P-47 Top speed without wing Pylons?

[DSR T-888]

I was curious of what the top speed of the P-47 would be without wing pylons. I found that the Fw-190 found a 8-10kph increase in speed with the removal of its ETC 504(Which is located under the fuselage. By using common sense, it would only make sense if the P-51 had a better increase of speed because the Mustang has 2 pylons under each wing of roughly the same size of the Fw-190's ETC 504. I found a 20kph increase in speed with the removal of the P-51B's pylons. So knowing that the P-47's pylons are nearly 3 times the size of the P-51's pylons; what would be the speed increase if we were able to remove the pylons on the P-47. Or are all tests on the P-47 completed without wing pylons.

Thanks

 

[drgondog]

The P-51A/B and A-36 pylons reduced top speed ranging 10-12mph. The P-51D/K/H pylons were re-designed and reduced the drag effect to 6-8mph.

Offhand most of the P-47C and D flight tests were done without racks IIRC until the later D's. I'll have to look.

 

[GregP]

I went over to WW2aircrafperformance and the files that are there for the P-47 that I looked at briefly didn't say whether racks were fitted or not. They gave the finish, model, and serial numbers but little else of use.

 

[Neil Stirling]

Performance without racks

http://www.wwiiaircraftperformance.org/p-47/p-47-tactical-chart.jpg

Neil

 

[drgondog]

Here is another insight to the P-51 vs P-47 vs P-38 performance comparisons. Read the operating parameters carefully - and reflect on the 'modern day' report comparing the F4U, F6F, P-47 and P-51D

http://www.wwiiaircraftperformance.org/mustang/Performance_Data_on_Fighter_Aircraft.pdf

Note that the P-38J/L turn data is developed using 80 pounds of force compared to 50 each for the P-47, and max tested was at 4G for each ship. Also notice that the P-51B is listed at 9000 pounds gross weight and the weight of the 'modern test' was for a P-51D with no guns, no 85 gallon fuel tank, no ammo and yet the 51 in roll and roll reversal ACM tracking was described as "very difficult with stiff controls'- yet in the late WWII tests linked above, the P-51 out rolled, out turned, out climbed the P-47 with same applied forces? and the P-38J/L only out rolled the 51 with 80 pounds of force and boosted ailerons, and out turned it with maneuvering flaps by 5%>

Free Pages Personnelles: Erreur 404 - Document non trouvé

This article is 180 degrees out of phase relative to stick forces and control co-ordination when compared to the 100+ pilots flying and remarking on the flight experience of the P-51D vs all the fighters at The Fighter Conference at Patuxent River.

 

[EKB]

I was curious of what the top speed of the P-47 would be without wing pylons. I found that the Fw-190 found a 8-10kph increase in speed with the removal of its ETC 504(Which is located under the fuselage. By using common sense, it would only make sense if the P-51 had a better increase of speed because the Mustang has 2 pylons under each wing of roughly the same size of the Fw-190's ETC 504. I found a 20kph increase in speed with the removal of the P-51B's pylons. So knowing that the P-47's pylons are nearly 3 times the size of the P-51's pylons; what would be the speed increase if we were able to remove the pylons on the P-47. Or are all tests on the P-47 completed without wing pylons.

Thanks

It depends on the specs and power settings. There is limited information about high speed trials with no wing racks or belly racks put on. There were at least two types of P-47 wing racks and several types of propellers. Hamilton-Standard props gave slightly better level speed performance than Curtiss-Electric props, the difference being about 5-8 mph depending on height (chart below shows results for two specific airplanes).

