Don't feel the least bit stupid over this, Reynolds number is a
horribly misunderstood thing.

In broad terms, it puts a value on the physical length of an airfoil
and the speed it's traveling. Say you have a 4 foot wing chord, and
the wing is travelling 100 mph will produce a R number around 3.3
million. That same airfoil scaled up to 8 feet will give an R at 6.6
million, or the 4 foot wing at 200 mph also gives 6.6 million, and the
8 foot chord going 200 mph gives an R of 13 million. An airfoil built
half the size, traveling at the same speed as another will give much
less lifting force. (not necessarily half) but that half size airfoil
travelling at twice the speed will act exactly the same as the larger
airfoil at the lower speed.

Reynolds number basically puts a value on the quantity of air working
on a wing for a given unit of time. If you reduce speed or reduce
size, then less air works on it. Increasing speed or increasing size
increases the amount of air working on it.

Hope this helps your understanding
Gerry

On Jun 22, 10:33*am, jan olieslagers
wrote:
It's been puzzling me for a long while and there it is again popping up
in the "WIG airfoils" thread: what is this sacred Reynolds number?
I tried our alther friend en.wikipedia but its theory was quite beyond
my level of education* and its examples of oil in a pipe were not really
illuminating - not to mention the spermatozoa and the Major League Baseball.

Is it a property of the wing, or of the whole plane, or do the fuselage
and wing and empennage &C each have their own Reynolds number?
I seem to understand this figure is a measure of aerodymanic quality?
Given a plane's weight and engine power, will it be faster (or slower)
for a higher Reynolds number?

Excuse my stupidity,
KA

*I am only a modest Solaris sysadmin, never went to university...