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 =3D 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 =3D 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