Glider
Captain
The Merlin maxed out at around 2,200hp but I do agree that with modern metals, fuels and management systems a reliable 3,000hp is more than possible.
If a WWII fighter engine were produced with today's technology, what would we get?
- Thread starter CobberKane
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wuzak
Captain
RM.17SM - 2620hp @ 3150rpm, +36psi boost, ADI, special fuel.
2380hp @ 3300rpm, +30psi boost in an accidental 15 minute run.
Eventually rated for 2200hp. It certainly shows that more was possible, especially if it was allowed to rev more.
MikeGazdik
Senior Airman
Maybe it was an Allison??? Could of swore I saw roller lifters or rockers????? puzzled.
Glider
Captain
We tend to look at the power but I would expect the engine to weigh a lot less than the originals. Modern engines rev at extrordinary speeds compared to the engines of old plus the adjustable valve technology and electronic systems allow for considerable improvements in performance.
Shortround6
Major General
Something to consider is that NOT all automotive engine technology could or would be transferred.
You do want to keep the aircraft engine as simple as possible.
Aircraft engines have one MAJOR difference from car and motorcycle engines.
There is/are NO artificial constraints on the engine size/displacement.
1. There are no taxes based on the size of the engine at time of purchase or on an annual basis.
2. There are no licencing or user restrictions based on engines size.
3. There are no 'racing' rules that limit displacement to certain sizes.
Aircraft engines are pretty much limited by two things.
1. Cost to manufacture/overhaul.
2. Power to weight ratio.
A large but light, slow revving engine may be preferable to a small but heavy 'buzz-bomb' engine.
Especially at overhaul time
You do want to keep the aircraft engine as simple as possible.
Aircraft engines have one MAJOR difference from car and motorcycle engines.
There is/are NO artificial constraints on the engine size/displacement.
1. There are no taxes based on the size of the engine at time of purchase or on an annual basis.
2. There are no licencing or user restrictions based on engines size.
3. There are no 'racing' rules that limit displacement to certain sizes.
Aircraft engines are pretty much limited by two things.
1. Cost to manufacture/overhaul.
2. Power to weight ratio.
A large but light, slow revving engine may be preferable to a small but heavy 'buzz-bomb' engine.
Especially at overhaul time
wuzak
Captain
Allison does have rollers. Not sure about lifters - Greg could help with the answer to that.
GregP
Major
The Allison has roller rockers and no lifters. The springs do it for lift and the pivoting clearance adjusters sit on top of the valve stem. The 12-counterweight crankshaft will handle 3600 rpm (cleared) and 4000 rpm (design speed). The tractor pullers Joe builds Allisons for in Europe today turn it at 4500 rpm and haven't broken an engine in years.
The 4-rotor wankel in the Mazda finished well down in the season, 9th and 10th in your post, so I discount it pretty much as generally not successful. A LOT of development and 1 major win (forgot about that one at Le Mans) is not a great advertisement for the engine in an aerial application. If the engine fails on an automotive race track, you can pull over and park. In an aircraft it is a life-threatening event, espccially in a military fighter aircraft which have never been noted as good gliders.
The 4-rotor wankel in the Mazda finished well down in the season, 9th and 10th in your post, so I discount it pretty much as generally not successful. A LOT of development and 1 major win (forgot about that one at Le Mans) is not a great advertisement for the engine in an aerial application. If the engine fails on an automotive race track, you can pull over and park. In an aircraft it is a life-threatening event, espccially in a military fighter aircraft which have never been noted as good gliders.
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Nice one Shortround. Interesting that horizontally opposed engines in light aircraft are little more complex than they were when they first came out. A true example of the saying If it ain't broke, don't fix it, if ever there was one. Greg, thanks for the explanation, I'd love to go to Reno one day!
