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1. 02:11 PM - Re: High Temps! (Kevin Shannon)
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Re: Rocket-List: High Temps!All great info thanks Tom, my cowling is a
very early HR II version and the exit ramp is not deep enough to clear
the exhaust pipes without cutting it off forward of the firewall. I see
now that I should have done it over back when I was building, made it
about an inch and a half deeper and extended it aft, which would suck
air out instead of creating turbulence. Looks like I have something to
do this winter!
Kevin Shannon
HR II
----- Original Message -----
From: Tom Martin
To: rocket-list@matronics.com
Sent: Saturday, November 07, 2009 5:36 AM
Subject: RE: Rocket-List: High Temps!
It is nice to see some action on the rocket list! Engine
cooling, especially with rockets, has been something that I have been
working on for quite a few years on quite a few planes. My focus has
not only been to properly cool the engine but to do so without
increasing drag. If you open the bottom of the cowling you will,
usually, improve cooling. However if not done properly this will also
increase drag and hence reduce speed. Yes I know that there will be
those that say that they have not noticed any degradation of speed but
that has not been my experience.
Lay on your back under your airplane and look up at the
firewall. If you can see the firewall you have increased the drag of
your airplane. The air exiting the cowling is pushing down that
firewall and creating turbulence with the rest of the exiting air and
the outside air that is rushing past the cowling. If you need more
opening it would be better to drop the floor of the cowling and extend
it aft. Yes this is more work but what it does, is to get the air
exiting the cowling going in the same direction as the air going past
the airplane. Internal ductwork in the lower cowling and cleaning up
the outlet area can also improve flow and reduce drag by increasing the
speed of the exit air.
All that work will be for naught if your inlets are not
formed properly. By that I mean that there should be no rough edges,
there should be a smooth transition area and tight seals around the
inlet and the upper plenum.
My work has been proven in the races that I have
participated in during the last few years
http://sportairrace.org/index.html note the recent Pagosa Springs race
where my average speed was 220.5 knots placing me in front of three,
count them three, Glassair IIIs. The HRIIs, over the last few years,
have not been doing that well in the races as compared to the F1s and
particularly in regards to John Huft=92s very fast RV8. He has been
kicking some rocket butt. You will not see huge exit air outlets on any
of the fast airplanes in these races. While you may not be interested
in racing, drag reduction, with improved cooling, will save you money on
each and every flight you take.
Checked by AVG.
Checked by AVG.
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Checked by AVG - www.avg.com
11/06/09 12:39:00
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