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Message
Hi Rusty,
K&W actually has a section
on the analysis of the cooling component of drag. I have skimmed over that
section and would need to go back to it to get a feel for what percentage of the
total drag it might be for an Rv. The sleeker and faster your design (i.e.
the lower the external drag factor) then the higher % of the total the cooling
drag becomes. So more important for the 200MPH+ crowd than say the 120 MPH
and below crowd.
I know there are some fairly reliable
overall estimates of the drag of an RV (CAFE reports and others), so if an
reasonably estimate of cooling drag could be calculated then we could sort of
determine how much cooling drag is or is not affecting your overall
performance.
Your radiator cooling capacity would
certainly appear to be more than you need given your low coolant temps (assuming
they are close to the money) with your current set up. But, the 2.85 and
higher rpm producing more power will eat up some of that.
On an average comparing the RPM Tracy gets with the
2.85, I would say you will turn approx 1000 rpm more than the 2.17 that would
mean in increase of approx 20% more BTU you will need to get rid of. Of
course with the faster acceleration and climb rate you could have more cooling
air - or the "overcapacity" in cooling would permit you to climb at a slower
airspeed and steeper angle. So I wouldn't change anything -
yet.
Ed
Ed Anderson
RV-6A N494BW Rotary Powered
Matthews, NC
----- Original Message -----
Sent: Wednesday, July 14, 2004 8:42
PM
Subject: [FlyRotary] Re: New Scoop
If you design and tailored your cooling system for cooling in
a steep climb on a hot day, you will have excessive cooling capacity at cruise
(read - more cooling drag) than is necessary.
Hey Ed,
I agree of course that
you would have more cooling drag, but do you have any idea what the drag
penalty would be for an RV style plane?
I personally want to be
able to climb at 100 kts, full throttle, on the hottest day, without
ever exceeding any temps. At the moment, I can, but the C drive and
new prop may change things some. I seem to have more
excess water cooling, than oil cooling, and eventually, I may have
to close up part of the radiator inlets.
FWIW, the other day it
was 92 degrees on the ground, and I climbed at 100 kts to 8k
ft, full throttle. The max oil temp was 195, and the max water
was 178. At 8000 ft, full throttle, temps settled in to be 183
for oil, and 130 for water. That was at 196 mph TAS, with plenty of
fairing work left to be done. As for climb performance,
I noticed that the EM-2 flight timer was on 7 minutes when I leveled out
at 8k ft. That's OK for now, but I expect to see that time to 8k ft be
less than 4 min with the C drive.
Rusty (just got home
with a motorcycle, more like a training
bike)
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