P-61 Endurance

[XBe02Drvr]

It had a lot of power (2 x R2800), but it was also a big aircraft (power/weight). It wasn't all that fast, and drag levels affecting top-speed and climb-rate (which wasn't very impressive) lead me to believe it wouldn't dive all that well.

It didn't dive all that well, as it was drag limited at the higher end, but according to the guy who flew it, its initial acceleration at full power was sufficient to overcome the energy loss from the roll in time to get a shot at the rapidly departing opponent. It's all about the P61 pilot using the appropriate tactic for the situation. An attacker diving in with a high closure rate gets the tight, flap aided turn treatment, while one "saddled in" at six o'clock and just coming up on firing range gets the tight roll reaction. In the latter case the avoided attacker doesn't have a large speed advantage, and with a Widow on his tail will be stuffing the nose down and bending the throttle over its forward stop. He will pull away, but not before he gets his picture taken.
Cheers,
Wes

 

[Zipper730]

I'm seriously lead to believe the turbo would have been the correct option for boosting performance. The twin-blower was good, but not enough...

 

[Admiral Beez]

I read somewhere that the P-61 had over 100 kills, does anyone know anything about these? Were they against bombers, fighters, were there any aces? How did the P-61 handle, was it simply a gun platform with a radar capable of stalking at night or could it dogfight?

Could the P-61 modified for range have operated as an escort for RAF Lancasters and Halifaxes? With its radar and a good IFF system it should be able to track and attack German night fighters.

 

[swampyankee]

The P-61 was, reportedly, very maneuverable, and able to turn inside of many single-engine fighters. It did have some success in combat; see Northrop P-61 Black Widow – Combat Record and Beware the Black Widow | History | Air & Space Magazine. It appears there were only eight squadrons to use the type, six in the Pacific and two in Europe.

 

[Milosh]

Could the P-61 modified for range have operated as an escort for RAF Lancasters and Halifaxes? With its radar and a good IFF system it should be able to track and attack German night fighters.

There was NF Mossies for that.

 

[XBe02Drvr]

There was NF Mossies for that.

And they were better at it than the Widow, in both speed and range. The P61 was conceived as an interceptor, not an intruder.

 

[Admiral Beez]

There was NF Mossies for that.

IDK that the NF Mosquitos were used for bomber escorts. My thinking on the P-61 is that it could direct its turret on target without necessarily changing course, at risk of crashing into a Lancaster.

 

[XBe02Drvr]

IDK that the NF Mosquitos were used for bomber escorts. My thinking on the P-61 is that it could direct its turret on target without necessarily changing course, at risk of crashing into a Lancaster.

AFAIK, the mossie intruders weren't "escorts" in the close support daylight sense, but rather free ranging hunters that homed on the electronic emissions of German night fighters, shooting them down wherever they could find them, often right over their bases.
Basic rule of night fighting: Positive ID! When it's pitch black, positive visual ID is generally a matter of exhaust pattern, something that usually can only be reliably determined from below and behind. No shooting at radar blips! Too many of the wrong people die that way.

 

[Peter Gunn]

It didn't dive all that well, as it was drag limited at the higher end, but according to the guy who flew it, its initial acceleration at full power was sufficient to overcome the energy loss from the roll in time to get a shot at the rapidly departing opponent. It's all about the P61 pilot using the appropriate tactic for the situation. An attacker diving in with a high closure rate gets the tight, flap aided turn treatment, while one "saddled in" at six o'clock and just coming up on firing range gets the tight roll reaction. In the latter case the avoided attacker doesn't have a large speed advantage, and with a Widow on his tail will be stuffing the nose down and bending the throttle over its forward stop. He will pull away, but not before he gets his picture taken.
Cheers,
Wes

To quote ensign Parker "Gee I love that kinda' talk..."

 

[MikeMeech]

AFAIK, the mossie intruders weren't "escorts" in the close support daylight sense, but rather free ranging hunters that homed on the electronic emissions of German night fighters, shooting them down wherever they could find them, often right over their bases.
Basic rule of night fighting: Positive ID! When it's pitch black, positive visual ID is generally a matter of exhaust pattern, something that usually can only be reliably determined from below and behind. No shooting at radar blips! Too many of the wrong people die that way.

