What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

Nose gear Theory..

I have been following this with much interest and since I am a fairly new pilot (450+ hours) and have little engineering knowledge, hesitate to offer an opinion. However, for my personal use and comfort, I have taken a few small/inexpensive and easy steps to increase my odds. These are such as small wood dampener, Matco axle and keeping my air pressure where it needs to be. I also ALWAYS follow safe technique for RV-A flying such as keeping the NG up as long as it stays up and always have the stick in my tummy while taxing. It seems trying to fix this NG issue is like wanting to fix a tail dragger from its inherent risk and unfriendliness. We all take more care landing a tail dragger and if it ground loops, the blame goes to the operator. How is that different with the NG model?

If there is a redesign that proves to be safer but does not require a major overhaul, then I will change it. But if I am back to building stage and specially the improvements are not significant then I will keep flying and practice safe piloting.
 
I did not torque the axle, but rather tightened to remove any slop in the assembly. The torque Van's recommended was to secure the bearings from turning in the yoke. The staking prevented that and allowed you to relieve the bearings so that the tire and wheel could spin easier.

I like the new style spacers some of you guys have developed and I would recommend that method. I always liked the Piper nose wheel design and this is similar. The Piper axle tube went through the yoke to machined plugs that went into the axle tube spacers, providing a way to adjust for bearing slop. The axle bolt went through the whole assembly from plug to plug and allowed preloading the bearings while still fully supporting the bearings. The picture attached is a little unclear, but the axle is a tube and the axle bolt is separate. The picture sort of implies it is intregal to the axle.

My best recommendation would be to copy what Piper did.

I have attached an SB that shows how the axle is configured. This SB was generated after a failure of one of the cups from overtightening. Just shows how important is is to remove slop from wheel bearings, but be wary of over torqueing them.

Roberta

http://www.aaib.gov.uk/cms_resources.cfm?file=/Piper PA-28-181 Cherokee Archer II, G-BNGT 05-06.pdf
 
Last edited:
Zero4Zulu said:
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.
Click to expand...

Have you seen the Van's video from around the year 1999, when they re-designed the nose gear? They had a large spinning wheel designed like a cam lobe that would spin at high speed & constantly beat against the gear leg & wheel. The new leg held up, where the old design failed rather quickly. Considering the leg is the shock absorber, I'm not convinced that removing some of it's "spring" ability, is the right approach. Afterall, RV's do drop through the flare once and a while.

L.Adamson --- RV6A
 
Leland said:
Last Thanksgiving I landed too slow at an airport I was unfamiliar with. My -9A stalled a foot or so above the runway, hit hard on the mains, and then immediately banged the nosewheel so that it "twanged". My best landings are done coming over the fence at 60 knots and rounding out until the mains kiss the runway, holding the nose off until elevator authority is nearly gone, and then lowering it. Full stall landings are not the way to go here.
Leland
Click to expand...

GrayHawk said:
Leland said:
Agreed! I took no stalling as a given, but will modify the list. I usually am at 80 mph over the fence, 70 mph over the numbers, which is about the same as your 60 knots. (5040' elevation airport) Also good point on gently lowering nose before elevator authority is gone.
Click to expand...

I am certainly no expert, but I have flown a bunch of RV's so my experience level is slightly higher than some, and I notice the way others fly. It is rare that I see a pilot in an -XA RV roll out with the elevator in the nose up position. If they don't bang the nose gear down, they relax the stick immediately after nose touch down. Even after there is "no elevator authority" the elevator still has the ability to reduce the pressure on the nose wheel on roll out. Watch the video of the RV flip over and you can plainly see the elevator in the neutral position.

Basically, the above can be condensed into: "Keep the stick in your gut until engine shut down." It will relieve some pressure off the nose wheel even when the engine is just idling and stoped. The prop wash gives some air over the elevator. Try moving the stick forward and back at 1500 RPM (or slightly above) and watch the nose of the plane.

The last point I would like to make is is that the effect of these bad landings is cummulative. Meaning, you might get away with several dozen bad landings, until the gear gives out. It's not just a one time occurance that breaks the nose wheel.
Click to expand...
 
Last edited:
L.Adamson said:
Have you seen the Van's video from around the year 1999, when they re-designed the nose gear? They had a large spinning wheel designed like a cam lobe that would spin at high speed & constantly beat against the gear leg & wheel. The new leg held up, where the old design failed rather quickly. Considering the leg is the shock absorber, I'm not convinced that removing some of it's "spring" ability, is the right approach. Afterall, RV's do drop through the flare once and a while.

L.Adamson --- RV6A
Click to expand...

Larry, a most relevant observation. I did not know about the spinning wheel test and the strut.

