P-47N/M vs P-51H

[tomo pauk]

The engine on the P-47 had a similar supercharger connected to the engine, but with different gearing and only 1 ratio (F7F and F8F-1 had 2 ratios + neutral, F8F-2 had variable speed drive).

There was no 'neutral' setting on the engines' superchargers on F7F and F8F.
'Neutral' setting was used only on 2-stage P&W engines, where that setting was available for the 'auxiliary supercharger', ie. the 1st stage (engine-stage S/C was always with 1-speed on these engines, as well as on their turbocharged siblings).

As the air gets thinner at high altitudes, higher compression ratios in the supercharger are required. There is a point of compression ratios where the efficiency of a single stage falls away, which means eve more power is required to give the desired air flow and pressure to the engine. Adding a second stage means that each stage needs a lower compression ratio to achieve the desired overall compression ratio.

(Compression ratio = output air pressure/input air pressure)

Todays term is 'pressure ratio' when talk about superchargers/compressors. Compression ratio being reserved for the cylinders themselves.

 

[wuzak]

There was no 'neutral' setting on the engines' superchargers on F7F and F8F.
'Neutral' setting was used only on 2-stage P&W engines, where that setting was available for the 'auxiliary supercharger', ie. the 1st stage (engine-stage S/C was always with 1-speed on these engines, as well as on their turbocharged siblings).



Todays term is 'pressure ratio' when talk about superchargers/compressors. Compression ratio being reserved for the cylinders themselves.

Yes, you are correct on both.

 

[pbehn]

It is fat with very wide sectional area, it should be more draggy than slender and long airframe like FW-190D9 or P-51H

You cant do aerodynamics with an uncalibrated eyeball, the P-47 is 7 feet longer than the long slender Fw-190. While the P-47 looks blunt nosed that nose was open so the air flowed through it not around. I dont know how it compares with say a P-51 but it certainly isnt as draggy as it looks

 

[drgondog]

Before the knowledgeable answer I'd like to try.
The F8F was a carrier borne interceptor maximized for lower, denser altitudes than the P-47. The 'Bolt was getting its second wind at higher, thinner altitudes with more power.
The TA-152 was a rush job and sent into action (armed) too soon, but not soon enough.
Republic had been tinkering with the P-47 for years. The super duper fast P-47s were prototypes and weren't for use in combat operational theaters.
The F7F is really cool and I know less about it than I do the TA-152 even though it's Grumman. Don't let Capt. Vick find out.

The P-47M flew with 56th FG from December 1944 through EOW.. absolutely correct that top speeds were at 30K+ when Full 2800 HP still available

You cant do aerodynamics with an uncalibrated eyeball, the P-47 is 7 feet longer than the long slender Fw-190. While the P-47 looks blunt nosed that nose was open so the air flowed through it not around. I dont know how it compares with say a P-51 but it certainly isnt as draggy as it looks

The P-47C/D Parasite Drag was about 30%greater than P-51B/D, slightly higher than 30% greater han P-51H. The F6F and F4U were 50% higher values for CPp.\

The 'wing' was primary source of Parasite Drag in normal speed ranges but all increasing experienced Mcr drag rise earlier than P-51B/D/H.

The P-47 wing had less induced drag (ditto F6F and F4U) than Mustang in low/medium speeds but CDi is very small realtively compared to CDp at high speeds.

The P-47M was faster than P-51H at 32K. If you lay the two V vs Alt and ROC vs Alt - the 51H exceeds the P-47MN at combat powerthrough most of the chart until afer the V=1650-9A hits FTH ~ 22K.

 

[Shortround6]

The P-47 is a lot more "draggy" than the P-51 however the uncalibrated eye will surprise most people.

Like the P-40 has about 12% less than a drag than a P-47, and that is equivalent flat plate area (counts the 300 sq wing).

The F2A-3 Buffalo has about 2% less drag then the P-47B and the F4F-3 has about 3 % more than the P-47B.
The F4U-1D Corsair has about 34% drag than the P-47B.

One powerful note, These figures are only good at rather low speeds and many of these planes had flow eddies or other problems that increased as the speed went up.

Large books have been written about drag and calculations for drag. Many large books.

One thing is that many beginners skip right over is that all planes being compared have to be being compared at the same altitude at the same atmospheric conditions.

 

[mig-31bm]

P-51H vs F8F-2: Aerodynamics. Power-to-weight. Though the F8F-2 did hold the time to climb record to 10,000ft for a while.

P-47N vs P51H - power at altitude.