- Thread starter
- #69
CobberKane
Banned
- 706
- Apr 4, 2012
You have to hand it to the reciprocating piston engine, it's seen off all alternatives over the years, including the rotary. Inevitably something will come along and knock it off it's perch but there doesn't seem any sign of it yet
Shortround6
Major General
Flat six air-cooled engines went through an interesting period back in the 1950s. Lycoming got a number of their engines up to 3400rpm using an 0.64:1 reduction gear (2176 prop rpm?) and put mechanical superchargers on the two biggest.
The six cylinder GSO-480 (480 cu in) gave 340hp max from sea level to 8,000ft at 3400rpm using 9lb of boost and could 'cruise' giving 240hp at 11,500ft at and weighed 498lbs.
The eight cylinder GSO-580 (580 cu in) gave 380hp max at sea level at 3300rpm using 5.8lb of boost and weighed 610lbs.
they were replaced by engines using larger cylinders.
The six cylinder IO-480 (540 cu in) gave 290hp max sea level at 2575rpm for 437lbs.
The eight cylinder IO-720 (720 cu in) gave 400hp max at sea level at 2650rpm and weighed 600lbs.
There were some more complicated geared and supercharged engines but most (all?) of them gave way to the gas turbine engines.
Something else to consider is the duty cycle. These aircraft engines were expected to cruise at 250-300hp for hours on end and last hundreds of hours between overhauls. the unsupercharged ungeared ones were supposed to go closer to 2000 hours than 1000 hours unless being used for crop duster duties.
Modern car and motorcycle engines spend an awful lot of their time at 20-30% of full power ( some powerful sport engines spend even less, how much power does a Porsche need to cruise at 60mph on the high way?) or how much power does a 1000cc motorcycle engine use to do the same thing?
Modern materials and modern technology can make a difference in aircraft engines, just don't expect quite the the same amount of improvement as car or motorcycle engines.
Also comparing unsupercharged engines to supercharged ones gets a little strange. Trying to design/build a modern Merlin to wind hundreds of RPM higher may work, especially now that you can't get the fuel it ran on but the old engines operated over a narrow rpm band ( 2 to 1?) and varied the amount of boost to vary the power (amount of air flowing through the engine). Modern unsupercharged engines operate at a near constant "boost" (actually negative or a partial vacuum) and vary the rpm (5 to 1 or even 10 to 1) to vary the power (amount of air flowing through the engine).
The six cylinder GSO-480 (480 cu in) gave 340hp max from sea level to 8,000ft at 3400rpm using 9lb of boost and could 'cruise' giving 240hp at 11,500ft at and weighed 498lbs.
The eight cylinder GSO-580 (580 cu in) gave 380hp max at sea level at 3300rpm using 5.8lb of boost and weighed 610lbs.
they were replaced by engines using larger cylinders.
The six cylinder IO-480 (540 cu in) gave 290hp max sea level at 2575rpm for 437lbs.
The eight cylinder IO-720 (720 cu in) gave 400hp max at sea level at 2650rpm and weighed 600lbs.
There were some more complicated geared and supercharged engines but most (all?) of them gave way to the gas turbine engines.
Something else to consider is the duty cycle. These aircraft engines were expected to cruise at 250-300hp for hours on end and last hundreds of hours between overhauls. the unsupercharged ungeared ones were supposed to go closer to 2000 hours than 1000 hours unless being used for crop duster duties.
Modern car and motorcycle engines spend an awful lot of their time at 20-30% of full power ( some powerful sport engines spend even less, how much power does a Porsche need to cruise at 60mph on the high way?) or how much power does a 1000cc motorcycle engine use to do the same thing?
Modern materials and modern technology can make a difference in aircraft engines, just don't expect quite the the same amount of improvement as car or motorcycle engines.
Also comparing unsupercharged engines to supercharged ones gets a little strange. Trying to design/build a modern Merlin to wind hundreds of RPM higher may work, especially now that you can't get the fuel it ran on but the old engines operated over a narrow rpm band ( 2 to 1?) and varied the amount of boost to vary the power (amount of air flowing through the engine). Modern unsupercharged engines operate at a near constant "boost" (actually negative or a partial vacuum) and vary the rpm (5 to 1 or even 10 to 1) to vary the power (amount of air flowing through the engine).
