The advantages of turbocharging vs supercharging piston aero engines are so great why did not every country use them in WW2. The US lead this field by a long way and OWNED high altitude combat in WW2. By 1939 the turbocharged B-17 was service ready so why did other countries, especially the "high-tech" Germans totally fail to get turbo'd planes working?
WW2 Turbochargers why not used by all?
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wuzak
Captain
Because the advantages weren't as great as you have just made out.
Shortround6
Major General
There were also more than a few manufacturing problems, and rather unforeseen, maintenance problems.
One might also check the British 2 stage Merlin to see how well the Americans "owned" high altitude combat.
The Russians tried to turbocharge just about everything short of the T-34 tank (every major Russian aircraft engine had at least one turbo version of EVERY major version). Due to shortages of certain alloys and manufacturing problems the list of experiments is also a list of explosions, fires, burst turbos or other mechanical failure.
It is also one thing to build turbos in experimental quantities, and quite another to turn out thousands every month.
The American maintenance issues weren't with the turbo itself, but with the turbo controls and with the ducting leading to and fro and the inter-coolers. Trying to keep the ducting air tight was often an on going battle.
One might also check the British 2 stage Merlin to see how well the Americans "owned" high altitude combat.
The Russians tried to turbocharge just about everything short of the T-34 tank (every major Russian aircraft engine had at least one turbo version of EVERY major version). Due to shortages of certain alloys and manufacturing problems the list of experiments is also a list of explosions, fires, burst turbos or other mechanical failure.
It is also one thing to build turbos in experimental quantities, and quite another to turn out thousands every month.
The American maintenance issues weren't with the turbo itself, but with the turbo controls and with the ducting leading to and fro and the inter-coolers. Trying to keep the ducting air tight was often an on going battle.
Merlins were British ?
Why am i just finding this out
Why am i just finding this out
As a Brit I put up my Spitfire of the latest marque in every year from 1939 to 45, now tell me which turbo US aircraft will "own" it at high altitude. The B17 was flying in 1939 it was not service ready especially for daylight raids in contested airspace it was first used by the RAF in July 1941
MIflyer
1st Lieutenant
Compare the high altitude performance of a P-47 and an F6F - or even more appropriately the Seversky AP-4 and the XP-41 - and you'll see that two stage supercharging using a turbo for the first stage was superior to mechanically driven supercharging..
In WWII the Germans recognized this and really wanted to use turbos on their aircraft. But turbos required large quantities of nickel and they had very little available. This also doomed the Me-262 and AR-234; they could never build enough of them to make a difference in the war. That business of Hitler dooming the German jets by saying to build the Me-262 as a bomber is B.S.!.
The Japanese planned to add a turbo to the A6M2 but found it to be too difficult. They tried using three speed single stage superchargers instead.
For the US turbos proved to be both an advantage and a trap. For heavy bombers they were great. Integrating them into fighters was a challenge. You needed a lot of room to both provide a turbo and an intercooler to make it effective. For the little P-39 the airplane was slower with the turbo installed than without!. The P-47 and P-38 had enough room because they were huge.
Go look up the Nov 2001 issue of Airpower magazine. I have a 4500 word article in there that goes into the subject in far more detail than we can here. .
In WWII the Germans recognized this and really wanted to use turbos on their aircraft. But turbos required large quantities of nickel and they had very little available. This also doomed the Me-262 and AR-234; they could never build enough of them to make a difference in the war. That business of Hitler dooming the German jets by saying to build the Me-262 as a bomber is B.S.!.
The Japanese planned to add a turbo to the A6M2 but found it to be too difficult. They tried using three speed single stage superchargers instead.
For the US turbos proved to be both an advantage and a trap. For heavy bombers they were great. Integrating them into fighters was a challenge. You needed a lot of room to both provide a turbo and an intercooler to make it effective. For the little P-39 the airplane was slower with the turbo installed than without!. The P-47 and P-38 had enough room because they were huge.
Go look up the Nov 2001 issue of Airpower magazine. I have a 4500 word article in there that goes into the subject in far more detail than we can here. .
Shortround6
Major General
Any two stage supercharger needs an intercooler. See P-63 for what happens without one. It was planned to have one but the supplier couldn't deliver.