 

[awack]

Ive read similar stuff on the p 51, test show a very good roll rate, especially at speed when compared to other prop aircraft, but ive also read that it has very heavy stick forces, forces as high as 20 pnds per G, that's the same as the me 109, other aircraft for comparison, fw 190=11/12 pounds per G, P 80A=also 11/12 pounds per G for elevators, Me 262= 6 pounds per G, the post war jet, the Vampire mk I is said to have very light aileron control, but has a roll rate of 70 degrees per second, that's around 5.1 seconds to complete a full 360 degree roll at between 270 and 300 mph at 10000 ft

About the subject, I wish I had some info, I do find what EKB posted very interesting, especially the p47 with over 2800 hp achieving 444 mph with racks,

 

[EKB]

The P-47s built with a larger 'C' series Turbo — which entered service in 1945 — could maintain 2800 bhp up to about 32,000 feet. However that rating was just an official safety limit approved by the USAAF. With more advanced fuels and additional ADI fluid, the R-2800 engine, including the older 'B' series, was capable of producing higher boost pressures and more power:


" An interesting footnote in the development of the R-2800, during World War II Frank Walker was charged with the task of testing the ADI system developed, in an emergency, for the R-2800. During the same time period Pratt Whitney was testing early development versions of the R-4360. Frank regarded the R-2800 as his baby and consequently wanted to prove to the world there was still life left in it. He made it a personal goal to keep up with the power output of the R-4360 with "his" R-2800. When reports came through that 3000 horsepower had been achieved with the R-4360 he met that challenge by boosting the R-2800 to ever higher manifold pressures and feeding it additional ADI fluid. With these changes, Frank met the 3000 horsepower challenge.
Then the R-4360 reached 3500 horsepower. No problem, Frank ran his R-2800 up to an amazing 140 in. Hg manifold pressure and fed as much ADI fluid as the engine could tolerate. Again, he matched the R-4360s 3500 horsepower.
When the 3800 horsepower threshold was achieved by the R-4360, Frank ran his R-2800 to a stratospheric 150 in. Hg to match the 3800 horsepower benchmark. However, Frank had to call it quits at 3800 horsepower; it would have been a difficult explanation to make to his superiors if he had blown up his R-2800 in the test cell.
What makes this story even more remarkable is the fact that Frank's R-2800 was a lowly "B" engine! And as Frank found out, not unnaturally, there is no replacement for displacement. Even so, for a while he gave the R-4360 and its development team a good run for its money. It would be difficult to imagine this kind of friendly rivalry and comradery in today's corporate, "design by committee" environment.
As a further endorsement of the R-2800's sound and rugged design, Frank made regular test runs of 3000 horsepower for one hundred hours."

See p.218-219
White, Graham. R-2800: Pratt Whitney's Dependable Masterpiece. SAE Incorporated, 2001.

 

[soulezoo]

Imagine P-47M with 3800 hp.

 

[RayB]

The P-47s built with a larger 'C' series Turbo — which entered service in 1945 — could maintain 2800 bhp up to about 32,000 feet. However that rating was just an official safety limit approved by the USAAF. With more advanced fuels and additional ADI fluid, the R-2800 engine, including the older 'B' series, was capable of producing higher boost pressures and more power:


" An interesting footnote in the development of the R-2800, during World War II Frank Walker was charged with the task of testing the ADI system developed, in an emergency, for the R-2800. During the same time period Pratt Whitney was testing early development versions of the R-4360. Frank regarded the R-2800 as his baby and consequently wanted to prove to the world there was still life left in it. He made it a personal goal to keep up with the power output of the R-4360 with "his" R-2800. When reports came through that 3000 horsepower had been achieved with the R-4360 he met that challenge by boosting the R-2800 to ever higher manifold pressures and feeding it additional ADI fluid. With these changes, Frank met the 3000 horsepower challenge.
Then the R-4360 reached 3500 horsepower. No problem, Frank ran his R-2800 up to an amazing 140 in. Hg manifold pressure and fed as much ADI fluid as the engine could tolerate. Again, he matched the R-4360s 3500 horsepower.
When the 3800 horsepower threshold was achieved by the R-4360, Frank ran his R-2800 to a stratospheric 150 in. Hg to match the 3800 horsepower benchmark. However, Frank had to call it quits at 3800 horsepower; it would have been a difficult explanation to make to his superiors if he had blown up his R-2800 in the test cell.
What makes this story even more remarkable is the fact that Frank's R-2800 was a lowly "B" engine! And as Frank found out, not unnaturally, there is no replacement for displacement. Even so, for a while he gave the R-4360 and its development team a good run for its money. It would be difficult to imagine this kind of friendly rivalry and comradery in today's corporate, "design by committee" environment.
As a further endorsement of the R-2800's sound and rugged design, Frank made regular test runs of 3000 horsepower for one hundred hours."



