What's new
Van's Air Force

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

Wheel pants warning

Platyius

Member
About six months ago I fitted wheel pants to my RV-12 and being new to the mechanics of wheel pants I followed Vans installation to the letter. I trimmed the fairings to the trim lines as directed, when fitting I felt there was too small a gap between the tyre and fairing so I made a greater clearance. This clearance seemed to match other RV?s in my hangar. After quite a few landings with no problems. The other day I landed on a hard runway and allowed the nose wheel to come down a bit too quickly, I heard a bit of a noise but took little notice until we got back to the hangar where I found I had ripped a large piece of out of the back of the nose wheel fairing.
I think the cause was the clearance between the fairing and tyre was too small and the tyre distorted as it hit the runway, increasing the circumference to increase enough to grab the back of the fairing.
I repaired the fairing and it is like new once again, and have increased the tyre clearance. I feel disappointed that Van?s didn?t give a minimum clearance between the tyre and fairing.
The only reason for this post is to alert other builders to allow enough tyre clearance on their wheel pants.
T. E.
 
Some Comments on Close Fitting Wheel Fairing Openings

I don't know how you landed or how you installed your fairings but I do have some experience with close fitting openings on wheel fairings for the purpose of increasing speed.

You can design fairing in such a way the exposed surface of the tire is no more than a continuation of the line of the fairing. Someone just sitting and thinking in gross practical terms might think otherwise but if you experiment and test and measure and modify and repeat you can get past that limited view.

The tire to fairing dynamics change when the bottom of the fairing gets closer to the ground and here are a couple of observations:

- The interference angles get much lower because the fairing interface is nearly tangent to the rotating surface of the tire. The front of the tire and the fairing can be in actual contact with weight off of the wheels. The same is true of the side interface. The rear is more of a challenge because the surface of the tire is rotating directly into the fairing edge there like a rotating piece of wood in a lath turning directly into the cutting tool. This can be dealt with a little care in the shape of the fairing edge down a little there to avoid a hard edge contact - shape the inner surface so it is more tangent to the rotating surface of the tire.

- when weight is on the wheels the deformation is very interesting - the tire compresses up into the fairing where the flare out is above the fairing edges. This is where the fairings are wider and can easily accommodate the wider tire. The way most wheel fairings are installed up high on the tires reduces the bare tire drag and provide normal operational clearances for big chocks, foreign objects on the surface and rough surface but they do not maximize the drag reduction or minimize the need for clearance gaps. If those fairings were extended down almost to the ground, the best speed configuration can be achieved.

To get the best of both worlds on our RV-6A I developed subfairings for racing in the Sport Air Race League (www.sportairrace.org) cross country air races a couple of years ago. The idea was to install them for racing and remove them for normal operations. They turned out to be so trouble free that I simply leave them on all the time. In instances where I have scraped the nose gear subfairing the damage has been easily reparable and caused no damage to the main fairing. The net gain in speed was approximately 3 kts over the original Van’s fairing configuration. Below is a photo of my latest nose wheel fairing configuration. Unfortunately my paint supplier mixed the wrong shade of imron in the latest can of paint I bought from him.

Bob Axsom

IMG_4750.jpg
 
Last edited:
Wow, nice stuff to know! I sure want to make such an added fairing for my 12 since I will practically never land on rough runways anyhow. Did you do that for the mains as well?
I would appreciate any guidance for making a mold for that.
 
Yes I did

There should be a thread ib the forum describing the development. Look for subfairing.

Bob Axsom
 
Instruction Call For 1/2" Clearance

I am working on the wheel pants right now and am approaching the finished condition, I hope. I too started by trimming to the scribe lines and then fitting to the wheel. I found that the sides had the required 1/2" clearance just using the scribe lines, but that the front and back were less than that, the back of the nose wheel fairing was considerably less than that. I trimmed them so that the minimum 1/2" clearance went all the way around.

I too would be interested in what clearance you had to start with. I think/hope that the 1/2" minimum is adequate, but if it isn't I'd like to know sooner rather than later.
 
I am working on the wheel pants right now and am approaching the finished condition, I hope. I too started by trimming to the scribe lines and then fitting to the wheel. I found that the sides had the required 1/2" clearance just using the scribe lines, but that the front and back were less than that, the back of the nose wheel fairing was considerably less than that. I trimmed them so that the minimum 1/2" clearance went all the way around.

I too would be interested in what clearance you had to start with. I think/hope that the 1/2" minimum is adequate, but if it isn't I'd like to know sooner rather than later.

Keep in mind what you are building........ A gap of 1/4" and a gap of one inch will make no difference on the performance of this aircraft.
 
About six months ago I fitted wheel pants to my RV-12 and being new to the mechanics of wheel pants I followed Vans installation to the letter. T. E.

I too would be interested in what clearance you had to start with. I think/hope that the 1/2" minimum is adequate, but if it isn't I'd like to know sooner rather than later.

Platyius said he followed the instructions "to the letter" so we must assume he verified he had the minimum 1/2" as specified on page 36-11 of the construction manual.

Experience has shown that 1/2 of clearance is adequate.
I would suspect an underinflated tire, a much harder nose wheel hit than it seemed, or probably a combination of both.
 
Wheel Pant to Tire Clearance

What clearance do others find good on RV-7A between tire and wheel pant. I'm doing my nose gear pant and it seems like it is done. But I have only 3/16 clearance on the sides, about 1/2 inch in front and over an inch in the rear. I see the plans call for 5/8ths clearance all around which seems like a lot.

So, really is 5/8ths needed?

thanks
 
I trimmed for the 1/2 inch spacing and have never had a problem. However, it should be noted that I had to trim quite a bit past the scribe lines to achieve the 1/2 inch all the way around. If one was to go strictly by the trim scribe marks it is quite possible there would be not enough clearance.
 
I trimmed for the 1/2 inch spacing and have never had a problem. However, it should be noted that I had to trim quite a bit past the scribe lines to achieve the 1/2 inch all the way around. If one was to go strictly by the trim scribe marks it is quite possible there would be not enough clearance.

The scribe lines are not, and never were, intended to indicate a final trim point on the RV-12 wheel fairings. It was intended to proved an opening large enough with the initial trim that the fairing can easily be fitted in place, without of trial and error as is required on the other RV's
It is actually not possible (with the main wheels anyway) to have a scribe line for the correct final trim profile, since the same fairing is used on the left and right side, but by design, the main wheel is not located in the exact center of the fairing.

This is way the manual prescribes marking and trimming to 1/2 clearance minimum after fitting.
 
Back
Top