Supercharger vs Turbocharger

[MikeGazdik]

Dinniss, That's why I said "apparent" compression ratio. As far as the engine is concerned its the same thing.

The down side of Turbo-superchargers is space/weight for a separate unit (the turbo) and the associated plumbing for exhaust and compressed air to the engine.

The second thing is that it takes pilots that understand how to use the flexibility of the turbo's capability.The P-38 suffered tremendously over northern Europe because pilots wer using poor techniques in engine management. High RPM and low MAP resulted in high fuel consumption and cold engines and turbochargers, when they went to full power the cold oil would not lubricate the engines/turbochargers (the turbo's have their own oil supply) and they failed.

Also an important point the P-38 mixture had two settings Auto Lean and Auto Rich. Auto Lean is used up to 2300RPM and Auto Rich above that. The extra mixture setting gave the P-38 pilot the added flexibility to get both power and fuel economy. However if the throttle was maxed and the prop set to max power before the mixture was set to Auto Rich the engine would detonate and explode!

And you have hit on the "secret" to making the P-38 the weapon it could be. The technology was one thing, but training was another. The pilots that were properly trained made the Lightning the aircraft it should be. I think the turbosupercharged engine, particularly in the P-38, was the escort fighter. The P-51 was economicaly the better answer but I feel the Lightning once fully developed with properly trained pilots was the better aircraft.

 

[wmaxt]

Mike, IT was the escort fighter of WWII. The AAF did a study after the war and found that P-38 escorts provided the the best escort of the war losing fewer bombers than any other AAF fighter escort. However this has several things to keep in mind
1. The P-51 was freed from the bombers to follow the E/A allowing a greater bomber loss rate as a trade for a greater E/A destruction
2. The P-38 was identifiable from a greater distance so E/A often bypassed the escorted bombers for unescorted bombers.
3. P-38s had 98% close escort which is better for bombers and bad for "Scoring"

P-38's escorted bombers on 1,600 mi missions in mid '43 in the Med. and 1,700 - 1,800 mi missions to Singapore in '45 No other fighter could have done it.

The real question is a bit more simplicity for the mechanical supercharger or a bit more capability for the turbo.

Simplicity was the ticket for the ETO giving over 5,000 P-51s in less than 2 years to fight the Germans

In the PTO the added capability of the turbos allowed the P-38s to escort Mosquito's all the way to Singapore or the Dutch east Indies oil fields.

 

[GregP]

Although not relly well understood, superchargers were MUCH better understood in WWII than turbochargers.

Sir Stanley Hooker was a supercharger genius and helped the merlin achieve what it did. Whish Allison had him on staff!

The turbochargers were OK, but not really well thought out in WWII. The P-39 installation was amateur at best.

From earlier, I never said turbo lag was a problem in WWII fighters, it was a general statement that turbo lag does not give as good a throttle response as a supercharger does, and that is true. Even the last turbochargerd Formula 1 cars were nowhere NEAR as driver friendly as the supercharged cars were.

Having both systems was heavy and complicated. I think the 2-speed, 2-stage supercharger was better for a WWII fighter, but the urbo guys will argue.

If I am not mistaken, the highest-flying WWII airplanes were both supercharged and turbosupercharged simulatneously.

The highest-flying aircraft of WWII were relatively experimental.

I believe the highest-flying were, in order:

1. Bristol 138: 62,407 feet; High-altitude research aircraft; Bristol Pegasus PE.VIS. Not really WWII, but higher than the rest and earlier, too.
2. Blohm und Voss BV.155: 57,305 feet, High-altitude-fighter; DB603A.
3. Henschel HS.130E: 50,712 feet; High-altitude recon; DB603B.
4. Focke-Wulf Ta-152H-1: 50,036 feet; fighter; MW-50 and GM-1 boost.
5. Aichi M6A Serian: 49,825 feet; submarine-launched seaplane; Aututa 32 V-12.

Extreme aircraft, not really friendly to maintenance or operational use.

