Submitted by N8RV on October 15, 2009
I seem to recall an article from a long time ago where a reader asked Peter Garrison about the value of waxing a plane. The article compared relative speeds between waxed and unwaxed planes. I am contemplating painting my RV with flat paint. Will a plane painted with flat paint fly any slower than one painted with glossy paint?
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October 16, 2009
Laminar wings depend on clean airflow and there will be a difference in efficiency when comparing flat paint to glossy. High-performance gliders actually have their wings made in a near-perfect mold and a waxed to perfection before a flight to achieve the best LD ratio. Dirt and bugs that build up on a wing also affect the lift and the drag and some super-critical airfoils like the ones used on Rutan canard homebuilts are even sensitive to rain drops on the surface. There have been accidents related to buildups on these airfoils and the designer even warns of these issues. Non-laminar airfoils are not as sensitive to paint choices but still benefit from clean a airfoil, so unless there is a good reason to paint if flat, go with gloss. Also, if your ever go down in a place that makes it hard to spot an aircraft, the glossy plane has the "reflective" advantage that makes spotting you easier. Whether or not you will notice the difference on your RV is debatable, but those seeking high performance use every advantage they can get. Jim
February 01, 2010
It's my understanding that if it's SMOOTH flat paint, it doesn't hurt you, even on a "laminar" wing. And there may be an advantage that in the rain the water doesn't bead up the same way. OTOH, I bet waxed paint is more durable and easier to remove bugs from.
I'll bet if you used sandable primer, patience, and a long sanding block, you could increase the extent of laminar flow, whether you were using gloss paint or not. But how much difference that makes on an RV, or how durable your paint job would be, I don't know. The sailplane guys sometimes do some sanding and rework to get more perfect, non-wavy shapes.
Avoid paint lines ahead of transition from laminar to turbulent flow. Aft of that, it doesn't matter much.
From everything I've read, it might be more worthwhile for you to look closely at cooling drag and lots of little intersections, air leaks, and details on your plane.
caveat: I'm a model airplane guy and not an aerodynamicist, though I am an engineer.
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