You have several things going on as turbos were not magic even you could build them.
1. as mentioned is the space required. A 1943 text book suggests 10 cubic feet being needed for a 1000hp engine. It is not linear, you don't need 20 cubic feet for 2000hp but something in between. Packaging is another problem. a 10 cubic foot box right behind the engine is probably not going work very well, tight radius bends in the duct work will decrease efficiency and even the Americans had trouble with overheating the turbine blades, one reason the US mounted the turbos a number of feet from the engine and exposed lengths of the exhaust pipe to cold air before they reached the turbo (P-47 excepted and that had even more distance from the engine to the turbo.
2. You need good fuel to see the kind of power the US was getting from the turbos. That or really big intercoolers. A B-17F was only using about 46in of MAP (about 8lbs boost) but at 25,000ft the temperature rise through the turbo was over 200 degrees F. actual temperature at the inlet to the carburetor even allowing for the low temperature at 25,000ft without an inter-cooler would have been around 175 degreesfF.
The intercooler was supposed to get the temperature back down to under 100 degrees F. To do that with an air to air intercooler you need about 3 times the mass airflow of cooling air as you have induction air.
US early turbo practices was to deliver sea level air pressure at not more than 100 degrees F to the inlet of the Carburetor. The engine supercharger was responsible for boosting the pressure to 46in or 49in or what ever that particular engine required. Now maybe you don't need 100/130 fuel to do this but 87 or 95 or 96 octane fuel is probably not going to work as well. You can forget the type of WEP levels the US got from P-47s and P-38s. The Americans were using good fuel, intercoolers and water injection on the radials. Using 2 out of three won't give the same results.
3. A turbo Japanese Zero might see about 1100-1200hp at 30,000ft or so (I don't have the books in front of me) at best, much better than a non turbo Zero but not a lot better than an F6F and not what was needed against P-47s or P-51s or even P-38s.
Other nations with fuel problems are going to be in a similar situation. A turbo can help bring the low level performance to higher altitude but it requires weight and bulk and it requires a fuel capable of working at the pressure/temperature you are trying to use at the higher altitudes. Please look at the problems the P-38G and H had even with 100/130 fuel because of inadequate intercoolers. Now imagine them trying to use fuel of less than 100/130 PN.
You have several things going on as turbos were not magic even you could build them.
1. as mentioned is the space required. A 1943 text book suggests 10 cubic feet being needed for a 1000hp engine. It is not linear, you don't need 20 cubic feet for 2000hp but something in between. Packaging is another problem. a 10 cubic foot box right behind the engine is probably not going work very well, tight radius bends in the duct work will decrease efficiency and even the Americans had trouble with overheating the turbine blades, one reason the US mounted the turbos a number of feet from the engine and exposed lengths of the exhaust pipe to cold air before they reached the turbo (P-47 excepted and that had even more distance from the engine to the turbo.
2. You need good fuel to see the kind of power the US was getting from the turbos. That or really big intercoolers. A B-17F was only using about 46in of MAP (about 8lbs boost) but at 25,000ft the temperature rise through the turbo was over 200 degrees F. actual temperature at the inlet to the carburetor even allowing for the low temperature at 25,000ft without an inter-cooler would have been around 175 degreesfF.
The intercooler was supposed to get the temperature back down to under 100 degrees F. To do that with an air to air intercooler you need about 3 times the mass airflow of cooling air as you have induction air.
US early turbo practices was to deliver sea level air pressure at not more than 100 degrees F to the inlet of the Carburetor. The engine supercharger was responsible for boosting the pressure to 46in or 49in or what ever that particular engine required. Now maybe you don't need 100/130 fuel to do this but 87 or 95 or 96 octane fuel is probably not going to work as well. You can forget the type of WEP levels the US got from P-47s and P-38s. The Americans were using good fuel, intercoolers and water injection on the radials. Using 2 out of three won't give the same results.
3. A turbo Japanese Zero might see about 1100-1200hp at 30,000ft or so (I don't have the books in front of me) at best, much better than a non turbo Zero but not a lot better than an F6F and not what was needed against P-47s or P-51s or even P-38s.
