enginehistory.org

[rcore]

For some reason an unofficial 500+ MPH speed achievement is associated with various experimental variants of the P-47: the R-2800-powered XP-47J; the Chrysler-powered XP-47H and the R-4360-powered XP-72.

Does anyone know what the actual top speed recorded for these various models is?

According to allpar.com:

[wpearce]

First off, I'm very sorry that I will not be able to recall all the specifics but I'll do my best. Secondly I don't think anyone knows what they really did for certain.

XP-47H - This was the Chrysler IV-2220 powered aircraft, two were built. One was damaged in a hard landing, both ended up being scrapped It's max estimated speed was 490 mph. The best is did was 414 mph. I think the engine was only producing 2200hp in stead of the 2500hp that is should have been and also the airframe had not gone through any aerodynamic clean-up. The 490 speed is often quoted as it top speed but it never achieved that. Weertman's "Chrysler Engines 1922-1998" book states this and gives the reference as the flight report produced by Republic (I think).

XP-47J - This was the special R-2800 powered, cleaned-up, lightened "Superbolt". This is the aircraft that supposedly did what your quote claimed the H did. Only one was built. Some references say it went 507, others 505, and others 504. But again there are some issues here for I remember reading that once it was handed over to the AAC they never got it above 480 or something. But I can not recall the specifics other than claims of a faulty gauge. I'm not certain if the slower flight had the bad gauge or the fast flights.

XP-72 - This was the R-4360 powered "Ultrabolt" further development of the P-47. Two were built; one had a four-blade prop and another had a 6 blade contra-prop. The contra-prop had an engine failure (I think) and it was bellied in but never rebuilt. The other was given to the boy scouts (or something odd like that) and later scrapped. Supposedly, people in charge of the project said it never went over 500 mph and some say 480 was the max achieved while others say 490. But the catch here is that it never had the engine that the plane was built for and that engine would have given it a lot more power. I think it never had the turbosupercharger installed or it was a much smaller unit than what was intended. It is estimated that it would have gone 540 at altitude with the specified engine.

In conclusion, I don't think the H ever did what it was supposed to do. I do think the J might have gone over 500 and it is widely regarded that it did. The 72 would have been king had the demand for it necessitated further development, but I don't think it went over 500. The confusion comes with so many similar aircraft doing similar things at the same time. Add to that the veil of secrecy and the fog of war and you get this conversation that we are having right now, where we will never be certain of who did what.

That was all from memory so take it for what it is worth. If you'd like, I can check my memory against a few references and post the results later in the week.
_________________
Bill Pearce

www.oldmachinepress.com

[rcore]

Thanks Bill!

I edited my original post to correct the nomenclature. I should know better

I'll have to read the Weertman book, since it's one reference I haven't read. There's probably a lot of other interesting material there as well.

The one common theme in the aircraft history references about this story is that no one quite knows for sure, so the boldness with which the author of my quote stepped up to claim the feat surprised me. But I assumed that the official recorded top speeds of these test aircraft are documented, which you point out. My hope has been that the XP-72 actually did the deed, but I was left with the impression over the years that the XP-47J was probably the one that topped 500 MPH, if any.

[wpearce]

Okay…. Of course I was not there and I do not know anyone that was there so everything below is from various references. Who knows where some of them got their info or how to check what they claim. Having said that I think we can think critically and come up with what makes the most sense.

XP-47H:
Weertman's "Chrysler Engines 1922-1998" book (which I do not have but downloaded the chapter on aircraft engine from the SAE for $7.50) states that 382 mph was attained with 2440 hp at 20,000 feet. He states that this showed the aircraft could achieve 414 mph at 30,000 feet with 2500 hp. He lists his source as "Functional Flight Tests on the XP-47H Airplane," Republic Aviation Corporation Flight Test Report No. FR-60 reported by J.F. Riley, Jan. 18, 1946.

Bodie in "Republic’s P-47 Thunderbolt" states the maximum recorded speed was 414 mph but that it had cooling issues and with the cooling doors open it could not exceed 394 mph.

Wagner in "American Combat Planes of the 20th Century" states the top speed was 414 mph at 30,000 feet and that it was well below the 490 mph expected.

O’Leary in "USAAF Fighters of World War II Volume Two" states the designers were hoping for a top speed of 490 mph, the best that the XP-47H could do was 414 mph.

Kasmann in "World Speed Record Aircraft" states the XP-47H was limited to 666 km/h (414 mph) instead of the expected 790 km/h (490 mph)

A number of others state the 414 mph without any other interesting info. A number or other books state 490 mph was the top speed and a few say that 490 mph was the top speed attained.

XP-47H opinion:
I think that 490 mph was the predicted speed but that either 414 mph or less was actually achieved. Another way to look at it is the H had more fontal area, more wetted area, more parasitic drag, and less power that the 475 mph YP-47M with the R-2800-57 engine and CH-5 turbosupercharger. What would make us think it was faster?

