[scsmith]

I just landed from doing the flight testing on my new elevator root fairings. These are very light-weight fiberglass fairings that improve the aerodynamics of the area between the elevator and the rudder, taking advantage of extra room, but no change to the gap to the rudder skin from the elevator trailing edge.

Tests were done at 7500 ft pressure alt, 63F OAT, 2400 RPM, 22.5 in Hg. MAP, 8.0 gph fuel flow. Tests both days had almost identical atmosphere (wind, OAT) with less than 5 kt wind, except for the first test with the fairings installed, which had a 19 kt wind. Despite that, the computed TAS from that test was extremely close to the other results - Gives great confidence in the results.

Baseline, no fairings, average of three GPS Speed Triangle tests = 166.6 KTAS
With fairings, average of four GPS Speed Triangle tests = 168.2 KTAS.

So it looks like the fairings are good for 1.6 kts.

Here's a couple of pictures. It is hard to descern the contour shape from the pictures - I will draw some stream lines on one and take another picture so you can see the gentle curve to a trailing edge provided by the fairing.

 

[scsmith]

We went through two iterations on the installation details. The first set I made had a joggle along the edge that slipped in under the elevator skin and root rib. This required making relief notches for the rivet tails and dimples on the inside. My plan was to put a couple of plate nuts on the fairings and install with 4-40 flat head screws. This presented a challenge for the trim tab portion, because there is no pocket at the root end. I also found that despite my best efforts, there was a rather distinct shape break at the joint that might cause flow separation.

So, we made a second set that fits over the outside of the elevator skin with about 1/2" of overlap. This first install used double-sided tape but we will remove that and bond the fairings on semi-permanently with RTV. The edge of the fairing was feathered to a nice smooth edge and the shape is aerodynamically better than the version that mounts inside. I do have molds for both styles so you can choose which you want.

 

[Ralph Inkster]

Looks very similar to the fairings I cooked up for Race 57. We didn’t test all the mods we put on the plane separately, so is nice to hear that this particular one did actually add to going a bit faster. Besides it really cleaned up that area visually!

Good job!

 

[Scott Hersha]

It looks nice, but I’m trying to see what is different than the standard Vans installation instructions in this area. It looks like exactly what I have done on my last six RV’s, except for the use of far fewer screws. Is there something different in your design? Not obvious on your pics.

 

[scsmith]

It looks nice, but I’m trying to see what is different than the standard Vans installation instructions in this area. It looks like exactly what I have done on my last six RV’s, except for the use of far fewer screws. Is there something different in your design? Not obvious on your pics.

Note I am not talking about the standard empennage fairing that fills the gap at the intersection of the horizontal stabilizer and the vertical stabilizer. I am talking about the fairings on the elevators.

The inboard edge of the standard elevator ends at the edge of the white paint in the pictures, except for about 1/2 inch that extends under the gray fairing. There are NO added screws. The new parts are the gray parts, providing a fair shape instead of the blunt inboard edge of the elevator root rib and skin. There is nothing in the Vans kit instructions to do anything like this. A few others have done this, including Ralph (above) and Jason Rovey (Race #76). The fairings are bonded on. Can be removed by carefully slicing through the RTV with a razor blade.

 

[scard]

Nice! It seems pretty intuitive, blocking the control surface ends. Those trailing edges look unique too.

 

[Scott Hersha]

OK. I think I understand. You are talking about the inboard end of the elevator where there is an abrupt edge near the fuselage, and you’ve faired this edge. I’m impressed that this fairing gives a 1.6 kts advantage. I would have thought that something this far aft, with dirty air would not make that much difference.