If a WWII fighter engine were produced with today's technology, what would we get?

[CobberKane]

It's easy to forget that the technology that produced the great aero-engines of WWII is seventy years in the past. On a power to capacity ratio the motorcycle in my carport makes a Rolls Royce Griffin look puny. So, forget the jet engine ever happened- if we designed an engine of the same dimensions as those used in the Spitfire, 109 or Thunderbolt with today's technology, how much power could we get? What would be the limiting factors? Where the hell is Lord Lucan? Answer these questions and eternal fame will be yours.

 

[wuzak]

Firstly, it is unfair to compare the specific power of a Griffon to that of a motorcycle because the power figures are measured differently. While a Griffon's rate combat/WEP is usually authorised for 5 minutes testing requires it be able to take that for longer. The Griffon also had to pass a type test, which required running at different loads for over 100 hours (UK type test was 114 hours, I think).

Secondly it is far easier to extract high specific powers from small cylinders.

Rolls-Royce's Stewart Tresilian proposed an X-16 engine of 10.3l (approx) with a maximum rpm of 7,500rpm. The supercharger would be taken directly from the Griffon, and would be the biggest part of the engine as seen from the end.

I should imagine that is the sort of thing we would see. It would be small, light and compact.

If you really require Griffon capacities then I would think an X-24 or H-24 using similar dimensions to the Sabre (Bore 5", stroke 4.75"), or an X-16 still with over square dimensions.

For an engine of Merlin capacity I would think an X-16 would do the job. If you really needed a V-12 of that capacity the bore would probably go to 6" and stroke to 5" (Merlin bore 5.4", stroke 6"; Griffon bore 6", stroke 6.6"). Rev capability would go up, and so would horsepower.

For a V-12 with short stroke and Griffon bore the power output would match historical Griffon power figures at a bare minimum.

 

[CobberKane]

My comarison of a Griffon to a modern motorcycle engine was flippant, to its also true that a motorcycle of the 1930s produced only a fraction of the power mine does. Let,s look at another way - if we were tasked with producing and engine today with similar output to the Griffon, what would it's configuration and capacity be with today's technology?

 

[Shortround6]

There were a few things going on that do not scale well.
No 1 is that the fuel/air mixture burns at the same speed regardless of the size cylinder it is in. WW II practice was to use fixed ignition timing with the goal of getting the the flame front to cross the cylinder ( fuel burn pretty much completed) when the piston was at a position that corresponded to being 20 degree past top dead center. This tended to limit the RPM that could be used or the cylinder size or both. Now we can use variable ignition timing (more advance) at higher rpm but that is only going to go so far. WW II engines were using dual ignition both for reliability and to get two flame fronts to complete the burn quicker. For PEAK power you can let the piston go lower in the cylinder before the fuel burn is complete but that doesn't help fuel economy much

As Wuzak has said it is easier to get power from smaller cylinders, one reason is cooling, if you double the bore of a cylinder you have increase the displacement (and the amount of fuel burned ) by four but only increased the area of the cylinder wall by 2. Granted the cylinder head has grown but you are trying to get rid of more heat per unit of wall/head area. You have also increased the distance heat must travel from the center of the piston to the cylinder walls. Yes we have better materials.

As Wuzak has already said, those engines were TYPE tested which means that they were deliberately run at less than full possible power in the interest of both longevity and reliability. The US standard for WER was the test engine engine had to survive 7.5 hours at the WER rating in 5 minute bursts. How well could you motorcycle engine stand up to NINETY full throttle (held at peak power) 5 minute hill climbs without a teardown? A few of those engine were pushed to considerably higher power levels in testing in test houses ( a large airplane engine coming apart at high speed is a pretty catastrophic event and it is best to have concrete walls between the engine and any operators).

 

[Airframes]

Are we discounting turbo-prop? If not, then the possibilities are huge.

 

[wuzak]

Are we discounting turbo-prop? If not, then the possibilities are huge.

