"The case for the P-47 Thunderbolt being the greatest fighter of the Second World War " (1 Viewer)

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It was obsolete by the time 150 PN fuel and 25 PSI boost was available, saying that the Merlin 50 was approved for 18 Psi mid 1943.
+18 psi was for the Mk.50M - the version with cropped impeller. Same for the Mk.45M.
Standard Mk.50 and Mk.45 were limited to +16 psi.
 
The following war-time Merlins were officially cleared for use of 150 grade and +25 lbs boost:

Merlin 24/224/25/225/26/27/66/266/70/71/76/77/100/101/113/114/130/131 and V-1650-7

All are listed in the respective airframe Pilot's Notes, and/or mentioned in Air Ministry/USAAF dispatches, as cleared for use of +25 lbs boost

Cleared when?

And when I mentioned the single-stage units, what I meant to say was that the two-stage units were cleared for +25psi at some point, but they didn't replace all the single-stage units overnight. They flew single-stage Spitfires for a long time before they wore out and there were enough two-stage units to replace most everything. Like everything else in WWII, a unit in service usually stayed in service until it could be replaced with a newer one in the normal course of operations.

Cheers.
 
It was a low altitude engine.

It used the turbocharger to be able to work at high altitude.
Read up on the Merlin Seafires like the LFIIC and the LFIIIC.

Superchargers and turbochargers use up power that could be used to drive the propeller. If you want high altitude performance, you need to drive a powerful blower somehow. The Seafire LFIIIC with its "cropped" impeller, was awesome, as long as you stayed below 9,000ft.

There is no free lunch.
 
How much of engine power was used by the turbocharger on the P-47 (for example)?
Hard to say, It pretty much killed an hope of exhaust thrust ;)

It may have cost some power due to increase back pressure in the exhaust system when the exhaust valves opened.

A booklet put out by General Motors during WW II compared 7 different supercharger set ups on a hypothetical 1000hp engine. Such an engine if operated at 20,000ft with the intake air pressure and temperature of sea level would (should?) give 1080hp simply due to the lower back pressure, nothing to do with exhaust thrust.
Merlin XX in a Hurricane had a pack pressure that varied from around 7 in/hg to 9 in/hg higher than the ambient air.

P-47s operating at high boost were often running 3-6in/hg higher than sea level pressure in their exhaust systems.

The Turbo wasn't "free" power but it was a whole lot less than the over 350hp that an F4U was using to drive it's auxiliary supercharger.
 
Merlin 25 tested for +25 lbs (Mossi FB Mk VI) Dec'43-Jan'44, cleared for use on ? May 1944 per Air Ministry memo, subsequently used on anti-V1 ops (beginning in July 1944 with Mossi NF Mk XIII/XIX aircraft) and Intruder(Ramrod?) & bomber escort operations

Merlin 25/76/100/113 cleared for +25 lbs, before 25 November 1944 Air Ministry dispatch to RAAF

Merlin 25/225 rated for +25 lbs as per late-war Mosquito FB Mk VI Pilot's Notes

Merlin 66 cleared for +25 lbs per, as noted in DED memo dated ? August 1944

V-1650-7 cleared for +25 lbs per 8th AF memo dated 24 August 1944, and DED memo dated 1 September 1944

V-1650-3/-7 and Merlin 266 cleared for +25 lbs per DED memo dated 6 September 1944

Merlin 66/266/70/71/76/77/100/101/113/114/130/131 and V-1650-7 cleared for +25 lbs per RDE memo dated ? January 1945

Merlin 76/77 cleared for +25 lbs per 2nd TAF memo dated 11 January 1945
 
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+18 psi was for the Mk.50M - the version with cropped impeller. Same for the Mk.45M.
Standard Mk.50 and Mk.45 were limited to +16 psi.
45M, 50M and 55M

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Hypothetical, how would a P47 go head to head in a one on one dogfight after the merge with a 190A or MkIX LF at low altitude?, the Jug pilot would haul the big girl around only to find the other two already in a firing position

There were some comparative combat tests done in the UK and the P-47D was considered just as capable as the 190A in a max rate sustained turning fight at low altitude.

Right down on the deck, the Jug was given a little advantage over the Wurger. But the 190A held an advantage at certain altitude bands.

Can't remember right now which service ran the tests though. Definitely western Allies though.
Bear in mind that tests with captured equipment aren't going to be 100% accurate to full performance.