XP-47J:
Bodie in "Republic’s P-47 Thunderbolt" states on July 11, 1944 the XP-47J equipped with a CH-3 turbosupercharger achieved 493 mph at 33,350 feet. A CH-5 turbosupercharger was installed and on August 4, 1944, 505 mph was achieved over a calibrated course at 34,450 feet by Mike Ritchie. This is from a report dated Aug. 5, 1944 by Ritchie. These dates and speed are repeated in a number of references. Further on, the book states that the Army Ohio flight tests were unable to get max power and could only achieve 484 mph at 25,350 feet and 2770 hp. The Official Performance Summary report states a max speed of 507 mph, while Republic’s Test Report No.51 (Jan. 27, 1945) lists the speed as 502 mph. Col. George Smith signed the report for B/Gen Craigie.

Wagner in "American Combat Planes of the 20th Century" gives the same top speed but lists August 5, 1944 as the date (which Bodie states was the date of the report).

O’Leary in "USAAF Fighters of World War II Volume Two" states 504 mph as the speed and Aug 5, 1944 as the date. It goes on to state that the USAAF only managed 493 mph and it is thought that the Republic claim could have been inaccurate because of faulty instruments. That was the speed Bodie reported the XP-47J did with the CH-3 turbosupercharger.

Kasmann in "World Speed Record Aircraft" states the XP-47J was timed at 813 km/h (505 mph) on Aug 5, 1944 flown by Mike Richie (missing the 't') and shortly after it reached 816 km/h (507 mph)

A number of others state the speed as 507, 505, 504, and 502 mph.

XP-47J opinion:
With the R-2800-57 engine and CH-5 turbosupercharger, lightened aircraft with aerodynamic improvements, it seems possible that it did archive 500mph + speed. It seems as though the people that were there thought it did go 500 mph +.

XP-72:
Bodie in "Republic’s P-47 Thunderbolt" states both XP-72s flew with R-4360-13 engines equipped with two-stage, variable speed mechanical supercharging equipment. Test pilot Carl Bellinger attained 480 mph at sea level in the No.1 aircraft (single prop). It goes on to say that "Bellinger flatly stated there were no flights with the XP-72 in excess of 500 mph." Bodie also states that had the planned production R-4360-19 with the fluid coupled supercharger been fitted, 540 mph would have been possible. He also says that the -19 supercharger type was never fitted.

Wagner in "American Combat Planes of the 20th Century" states 405 mph at sea level and 490 mph at 25,000 feet.

O’Leary in "USAAF Fighters of World War II Volume Three" states the R-4360-13 powered XP-72 achieved 480 mph while the proposed production r-4360-19 powered P-72 was estimated 550 mph at 25,000 feet.

Kasmann in "World Speed Record Aircraft" states the XP-72 achieved 772 km/h (482 mph) at sea level with a predicted top speed for the production machines of 811 km/h (504 mph), with a figure of 870 km/h (540 mph) at 8 km altitude (26,000 feet).

A number of other references say either 480 or 490 mph. Some say sea level other say 25,000 feet. The output of the -13 seems to be around 3500 hp while the -19 is listed as 4000 hp. White in “R-4360” lists both engines as producing 3000 hp but I think that is the engine themselves without the supercharger.

XP-72 opinion:
I think that 480 mph was achieved and perhaps 490 mph at 25,000 feet. It seems pretty clear that 500 + would have been obtainable had the R-4360-19, fluid coupled variable speed supercharger, and P-72A been built.

As a side note, I have read a few accounts of two aircraft from the same production run that had different flying characteristics and top speeds. I think in some cases like the XP-47J and XP-72, the 10 mph difference of opinion on top speeds works out to be 2%; statistically negligible. Obviously the 414 mph vs. 490 mph for the P-47H is much harder to overlook as an anomaly.

I feel the XP-72 had the greatest speed potential with its "production" powerplant and turbosupercharger. I also feel that the XP-47J did break the 500 mph barrier. And finally, the XP-47H was a dog by comparison.

I should also add that other works I consulted include:

Angelucci and Bowers "The American Fighter:
Door and Donald "Fighters of the United Stated Air Force"
Green "famous Fighters of the Second World War"
Green and Swanborough "US Army Air Force Fighters Part 2"
Jones "US Fighters"
Stoff "The Thunder Factory"
White "R-2800"
White "R-4360"

and others that were less helpful.
_________________
Bill Pearce

www.oldmachinepress.com

[tfey]

There is a gent in California who has collected quite a
bit of novel information on the XP-72 that may rewrite or at least adjust the exisitng histories on these two aircraft. No timetable for publication or release of the information. He was surprised and happy to find information on the Aeroproducts contra prop units on the AEHS website. Score one for the AEHS.

The XP-47H never got near 500 mph; too many developmental issues. Quite a bit of complicated plumbing and systems on that ship. The last AEHS Convention had 2 engineers that worked on the Chrysler program; fascinating to talk with them.