Non-turbo P-61: Northrop's idea or the Army's?

[Stephan Wilkinson]

I have seen it written that Jack Northrop himself decided to leave the weight of turbochargers and intercoolers off the P-61, and I have seen it written that he vigorously lobbied to make the engines turbocharged but the Army overruled him. Anybody have any evidence for one or the other? (Obviously I'm talking P-61A and B, since the C was turboed.)

[Randy Wilson]

From Northrup's Night Hunter P-61 Black Widow by Jeff Kolln, page 29:

"The XP-61C was essentially the same Black Widow airframe powered by 2,800-hp Pratt & Whitney R-2800-77 engines with General Electric CH-5 turbo-superchargers. With this increase in power, the XP-61C was estimated to have a top speed near 430 mph at an altitude of 30,000 feet. Engineers at Northrup had initially decided not to install turbo-superchargers on earlier P-61s since they were worried that the increased fuel consumption would adversely affect loiter times. With the development of the C-model, however, they decided that the performance gains more than offset any penalties in fuel consumption."

Hope that helps some. Randy

[Randy Wilson]

Another view point from Northrop P-61 Black Widow by Garry R. Pape and others, page 18:

"A two-stage, two-speed, intercooled mechanical supercharger was part of the R-2800 powerplant designated for the P-61 as initially designed for the Air Corps. The thinking in some circles was that the added weight and complexity of a turbosupercharger installation was not necessary. This line of reasoning was not accepted by all at Northrop, where such designers as Dr. William R. Sears, Irving L. Ashkenas and John M. Wild felt that the extra horsepower the turbosupercharger provided was necessary. As it turned out, the anti-turbosupercharger forces prevailed."

I believe the initial engine for the XP-61 was the P&W R-2800-25 (of which only 5 were built), which experienced failures and was replaced by the R-2800-10.

Randy

Last edited by Randy Wilson on Mon Sep 08, 2014 4:15 pm, edited 1 time in total.

[Stephan Wilkinson]

Thanks, Randy. I don't trust the Kolln book; it has a number of errors. The Pape book sounds a little more specific and believeable.

[Randy Wilson]

One more bit of info from R-2800 Pratt & Whitney's Dependable Masterpiece by Graham White, pages 471-473 regarding the engines in the first P-61s:

"Inter-service rivalry and different philosophies meant that the Navy procured and developed their own engines and the Army Air Forces did likewise. Contributing to this state of affairs was the fact that the Navy did not have high hopes for turbosupercharging whereas the Air Force did. Consequently, the Air Force paid for the development of the General Electric Type B and Type C turbosuperchargers. The Navy, on the other hand, paid for the development of gear driven, two-stage, supercharging. Therefore it was somewhat surprising to see the YP-61 and P-61A powered by a Navy engine, the "B" series R-2800-10 normally seen powering the F6F Hellcat. The -10 was soon replaced by the very similar -65W. The primary difference was the -65 used G.E. ignition and water injection. With the introduction of the P-61C a very different engine was used: the -73/-77s that were "C" series, single-stage, single-speed engines. Additional boost was provided by a G.E. CH-5 turbosupercharger."

Typically, engine dash numbers that are even are Navy engines and odd are Army, for those that may not know that. Again, I hope all this helps with the original question.

Randy

P.S. Stephan - just saw your reply. I'm not well read on the P-61 but it does seem odd that when the change was made from the -10 Navy engine to the -65 Army one, that a turbo-supercharged engine wasn't considered. Of course there was a very high demand for them in the heavy bombers, which may have had some effect. All the best.

Last edited by Randy Wilson on Mon Sep 08, 2014 4:25 pm, edited 1 time in total.

[Stephan Wilkinson]

And that book is on my shelves. Never thought to consult it...