Razorback P-47 horsepower question

Hello. I am new to the thread and have had a casual interest in aviation/ww2 aviation since i was a kid (now 25).

For a while I've had question that I can't seem to find any documents on, relating specifically to the late war settings of the R-2800 engine (75in man pressure, 150 oct gas) and the older razorback P-47D Thunderbolts:

The D-25 and later models got heavier due to additional fuel capacity, and also ran the higher power settings for the R-2800. Are there any examples of the older (lighter) P-47s running there higher power settings? Would that not make them the best performing P-47s -maybe barring the M- since they have the stronger engine and lighter airframe with less internal fuel?

Any info on this would be great, thanks.

Laze_and_Blaze said:

For a while I've had question that I can't seem to find any documents on, relating specifically to the late war settings of the R-2800 engine (75in man pressure, 150 oct gas) and the older razorback P-47D Thunderbolts:

Click to expand...

Seems like 70 in Hg boost, available via the water-alcohol injection and the 150 grade fuel, was the maximum. Engine on the P-47D was making 2800 HP under these conditions.
link
(I's advise downloading all the interesting graphs and tables from that site)

Laze_and_Blaze said:

The D-25 and later models got heavier due to additional fuel capacity, and also ran the higher power settings for the R-2800. Are there any examples of the older (lighter) P-47s running there higher power settings? Would that not make them the best performing P-47s -maybe barring the M- since they have the stronger engine and lighter airframe with less internal fuel?

Click to expand...

The initial water-alcohol injection system was good for 56 in Hg on the 130 grade fuel, up to 2300 HP. That was quickly improved with the next version of the system, that allowed for 65 in Hg on 130 grade, for up to 2600 HP. In theory, that plus the 150 grade fuel would've allowed for 70 in Hg and the already mentioned 2800 HP.
If such a combo was on the razorback P-47, yes, that would've been the best-performing P-47s before the P-47M. Combine it with the paddleblade prop, and our new-old P-47 would've been quite a climber among it's Thunderbolt brethren.

tomo pauk said:

Seems like 70 in Hg boost, available via the water-alcohol injection and the 150 grade fuel, was the maximum. Engine on the P-47D was making 2800 HP under these conditions.
link
(I's advise downloading all the interesting graphs and tables from that site)



The initial water-alcohol injection system was good for 56 in Hg on the 130 grade fuel, up to 2300 HP. That was quickly improved with the next version of the system, that allowed for 65 in Hg on 130 grade, for up to 2600 HP. In theory, that plus the 150 grade fuel would've allowed for 70 in Hg and the already mentioned 2800 HP.
If such a combo was on the razorback P-47, yes, that would've been the best-performing P-47s before the P-47M. Combine it with the paddleblade prop, and our new-old P-47 would've been quite a climber among it's Thunderbolt brethren.

Click to expand...

Thanks for the reply. If I'm reading correctly, the newer D models got the better injection and therefore the older D's couldn't run the higher power?

Laze_and_Blaze said:

Thanks for the reply. If I'm reading correctly, the newer D models got the better injection and therefore the older D's couldn't run the higher power?

Click to expand...

If the older Ds (and some Cs, that were also trialed with water-alc injection) were retrofitted with the new systems, and their engines were tested and approved for greater boost, they were also allowed to make such power in everyday service.
The 1944 test reports are lacking in mentioning, for example, the -21 engine, that was used on many, if not most of the pre-1944 P-47s - perhaps people in charge were not willing to have the engines with many working hours to be pushed beyond 2300 HP?

Laze_and_Blaze said:

Hello. I am new to the thread and have had a casual interest in aviation/ww2 aviation since i was a kid (now 25).

For a while I've had question that I can't seem to find any documents on, relating specifically to the late war settings of the R-2800 engine (75in man pressure, 150 oct gas) and the older razorback P-47D Thunderbolts:

The D-25 and later models got heavier due to additional fuel capacity, and also ran the higher power settings for the R-2800. Are there any examples of the older (lighter) P-47s running there higher power settings? Would that not make them the best performing P-47s -maybe barring the M- since they have the stronger engine and lighter airframe with less internal fuel?

Any info on this would be great, thanks.

Click to expand...

