Oliver Arend schreef:

The Reynolds number is determined as

Re = v * L / nu

v is the speed of the airflow,
L is the "characteristic length" (I'll get into that)

OK OK thanks but that wasn't really my question.
Excuse me if I wasn't clear enough, what I really meant to ask is
"when designing a plane, need I be concerned about the Reynolds number
and if so, in what way?" My first understanding was that it is a
property of the airfoil, that seems wrong now.

( ... )

This means you can get an infinite number of Re on an airplane, just
as has been written. It cannot (really) be chosen, but is determined
by size and operating conditions of the airplane.

But NOT by the airfoil, then? Does one first determine the (max?) Re the
plane will be operating at, and choose an airfoil accordingly?

In short, you need it if you (seriously) want to design an airplane
and estimate its performance.

That is a very useful answer to me.

But the difference between wind tunnel testing and reality is much
greater than the difference between Re = 1 * 10^6 and 2 * 10^6, so it
doesn't really matter for homebuilders. It can become interesting for
builders of high-performance model airplanes and of course
aerodynamically challenging tasks such as designing sailplanes.

So if I'm not wanting the ultimate bit of performance from my DreamBird,
I needn' t bother too much? How then do I go about selecting an airfoil?


PS1 I am very happy with the tone of this discussion: only positive
reactions, and people willing to accept correction. It's one of the
reasons I like to lurk a bit here, and even dare to launch some
questions about a silly dream I am not likely to ever realise.

PS2 Oliver, verstehe ich gut du bist Deutsch? Das koennte mal Spass
machen, anderes als Englisch zu schreiben...