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.
Doug Dempsey
N6415Q and RV7 in process
Colorado, USA