Dumb Questions. Engine RPM.

[davebender]

A WWII era Jumo 213 V12 engine ran at a maximum of 3,250 rpm. Modern day Formula 1 V8 engines run at 18,000 to 20,000 rpm.

How can a reciprocating engine turn that many RPMs without flying apart? What are the technical leaps which made the huge RPM increase possible while maintaining some reliability?

[Shortround6]

For one thing the modern engine uses a much shorter stroke which means the pistons are actually moving somewhat closer in actual speed. The Jumo had 165mm stroke while it is possible for a modern F1 engine to have a stroke as short as 40mm so 4 revolutions of the modern engine equal 1 of the old one.
Gas valve springs keep the valves from floating.

Nobody was using titanium connecting rods or other exotic alloys for stressed parts in WW II.

Better casting/forging techniques. different materials, better understanding of vibration patterns, gas flow theory, better bearings and better lubrication and just about every aspect of engine technology has changed. Sometimes in big leaps and in other areas or times slow grinds. It has been over 65 years since the Jumo 213 after all.

[davebender]

Makes me wonder what modern fighter engines would look like if jet and turbo-prop technology didn't exist. Would we have 10,000 hp piston engines? Or maybe a 10,000 hp Wankel engine?

[Mustang nut]

A WWII era Jumo 213 V12 engine ran at a maximum of 3,250 rpm. Modern day Formula 1 V8 engines run at 18,000 to 20,000 rpm.

How can a reciprocating engine turn that many RPMs without flying apart? What are the technical leaps which made the huge RPM increase possible while maintaining some reliability?

I think formula 1 engines are now restricted to 16,000 RPM as a cost saving measure the extra 2 to 4 thousand RPM cost the teams millions. Shortround covered most of the bases except fuel. When fuels wernt controlled in F1 the teams or their sponsors spent millions and it made a big difference to performance and the fuels used in WWII had a major bearing on performance.
Honda raced a 500 cc V4 which revved to 20,000 RPM oval pistons and 8 valves per cylinder. F1 probably showed what was possible in the days when Turbos were allowed 1.5 Litre engines (i think) producing around 1000 BHP, but since only a few cars finished the race in that era no one would ever put those engines in a plane.

It is quite easy to make something turn at 20000 RPM but getting it to produce power is another matter from my maths 20000 RPM is 166.7 explosions per second.

[Shortround6]

Makes me wonder what modern fighter engines would look like if jet and turbo-prop technology didn't exist. Would we have 10,000 hp piston engines? Or maybe a 10,000 hp Wankel engine?

Probably not. you need torque to turn the propeller and the gearing needed to turn a 16,000-20,000rpm crankshaft down to a 1500rpm or so propeller speed might eat of some of the weight savings. You also need the radiator or airflow to cool 10,000hp.
There are defiantly diminishing returns. you also need to be able to turn that power into thrust. See a C-130 for a prop that handles just under 5,000hp.

[davebender]

The turboprop powered Tu-95 has engines producing 14,800 shp each. Max speed is 575 mph. So why can't you have a prop driven fighter with a 14,800 shp piston engine?

[wuzak]

I think formula 1 engines are now restricted to 16,000 RPM as a cost saving measure the extra 2 to 4 thousand RPM cost the teams millions. Shortround covered most of the bases except fuel. When fuels wernt controlled in F1 the teams or their sponsors spent millions and it made a big difference to performance and the fuels used in WWII had a major bearing on performance.
Honda raced a 500 cc V4 which revved to 20,000 RPM oval pistons and 8 valves per cylinder. F1 probably showed what was possible in the days when Turbos were allowed 1.5 Litre engines (i think) producing around 1000 BHP, but since only a few cars finished the race in that era no one would ever put those engines in a plane.

It is quite easy to make something turn at 20000 RPM but getting it to produce power is another matter from my maths 20000 RPM is 166.7 explosions per second.

The current engines are V8s of 2.4l and restricted to 18k rpm. The V8 regs were introduced in 2006 to reduce power from the 3l V10s that had been powering F1 exclusively since 1999. In 2006 the engine rpm was unrestricted, and one or two engines could rev beyond 20k. The engine freeze was introduced for 2007, which meant no more searching for extra hp and extra rpm. IIRC the rpms were restricted to 19k then too, and reduced to 18k a couple of years later.

For the extra revs to be worthwhile a lot of work went into reducing friction.

The 1.5l turbo engines ran to 12k-15k rpm. For 2013 the engines have been specified as 4 cylinder turbo units with a limit of 12krpm (there is currently uncertainty over these rules as one engine manufacturer doesn't want them, two others think they are too expensive, leaving one totally in favour).

[Trilisser]

Well, one can. However, I cannot even comprehend that one could build a 10,000 hp (or 14,800 hp) piston aircraft engine that would have an acceptable life and power/weight ratio. You can have one of them, but not both. Unless it would be a coupled power plant, e.g. 4 x R-4360 geared to a common gearbox unit.

[Trilisser]

As for the F1 racing, the sport has gone downhilln ever since the 1.5 litre turbo engine were banned. IMHO the F1 racing is the king of motor car racing and should thus have minimum on design limitations. Personally the only engine design limits should be that that a standard race is completed with a certain amount of energy. In other words, all teams would be free to use any generally available fuel (ethanol, diesel oil, gasoline etc.) or any engine (piston/gas turbine) just as long as the fuel burned during a single race would not exceed in energy content a specified limit.

[Shortround6]

The turboprop powered Tu-95 has engines producing 14,800 shp each. Max speed is 575 mph. So why can't you have a prop driven fighter with a 14,800 shp piston engine?

I guess you could but after you stuff in the 14,000hp engine and the 18.4 ft diameter contra rotating prop to go with it you are going to have one very big, very heavy fighter plane. And it may only be 20-40mph faster than a plane with 1/3 the horsepower. The landing gear would certainly be a sight to see.

[davebender]

How about a tandem prop arrangement similiar to the Do-335? Use two smaller engines rather then a single monster engine. Such an arrangement is better for damage control as you can still limp home after an engine hit.

[wuzak]

How about a tandem prop arrangement similiar to the Do-335? Use two smaller engines rather then a single monster engine. Such an arrangement is better for damage control as you can still limp home after an engine hit.

You could use an arrangement similar to the Bristol Brabazon
http://www.flightglobal.com/imagearc...abazon-MK1.jpg

Or the Macchi MC.72
http://www.warbirdphotographs.com/St...i-MC72-13s.JPG

[wuzak]

Or like the Kawasaki Ki-64
Kawasaki Ki-64 - Wikipedia, the free encyclopedia

[davebender]

What are the advantages and disadvantages of these layouts?

[engguy]

A WWII era Jumo 213 V12 engine ran at a maximum of 3,250 rpm. Modern day Formula 1 V8 engines run at 18,000 to 20,000 rpm.

How can a reciprocating engine turn that many RPMs without flying apart? What are the technical leaps which made the huge RPM increase possible while maintaining some reliability?

Lightweight strong components for one, elimination of valve springs another as they most likely would be bouncing like crazy, so air replaced them. Electronic fuel management, and ignition control. And lots of thinking out of the box engineering too. Tribology helped too, as did aerodynamics for induction and exhaust. I'm sure many millions of dollars by all the various companys were used as well. As with any engineering endeavour there were probably some failures on the way, and some messes to clean in dyno rooms.