When the OP suggested no jets I think he probably meant no turbines - jets, turboprops/turboshafts.

 

[Airframes]

Shame - there could be some interesting thoughts there.

 

[dobbie]

It's easy to forget that the technology that produced the great aero-engines of WWII is seventy years in the past. On a power to capacity ratio the motorcycle in my carport makes a Rolls Royce Griffin look puny. So, forget the jet engine ever happened- if we designed an engine of the same dimensions as those used in the Spitfire, 109 or Thunderbolt with today's technology, how much power could we get? What would be the limiting factors? Where the hell is Lord Lucan? Answer these questions and eternal fame will be yours.

Nothing really wrong with the WWII designs per se-they are sound designs even for today. The increased capability would be mostly centered around the use of better/lighter/stronger alloys which would allow higher continuous RPMs from lower rotating mass, computer controlled ignition and direct injection systems and much improved supercharging.

 

[yulzari]

Perhaps a closer guide to the use of modern materials and technology is the Formula 1 engine. Simplisticly put, in @1970 it produced 400 bhp at 10k rpm. 40 years later it could put out 950 bhp at 20k rpm (rpm was then limited by the rules.).

This suggests that new materials and ignition control only increased the power from 13.33 bhp per litre per 1k rpm to 15.83 per litre per 1k rpm or barely 19%. The bulk of the total power increase came from the increase in rpm. As the late Keith Duckworth used to say; horsepower is the size of the bang multiplied by the number of bangs per minute.

So 40 years of intensive research increased the size of the bang by 19%. It did double the number of bangs per minute.

Now the sheer mass of a WW2 engine is not going to double in rpm even with the best modern materials. However it would increase with all the caveats such as increased power loss in gearing to keep propellor tip speed within practical limits.

There is a WW2 period example in the Napier Dagger where Halford tried to increase revs with smaller cylinders in just such a pursuit.

Where it might lead to is smaller engines to gain in revs what it loses in capacity and modern engine management and fuel blending will allow higher boost pressures also so my prediction would basically be as per Tresillian's high boost X16 10 litre with electronic ignition mapping and high temperature tolerant fuel blends.

This would be for fighters. Large bombers and maritime search/strike would go down the fuel/weight efficient route with turbo diesels with all possible energy put back into the engine. In other words if fighters have a high tech Napier Dagger then bombers would have a high tech diesel Napier Nomad.

There are considerable returns to come from supersonic propellor blades using high rpm without heavy and power wasting gearing (and horrible shock wave and acoustic issues).

A Tresillian 10 litre X16 is about 1,000bhp at best Merlin comparison, 1,200 bhp with modern 'bangs at 3,000rpm, 1,800 at 4,500 rpm and fit in an airframe of half the dimensions of a Spitfire so vastly less weight. Certainly it could approach transonic speeds.

However, once you start playing with the drive methods then you approach a grey area. When does a ducted fan become a fan jet. I think that exploring the use of a piston engine to power a compressor and burning fuel in the compressed air will inevitably result in someone linking the compressor to the high pressure burning exhaust to drive it and invent the jet engine anyway.

 

[GregP]

Been inside a lot of Allisons and they are 4-vavles per cylinder with overhead camshafts that are gear driven, so the technology is pretty good. You might remember that 35 years ago or so, we did tune ups every so often, to the tune of about every 6,000 miles or so. Today most cars can go 100,000 miles between tuneups.

Did something magic happen? No, we went to direct fuel injection, so each cylinder gets a correct mixture and we don't have some running rich while others run lean. I think moving to direct fuel injection would cure MANY WWII engine woes and extend the life. With today's technology, I think you could get 2,500 HP from something like 1,000 cubic inches and still have reliability and logevity for aerial application. It would probably have several turbbochargers in addition to the supercharger and the mixture could be made automatic. The avionics would be glass panels and the capability would be staggering.

