the working group undertake. I have extensive aircraft engineering experience, especially with landing gear. My experience comes from 20+ years of structural engineering experience on the F-111, A-10, A-7 fighter fleets.

The tests should yield what impulse spectrums will cause sufficient deflection to catch the NLG lower nut. Once that is known then solutions to prevent the deflections can be undertaken through systematic design. Estimated cost is about $5K. Just looking for individuals who want to proceed in an orderly and systematic manner

 

[LifeofReiley]

I remember one case in particular where a pilot (one of the members of this group) landed and as crossing the intersecting runway, had the gear twist fold under and flip the plane. This happened on paved runway at a towered airport. This was not a case of landing too fast or dropping in a chuck hole. Having thought about this as I build my very very slow build -6A I have thought about this a while. In the old days, when I used to work on cars and trucks, they had helper springs. Many trucks still have leaf springs with progressive stiffness (K factor). I have wondered if a similar approach could be used on the nose gear. I have wondered if we could mount a single leaf spring over the top of the area that flexes when the nose gear starts to fold and clamped above and below that point. In normal situations the leaf would have no effect but when the leg starts to bend into the switch blade position, a hard rubber block would start to be compressed between the gear leg and the much higher stiffness leaf spring. This might be enough to keep the leg from folding farther but would probably sacrifice the vertical part at the fork. The loading on the mount would have to be analyzed in this case. Just a thought and perhaps my mechanical engineering colleagues with FEA could model something like this. Just the idle thoughts of an E.E. I would be interested in supporting a redesign.

Paul
N694BP reserved

Previous Damage un-detected or found after previous hard landing IMO... I'll give you another hint. From all the pics I've seen of fliped RV "A" models in the last 10-12 flips, which direction does the NG fold?

 

[Bugsy]

Im in

Ill chip in

 

[Bill Wightman]

FEM could be used to model the gear leg and take a good look at deflection characteristics at various load levels and loading scenarios. But this is very much a dynamic situation, with the NG and MLG acting as undamped springs. Atop those springs sits the airplane... if excited at the right (wrong) frequency and enough amplitude the NG fails.

So, its a problem that has to do with the airplane's longitudinal moment of inertia, and spring rates for the landing gear. The test rig that Doug spoke of would be used to set up the system of forces so they can be analyzed and a fix designed. Absent that, any kind of TLAR engineering would be a shot in the dark, possibly one that might make the problem worse. Proceed with caution....

 

[kymjon]

We may well already have the solution to a better NG. The RV10 NG flex's on the hinge point and shock is absorbed by the rubber donuts. The leg appears to be rigid and does not flex back but up and down. Cirrus and Pulsar to name a couple have similar leg designs to the RV10 and don't seem to have the problem either.

There are close to 300 RV10's flying and none of those have ended up on their back. Maybe the answer is to look at the engineering for that design.

Most of the photos I have seen show the aircraft with full flaps after the accident and perhaps that contributes to the failure if the aircraft hits a bump and bounces there is a strong forward pitching moment. When the nose wheel strikes the ground the yoke would act as a leaver bending the lower part of the leg back and allowing the spat and nut to strike the ground. The momentary G force when the front comes down may be a lot more than imagined.

I fly off a grass strip and set up approach speeds so that I am no more than 65 knots when I commence the flair and hold off until the aircraft settles on with the stall warning blowing and then progressively pull the stick back to hold the nose off as long as possible. I also limit flap to 20 degrees to reduce the forward pitching moment.

I still worry that one day all the planets will align and I will end up with a brown sky

 

[Captain Avgas]

Here's few thoughts on this topic that readers might like to consider.

It is highly unlikely that there will be any simple retrofit design mod to the existing RV two-seat nose gear system that will significantly improve structural redundancy. The problem with the existing design is that it is an over-simplification of a complex structural requirement and better suited to lighter aircraft. And the problem has been exacerbated over the years by Vans increasing MTOWs, and builders opting for bigger engines and CS props. What may have worked marginally at the lesser nose gear loads of yesteryear is now truly struggling.

The ultimate structural solution will probably be a dampened pivoting system such as exhibited on the RV10, Cirrus and many other light aircraft (I don't hear of too many nose gear failures on the RV10). It should be possible for Vans to design a dampened pivoting system for their two place aircraft that does not impinge on top speed or add significantly to weight. And that is probably the way they will go in due course.

Forget about raising money for an independent third-party design solution....only Vans can re-engineer the nose gear because anything that will work will require significant changes to the engine mount.

HOWEVER (and consider this). The redesign of the engine mount will be a disaster of sorts for all existing owners or advanced stage builders because a nosegear upgrade will require removal of the engine, replacement of the mount and nose gear, and the refitting of systems that conflict with the new mount. Expect this to be a major project and to be very very expensive.

