Cleaning up an airplane

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Well-Known Member
Jul 30, 2004
Grenora, ND
Now I'm not looking for more speed out of my plane (it will probably go faster while on the trailer going down the freeway:p: ), but I would like to clean it up a bit.

I was thinking of using streamlined strut tubing for the eight struts that stick out in the wind plus making something to cover the axle tube. I have a pair of C152 wheel fairings that I can make work (they need some TLC though). I was thinking of more rake in the windshield but that might cause some aero probs with the tail.

The other thing I was thinking of changing are the wing tips. Now I don't know squat about how different wing tip designs affect lift, drag. If anyone knows about some easy to understand info on this it would be most helpful. What I am looking for is a simple to cover design that I can install flush mount lights in. The wing tip bows that are on my plans don't allow a flush mount that is visible from above, below, and the side. I was thinking of something that I could make out of foam and glass.

I'll have a spinner on the prop and the cowling shape will be driven mostly by engine size and cooling requirements. Basicly I'll think about that when I decide on an engine.

Can anybody else think of where I can "clean up" my Avenger?:smile:


Well-Known Member
Mar 2, 2003
Western Washington
There are probably a few areas where you could make some improvements however, as you said, it still may go faster down the freeway.

Your indicated use of streamlined tubing is a great start. Round shapes are very draggy (actually more draggy than even a square shape of equivalent frontal area) so going to streamlined tubing will do a lot. Wheel fairings and gear clean-up will also go a long way to improving the airplane's drag profile.

Making some fancy wing tips however will most likely not do anything for you (wing loading too light) except add quite a bit of work and of course, maybe a bit of weight. If you want to do this for aesthetic appeal than go ahead but don't expect any really measurable gains.

More rake in the windshield may be of some benefit but here it really depends on the current design and how the new shape would affect the localized flow. Off the top of my head though, if the current widshield is a relatively blunt and simple wrap, then the added rake might be of some benefit. Don't worry about the tail, the windshield flow will not be of any considerable effect back there.

The other two areas of drag are interference and cooling. The former is realtively easy to take care of since it will primarily involve making nice fillets in any area where two structures come together. This includes the wing-to-fuselage interface, the strut-to-wing and strut-to-fuselage interfaces, landing gear mounting, etc. The fillet is especially important in areas where the structures form an angle that is 90 deg. or less between them.

Cooling drag can really be an issue since if this is done incorrectly, it can account for as much as a quarter of the airplane's drag count. The important thing to remember is that in cooling an air or water cooled engine, the efficiency of the installation is primarily a function of the cooling flow's exhaust, not the size or shape of the inlets. The best way to remember this is something I was told about ten years ago - think of inlets as just that, they "let" air in. You cannot ram more air in by making them bigger. The only way to get more air flowing through the cooling system is by reducing the back-pressure within. The only way to do that is by making a good and efficient air flow exhaust geometry.

Other than that, the cleanliness of your airplane will depend on your build quality as well as attention to areas of flow leakage (door seals, control gap seals, etc.).
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