P-47M/N?

[juzz]

Allison V-1710 could do 72" MAP in it's standard form, no mods necessary. RAAF pilot said he pulled six feet of mercury for about 15 minutes while running from Japanese fighters in his P-40. Reason he could do that is because that engine(like most US  and UK engines) had no automatic boost control. This sort of thing is probably why we don't have 100% realistic engine controls.

[ 08-16-2001: Message edited by: juzz ]

[eddiek]

Many thanks, Widewing.  The opportunity to interview many of these people has passed, and I apologize if I am imposing on you.  You just seem to have made all the right connections, and already have a lot of information in hand, or have knowledge as to where it is.

Thanks again.    

[niklas]

The aircraft actually attained 507 mph at an altitude of 34,300 feet.

LOL, mach 0.76 in a level flight with a prop driven plane.
Even the world record machines didnīt reached more than mach 0.6 - 0.65.

Donīt believe everything. At mach 0.76, no propeller will produce much power anymore.

niklas

[Widewing]

Originally posted by niklas:


LOL, mach 0.76 in a level flight with a prop driven plane.
Even the world record machines didnīt reached more than mach 0.6 - 0.65.

Donīt believe everything. At mach 0.76, no propeller will produce much power anymore.

niklas

Niklas, I suggest you rethink your statements. These numbers were recorded by calibrated airspeed indicators, oscillographs and instrument cameras. Moreover, the performance numbers were signed-off by the USAAF, who supervised the prototype testing, which was initially performed out of Republic's Farmingdale, Long Island facility. 507 mph at 34,300 feet was certified by the USAAF. Later, when the aircraft was tested at Langley, it could only manage 489 mph. A tear-down inspection of the R-2800-57 revealed burned valves on virtually every cylinder, eventually determined to have been caused by an improperly rigged mixture control.


If you find the XP-47J incredible, consider the XP-72. This prototype achieved 490 mph @ 25,000 ft, and did so with an engine making nearly 500 hp less than the production version (R-4360). Rate of climb was just about 5,300 fpm and engineering estimates placed maximum speed at greater than 510 mph.

My regards,

Widewing

[niklas]

your calibrated airspeed indicator may work correctly at normal mach numbers, but not at mach numbers > 0.6. And film cameras only film the error, so what?

Dive Tests usually recorded the altitude loss over time, this was often the only possible method to get TAS.

If you want to fly relly fast with transsonic speeds, then fly LOW!
490mph @ 25k makes more sense than 507mph@34k!
 http://buerger.metropolis.de/luftwaffe/flight/compressibillity/flight_compress.html

read those pages, youīll find even the critical mach number for the P47 in it...
 
niklas

[Widewing]

Originally posted by niklas:
your calibrated airspeed indicator may work correctly at normal mach numbers, but not at mach numbers > 0.6. And film cameras only film the error, so what?

Oh, I see now... The engineers at Republic and Langley were idiots! Who would have guessed?

The fact is that the XP-47J was fitted with a 22 inch long extended air-data probe precisely for the purpose of eliminating error.

 

Dive Tests usually recorded the altitude loss over time, this was often the only possible method to get TAS.

Incorrect. In the case of the XP-47J, an air-data probe with pressure transducers and onboard analog time correlated recording via oscillograph and film were used to collect speed data. This data was then reduced postflight by precision calibrations with corrections for bias, compressibility, and position error. This data was then analyized by a team of four engineers and reviewed by NACA. Virtually the same equipment and methodology was employed to confirm the first supersonic flight of the Bell XS-1 (X-1)just 4 years later. NACA employed one addition tool to support their conclusions. This was a theodolite radar, producing yet another analog record. A radar was not used to track the XP-47J. However, all the radar did was to confirm, not establish actual airspeed.

 

If you want to fly relly fast with transsonic speeds, then fly LOW!
490mph @ 25k makes more sense than 507mph@34k!

Are you saying that true airspeed is less at 34,300 ft than it is at 25,000 feet, based solely upon altitude?

 

http://buerger.metropolis.de/luftwaffe/flight/compressibillity/flight_compress.html

read those pages, youīll find even the critical mach number for the P47 in it...

