Welcome, Al
Yes, Swapping Dt for Dt or DeltaT just
looks sexier {:>).
I agree with your assessment of Meredith
effect, certainly useful and helpful when done properly to offset cooling drag,
but have never seen any evidence/proof that there was a net thrust (probably for
the primary reason you mentioned).
Ed
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Al Gietzen
Sent: Wednesday, December 23, 2009
8:12 PM
To: Rotary
motors in aircraft
Subject: [FlyRotary] Re: Air Flow
Question
As far as I can tell, thrust
recovery in the P-51 is legend. Never found anything in the way of proof that
it really occurred.
The most detailed, and what I believe to
be authentic, analysis of the P-51 scoop legend is that there is no net thrust
– ever. There are certain conditions where it is basically 1 : 1
offsetting drag (top speeds, and in dives); and yes, the outlet velocity may
get slightly higher than inlet, but the air is less dense so has less momentum
per unit volume. For most operations it was in the 1 to .85-.95 range,
which is excellent.
Anything we can do to accelerate the air
back toward the free stream and velocity, and have it exit in the direction of
the free stream, helps. An efficient converging duct with an outlet area
in the range of 1.3 to about 1.6 is good, and the ratio of choice depends on
the temperature increase of the air – which depends on the mass flow rate
through the core. (Higher DT, higher ratio). Analysis that I have seen (and verified) suggests
minimum drag and radiator weight is achieved with DT in the range of 50
– 75F, core thickness 2 1/4 – 3”; and yeah, there are set of
assumptions involved, so YMMV.
That’s my story; and I’m
sticking to itJ.
BTW, ED, thanks for the tip on the D; that is very cool.
Al G
__________ Information from ESET NOD32 Antivirus, version of virus signature
database 3267 (20080714) __________
The message was checked by ESET NOD32 Antivirus.
http://www.eset.com