For those who do not want to pay for the upgrade (free of course on all new kits) expect a MAJOR devaluation of aircraft value.

So there's the sad truth for all RVA owners/advanced builders. If there's no change to the nosegear you lose....and if there IS a change you will also lose!!!

 

[FresnoR]

Forget about raising money for an independent third-party design solution....only Vans can re-engineer the nose gear because anything that will work will require significant changes to the engine mount..

For those who do not want to pay for the upgrade (free of course on all new kits) expect a MAJOR devaluation of aircraft value.

So there's the sad truth for all RVA owners/advanced builders. If there's no change to the nosegear you lose....and if there IS a change you will also lose!!!

This is the reason we will probably not see Van's come up with a solution, and why there is the need for a 3rd party.

It may end up requiring a new motor mount, and extensive modification to an existing aircraft, however this should not be the reason to do nothing. Find a way to put a robust nose gear on the "A" models, and give owners/builders the choice to install it.

At least with an available mod, people will have that choice, and this debate can settle down a bit, because those people who are truely concerned, have a direction they can go. Those that want it to remain, can...

 

[RV7Ron]

Those interested in participating in a NLG working group to explore the -A failure modes and potentially come up with an engineering fix, please contact me. We need financial supporters as well as technicians and engineers.

Doug Kronemeyer
916.967.1639

Doug, As I said earlier in this thread, I am an ME but I have no aircraft design experience but am very interested in this topic. Put me down as someone who would be willing to help out with my services in this endeavor. I dont have the experience to lead the effort, but I could contribute in other ways.

 

[David-aviator]

I cursory survey of the participants of this thread reveals that the overwhelming majority of those expressing concern for the NG issue are dreamers and/or builders - not pilots flying with the NG.

Those flying are chiming in, but in general are not as intense regarding the problem. There is concern but in general they understand the limitations and their own limitations. Some have suffered the consequences, including myself, but we are not ready to through out the baby with the bath water.

Someone pointed out that the NG design originally did not anticipate a heavy 200HP engine with CS prop. That could be true.

With regard to that matter, when I was flying with the Subby H6 the NG weight was 364 pounds. Since converting the the Barrett IO360 light weight engine with a Catto prop, the NG weighs in at 244 pounds. It makes a huge difference with regard to stress on the NG structure and the flying qualities of the airplane - all for the better.

I submit, if you are building a trike, go light. Everything works better including the dreaded NG.

 

[prkaye]

an -A model pilot

I'll chime in now, as one of the active -A model pilots (albeit a very new one). The frequency of -A model flips does concern me, a lot. I am still undecided if I will brave the grass, although I think I probably will next year. But I would LOVE to see a feasible retrofit that would provide a larger nosewheel, more robust leg etc, if only to give me an added margin of confidence.

I recently installed the new staked Matco Axle, and trimmed back my rubber dust seal so that my wheel spins totally freely. Prior to this mod it would stop almost instantly when I tried to spin it. When i land, I keep the nose gear off the pavement as long as possible... but unfortunately this makes my landing-roll ridiculously long... like 3000 feet! I found if I touch the brakes the forward momentum forces the nosewheel down earlier, but if I don't touch the brakes I just roll and roll and roll. Of course on grass the extra drag on the mains as they roll would slow me down much quicker without needing brakes. I haven't started playing around with flaps on touchdown yet.

that the NG design originally did not anticipate a heavy 200HP engine with CS prop.

Now that is a very interesting thought. If it were possible, it would probably be very useful to do a survey of all the flips we've seen how many were loaded with such nose-heavy equipment?

 

[ferret]

Here's few thoughts on this topic that readers might like to consider.

It is highly unlikely that there will be any simple retrofit design mod to the existing RV two-seat nose gear system that will significantly improve structural redundancy. The problem with the existing design is that it is an over-simplification of a complex structural requirement and better suited to lighter aircraft. And the problem has been exacerbated over the years by Vans increasing MTOWs, and builders opting for bigger engines and CS props. What may have worked marginally at the lesser nose gear loads of yesteryear is now truly struggling.

The ultimate structural solution will probably be a dampened pivoting system such as exhibited on the RV10, Cirrus and many other light aircraft (I don't hear of too many nose gear failures on the RV10). It should be possible for Vans to design a dampened pivoting system for their two place aircraft that does not impinge on top speed or add significantly to weight. And that is probably the way they will go in due course.

Forget about raising money for an independent third-party design solution....only Vans can re-engineer the nose gear because anything that will work will require significant changes to the engine mount.

HOWEVER (and consider this). The redesign of the engine mount will be a disaster of sorts for all existing owners or advanced stage builders because a nosegear upgrade will require removal of the engine, replacement of the mount and nose gear, and the refitting of systems that conflict with the new mount. Expect this to be a major project and to be very very expensive.