Since we are moving to modern technology, we could go to a pusher if one rotary cannon is used or two in the wings if a tractor layout is used. It wouldn't need as many bombs because they'd be smart bombs or even retarded smart bombs (with devices to slow the bomb so the aircraft can escape the blast at low altitude) or even cluster ammunition. A P-51 like plane with a rotary cannon or two, smart ammunition, and 4 sidewinders would be a tough customer.

Conversely, if WE had them, then Germany would also have them, and the fight would get even more costly than it was. It certainly wouldn't drag on for 5 1/2 years with today's technology! Might be over in less than 6 months. If the powers remained the same, then the Battle of Britain might well have been successful unless we presuppose that the modern Bf 109 also had very short legs. Even if true, 15 minutes over England with smart ammunition and air-to-air missiles might make a huge difference in outcome, not to mention the participation of attack helicopters that surely would spring up with all those neat engines available.

Of course, with modern technology, we'd KNOW they were coming, how fast, from where, and would probably just send the drones in to take out the forward airfields, so maybe they wouldn't make it across the channel unless they drove through the tunnel in force in BMW armored cars or everyone caught the scheduled hovercraft at the same time.

Some really important developments are the vast improvement in submarines and the vast improvement in main battle tanks. I bet the trusty German BMW sidecar motorcycle would change somewhat, too!

There have been a number of adventure / science fiction novels written around this very premise, and somehow the Nazis still manage to lose ... on paper, but wreak incredible havoc as they do so. I liked the movie "Final Countdown," where a modern aircraft carrier was dragged into 1941 the day before Pearl Harbor. An F-14 versus an AT-6 made up to look like a Zero was pretty entertaining! The 1941 people were blown away by the arrival of turbine helicopters.

Maybe all we'd really have to do to stop Germany is disable their internet and business wopuld grind to a halt. I'm also fairly sure the press would not be allowed to transmit front-line battle pics around the world like they do now.

 

[vinnye]

You might have seen reliable high hp versions of the Sabre engine that were reliable from the start. 3000+ hp on tap - put a decent contra rotating prop on it and you have a good starting point!

 

[CobberKane]

I'm way behind you guys in engineering nous, but it seems to me that the following post WWII developments would have the greatest effect on output
1. Electronic ignition
2. Electronic fuel injection
3. Turbo/supercharger technology

Of course, then increased level of tuning is going to have ramifications for engine wear and reliability, but we also have options like metalurgical advances and ceramics to help.
The elephant in the room would be cooling, I guess. Could some sort of evaporative system be made to work, and be more efficient?
One other thought - the post proscribes jets, and by inference turboprops, but what about Wankel rotaries? Any potential there?

 

[GregP]

I used to race Wankels in the SCCA (Sports Car Club of America), and have seen the Mazda 3-rotor Wankels run. It's a pretty decent engine when displacing 1,200 or 1,300 cc (the 12A and the 13B), but as it gets bigger, it runs into problems. The power is smooth, but you have to bridge-port it and put in racing apex and tip seals to make any decent horsepower, and you have to pin the main rotor gear (in 3 places) to keep it from slipping in the mount at high RPM.

They aren't bad as small engines but I'd have to see a big one run well before making any bets on it. I'd say stick with a piston and race the tiny Wankels in Austin-Healey Sprites / MG Midgets. WAY fun.

When pinned and bridge ported, we got 225 - 235 HP out of it and had them in Sprites with an all-up racing weight of 1,500 pounds (minus the driver). They were QUICK! You could do a street port job and get 170 - 180 HP and have a Sprite that could beat a Corvette ... just use the Mazda running gear and manual transmission. You had to beat the heater box in to get the bell housing to fit and had to come up with a transmission mount yourself, but it was worth the effort. Wish I still had one!

 

[wuzak]

Perhaps a closer guide to the use of modern materials and technology is the Formula 1 engine. Simplisticly put, in @1970 it produced 400 bhp at 10k rpm. 40 years later it could put out 950 bhp at 20k rpm (rpm was then limited by the rules.).

