Bill Freeman wrote:

           SNIP

With  an ideal diffuser and a limit condition the pressure would
be infinite the velocity near zero.

How about "pressure would be static pressure" not infinite.
I really hate running into infinite pressure, it just crunches up
EVERYTHING!       :-)

Core drag would be near zero and the system would make a
damn fine engine or waste heat energy recovery system when the
air was finally speeded up in the exit nozzel to provide thrust.

Hoerner Fig 17 suggests just that.
Look at the left side of the chart.

w can be taken as the velocity through the core and
V the velocity of the airplane. C sub da is the overall
drag coefficient of the system.

Perhaps this is an argument for thick.


Paul Lamar         hoefig17.jpg

I think that Jeff is right (thin is best) for cars or any system
which uses little or no duct sophistication (cars or AC
NOT purpose-designed for a radiator, unlike P51) but at some point
the heat gained by the air can help provide thrust with
sophisticated ductwork (nozzle on rad outlet to accelerate the
heated air) and a lot of testing, lowering overall system drag.

The key is to look at the equations  (heat exch efficiency loss
due to poorer delta T in thick vs heated air accelerated to provide
thrust with a post-rad nozzle system) and see if the amount of
heat added has a prayer of giving USEFUL thrust, and whether
you can fit in and want to build a super effiecient diffuser
and nozzle system.   Most of us are not going to have the
time or room for a really super duct system, so the thin
is probably best, take your lumps in drag, save a year of
development time.  Probably crack the throttle a hair more
an forget it, so much for efficiency.

Bill

 
The Aircraft Rotary Engine Newsletter.              Powered by Linux.

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