Wasn't the F8F-2 supposed to have higher power to weight than P-51H? or is it the other way round?
Also, iam very curious how come the F8F-2 hold time to climb record even though the Climb rate of P-51H supposed to be better at all altitude according to the chart

The P-47M flew with 56th FG from December 1944 through EOW.. absolutely correct that top speeds were at 30K+ when Full 2800 HP still available

The P-47C/D Parasite Drag was about 30%greater than P-51B/D, slightly higher than 30% greater han P-51H. The F6F and F4U were 50% higher values for CPp.\

The 'wing' was primary source of Parasite Drag in normal speed ranges but all increasing experienced Mcr drag rise earlier than P-51B/D/H.

The P-47 wing had less induced drag (ditto F6F and F4U) than Mustang in low/medium speeds but CDi is very small realtively compared to CDp at high speeds.

The P-47M was faster than P-51H at 32K. If you lay the two V vs Alt and ROC vs Alt - the 51H exceeds the P-47MN at combat powerthrough most of the chart until afer the V=1650-9A hits FTH ~ 22K.

So apparently P-47N is slower than P-47M, and basically the reason that P-47 is so tremendously fast is because it can keep the engine out put at extremely high altitude when engine of other fighter basically run out of air. At low and medium altitude then P-47 speed is actually quite bad

 

[mig-31bm]

Piston-engined aircraft were too slow -- even the fastest fighters of the era -- for cross sectional area, nose shape, or volume distribution to dictate drag coefficient. What counts are wetted area and avoidance of separation. While the P-51 was the lowest drag piston-engined fighter of the era, largely due to superlative cooling system design, virtually all other single-engined, piston-powered fighters clustered, indistinguishable by engine type in a narrow range of zero-lift drag coefficients.

The idea that US fighters, except the P-51, succeeded because of sheer brute engine power is a blatant falsehood.

Even sport car and high speed train have to care about their nose shape , and they are no where near as fast as piston fighter. So I have a hard time believe that the cross sectional area, nose shape, or volume distribution of these fighter don't affect their top speed

 

[swampyankee]

Even sport car and high speed train have to care about their nose shape , and they are no where near as fast as piston fighter. So I have a hard time believe that the cross sectional area, nose shape, or volume distribution of these fighter don't affect their top speed

Nose shape merely needs to be good enough to prevent separation at normal operating angles of attack and yaw. Same for volume distribution. When transonic flow becomes a major design issue -- usually at operating speeds of 350 KIAS or so -- volume distribution becomes quite important. 450 KIAS at 25,000 ft is about 525 KTAS, considerably faster than any piston-engined aircraft.

 

[pbehn]

The P-47 is a lot more "draggy" than the P-51 however the uncalibrated eye will surprise most people.

Like the P-40 has about 12% less than a drag than a P-47, and that is equivalent flat plate area (counts the 300 sq wing).

The F2A-3 Buffalo has about 2% less drag then the P-47B and the F4F-3 has about 3 % more than the P-47B.
The F4U-1D Corsair has about 34% drag than the P-47B.

One powerful note, These figures are only good at rather low speeds and many of these planes had flow eddies or other problems that increased as the speed went up.

Large books have been written about drag and calculations for drag. Many large books.

One thing is that many beginners skip right over is that all planes being compared have to be being compared at the same altitude at the same atmospheric conditions.

I just meant that simply looking at pictures and drawings doesnt have scale. A P-47 compared to a Bf109 was 10 ft longer and had 10ft more wing span, it was twice as heavy in dry weight but had 1000+ BHP more. To me, the bubble tops look sleek, but they were huge compared to many others.

 

[tomo pauk]

I think we must, when talking about 'drag', specifically note if the talk is about the the Cd0 (drag coefficient at high speed; does not have a measuring unit: MTT was noting IIRC 0.0232 for the BF 109F-4; P-39 was supposed to be at 0.0217, P-47 at 0.0213, same as Spitfire V; F2A was supposed to be at 0.0300 - yikes; American data per AHT pg. 113) or when it is the 'equivalent flat plate' is talked about (in sq m, or in sq ft; accounts for the size of aircraft wing, since it was = Cd0 x wing_area). The later measurement stick will obviously favor smaller A/C, the former will favor bigger A/C.
Equivalent flat plates are noted, in sq ft, as 4.63 for P-39, 6.39 for P-47, 6.27 for the F2A (same source as above; I think that S Shortround6 is thinking about these values when comparing the P-47 to the Buffalo). A clean Bf 109F or late G will be around 4 sq ft (ballpark of P-51), thanks to it's small wing and not overly bad Cd0.