See p.218-219
White, Graham. R-2800: Pratt Whitney's Dependable Masterpiece. SAE International, 2001.

150 in. Hg! Really?

The post above, from the US government, indicates that the R-2800 produced 2840HP with 70 in. Hg of boost. That implies that the R-2800 would require about 110 in. Hg of boost to produce 3800HP. In any case, could any air-cooled engine withstand 150 in. Hg of pressure?

 

[GregP]

We get armchair experts every year ar Reno who say the Merlin type engine cannot make 3,850 Hp and turn 3,400 rpm, but they do it every year, at least for a couple of laps (laps 1 and 2 anyway).

The armchair experts ARE correct in one way, the top racing "Merlins" aren't really Merlins ... they have Allison G-series rods, custom pistons and cams, modern mags, and some very good modern sensors and monitoring equipment.

These guys also say they don't believe these engines will pull 150 inches of Mercury. Of course they won't in stock form. But the racers aren't running a 6.0 : 1 compression ratio either. The real CR of a top-tier racing Merlin is lower than 6.0 : 1, allowing the high boost.

 

[EKB]

The post above, from the US government, indicates that the R-2800 produced 2840HP with 70 in. Hg of boost. That implies that the R-2800 would require about 110 in. Hg of boost to produce 3800HP.

If you refer to P-47D AAF No. 42-26167, the USAAF engineering report for 70" Hg @ 2700 rpm indicates 2840 bhp at 10,250 feet and 2790 bhp at ground level. The chart does not indicate if the numbers are specific to the engine installed, or generic figures based on previous testing.

Frank Walker's R-2800 was run on a test stand at Pratt Whitney. I know where the Turbo is on a Thunderbolt but I have no idea how Walker set up his boost system in a shop environment. It was not explained by the author. Presumably, the test engine was not spun higher than the usual limit of 2700 rpm to obtain readings. I don't understand how you calculated for the possibility of 3800 bhp at a lower manifold pressure than 150" Hg, so I can't comment on that score.

 

[RayB]

If you refer to P-47D AAF No. 42-26167, the USAAF engineering report for 70" Hg @ 2700 rpm indicates 2840 bhp at 10,250 feet and 2790 bhp at ground level. The chart does not indicate if the numbers are specific to the engine installed, or generic figures based on previous testing.

Frank Walker's R-2800 was run on a test stand at Pratt Whitney. I know where the Turbo is on a Thunderbolt but I have no idea how Walker set up his boost system in a shop environment. It was not explained by the author. Presumably, the test engine was not spun higher than the usual limit of 2700 rpm to obtain readings. I don't understand how you calculated for the possibility of 3800 bhp at a lower manifold pressure than 150" Hg, so I can't comment on that score.

The R-2800 produced 2000HP with 52" Hg of boost and 2840HP with 70" Hg of boost. Perhaps a linear projection doesn't work here but it doesn't sound like it would be necessary to go all the way to 150" to produce 3800HP. The Merlin produces 3800HP at more than(?) 150 in Hg but it does start at 1700HP with 67" Hg. Again, can a radial - as opposed to an in-line - engine be run at 150" Hg?

 

[GregP]

The Merlin, depending on model number, starts at 1,490 HP at 3000 rpm and 61" HG MAP in M.S. gear at sea level for the V-1650-7. It goes to 1,580 HP for all the same at 8,500 feet and 1,400 at all the same except F.S. gear at 21,000 feet. Supercharger change height is 13,400 feet.

It goes to 1,630 HP at 3,000 rpm, sea level in M.S. gear and 67" HG MAP; 1,700 HP at 5,750 feet same other variables at 5,750 feet; and 1,555 HP at 3,000 rpm, 67" HG MAP, F.S. gear at 17,750 feet. Supercharger change height is 10,500 feet at this MAP.