For those who do not want to pay for the upgrade (free of course on all new kits) expect a MAJOR devaluation of aircraft value.

So there's the sad truth for all RVA owners/advanced builders. If there's no change to the nosegear you lose....and if there IS a change you will also lose!!!

Bob, I think your conclusions are nothing but guess work. If the forcing function spectrums are clearly known, there are several possible fixes that could be very inexpensive and would not require any structural changes.

A possible reason Vans is not able to solve the problem is that they have been unwilling to invest in performing a dynamic analysis. Remember, you always start with a baseline, and then measure changes to the baseline as you do modifications. The response of this gear is sufficiently erratic as to preclude safe flight tests. The required testing can only be safely conducted in a test stand.

 

[David-aviator]

I'll chime in now, as one of the active -A model pilots (albeit a very new one). The frequency of -A model flips does concern me, a lot. I am still undecided if I will brave the grass, although I think I probably will next year. But I would LOVE to see a feasible retrofit that would provide a larger nosewheel, more robust leg etc, if only to give me an added margin of confidence.

I recently installed the new staked Matco Axle, and trimmed back my rubber dust seal so that my wheel spins totally freely. Prior to this mod it would stop almost instantly when I tried to spin it. When i land, I keep the nose gear off the pavement as long as possible... but unfortunately this makes my landing-roll ridiculously long... like 3000 feet! I found if I touch the brakes the forward momentum forces the nosewheel down earlier, but if I don't touch the brakes I just roll and roll and roll. Of course on grass the extra drag on the mains as they roll would slow me down much quicker without needing brakes. I haven't started playing around with flaps on touchdown yet.



Now that is a very interesting thought. If it were possible, it would probably be very useful to do a survey of all the flips we've seen how many were loaded with such nose-heavy equipment?

Phil,

...like 3000 feet! That is ridiculous.

What is your touch down speed?

 

[RVbySDI]

I am flying an "A" model on grass now

I have refrained from chiming in here as I am not an engineer. However, I feel I should at least give my feedback on this issue since I am flying my RV9A off of a 3000' grass strip now.

I am still in phase I flying and only have 30 hours total on the airplane so I do not feel my experience should be taken in the same vein as, say, Mel's who has been flying his 6A off of his grass strip for many many years (16 or so if I remember reading a while back). However, I can say I am not overly concerned about whether my NG will be able to successfully handle our grass strip. To date, it seems to be doing just fine. Of course as others have posted here, and I agree with their posts, just because I have successfully landed numerous times on grass does not mean I might not encounter a problem in the future.

The truth is we have a 7A on our field that did have a NG collapse a few years ago. That pilot does admit that it was pilot error that contributed a great deal to that collapse. Perhaps had the nose gear been designed differently he could have avoided the incident but the truth is pilot technique does matter on these planes. Unless you all are successful in getting Van's to put out a new design we are going to have to face the facts that we cannot land A model RV's like Cessna 150's. The tolerances for failure are not as large as for those beefy planes that were designed for training abuses.

I am amazed at the relative ease at which a pilot can fly these RV's. My 9A is the most incredible plane to fly I have ever piloted. I would include the ease at which it takes for me to land it also when saying this. It practically will land itself if the approach is a stable one. However easy they are to maneuver though, they still take a great deal of technique and control to keep the nose gear from being damaged on the ground when landing or taxiing. I take that into consideration every single time I am in my 9A while on the ground. It does not matter whether I am on pavement or on grass the technique is always the same. KEEP THE NOSE GEAR OFF THE GROUND!! When the NG is on the ground I try to taxi at a slower speed and look out for unusual surface undulations. I baby my nose gear when on the ground no matter what surface I am on.

I know I am only talking about pilot technique in this post and everyone else is discussing the design issues involved in the construction/reconstruction of the nose gear but I truly feel there are issues of pilot technique that cannot be overlooked in these incidents. Other than the local pilot I mentioned above, I do not personally know any of the pilots who have experienced a NG incident. I truly am sorry for their losses and do not intend to imply that their incidents were strictly pilot error. Although the one pilot I do know did admit that he made a mistake during his incident that was a critical cause for his NG failure.

I will continue to fly my 9A out of our grass strip. We maintain our surface very well and feel it is one of the smoother grass strips I have seen. Like others though, I will not fly into just any grass strip. I will only do so if I have been able to examine it with a critical eye before hand and can assure myself that I would not run into problems.

Oh, I double checked my W&B numbers to see what my NG weight showed. My numbers show the NG to have 260# on it with the plane empty. I think that falls within an acceptable range for the A models.