Other nations with fuel problems are going to be in a similar situation. A turbo can help bring the low level performance to higher altitude but it requires weight and bulk and it requires a fuel capable of working at the pressure/temperature you are trying to use at the higher altitudes. Please look at the problems the P-38G and H had even with 100/130 fuel because of inadequate intercoolers. Now imagine them trying to use fuel of less than 100/130 PN.
With so many cars and trucks fitted to turbos it is easy to forget that they took time to sort. They operate at very high RPM and very high temperatures, sortin the metallurgy and lubrication takes time. Also a turbo is not entirely free power, you lose exhaust thrust and there is a small drop in engine power caused by the pressure in the manifold.
Shortround6
Major General
We also have to remember that with cars and trucks, for the most part, the altitudes are 5000ft and under.
at sea level a turbo that has a 2:1 pressure ratio can give you 14.7 lbs of boost or 59.84 in of MAP.
At 20,000ft such a turbo gives you 27.5 in of MAP or about -1.2 lbs of boost.
at sea level a turbo that has a 2:1 pressure ratio can give you 14.7 lbs of boost or 59.84 in of MAP.
At 20,000ft such a turbo gives you 27.5 in of MAP or about -1.2 lbs of boost.
This is a classic case of theory, excellence and practicality being in conflict. A turbo first stage and supercharger second stage may well be the best theoretical solution but which engine and airframe will it be applied to in 1939. Whether a water cooled V or a rotary air cooled engine you need a big airframe and also in terms of logistics both a supercharger and a turbo.
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- #11
Its interesting that the only two mass production fighters with turbos was the P-47 with its fat fuselage and the P-38 with seperate engine nacelles, the need to keep the WW2 metallurgy turbo away from the hottest exhaust gases probably doomed it on other prototypes that tried it.
A well designed supercharger like on the Merlins did a fine job and more compactly and without complex controls like I saw on a Youtube video of US B-25 and P-38 training video https://www.youtube.com /watch?v=tikLgimgT7w
Still I wonder what the hp loss of a 2 stage high speed blower is?
A well designed supercharger like on the Merlins did a fine job and more compactly and without complex controls like I saw on a Youtube video of US B-25 and P-38 training video https://www.youtube.com /watch?v=tikLgimgT7w
Still I wonder what the hp loss of a 2 stage high speed blower is?
parsifal
Colonel
From this site:
Which Is Better, Turbocharging or Supercharging?
'
"Turbochargers are superb power enhancers at high engine speeds but are known laggards at low r.p.m. This is because the energy that drives the pinwheels inside a turbo comes from the exhaust stream; the force is greatest when the engine is turning its fastest.
Superchargers have opposite characteristics. Because they are spun by the engine's crankshaft, usually through a belt drive, this type of booster is ready to deliver air even at low speeds. However, at very high r.p.m., a supercharger can impede air flow and, therefore, power production. Theoretically, the best of all worlds would be using a supercharger to increase low-speed output and a turbocharger to add high-r.p.m. muscle.
That was VW's thinking with the Twincharger engine, first offered on 2006 Golf and Touran models in markets outside of the United States. The goal was to coax the acceleration of a larger power plant from a 1.4-liter 4-cylinder engine without a penalty in fuel-consumption".
So with that said, were turbocharged aero engines a bit more sluggish at lower speeds or lower revolutions?
Which Is Better, Turbocharging or Supercharging?
'
"Turbochargers are superb power enhancers at high engine speeds but are known laggards at low r.p.m. This is because the energy that drives the pinwheels inside a turbo comes from the exhaust stream; the force is greatest when the engine is turning its fastest.
Superchargers have opposite characteristics. Because they are spun by the engine's crankshaft, usually through a belt drive, this type of booster is ready to deliver air even at low speeds. However, at very high r.p.m., a supercharger can impede air flow and, therefore, power production. Theoretically, the best of all worlds would be using a supercharger to increase low-speed output and a turbocharger to add high-r.p.m. muscle.
That was VW's thinking with the Twincharger engine, first offered on 2006 Golf and Touran models in markets outside of the United States. The goal was to coax the acceleration of a larger power plant from a 1.4-liter 4-cylinder engine without a penalty in fuel-consumption".
