Paint ridges on wings

[springcanyon]

I'm just beginning to think of paint schemes. If a chosen paint design requires paint trim lines running parallel with the wings, near the leading edge, is it possible to affect flight characteristics? I know I can make trim lines pretty smooth, but still there is bound to be a slight bump.

I welcome opinions.

Thanks,
Don Owens

 

[Ironflight]

Hi Don,

I have trim lines parallel to my leading edges, and the airplane flies the same speed after paint as it did before....one data point!

Paul

 

[John Clark]

Paint stripes

In deep theory, maybe. In the practical world there are so many more things to deal with first. The average "tin" airplane is so far from perfect in surface development that the paint stripes are going to be way down the list. The limitations that come with construction from (mostly) flat sheet metal will never match a (hate to use the word) plastic airplane. If you have ever seen Cory Bird's "Symmetry" it makes an RV look pretty basic. Then you get into a discussion of boundary layer and whether it makes any difference.

http://en.wikipedia.org/wiki/Boundary_layer

My experience is that the airspeeds in my RV8 didn't change a bit when going from primer to finished paint. And yes, it has a spanwise color change with a stripe.

John Clark
RV8 N18U "Sunshine"
KSBA

 

[szicree]

If a thousandth of an inch discontinuity in the surface is gonna screw up the way my plane flies then I'm gonna have to start all over.

 

[gmcjetpilot]

Well splitting hairs

I welcome opinions. Thanks, Don Owens

Any span wise ridge in the first few inches would be kinda bad if you are a purest. Some say they slow down when thier wing has bugs on it. The pressure gradient is very high on the leading edge back a few inches, say where it's highly curved. We're splitting hairs literally, but paint trim ridges can be thicker than a human hair. Paint might be 0.003" to 0.007". If you put the trim on thick it could be more. Vinyl is going to be double the thickness. If you go with a base clear coat system it will not matter since the clear coat fills in the trim lines. I would go back at least 6"-10" from the leading edge. The effect is probably small unless the paint trim is crazy thick. Ironically the classic RV paint scheme Van and many buiders used featured wing leading edge stripes, running span-wise near the leading edge. They are not as popular as they once where, but they where back about 8" to 10" at least.

Take any RV and put some tape down the wing span wise behind the leading edge a few inches and go fly to see affect on stall and top speed. I think you might see a few mph at both ends of the tape is in the right spot (ie wrong spot). I could be wrong but it would be easy to find out. If a hand full of VG's near the leading edge of the wing affects the stall and top speed a ridge of tape may also have some effect.

Fuselage? The boundary layer is probably too thick to matter but again stripe or trim lines perpendicular to the free air stream is not as desirable. The worst spot on the fuselage besides the fwd part of the cowl, is the fuselage right at the wing leading edge and tailing edge. Some thick vertical trim stripes there may be a bad idea aerodynamic wise. Vinyl could be a lot thicker than paint.

 

[az_gila]

Thinner....

....... Vinyl is going to be double the thickness. ......

George, the 3M premium vinyl recommended for outdoor use is only 0.002 thick.

Probably thinner than a good paint layer....

gil in Tucson

 

[springcanyon]

Thanks!

Thanks to all for very thoughtful replies.

Don Owens

 

[AX-O]

All I will say is to be careful. When I was in Naval Test Pilot School about 1.5 years ago. We talked about how the smallest things can affect the way aircraft handle. One of the examples given was a published article about how an experimental aircraft flew without any problems with the current paint job but when the owner decided to paint a trim stripe on the wing, all @#$%^ broke loose. He did just what you asked. He painted a trim line parallel to the wing ending just a few inches behind the leading edge. The effects of that trim line were so severed that he almost crashed on take off. He reported terrible flight characteristics and handling qualities. He also said the landing was very sporty. The instructors were trying to show us how dangerous flight-testing can be and how the smallest changes can have huge impacts.

Turns out the trim stripe was enough to separate the airflow very early over the wing. That created turbulent flow and stall like conditions over the wing. The stripe was removed and all flight characteristics returned to normal. If I find the article, I will give you the information so you can read it. The aircraft was made out of glass.

I won?t do that on my plane.