 

[n5lp]

...I do not feel my experience should be taken in the same vein as, say, Mel's who has been flying his 6A off of his grass strip for many many years (16 or so if I remember reading a while back)...

A little correction, if you are talking about Mel Asberry. He owns an RV-6, not an RV-6A. He did fly the RV-6 for many years off his unpaved, but now paved strip. But then there doesn't seem to be much of an issue with the non-A models.

 

[RVbySDI]

A little correction, if you are talking about Mel Asberry. He owns an RV-6, not an RV-6A. He did fly the RV-6 for many years off his unpaved, but now paved strip. But then there doesn't seem to be much of an issue with the non-A models.

My apologies for the incorrect information. I sure thought he posted that he was flying an A model off of grass.

My real point was to say that I really don't have much experience flying off of grass compared to others on here but that I wanted to state I am doing so.

 

[cropdusterengineer]

my opinion (I'm sure it will be unpopular)

I feel strongly that proper pilot technique would fix this "design problem" in many cases.

Go out to your local big city FBO that has a Cirrus available for rent. Buy a Dr. Pepper, find a nice, shady park bench to sit on, and watch these student pilots and low-time private pilots land 10 knots too fast on the nose wheel time after time after time (and the instructor, who is far too qualified and experienced to be bothered with flight instructing never corrects them or offers suggestions).

Do some research on the number of Cirrus landing accidents that have happened in the last few years.

Pilots, as a group, have gotten very sloppy with their landing technique.

CDE

 

[rvator51]

When we were at Oshkosh in 2008, there was a RV taxiing in the homebuilt camping area. He put a huge bend in his nosegear leg just taxiing to a spot to camp. So even taxiing at a slow speed can bend the nose gear if you hit a rough spot (hole?).

 

[PCHunt]

Yikes!

When i land, I keep the nose gear off the pavement as long as possible... but unfortunately this makes my landing-roll ridiculously long... like 3000 feet! I found if I touch the brakes the forward momentum forces the nosewheel down earlier, but if I don't touch the brakes I just roll and roll and roll.

Yikes! The only thing I can think of that would cause this is an idle speed that is set WAY too high. What is your idle speed, closed throttle, fully warmed up engine, on the ground at zero airspeed? Fixed pitch or C/S prop? (PS: The correct answer is as low as you can get it to run, which should be around 400-450.)

You aren't landing on a downhill runway, are you? I can't imagine a 3000' landing roll in any RV aircraft.

I am assuming you are touching down in the first 500' or so of the runway, at or just above stall speed??

 

[John Clark]

Nutin' new...

I feel strongly that proper pilot technique would fix this "design problem" in many cases.

Go out to your local big city FBO that has a Cirrus available for rent. Buy a Dr. Pepper, find a nice, shady park bench to sit on, and watch these student pilots and low-time private pilots land 10 knots too fast on the nose wheel time after time after time (and the instructor, who is far too qualified and experienced to be bothered with flight instructing never corrects them or offers suggestions).

Do some research on the number of Cirrus landing accidents that have happened in the last few years.

Pilots, as a group, have gotten very sloppy with their landing technique.

CDE

I have a hangar with a good view of the action. Here is a photo of the last one, a classic fast, porpoising landing. It came within a few degrees of going over but settled back on the mains. The pilot, of course, blamed the airplane.

John Clark ATP, CFI
FAA FAAST Team Member
EAA Flight Advisor
RV8 N18U "Sunshine"
KSBA

 

[danielhv]

I feel strongly that proper pilot technique would fix this "design problem" in many cases.

Go out to your local big city FBO that has a Cirrus available for rent. Buy a Dr. Pepper, find a nice, shady park bench to sit on, and watch these student pilots and low-time private pilots land 10 knots too fast on the nose wheel time after time after time (and the instructor, who is far too qualified and experienced to be bothered with flight instructing never corrects them or offers suggestions).

Do some research on the number of Cirrus landing accidents that have happened in the last few years.

Pilots, as a group, have gotten very sloppy with their landing technique.

CDE

I agree with all of this.

 

[David Paule]

A few quick observations.

1. A dynamic analysis of the existing landing gear is not prohibitively expensive nor time-consuming.

2. A redesign would need to consider these two factors (among others, of course):

a) The force vector direction, and

b) The beam-column stability of the nose gear assembly.

3. The situation has two phases:

a) An elastic load event which terminates in a fork or nut contact with the ground, and

b) An load event which collapses the nose gear strut. The collapse appears to include a beam-column inelastic failure of the strut.
.

 

[danielhv]

When we were at Oshkosh in 2008, there was a RV taxiing in the homebuilt camping area. He put a huge bend in his nosegear leg just taxiing to a spot to camp. So even taxiing at a slow speed can bend the nose gear if you hit a rough spot (hole?).

