Why or why not turbo chargers

[drgondog]

[QUOTE=Shortround6;540601][QUOTE=Clay_Allison;540583]To an extent, yes. The Germans figured out they could wait for the escort fighters (mostly P-47s) to turn around and then lay into the bombers. Obviously both planes were fighting in the PTO as well, but in the ETO it was the P-51 that took the fight to the enemy in a huge way. Unsurprisingly, it was not a turbocharged fighter.

Well that worked right up until the P-47s stared flying relays. One group flying over the Dutch airfields, another flying with bombers and yet a third flying directly to the target area at economical cruising speed to meet up with bombers and escort them back. By the time the Mustangs began to show up in any real numbers the P-47s were being fitted with under wing drop tanks, while still shorter ranged than a clean Mustang a Range of 790 miles at just under 300mph wasn't too shabby. Late model Ds could carry even more fuel. Uneconomical to be sure but that might have had something to do with the size and weight of the P-47 and not necessarily the type of supercharger on the engine.

You are the one who keeps compalining about high altitude performance, An early P-47 D was about 20mph faster than a B model Mustang at most altitudes over 30,000ft.

The contemporary P-47D-10 in ETO at same time as P-51B-1 and -3 would not exceed the 51B in anything except rate of roll, which was superior. Dive and zoom is a toss up. Acceleration and turn and climb and level speed and range go to the 51B. The critical altitude of the D-10 was 25K, for the P-51B-1 29K so the advantage went to 51B-1 for all high altitudes..

Top speed with full internal load of fuel for the P-47D-10 w/Paddle props @2700 Rpm and 56Hg/WI was ~ 430 and went down hill as altitude was increased over 25K. The 51B-1 critical altitude was 29.8K feet and had top speed of 437 with full internal load and 50% higher climb rate..

By the time the P-47D-25 arrived, of course the high altitude performance increased to par with the 51B at 25K, slightly faster at 23K, when using the higher octane fuel at 70in Hg. Then the 47D-25 and newer increased speed above 30K as higher hp engines were installed

The P-51B-1 at 30K was faster than the 47D-25 at 30K at only 51" Hg and still had a better climb rate.

If you want to boost P-47D performance comparisons vs the P-51 you want to compare P-51D vs the contemporary 47's as it had the 1650-7 Merlin set for better performance (vs 51-1 and -3 and -5) at middle to 25K than the 1650-3 engine.

and then there was the range 'thingy' advantage which was stepped up again with the 85 gallon fuse tank mods until the production -5.

The P-47s were strictly relegated to Penetration and Withdrawal Support until the late model D's arrived in numbers and by that time most were going to 9th AF as the 8th was filling up with Mustangs to replace the P-38 ad P-47 Groups.

The premier 47 group, the 56th, virtually never went past Hanover/Kiel to the North and Stuttgart to the South until December 1944. Their last huge month was March - coincidently the start of the Berlin missions - and by that time the 4th, 354th, 355th, 357th and 363rd were equipped with Mustangs and the limit of 47 range was Dummer Lake.

Clay is right that LW tactics, pre Mustang, was to wait for the 47s to turn back. There were only two P-38 groups through February and they were easy to spot and therfore decide whether to engage or go somewhere else along a 100 mile bomber stream.

[Shortround6]

Sorry, I was going by numbers from here: P-47 Performance Tests

See numbers for P-47D-10 dated 11 October 1943 and

http://www.wwiiaircraftperformance.o...level-blue.jpg

I see that I made a mistake in using the numbers from the P-51B-15 instead of the B-1.

I have read other places that the paddle blade props weren't fitted to new planes until the -20 or -22 aircraft. Of course older aircraft could easily have been refitted.

I am not trying to say that the P-47 was better than the P-51 but Mr. Allison's seeming contention that the AAF was helpless and or useless before the advent of the Mustang is wearing a bit thin.