 

[Rick65]

I am interested in the basis for the inclusion of the Seiran in your list as it seems contradictory to it's intended role and a quick internet search found multiple sources quoting a ceiling of 9900m or about 32,500ft.
However lots of internet information is recycled from a limited number of sources so if they are wrong so are all the rest.

 

[Shortround6]

Although not relly well understood, superchargers were MUCH better understood in WWII than turbochargers.

Sir Stanley Hooker was a supercharger genius and helped the merlin achieve what it did. Whish Allison had him on staff!

The turbochargers were OK, but not really well thought out in WWII. The P-39 installation was amateur at best.

Having both systems was heavy and complicated. I think the 2-speed, 2-stage supercharger was better for a WWII fighter, but the urbo guys will argue.

Just so we are clear here, The Merlin (and two stage Griffons) used two impellers ( superchargers ) on a single shaft driven from a 2 speed gearbox so that both impellers turn the same speed at the same time. The P&W two stage superchargers used two shafts. the "engine" supercharger was one speed while the auxiliary supercharger had 2 speeds AND a neutral. ALL United States service Turbo charged planes used a two stage set up, a single speed engine driven supercharger plus a variable speed turbine driven auxiliary supercharger (the turbo). The P-63 used an Allison with a single speed engine supercharger and a mechanical (hydraulic) variable speed auxiliary supercharger. To get the best performance (non racing) from a two stage system an intercooler of some sort must be used. With the two stage systems (of any kind) compressing the air 5-6 times the surrounding air at altitude the intake air temperature from the heating of compression can become the limiting factor on boost used. Only the P-63 did not use an inter cooler of some sort ( and Allison tried). The intercoolers were a limiting factor on the P-38 G and H models.

If I am not mistaken, the highest-flying WWII airplanes were both supercharged and turbosupercharged simulatneously.

Not sure what you mean by this. since ALL American service planes used both an engine driven and a turbocharger at the same time they are using them simultaneously.

The highest-flying aircraft of WWII were relatively experimental.

I believe the highest-flying were, in order:

1. Bristol 138: 62,407 feet; High-altitude research aircraft; Bristol Pegasus PE.VIS. Not really WWII, but higher than the rest and earlier, too.
2. Blohm und Voss BV.155: 57,305 feet, High-altitude-fighter; DB603A.
3. Henschel HS.130E: 50,712 feet; High-altitude recon; DB603B.
4. Focke-Wulf Ta-152H-1: 50,036 feet; fighter; MW-50 and GM-1 boost.
5. Aichi M6A Serian: 49,825 feet; submarine-launched seaplane; Aututa 32 V-12.

Extreme aircraft, not really friendly to maintenance or operational use.

1. The Bristol used a remote auxiliary supercharger driven by a shaft, I believe it was not clutched in until an altitude of over 30,000ft was reached? But no turbo. It did use a sizable intercooler however. see: http://www.airwar.ru/image/idop/xplane/b138/b138-4.jpg
2. Blohm und Voss BV.155 was turboed and kept an engine driven supercharger, those large housings out on the wings are the intercoolers which shows the problem of using enough superchargering (of any type) to operate at high altitudes.
3. Henschel HS.130E, didn't use a turbo. It used a DB605 engine in the fuselage driving a large supercharger to supply air to the DB603 engines out on the wings. It worked but could hardly be called either light or compact.
4. Focke-Wulf Ta-152H-1 was supposed to use a 3 speed 2 stage supercharger and the GM-1 ( nitrous oxide) was a way of carrying supplemental oxygen in the plane to augment the air from the supercharger set up.

 

[tomo pauk]

Although not relly well understood, superchargers were MUCH better understood in WWII than turbochargers.

Sir Stanley Hooker was a supercharger genius and helped the merlin achieve what it did. Whish Allison had him on staff!

The turbochargers were OK, but not really well thought out in WWII. The P-39 installation was amateur at best.

From earlier, I never said turbo lag was a problem in WWII fighters, it was a general statement that turbo lag does not give as good a throttle response as a supercharger does, and that is true. Even the last turbochargerd Formula 1 cars were nowhere NEAR as driver friendly as the supercharged cars were.