How fast was he taxiing? Was the elevator being held all the way back to keep the weight off the NG? How heavy was he loaded? Im sure he had camping gear, clothes, some food and/or drinks, a friend maybe, etc. Did he ALWAYS land and taxi with the elevator up keeping the NG light? If not, how do you know that the gear wasn't already becoming weak due to poor technique for who knows how long?

So many factors play into each incident. To assume NG's collapse while just taxiing and nothing else contributed to it... just a poor victim that had no role in the failure just doesn't seem possible...

 

[danielhv]

I have a question for those that are trying to re-invent the NG here... You can do your load testing, and all of the engineering work mentioned in the previous posts... but how would one simulate a dip in the runway? A hole, rock, or anything else that would cause the NG to catch?

Here is another thought... there are several aftermarket tailwheels out there that offer greater clearence than the stock one from vans. (Bell for instance.)... and the apparent problem with the NG's seems to be the nut catching and digging in... would it not be easier to just redesign the fork to allow the nut to be put on top or some other fastening solution? That seems easier than redesigning the entire NG...

 

[RVbySDI]

I have a question for those that are trying to re-invent the NG here... You can do your load testing, and all of the engineering work mentioned in the previous posts... but how would one simulate a dip in the runway? A hole, rock, or anything else that would cause the NG to catch?

Here is another thought... there are several aftermarket tailwheels out there that offer greater clearence than the stock one from vans. (Bell for instance.)... and the apparent problem with the NG's seems to be the nut catching and digging in... would it not be easier to just redesign the fork to allow the nut to be put on top or some other fastening solution? That seems easier than redesigning the entire NG...

I have often thought about moving the nut to the top. However, I am sure there would be ramifications for the free castering properties that currently exist with these nose gear. My thought would be there would end up being a need to reevaluate the steering properties of the airplane if this were to happen.

 

[Mike S]

Just a bit of mindless rambling here.....

Flat cross section spring, to prevent sidewise deflection, with a banana shape curve to preclude tuck under, and a Scott 3200 tailwheel unit mounted to it.

End of spring would have to be turned back to hold the Scott in correct orientation.

I will go back to sleep now

 

[sprucemoose]

When we were at Oshkosh in 2008, there was a RV taxiing in the homebuilt camping area. He put a huge bend in his nosegear leg just taxiing to a spot to camp. So even taxiing at a slow speed can bend the nose gear if you hit a rough spot (hole?).

I remember this, as I was right there when it happened (I was leading him back to parking on my scooter.) The details are a bit fuzzy, but I'm almost certain that there was a hard landing or other incident that occurred immediately prior to the nose gear failing during the taxi on the grass. I would be careful about using this as a data point in the discussion without having the full story.

 

[prkaye]

Rivethead, the wooden dampers are specified only for the main gear, and there only to reduce a shimmy, *if needed*. It's not intended as a structural reinforcement.

I'm certainly no expert, but why isn't simply using a deeper fork to accommodate a larger-diameter nosewheel a good solution? This would keep the nut higher off the ground, and a bigger wheel is more able to roll over dips and undulations rather than get stuck. Perhaps this is a really niave idea, but it seems like it would be a super-simple thing to install on the existing gear leg, and might make enough of a difference to dramatically reduce the incidents of nose-overs?

 

[az_gila]

On the early -6As...

Rivethead, the wooden dampers are specified only for the main gear, and there only to reduce a shimmy, *if needed*. It's not intended as a structural reinforcement.
....

...with the "old" nose gear leg, the wood stiffener was actually the wheel fairing. No fiberglas "shell" fairings were originally available.

It may not have been intended as a stuctural reinforcement, but it probably acted like one - and presumably moved the failure point to the motor mount plug-in tube entry by removing "springiness"...

 

[TOAD]

Look at the post from WAM120RV

Look at the post from WAM120RV

http://img243.imageshack.us/img243/1809/27012010311.jpg

Could you post a larger picture? Thanks.... I struggled trying to figure out what you had.

This has the nut on top and is reinforced at the bend to the fork. This is not a hack there is some real merit to it. Additionally the load profile is the same so it preserves the load design and takes one failure point out of the equation. Who is against that? If the sleeve continues up a bit further it looks to me like this could be a method to tune the design. Let?s give our fellow builders some credit.

WAM120RV I applaud your effort. All you are asking for is a NG to work with. Does anyone have one for him?

 

[N8RV]

Boy, am I glad I built a taildragger!

Now, before anyone gets his knickers in a twist over that ...

Like a lot of low-time TD builders, I had some fears and apprehensions with building one. The mystique of conventional gear airplanes and the horror stories of ground loops can cause anyone to hesitate. However, when I started building, I still had enough ego left to tackle the unknown and overcome the fear.