So with that said, were turbocharged aero engines a bit more sluggish at lower speeds or lower revolutions?
Shortround6
Major General
I tend to doubt it. Near sea level the turbo didn't do much anyway as all (or almost all) the boost was coming from the engine supercharger.
All the US turbos were two stage systems with the compressors in series.
At high altitudes and in cruise you still had the engine supercharger supplying a modest amount of boost should the throttle be fully opened.
The trouble with trying to compare airplanes and cars is that on the airplane the propeller performs 3 functions. It takes the place of the tires as it transfers the power/torque to the air, bite or grip if you will. It takes the place of the transmission. Fine pitch is low gear and course pitch is high gear. how far the airplane travels per revolution of the propeller/engine. and 3rd it provides a flywheel effect.
Trying to accelerate a 300-500lb propeller from 750rpm to 1500rpm is going to take a little while without counting the prop changing pitch in the mean time. The prop may have to go from a course pitch to a finer pitch as the revs go up and then back to increasingly course pitch as speed of the aircraft increases once the engine has hit or approached max rpm.
It could take a Spitfire MK V 2 minutes to go from around 200mph to full speed. I don't have number for most of the other WW II fighters.
Granted it takes a while for a large aircraft turbo to go from idle (5-8000rpm?) to full speed.
cars often operate at a fraction of the full power, cruise on the highway (at least here in the US at 70mph and under) is done at around 20hp or less (dead flat and no wind). I doubt most planes cruised at anywhere near that fraction of power.
All the US turbos were two stage systems with the compressors in series.
At high altitudes and in cruise you still had the engine supercharger supplying a modest amount of boost should the throttle be fully opened.
The trouble with trying to compare airplanes and cars is that on the airplane the propeller performs 3 functions. It takes the place of the tires as it transfers the power/torque to the air, bite or grip if you will. It takes the place of the transmission. Fine pitch is low gear and course pitch is high gear. how far the airplane travels per revolution of the propeller/engine. and 3rd it provides a flywheel effect.
Trying to accelerate a 300-500lb propeller from 750rpm to 1500rpm is going to take a little while without counting the prop changing pitch in the mean time. The prop may have to go from a course pitch to a finer pitch as the revs go up and then back to increasingly course pitch as speed of the aircraft increases once the engine has hit or approached max rpm.
It could take a Spitfire MK V 2 minutes to go from around 200mph to full speed. I don't have number for most of the other WW II fighters.
Granted it takes a while for a large aircraft turbo to go from idle (5-8000rpm?) to full speed.
cars often operate at a fraction of the full power, cruise on the highway (at least here in the US at 70mph and under) is done at around 20hp or less (dead flat and no wind). I doubt most planes cruised at anywhere near that fraction of power.
MIflyer
1st Lieutenant
"So with that said, were turbocharged aero engines a bit more sluggish at lower speeds or lower revolutions?"
Well, note that the US used BOTH mechanical superchargers and turbos - when we used a turbo. The B-29 had Three superchargers on each engine, one mechanical engine driven and two turbos.
On the P-38 pilots were advised to make sure that BOTH turbos were spun up before takeoff. The reason is obvious.
Also note that the BF-109 used a fluid coupled single stage supercharger that fed power gradually to the supercharger and eliminated the "thump" when the V-1650 switched supercharger gears and that made fighting at that altitude (18,000 ft) so challenging. On the other hand at low altitudes the BF-109 supercharger absorbed more power than it provided boost. There is at least one combat report of 109's sneaking up on P-38's at low altitude, being discovered just before they got into gun range and then having their intended victims seem to just disappear before their very eyes. Similarly, an FW-190 pilot who thought he was sneaking under the Allied top cover was shot down by an A-36A and then asked the "Apache" pilot, "How did you catch me, as fast as I was going?" Of course the A-36A supercharger was optimized for about 5000 ft.
By the way see those little "fins" on the inboard side of the turbos on a P-38? On the early models they had the Allison supercharger set to provide lower boost and depended on the turbo for more boost. That resulted in the turbos overspeeding at high altitude and exploding. Those fins were "armor" to protect the pilot against the airplane's own turbos. They raised the boost on the Allisons to help keep that from occurring but left the "Turbo Armor" in.
