Fairing suggestion

[Bob Axsom]

I was out at the airport working on a cowl mod when up walked Cris Ferguson telling me that the man I gave a ride to a week or so ago is going to sell his Swift and buy an RV-7 kit. In the course of conversation about drag reduction he mentioned the posibility of adding a fairing to the leading edge of the wing where it joins the fuselage. He said the current thinking has moved away from the full wing root fillet toward a small leading edge cuff only. Has anyone tried this on an RV?

Bob Axsom

[gmcjetpilot]

Tracy has a very fast RV-6 on the west cost. He tried the big swoopy wing body fairing and found it did nothing. He went back to the flat metal cuff and rubber seal.

The original RV-4 had the LE cuff and than sheet metal fillet the rest of the way. This is verses the current flat metal filler and rubber seal. I had the old style on my RV-4 and switched to the new way of closing the wing / body gap. I prefer the latter. It is cleaner looking. As far as speed I never really measured it because I made many changes and did not keep track of it, but doubt it made much differnce by it self, although my plane went faster with the flat cuff, but that was no doubt from other changes made at the same time.

I found that the LE cuff ends up having details like where it meets the side of body and is draggy. For some reason the fillet fairings are just not that effective. Sam James sells a whole fiberglass side of body set up. I guess if you put it on and used body filler it can't hurt. However from a building stand point it is more work, more holes in the body and weight.

Dave Anders with the fast RV-4 just has the flat fairing and rubber seal, no curved cuff.

I think it is just cleaner and lighter to go the way Van does it now.

George

[Bob Axsom]

You are probably right but I may do some experimenting with some cuff type leading edge only fillets. I think I threw away all of my modeling clay when I moved but that is the way I would go about it - clay molds and fiberglass. If I came up with a version that actually improved the speed, I would install a couple of platenuts in the flat closure strip (one bottom, one top) near the leading edge wrap around and tie the forward extension to the fuselage with sheetmetal screws. It is not an urgrent thing but I appreciate the actual experience information you provided. My opinion is if there are any gains they would be caused by the elimination of some parasitic drag right at the impact point of the leading edge where it butts up against the fuselage. Cris designed and built the biplane for Jeff Lo that is nudging up against 300 mph and he is always looking for any little peformance gain he can get. I'm not quite that radical but it's addictive.

Bob Axsom