Early war fighters, what was supercharged and what wasn't?

[pinsog]

Were the P39 and P40 allison engines completely naturally aspirated? What about the early 109, Spitfire and Zero? I know the Wildcat had an engine driven supercharger, just not sure about the others.

[Marcel]

Bristol Mercury was supercharged. it powerd many types like:
* Airspeed Cambridge
* Blackburn Skua
* Boulton Paul P.108
* Bristol Blenheim
* Bristol Bolingbroke
* Bristol Bulldog
* Bristol Bullpup
* Bristol Type 101
* Bristol Type 118
* Bristol Type 133
* Bristol Type 142
* Bristol Type 146
* Bristol Type 148
* Breda Ba.27
* Fairey Flycatcher
* Fokker D XXI
* Fokker G.1
* General Aircraft Hamilcar X
* Gloster Gamecock
* Gloster Gladiator
* Gloster Gauntlet
* Gloster Gnatsnapper
* Gloster Goring
* Hawker Audax
* Hawker F.20/27
* Hawker Fury
* Hawker Hart
* Hawker Hind
* Hawker Hoopoe
* Hawker F.20/27
* IMAM Ro.30
* Miles Martinet
* Miles Master
* PZL P.11
* Saab 17
* Short Crusader
* Supermarine Sea Otter
* Valmet Vihuri
* Vickers Jockey
* Westland Interceptor
* Westland Lysander
So quite a number of a/c.
I'm sure many other engines were similar.

[Juha]

Hello Pinsog
as a rule WWII era engines used in combat a/c were supercharged, also Allisons used in P-39 and P-40 were, but IIRC they had only single speed single stage superchargers at least early on. Also Spitfire, Bf 109E and Zero had supercharged engines, 109 had variable speed supercharger with hydraulic coupling.

Juha

[Milosh]

Originally Posted by pinsog

Were the P39 and P40 allison engines completely naturally aspirated?

That is one of those myths that won't go away. The P-39 lost its turbocharger but many people get confused between turbo and super charger.

[Shortround6]

Basicly around 500hp was the dividing line. Over 500hp the engine had a supercharger of some sort. Under 500hp and there is a good chance it didn't. There are exceptions to this with a few engines in the 200-300hp range having superchargers and a few older engines (as has been noted, rarely used in combat aircraft still in service) of 600hp or little more without superchargers.

A lot of confusion comes in because various writers seem to confuse the lack of a high altitiude supercharger with having no supercharger.

Even in the very Early 30s the R-R Kestral was availabel with NO supercharger, a low altitude supercharger (peak power at 4,000-6,000ft) and a 'High' altitude supercharger, good for a peak power at 11,000-14,000ft.
All American large radial engines had supercharges fom the late 20s on. But a lot of them provided only a few pounds of boost and and provided peak power at 4,000-7,000ft. As gasoline got better and more boost could be used (higher pressure) the altitude ratings went up.

even the Engines in the T-6 were supercharged

[pinsog]

That answers my question. I wondered if they were like, say the 2 stroke Detroit Diesels and had, basically a built in supercharger. I knew they didn't have turbo chargers, the P38 and the P47 had turbochargers along with the B17 B24 B29 and prbably some bombers I missed. When they talk about 2 stage superchargers, do they mean 2 speed supercharger with a 2nd gear ratio it shifts into?

[Milosh]

Two gear ratios and two stages of supercharging like on the Merlin 60 series engines.

The Merlin 20 and 50 series engines had two speeds and one stage of supercharging, iirc.

Typically on a 2 stage supercharger the boosted pressure from the 1st stage was fed to the 2cd stage. An intercooler (charge cooling) was usually between the 2 stages.

[MikeGazdik]

And the Allison in a P-38 is turbo-supercharged. The Allison has the intregal engine driven supercharger like the P-39, but also has the turbocharger as well.

[Shortround6]

All production aircraft that used turbochargers in WW II also had an engine driven supercharger and so used a two stage system.

[MikeGazdik]

Originally Posted by Shortround6

All production aircraft that used turbochargers in WW II also had an engine driven supercharger and so used a two stage system.