P47D-23
R-2800-59
2300 HP @ 2700 RPM SL-28,000 ft 61.0 in Hg A.R. War Emergency 5 min
2000 HP @ 2700 RPM SL-34,000 ft 52.0 in Hg A.R. Military 15 min
1625 HP @ 2550 RPM SL-40,000 ft 42.5 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P47D-25
P47D-27
R-2800-59
2600 HP @ 2700 RPM SL-25,000 ft 64.0 in Hg A.R. War Emergency 5 min
2000 HP @ 2700 RPM SL-27,000 ft 52.0 in Hg A.R. Military 15 min
1625 HP @ 2550 RPM SL-29,000 ft 42.5 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P-47M
R-2800-57
2800 HP @ 2800 RPM SL-32,600 ft 72.0 in Hg A.R. War Emergency 5 min
2100 HP @ 2800 RPM SL-37,000 ft 54.0 in Hg A.R. Military 15 min
1700 HP @ 2600 RPM SL-30,000 ft 43.0 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P-47N
R-2800-57
R-2800-61

The P-47D-23 would be the last of the Razorback Thunderbolts.
The P-47D-25 would be the first of the Bubbletop Thunderbolts and is the same as the D-27. Difference is mostly Propeller. D-25 uses Hamilton Standard while D-27 uses Curtiss-Electric.
The Ratings on P-47M and P-47N are the same. Note that the C series R-2800 runs at a slightly higher RPM.

- Ivan.

Only the P-47M had a 2,800 hp R-2800 installed from the factory as far as I know, and operational P-47 units extremely rarely ever exceeded about 2,200 - 2,300 hp regardless of variant, other than the P-47M. Seems like the P-47N was the exception, sometimes making 2,500 hp. For some reason, that was about the limit of reliable horsepower for the R-2800 in WWII in normal service.

The 2,800 HP unit in the P-47M gave considerable trouble if used at that power level in service, but was generally OK at 2,500 hp or so if using good fuel. The serviceability of the P-47M was not very good compared with the normal 2,000 - 2,350 hp engines in other models.

That from many former P-47 pilots over two decades of talks.

GregP said:

Only the P-47M had a 2,800 hp R-2800 installed from the factory as far as I know, and operational P-47 units extremely rarely ever exceeded about 2,200 - 2,300 hp regardless of variant, other than the P-47M. Seems like the P-47N was the exception, sometimes making 2,500 hp. For some reason, that was about the limit of reliable horsepower for the R-2800 in WWII in normal service.

The 2,800 HP unit in the P-47M gave considerable trouble if used at that power level in service, but was generally OK at 2,500 hp or so if using good fuel. The serviceability of the P-47M was not very good compared with the normal 2,000 - 2,350 hp engines in other models.

That from many former P-47 pilots over two decades of talks.

Click to expand...

Hello GregP,
I don't believe the typical P-47 had a torque meter installed as standard equipment, so what settings were the effective "limit" for normal operational use? In other words, was it just a reduction in manifold pressure or in RPM as well? For the C model R-2800, was the extra RPM range not actually useful?

Perhaps this is why the SEFC for the P-47D-23 lists lower settings than for the D-25 and D-27 even though all had the same -59 engine.

- Ivan.

I've gathered stuff for 25+ years to help game developers starting back in the day of large online multi-player games that include just about every aircraft used in WW2.

Here's a link to my GD folder stuffed with P-47 data from many sources. Have a field day folks.

Robert Johnson had his P-47D-5 in 1943 modified by his mechanics after the P&W guys visited 56thFG and told them how to get more boost.

I'm not sure of the date, but we began to receive the D-model in late May or early June of 1943. After "Half-Pint" had been so badly shot up, I was assigned a D-5 and named it "Lucky." Lucky was my best P-47 and I think it was the fastest airplane in the ETO. I never raced all the airplanes there, but Lucky had all the speed I ever needed.
She had a water-injection system. I never had to use the water-injection in combat, but tested the system now and then to make sure it was working. I'd switch it on, push the throttle up to 72" of manifold pressure and get smacked from behind by the headrest. Lucky had been sandpapered and waxed smooth and we had a terrific crew.

Click to expand...