A long time ago I read there was a standing order for some of 1943 that P-47 pilots didn't dogfight German single engine fighters below about 16,000 feet.

Mk IX testing vs the P-47 gave a decided advantage to the Spitfire all the way up to max rated altitude for the Merlin 61. So roughly 25-27,000 ft.
 
It's like S Shortround6 says. The engine is actively pumping air to turn the turbocharger. This may be more efficient than using torque from the driveshaft, but it takes power to drive a compressor.
I was hoping that you know the answer to a specific question:
How much of engine power was used by the turbocharger on the P-47 (for example)?

Alas.
 
I was hoping that you know the answer to a specific question:
How much of engine power was used by the turbocharger on the P-47 (for example)?

Alas.
That is something I haven't ever been able to track down. Main reason being the turbo using waste energy from the exhaust
to put more air into the engine for more power. The only main concern seems to be how much extra power is be gained rather than
how much was lost to create it.
 
That is something I haven't ever been able to track down. Main reason being the turbo using waste energy from the exhaust
to put more air into the engine for more power. The only main concern seems to be how much extra power is be gained rather than
how much was lost to create it.
The exact figure will be highly speed (i.e throttle) and altitude dependent.
 
Can't find the trials I was thinking of, but here are some comments on turn performance from the January 1943 tactical trials of the P-47C from the AFDU at Duxford:

P-47C vs Spitfire IX (Merlin 61)
  • The rate of turn of the Spitfire is naturally superior to the heavier P-47 and in turning circles it was found that after four turns the Spitfire could get on the P-47's tail and remain there with a chance of shooting with correct deflection. When 'bounced'; if a climbing turn towards the attack were made, either aircraft was able to evade the other, but if the climbs were continued, the Spitfire was able to draw away above for another attack.
vs Typhoon IB
  • The P-47C was considered far superior in rate of roll to the Typhoon, and at 20,000 feet in turning circles proved itself slightly better.
vs Mustang X
  • The rate of roll of the P-47 is considerably better than that of the Mustang, which cannot follow sudden changes in direction. In rate of turn, howeverm the two aircraft are practically identical.
vs P-38F
  • In turning circles the P-38 was slightly better and was certainly able to turn so slowly in a climbing turn, especially to the right, that the P-47 was unable to follow. When 'bounced' by the P-47, the P-38 was able to turn very sharply and decelerate much more quickly than the P-47.

Here's US tests of a captured FW190A (not sure exact sub-type, but either an A4 or an A5) vs a P-47D4 performed in Italy in December 1943. Testing was conducted between sea level and 10,000 ft. The FW-190 was noted as being in "exceptionally good condition for a captured airplane":

Turning:​
  • Turning and handling in excess of 250 mph: The two airplanes alternately turned on each other's tail, holding in the turns as tightly as possible, and alternating the turns from right to left. The P-47 easily out-turned the FW-190 at 10,000 feet and had to throttle back in order to keep from over-running the FW-190. The superiority of the P-47 in turning increased with altitude. The FW-190 was very heavy in fore and aft control, vibrated excessively and tended to black out the pilot
  • Turning and handling in below 250 mph: Turns were made so rapidly that it was impossible for the airplanes to accelerate, and the ability of the FW-190 to hang on its propeller and turn inside the P-47 was very evident. The FW-190 was also able to accelerate suddenly and change to a more favorable position. It was found, however, that the P-47 could gain by making slow turns on an oblique axis. The FW-190 accelerates slowly in the dive and when the P-47 pulls up to the top of the oblique axis, the FW-190 has insufficient speed to follow through.
 
Additional report from the AFDU on the P-47C vs the 190A, dated July 1943. Not sure the exact sub-type, but probably one of the captured A-4/U8 Jabos that had force landed in the UK earlier in 1943.

7. When at 26,000 feet, the Thunderbolt, if jumped by the FW.190 was unable to evade effectively by diving away. If the Thunderbolt was turned in to an attack made from slightly to one side, the FW.190 was able to follow and shoot for a moment at the beginning, according to the range at which the evasion commenced and again following the turn which finally held it. Any attempt by the Thunderbolt to make climbing turns was fatal, as the FW.190 easily out-climbed it and obtained a burst as it came in and a second one after repositioning in the climb.

