There are a lot of claims for some waxes but I have never seen any speed difference between the plane covered in dead flies and dirt, and it being clean.
Is there any theoretical support for a “wax” doing anything? IMHO it will be sitting in the boundary layer – together with dirt and insects.
It depends on the aircraft type and and its “type” of aerodynamics. Most “spamcans” are not affected by dirt. High performance gliders are a different story.
The precision of the airspeed indicator by far precludes any scientific testing :-)
A real laminar airfoil like in a high performance glider will be affected. Any of our airplanes? I highly doubt it.
But when i give the Cirrus a good polish it definitely feels faster :-)
But when i give the Cirrus a good polish it definitely feels faster :-)
And looks faster too!
Never seen any effect on my aircraft. But then, it almost always pretty clean.
Its probably depends on the aircraft. Mine is a Robin HR100/285, it is parked outside so the paint is weathered and it gets dirty. After a wax polish it gains about 5kts at typical cruise at FL100. I would have thought that a little roughness would help boundary layer attachment, however that would improve lift – but would it reduce drag? Incidentally its also affected by weight in cruise. Heavy and dirty is nearly 10kts slower than mid-weight and polished.
I would agree that differences of 5kts or less are not easily noticed due to normal indicator inaccuracies, however in a steady cruise at FL100 with no turbulence quite small changes are noticeable.
I was chatting to the UK distributor of a new type of fabric, called Oratex. In it’s self coloured, natural state it has a distinctive weave finish. Apparently in test flights on a Robin DR400 it makes the aircraft fly faster and stall at a lower speed, which is a phenomenon similar to the improvements brought about by turbulator tape and vortex generators.
Surely dirt might have the same effect?
I can see why Oratex might reduce stalling speed, but why would it make the aircraft go faster? AFAIK vortex generators carry a speed penalty.
Decreased lift (efficiency) will cause massive increase in induced drag. Snow and ice doesn’t increase parasitic drag much, but could destroy lift altogether.
Looking at the way shark skin is structured proves that “smooth” isn’t necessarily “fast”. Recent research suggests that if anything the riblets are reducing drag.