If you are looking for stories of very fast P-47s, look for "Wonderful Winnie".
That was one of the very rare P-47M in the ETO. It didn't have quite the acceleration of a P-51, but it had a much higher top end and the pilot would challenge P-51s to drag races and collect the winnings from wagers.

- Ivan.

There was already an outlaw auto-racing culture in USA pre WW2, I bet a backyard hotrod mechanic, hand finishing a P&W could get a decent amount more power than the ones they slapped together in mass production. There are a few articles on it, but R.Johnson's crew were real enthusiasts, the P&W tech guy who visited told them how to modify it for the extra boost, so already in late 1943 P&W knew how to make a -57 motor.

Ivan1GFP said:

P47D-23
R-2800-59
2300 HP @ 2700 RPM SL-28,000 ft 61.0 in Hg A.R. War Emergency 5 min
2000 HP @ 2700 RPM SL-34,000 ft 52.0 in Hg A.R. Military 15 min
1625 HP @ 2550 RPM SL-40,000 ft 42.5 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P47D-25
P47D-27
R-2800-59
2600 HP @ 2700 RPM SL-25,000 ft 64.0 in Hg A.R. War Emergency 5 min
2000 HP @ 2700 RPM SL-27,000 ft 52.0 in Hg A.R. Military 15 min
1625 HP @ 2550 RPM SL-29,000 ft 42.5 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P-47M
R-2800-57
2800 HP @ 2800 RPM SL-32,600 ft 72.0 in Hg A.R. War Emergency 5 min
2100 HP @ 2800 RPM SL-37,000 ft 54.0 in Hg A.R. Military 15 min
1700 HP @ 2600 RPM SL-30,000 ft 43.0 in Hg A.R. Normal Rated Unlimited (Max Continuous)

P-47N
R-2800-57
R-2800-61

The P-47D-23 would be the last of the Razorback Thunderbolts.
The P-47D-25 would be the first of the Bubbletop Thunderbolts and is the same as the D-27. Difference is mostly Propeller. D-25 uses Hamilton Standard while D-27 uses Curtiss-Electric.
The Ratings on P-47M and P-47N are the same. Note that the C series R-2800 runs at a slightly higher RPM.

- Ivan.

Click to expand...

The D-27 had the fin extension to make up for loss of the "razor back" fuselage area. The -M had trouble with the pressurized ignition harness initially, which limited their combat use late in the ETO.

daviemax said:

The D-27 had the fin extension to make up for loss of the "razor back" fuselage area. The -M had trouble with the pressurized ignition harness initially, which limited their combat use late in the ETO.

Click to expand...

Actually, the Fin Fillet did not become factory standard on the Bubbletop P-47 until the D-40 model. Some earlier models were retro-fitted-30 though. The pressurized ignition harness would only have been a problem at fairly high altitudes. At lower altitudes such as below about 30K, it doesn't show up.

Just Note: WWII radial a/c engines were assembled from many , many, small parts, each with it's own range of tolerances. There was apparently no attempt to "match" parts to improve output, as long as tolerances were met. As a result, power outputs could vary considerably, perhaps two hundred horsepower or more. I had a conversation with a WWII P&W engineer some years sgo and he remembered being sent to one of the auto manufacturers plants where there had been a high rate of R-2800s failing acceptance tests. He decided there was nothing inherently wrong with the engines other than a stack-up of assembly tolerances resulting in lower out on the test stands. The solution was simply to open up the lower end of acceptable HP output. My understanding was the new lower limit was on the order of 100 HP. Also note: Aircraft are also assembled from many , many, small parts, each with it's own range of tolerances. Aerodynamic performance of 2 successive craft coming off the line may vary considerably. Mix a low HP with a "draggy" airframe and you have a DOG, I am certain every squadron has one and nobody wants to fly it. The opposite also happens as tolerance stack-up can work in both directions and you will have a "Hot" one. So be a bit careful analyzing performance beyond three significant figures, engineers like numbers with lots of numbers behind the decimal. The real world does not work that way. I was a pilot for over 60 years, even with more modern jet aircraft I flew, I remember real DOGS and vice versa. To paraphrase an old show tune, " The things that your liable to read in the handbook, it ain't necessarily so.

ArtieBob. BS physics, MA History, PEME. 1937-?