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Yaw cause by nose wheel pant...

Michael Burbidge

Well Known Member
I have about a 3/8 ball yaw during cruise (takes right rudder to correct), caused by the nose wheel pant. I've determined this by flying with different combinations of main, nose, fairings and pants.

I was surprised that it was the nose wheel. I would think it would naturally castor to be aligned with the slip stream.

I'm not keen on redoing the nose wheel pant, particularly when I'm not sure what the problem is. Is it acceptable to correct the yaw with a trim tab on the rudder? I guess I'm asking if a 3/8 ball is too much yaw to correct with a trim tab.

Michael-
 
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I have about a 3/8 ball yaw during cruise (takes right rudder to correct), caused by the nose wheel pant. I've determined this by flying with different combinations of main, nose, fairings and pants.

I was surprised that it was the nose wheel. I would think it would naturally castor to be aligned with the slip stream.

I'm not keen on redoing the nose wheel pant, particularly when I'm not sure what the problem is. Is it acceptable to correct the yaw with a trim tab on the rudder? I guess I'm asking if a 3/8 ball is too much yaw to correct with a trim tab.

Michael-
Before doing anything else, make sure your nose fork friction is still correct. It is normal for it to loosen up a couple times when first new.
If it is loose, the spiral flops from the prop will deflect it and cause a change in yaw trim.
 
Thanks...

I'll check the break out force. Wow, if that turns out to be the problem, I would have never discovered it.

22 - 25 pounds if I remember correctly.

Michael-
 
Hello

Today I was setting the preload force as Vans mentioned to the 22 lbs. I did not flown the plane, still the last steps to do. I remembered there was a video that showed different preload-szenario's.

I hope it is fine if I link this video form unknown source again: https://www.youtube.com/watch?v=IrnDztLJbSI&noredirect=1

I hope it helps.

Interesting video - if prop swirl is causing it, the engine would seem to be rotating backwards from a normal Lycoming. Must be something else going on here...
 
What Scott said... I have had this happen several times on the 'A' models. You can verify it by performing a hard slip in cruise for a moment to re- center the nose wheel. If it stays straight for several seconds and then returns to the OUT condition, that's probably the culprit. Last time I experienced it, it had a strange roll/yaw action...
 
So if the nose wheel is in a constant slip isn't it producing more drag? Maybe we should try to slip it into an angle after take-off.

-Andy
 
Right direction for my yaw...

Wow the video was interesting. I don't know how prop swirl would cause the nose wheel to slip in that direction, but that is the direction that would cause the yaw I'm experiencing. Will follow Joe suggestion to diagnose next flight.

Michael-
 
Tightened nose wheel fixed the yaw...

I checked the nose wheel break out force yesterday. In one direction it was 22 lbs. in the other it was 20 lbs. (The direction the nose wheel would be deflected by propeller spirals) I tightened it one flat and my yaw problem almost completely disappeared.

Thanks for the help, I never would have found the problem!

Michael-
 
I checked the nose wheel break out force yesterday. In one direction it was 22 lbs. in the other it was 20 lbs. (The direction the nose wheel would be deflected by propeller spirals) I tightened it one flat and my yaw problem almost completely disappeared.

Thanks for the help, I never would have found the problem!

Michael-

Now to figure out why your engine is running backwards...:confused: Does anyone have an explanation as to why the yaw of the nose wheel is against the swirl of the prop, at least in these two cases (OP + video)?
 
or maybe the prop swirl effect is stronger on the nose than the trailing edge of the wheel pant....or maybe it is that damned Coriolis effect!
 
Or maybe the nosewheel pant is not exactly symmetrical, which might cause more sideways "lift" on one side. :confused:

Just a WAG. Maybe an aerodynamics "boffin" will chime in.........

Maybe the prop "wash" doesn't swirl as much as is commonly thought....

Now that we know how to fix it, maybe it doesn't matter exactly what causes it. We just tighten down our nuts and press on! :p
 
Now that we know how to fix it, maybe it doesn't matter exactly what causes it.

That has been my way of dealing with it.
My head starts to hurt any time I start thinking about it......

Later after posting, I had to laugh at my self because I realized I didn't write what my brain was thinking (and some of you joking about it didn't tip me off.