Hi
It was rather more complicated than that, during 1944-45, Mosquito night fighters escorted the bomber stream, flying alongside and weaving above it. Other Mosquito aircraft were night intruders over German night fighter airfields and Mosquito NFs also flew around German night fighter beacons to catch some there. This meant that the German night fighter force were liable to be attacked taking off and landing at their airfields, when they were holding around their beacons before being directed to the bomber stream and also had to be aware the British bomber stream also contained night fighters. The ID problem was partially solved by fitting the Type Z (also earlier Type F) infra-red equipment to British aircraft, for example at the rear of the aircraft where the 'headlights' could be seen by the escort night fighter (through filters on goggles), also it is seen on the Lancaster's bomb aimers perspex (the RAF Museum's Lancaster has the housings fitted) so if they came to the rear of another bomber the rear gunner would see the 'headlights' through his filters.
The drawing below from page 107 of 'Confound and Destroy' by Martin Streetly, gives a good impression of defending the bomber stream in 1944-45.

Mike

 

[Zipper730]

To get back onto topic: It would appear that the first ideas which appeared in August of 1940 called for an endurance of 8 hours (fly CAP over a city at night), followed by the first issued specifications calling for 2 hours at maximum-continuous power which would have come around on either October 22, 1940, or December 5, 1940 when Northrop Specification 8A (NS-8A) was drawn-up.

I'm unsure if the 2-hour max-continuous requirement fully superseded the 8-hour endurance-requirement, or was simply added on to the existing specifications (it was noted the P-61A could pull 10 hours endurance)?

The original spec called for a 2-hour endurance at full throttle; I hope to be copying the original flight test results later this week...

I'm not sure if you ever managed to get your hands on those, but if you do: I wouldn't mind seeing it...

 

[Koopernic]

I think if the 368 mph P-61B had of been issued to RAF fighter command it would have been not quite useless. The Me 410 and Ju 88S could outrun it. Even the Dornier Do 217M could manage 346mph on a good night While He 177 using a diving approach would be very hard. So the P61A/B would be poor at protecting the UK. It would be confined to intercepting Ju 88A4 light bombers, an aircaft that shouldn't be used anymore against the UK. It would have its work cut out intercepting a Me 264 in its final 40 minute dash production of that aircaft proceeded in 1943/44. It's ability to patrol long periods might on occasion intercept Luftwaffe long range maritime patrol craft as the broke into the Atlantic or it might protect convoys. Hypothetically if the P61B had of been issued to the Luftwaffe it wouldn't be able to intercept the Mosquito. It would be a good Lancaster killer, the guns used as a sort of schräge Musik Guns, potentially aimed by the radar.

 

[BiffF15]

I think if the 368 mph P-61B had of been issued to RAF fighter command it would have been not quite useless. The Me 410 and Ju 88 could outrun it. Even the Dornier Do 217M could manage 346mph on a good night While He 177 using a diving approach would be very hard. So the P61A/B would be poor at protecting the UK. It would be confined to intercepting Ju 88A4 light bombers, an aircaft that shouldn't be used anymore against the UK. It would have its work cut out intercepting a Me 264 in its final 40 minute dash production of that aircaft proceeded in 1943/44. It's ability to patrol long periods might on occasion intercept Luftwaffe long range maritime patrol craft as the broke into the Atlantic or it might protect convoys. Hypothetically if the P61B had of been issued to the Luftwaffe it wouldn't be able to intercept the Mosquito. It would be a good Lancaster killer, the guns used as a sort of schräge Musik Guns, potentially aimed by the radar.

Just out of curiosity what do you base your assumption on that the P-61B in the RAF role / use would have been "not quite useless"? Is it based on speed alone, after action reports? The reason I ask is cruise / operational speeds are not usually top speed / dash speed. I would think most night fighters had "enough" speed advantage during the intercept to get most adversaries. If the adversary was hauling the mail he was drastically limiting his time on station and therefor usefulness. Not trying to stir up the sh-t, just curious what your criteria for being of use is and why.

Cheers,
Biff

 

[Koopernic]

Just out of curiosity what do you base your assumption on that the P-61B in the RAF role / use would have been "not quite useless"? Is it based on speed alone, after action reports? The reason I ask is cruise / operational speeds are not usually top speed / dash speed. I would think most night fighters had "enough" speed advantage during the intercept to get most adversaries. If the adversary was hauling the mail he was drastically limiting his time on station and therefor usefulness. Not trying to stir up the sh-t, just curious what your criteria for being of use is and why.