[billswagger]

[QUOTE=drgondog;541880][QUOTE=Shortround6;540601]

To an extent, yes. The Germans figured out they could wait for the escort fighters (mostly P-47s) to turn around and then lay into the bombers. Obviously both planes were fighting in the PTO as well, but in the ETO it was the P-51 that took the fight to the enemy in a huge way. Unsurprisingly, it was not a turbocharged fighter.

The contemporary P-47D-10 in ETO at same time as P-51B-1 and -3 would not exceed the 51B in anything except rate of roll, which was superior. Dive and zoom is a toss up. Acceleration and turn and climb and level speed and range go to the 51B. The critical altitude of the D-10 was 25K, for the P-51B-1 29K so the advantage went to 51B-1 for all high altitudes..

Top speed with full internal load of fuel for the P-47D-10 w/Paddle props @2700 Rpm and 56Hg/WI was ~ 430 and went down hill as altitude was increased over 25K. The 51B-1 critical altitude was 29.8K feet and had top speed of 437 with full internal load and 50% higher climb rate..

By the time the P-47D-25 arrived, of course the high altitude performance increased to par with the 51B at 25K, slightly faster at 23K, when using the higher octane fuel at 70in Hg. Then the 47D-25 and newer increased speed above 30K as higher hp engines were installed

The P-51B-1 at 30K was faster than the 47D-25 at 30K at only 51" Hg and still had a better climb rate.

If you want to boost P-47D performance comparisons vs the P-51 you want to compare P-51D vs the contemporary 47's as it had the 1650-7 Merlin set for better performance (vs 51-1 and -3 and -5) at middle to 25K than the 1650-3 engine.

and then there was the range 'thingy' advantage which was stepped up again with the 85 gallon fuse tank mods until the production -5.

The P-47s were strictly relegated to Penetration and Withdrawal Support until the late model D's arrived in numbers and by that time most were going to 9th AF as the 8th was filling up with Mustangs to replace the P-38 ad P-47 Groups.

The premier 47 group, the 56th, virtually never went past Hanover/Kiel to the North and Stuttgart to the South until December 1944. Their last huge month was March - coincidently the start of the Berlin missions - and by that time the 4th, 354th, 355th, 357th and 363rd were equipped with Mustangs and the limit of 47 range was Dummer Lake.

Clay is right that LW tactics, pre Mustang, was to wait for the 47s to turn back. There were only two P-38 groups through February and they were easy to spot and therfore decide whether to engage or go somewhere else along a 100 mile bomber stream.

Drgondog, i think we went back and forth on another thread a few months ago that brought comparisons of the P-51B and P-47C (might have been an early D).
It was determined that the 47 had a better zoom climb performance, out of level flight and even more so out of a dive. The P-51 had the edge in acceleration while the P-47 had better dive performance, however in most respects they were similar in performance.


Needless to say, the range of the Mustang is what gave its prowess. In a lot of ways i think its over rated as a fighter (IMO), but the remarkable thing is that the 51 was able to fly such long distances and still compete as a fighter plane.

[drgondog]

Sorry, I was going by numbers from here: P-47 Performance Tests

See numbers for P-47D-10 dated 11 October 1943 and

http://www.wwiiaircraftperformance.o...level-blue.jpg

I see that I made a mistake in using the numbers from the P-51B-15 instead of the B-1.

I have read other places that the paddle blade props weren't fitted to new planes until the -20 or -22 aircraft. Of course older aircraft could easily have been refitted.

I am not trying to say that the P-47 was better than the P-51 but Mr. Allison's seeming contention that the AAF was helpless and or useless before the advent of the Mustang is wearing a bit thin.

ShortR - the P-47-10 was fitted with paddle blade kits at 56th FG in Jan 1944 and rest of 8th FC in Feb-Mar 1944. Major difference in low to medium climb performance and some in dash speed.

The P-51B-7 thru -15 had the 1650-7 which was wonderful through the low/middle altitudes

The Jug was never 'hopeless' but it didn't have the range to engage in the big airbattles April-November, 1944

[drgondog]

[QUOTE=billswagger;542098][QUOTE=drgondog;541880]

Drgondog, i think we went back and forth on another thread a few months ago that brought comparisons of the P-51B and P-47C (might have been an early D).
It was determined that the 47 had a better zoom climb performance, out of level flight and even more so out of a dive. The P-51 had the edge in acceleration while the P-47 had better dive performance, however in most respects they were similar in performance.

