JordanGrant

JordanGrant

Well Known Member
I just got back from test-flying my RV-6 with the wheel fairings on for the first time. First of all - WOW, that does make a speed difference. I didn't do extensive testing, but I certainly believe it could be on the order of 15 kts of speed!
Now, the problem: At speed (170kts), I'm getting nearly 2 ball widths on the turn and slip, to the right. I don't have a calibrated leg, but it feels like 80+ pounds on the right rudder to center the ball. Without fairings, its about 1/2 a ball right. Fairings are definitely not on straight.
My plan:
1) I'm going to test fly it without the leg fairings (wheel pants only) and see what I get. Maybe I can narrow it down to leg fairings or wheel pants causing the majority of the problem. I'd like to fly it with the leg fairings only (no wheel pants), but there is nothing on the bottom on the leg fairing to keep it aligned to where it "would" be with the pants on. So I don't know the effectiveness of that idea.
2) gmcjetpilot, if you're reading this, I found an old post of yours that described using dye on your fairings to test their alignment. Could you pass some details on that process? Has anyone else out there tried it?

Cheers, all.
 
Something is a little off

Hey Jordan,

Something is off a little. I only got about a half ball out, which is about where it was without them.

Re-install checking all measurements and try again. Get this one right for more speed and economy.
 
String method?

Hi Jordan,
When we installed ours (on the 6A) we had the plane levelled fore and aft and dropped a plumb bob from the fuselage, to the floor front and rear and snapped a chalk line on my hangar floor. Next, we measured outward to the center of the bottom of the tire and snapped a second line, parallel to the center one. Another on the other side of the airplane. These lines were used to align the wheel pants perfectly parallel to the fuselage centerline, using a builder's square up to the front and rear of the pants, with it's corner on the line.

As far as the gear leg fairings, you can sit behind the airplane, on the line, behind the tire and look at the leg fairing up and down and see the same amount of thickness to the left side and the right side of the trailing edge as you rotate the fairing a little. You can go half way up the leg fairing, mark that spot and drop a plumb bob from that point and snap another line, parallel to all the others and use the string method. Clear us mud, eh?? :confused:

I believe that the leg fairings are by far the most influential on yaw.
Good luck,
 
pierre smith said:
I believe that the leg fairings are by far the most influential on yaw.
Good luck,
Click to expand...
I used to think the same thing, but I don't anymore for a couple of reasons. First, I think the ability of the gear leg fairings, which aren't solid, to move the tail over two balls is highly unlikely. Look at the force on the pedals to center the tail. How much force would the gear leg fairings need to apply, from up front no less, to move the tail that far? Probably way more than they are capable of delivering.

Second, I had a chance to mess with my fairings on my Rocket since I had to replace my lower gear leg intersection fairings once I corrected a wheel alignment problem. I found my original alignment was quite a bit off and correcting it had zero effect on the ball.

I now believe that there are two things that greatly affect the rudder trim, the vertical stabilizer alignment and the bend in the trailing edge of the rudder. I was amazed by the impact of the second one. In the same way you correct a heavy aileron by squeezing the light one, try lightly squeezing the "light" side of the rudder first. That may be all you need.

Irregardless, you cannot get the airplane to fly with the ball centered in both slow flight and cruise speed without a trim tab of some kind. I finally added a small one to my rudder, along with all the other changes mentioned above, and I have the ball nearly centered in both flight regimens.

My suggestions are based solely on my experience and may or may not work for you. If others have changes the alignment of the gear leg fairings and that centered the ball for them, that's great. It just didn't do a thing in my situation.
 
pierre smith said:
As far as the gear leg fairings, you can sit behind the airplane, on the line, behind the tire and look at the leg fairing up and down and see the same amount of thickness to the left side and the right side of the trailing edge as you rotate the fairing a little. You can go half way up the leg fairing, mark that spot and drop a plumb bob from that point and snap another line, parallel to all the others and use the string method. Clear us mud, eh??
Click to expand...

Pierre,
I'm not a smart man, so forgive me. The leg fairing alignment process never made sense to me, to be honest. The parallel line method makes sense on the wheel pants, because I can find a leading edge and trailing edge on it to align. Since the gear leg fairing has a sweep to it, how can I find two points on the leading/trailing edges that should be parallel with the centerline?

So what you did was just find 1 point, drop a plumb bob, snap a parrallel line, and then visually check the alignment while standing (crouching) on that line. Am I reading you correctly?
 
I took a different approach on this alignment procedure. Call me silly but assuming symmetry on both left and right main gear legs and actual tire location. I measured across and diagonal and assured that both wheel fairings are parallel with one another. Hope it works out.

http://www.jeffsrv-7a.com/WHEELS/06-08-21.htm

-Jeff
 
Leg fairings

Hey Jordan,
The string method for the leg fairings goes something like this. Basically, you wrap a long string, 10 feet or so, around the front of the leg fairing and pull both ends toward the rear of the airplane but parallel to the centerline of the airplane. With the ends of the string held together, with the string tight, there will be a space between the string and the trailing edge of the leg fairing. The distance of each string from the trailing edge of the fairing (about 1/2") should be the same. Rotate the fairing a little to get the distances even. Two guys/people make this a lot easier.
Regards,
 
One more thing

and make sure the airplane is level fore/aft and side to side as well as elevated off the ground (jacked up) a couple of inches when doing any measurements as the gear legs move when weight is taken off of them.
 
Pierre:
Now that makes sense. For some reason, I never comprehended that procedure before - obvious in hindsight, of course. Well, I didn't do it that way, and that's one reason why mine are off.

I went out and did some test flying today. I took off the wheel pants and flew with upper intersection and main leg fairings only. I got about 1.5 ball-widths off on the T&S that time. Then I removed the upper intersection fairings as well. With only the leg fairings, I got 1.3-1.5 ball-widths, so maybe a slight change but not much. This all leads me to believe that the majority of the problem is in the gear leg fairings, vice the wheel pants. Tomorrow, I'm going to go try just the pants, without gear legs, and see what happens.

Additional conclusions from this little 1-data point test is that a significant drag reduction is occurring from just the leg fairings. And I noted about 1-2 knots speed increase from the upper fairings alone.
 
Stand Back Burrito

If you stand back about 30 feet behind your plane (best if you're plane can be eye level, like stand down hill, then you can set your leg fairings by eye. At least you'll see where you're problem is.
 
Get the wheel pants straight, don't worry about the gear leg fairings. I got the wheel pants straight and let the gear leg fairings find their own center. I just left the hose clamp at the top of the gear leg fairing just loose enough so that they stayed up, but could still be twisted a bit. Then I just flew the plane a couple of times and tightened up the hose clamps. The air pushed the gear leg fairings where it wanted them to be.

Wish there was a way to do that with the wheel pants.
 
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