Originally Posted by
megan
The following is what Ed Schmued had to say re the radiator design
Thanks for that, Megan - an interesting piece. I would only take issue with one part (which I'm sure was an unintended "mispeaking" at the time because Ed Schmued definitely know what he was talking about!), where he says:
The distribution of power is approximately as follows: 100 percent energy in fuel is put into the engine, but about 30 percent of this has to be radiated into the air to cool the engine. Another 30 percent of the energy is lost in the exhaust heat of the engine. Then 25 percent is usually used on the propeller. This amount of power drives the airplane, overcoming the drag, so 15 percent of the fuel energy is lost in mechanical friction.
The energy dissipated in friction will of course be converted into heat which is included in the "30% radiated into the air" that he mentions - it can't be a separate element in this sum. I don't doubt his figure for the overall thermal efficiency (25%), but I would add the frictional losses and cylinder cooling losses together to get a ballpark number for the radiator sizing. So if it's a 1,000bhp engine I would expect the radiator and oil cooler to have to dissipate a large chunk of the 1,800bhp (~1.3MW) of heat dumped to the engine casing. Somewhere I have a piece in one of Ricardo's books which suggests that for watercooled engines like the Merlin and Sabre over half the thermal energy dissipated through the engine casing comes out as radiated heat (he was suggesting this is the only reason that aircooled engines didn't melt!), so I'd suggest that for a 1,000BHP engine the radiator and oil cooler would need to be able to dissipate at least 800BHP (~600kW) at full power - 80% of the nominal power dyno'd at the propshaft.
PDR