Since just for 4 designs (B-17/24, P-38/47) it was produced some 180 thousands turboed engines in USA (plus what ever spares were produced for those), I'd reckon that turbo was a pretty mature stuff for the WW2. If Rolls-Royce P&W were superb in two-stage designs, that does not qualify the majority of mech-supercharged engines (= single-stage ones) their manufacturers as better than their turboed counterparts.
Formula I engine in turbo variation were never intended to be driver-friendly, but HP-monsters. IIRC the BMW design from the 1970s was featuring a turbo-charger as big as the 'naked' engine; the turbo-lag was huge, but so were 1300 HP from the 1500 cc.
But I agree that even in today's VTG turboed cars the lag can be felt, I drive one Not that the lag matters to me.

 

[davparlr]

sorry i was confusing with engine variants

-57W data are for 72"? and that for 18W?

I am not sure what the boost was for the 18W engine, but I don't think the Navy was using the 44-1 fuel so it most likely was not the same as the -57 engine. However, that was not the point, which was showing the difference turbos made. The F4U-4 lost 26% of its power, 620 hp, from SL to 30k, the P-47M/N lost zero. Difference increases as altitude goes up. At 35k F4U-4 loses 52% of its power (1230 hp), the P-47M/N loses only 7% (200 hp). As a further comparison, the noted high altitude Ta-152H loses 46% of its power (950 hp) at 35k, which helps explain why the P-47M is 20 mph faster than the Ta-152H at this altitude.

 

[GregP]

The Serian was produced asboth a floatplane and as a landplane. One landplane was modified for high altitude. Yes, it was a prototype, but I could argue taht the Ta-152H was, too, since so few were produced. Main thing is, it happened during WWII. Naturally, all these altitude records have been eclipsed, even by drones, but during or before WWII, these planes flew what must be considered as the highest.

About the turbos, I KNOW the turbos were installed into bombers as well as the P-38's and P-47's. None of those installations were optimum and they were not at the cutting edge of power. I stand by mu statement taht turbocharging was not nearly as well understood as supercharging was in WWII, notwithstanding numerous small bomber engines taht were essentially turbo-normalized. That is, they were turbocharged so as to produce sea level rated pwoer at higher altitudes, not to give higher horsepower than otherwise possible.

 

[Siegfried]

3. Henschel HS.130E, didn't use a turbo. It used a DB605 engine in the fuselage driving a large supercharger to supply air to the DB603 engines out on the wings. It worked but could hardly be called either light or compact.

I think the fueselage engine was a DB605T, that is T for turbo, so turbo super charging was used, albeit indirectly.

 

[wmaxt]

In the 1920's the Army Air Corps mandated that its aircraft be turbocharged, and experimentation on better turbo's began then. By the late 1930's turbo's were understood in themselves but practical experience was not really that great. The biggest problems were the metallurgy and the control of the related systems. On the whole Greg's assertion that turbo's or at least turbo's and their related systems were not well understood is true. The level of complexity required for their best usage was just being understood. Control of the later turbo's on the P-38 was much better than earlier versions.

Mechanical superchargers had been researched by everyone else and were less technologically complex and pretty much perfected for aircraft by the late 1930's.

Supercharging as a whole was intended to maintain sea level performance at altitude, it wasn't until the later years of the war that higher boost was experimented with to boost performance over the sea level rating.

 

[Shortround6]

About the turbos, I KNOW the turbos were installed into bombers as well as the P-38's and P-47's. None of those installations were optimum and they were not at the cutting edge of power. I stand by mu statement taht turbocharging was not nearly as well understood as supercharging was in WWII, notwithstanding numerous small bomber engines taht were essentially turbo-normalized. That is, they were turbocharged so as to produce sea level rated pwoer at higher altitudes, not to give higher horsepower than otherwise possible.

