this is the nub of it:-
It is the purpose of the report to show that, by correct design of low velocity cooling systems, in which the surface (whether in the form of honeycomb radiator or of fins on the cylinder heads and barrels) is exposed in an internal duct, the power expended on cooling does not increase with the speed of flight, but that, on the contrary, it should diminish to vanishing point at a practicable speed beyond which the cooling system contributes to the propulsionMake a duct that slowed the air down a lot before adding the heat (large radiator area after a divergent duct)
Vary the exhaust area of the duct with flight speed and power setting, (in a similar way to the afterburner nozzles of a military gas-turbine engine, which is also adding heat to a compressed air stream).
Slow airflow (compression in divergent duct)
Add heat (radiator core)
Accelerate airflow (convergent duct, unless choked M=1)
Later large air-cooled radials also used this principal, although Meredith at RAE first proposed it, North Amercan are thought to be the first to deliberately engineer it into an aircraft, or fully integrate it from initial design. Whether de Havilland fully appreciated what their l.e. Mosquito radiators were doing is a moot point but the early Spits were definitely throwing performance away with their coolers - lots of it.
NB. Heat from cooling water, oil and intercoolers was being used... the exhaust gas energy was something else that Meredith worked on. What level F1 cars derive benefit today I don't know, but they sure know about all this, as they're in a similar power category.
Out of interest, one of RR's last piston engine projects (only 7 years work, never put in an aircraft!), was the Crecy, a turbocharged 90 degree V12 sleeve-valved 2-stroke of about the same capacity as a Merlin (27 litres, e.g. small in warbird aero-engine terms).
Although rated at about 3,000 bhp, it was run up to over 5,000 BHP reliably for hours on end - and at that speed (3,000 rpm +), being a 2-stroke, produced over 600 impulses/second to the turbochargers, each from a 2.2 litre cylinder - plenty enough for boost and bypass waste-gating to produce jet-thrust. It was very light too , maybe the ultimate piston aero-engine -certainly some think so!
[ Edited on 9-1-2006 by HarryMann ]