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Hi Pat,
Yes, I was a bit disappointed to see the results
of the Lipps prop on an RV-6 - especially after seeing what it did to improve
performance on the bi-plane. I was wondering why we had not seen the
expected (Hoped for?) increase. The cowl blocking explanation certainly
sounds reasonable. Perhaps if an older Rv-4 or RV-3 was chosen (with their
smaller cowl frontal area) as a test bed, the results might be more impressive.
.
The cowl certainly makes a difference. One
cold morning at Tracy Crooks when I had the 76 " dia prop and was running it up
to check static rpm - there was a very loud and audible(is that redundant?)
"Whop! Whop!" being generated by the prop. We came to conclusion
that the prop's airflow was probably being varied between the vertical (less
cowl) and the horizontal (more Cowl) areas as the prop went around causing it to
stall and unstall.
So I agree that (as always) there are different
considerations and factors that just airflow alone when deciding how and where
to place your radiators. But, in my opinion, cooling
considerations is the first order of business in radiator placement - if it
doesn't cool adequately then all else is moot {:>).
Drag considerations is more dependent on
the air speed regime you will be operating at. A bit extra cooling drag on
a slow mover has less impact than on a Lancair or Canard type - so the amount of
effort in eliminating drag probably should be based on the amount of benefit
expected with the drag reduction on performance and/or
economy.
Again, just My 0.02
Ed
----- Original Message -----
Sent: Thursday, May 01, 2008 8:18
PM
Subject: [FlyRotary] Re: radiator
orientation?
You are correct, Mark,
Minimizing or eliminating laminar flow next to metal - in other words causing
the laminar flow in the boundary layer to become turbulence does promote heat
transfer. It also increase skin friction and drag. However, if the
turbulence gets to the point of causing air flow separation then that hurts
both cooling and the drag factor. So like most other things involving
aircraft - compromise is called for.
My cores are slanted - but, only because
I could not fit them in the space I had allocated for them any other
way. Otherwise they would be perpendicular to the air flow.
Clearly slanted cores do work and most of the time we install them in that
orientation due to space constraints or aesthetics as Pat Panzera indicated in
his response.
Paul Lipps has seen
great performance gains with his unique propeller design when bolted to his
Lancair 235 and the Phantom Biplane, both of which have very streamlined
cowls.
When he tried it on a
stock RV6, it seems that too much of the cowl frontal area blocked thrust from
the propeller.
It’s like if you had
a 60” diameter prop bolted to a 72” diameter radial engine.
If you are not
familiar with Paul, his plane or his prop, here’s an electronic copy of an
issue CONTACT! Magazine that has the information.
http://www.contactmagazine.com/Issue79/Issue79.pdf
Pat
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