Over Japan the Japanese were too smart to fight the P-51 at higher altitudes, preferring to stay down around 15,000 ft, where their superchargers were operating at near optimum while the Mustang's was starting to top out, being in Low Speed until 18,000 ft. One of the squadron leaders on Iwo told his crew chief to replace the momentary contact test switch used to test the supercharger high speed function with a non-spring loaded switch so he could override the aneroid device and get 2 stage boost lower than 18,000 ft. The Packard rep said, (insert Scottish accent), "No Captain, you canna do that! You'll bloooow up the engine!" They did it anyway and it worked great. Of course, with the B-29's at 25,000 ft o daylight raids they were not going to be bothered by Japanese fighters 2 miles below, but no fighter pilot was going to fly all the way to Japan and resist the urge to make a kill.
Well, note that the US used BOTH mechanical superchargers and turbos - when we used a turbo. The B-29 had Three superchargers on each engine, one mechanical engine driven and two turbos.
On the P-38 pilots were advised to make sure that BOTH turbos were spun up before takeoff. The reason is obvious.
Also note that the BF-109 used a fluid coupled single stage supercharger that fed power gradually to the supercharger and eliminated the "thump" when the V-1650 switched supercharger gears and that made fighting at that altitude (18,000 ft) so challenging. On the other hand at low altitudes the BF-109 supercharger absorbed more power than it provided boost. There is at least one combat report of 109's sneaking up on P-38's at low altitude, being discovered just before they got into gun range and then having their intended victims seem to just disappear before their very eyes. Similarly, an FW-190 pilot who thought he was sneaking under the Allied top cover was shot down by an A-36A and then asked the "Apache" pilot, "How did you catch me, as fast as I was going?" Of course the A-36A supercharger was optimized for about 5000 ft.
By the way see those little "fins" on the inboard side of the turbos on a P-38? On the early models they had the Allison supercharger set to provide lower boost and depended on the turbo for more boost. That resulted in the turbos overspeeding at high altitude and exploding. Those fins were "armor" to protect the pilot against the airplane's own turbos. They raised the boost on the Allisons to help keep that from occurring but left the "Turbo Armor" in.
Over Japan the Japanese were too smart to fight the P-51 at higher altitudes, preferring to stay down around 15,000 ft, where their superchargers were operating at near optimum while the Mustang's was starting to top out, being in Low Speed until 18,000 ft. One of the squadron leaders on Iwo told his crew chief to replace the momentary contact test switch used to test the supercharger high speed function with a non-spring loaded switch so he could override the aneroid device and get 2 stage boost lower than 18,000 ft. The Packard rep said, (insert Scottish accent), "No Captain, you canna do that! You'll bloooow up the engine!" They did it anyway and it worked great. Of course, with the B-29's at 25,000 ft o daylight raids they were not going to be bothered by Japanese fighters 2 miles below, but no fighter pilot was going to fly all the way to Japan and resist the urge to make a kill.
MIflyer
1st Lieutenant
"I doubt most planes cruised at anywhere near that fraction of power."
Yes! Typical high speed cruise is 75% power. Economy cruise is 65% power. When just tooling around the local area I'm at about 2100 rpm, or about 55% power. One big problem with using automobile engines in aircraft is that they are not designed to deliver that kind of power for extended periods; they tend to overheat and wear out the valves if you try. Truck engines are a bit better in that regard. A while back a guy built a 75% scale P-6E. He put a big auto engine in it ,figuring that if he operated it at only 75% power he would be Okay, and in terms of "scale" it would be the right size for the airplane in terms of weight and power. I don't know how it worked out for him in the long term.
Yes! Typical high speed cruise is 75% power. Economy cruise is 65% power. When just tooling around the local area I'm at about 2100 rpm, or about 55% power. One big problem with using automobile engines in aircraft is that they are not designed to deliver that kind of power for extended periods; they tend to overheat and wear out the valves if you try. Truck engines are a bit better in that regard. A while back a guy built a 75% scale P-6E. He put a big auto engine in it ,figuring that if he operated it at only 75% power he would be Okay, and in terms of "scale" it would be the right size for the airplane in terms of weight and power. I don't know how it worked out for him in the long term.
