Must see video for nose wheel builders.

Captain Avgas · #1 02-26-2007, 09:22 PM

There have been some very lengthy threads dedicated to the RV nosegear and ongoing failures thereof. Some people believe the gear has an intrinsically and fatally flawed design.

Other people maintain that there is nothing wrong with the nosegear and that incorrect aircraft handling is the sole root cause of all the failures.

But anyway I think that most people have now gravitated to the middle ground and have concluded that the Vans nosegear (on the two seaters) is a somewhat fragile device that is intolerant of poor landing technique.

At any rate the video below has been around for a while but is fascinating viewing if you have not seen it. Turn on your sound for the speed reports.

It's the nose gear of an RV6A.

It gives plenty of incentive for RV pilots to keep the nosewheel off the ground during both landing AND take-off at any speed over about 15-20 knots.

I wonder if Dick Van G has ever seen it.

www.eaa538.org/azwing/pictures/nosegear.wmv

szicree · #2 02-26-2007, 09:35 PM

Please forgive my ignorance, having never flown an RV, but are you saying the stick was full aft at 42 mph and the nose wheel is planted to the pavement?

Captain Avgas · #3 02-26-2007, 10:07 PM

Quote:

Originally Posted by szicree

Please forgive my ignorance, having never flown an RV, but are you saying the stick was full aft at 42 mph and the nose wheel is planted to the pavement?

Steve, on 9/28/06 Tom Velvick of Peoria, AZ, reported on Van Airforce that this video was of his friend's RV6A and that it was filmed while the stick was "aft". But, like you I have some reservations about that. At any rate the viewing is compelling, aft stick or not.

He accelerates to "41 miles per hour". I don't know if that's statute miles or nautical miles. If it's the latter his max speed is 35 knots.

walter · #4 02-26-2007, 10:16 PM

I wonder how much the following could affect the shimmy we see on the video;
Runway surface, Tire inflation, Nose Wheel bearing torque, weight on nose
gear.

Perhaps the shimmy would Not be there if there was more pressure on the
nose gear at those low speeds, ie with the stick neutral. Just guessing. I
always keep the stick back on the rollout and subsequent taxi and never noticed
a nose gear shimmy.

It appears the video was taken specifically to document an issue the pilot/owner
knew about. Was the issue resolved? Who took the video?

lostpilot28 · #5 02-26-2007, 10:21 PM

That is an interesting video. What is the max speed before the nose-gear leg overstresses the frame, or breaks something? I can't help but think that there's a tolerable limit to the flexing and it's actually a desired trait. You wouldn't want it to be so rigid as to let the airframe absorb the shock, would you?

lostpilot28 · #6 02-26-2007, 10:28 PM

Quote:

Originally Posted by walter

I wonder how much the following could affect the shimmy we see on the video;
Runway surface, Tire inflation, Nose Wheel bearing torque, weight on nose
gear.

Hi Walter,
I could be wrong, but I don't see any "shimmy" in the video. I'm defining shimmy as the left & right swing of the tire & fork. What the video is showing appears to be a dampening effect from a "non-smooth" runway (I'm guessing there are very few, if any perfectly smooth runways). Very similar to what the suspension on a car would do on a freeway.

The only problem on the RV is that you have the spring to absorb the bumps, but nothing to dampen it. Ever see a car driving down the freeway with bad shocks and the tire is bouncing along under the car?

walter · #7 02-26-2007, 10:33 PM

Quote:

Originally Posted by lostpilot28

Hi Walter,
I could be wrong, but I don't see any "shimmy" in the video. I'm defining shimmy as the left & right swing of the tire & fork.

Ok maybe my definition of shimmy is incorrect. But it "looks" like a fore
to aft shimmy. The reason you don't see a car tire "shimmy" for and aft
is because it can't, by design, or you would be all over the road.

If you look at the shimmys the mains have it's generally fore and aft as well,
primarily. I haven't seen too many side to side shimmys.

Since it's just a straight piece of steel, it can move in all perpendicular
directions to the shaft direction, not just left and right. It's interesting
though. This may end up being one of "those" threads

n468ac · #8 02-27-2007, 05:21 AM

Hmmmm... I can plant the stick full aft and be riding on the mains with 50 feet, even at gross weight. We've seen this type of movement in our RV6A, but it was before we added a wood stiffener to the nose gear and changed our take off procedure. I heard from Van's that the nose wheel is only for taxiing not driving down the run way.

Jamie · #9 02-27-2007, 05:25 AM

Now the question to ask is....

Is the dampening effect (or shimmy...whatever we want to call it) exists in every RV nosewheeler? If it exists in some and not others, then obviously there is some difference between them and we should look for that difference.

Would a wooden stiffener on the nosegear help at all?

I have seen a couple of nosewheelers landing and I noticed this effect but it didn't seem that severe. I've also seen others landing and it didn't seem to happen at all.

Given the forces involved here my non-engineering mind tells me it's the 'rolling' resistance of the tire being too high.

Let's please keep this thread limited to facts and troubleshooting and abstain from peanut gallery comments.

I wonder if others wouldn't be willing to try this out to see what the result would be. You can easily do this with small cameras you can get from Fry's...around 40 bucks and it'll plug into a regular camcorder.

Captain Avgas · #10 02-27-2007, 05:54 AM

Quote:

Originally Posted by Jamie

Let's please keep this thread limited to facts and troubleshooting and abstain from peanut gallery comments.

Jamie, a top suggestion.

If Tom Velvick is tuned in to this thread perhaps he can provide an update on whether the owner of the relevant RV6A has been able to eradicate this oscillation...and how he achieved it.