A different example...

A golf ball operates at a very low Re (small length and low speed),
so it's form drag would be very high - without the dimples.

The dimples trip the boundary layer forcing a premature turbulent transition
in the boundary layer. This turbulent layer provides a high energy boundary
layer that reduces form drag by reducing the boundary layer thickness.
The dimples, in effect, increase the Re.

Back to wings:

In choosing airfoils (and thus wing areas), Re is important because all airfoils
do not work equally well
at all Re.

Laminar airfoils generally don't work very well at exceptionally low Re.

The 5 digit NACA series, as an example, don't do well below Re of 2 million.

On that little low wing single seater I was sketching on a while back, the
wing tips are only 24" chord. At landing and take off speeds ( 40 mph?)
the tips aren't making very much lift!

That leads to higher take off speeds (or a larger wing?), lousy aileron response
at low speed, and makes it very easy to encounter a tip stall (roll on take off
any one?).

But the rest of the wing, due to longer chord looked to be fine.

So my "solution" was to change from a 23015 airfoil at the root to a
2412 (a 4 digit - or turbulent flow airfoil) at the tips.
(That would be a lofting nightmare - without CAD)

This airplane was also supposed to operate at higher than "usual" altitudes
(12,ooo+ feet for cruise) the same thing could have happened in cruise.

The thinner (lower density) air lowers Re to the point that we could possibly
encounter high speed tip stalls...


Now, does that mean that small chord wings can not operate at low speeds?
Of course not.
But we left wing size, efficiency and altitude out of the question.


Richard