The later is also sometimes noted in lbf in specified speed, eg. Hurricane I was supposed to have that drag value of 76-79 lb at 100 m/s; Spitfire V was at 61-63 lb; Fw 190A at 65 lb; Mustang X at 63 lb (all values per AVIA 28-3030). Mosquito was at 121 (1-stage engine), or 145 (2-sage engine), per same source.

 

[Graeme]

Even sport car and high speed train have to care about their nose shape , and they are no where near as fast as piston fighter. So I have a hard time believe that the cross sectional area, nose shape, or volume distribution of these fighter don't affect their top speed

Whatever the Thunderbolt's nose shape - bloody fast in a dive!?

(James Holland - Big Week)

 

[pbehn]

Even sport car and high speed train have to care about their nose shape , and they are no where near as fast as piston fighter. So I have a hard time believe that the cross sectional area, nose shape, or volume distribution of these fighter don't affect their top speed

The nose of a P-47 is open, the air goes in and through it, that is how it is cooled, it doesnt have the radiators and air scoops that water cooled engines have. Cowling design and cooling of radials improved with time.

 

[mig-31bm]

Whatever the Thunderbolt's nose shape - bloody fast in a dive!?

View attachment 650511

(James Holland - Big Week)

That because it also very heavy, and when you dive, being heavier is better because it add force in the direction of travel due to gravity.
But if you look at top speed at sea level of these aircraft, it is quite clear that P-47 is quite draggy. It is rather slow despite having very powerful engine.

 

[SaparotRob]

The P-47 wasn't developed for sea level air superiority. That's not where the bomber streams were.

 

[mig-31bm]

The P-47 wasn't developed for sea level air superiority. That's not where the bomber streams were.

yes, but iam talking about the drag of it.
The reason P-47 could achieve tremendous speed is pretty much due to the fact it can keep up the engine output up high while others lose their engine power.
But when all aircraft can have their engine output, it is pretty evidence that P-47 is draggy given how slow it is

 

[GregP]

Weight has nothing to do with dive speed or dive acceleration. Gravity pulls a small ball bearing down at the same speed and acceleration as a boulder. Power to weight helps with dive acceleration and drag limits dive speed. When thrust equals drag, you don't go any faster, even with gravity helping.

 

[mig-31bm]

Weight has nothing to do with dive speed or dive acceleration. Gravity pulls a small ball bearing down at the same speed and acceleration as a boulder. Power to weight helps with dive acceleration and drag limits dive speed. When thrust equals drag, you don't go any faster, even with gravity helping.

I don't see how weight can "have nothing with dive speed and dive acceleration"
Weight is literally the reason why you can dive at higher speed and higher acceleration than you can fly horizontally. When diving, weight does have a force vector in the direction of travel, the steeper the dive angle, the bigger this force component will be, basically increasing your "thrust"

 

[Howard Gibson]

Piston-engined aircraft were too slow -- even the fastest fighters of the era -- for cross sectional area, nose shape, or volume distribution to dictate drag coefficient. What counts are wetted area and avoidance of separation. While the P-51 was the lowest drag piston-engined fighter of the era, largely due to superlative cooling system design, virtually all other single-engined, piston-powered fighters clustered, indistinguishable by engine type in a narrow range of zero-lift drag coefficients.

The idea that US fighters, except the P-51, succeeded because of sheer brute engine power is a blatant falsehood.

You have two kinds of drag, pressure drag, and friction drag. Pressure drag is a function of frontal area, much bigger on anything with a radial engine. Friction drag is a function of the total surface area of the aircraft, also fairly large on a P-47. It is worth looking at scale models. An Fw 190 is a surprisingly small aircraft. Its friction drag may well have been less than that of a Spitfire.

 

[Howard Gibson]

In the P-47 the turbocharger is that second compressor. The exhaust gases drive the turbine which drives the compressor. This doesn't cost much, if any, power at the crankshaft.

The engine has to pump air out of the cylinders through the turbine. I am not totally into turbochargers. They may be more efficient than engine driven superchargers. They still use significant power

 

[Howard Gibson]

Whatever the Thunderbolt's nose shape - bloody fast in a dive!?

View attachment 650511

(James Holland - Big Week)

700mph is supersonic at 30,000ft. According to Eric Brown, the P-47's tactical Mach number was 0.71. Any faster than that, and you were in trouble. This is one of the reasons most of the P-47s were replaced with P-51s.