Now that I'm a high-timer (I have over 100 hours now!), I can pontificate about the finer aspects of taildragges vs nosedraggers.

When I owned and flew a Yankee, I wasn't smart enough to work hard at keeping the weight off the nosewheel while taxiing, and it was never a problem. However, I'd been warned about the Yankee's propensity for PIOs, and went to great lengths to avoid getting into one.

As has been well-stated by others on this thread, Van's designs are, like all aircraft designs, compromises. The RVs are designed for simplicity, economy, strength and speed. To accomplish those ends, some things have to be sacrificed. I can cruise faster than my friend in his C-206, but he can haul several people and their luggage. I can only do that one at a time.

Likewise, the front end of most spam cans is more rugged than an RV's, designed to take more abuse than an RV -- including landing on rougher surfaces and absorbing that abuse -- but that strength comes at the cost of complexity, expense and speed.

When I was learning to fly Smokey, I had several moments where I wondered if I'd have been better off building an -8A. The nosewheel issue had never occurred to me. Looking back (now that I'm an accomplished and masterful taildragger tamer ), I realize that driving a nosedragger has limitations, too. Different from those of the taildragger, but limitations nonetheless.

I fully understand and appreciate the dilemma and the desire to make the nose gear a *little* stronger, but maybe the best solution is to refine our piloting techniques and accept the limitations of the design, just as taildragger pilots accept that their landings may be more demanding on some days than those of nosedragger pilots.

I think we could ALL use some refinement of our landing techniques. I'd bet lunch that the vast majority of us land at much higher speeds than necessary. I know I do. I'm gonna work on that ...

 

[Bevan]

been done.

A redesign has been successfully completed and flown. Apparently working out very well on "less than perfect" strips. The mod seems straight forward enough (to me), only adds a few pounds. Maybe someone wants to mass produce these? I would buy one for sure, as I'm contemplating doing one for myself.

BTW, many, if not most, of the nose-overs (as I recall) have occured on rollout at the speed that the elevator has no effective usefulness. Some even occured while taxiing. Until we can find a way to slow to a taxi without going through this translational speed range, we will have to deal with this issue.

See http://mesawood.info/myrv7a/building/newgear.htm

Bevan
RV7A not flying yet.

 

[danielhv]

A redesign has been successfully completed and flown.

See http://mesawood.info/myrv7a/building/newgear.htm

Bevan
RV7A not flying yet.

And there ya have it folks!! Problem solved!

Very interesting write up... Its amazing the size difference in the side by side view!

 

[RV7Ron]

A redesign has been successfully completed and flown. Apparently working out very well on "less than perfect" strips. The mod seems straight forward enough (to me), only adds a few pounds. Maybe someone wants to mass produce these? I would buy one for sure, as I'm contemplating doing one for myself.

BTW, many, if not most, of the nose-overs (as I recall) have occured on rollout at the speed that the elevator has no effective usefulness. Some even occured while taxiing. Until we can find a way to slow to a taxi without going through this translational speed range, we will have to deal with this issue.

See http://mesawood.info/myrv7a/building/newgear.htm

Bevan
RV7A not flying yet.

...some ingenuity at work. Love to see this sort of stuff...bravo to the designer if it indeed solves the problem.


in·ge·nu·i·ty

   /ˌɪn

dʒəˈnu

ɪ

ti, -ˈnyu-/ [in-juh-noo-i-tee, -nyoo-]

–noun, plural -ties for 3.

1. the quality of being cleverly inventive or resourceful; inventiveness: a designer of great ingenuity.

2. cleverness or skillfulness of conception or design: a device of great ingenuity.

3. an ingenious contrivance or device

 

[FresnoR]

I have seen this before. Looks interesting, but remember the designer replaced the original nose gear fork and tire with a modified RV10 fork and 500 x 5 tire. Nothing was done with the gear leg, and some would argue the added weight and size of the modification would only add to the stress on the leg.

 

[RVbySDI]

And there ya have it folks!! Problem solved!

Very interesting write up... Its amazing the size difference in the side by side view!

I sure wish it would be that easy. Just install a larger fork and a larger wheel and be done with it. However, if you read through all of the details of Bob Trumpfheller's page you will find this link:
http://mesawood.info/myrv7a/building/nosegearmodinfo.html

The link provides some discussion of the possibility of creating more bending forces after the mod. Given this, Bob's mod may not necessarily solve the problem.

 

[RV7Ron]

the nose gear mod is only a 3.1 lb delta...thats very reasonable. I would take that in a second if it fixes the problem. And you get more ground clearance as well.

 

[LifeisGood]

landing distance.......