You have to be careful on the timing and the model - the 47C was compared against the P-51A (as well as P-38F) and what you say is true.. but not when comparing the 51B-1 vs the 47D-10 in comparable timeframes


Needless to say, the range of the Mustang is what gave its prowess. In a lot of ways i think its over rated as a fighter (IMO), but the remarkable thing is that the 51 was able to fly such long distances and still compete as a fighter plane.

All opionions are worthy. The key is that the Mustang killed the Luftwaffe over Germany, not the P-47 and not the P-38 and not the Spit and not the Tempest and not the Yak and not the Laag.

[billswagger]

[QUOTE=drgondog;542194][QUOTE=billswagger;542098]

All opionions are worthy. The key is that the Mustang killed the Luftwaffe over Germany, not the P-47 and not the P-38 and not the Spit and not the Tempest and not the Yak and not the Laag.

another key is that with out the Spitfire, (or YaK) we would've never needed the P-47 or 38.
with out the 47 or the 38, we wouldn't have needed the later Mustang.
Each plane had its place in the war.
All planes shot down the Luftwaffe, if you'd like to hype up the Mustang for doing it over Germany then so be it.

[Clay_Allison]

Sorry, I was going by numbers from here: P-47 Performance Tests

See numbers for P-47D-10 dated 11 October 1943 and

http://www.wwiiaircraftperformance.o...level-blue.jpg

I see that I made a mistake in using the numbers from the P-51B-15 instead of the B-1.

I have read other places that the paddle blade props weren't fitted to new planes until the -20 or -22 aircraft. Of course older aircraft could easily have been refitted.

I am not trying to say that the P-47 was better than the P-51 but Mr. Allison's seeming contention that the AAF was helpless and or useless before the advent of the Mustang is wearing a bit thin.

Not helpless, not useless, just not nearly as good as they could have been if they had not obsessed over turbocharging to the exclusion of multi-stage supercharging. I think better decisions could have led to a reliable P-38 in the ETO (which would have dramatically improved the survival rates of our bombers). Also better P-40 performance, especially in North Africa and probably in Asia versus the A6M Zero.

[drgondog]

[QUOTE=billswagger;542247][QUOTE=drgondog;542194]

another key is that with out the Spitfire, (or YaK) we would've never needed the P-47 or 38.
with out the 47 or the 38, we wouldn't have needed the later Mustang.
Each plane had its place in the war.
All planes shot down the Luftwaffe, if you'd like to hype up the Mustang for doing it over Germany then so be it.

BillS - please check your facts against the statement I made - "The Mustang killed the Luftwaffe over Germany" - that is where the battle for air supremacy was a.) lost before the Mustang, when all other fighters were either restricted from target escort by range (P-47, Spitfire, etc) or P-38's high performance issues in the F and G and early J's, and b.) where the LW was losing ~1000 pilots per month in March, April and May 1944.

If you think it is hype - look at the statistics of German aircraft shot down on Target escort versus Penetration and Withdrawal escorts.

[Shortround6]

Not helpless, not useless, just not nearly as good as they could have been if they had not obsessed over turbocharging to the exclusion of multi-stage supercharging. I think better decisions could have led to a reliable P-38 in the ETO (which would have dramatically improved the survival rates of our bombers). Also better P-40 performance, especially in North Africa and probably in Asia versus the A6M Zero.

The Army may have been slightly obsessed with the Turbo-charger but not to the extent you seem to think.
They did test (pay for) at least one two-stage supercharged plane in 1939.
Work on the turbo for the Allison started in early 1933. GE (not Allison) got the $10,006 contrat to supply a turbo in 5 months. this early model was only supposed to provide sea-level air pressure to the engine supercharger up to 20,000ft.
By 1937-38 progress was not good enough for service work.