This suggests that new materials and ignition control only increased the power from 13.33 bhp per litre per 1k rpm to 15.83 per litre per 1k rpm or barely 19%. The bulk of the total power increase came from the increase in rpm. As the late Keith Duckworth used to say; horsepower is the size of the bang multiplied by the number of bangs per minute.

It isn't just the rpms that drove power up. The increased rpms needed a lot of work in the combustion chamber and the intake and exhausts to maintain the BMEP to a high enough level such that the added rpms gave benefit.

In 1989 turbos were outlawed. The new engines were 3.5l V8s, V10s and V12s. They made between 700 and 750hp, revved to around 14-15,000rpm.

Compare that the current engines - 2.4l V8s revving at 18,000rpm (restricted - unrestricted, in the 2006 season, the engines would regularly see over 19,000rpm and were able to crack 20,000rpm in testing) making approximately 720hp.

The increase in rpms came about through ever more extreme bore:stroke ratios. The current V8s have a maximum bore of 98mm which has led to tiny strokes of less than 40mm.

 

[syscom3]

The R2800, R3350 and R4360's all had continued development after the war. I think the R4360 had the ultimate evolution in design by being a turbo compound design with some type of "jet effect" being harnessed by the large quantity of hot exhaust.

What did these engines in, was the enormous fuel consumption with relatively low efficiency. And they were maintenance nightmares from the get go.

 

[wuzak]

I'm way behind you guys in engineering nous, but it seems to me that the following post WWII developments would have the greatest effect on output
1. Electronic ignition
2. Electronic fuel injection
3. Turbo/supercharger technology

Of course, then increased level of tuning is going to have ramifications for engine wear and reliability, but we also have options like metalurgical advances and ceramics to help.
The elephant in the room would be cooling, I guess. Could some sort of evaporative system be made to work, and be more efficient?
One other thought - the post proscribes jets, and by inference turboprops, but what about Wankel rotaries? Any potential there?

Those are very important factors.

I would add that the fuel injection would probably be direct injection. This would aid in efficiency.

Materials is an area which would improve the engine, as stated above. Computer aided design/finite element analysis would allow the engine to be more compact and lighter weight while maintaining reliability and strength.

Piston design would be updated to modern slipper piston types.

 

[nuuumannn]

Electronic engine management would contribute to almost every facet of powerplant operation, from fuel distribution and consumption, spark timing, propeller pitch governing etc. Such changes in the fabric of the engines themselves would certainly see changes in the way the entire airframe and systems were managed and the way that information was presented to the pilot. As things are today, avionic systems would proliferate and more black boxes would be shoe horned into nooks and crannies around the airframe. More Spooks = fewer guys on the hangar floor getting dirty!

 

[tyrodtom]

Oh no, a F-35 with a prop.

 

[GregP]

At cruise (1,300 HP) the R-3350 is about 100 US gph per engine and the R-2800 is about the same or very slightly less for about 100 less cruise HP. You CAN get them a bit less, but you risk the engine if you lean too much.

You can get a Merlin 66 down to about 55 US gph per engine but any lower and you risk being too lean and having a very expensive event experience. We figure them at 60 US gph and don't really lean it any further than that these days. Maybe in WWII, when a government was paying for the engine, maintenance, and overhauls, you could get down to 46 US gph per engine, but NOBODY does that today since WE pay for the mistakes.

 

[GregP]

If I were specifying the avionics today, I'd want a reliable system that give good performance, but not the best that can be gotten. I'd rather have a reliable very good plane out there in numbers than the absolute best plane in fewer numbers that usually sits in the hangar being worked on.

Gimme' a Skyraider with modern avionics, a modern engine of 3,500 HP, and some smart weapons and I'll show you what an attack plane can do! I want the rotary cannons, too! No more rat-tat-tat ... more of a hummmmm ... and target gone. I'd rathre have a turboprop, but if that's out, a piston did just fine in the real beast, so it should do at least as well with a more reliable modern engine.