It is sort of yes and sort of no on the last part. The engine supercharger provided the boost at low altitude (sea level) over and above normal sea level pressure or power. While gear driven (or hydraulic ) could easily supply enough boost at sea level( SL) using a low ratio it took more power to turn a high ratio that could provide better power at altitude. In the late 30s engines with sigle speed superchargers were often described as ground boosted, medium supercharged or fully supercharged, depending on the gear ratio used on the supercharger. The ground boosted engine offered the most power at SL or take off because it's supercharger took the least power to drive, it heated then intake charge the least and allowed the engine to run with throttle plate/s wide open rather than part open like the altitude engines needed to do to keep from over boosting. The American turbo system allowed the use of ground boosted rated engines at high altitudes with little drop in performance.
Let us not confuse the limits of the parent engine with the limits of the supercharger system. The P&W R-1830's development rather slowed down or practically stopped fairly early in WWII. P&W effort went into the R-2800 and the R-4360. Wright had to redesign the crankcase, crankshaft, rods, cylinders, cylinder hold down bolts and cylinder heads to get the R-1820 past 1300hp and get to 1425 HP. Allison went through a number of versions and at several points in time the engines in the P-38 could give more power than the equivelent engine/s in the P-39/P-40 because they could use a lower gear to drive the supercharger and depend on the turbo charger to make up and exceed the difference at altitude. I don't have my books in front of me at the moment but if memory serves an Allison with 8.80 gears was good for 1325 HP for take off and 1150 HP at 11,500-12,000 ft while a similar engine with 9.60 gears was good for 1200 HP at take off and 1150 HP at 15,000-15,500 ft. Some P-38 engines used 7.48 gears and had 1425 HP for take off and the turbo allowed this rating to be held much higher. So in a sense the turbo allowed higher power to be used. Air cooled engines didn't like over boosting as much as liquid cooled engines did. The R-2800s in the P-47M-N used a different cylinder and cylinder head with much different cooling abilities than earlier R-2800s.
It could take several hundred(300-400 for the bigger engines) horsepower to run a second stage super charger over and above the power needed to run the primary or 1st stage ( one closest to engine) and engine block,crank,cylinders,heads,etc needed to be able to stand up to the extra power even if it wasn't showing up as crankshaft or output power.

 

[Shortround6]

I think that the idea that "turbos" were not well understood is a mistake. The turbocharger is made up of two elements, the turbine that drives it and the compressor that actually does the supercharging. The compressor design wasn't much different than most people's mechanical drive compressors. In fact with General Electric supplying the compressor designs to both P&W and Wright until about 1937 and Allison making supercharger parts for both of them under subcontract to GE there may not have been much difference in design at all between them. Now it is true that by 1944/45 a lot had been learned by many countries about supercharger design compared to what was known in 1937 ( some 1930s German impellers look very strange to modern eyes) that is not the same thing.

 

[wmaxt]

The principal, and operation of turbo's was thoroughly understood but just how to control them efficiently was just coming of age technologically. It took WWII to push the knowledge of turbochargers to their ultimate configuration.

Early P-38 turbo/waste gate controls worked but there were some operational and maintenance issues, by the J series very few problems were encountered and the systems were easier for the pilot to manage.

At wars end turbo compounding and related technologies were being tested. In the -90's turbocharging technology expanded greatly giving us much more responsive and efficient power than ever before. Today with electronics WWII designers could have only dreamed of and new materials and configurations are still changing the face of turbocharging.

 

[Siegfried]

I think that the idea that "turbos" were not well understood is a mistake. The turbocharger is made up of two elements, the turbine that drives it and the compressor that actually does the supercharging. .

And the wastegate which needs to be controlled and its own ducting and exhaust. Diesels don't need one.

 

[greybeard]

Turbosupercharger is definitely better than mechanically driven supercharger, especially for aircraft powerplants. Drawbacks, which are lost jet exhaust thrust, higher weight and so-called "turbo lag" are by far compensated by overall performance.

It's only a matter of available technology if one uses one or another.

During WWII only U.S.A. did have that technology and required materials available in quantity. Others like british and german were forced to apply only to jets.