The most I have is 1,940 HP at sea level, 80.8" HG MAP; 3,000 rpm, sea level, and 1,810 HP, F.S.Gear at 12,000 feet, 80.8" MAP; 3,000 rpm. Supercharger change height is 5,000 feet at this MAP.

All these numbers were "typical" and were generated running the stock compression ratio (CR), stock rods, stock cams and valves, and stock supercharger gear ratios. The Reno racers lower the compression ratio, mix and match supercharger gears, run Allison G-series rods, use custom pistons with tops designed for power (not flat-tops), Dwight Thorne racing cams, spray bars, carefully ducted ram air and radiators, ADI, modern telemetry that can measure the air-fuel ratio as it runs, and also some run a torque meter to get a real time horsepower readout. Most are ported and polished, too, improving flow. The stock Allison and Merlin flow surfaces are somewhat rough when compared with a polished unit.

So the modern Merlins are basically unrelated to the wartime Merlins except they start with Merlin engine blocks and crankshafts ... and a stock crankshaft is NOT guaranteed. They also run NOTHING similar for fuel and would not likely last for a 1,000 mile mission even at lower power levels. The racers WOULD run CRs as low as 4.0 : 1 if they could get it to start at that setting, but it won't start at a CR that low ... you can't spin it fast enough with a stock starter to make it fire, and the return on investment is not there for anyone to develop a new starter that can spin it fast enough to fire at that CR. You might be able to do it with an external starter if you could figure out how to disengage it when the engine fires.

Last the Merlin sprays oil on the reduction gears going into the inward-rotating side and you'd have to change that to the outward rotating side to get it to handle more than 3,400 rpm .... maybe 3,600 rpm. The Allison sprays oil on the outward turning side and doesn't get gear errosion due to incompressible oil at even 4,500 rpm when it is used in tractor pulls at that speed.

I'm not too sure where the limit for HP was for a stock Merlin, but the limit would come from the stock rods. According to Lovesy they ran one at some 2,650 HP. Today we KNOW they were only reliably good for something around 2,500 - 2,700 HP and then will break rather spectacularly. That's why they go to Allison G-series rods for racing at Reno.

If I were racing a stock Merlin, I'd stop at 2,400 HP until I got Allison G-series rods, and they are getting scarce as they only made some 750 sets and most were scrapped when they scrapped the engines. Of course Merlin block are getting scare, too, so that's why I'd stop at 2,400 HP on stock rods. Engine blocks ain't cheap these days. I know someone who has 12 more sets of G-series Allison rods, but they are only avialable in complete sets and aren't cheap. He not only has them, but can balance them to within 0.5 grams of one another, closer if you want to pay for the effort.

 

[Balljoint]

Greg, by "not flat top" do you mean still unnotched but perhaps dished? With higher RPM it would seem that swish and swirl and a smooth combustion chamber would become important for flame front propagation. After the Ramp Head fiasco, RR seems to have abandoned efforts in this regard and Riccardo was off working on rotary valves.

 

[drgondog]

A few words of caution when evaluating performance;

read carefully what the test conditions are with respect to Gross Weight at takeoff, external arrangements (pylons/no pylons), table Horsepower generated as a function of boost and RPM - and recognize that not every engine of that series performs to Spec, match Gross weight to pilots test report concerning fuel and ammunition loading per spec relative to combat load out..

Any notes concerning special preparation such as covering gun ports, sanding surface of wings, sealing other gaps, absence/presence of such external features as antenna, radio cables, armament (i.e. 20mm vs 50 caliber for Mustang is huge difference), altitude for the run as many top performers like a P-47M or P-51B at 30,000 feet is running into compressibility drag rise for the airframe and propeller tips - so look for discussion of corrections to test results.

