Bill Freeman wrote:

Paul,

Just a note to agree on the external diffusion topic.
Ever notice that the Corsair, Hellcat, Wildcat, Bearcat,
Tigercat, etc.had no spinner and that big old
"obviously"draggy air inlet to the cowl?  Grumman
tested a big spinner and got nothing of value.
The key is that the shape of the cowling is causing
the air to flow strongly outward at the leading edge,
and (as Fred has said) the actual stream tube that
feeds the cowling inlet is much smaller than the
cowling inlet.  SO - the expansion (diffusion, and pressure
increase) is occuring feet ahead of the inlet, and
since the local speed around the prop hub is low,
the spinner is not useful. Air vel is low press is high.
Effective diffuser length is many feet, for free.

I've got a copy of a captured German tech paper
around here somewhere, reprinted by NACA just
after WWII, took me a while to understand what was
going on, but the streamlines are the real story.
Built my air inlet for my cabin heat on the LE the same
way and it works like a charm - lots of high pressure
air saw no cruise speed change even tho it looks draggy.

Bill

PS Jeff is right, you need a sketch of the streamlines to
follow this the first time - and it is important to understanding
a whole (non-obvious) class of inlets.  I'll sketch it up, or
find my NACA paper if you want.

That NASA paper would be nice. You want to FAX it or mail it
or bring it with you to Sun & Fun?

PL
 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org