Allison did start work on a mechanical 2 stage supercharger on Nov of 1938. They did get experimental versions under test by 1940.

Now in 1940 they were still trying to improve on GE's rather poor performing superchargers, which Allison did. Just not the extent of improvement that R-R was getting per impellor.

as an example Allison was getting 1150HP at 3000rpm at 21,000ft using 49.7in of boost. This doesn't sound bad except for the fact that the engine was developing around 1630 Indicated HP. 147hp for friction, oil pumps, coolant pumps and other drives, aproxomatly 120 hp needed by the engine supercharger and about 220 HP needed to drive the auxilary stage. This early test engine also used a single speed drive for the aux supercharger. This was soon changed to a variable speed hydraulic drive. The first set up was intended for the Curitiss P-60 while the second set up was actually flown in Bell XP-39Es.

"The fuselage was lengthened by 1.75 feet to accommodate the longer -47 engine."
"Empty and loaded weights were 6936 lbs and 8918 lbs respectively, making the XP-39E the heaviest of all Airacobra variants. During tests, a maximum speed of 386 mph at 21,680 feet was attained, which was much better high-altitude performance than other Airacobra variants. An altitude of 20,000 feet could be reached in 9.3 minutes."
"About two weeks after its maiden flight, the first XP-39E crashed during spin tests on March 26, 1942."

These quotes are from:Bell XP-39E Airacobra

It took R-R 15 months to do the work on the two stage Merlin and they already had the Vulture supercharger sized for about a 1700HP air flow at altitude.

So in 1938 the Army would have had to figure out that the Turbo wouldn't be ready even 4 years in the future, and try to speed up Allisons work by well over one year to get any numbers into service by spring of 1942.
Allison would not only have to figure out the configuration but also substationaly improve basic compressor perfomance. Improving compressor efficency has the triple benifit of requiring less power to drive the supercharger for a given airflow (power) meaning more power to the prop. Lower heating of the charge temperature meaning higher air density and more power. And the lower charge temperature also offers either a higher boost limit or a greater safety margin from detonation. In a two stage system a more efficent compressor also means you can use a slightly smaller intercooler.

[Clay_Allison]

The Army may have been slightly obsessed with the Turbo-charger but not to the extent you seem to think.
They did test (pay for) at least one two-stage supercharged plane in 1939.
Work on the turbo for the Allison started in early 1933. GE (not Allison) got the $10,006 contrat to supply a turbo in 5 months. this early model was only supposed to provide sea-level air pressure to the engine supercharger up to 20,000ft.
By 1937-38 progress was not good enough for service work.

Allison did start work on a mechanical 2 stage supercharger on Nov of 1938. They did get experimental versions under test by 1940.

Now in 1940 they were still trying to improve on GE's rather poor performing superchargers, which Allison did. Just not the extent of improvement that R-R was getting per impellor.

as an example Allison was getting 1150HP at 3000rpm at 21,000ft using 49.7in of boost. This doesn't sound bad except for the fact that the engine was developing around 1630 Indicated HP. 147hp for friction, oil pumps, coolant pumps and other drives, aproxomatly 120 hp needed by the engine supercharger and about 220 HP needed to drive the auxilary stage. This early test engine also used a single speed drive for the aux supercharger. This was soon changed to a variable speed hydraulic drive. The first set up was intended for the Curitiss P-60 while the second set up was actually flown in Bell XP-39Es.

"The fuselage was lengthened by 1.75 feet to accommodate the longer -47 engine."
"Empty and loaded weights were 6936 lbs and 8918 lbs respectively, making the XP-39E the heaviest of all Airacobra variants. During tests, a maximum speed of 386 mph at 21,680 feet was attained, which was much better high-altitude performance than other Airacobra variants. An altitude of 20,000 feet could be reached in 9.3 minutes."
"About two weeks after its maiden flight, the first XP-39E crashed during spin tests on March 26, 1942."