It's in the area of 100 hp in M gear and over 250hp in S gear from what I've found.
I'd recommend as MIflyer posted above to get a copy of Airpower 2001 Volume 31 no. 6 to increase your knowledge. You can get a copy here for $8.00. It's well worth getting.
Amazon product ASIN B001TM8ESIView: https://www.amazon.com/Airpower-Vol-No-November-2001/dp/B001TM8ESI
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In general, there were challenging technical problems:
- High temperature alloys were required for exhaust ducting and turbine blades
- Reliable and effective controls were required (overspeeding could result in rapid failure)
- Mechanical resonance issues could result in vibration (leading to fatigue failures)
- Efficient intercoolers needed to be designed if the advantages were to be fully exploited
- Installations needed to be designed that would minimize drag
Note that, although the US had the most experience (and success), turbosupercharged developments of some engines, notably the R2600 seem to have been unsuccessful. Even after WWII, commercial airliners continued to rely on mechanically supercharged engines. The later (and much more complex) turbo-compound engines were used in the last generation of piston engined airliners with some success, though reliability suffered.
There were also significant disadvantages that had to be considered:
- The possibility of extracting jet thrust from the exhaust was lost (if the later and not very successful VDT concept is excluded)
- The turbo lag affecting throttle response was a problem in some applications, such as carrier operations
- Considerably more space was required than for alternative mechanically driven two stage supercharger arrangements
- There was no advantage at low altitudes - the extra size and weight of the turbosupercharger installation was not offset by any gain in power
There were significant practical issues in installing turbosuperchargers in single engined aircraft. The P-47 installation worked, in part because it was possible to place the turbosupercharger in the rear of the plane and provide internal ducting for air and exhaust gases without incurring a large drag penalty. Attempts to add turbosuperchargers to single engined fighters using inline engines were generally much less successful - the XP60A (Curtiss XP-60 Prototype Fighter Aircraft) and FW190A come to mind. Note that the P-63 went with versions of the Alison engine having 2 stage mechanically driven superchargers.
rinkol, post:
In general, there were challenging technical problems:
- High temperature alloys were required for exhaust ducting and turbine blades
The US had those in quantity.
- Reliable and effective controls were required (overspeeding could result in rapid failure)
The D,M and N models had them.
- Mechanical resonance issues could result in vibration (leading to fatigue failures)
That's true for all mechanical machines.
- Efficient intercoolers needed to be designed if the advantages were to be fully exploited
No different than 2 stage mechanical units.
- Installations needed to be designed that would minimize drag
No doubt about that.
Even after WWII, commercial airliners continued to rely on mechanically supercharged engines.
You don't need a 2 stage system when your flying at the altitudes most Commercial aircraft were flying at the time. Most used single stage; although a couple not long before the jet age did use turbo-compounds.
There were also significant disadvantages that had to be considered:
- The possibility of extracting jet thrust from the exhaust was lost (if the later and not very successful VDT concept is excluded)
Oh there's thrust alright, just not as much. The Jug only lost 20hp +/- in the climb instead of a couple of hundred for those without a turbo and using 2 speed/2 stage mechanical units.
- The turbo lag affecting throttle response was a problem in some applications, such as carrier operations
I agree. I suppose that's why Col. Zemke says he never pulled power off when attacking; always diving balls out.
- Considerably more space was required than for alternative mechanically driven two stage supercharger arrangements
I agree
- There was no advantage at low altitudes - the extra size and weight of the turbosupercharger installation was not offset by any gain in power.
Correct - There is no advantage, then again the Turbo totally out performed mechanical 2 speed/2 stage supercharging at 28-30,000 ft. Also the turbo didn't add extra weight. On the R-2800 it was in fact somewhat lighter than the mechanical setup used in Navy fighters. It would've been great to have a Stanley Hooker working in the states.
There were significant practical issues in installing turbosuperchargers in single engined aircraft. The P-47 installation worked, in part because it was possible to place the turbosupercharger in the rear of the plane and provide internal ducting for air and exhaust gases without incurring a large drag penalty. Attempts to add turbosuperchargers to single engined fighters using inline engines were generally much less successful - the XP60A (Curtiss XP-60 Prototype Fighter Aircraft) and FW190A come to mind. Note that the P-63 went with versions of the Alison engine having 2 stage mechanically driven superchargers.
