Was the Republic XP-47J speed record legit?

[Stephan Wilkinson]

In August 1944, using calibrated instruments, Republic test pilot Mike Ritchie flew an XP-47J, a Super Thunderbolt prototype, to a supposed speed of 505 mph at 33,350 feet, This was said to be the highest speed attained by any prop-driven WWII aircraft during the war, and it was considered official and legit by the USAAF. There were, of course, no FAI observers or record-setting apparatus; Republic was simply fight-testing an aircraft, not trying to set a record.

In 1969, Darryl Greenamyer set a world speed record of 483 mph in a modified Bearcat using doped fuel and a highly modified engine. (The Republic XP-47J was a military airplane carrying guns, radios and standard paint, and without any special preparation.) In August 1979, Steve Hinton broke that record with the Red Baron, doing 499 mph. Not until Lyle Shelton flew almost 524 mph in August 1989 was the 500-mph barrier officially broken.

What am I missing here? Was the XP-47J speed bogus?

[Pim-Pouw]

What am I missing here? Was the XP-47J speed bogus?

Probably the 33,350 feet altitude

[menards]

All of those official speed runs are at a couple hundred feet AGL through a timed course. At FL330 things are different. The speed was probably legit at that altidude.. but would have been slower at sea level. Anson Johnson supposedly had some fast runs in his P-51 racer (no belly scoop and a lighter weight merlin) in the late 40s but they weren't verified due to faulty timing equipment.

[Stephan Wilkinson]

Of course. What was I thinking? Thank you for pointing that out.

[CAPFlyer]

First, the speed was at altitude. All of the record attempts are done at near surface AGL (see the video of Steveo's attempt, which is not a certified record since he didn't get the requisite 1% bust) in much thicker air. The XP-47J with a True Airspeed of 505 MPH was actually flying at an Indicated Airspeed of ~265 MPH. Lyle's attempt was at Las Vegas, NM, with an average altitude around 7000 ft, so his Indicated Airspeed was ~415 MPH.

Second, the XP-47J wasn't flying on a "closed" course. All official speed records are set with multiple passes over a measured course. For land speed records under the FIA, this is 2 passes over a 1km or 1 mile course in opposite directions. For aviation under the FAI, the piston course is 4 passes over a 3km course in alternating directions. This is what got Steveo on his attempt since he had both inconsistent wind and engine problems, his first 2 passes were good, the engine started having problems on the 3rd and the last pass had an extra headwind component as the wind began to come up slowing him even further. Even though the alternating directions is designed to help negate the wind, if the wind is higher or lower between passes, it can't be fully cancelled out. BTW, for jets, the course is significantly larger, usually 25km.

[Neal Nurmi]

There is also a 15 km any altitude speed record. Frank Taylor set it at 517 mph in 1981, and David Price flew the same aircraft over Mojave at a reported 535 mph or so in 1997 or 98. The latter attempt never became official due to camera and timing difficulties, but reputable speeds were recorded by other means. These attempts were done at fairly high altitude.

[Neal Nurmi]

duplicate post -- either stupid software or stupid user...

[Flat 12x2]

The official prop-driven record (any altitude) was set in 1960 by the Tupolev Tu-114 at 545mph

[Speedy]

For the record, the claims made by Anson Johnson and his modified P-51 were just that...claims. In later years, he admitted that he made those numbers up in an effort to find a sponsor so he could make a legitimate attempt on Fritz Wendell's record.

Even before he admitted the numbers were fabricated, I had suspected them. He claimed they were over 500 at sea level in humid air in Florida. If you look at any of the low altitude speed records, they are all set at high agl-- 1969 Edwards AFB (483 mph at 2,303 feet MSL), 1979 Tonopah, NV (499 mph at 6,047 feet MSL), 1989 Las Vegas, NM (532 mph at 6,424 feet MSL) and 2017 in Idaho (533 mph at 5,500 feet MSL). NO WAY a P-51 with 1940's modifications and engine technology could go over 500 at sea level.

[menards]

For the record, the claims made by Anson Johnson and his modified P-51 were just that...claims. In later years, he admitted that he made those numbers up in an effort to find a sponsor so he could make a legitimate attempt on Fritz Wendell's record.

Even before he admitted the numbers were fabricated, I had suspected them. He claimed they were over 500 at sea level in humid air in Florida. If you look at any of the low altitude speed records, they are all set at high agl-- 1969 Edwards AFB (483 mph at 2,303 feet MSL), 1979 Tonopah, NV (499 mph at 6,047 feet MSL), 1989 Las Vegas, NM (532 mph at 6,424 feet MSL) and 2017 in Idaho (533 mph at 5,500 feet MSL). NO WAY a P-51 with 1940's modifications and engine technology could go over 500 at sea level.

With all due respect, N13Y was not a slouch. the "1940's technology" of a lightweight merlin and streamlining the fuselage went a long way in achieving some fast speeds.

[Speedy]

I'll say it again: he admitted that he made those numbers up in an effort to find a sponsor. Those were Anson's own words.

While he may have had a low altitude Merlin and the whole clipped-wing/no scoop thing going...he also had a stock D-model canopy on top.

No slouch....agreed. Fast enough to break Fritz's speed record at sea level in a warm, humid environment? Not a chance.