GB

 

[Shortround6]

The Turbo lag doesn't really apply to aircraft. Aircraft seldom make multiple large throttle changes in a very short period of time. Both the propeller and the supercharger impellers act as rather substantial flywheels which limit rapid rpm change in any case.
Modern turbo set ups should not be confused with WWII turbo set ups. In the post war era a number of civil aviation engines used gear driven superchargers (Lycoming, Continental, De havilland, and others) during the late 40s and 50s. By the early 60s almost none were left, they had been replaced by turbo superchargers much like the ones used in cars today. These were all single stage systems without intercoolers.
The Turbo set ups of WW II were almost all (I may have over looked a few experimental set ups) two stage systems. The Turbos did impose penalties of weight, bulk and drag. Wither they were better or not depended on the altitude the plane was expected to operate at. There were cross over points, no one system was the best at all altitudes.

 

[davparlr]

Adding all of these factors of greater bulk and lost jet thrust together and the turbo supercharger looks marginal for high speed aircraft where the jet thrust is of great import.

If the Ta-152H with the Jumo 213E engine had been equipped with a P-47M type turbo supercharger, i.e., flat rated to 33k, instead of the GM-1 set up, its power available at 40k ft. would be approximately 1824 hp or about 900 hp more than the Ta-152H without GM-1. With GM-1, the turbo supercharged would have 744 hp more power. The numbers are probably even more favorable to the turbo since the 213 engine would not be powering the second stage compressor that the GM-1 version would have to do (see Shortround6 post #5), which would probably offset any jet thrust. Weight would probably not be a big issue since the GM-1 with is associated 85L of nitrous would not be carried. Bulk could be a factor, but, again, the GM-1 system with tank would not be carried. I suspect that the Germans understood this since it was trying to develop turbo engines, including the 213.

Can you imagine how the Ta-152H would perform it it had a flat rated engine to 33k, and over 90% SL power at 40k?

 

[Shortround6]

The advantages of the turbo-charger may have changed with both fuel and time.

For a hypothetical let's look at the Merlin in 1939.

In MK III trim and with 87 octane fuel it was good for 880 HP for take off and kept increasing power until it hit 1030 HP at 16,250ft after which power fell off with altitude. As the MK X with a 2 speed supercharger it was good for 1075 HP for take off, 1130 HP at 5250 ft and 1010hp at 17,750 ft. Basically the 6.39 supercharger gear took much less power to drive, heated the air less and allowed a wider throttle opening than the 8.58 gears in the MK III while the 8.75 gears in the high gear setting of the MK X offered only slightly better power at altitude. Now we know that the basic engine would stand up to 1130 HP if not actually between 1200-1300hp with higher boost.
If equipped with a turbo as an auxiliary supercharger the Merlin could have used an even lower gear that would have allowed between 1130-1200hp at sea level for take-off and kept that power all the way to 24-25,000 ft. Obviously some aircraft would have benefitted from that kind of power increase.
However the down sides would be an increase of approximately 325-425lbs of power plant weight and the need for 10-13 cubic feet of volume in the aircraft per engine. A bomber may have been able to house such an installation much better than a small fighter like the Spitfire. The further from the engine the turbo goes the more volume is needed by the ducts leading to and fro. The more volume needed the larger (heavier) the fuselage and the more drag. In the Spitfire the space right behind the engine is taken by the fuel, which has to be on or close to the CG so moving it has limited options.
Once 100 octane fuel became available the existing supercharger was able to use more boost down low (although it didn't change the power at over 16,250 ft) which helped the low altitude performance with no extra weight or drag.
We now get into the exhaust thrust or power.
I don't have the figures for the MK III or X but the figures for the MK XX are available. This somewhat more powerful engine is credited with the following in a Hurricane II.
At 15,000ft and 48.24in boost with a back pressure of 23.2in and a charge flow of 140.5pm/min the ejector HP was figured at 86.5hp at 325mph.
At 20,000 ft and 48.24 in boost and a back pressure of 22.3 in and a charge flow of 144.0lb/min the ejector HP was figured at 113 at 335 mph.
At 20,0000 ft and 50.67 in of boost and a back pressure of 23.2 in and a charge flow of 151.0 lb/min the ejector HP was 126.8 at 340 mph.
At 25,000ft and 42.12in of boost and a back pressure of 19.6in and a charge flow of 129.1lb/min the ejector HP was 107.2 at a speed of 330mph.
At 30,000ft and 34.30in of boost and a a back pressure of 16.3in and a a charge flow of 107.2lb/min the ejector HP was 89 at 317 mph.