8. When the Thunderbolt was on the offensive, if the FW.190 turned to evade, the Thunderbolt was always out-turned and only had a chance of an early surprise shot. If the FW.190 climbed and turned, the same thing happened but the FW.190 got away more easily at a steeper angle of climb. Only when the FW.190 attempted to dive away was the Thunderbolt able to get in effective shooting and hold its position.

9. The same results were obtained at 6,000 ft and from this height the Thunderbolt could still draw away from the FW.190 in a dive. It appeared that near ground level the comparative manoeuverability of the Thunderbolt improved slightly over the FW.190 and that it could about hold its own in turns. The latter's pilot, not being accustomed to the aircraft, may not have been turning quite as tightly as possible.
Conclusions.

10. The Thunderbolt can only evade the FW.190 successfully by diving; it is out-classed in the climb and general manoeuverability, with the possible exception of combats at ground level.​
 
I was hoping that you know the answer to a specific question:
How much of engine power was used by the turbocharger on the P-47 (for example)?

Alas.
Like Calum has said there is no fixed answer.

The turbo used the exhaust gases and since about very roughly about 1/3 of the energy of the fuel goes out the exhaust pipe/s you do get a very useful benefit from the exhaust gases.
However the benefit does come with the minus of raising the back pressure in the exhaust. But since the difference varies with altitude (and ambient air pressure) and varies with the work you are trying to do (turbo spins at different RPM at different altitudes) there is not "fixed answer"


Altitude
Feet
R.P.M.
Manifold
Pressure
"Hg.
Turbo
R.P.M.
Specific
Fuel
Cons.
lbs/hp/hr
B.H.P.
True
Speed
m.p.h.

5,000​
2700​
52.0​
6,800​
.78​
2000​
352​
15,000​
2700​
51.0​
11,800​
.77​
2000​
386​
25,000​
2700​
51.7​
16,900​
.78​
2000​
420​
27,800​
2700​
52.0​
18,250​
-​
2000​
429​
30,000​
2700​
47.5​
18,250​
-​
1845​
426​

From P-47 Performance Tests

Since the R-2800 can make 2000hp at 2700rpm at 52in pressure at 1500ft (or so) the turbo is doing no work and most of the exhaust is going out the waste gates. Very little more pressure or losses than the exhaust in a B-26. As the plane climbs the waste gates close and the turbo spools up. The power required goes up with the square of the speed of the turbine. Turbo is making nearly 9 times the power that it did at 5,000ft.
However that is not the power the engine is "paying". The engine is paying the increased back pressure in the exhaust system over a "free exhaust" but since the cost equals exhaust back pressure / ambient pressure at altitude it is changing at each altitude. Now the amount of air coming from the turbo lets the engine make as much power as it did at sea level (up to 27,800ft) so it masks the power lost to the back pressure.
Also note that the turbo gets more 'efficient' as the altitude goes up as the pressure difference between the inside of the turbo is much greater at high altitude due to the lower outside air pressure.

Just like the engine thrust in the Merlin varies with the exhaust veleocity varying with the air pressure of the ambient air. Merlin XX exhaust Veleocity varied from 1395fps at 15,000ft to 1901fps at 30,000ft mostly (but not entirely) due to the air pressure dropping nearly in 1/2. What is the exhaust thrust of a Merlin XX engine? Thrust is mass times velocity. Merlin is also making less exhaust thrust due to less mass (less fuel/air) in the charge flow.

Unlike exhaust thrust from a Merlin, Allison, DB 605, BMW 801 etc the actual power as opposed to thrust does not depend on the speed of the aircraft.
The engine in the P-47 is going to give you 2000hp at 2700rpm at 51.0-52in of pressure regardless of if you are flying straight and level at high speed or doing a climbing turn at best climbing speed.
 
Actually, we DID make jokes about the Gremans. Seems like it was about 10 - 12 years back. A new member consistently misspelled Germans as Gremans and we took it up, ran with it, and created a partial Greman history line. We were going to complete it, but the subject died just when it was getting interesting.

He left and never came back. We were just having fun, and didn't mean to run him off.

I bet FlyboyJ remembers the Gremans. If not, maybe he was at Reno at the bar after the Gold final ... maybe.

Anyway, no more Gremans. Promise, unless it is brought up by somebody else up yet again. If so, we could run with it again. The Gremans haven't gotten any better over the years. They're still despicable. :)

I'm Greman and Riish.
 

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