 

[GregP]

Most of the top-tier teams won't tell you anything about the pistons they run, but the few I have seen were dished to lower the compression ratio. Some teams have tried a few pistons before they found the one that would start with the lowest compression ratio. It has to start in order to race and finish ... You can probably fighure out the CR since stock was 6.0 - 6.5 : 1 and they won't start at 4.0 : 1. So the real CR is between those values somewhere.

It is the same in auto engines. In the late 1960's we used to run 12.0 : 1 compression to get normally-aspirated power and port and polish, but you'd blow the heads off if you tried to supercharge that engine. To run a blower and get decent, reliable power, the CR drops considerably. Porting and polishing take on less importance when you run boost because the intake is under pressure.

That why the LS-1 Camaro bolt-on blowers from Paxton or others were only running 5 - 6 psi of boost since the stock LS-1 had an 11 : 1 CR. You can run 25 pounds of boost, but not at an 11 : 1 CR, and not on pump gas. Same for the 1980's turbo Buick V-6. The boost was set to be relaible so the manufacturer didn't come up with a raft of broken warranty repairs.

So I would not be surprised if an R-2800 radial could be boosted to 150 inches, but certainly not at stock CR. Stock was around 6.65 : 1. Normally an R-2800 is running lower boost than a Merlin. I think they mostly ran in the range of under 70.0 inches with water injection late in the war in P-47s and other installations. Without ADI, they were probably down in the 50's, probably 56 inches or so, and down to 25 inches HG or less at cruise.

For some reason, the inline engines generally show the manifold pressure in their specs and the radials don't, I have no idea why.

There are a number of very interesting design aspect to the R-2800, among which are pressuriized distributors and individual coils out on the heads near the spark plugs, which were found to be necessary above 30,000 feet or so. Otherwise the air lost it's insulating capabilities and the plugs would stop firing. The inlines had less problems here because the ignition wires were shorter and the firing energy didn't dissipate as much. It is MUCH shorter from the distributor to the farthest plug on a Merlin than on an R-2800's longest run.

 

[Balljoint]

Thanks Greg. You precipitated a head-slap insight on my part – with the low mechanical compression ratios and four valves in the big blown engines it's going to be near impossible to provide squish or tumble.

I raced Alfas –won several Nationals- back in the seventies. Like you I ended up running a rotary when 12 hr. rebuilds got old.

 

[GregP]

The Mazda rotaries were and are great fun to race. While everyone else is fractically working on their engines, the rotary guys are checking tire pressure, polishing the car, and getting the windslield clean.

We found the 12A and 13B were almost identical in performance after bridgeporting. Stock they were 90 - 120 hp depending on year and model. Mildly ported they were 150 hp or so. A street port would get you 180 hp, and a full bridgeport job will get 220 hp or so ... maybe 240 if you happen to get it just right. Most were in the 220 hp range.

But 220 hp in a 1,500 pound Austin Healy Sprite will run away from a Corvette ... up to about 140 mph or so. At that point the front end gets REALLY light and you don't want to go any faster unless you are suicidal or have downforce taht would take you out of the class.

The downside will be the heat and the noise. A 4-stroke fires once every other revolution. A 2-stroke fires once per revolution. A rotary fires three time per revolution, has VERY hot exhaust, and will definitely wake the neighbors without a good muffler ... which we didn't run on a race track. If you don't insulte the exhaust pipe somehow, the floorboard on the rider's side will get hot enough to melt Vibram soles, but the race car wasn't built for grocery shopping anyway, and we alwasy ran the exhaust down the rider's side so the driver wouldn't get baked during an outing. We also trashed the Austin Healy brakes and out on Mazda disc brakes. WAY better. If you get the chance, look for a 5-speed gearbox from a station wagon. It beats the 4-speed every time. You DO have to make a transmission mount and beat the heater box in with a sledge hammer to get the transmission to fit.

This stuff definitely belongs in the off topic forum.

 

[BiffF15]

Greg,
I had an 85 RX-7 GSL-SE (13B rotary). Loved that thing, rev all day long and fun to drive! Not much in the torque department, but really fun to run around in!
Cheers,
Biff