Modern aircraft engines still operate at a near constant RPM (or a very narrow band) and vary the manifold pressure (boost) to vary power.
E.G. you may take-off at max throttle and RPM (29" MP, and 2800 RPM)
Climb at max continuous (25" MP and 2500 RPM)
Cruise (23" MP and 2400 RPM)
Approach (15" MP and 2400 RPM)
Of course, if you're talking car/motorcycle engines, then you can't vary one without altering the other.
OldSkeptic
Senior Airman
- 509
- May 17, 2010
Beat me to it. Type approved for production as well..
2,400bhp+ for the RM17SM was quite possible for production, even more. With modern technology, particularly modern oils, 2,600-2,800 (with water injection) should be possible.
The 'forgotten factor' oils, what they could have done with our high temp multigrade oils. At the time it was a major limiting factor in performance, particularly continuous performance.
Apart from that maybe a little (for the Merlin) more revs. But that is a piston speed and flame propagation limit. And really we can't improve much on the materials they used at the time. Heck they still use some of the RR alloys today in areas like Formula 1.
Computerised control systems could have optimised performance, particularly things like cruise economy, perhaps even short burst maximum power by super over riching (as per the C3 system used by the Germans).
Things like variable vane super/turbo chargers (actually trialled by the Germans from memory) could have helped, especially with the computerised control systems. Not sure you'd be able to get much more maximum power, but you could get better power/economy at cruise speed.
So overall I'm not sure, at least for operational purposes (Reno racers don't count) you could get a lot more power, a not insignificant bit more of course, but my gut feel that the real winners would be in areas like cruise efficiency.
swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
One can see a hint how modern fighter piston engines could go by looking at something like NASA's GAP program in the early 1980s, where the concentration went pretty quickly to highly supercharged two-stroke diesels with no mechanical driven scavenge pump. Another hint would be the Napier Nomad.
Two-stroke diesels with the required power density are just not possible. They suffer from a number of problems that are insurmountable. Proper lubrication and side port erosion are the two I recall. In any event you can actually equal the power density of a two stroke with a good turbocharged four stroke. This is something EMD has discovered the hard.
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
Ayuh
Shortround6
Major General
Diesels may be the only route as such concoctions as 108/135 and 115/145 are thing of the past for a number of reasons, two of which are cost and safety in handling. OSHA would have conniptions if anyone tried to introduce those old fuels again with some of their toxic components.
GrauGeist
Generalfeldmarschall zur Luftschiff Abteilung
Not to mention the fact that diesel fuel congeals at higher altitudes...
Shortround6
Major General
Could try running the diesels on jet fuel.
Edit> I would note the Germans flew diesel powered aircraft at 40,000ft or above during WW II so it doesn't seem that diesel fuel congealing is an insurmountable problem.
Edit> I would note the Germans flew diesel powered aircraft at 40,000ft or above during WW II so it doesn't seem that diesel fuel congealing is an insurmountable problem.
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swampyankee
Chief Master Sergeant
- 3,954
- Jun 25, 2013
...and the whole endemic neurological damage due to lead poisoning.
Shortround6
Major General
I am not sure that some of the aromatic compounds were any less dangerous (Benzine?) , not to say there aren't some carcinogenic compounds in diesel exhaust.
The high octane/performance number fuels of the last part of WW II and during the 40s and 50s required a disproportionate amount of crude oil/base stock. You got much fewer gallons of high performance fuel per barrel of crude oil/base stock than for lower grades of fuel. They also required much more elaborate refinery set-ups and often large quantities of materials from the chemical industry.
The high octane/performance number fuels of the last part of WW II and during the 40s and 50s required a disproportionate amount of crude oil/base stock. You got much fewer gallons of high performance fuel per barrel of crude oil/base stock than for lower grades of fuel. They also required much more elaborate refinery set-ups and often large quantities of materials from the chemical industry.