... but unfortunately this makes my landing-roll ridiculously long... like 3000 feet! ...... but if I don't touch the brakes I just roll and roll and roll. [/avy QUOTE]


I wouldnt worry too much about your "ridiculously long" landing roll...unless your runway is shorter than 3000 feet... I dont use my brakes unless I have to...too expensive!!...and normaly use atleast 3000 feet before getting somewhat slow enough to make a turn off the runway.
I'm pleased to report that 3 years of fun RV-ing, I have yet to replace a single brake pad.

And as for landing speed and idle prop rpm, my Catto needs 600-650 to run smoothly, and...flame suit on...I stop looking at my airspeed-o-meter once I cross the numbers. I cross them at 75 kts - plus or minus a few cuz I'm no Chuck Yeager - then bring the throttle to just above idle -maybe 1000 rpm, and let the ol' girl land when she's ready. No reason to force her to stop flying - she doesnt do that to me, so I don't do that to her. Disclamer - I'm fond of the wheel landings, so that increases my landing speed a touch. Ok, flame suit off...

 

[Jkkinz]

Boy this discussion is reminiscent of the many 2008 ng discussions when the A's seemed like they were going noseover far too often. I was as interested in the safety of the ng as is anyone else and I even sent a long letter to Van's voicing my concerns and asking them what they plan to do to correct the ng. I got an immediate response from Gus that let me know that they do monitor the forum and they were indeed aware of our concerns.

I am confident that the fork design change was in direct response to our concerns. So those that think that VAN's is oblivious are just wrong. They are watching and listening.

Since I am a very slow builder, I read the forum on a regular basis and I haven't heard of near as many ng mishaps since the fork design change was made. Their design team no doubt is aware of any design trade offs necessary in the A's and feel secure that the design is safe as long as you use good piloting skills and don't push it too far.

Just as a side note I have the new fork and I have replaced the Van's nosewheel with the Grove wheel.

JMHO, take it for what it is worth

 

[FresnoR]

So just for arguments' sake, what would it take to get the RV-10 nose gear assembly on a 7 or 9?

 

[SteinAir]

I remember this, as I was right there when it happened (I was leading him back to parking on my scooter.) The details are a bit fuzzy, but I'm almost certain that there was a hard landing or other incident that occurred immediately prior to the nose gear failing during the taxi on the grass. I would be careful about using this as a data point in the discussion without having the full story.

Was that perchance a brilliantly colored Orange/Yellow RV? Just curious....

 

[TSwezey]

I can tell you they did it right with the RV-10 nose gear. If I had a smaller -A would look to puttting a bigger fork and tire up there. Less chance to dig in.

My question for all the -As that went over what was the CG location and overall weight? If you are nose heavy, carrying a little extra speed, have the flaps down and not pulling full back on the elevator you are setting yourself up for a bad situation. But sometimes you can being doing everything right and just hit a hole.

 

[az_gila]

But the extra weight...

.....
The link provides some discussion of the possibility of creating more bending forces after the mod. Given this, Bob's mod may not necessarily solve the problem.

...will certainly change the resonant frequency of the system, and that seems tied into the overall problem.

 

[Pmerems]

Is there really a simple fix?

I have been following this thread for some time. I too am building a RV-7A and am weeks away from completion. No kidding I really am almost ready for final assembly and inspection.

Warning: This maybe a long winded post.

The nose gear issues have been concerning me since seeing the nose over video in England some years ago. It has made me question if I made the right decision building the "A".

I have in my possession the bent nose gear leg from the RV-9A builder that nosed over in So. California. I performed a hardness test on it to verify that it was properly heat treated (it was). It is a constant reminder of the issues concerning the nose gear sensitivity.

I am Mechanical Engineer (design) in the defense industry and have been involved in several extensive testing of our "No doubt, work the first time products-our products only have to work once or people die." but the most dynamic testing I have ever witnessed was when I was interning at Grumman Aerospace Corp. It tests of the F-14 landing gear during simulated carrier landings. It was done in a lab and was frightening to watch. I have never seen metal bend and twist under such dynamic loading since that test. It left a imprint in my mind just how dynamic the landing event is and how complex the analysis is to properly design a gear system to survive in that environment. If you compare the F-15 to the F-14 you will see that the f-14 is about 10,000 lbs heavier then the F-15. They are roughly the same size, have two massive engines and fly really fast and carry (or carried) lots of bombs and missiles. The main reason the F-14 is that much heavier is to survive the carrier landing and takeoffs.

Now to the main point of my post.

Van made certain compromises when coming up with the "A" model. He had to morph an existing design (RV-6) without making major structural changes. This may have played a huge role in the nose gear design choice that was made.