Cheers,
Biff

Mainly on the lower speed of the P68B over the various NF Mosquitos (some of which needed nitrous oxide to to haul in a Me 410 (encounter report on ww2 performance Testung) and the approach to Luftwaffe used to avoid interception which was a dive on penetration. I think attrition on He 177 was about 6% over the total baby Blitz campaign so it show even the Mosquito was challenged.

Its worth reading Gebhard Adders book on the history of the German Night Fighter Force. The. RAF would jam and create spoof raids (eg with windows dropping sterling's that would turn into mine laying operations or small forces dropping windows that split off). The result was that German night fighters were dispatched in the wrong direction and when the spoof was discerned, which it even would be, they burned out engines trying to get to the right area. If they got into the bomber stream the jamming and interferance was not to severe and the radars were useable ober short distances but this was hard. Interceptors benefit from speed it's no good having range if you can't get there in time.

 

[Dana Bell]

Hi Koopernic,

The P-61B didn't have the range/endurance or speed to operate over Germany. Most of the performance figures quoted in secondary sources are based on Northrop estimates, which would eventually be disproven in AAF tests and operational missions.

Wright Field reports on the XP-61 complained of performance problems adding the note that production versions would have even lower performance. Some of the most effective missions were flown without the turret and third crewman, but the aircraft still couln't cut it.

One 3-page ETO report started by complaining that the P-61 lacked speed, altitude, and endurance, but that the turret would probably make up for those deficiencies; the last page of the report recommended that the turret be deleted from all P-61s...

Cheers,



Dana

 

[MIflyer]

Did North American ever propose a P-51N like the F6FN or F4UN?

There was at least one P-51D modified with a radar and a canopy that split open aft of the regular cockpit so they could accommodate a radar operator. But it seems to have been used to help daylight P-51 units identify aircraft at longer ranges than could be done visually.

Of course, NAA's answer to the nightfighter requirements was the P-82, and THAT would have been by far the best nightfighter of WWII, with range, speed, and maneuverability to spare.

 

[GregP]

I didn't read the rest of the thread yet, but ... one early question was P-61 endurance.

The P-61 carrier 640 U.S. gallons internally. Assume full internal fuel and assume the aircraft is at ... say ... 18,000 feet. Max Cruise was 91 gallons per hour.

So, assume it magically gets transported to 18,000 feet and is running at Max Cruise (91 gph - gallons per hour). Also assume you need 1/2 hour reserve fuel. That leaves 595 gallons and translates into 6.54 hours of endurance. Now, a real P-61 doesn't magically get transported to 18,000 feet; it has to climb up there. The fuel burn would be higher than 91 gph, but the aircraft WOULD be in the air and ready for use.

I'm guessing the endurance would be about 6 hours, give or take a bit.

 

[MIflyer]

I'm guessing the endurance would be about 6 hours, give or take a bit.

In the book "Queen of the Midnight Skies" it says the USAAF was disappointed in the range of the P-61 in the Pacific, being no better than a P-38M in that respect, which was about 700 miles, and that was major criticism of the Black Widow. No doubt they wanted to fly intruder missions over Japanese airfields but in the Pacific Long Range meant Looooong Range

 

[33k in the air]

I didn't read the rest of the thread yet, but ... one early question was P-61 endurance.

The P-61 carrier 640 U.S. gallons internally. Assume full internal fuel and assume the aircraft is at ... say ... 18,000 feet. Max Cruise was 91 gallons per hour.

So, assume it magically gets transported to 18,000 feet and is running at Max Cruise (91 gph - gallons per hour). Also assume you need 1/2 hour reserve fuel. That leaves 595 gallons and translates into 6.54 hours of endurance. Now, a real P-61 doesn't magically get transported to 18,000 feet; it has to climb up there. The fuel burn would be higher than 91 gph, but the aircraft WOULD be in the air and ready for use.

According to the Pilot's Flight Operating Instructions manual for the P-61A, at a gross weight of 27,000 to 28,000 lbs:

Climb to 15,000 feet consumed 150 gallons (includes warm-up and take-off allowance)
Cruising at 15,000 feet at a TAS of 230 mph consumed 150 gallons per hour (Column IV; no figures were given for Column V)

Note that in this particular PFOI the climb and cruise figures are preliminary, and had yet to be flight checked.

 

[Vincenzo]

230 mph don't look as max cruise, is possible that 91 was for each engine?