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I think the whole notion of cooling drag on pushers has a lot more to it than the most efficient inlet. Like if you can maintain attached flow to the end of the cowl you'll get a lot more and better air flow into the prop disc and that's HUGE. Different cooling air inlet schemes have different effects on the flow over the cowl downstream of the inlet. If the cowl tapers too sharply at the aft end (like Cozys and most EZs) you get a large eddy and a lot of turbulence around the lower aft cowl. I think Burt's original P-51 scoop was very bad in this respect and that's why he went to the NACA duct. The EZ speed merchants are going with much gentler upsweep of the aft lower cowl and boat-tail shape of the lower cowl as well as putting down draft air inlets in the upper cowl cheeks for better flow over the cowl (and using the original profile - the NACA ramp - to reduce the sudden upsweep of the aft lower cowl)
It's more than a matter of just inlet frontal area ... Jim S.
Dale Rogers wrote:
Hi Thomas,
I'm having a little trouble identifying whether or not you're just playing "devil's advocate".
On the assumption that you are completely serious, it's worth considering the following:
[1] WRT canard pushers:
A - Burt Rutan started out with a P-51 style scoop on the Vari-EZ. IIRC the early Long-EZs also had them. He later changed to the NACA scoop because it was more "efficient" in some combination of cooling efficiency vs. drag.
B - Nat Puffer rescaled the NACA scoop such that it does, in fact, provide sufficient cooling for a 180 HP Lycosaurus.
His design will go 200 MPH on less than 13 gal/hr - which suggests a low-drag desgin. see: http://www.cafefoundation.org/aprs/Cozy%20IV%20APR.pdf
That same scoop will also provide sufficient cooling for a 200+ HP Turbo-charged rotary even routed through multiple heat exchangers. [2] Sound empirical evidence ALWAYS trumps theory.
[3] Good engineering practices suggest that it is unwise to experiment with too many things at once. In the event that something goes awry, one may encounter considerable difficulty in ascertaining *which* component or subsystem caused the problem. If one wants to experiment with improved cooling systems, it would be wise to start from a solid baseline of a system that is _known_ to work, and change one item at a time. Good luck.
Dale R. ......................|......(___.......|
COZY MkIV-R13B #1254 .........|----==(___)==----| Ch's 4, 5, 9, 16 & 23 in progress ..o/ | \o
http://www.canardzone.com/forum/showthread.php?t=1388
(Cedat Fortuna Peritis)
From: "rijakits" <rijakits@cwpanama.net>
Date: 2005/10/18 Tue PM 11:26:36 EDT
To: "Rotary motors in aircraft" <flyrotary@lancaironline.net>
Subject: [FlyRotary] Re: flyrotary_Web_Archive Re: Banishment
Hi John,
it was me, Thomas J. babling below, don't blame Monty for it!
----- Original Message ----- From: John Slade
To: Rotary motors in aircraft
Sent: Tuesday, October 18, 2005 10:25 AM
Subject: [FlyRotary] Re: flyrotary_Web_Archive Re: Banishment
Hi Monty,
( I admit I am NOT a fan of EWP quite yet...., however stand to be corrected)
I think Rusty used one with success in hot weather. I'm also waiting to see
the EWP prove itself, but at least over here we're open to the possibility.
I believe Rusty's system still kept the engine driven WP in addition to the
EWP. Rusty?
# NACA scoops work: Well I guess you if you make them big enough
Let me rephrase, then. The Cozy plans NACA scoop is sufficient to cool a turbo
rotary.
of course, BUT there are better and more efficient ways to get cooling air
in!
I think, for a pusher, the NACA is the least draggy solution we know. I may be
wrong.
But one should take advantage of his list of resources and really dig in
IMHO There's too much untruth and incorrect / unproven theory buried in the
truth to make the exercise worthwhile
I am refering to the references to the books of Kuchemann & Weber and Kays &
London. It is "hardcore" reading but at least some of it "seems to make sense"
even for the layman.
Remember the inventors of the NACA-duct did recommend to NOT use it as a
pressure-recovery intake (what we need for our our car style radiators)
Unfortunately they "look" rather sporty, so we fall for them....
Also even the P-51 style scoop doesn't do the best for efficiency. In one of
the books it is mentioned somewhere (IIRC), but there were one or two testships
with modified scoops (according to K&L I think....), which improved efficiency
over the last production system. However that one was good enough, so the new
one never made it to the masses and then WW2 was over and the jets on the
doorstep.
Once you get really into aerodynamics concerning effiecient cooling, it starts
to hurt seeing people fight for cooling but having bad/inefficient systems.
As mentioned before, for me the road will be the fun, not so much the
destination, so when I get to it I will really enjoy doing lots of experiments!
Don't hold your breath though....:)
Now PL the pope, made me look at these books (actually only parts of it...).
Also remember (again...) these facts do not come from grumpy old man, but are
facts from respectable sources - he just pointed the finger in the right
direction.
# Earth round?? Obviously you never fell off the edge yet!! Actually it has
the shape of a trochoid!! - bet you didn't know that!
I did say almost. :)
Right!
Regards,
John
Saludos,
Thomas
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