I have seen some builders who have implemented some of their own changes to the design thinking they are making a real improvement. However the failure mode of the gear leg is complex. An example is the builder who changed the fork and increased the wheel diameter. The thought was it increased the height of the nut above the ground. However his changed also increase the yoke length which increase the moment (torque) on the gear leg. Unfortunately after all that work his RV flipped. His attempt to improve the design may have actually increased the chance that it would fail.

I work with a lot of smart engineers with all the right analysis tools but unless you can demonstrate through testing, first by actually failing a nose gear of the current design and then test the new improvements under the same conditions, it is unlikely you can prove that a fix really fixes the problem.

We believe that if we can get the nut higher off the ground then we don't have a problem, right? But what happens when the gear bends (nut hasn't hit the ground yet) and the wheel pant hits the gear leg and then the tire hits the wheel pant and the tire stops spinning dramatically increasing the torque on the gear leg, causing it bend more, then the nut hits the ground.

My point is that it needs to be looked at as a system. It is not just the wheel size, yoke, gear leg it is all of these.

It would be nice to believe any improvement would help but unless we truly understand the event (aircraft loading, speeds, surface conditions, etc) and actually fail a gear (capture the event on close-up video) we won't truly understand how to fix it and if the fix would really work.

A (properly loaded) nose gear, yoke, wheel installed on a simulated engine engine mount nose gear socket mounted on a test rig towed behind a pickup truck on a grass/field (with gopher holes) at 50-60 mph wouldn't be to far out of the question as a test bed. You don't have to go Mach 1 to test the concepts out.

I am sure a Aerospace and Mechanical Engineering Department at a University might be interested in offering it up as a senior project for their students. Back in the day I would have jumped at the chance on working on this as a senior project. So one option might be to pool some money, and offer it to a University to take on the challenge.

I have some University contacts here at the U of A, but maybe a University closer to Van's might be more appropriate.

Food for thought, your mileage may vary.

 

[AlexPeterson]

Bump this as it is very pertinent to a couple other threads currently raging...

 

[IowaRV9Dreamer]

So just for arguments' sake, what would it take to get the RV-10 nose gear assembly on a 7 or 9?

Rick, thanks for posting the excellent and relevent picture.

What is striking to me is that the -10 nosegear seems to allow some vertical motion without significant deformation of the spring steel. I imagine that if one were to push upwards on the wheel from the bottom, the rubber donuts would compress pretty far before the steel began to bend significantly. Because of the length of the gear leg, a small compression at the donut must equal a large movement at the wheel.

I wonder how much suspension travel happens with "mostly" the dounts compressing... even 2-3" would be great. As the rubber compresses and releases its energy, it isn't going to flip the plane over. It is a much more "lossy" spring (aka damper) than the steel gear leg.

Very nice design. I'd be willing to change out my mount and gear for that design. I know it would likely weigh more, but the nosegear weight limitation would likely be different (or non existant). The weight & balance shift that would occur might be able to be offset by moving the engine back a fraction of an inch.

 

[koda2]

Cleveland?

Alex,
In response to your original question, I have a similar setup. My 1996 nosegear includes a Cleveland wheel and the setup is different than later kits.
Below are two pictures comparing a 7A nosewheel set up with a 6A on the right. The 6A also came with the big nose fork which I have replaced with the one on the left.

Dave A.
6A build

 

[Zero4Zulu]

NG diameters

I was just measuring the NG for an idea I have for a bolt on damper/stopper to limit the aft movement of the NG.

The failure occurrs when the gear is deflected aft to a point it can't recover and gives way. The whole nut thing is when the failure is imminent. Just imagine the angle that would have to be present to have the nut contact earth.

I measured the diameter at the lower bend(1.010 dia.). 8" up the leg (.910 dia.) and at the socket it tapers up to 1.125". The leg is actually reduced in diameter .100" right where they appear to fail. That seems and actually looks pretty dramatic. Just slide your and up and down the leg and you can feel the thin area.

If the gear leg was just an even taper from the lower bend up to the socket that would be a pretty substantial strength improvement. Any engineering thoughts about this? I know it would remove some spring from the leg.

****, right now they are designed to fail if you ask me. I know, I know, keep the stick in your gut.

 

[jlk]

Well here goes:

I would contribute to do a study as Pmerems suggests. We must establish whether there is a problem and what the failure mode is, all the rest of the conversation here is speculation.

If, and it is a big if, there is ample evidence that there is a problem, then it will be in Van's court to improve the design. Van's will be compelled by their additional liability in this matter if a study bears out a design problem.

We as builders and fliers of Van's aircraft cannot redesign the gear in this forum, we can fund a study.

 

[ron sterba]

I saw a oleo strut on a 6A recently. Time will tell gentleman. When I hear more I'll let you know. Hope to find out more in the weeks to come.