Quote:
Originally Posted by Kurfürst
Compared to that theory, German DB 601 was same size as weight as single stage Merlin, 605 actually lighter then two staged Merlin, while the French 35-liter class Hispano Suize V12s were considerably lighter than both.
The only practical way a smaller displacement engine can keep up with larger ones is by heavy supercharging, but that does not comes free, superchargers and their systems add weight, and so does decreasing fuel effiency: more fuel need to be carried for same range.
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Actually, if you do the thermodynamic analysis, you'll tend to find that supercharging doesn't particularly damage fuel efficiency, provided that you have reasonable component efficiencies and make a fair comparison (which is the difficult bit).
Power:weight at sea level will tend to be fairly insensitive to supercharge because the supercharged engine sees higher pressures and therefore has to be heavier, whilst OTOH the unsupercharged engine is bigger. So you end up with a small area of thick metal vs a large area of thick metal.
The supercharged engine has a higher power density, and this will tend to make life harder for the cooling system.
If you compare at fixed cruising speed, there will be an optimum degree of supercharge, beyond which you'll lose more from the increased cooling problems than you've gained from the smaller engine. OTOH, because the supercharged engine is smaller, it has less non-cooling drag, and so you'd expect to cruise faster, which helps to make the radiator smaller.
In the end, the trade space is complex, and it isn't especially easy to make a general case that one approach to engine design is better than another. Hence the diversity of engine designs; if there was a trivial optimum then engine designers would have swiftly converged upon it, and the world would be a much less interesting place.