These quotes are from:Bell XP-39E Airacobra

It took R-R 15 months to do the work on the two stage Merlin and they already had the Vulture supercharger sized for about a 1700HP air flow at altitude.

So in 1938 the Army would have had to figure out that the Turbo wouldn't be ready even 4 years in the future, and try to speed up Allisons work by well over one year to get any numbers into service by spring of 1942.
Allison would not only have to figure out the configuration but also substationaly improve basic compressor perfomance. Improving compressor efficency has the triple benifit of requiring less power to drive the supercharger for a given airflow (power) meaning more power to the prop. Lower heating of the charge temperature meaning higher air density and more power. And the lower charge temperature also offers either a higher boost limit or a greater safety margin from detonation. In a two stage system a more efficent compressor also means you can use a slightly smaller intercooler.

It's not just that they should have known the turbo wouldn't be ready, they should have known that it would never fit in a smallish single engine fighter like the P-39 or P-40 because it was too large. That should have been obvious in 1938. I think they could have speeded up development with more funding.

[Shortround6]

It's not just that they should have known the turbo wouldn't be ready, they should have known that it would never fit in a smallish single engine fighter like the P-39 or P-40 because it was too large. That should have been obvious in 1938. I think they could have speeded up development with more funding.

How could they know the trubo wouldn't be ready?

The turbo probably wouldn't have fit in the P-40, it certainly didn't fit in the P-39.
Of course it was the intercooler that didn't fit in the P-39 and you need an intercooler to get any 2 stage supercharger up to it's full potential.

Notice the stretch job that Allsion needed to get the second stage in the P-39?
And still no intercooler.

the 1938-39 two stage mecanical superchargers just may not have worked all that well. Of course there was only one. The P&W version in 1939. If it used two of the low effeciency stages of the time, and there is no reason to beleive it didn't, it may just have sucked up too much power and been too close to detonation limits to be worth doing much more with until some other things changed.

Please note that in the example give above for the Allison changing from a mecanical drive 1st stage supercharger to a turbo supercharger would have changed the propeller HP from 1150 to 1370 for the same fuel burn. Granted this would have lost any gain from jet exhaust but this was not well understood at the time. There also would have been about an 80-90 HP loss because of back pressure in the Turbo exhaust manifolds at 20,000ft.

But please note that both the exhaust jet thrust and the loss from back pressure in the manifolds change with altitude.

A turbo system has 3 components. The compressor itself and any ducting needed to get air from the outside of the plane to the compressor inlet, the intercooler and any ducting to get the induction air from the first stage to the intercooler and from the intercooler to the second (engine) stage plus the ducting needed to get cooling air to the intercooler and back out of the airplane, and 3rd the turbine, controls and exhaust pipes to get the exhaust gass from the engine to the turbine.

A mecanical drive 2 stage system aslo has three components. the first two are the same as the turbo. the third is the drive system that replaces the turbine and waste gates/controls. This can be a simple shaft or it can be a two/three speed gearbox or variable hydraulic clutch.

While it can be a bit smaller and lighter than the turbo I am just not seeing a huge difference unless you do something really different, like leave out the intercooler. Of course this severely affects the systems ability to make power at high altitudes. Allison tried to use water injection instead of an intercooler but this was only patially succesful and you should note that later P-47s, Corsairs, Hellcats and P-38s all used BOTH intercoolers and water injection. As did late model Mustangs.

It is also quite easy to say speed up development NOW. given the size of the Allison company in 1938-39 and the general lack of knowedge about superchargers in the US at the time, Allsion was working on their 4th (?) compressor when they started on the two stage system while R-R had already supercharged at least 5 different production engines BEFORE Hooker showed up.

[davebender]

How could they know the trubo wouldn't be ready?

They can't. Neither can they say for sure that turbochargers will work just fine. The prudent thing would be to develop both turbochargers and superchargers and then chose the superior system based on operational performance.

[Shortround6]

They can't. Neither can they say for sure that turbochargers will work just fine. The prudent thing would be to develop both turbochargers and superchargers and then chose the superior system based on operational performance.

