Now and then, we get a little
gold nugget of information that is easy to understand and useful, like the one
below. Thanks for sharing.
Bob Rogers
(building a Mustang II with a Mazda 13B
turbo)
-----Original Message-----
From: Rotary motors in aircraft
[mailto:flyrotary@lancaironline.net] On
Behalf Of Shearbond@aol.com
Sent: Monday, April 04, 2005 9:49
AM
To: Rotary motors in aircraft
Subject: [FlyRotary] Cooling Inlet
Areas/Bernie's RV9
From my
work on Compact Heat Exchangers especially as related to my friend's 13B
powered RV-3, Bernie has plenty of heat exchanger "frontal area"
and "volume".
That
said, there are two further considerations in the "gotta have"
category to be able to confidently taxi out and T/O WOT for as long as one
wants in Military Air (+40 deg F over std.) conditions.
First....if
cooling air can't get out, it can't get in. That is: adequate air exit
area is absolute. The exit area must be sufficient for both coolant and
oil cooling exit air. For 200 HP that is about 2.1(oil + coolant
+ now heated air) x .30 x HP or 2.1 x .30 x 200 = 126 sq. in.
total for 200 HP.
Yes,
that is larger than an air cooled engine would require but investigate the
temperature differentials between a 350 deg F air cooled cylinder and a 200 deg
F hot coolant and one will quickly realize that there must be more lbs. of air
flow for a coolant cooled engine.
Second,
even if cooling can get out, if it can't get in, it can't be there to cool
the heat exchangers. Rule of thumb: 0.3 sq. in. of cowling inlet air
opening per HP. 200 HP x .3 = 60 sq. in. Note: This assumes a
reasonably shaped inlet cowl which has been discussed online often. IMHO:
Berni's plane inlet shape and inlet cowl is fine, but I question his
inlet opening area.
Note:
the exhaust area requirement is greater than the inlet combination of oil
and coolant due to the now considerable hotter air temperature. Rule of
thumb: Coolant air inlet opening for 200 HP coolant cooled engine ~60 sq.
in., oil inlet opening ~30 sq. in. equals a total opening of 90 sq. in. A
good place to start with exhaust opening is 1.4 times the inlets or 126 sq.
in. Close the exit area down with cowl flaps to as little as 80% of the
inlet combination at cruise conditions!
Don't
mean to start another stream of threads on an old subject, but we sweated over
this one for 3 months and 3 systems and one might save a lot of time by
comparing ones system to these simple "works great" rules of thumb
which are the result of LOTS of technical and experimental work.
N6415Q
and RV7 in process