It does support my feeling that the strut is most adequate, the challenge is keeping the nose of the NG from digging into a soft surface or catching an irregular lip or hole, and bending aft.

In every failed NG, that is what happens. It may be aggravated by tight bearings acting like a brake, or the tire low on pressure getting caught on a wheel pant with little clearance, a very hard landing, but the end result is the nose of assembly getting caught on something and bending the bottom of the strut aft.

That is what led to the modification that raised the nut one inch. The idea did not come from this forum, it came from a study by a guy at the NTSB. Consequently, Van's had to act on it. Raising the nut certainly provided for a greater margin of deflection before the bending occurred but it did not provide any improvement if the deflection was such that the nut made contact with what ever was being run over.

The attached image is of from my event in 2003.



Uploaded with ImageShack.us

I did not save the strut, but clearly it was mostly bent at the wheel. The upper part of the strut was bent slightly.

My perception of the problem may be in error and I may well be bitten again, but as of today after flying with the system for the past 5+ years, mostly off of turf, I feel comfortable with it. I do not worry about it. But I do try to be aware of surface conditions and make every effort to not land on the NG but only the main wheels.
 
Although my Rv is an 8, I'm getting on in years now and I thought about a 7A for my old age - if I ever keeled over my bride could put a side-by-side nose-wheel back on the ground quite safely and she deserves to see the side of my head after all these years! It would also give me an excuse to become a repeat-offender, two van man. And guess what, I could always sell it and keep the 'DUDE'.

However, I have flown lots of the A variety and once when testing a new US import here in UK I did have a near miss withthe nose-wheel issue. It was a 7A with a 180hp engine and constant speed prop. It also was airways equipped and weighed in at about 1150lbs(forward cg & lots of weight on the noseleg). I flew my 8 over to the grass strip where it was located and noticed that although the ground was reasonably smooth, there were a series of ridges rather like a swell at sea.

There were no problems with the take off or in the air but I was very, very careful when landing to be on speed (60kts) and tried to avoid the bumps by lading at the very start of the strip. I held it off and got the stick right back after touchdown. Nevertheless I was unable to prevent the nosewheel hitting one of the 'waves' in the ground. This kicked the nose wheel back into the air and I almost hit the tail bumper. As I struggled to maintain a nose up attitude the ground came up and hit me again! Up went the nose again, even higher and I thought how stupid I was going to look upside down.

Anyway the beast calmed down and the everything was well. The point of this post (what I learned) is that I suspect that the smooth ridges on the ground in some way coincided with the natural harmonic of the nosewheel leg and even though I was decelerating this caused the pitching to be amplified. So there's bumps and there's different bumps! The next time I flew from there I waited till the wind was from the other end!

I'll still build the 7A and be very careful - I'm still learning after 50 years of flying.
 
Can an ME confirm this?

Geico266 said:
.....
The last point I would like to make is is that the effect of these bad landings is cummulative. Meaning, you might get away with several dozen bad landings, until the gear gives out. It's not just a one time occurance that breaks the nose wheel.
Click to expand...

Few (none?) of the failures seem to involve a physically broken nose gear leg, so cracking caused by previous bad landings is not likely. Most failures are extreme bending.

So, can a piece of spring steel be reduced in strength by previous large deflections if no permanant set has taken place?

A permanent set would be visible in how the plane sits and the ground, and a change in the pivot angle would probably affect taxying...

Can an ME help here?
 
FresnoR said:
So just for arguments' sake, what would it take to get the RV-10 nose gear assembly on a 7 or 9?

rv-10.jpg
Click to expand...

Weight and balance, I guess ...
 
I think as well as weight and balance, also size/complexity/space limitations inside the cowl that deter this type of nose gear.
 
eurof2 said:
I think as well as weight and balance, also size/complexity/space limitations inside the cowl that deter this type of nose gear.
Click to expand...
That may be but none of those are insurmountable obstacles that could not be overcome. If the W&B can be maintained within an acceptable range all of the other issues can be overcome.
 
You are correct that a permanent set can be set if it has been damaged, but if it is a slight permanent set, it may not be noticeable and the difference in how it taxi's may not be noticeable also.

This slight damage may not be enough to cause a complete failure, but enough to make it easier for a complete failure later on with a less drastic 'hit'..

Just one train of thought here...
 
bignose said:
Weight and balance, I guess ...
Click to expand...

It's just bigger version of what we have suited for the extra weight of the 6 cylinder engine it supports. For sure in time someone will figure a way to prang it on hard enough or find a deep hole and dig that nut in also.
 
Please stick to the thread topic...

az_gila said:
Few (none?) of the failures seem to involve a physically broken nose gear leg, so cracking caused by previous bad landings is not likely. Most failures are extreme bending.

So, can a piece of spring steel be reduced in strength by previous large deflections if no permanant set has taken place?