What I meant to say was Coandă effect. It has very real applications and influences in aerodynamics.
One notable one is NOTAR Helcopters
It is probably not related to the cause at all, but since I haven't been able to make any other sense of it, I wonder if it might be somehow induced by the angular flow from the spiraling flow off the prop.... there goes my head hurting again....
 
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Gyroscopic precession? Problem is, Joe reports that if you straighten it in flight with a slip, it returns, and that doesn't make sense, if the wheel isn't spinning anymore.
 
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Maybe the wheel IS spinning. My Grove wheel has very little rolling friction and Allan's bearing mod may have even less.

Bevan
 
Maybe the wheel IS spinning. My Grove wheel has very little rolling friction and Allan's bearing mod may have even less.

Bevan

In the video, there is no roll of the airplane during the time the nose wheel is yawing. If gyroscopic precession were causing it (meaning the wheel is spinning), it would only happen during a roll event. Good mystery!
 
I know someone mentioned above that the video was from an "unknown" source. This is actually Brian's Unrein's (Blahphish on the forums) RV10. I remember watching this video a while back . . . You may want to contact him directly or send him a PM.
 
And if you really can't find the culprit at the end of the day, you could always add a simple aluminum trim tab to the back of the wheel pant, just like on the rudder...
 
And if you really can't find the culprit at the end of the day, you could always add a simple aluminum trim tab to the back of the wheel pant, just like on the rudder...

...This what I was thinking as well! It would be very interesting just for a test to see the effect. But wait! Here is a potentially new product. "The all electric wheel pant trim kit" :rolleyes:
 
Did you check to make sure that you haven't lost the little plug that covers the valve stem access for your tire?

Also, before you go cutting and/or adding things, try taping over the seams in the nose wheel pant to see if you've got a strange airflow going on.
 
The NW video was very revealing and confirms some suspicions that I've had.

From my own experience, during an RV-7A landing, I experience a significant shimmy event, which I believe was initially caused by low nosefork breakout force. There was a pretty good gusting crosswind from the right that day and immediately after de-rotation/NW touchdown, there was a significant vibration from the nose gear. Fortunately with those winds, the ground speed was quite low at de-rotation and the event didn't last long. It was later found that the breakout force had creeped to a lower than standard value probably due to wearing of the Belville washers.

On another occasion, while formation landing in trail, I watched the same type of event occur on an RV-6A directly in front of me. Since we are usually quite close (<300-500'), it was quite easy to see the nosewheel fairing swinging back and forth in the breeze on this aircraft while the pilot dealt with a left crosswind, power changes, and associated turbulence from aircraft directly in front of them. Normal stuff if you are used to doing formation arrivals... In the flare as the pilot pulled the power to idle, the nosewheel cocked to more align with the crosswind. Then at de-rotation/touchdown it was quite evident that the nosewheel acted like an unbalanced shopping cart wheel and vigorously vibrated for 3-5 seconds as it dissipated energy trying to align itself with the opposing forces of crosswind, runway, and prop blast. I later asked the pilot if they had a nosewheel shimmy event, to which they replied to surprised, "Why Yes, how did you know..?" :eek: Clearly the breakout force was not set high enough...

And yes, nose, main, and tailwheels do spin in flight, although not as fast as you might guess. If you even are in formation, especially Close Trail looking up at a tailwheel, you will notice that some (with good bearings) spin slowly in flight. Nosewheels also do spin sometimes depending on the model and torque setting used by the builder. I'm guessing that this is not a factor as the rotation is generally quite slow.
 
Hello

Today I was setting the preload force as Vans mentioned to the 22 lbs. I did not flown the plane, still the last steps to do. I remembered there was a video that showed different preload-szenario's.

I hope it is fine if I link this video form unknown source again: https://www.youtube.com/watch?v=IrnDztLJbSI&noredirect=1

I hope it helps.

The "unknown source" of the YouTube video is the Unrein family (Brian and Brandi) who built their RV-10 and live in the Atlanta area.
 
The prop is turning clockwise as viewed from the cockpit. You are seeing the stroboscopic or "wagon wheel" effect.

http://en.wikipedia.org/wiki/Stroboscopic_effect

Uh, yeah, I've been watching my prop go clockwise for quite a few hours now, so I kind of have that part figured out.

Prop swirl would make the nose wheel yaw the other way from what is being experienced; hence the whole discussion about the cause.
 
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