Year long discussion of "Another nosegear failure" -09/19/2010

[Danny7]

Originally Posted by penguin

Guys,

Its heart breaking to see another airplane that is the product of many hours of work on its back, but I think most of you are jumping to conclusions that are not supported by the available data. Raiz has studied our noselegs in detail (see http://www.vansairforce.com/communit...ad.php?t=61178) - and shown that the basic problem is that the leg is unable to take significant loads without folding, these isn't sufficient travel available. If the nut hits the ground the leg has probably already failed. I don't know what to do to fix it, but the basic problem is that too much load was applied to the leg - for whatever reason.

Ensuring there is minimum static load on the nosewheel and avoid anything other than light braking on a bumpy surface are two ways to minimize the liklihood of collapsing the nose gear. I will continue to land my 6A on grass airfields, but only when I know that there are no bumps/holes that might load up the nose gear near to its limit.

Pete

Raiz himself has admitted it is only a model at this point, with no practical validation. he has good data but it is really as much a theory as anything else out there. Only after physical testing validation will it be "proven"

[bgaston]

RV-9A Pilot/Owner
Always....always...always keep the weight off the nose gear!
Whether it is during taxi or landing. I was taught ( by a great instructor out in Scappoose Oregon) to give the nose gear lots of respect. I have found that it takes very little effort (or skill) to stay off nose wheel and keep the weight on the main gear.

[Geico266]

Gppd work Bob, keep us informed.

Did the pilot have the stick back on roll out? You said he pulled it back after the bang. It makes no difference, just curious as to what he says. Does he usually land with the stick in the gut like a TD?

[Jamie]

Rocket Bob:

The NTSB's investigation of the RV nosewheel failures found one consistent trend -- low time in type. How much time did your friend have in RVs?

I'm not going to say that the nosehweel can't be improved or even that there isn't a "design flaw". I do believe there is room for improvement. However, look at youtube videos of RVs landing -- absolutely ZERO soft-field technique in many of the videos I just cringe while watching them.

If you put the nosewheel down on an RV-XA less than 3 seconds after the mains, YOU ARE NOT LANDING PROPERLY.

With my 7A, 180HP O-360, C/S prop I can typically hold the nose off the ground at or above 28kts. If your nosewheel is on the ground (in take-off or landing) at say, 35-40kts YOU ARE NOT FLYING THE AIRPLANE PROPERLY!

[kymjon]

When you look at the nose gear design the thing that stands out to me is that being made of spring steel it can move in any direction. The Sky Star design which is a solid leg pivoted off the firewall with rubber donuts for suspension allows the leg to only go up and down not backwards.

I agree that pilot error can be a factor in the failures but really lets be honest an occasional landing is not perfect and there should be a margin of safety in the design. The leg needs to be a lot stiffer with flex higher up to stop the tendency to roll under. I am also suspicious of the front tire pressure as given the narrow clearance between the wheel and the fork any momentary deformation of the tire could jam the wheel in the fork causing the leg to drag back.

I have an RV6A and operate off grass but have become very careful with landings using a nose high attitude with the stall warning blaring at touchdown and getting the stick back as far as possible as soon as possible. After reading these forums I have increased the tire pressure to well over 30 psi. I have the latest leg and fork and solid spacer on the axle.

[AlexPeterson]

Originally Posted by Jamie

Rocket Bob:

The NTSB's investigation of the RV nosewheel failures found one consistent trend -- low time in type. How much time did your friend have in RVs?

I'm not going to say that the nosehweel can't be improved or even that there isn't a "design flaw". I do believe there is room for improvement. However, look at youtube videos of RVs landing -- absolutely ZERO soft-field technique in many of the videos I just cringe while watching them.

If you put the nosewheel down on an RV-XA less than 3 seconds after the mains, YOU ARE NOT LANDING PROPERLY.

With my 7A, 180HP O-360, C/S prop I can typically hold the nose off the ground at or above 28kts. If your nosewheel is on the ground (in take-off or landing) at say, 35-40kts YOU ARE NOT FLYING THE AIRPLANE PROPERLY!

Well, it depends completely on loading. On landing (with a config like C/S, 180hp), if the pilot is light, the tanks are full, no baggage, it will be impossible to keep the nose off at those low speeds, unless there is a strong headwind, or you've put lead in the tail. Empty tanks, baggage, then yes, it will stay up longer, a lot longer. Full up elevator is as good as it gets. During take-off, the nose will of course come up much faster, as it's breezy back there with full power.

The 8A drivers must see a fairly extreme variation in the nose up speed, depending on whether bubba is in the back or not.

[Jamie]

Originally Posted by AlexPeterson

Well, it depends completely on loading. On landing (with a config like C/S, 180hp), if the pilot is light, the tanks are full, no baggage, it will be impossible to keep the nose off at those low speeds, unless there is a strong headwind, or you've put lead in the tail. Empty tanks, baggage, then yes, it will stay up longer, a lot longer. Full up elevator is as good as it gets. During take-off, the nose will of course come up much faster, as it's breezy back there with full power..

Yes, it will vary, but not that much. I ALWAYS, WITHOUT QUESTION have it off the ground above 35kts (notice I said I typically can hold it off the ground at 28kt). Most of my flights are solo and local (hence no baggage).

Also, I see that you have a -6A which I only have about 25 hours in so maybe they are slightly different (I know they have different gear leg geometry)?

[apkp777]

I am not an engineer so I can't speak to the design of the nose wheel. However, I know lot's of guys are choosing nose wheel aircraft because of the idea that some how a tail wheel is "harder" to fly. The truth is, it's just not the case. With good training and technique, the tail wheel is just as easy and at times more fun than a nose wheel. And, with the apparent nose wheel troubles, if there are those on the fence, don't worry about choosing a tail wheel version of the RV. Even the -9, is a great tail wheel option and though a challenge to land at times, it's very durable and even a "bad" landing is very easy to salvage.

[Flybuddy2]

Originally Posted by Snowflake

I'd be interested in knowing whether other tricycle gear aircraft with a similar configuration (Grumman's, perhaps?) have similar problems.

I owned a FG Velocity prior to a 6A and also have time in Tigers. Very similar setups to Vans but in both cases they are stronger, less springy setups. The Velocity downtube was larger and pivoted at the top held against a high compression rubber bar. The lower assembly is nearly identical to an RV but the nut is higher. Funny part is that there is no weight on the Velocity gear leg as the engine is in the back. The lack of weight actually increases the shimmy problem though. Grummans have larger, more rigid downtubes and do not have this problem although they also have shimmy issues if the kickout force is too light.

[L.Adamson]

Originally Posted by apkp777

I am not an engineer so I can't speak to the design of the nose wheel. However, I know lot's of guys are choosing nose wheel aircraft because of the idea that some how a tail wheel is "harder" to fly.

Not really. I just didn't like the looks of the "6" in squatting position from certain angles. The wings are just too short, which made the 6A look more substantial from a ground view. Other than that, the A models do have more frontal visibility, and are slightly easier to deal with in cross winds.

However, just like anything else, I'm ready for a change (just for something different), and a TW would be just fine. How much would a conversion cost....?

L.Adamson --- RV6A