I am quite familiar with Gus Pappas. During his tenure at Republic, he was instrumental in cleaning up the design of the XP-47B, as well as the P-43 and XP-47 (Allison powered lightweight prototype never advancing beyond mockup). If my memory serves me well, Pappas was one of the advocates who insisted that it would be impossible for an aircraft to exceed Mach 1 due to the enormous pressure rise associated with transonic speeds. Obviously, he was very wrong. I believe that it was Pappas who refused to accept German research into swept wings, and lost much of his luster when the relatively low powered XP-86 slipped through Mach 1 with ease.

His remarkable claim that the P-47 could reach Mach .90 was conclusively proven wrong when post war (1947-49) testing of a P-47D-30-RE established beyond doubt that the Thunderbolt could not exceed Mach .833 under any circumstances. Why? Because at this speed the propeller enters the deep transonic range, with the shock wave quite literally preventing air flow through the prop. In effect, the propeller becomes a giant circular airbrake.

My regards,

Widewing

[niklas]

I didnīt called the engineers idiots.

Where did the calibration happened? Near sealevel, with 20°C?? How can you know that at -80°C in very thin air, where ice particles etc. can influence the instrument, everything is working still as good as near sealevel?
They did a radar tracking? How did they know about the current wind in 35k?

 

Are you saying that true airspeed is less at 34,300 ft than it is at 25,000 feet, based solely upon altitude?

This can happen, yes. Itīs all a function of mach number in those heights with such high speeds.
The german comet had itīs top speed in only 10000ft, though his engine produced more thrust in 20k compared to sealevel.

Pappas was not the only one who didnīt see a way to pass through the barrier of sound. People of this time had sometimes strange ideas, some even thought that the only way  to do it is with the help of nuclear energy.

 

the Thunderbolt could not exceed Mach .833 under any circumstances. Why? Because at this speed the propeller enters the deep transonic range, with the shock wave quite literally preventing air flow through the prop. In effect, the propeller becomes a giant circular airbrake.

Exactly. And you want to tell me that the Thunderbolt did mach .76 in a level flight, without the help of gravity? Just look at the mach number of the propeller tip...

I would like to see the naca report, or some original graphs, but i would be suprised if you can show me some docs.

niklas

[Daff]

Hmm so know we are refuting the results of an actual testflight?...guess Yeager never did break the soundbarrier, then  

The winds will be irrelevant, if you do a IAS to CAS conversion...and it doesnt get much colder than -56 C' @ 34k. (As the temperature  pretty much stops dropping above 24k).

Daff

[Widewing]

Originally posted by niklas:
I would like to see the naca report, or some original graphs, but i would be suprised if you can show me some docs.

Try:F-47 dive data

My regards,

Widewing

[eddiek]

Daff, ya gotta remember that some folks think the only accurate tests were conducted by the Luftwaffe.  Put two test results out in front of them, one conducted by the LW, the other conducted by USAAF, RAF, whatever, and they will dispute whatever the Allied tests show (unless it says a LW plane was better than an Allied one), and claim the LW test as holy and undeniably accurate (unless it shows an Allied plane as better in any way).
If this was the "real world", I might find the arrogance and attitude of Aryan superiority insulting......as it is, it's good for a chuckle and maybe a raised eyebrow.  
All the light hearted, and some not so light hearted, claims of total LW superiority, their planes were better in every way, etc....when you start talking about RL things done to the planes, that all changes.  Witness the Rumble this year.....which 2 planes were singled out as the cause of the Axis defeat.......P47D-11 and the Spit.  RAF fans want a later model Spit, or one closer to RL with correct wings, engine, armament.  "You have to perk that" is some LW'ers reply, even tho they have 1944-45 aircraft available to them.    

[Widewing]

Originally posted by niklas:
I didnīt called the engineers idiots.

Where did the calibration happened? Near sealevel, with 20°C?? How can you know that at -80°C in very thin air, where ice particles etc. can influence the instrument, everything is working still as good as near sealevel?
They did a radar tracking? How did they know about the current wind in 35k?