Correct - except the P-63 had a geared first stage and fluid coupled second stage. Yes I know I'm being picky.
The Russians, Japanese, and German's all understood what a turbo could do for high altitude combat, since almost all of their aircraft were single stage mechanical units they wanted them badly. They all had working experimental examples. The Germans problem was the amount of nickel needed not only for the turbo, but also for the exhaust piping. The Russian's had some working examples; had some issues, then realized there was no need for high altitude performance. Japan's issue was they ran out of time.
In general, there were challenging technical problems:
- High temperature alloys were required for exhaust ducting and turbine blades
The US had those in quantity.
- Reliable and effective controls were required (overspeeding could result in rapid failure)
The D,M and N models had them.
- Mechanical resonance issues could result in vibration (leading to fatigue failures)
That's true for all mechanical machines.
- Efficient intercoolers needed to be designed if the advantages were to be fully exploited
No different than 2 stage mechanical units.
- Installations needed to be designed that would minimize drag
No doubt about that.
Even after WWII, commercial airliners continued to rely on mechanically supercharged engines.
You don't need a 2 stage system when your flying at the altitudes most Commercial aircraft were flying at the time. Most used single stage; although a couple not long before the jet age did use turbo-compounds.
There were also significant disadvantages that had to be considered:
- The possibility of extracting jet thrust from the exhaust was lost (if the later and not very successful VDT concept is excluded)
Oh there's thrust alright, just not as much. The Jug only lost 20hp +/- in the climb instead of a couple of hundred for those without a turbo and using 2 speed/2 stage mechanical units.
- The turbo lag affecting throttle response was a problem in some applications, such as carrier operations
I agree. I suppose that's why Col. Zemke says he never pulled power off when attacking; always diving balls out.
- Considerably more space was required than for alternative mechanically driven two stage supercharger arrangements
I agree
- There was no advantage at low altitudes - the extra size and weight of the turbosupercharger installation was not offset by any gain in power.
Correct - There is no advantage, then again the Turbo totally out performed mechanical 2 speed/2 stage supercharging at 28-30,000 ft. Also the turbo didn't add extra weight. On the R-2800 it was in fact somewhat lighter than the mechanical setup used in Navy fighters. It would've been great to have a Stanley Hooker working in the states.
There were significant practical issues in installing turbosuperchargers in single engined aircraft. The P-47 installation worked, in part because it was possible to place the turbosupercharger in the rear of the plane and provide internal ducting for air and exhaust gases without incurring a large drag penalty. Attempts to add turbosuperchargers to single engined fighters using inline engines were generally much less successful - the XP60A (Curtiss XP-60 Prototype Fighter Aircraft) and FW190A come to mind. Note that the P-63 went with versions of the Alison engine having 2 stage mechanically driven superchargers.
Correct - except the P-63 had a geared first stage and fluid coupled second stage. Yes I know I'm being picky.
The Russians, Japanese, and German's all understood what a turbo could do for high altitude combat, since almost all of their aircraft were single stage mechanical units they wanted them badly. They all had working experimental examples. The Germans problem was the amount of nickel needed not only for the turbo, but also for the exhaust piping. The Russian's had some working examples; had some issues, then realized there was no need for high altitude performance. Japan's issue was they ran out of time.
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Shortround6
Major General
Actually turbo engines need better intercoolers because the turbo was compressing air more (heating it) at the higher altitudes.
R-2800-8 with a two stage started dropping pressure at around 23,000ft including RAM. Even an Early P-47 could hold pressure to 27,800ft in level flight.
After WW II the long range piston planes moved to flying at 20,000ft and above pretty quick. The turbo compound gears the turbo units to the crankshaft and they do NOT provide boost to the intake system of the engine. The Boeing 377 Stratocruiser did use turbo charged engines.
You have thrust figures for the P-47 exhaust? I have never seen any figures for the exhaust thrust of the R-2800 in any form, I am sure they exist somewhere.
more later.
MIflyer
1st Lieutenant
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