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#34
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On Tue, 15 Jul 2003 11:54:37 -0600, "Bill Daniels"
wrote: Another area where I would like to see some experimental data is the "Radiator Ramjet" (just to pick a controversial term) where the radiator is in a tube and the heated air exits the rear of the tube at a higher velocity than the cool air entering the front of the tube, theoretically producing a small amount of thrust that offsets the drag of the radiator. Bill Daniels "Jay" wrote in message . com... Hi Bill, You don't need experiental data for this Bill, you just described the P-51 Mustang cooling system. However, even with three heat exchangers putting out heat into the exhaust air and a 1400 horsepower engine producing the heat, the Mustang never actually managed to get a net thrust out of the system. In addition, the point where the cooling system was ***ALMOST*** equalling drag was a very specific speed and altitude. I forget the exact height but it was above 20,000 feet and the speed was over 300 mph. Only under those circumstances did the power being generated and the speed being flown produce the necessary heat to accelerate the exhaust air flow to nearly cancel out cooling drag. By the way, most of the cooling systems did this to some fashion, but the Mustang was the first to actually design the cooling system to really benefit from it. This concept was researched and written up by a British aerodynamicist by the name of Meridith, and the produced thrust became known as the "Meridith Effect". North American designed the Mustang's system using the best aerodynamicists available at the time and with virtually unlimited resources to manufacture the kind of heat exchangers that would work in this environment. By the end of WWII, almost all research into liquid cooled systems came to a halt as jet powered aircraft became the future for military aircraft. I'm not an aerodynamics engineer, just a home builder. But my impression is that most relatively slow homebuilt or GA airplanes do not produce the heat needed to really accelerate the exhaust flow to make much out of the Meridith Effect. After all, we're always leaning out and cruising at reduced power settings. We have big wings, for the most part, and a lot of drag. Something really slippery like a Long EZ or Vari EZ or Glassair or Lancair might be fast enough to benefit, but getting the cooling system designed and fitted within the tiny wetted area of the fuselage might be nearly impossible. From my personal point of view, it's far more important to make sure the cooling system does the job all day and every day and on the ground too than to agonize over a few mph, real or imaginary. Corky Scott |
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