P-61 Performance (1 Viewer)

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MIflyer

1st Lieutenant
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May 30, 2011
Cape Canaveral
Barrett has mentioned the questionable performance of the P-61. I recently obtained a copy of the P-61 Pilot's Training Manual. Note what it says:

P-61 Flight Manual9.png


Not that it says the P-61 "edged out" the P-70 in speed at all altitudes. This is not a ringing endorsement. The P-70 was a modified A-20, the aircraft being made available because they were supposed to be the turbosupercharged version of the airplane, a program that was canceled because a turbo failure caused a crash (of course I am not sure anything ever equipped with a GE turbo did not have a prototype crash). So the aircraft did not have turbos added and became P-70's, most of which were used for training in Florida. The P-70 was at best a minimally capable night fighter, not really being fast enough or fast climbing enough for the job, and being only lightly armed. It was built only in small numbers and its limitations in the Solomans Islands campaign led to a local adaptation, a P-38F being equipped with radar. And except for climb and altitude performance the P-61 seemingly was only a little better than the P-70. The P-38M was found by the combat users to be better than the P-61 in terms of performance but no more effective overall since the guy in the back seat running the radar apparantly was almost useless for aiding in spotting targets visually.

Now, the P-61C, which was equipped with tubosuperchargers liek the P-47 rather then the P-61A and P-61B engines which were like the F4U and F6F, was a much faster airplane, exceeding the performance of just about every other WW2 night fighter. But it was effectively a postwar airplane, by which time a radar equipped P-82C probably would have proved to be far superior.

P-38nghtFtr-1.jpg


Lockheed P-38M.jpg
Screenshot 2024-11-23 at 16-09-07 P-70 at DuckDuckGo.png
Screenshot 2024-11-23 at 16-04-35 Northrop P-61C Black Widow National Museum of the United Sta...png
 
The performance differences are significant. What is questionable about it?
P-70 speed peaks near 15000 ft - 306 mph TAS with 2300 RPM, at 27000 lbs, climb rate at this height ~450 ft/min ( combat power ), ~1130 ft/min initial
P-61 A/B speed peaks at 20000 ft - 346 mph TAS with 2550 RPM, 30000 lbs. (At this height, P-70 is 290 mph). Initial climb 29000 lbs 2560 ft/min, still climbing 1900 ft/min at 15000 ft.

I don't have data for the P-61C, other than prop diameter was increased by 6 inches.
 
re P-61 maximum speeds

Somewhere on the internet (I think) there are flight test reports on the P-61A and B. I do not remember for sure if they were on the net (if so I did not download them) or if I ran across them in hard copy, but I have a summary of the results in my notes.

Performance tests of the P-61A Airplane
Memo Report No. Eng-47-1796-A
26 August 1944

Standard production P-61A-1-NO but fitted with R-2800-65W engines, tested with/without turret installation
TOGWs were 29,240/27.600 lbs

Vmax___________Altitude_____Engine Setting
363/365 mph____22,500 ft____Normal power (2550 rpm at 49.5"Hg)
360/363 mph____21,600 ft____Military power (2700 rpm at 53"Hg)
369/372 mph____17,600 ft____WEP (2700 rpm at 60"Hg with ADI)

The speeds were run through the full standard correction process.
 
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