Best/Worst Allied Piston Aircraft Engines 39-45

[Kevin Renner]

We've had the Bomber Threads and now the Fighter Thread. But lets face it. All of them are hanger queens with out the complex assembly of castings and forgings up front converting high octane gas into horsepower.

Best Allied Fighter

A three way tie.

First the Rolls Royce Merlin. Its birth as the Kestral was actually a British response to the Best Cast Block water cooled inline of the 20s The Wright D-5. The Merlin saw continueing advances in HP and TBO throughout its service.

Second the Pratt & Whitney R2800. Perfect out of the box it set the stage for the greatest piston engine of all time the R4360. It was the engine that proved that a high speed fighter did not have to have an inline V-12 up front but could have a radial instead and not give away anything.

Third the Rolls Royce Griffon. When the Merlin was getting towards the end of its development string R-R went back and dusted off the R-types bore and stroke and built an engine to fit into any aiframe that could take the Merlin

Worst Allied Fighter

The Allison simply because it never really lived up to its potential. Early on the USAAC decided that turbo-supercharging was the way to go. But shortages of the alloying elements for the exhaust side turbines caused far too many Allison's to be built with poorly engineered gear driven superchargers. Or none at all.

The Rolls Royce Eagle. A power plant that never saw service during the war it robbed the British Air Ministry of the skills and time that could be used on other projects

Best Allied Multi Engine Applications

Once again the Merlin. Its insertion into the Avro Manchester when the Vulture was a failure produced agruably the best bomber of the war

Second the Wright R1820 that went into the B-17

Worst Allied Multi Engine Application

This will cause some hard feelings amongst some but any of the sleeve valve engines. As wonderfully suited they may of been for multi engined transports due to their lower specific cnsumption in transport application or long range ocaen recon they have a major drawback IMO. Their manufacturing is excessively complex and expensive for military aircraft seeing combat. This cost in terms of the number of poppet valve engines that could be built for the same cost and manhours is something that most nations can not afford in a wartime situation.

 

[rip89]

One winner - merlin powerd the following Spitfire, Hurricane, Mosquito, Lancaster, Hornets and Mustangs to name the great planes, also whitleys, early halifaxes some wellingtons and some Beaufighters to name good solid planes, also the battle, defiants and fulmars, but that wasn't the engines fault. Stayed in production throughout the war.

Worst hmm The RR Vulture blew up and caught fire, just what you want in an engine.

 

[Riain]

I think it's a bit rough to call the Napier Sabre a crappy engine when RR robbed it of the support it needed in its early years yet it still was pushing out 2200hp in 1941 and 3000hp (5000 in the bench) in 1945. The Bristol Hercules and Centaurus were also top-notch engines with sleeve valves, I'm a big fan, after all the Centaurus drove the Sea Fury to victory over Mig 15s in Korea.

 

[Kevin Renner]

Oh, I don't think the Sabre was a crappy engine at all. Its just that sleeve valve engines by their very nature are more expensive and time consuming to produce. Each cylinder has three different fits to contend with. Piston to Sleeve, Sleeve to Cylinder and Sleeve to Junk Head. Plus the gear train needed to run the eccentric cranks that operate the sleeves. For a transport A/C that needs to operate as efficently as possible the sleeve valve makes sense*. For a military A/C that frankly may be lost any time it goes on a mission it doesn't make sense at all. If the sleeve valve H-24s were such a good idea why did Pratt & Whitney drop them when the Air Corps gave them the chance. And P&W had their two H-24s running on test before Napier's Sabre. The X-1800 was giving 2000HP and the H-3130 was giving 2650HP. And just what is the point of them when you have the R2800 already giving 2000HP and the R4360 in development. Plus the R2800 was much more readily produced by other manufacturers (the same is true of any radial poppet valve engine). Just who produced sleeve valve engines for the RAF besides Bristol and Napier?

* Actually in the transport field the Diesel makes even more sense. But then look at Napiers attempt at that. The Nomad. And when that didn't work out they built the Deltic for rail use. Complexity for its own sake is not a virtue

 

[Riain]

I think sleeve valves get a bad rap, people focus on their few negatives rather than their many positives. I think the complexity argument is a bit of a dud, an 18 cylinder sleeve valve, multi-stage supercharged fighter engine isn't that much more complex that it's poppet valve counterpart but is more compact and inherently more powerful for it's size and displacement. What's more we're talking about military aircraft here, what about them isn't complex, and since when would commanders give up the chance of tactical superiority because the engine which would obtain it is complex? Politicans and commanders just tell the techos to stop bitching and fix the complex but high performance part.

As for who produced them, well RR V12s didn't need sleeve valves because they already had compact and efficient 4 valve heads, and it was the widespread adoption of multivalve heads which killed the sleeve valve. However radial engines were generally built with 2 valve hemi heads, and against these the sleeve valve wins easily in terms of volumetric efficiency.

A POD for sleeve valve aero engines to be recognised as supreme could be having the FAA handed back from the RAF to the RN in 1923, instead of this proposal narrowly failing. Thus RN-FAA development closely mirrors OTL USN and IJN developments for the next 15 years, so that by 1939 the RN-FAA has numerous carriers each with 60-70 planes of the calibre of the Skua, Buffalo and Devastator but all fitted state-of-the-art sleeve valve radial engines. Such planes and their inevitable successors in turn could achieve much more than the OTL FAA and give credibility to sleeve valve engines that is lacking today.