rv6ejguy said:
As someone who has actually done this and know of others who also have, I'd have to disagree with you on the basic point above. As we incorporate proven concepts from WWII liquid cooled aircraft and combine this with modern aluminum heat exchanger design, it is clear that the cooling drag penalty compared to air cooled engines approaches parity when done properly.
You are correct in saying that proper diffuser/ duct shape and length is critical to achieving this and that cowling mounted radiator designs are unlikely to offer effective low drag performance due to packaging and short lengths.
Belly or wing mounted rads with exit airflow control on tractor aircraft offer the best solutions and we are fitting these now to new aircraft under construction. Reg Clarke has been flying these setups for years now with excellent results.
Actually, I think we're on the same page...
As you state on your website:
"....I believe that even with a properly designed diverging, converging duct containing the heat exchangers, that the liquid cooled engine probably cannot achieve cooling drag numbers similar or superior to an air cooled installation. Others may not agree, but I don't see any of the liquid cooled RVs exceeding the Lycoming powered RV speeds at lower altitudes with similar installed hp."
I'm not clear where you disagree with my comments in responding to Mickey Coggin's suggestion that "cooling issues are no more difficult to solve than with a lycoming". I was referring to the level of effort involved, especially in reaching parity with air-cooled re cooling/speed/hp. Your excellent efforts to properly cool your RV6A seem to concur.
The complexity, weight, engineering investment, etc etc all contribute to the basis of my comments re difficulty in matching air-cooled numbers. CAN it be done? Probably. Will it be easy? No.
Most of my efforts have been with turbo intercooled liquid pusher installations for military UAV platforms, but there's a tractor setup being tested in the RV performance envelope, namely 200hp/200mph. As expected, the belly rad has demonstrated best cooling/drag/weight combination so far.
As you say, belly scoops/rad is the best solution per P51, WWII, etc. To the best of my knowledge, no one has yet incorporated a belly rad solution in an RV. I'd love to see it done b/c I think this is the best answer for Subie cooling/drag problems.
Ironically, I fly a Lyclone-a-saur. No time for building my own wet pylon racer (yet!).