A permanent set would be visible in how the plane sits and the ground, and a change in the pivot angle would probably affect taxying...

Can an ME help here?
Click to expand...

For steels, previous stress cycles will "consume" fatigue life, but not change the strength or stiffness of the steel, up until such time that significant cracks develop. The tip over events on the current design of nose gear are not due to cracks in the steel. If no permanent set has been created, strength/stiffness is unaffected. Previous stress cycles are not contributing to the classic tip over events.

This thread was started several years ago to discuss a theory that the wheel bearing/axle design was the core problem with tip over accidents. I stand by that still.
 
RV-10 nose gear

I
t is a larger and stronger version, and it provides suspension travel. This sounds a lot like what people have been talking about. It may be enough to dampen the forward momentum enough to keep the aircraft from "pole-vaulting? There are obvious systems and geometry questions, but it?s an idea.

I really like the idea of getting a university to study the existing nose gear.

Hey Paul, what type of ?donation? do you think it would take to get U of A to do this?
 
Guys, I realize I may be out of line, but if the firewall can support the gear, there are lots of options out there, both strong and light. (maybe not AS light, but better than Cessna) I love the RV and looked very hard at the RV as a potential build, but eventually had to go with my mission/cost/build experience and built a 4 place Jabiru kit. The nose gear on my plastic airplane is very substantial, and while the geometry is a little different, I think the idea could be adapted easily. It allows for steering, although, as a tailwheel pilot, I miss the differential braking as steering, and would gladly substitute a castoring nosewheel. The gear itself is very simple, and would be relatively easy to make to appropriate dimensions. the Gross weight of the Jabiru is 1600 lbs. I'm not sure if the design and mounting would transfer to the RV firewall design, and I am far from an engineer, but I thought I'd throw it out there.

Jabirufrontgear.jpg


KB
 
Last edited:
AlexPeterson said:
This thread was started several years ago to discuss a theory that the wheel bearing/axle design was the core problem with tip over accidents. I stand by that still.
Click to expand...

This thread and the newer one "group effort to design a new---" appear to have been merged, unfortunately.

I understand that the two threads were quite similar is subject matter, but the direction of the discussion was a lot different.

I suspect most of the replies will be directed toward the newer thread content/goal.
 
Mike S said:
This thread and the newer one "group effort to design a new---" appear to have been merged, unfortunately.

I understand that the two threads were quite similar is subject matter, but the direction of the discussion was a lot different.

I suspect most of the replies will be directed toward the newer thread content/goal.
Click to expand...

I have searched in the moderator control panel and cannot find an unmerge tool. As such I will re start a thread titled group effort for a new Nose gear design and the content/goal discussion can continue there and anyone who posted in the pre merge thread can cut and paste their contribution there.

http://www.vansairforce.com/community/showthread.php?p=469927#post469927
Click to expand...
 
Last edited:
Well, OK...maybe this fits in with the current thread topic. I can't tell. Moderators, feel free to (re)move my post as necessary.

Rather than completely re-design the nosegear leg, what's wrong with the idea of adding a "skid" to cover the nut? I don't think the epoxy ones being discussed would be strong enough (maybe they are), so why not make an aluminum or steel "ramp" that is attached to the nosegear leg between the nut and fork, and that extends forward and ramps upwards to help prevent the nut from digging in? :confused:
 
lostpilot28 said:
Well, OK...maybe this fits in with the current thread topic. I can't tell. Moderators, feel free to (re)move my post as necessary.

Rather than completely re-design the nosegear leg, what's wrong with the idea of adding a "skid" to cover the nut? I don't think the epoxy ones being discussed would be strong enough (maybe they are), so why not make an aluminum or steel "ramp" that is attached to the nosegear leg between the nut and fork, and that extends forward and ramps upwards to help prevent the nut from digging in? :confused:
Click to expand...

There are at least two designs on this (search the threads): my fiberglass skid plate, and a welded aluminum plate. I think that the new gear leg has minimized the requirement for any form of skid plate.

The issue with the Van's gear leg in my opinion is that it has limited torsional and transversal stability. Put another way, a gear leg that is rectangular or oval in cross section would limit the flex to the fore-aft/up-down dimensions (not side to side or twisting).

I have a friend that crushed two cervical vertebrae when his 7-A pitch-poled due to a hard landing. Yes, the landing was the cause, but the gear leg was a contributor.

This is my last post on this issue because it's been beat to death in other threads. It's a limitation of the design-- we have to get over it and move on. You had to takeoff and land the Spitfire in 3-point attitude or the prop would contact the ground. Pilots learned this and adapted. It became a 'feature' not a 'bug'!

