enginehistory.org

[jjuutinen]

I just reread some parts of Graham´s book on the subject and I couldn´t help thinking that air cooling was not the way to do it for high (say 3000+ hp) engines as it seems that many of the problems centered on overheating on one hand and shock cooling on the other.

I also wonder why were US makers so reluctant to adopt automatic engine controls for their large piston engines while being happy to adopt them for jets? The presence of automatic single lever controls would probably have helped to avoid "abusive" engine conditions.

Regarding abuse, I remember reading in a British article on the Airspeed Ambassador that its Centauruses didn´t detonate even when the prop lever was pulled back at full throttle. So reminisced a former Ambassador pilot.

[jstpierre]

[gwhite]

Air cooling was the way to go for commercial applications. If you look at the QEC for, say, a Northstar it’s amazing that this complex system was kept maintained. For military applications where costs are of a secondary consideration we get into the age old argument of air cooled vs. liquid cooled. This one will never be resolved. US air lines figured that a competent flight engineer could do just as good a job as automatic controls based on the less complex systems, less to maintain etc., a flight engineer was a better bet.

[jjuutinen]

I really don´t buy the liquid cooled complexity issue. After all, if it was so severe, roadsides would be lined with automobiles with cooling failures.

Plus that the comparison between the Merlin and e.g. the R-2800 isn´t fair at all. Better compairison could have been with e.g. a civilian Griffon.

As for costs, much depends on fuel costs. If fuel is cheap, you can have inefficient (=air cooled) engines.

[jrussell]

If liquid cooled engines are so superior, why are all the successful, high horsepower ( 3000+ hp) engines air cooled? Also, did any high performance liquid cooled engines ever equal the s.f.c of the turbo compound 3350 ? Admittedly, a very touchy engine.
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It runs best just before it blows!

[jjuutinen]

Yes, the turbo-compound V-1710 did beat its sfc. If non turbo compound models are compared, all high performance liquid cooled engines beat their air cooled companions at hgigh power settings. E.g. at non-ADI combat power the R-2800 has some 30% higher sfc than the comparable Merlin power setting. And, by the way, the old Napier Lion beat the TC18 as well.

If German engines DB 605, Jumo 211J, Jumo 213 and BMW 801 are compared (all 4 have direct fuel injection), the 3 first (liquid cooled) achieve better sfc at all settings, the advantage increasing with higher power settings. In general, it is clear that Germans were concentrating on liquid cooled engines (Jumo 213, DB 603, Jumo 222) in the high power piston engine sector by the end of the war.

As for the first question: with luck. Most of the most experienced makers of liquid cooled engines were in Europe. German makers were for obvious reasons out of the post war market and the best 3 British candidates, the Sabre, the Nomad and the sleeve valve Eagle, didn´t enjoy the financial position the R-3350 and R-4360 development had. To use the civilian Merlins as examples on the "complexity" of liquid cooling is dishonest for no American radial engine was so purely tailored for fighting aircraft.

[wallan]

Most automotive engines are watercooled as it is easier to control emissions & fuel economy. Plus, aircooled engines rely too much on overfueling to help cooling. The fact that almost all watercooled engines have a sealed pressurised coolant system, and the vast improvement in polymer products, (hoses in particular) means that there are much fewer failures.

[rinkol]

During the late 1930s, the permissible operating temperatures of liguid cooled engines were increased by two measures: the use of ethylene glycol based coolants, and the pressurization of the cooling system. The latter is particularly important in high performance aircraft applications since the coolant boiling point would otherwise decrease significantly at high altitudes.

Important differences between aircraft and automotive applications is that the allowable pressure differential with outside air would have to be higher for the former case due to the need to operate at higher altitudes and also the need to minimize the cooling capacity to save weight and drag. When ethylene glycol coolant was introduced, there were many problems with leaks due to corrosion and the mechanical properties of the coolant. While these were addressed through improvements in the design of cylinder joints and other components, the liquid cooled aircraft engines still required considerably more maintenance than their air cooled counterparts. This was one reason for the US Navy, and for the most part, the Japanese Navy, abandoning liquid cooling at an early stage.

One of the differences between the F/J and earlier versions of the Junkers Jumo 211 was supposed to be a pressurized cooling system.

I'm not sure of the time where automotive coolant systems became pressurized. I do recall examining engine installations in late 1940s Fords and marvelling at the seemingly immense size of the radiator. While this might have been necessitated by the inefficiencies associated with the side valve layout, I suspect it had something to do with the absence of pressurization or conservatism wrt the allowable pressurization level.

Robert

[jjuutinen]

I am aware of this. Though I am still unconvinced by the maintenance increase being DECISIVE. After all, I will eat my hat if someone can prove that e.g. the two-stage variants of the R-2800 had significantly lower maintenance requirements than the two stage Griffons in everyday squadron service.

[szielinski]

There is also more flexibility with air cooling in aviation installations, as the velocity of the air is much higher than in an automotive situation - which may be a factor in the near universal adoption of liquid cooling in that application.
(would be funny, though, can you imagine being in gridlock and all these cars have gills opening and venting hot air - maybe an extension of the driver's frustration )
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“Make everything as simple as possible - but not simpler” – Einstein.

[rwahlgren]