Please note that the "turbo" is just a way of driving a supercharger.

THe US in the form of General Electric had been working on turbochargers since the end of WW I.
However these early set ups were single stage turbosuperchargers. During the 20's and early thirties the engines and fuels wouldn't stand or support high levels of boost. THe army was confidant enough to order the P-30 at the end of 1934. see:
Consolidated P-30 - Wikipedia, the free encyclopedia

Ir was because of this expertise that GE became the "GO TO" company for superchargers by regular engine companies Like P&W and Wright. THis bias of GE towards the Turbocharger lead to problems in the late thirties. Since they had almost unlimited power to drive the compressor from the turbine (comparitivly speaking) GE wasn't as concerend with compressor efficiecy as they might have been. This was compounded by the early adoption of the intercooler. An inefficient compressor not only takes more power to run, it turns that extra power into heat. The low octane fuels of the time wouldn't tolerate high charge temperatures. With the power question solved by the turbine and the heat problem covered by the intercooler GE continued to develop the turbine section. By the late thirties P&W and Allison both thought they could do better designing their own supercharger compressor sections than GE. Maybe Wright did too but I haven't seen that in writing yet.

Going back to the P-30, the turbo supercharger in that plane did little to boost the power at sea level over the non-supercharged versions of the engine. It did allow the engine to keep making sea level power to 15,000 ft or more. IN effect the turbo acted as a vairably speed drive on a single stage supercharger and one that made more power to drive the supercharger the higher it went without taking any power from the engine to boot. By the mid to late thirties fuel had improved to the point where engines could using superchargeing at ground level to boost performance. The P-30 was using an old engine from the 20s that would not stand much higher outputs.

The problem started to become how to get this "boosted" performance at higher altitudes. The supercharger compressors would only multiply the ambiant air pressure so many times. 2.7-2.8 was considered very good in the last of the 30s. If your engine required 1.4 times sea level pressure to amke it's "rated power" then that limited how high you could go before your supercharger reached it's limit and power started to fall off.
From a supercharger standpoint there were two options.
Design more efficient compressors with higher pressure ratios.
use two compressors in series, one blowing into the other to give a higher overall ratio. This is actually more efficient than using a single compressor. It requires less power to drive the compressors and creates less heat in the intake charge air.
Once you decide to use two compressors, how do you drive them. Both mechanicaly or one mechanicaly and one with an exhaust turbine (turbo).
IN the late thirties exhaust gas thrust was still a therory to many peaple. The XP-40 as originally flown had "streamlined exhausts" hiddin in a duct.
Please note that for an engine delivering 1000-1200HP to the propellor the "EXTRA" stage or 1st stage of a two stage supercharger can suckup over 200hp to drive it.
In other words if you want 1200hp at 20,000ft plus and you DON"T use a turbosupercharger as the first stage you actually have to build and engine capable of 1400hp or more at sea level if you took the 1st stage off the engine. The pistons, rods, crankshaft engine block etc. have to stand up to the greater load.

It is not quite a case of picking a "superior system based on operational performance" because so much has to be designed into the engine to use one system or the other to full advantage.
And operatiol performance would always favor the turbo-supercharger installation if performance at altitude was the measure. see:

http://www.zenoswarbirdvideos.com/Im...-47/47SEFC.gif
and
http://www.zenoswarbirdvideos.com/Images/F4U/F4USEC.GIF

To see how the P&W R-2800s performance drops off with altitude.

BOTH engines/aircraft are equiped with TWO STAGE superchargers WITH INTERCOOLERS.

THe P-47 has a turbo. the Corsair has a mecanical drive with nuetral (no boost from 1st stage)for low altitudes, low gear for medium altitude and high gear for high altitudes. Please note the military power ratings.
At 23,000ft the Corsair engine is using 350Hp to drive the 1st stage supercharger in high gear.

Now if your aircraft has no need of high altitude work you can of course drop the 1st stage no matter how it is driven allong with the intercooler and wind up with a smaller, lighter aircaft.