I believe that you are ill imformed. For starters, temperature will stabilize at just about -56°F, regardless of altitude. Secondly, properly instrumented test aircraft will be fitted with thermocouples to sense outside air temp. I suspect that you don't have any knowledge or understanding about how flight testing is performed, nor the methodology of collecting and evaluating data. No crime in that. However, it does make your argument seem somewhat more than silly.
 

Exactly. And you want to tell me that the Thunderbolt did mach .76 in a level flight, without the help of gravity? Just look at the mach number of the propeller tip...

Let's stop and think about tip speeds. The XP-47J had a reduction gear ratio of .47 to 1. In other words, the propeller turned .47 revolutions for every revolution of the crankshaft. So, at 2,700 rpm, the prop is turning at 1,269 rpm. Measuring 12.8 feet in diameter, the extreme tip travels roughly 40.2 feet/rev. 1,269/60 = 21.15 rev/sec. Therefore, 21.15 x 40.2 = 850 ft/sec would be the rotational tip speed. The speed of sound at 34,300 ft is very near to 670 mph, or 983 ft/second. Rotational tip speed is right around Mach .87. However, the propeller is also moving forward. It's actual motion is best described as being helical. The equation used to calculate this is: Vtip = Sqrt(Vrotation^ + Vfwdvel^). So,
850^ = 722500 + 743^ = 1274549. The square root of 1274549 = 1,128 ft/second. Therefore, the extreme prop tips are at Mach 1.14 at 507 mph. Working the equation for various blade stations, one discovers that about 17% of the prop is experiencing a substantial drag rise. Nonetheless, the loss of efficiency is somewhat less than that. Don't depend on Gus Pappas' drag rise calculations. They do not account for the chord to thickness ratio of the prop blades, which generally was in the 3-5% range. Compare that to 8% for the Bell XS-1 wing. Indeed, low ratio wings suffer minimally from compressibility, and propellers even less so. The limiting factor as concerns prop driven aircraft was not so much the drag rise of supersonic tip speeds, but the drag rise of the prop disk as a whole.

My regards,

Widewing

[hazed-]

like ive said before..if it was produced during the war but low numbers or v late addition BUT IT SAW ACTION it should be available at resonable/high perk cost.if it didnt see action very expensive perk.Same for all planes.The rarer the harder to get i say.
plus if any plane used too much a temporary perk status.(this being dynamic tour/tour or map/map)

[Hristo]

Originally posted by eddiek:
 Witness the Rumble this year.....which 2 planes were singled out as the cause of the Axis defeat.......P47D-11 and the Spit.  

Wrong ! It was about pilots, not planes. Rumble was won 15:0 by Allies due to better pilots and squads fighting against poorly organized and harshly put together pilots. Also, many of the experinced types on our side were missing.

[gripen]

Widewing,
The R-2800 C-series was rated at 2800rpm, I don't know how it was rated at the XP-47J. Also the propeller of the XP-47J seems to be (according to the pictures) similar large one as in the later D models, 13ft or more (spinner is also huge). Then it also should be noted that compressebility starts to affect to the propeller around tip speed mach O.8 see  this NACA report.

gripen

[ 08-17-2001: Message edited by: gripen ]

[niklas]

Widewing, i actually wanted to see docs about the 507mph flight.
But if the max. mach number of a p47 was really 0.833, then it confirms my opinion. So thx for the link.

Daff: Noone is interested in the speed that was actually reached in the X-1, and whether the speed claim was 50mph to high or to low compared to the true speed. The important point is that it broke through the barrier of sound. Few people remember the topspeed of the X-1 today.
When you do radar measurements, the wind is not irrelevant. That was my point, not IAS > TAS.

Temperature starts to stop over 36k btw. But -80°C was indeed a bit too much if you compare it to the standard atmosphere   (though atmosphere conditions can vary a lot)

With 2800rpm the tip is travelling at mach  ~1.18. That means from a radius of ~9ft on(70% of total propeller radius) the propeller blade is already moving supersonic.

No way to reach 0,76 in a level flight this way. It would be interesting to read the original report.

niklas