Exactly. I think like you pointed out, most of the confusion is from writers unfortunatley. They were not "gearheads". I doubt if many of them really knew that much about engines. They wrote stories really well, and did great interviews, but were lacking in the understanding of engines.

[Watanbe]

This my sound like a stupid question, but did they the super/turbo combo so that it would operate effectively at different altitudes?

When I think turbos and superchargers I can't help but think of cars. I know in cars a supercharge generally provides better response and less "lag" and can be run at higher compression ratios but without as much boost as a turbo.

[MikeGazdik]

The only thing I can say to your question is I believe a Turbocharger has much less (or some say not any) parasitic loss. The gear driven supercharger is driven directly, geared, to the engine. So just turning the compressor is using up horsepower. Now obviously it develops far more than it uses, but it does consume power. The Turbo charger by nature is being powered by what is normally only waste, the exhaust gas. So most if not all of the power it provides is pure bonus.

Because the Turbo takes less power to develope boost, is why it is more fuel efficient than an engine that is supercharged by a 2-stage supercharger only. ( side-note) I cannot remember the numbers but that was one of the factors why Lockheed did not use a 2-stage Merlin to power later P-38's. I read that they did in fact look into this option. The fuel consumption for the Merlin was much greater than the turbosupercharged Allison, which would have reduced the range of the P-38 significantly.

[Shortround6]

The needs of aircraft and cars are somewhat different. Aircraft usually don't need the quick throttle response of cars. Very few aircraft need go from full throttle to brake or part thottle a dozen times a minute like a race car on a curvy course.
Aircraft have to dea with vastly different atmospheric conditions that cars do not (unless they are racing up Pike's peak

Large aircraft engines also have the propeller which acts like a giant flywheel. 300-600lbs+ revolving at 1500-2000rpm isn't going to change speeds in fractions of second either.

By the way, I drive a turbo supercharged diesel fire truck, I KNOW how bad turbo lag can be
Not that it has to be.

Air densities that can change to 1/4 of what they were 20 minutes before ( or reverse) and temperature changes of of over a hundred degrees (F).

A turbo on an airplane does have some parasitic loss. It was estimated by General Motors at about 8% at 20,000ft compared to 0% at sea level but then the Turbo wasn't providing any boost at sea level. The Turbo also cuts way down on the abilty to use exhaust thrust.
Another difference between airplanes and cars, one of the formulas (out of many)for figuring exhaust gas thrust:

Efficiency = 2(airplane speed)/(velocity of ejection)

It was considered that the velocity of ejection was about 2,000fps in a well designed system so efficiency went up rapidly with speed.

Mike is quite correct about the P-38 and Merlins however. design estimates put the loss of range anywhere from 8-33% depending on which model of engine and which cruising conditions were being compared.

[timshatz]

I'd read some time ago that one of the benefits of the P51 was the boost (not sure if it were Super or Turbo or both) exhausts were 90% efficient in terms of thrust from the back of the aircraft.

Evidently, the Mustang wasn't just slippery in design but also in the exhaust sense.

[tomo pauk]

Originally Posted by timshatz

I'd read some time ago that one of the benefits of the P51 was the boost (not sure if it were Super or Turbo or both) exhausts were 90% efficient in terms of thrust from the back of the aircraft.

Evidently, the Mustang wasn't just slippery in design but also in the exhaust sense.

The usage of exhaust gasses to provide added thrust was used as early as Battle of Britain. However, when the fast gear of supercharger of RR engined Mustangs kicked in, the plane was lightning fast for the era.

Further about supercharging:

Mustang (both Allison and RR engined) did have only engine-driven ( a.k.a. mechanical) supercharger. The exhaust was therefore left free through exhaust pipes, with benefit of additional thrust. The additional thrust rises with altitude, adding to the propelor's thrust up to (educated guess) 30% in practical combat altitudes. Planes using this effect were numerous, including Hurricane, Spitfire, P-40, Bf-109, late Zeroes etc

The engines that were using exhaust gases to power the turbine of turbocharger obviously couldn't use those gases again, eg. no additional thrust for P-47, P-38, B-17 etc.

So, despite harvesting the exhaust gasses, the WW2 planes with turbochargers were not that faster (or not at all) then planes that had their engines supercharged via mechanical supercharger.