V
 
Okay... we can just teach and be proactive(a weekend school)... how to fly an RV-A on/off a grass strip, and include proper landing and approach, and research the landing strips you fly into. :eek:
 
I want to know why I developed a nose wheel flat a week ago. Fortunately it happened after I pulled up to my hangar after a puppy flight.

I did find a small hole/leak in the sidewall of the tube (unknown cause at this time).

While repairing that, I took advantage of things read here to open up the wheel pant fairing a bit at the bottom aft section of the opening. Intent is to minimize the chance that the tire will catch the fairing and contribute to a problem.

My carbon fiber skid plate is 0.1 inches thick in the area near the nut. I can't provide an analysis of its ability to protect the nut in a similar case to the one that started this discussion, but it looks OK (TLAR analysis).

I have the shorter gear leg, new fork, I don't fly out of grass strips (except rare occasion like at Mulege Mexico), and I will also be aware to be cautious around asphalt/concrete irregularities.

I am not worried.
 
Ron Lee said:
I want to know why I developed a nose wheel flat a week ago. Fortunately it happened after I pulled up to my hangar after a puppy flight.

I did find a small hole/leak in the sidewall of the tube (unknown cause at this time).
Click to expand...

The tubes for the Lamb tire are not that great, best way to prevent flats is to:
1) use plenty of talc when assembling

2) keep the pressure above 40 lbs. this helps prevent the flexing between the tube/tire that causes the wear spots on the tube.
 
I can't seem to find the max weight limit on a 6A nosewheel.. Anyone know where to find it? The orginal manual only has an example.. Van's specs on their website doesn't have it... Thanks Sheldon
 
Thanks Walt. I added tire talc to the inside of the tire and outside of the tube. Should have been plenty plus I went to 40 PSI on the pressure.

I looked for a Michelin leak stop type tube but have not found it in the right size.

I also noted after putting the aft fairing on that there was less than desired clearance with the tire so I took it off and removed about 1/4" more. I read and take advice here and put it to use.
 
allbee said:
Yup you are so right. I see all the time, RV's landing flat with a nose wheel, that is a definate no no. Heck I remember back when I was learning to fly, I thought I did a good landing, than the instructor said, " that was awful". I said what? he said you landed on the nose wheel. Oh, I said, your not suppose to do that, he said no way, try again. I made him happy by doing touch and goes without touching the nose wheel on the runway. It was actually fun and I felt it was a test of my ability to land correctly.
Click to expand...

Every RV A Pilot should train this "ad - infinitia", until he is able to land like this with his eyes closed !!!
 
kentb said:
Accidents do happen, but I think that most of the problem that have been experienced are do to not understanding how to land the plane.

I would suggest that the money could be better spent with a good flight instructor.

Not trying to be negative about this effort, but if you redesign the aircraft to be tolerant of poor landing skills, it won't fly the same.
I do enjoy the way my 9A flies.:)

Kent
Click to expand...
I'd easily sacrifise 5 knots of speed against a reliable nosegear I can trust on.For me, even the main gear when exposed without fairings, looks very fragile, like a spyder or moskito... In todays spacecraft era, there has to be a resistant and light material to fix this "child desease"of the A models.Vans schould adapt the 10's system to the right proportion of his younger brothers, and that's it.
 
To each his own.

bignose said:
I'd easily sacrifise 5 knots of speed against a reliable nosegear I can trust on.
Click to expand...

I am not willing to give up the speed. This is not my first aircraft. I moved up to this one to gain as much performance as I could afford.
I will take the small increase in risk.

Everyone gets to make his/her choice as to the trade offs.


Kent
 
I do _all_ my landings with my eyes closed. It is too scary to look.
__________________
Click to expand...
Right on Kev, that's the way I was taught too! Every pilot should strive to be a "left seat spectator". I mean, why participate in a hazardous activity when you don't have to, right?
 
Landing Gear Patents

We have all heard the phrase "Those who cannot remember the past are condemned to repeat it."

There's a wealth of knowledge in old patents, I've attached a few examples below of landing gear design from the 1940's era.
These clever designers faced many challenges of the time, most aircraft had to operate from grass strips in extreme conditions with minimum maintenance and surprisingly they successfully achieved results without the advantages of Computer Aided Design (CAD) and Computer Aided Manufacturing. (CAM)

I only point these out as patents are the modern day history book of innovation and they are often overlooked at great cost.


http://www.google.com/patents/about?id=3v9SAAAAEBAJ&dq=2263717

http://www.google.com/patents/about?id=-dhFAAAAEBAJ&dq=2211484

http://www.google.com/patents/about?id=rBVhAAAAEBAJ&dq=2490560

http://www.google.com/patents/about?id=qhhQAAAAEBAJ&dq=2646948
 
You must log in or register to reply here.
Back
Top