The ejector jet velocity in FPM was 1395, 1695, 1788, 1840, and 1901 respectively.

While the jet thrust is a product of the charge weight (mass) and jet velocity the jet horse power is the jet thrust adjusted for speed or efficiency. The closer the match to the jet speed the speed of the aircraft is the more "power" you get from the same thrust.
A Spitfire will get the same power from the exhaust as a Hurricane II if both at are at the same speed and a altitude but the Spitfire will get more benefit as it exceeds the speeds the Hurricane can go. A bomber will get proportionately less power from the exhaust as it can not travel ( Mosquito excepted) as those higher speeds.
The more charge weight you can stuff through an engine the higher the jet thrust goes, an engine running 60in of manifold pressure should have about 33% more jet thrust than the same engine at 45in of manifold pressure but this requires fuel that will keep the engine from self destructing at 60in of manifold pressure.

 

[Siegfried]

If the Ta-152H with the Jumo 213E engine had been equipped with a P-47M type turbo supercharger, i.e., flat rated to 33k, instead of the GM-1 set up, its power available at 40k ft. would be approximately 1824 hp or about 900 hp more than the Ta-152H without GM-1. With GM-1, the turbo supercharged would have 744 hp more power. The numbers are probably even more favorable to the turbo since the 213 engine would not be powering the second stage compressor that the GM-1 version would have to do (see Shortround6 post #5), which would probably offset any jet thrust. Weight would probably not be a big issue since the GM-1 with is associated 85L of nitrous would not be carried. Bulk could be a factor, but, again, the GM-1 system with tank would not be carried. I suspect that the Germans understood this since it was trying to develop turbo engines, including the 213.
Can you imagine how the Ta-152H would perform it it had a flat rated engine to 33k, and over 90% SL power at 40k?

FW did try to develop the FW 190C "Kanguruh' with turbo charger: the result shows how difficult it could be to integrate a turbo-supercharger:

It seems to have been rejected on grounds related to reliabillity which was probably linked in with the alloys used: which were stainless steels. (Sicromal, the alloy used, seems to have become usable in the BMW 801T and BMW 003 turbojet via cooling methods)

I'm not sure how feasible it would be to combine high boost with Nitrous Oxide. However Nitrous Oxide did not have to be used in large quantities nor was it bulky: it was injected at a rate about equal to the fuel consumption. The rate the Ta 152 consumed was either 50, 80 or 130 (of my imperfect memmory) grams per 100 grams of fuel. The idea for the Me 109 and FW 190 had been to provide a tank of about 130L which could be used for water methanol, extra fuel or cryogenic NOX depending on mission profile however TA 152 had greater capacity however plumbing and control issues prevented the widespread use of this multipurpose arrangment.

There seems no doubt the turbo charger did provide better performance, the German super high altitude fighter the BV.155 used one and was expected to exede the improvised Ta 152H. (though turbo is conspicuously absent on the R-4360 of the B-36B)

About the only German use of the turbo supercharger was in the BMW 801T which was used in a few Ju 88S-3 and Ju 388L, these engines had the turbosupercharger, engine, cowling and intercooler integrated into one package

 

[Siegfried]

The more charge weight you can stuff through an engine the higher the jet thrust goes, an engine running 60in of manifold pressure should have about 33% more jet thrust than the same engine at 45in of manifold pressure but this requires fuel that will keep the engine from self destructing at 60in of manifold pressure.

I think it was better than that, the two stage superchargers would also be blasting their air into a low pressure ambient, which also improves thrust. Higher pressure should lead to both higher mass flow and higher exhaust gas velicity. The thrust is given by F =dm/dt x v. Jet thrust is also of greater value at higher speeds where mach effects reduce airscrew efficiency