X-Mozilla-Keys:                                                                                 
Al Gietzen wrote:

Paul;

Back again to the table of coordinates for the ideal diffuser from
Kuchemann.  I understand that the numbers are the distance from the
centerline.  I also conclude that it assumes a square duct; i.e.; the
dimensions are varying in height and depth; otherwise you don't get the area
ratios given.  Have I got this right?

This is definetly 2d Al. K&M does not have 3D coordinates or data.
Hopefully some one will take Chuck's lead on flow instrumentation
using CPU cooler fans and a water manometer and run some numbers 
on flying examples. I will be testing a 2D angled rad later
this week. The local helicoptor brush  fire dept. took priority over
my rad wind tunnel :-) PL

It seems like this is very useful data in that for whatever shape your duct;
the rate of variation of the area can be used.

I think I see what you are saying there. Because it is 2D you can read 
between the lines and assume it is area ratios.

It also seems that to worry a lot about diffuser design and rad pressure
drop is somewhat defeated a configuration where the air is simply dumped out
the back side of the rad where it slows suddenly to near zero velocity (big
exit loss), and then is accelerated suddenly (entrance loss) at the cowl
exit.  For low drag loss, you need the duct it out as carefully as you duct
it in (as in Tim England's Velocity).  What d' ya think?

Most of the fast airplanes today deal with this problem. Rare Bear,
Dave Anders, Tracy Saylor, Nemesis you name it.

You have a point there but don't forget Tim England's increased frontal
area and drag coef. for that increased frontal area. The duct could
be narrower or a NACA duct used to feed an internal rad on pushers. PL

And, sorry; in my earlier posting I referred to him as "Dan" England.  I
think he made music with John Ford Coley.  Whatever.

Al Gietzen

BTW I don't really think external diffusion is totally free.
If you have more air going around the outside of the cowl you have
more velocity and drag from that source.

Paul Lamar

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