P-61 Endurance

[IdahoRenegade]

I seem to recall reading something many years ago about the P-61 having an excellent sustained turning radius, as good or better than many single-engine fighters (when using Fowler flaps as maneuver flaps). Any truth to that? No idea where I read that-seems hard to believe given the size of this beast.

 

[swampyankee]

Did North American ever propose a P-51N like the F6FN or F4UN? Or once the P-38N was in the pipe no USAAF single place night fighters were pursued?

The USN was under tighter constraints than the USAAF: they needed a night fighter, but were a) in a rush, b) needed something that could operate routinely off a carrier, and c) were leery of operating twins off carriers. The USAAF started looking for a night fighter earlier and had no size constraints.

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?

I've read it could turn very well,

 

[swampyankee]

I seem to recall reading something many years ago about the P-61 having an excellent sustained turning radius, as good or better than many single-engine fighters (when using Fowler flaps as maneuver flaps). Any truth to that? No idea where I read that-seems hard to believe given the size of this beast.

I've seen the same reports, which may just mean we read the same, potentially flawed, secondary sources.

 

[Zipper730]

D Dana Bell ,

I'd like to just be clear on something: Is the Shrike the first proposals for the P-61, or a design that existed before?

 

[Dana Bell]

Hi Zipper,

I can't say - my primary sources haven't yet mentioned the Shrike, and I've not been able to return to my own P-61 research. (We had a bad car crash in August and, while no one was seriously injured, we're still not caught up on the many things we planned to take care of in the autumn.)

Hap Arnold first asked for a 3-seat, twin-turret version of the P-38 or the Grumman F5F - neither of which could carry that kind of crew and armament. A week later he asked for an entirely new design, and Northrop soon had a contract. All this was for a turret and radar system that had not yet been developed. If the Air Corps knew of the Shrike concept, they may have called Northrop to take it on. But I've only seen the Shrike in secondary sources, so I've no idea how it fit into the P-61 story.

Cheers,



Dana

 

[Zipper730]

I can't say - my primary sources haven't yet mentioned the Shrike, and I've not been able to return to my own P-61 research. (We had a bad car crash in August and, while no one was seriously injured, we're still not caught up on the many things we planned to take care of in the autumn.)

Sorry about that, I hope everything works out.

Hap Arnold first asked for a 3-seat, twin-turret version of the P-38 or the Grumman F5F - neither of which could carry that kind of crew and armament.

For the P-61?

 

[Zipper730]

I seem to recall reading something many years ago about the P-61 having an excellent sustained turning radius, as good or better than many single-engine fighters (when using Fowler flaps as maneuver flaps). Any truth to that? No idea where I read that-seems hard to believe given the size of this beast.

I'm not sure about sustained agility, but as for the ability to maneuver, it was quite maneuverable for a plane that was the size of a light/medium bomber.

As a general rule of thumb, one can determine the speed at which an aircraft can pull a specific g-load by multiplying the stall speed by the square root of the g-load...

... though I would assume power-on stall would be the best determiner, others have said power-off is the best (and others saying somewhere between), based on the power-off stall speed: You'd be able to achieve this g-load at a minimum speed of 287.1 mph at 27000 pounds (106.25 mph is the stall speed for that weight).

One can determine turning circle via the formula A = V^2/R

A = Acceleration / G-load. You could use 32.17405 f/s or 9.80665 m/s
V = Velocity: In f/s or m/s
R = Radius: In feet or meters

With the figures listed, you end up with a turning radius of 754'9" or 230.1m.

 

[MIflyer]

The official history of the USAAF described the P-61 as its "most maneuverable fighter." A pilot who did a lot of P-61 test flying said that with a trained crew and the top turrent operational he thought he could take on any four WWII prop fighters and win.

 

[gjs238]

.

 

[Zipper730]

The official history of the USAAF described the P-61 as its "most maneuverable fighter."

Ironic. That said, the maneuvering figures I got were based on the power-off stall. I should point out that I'm not totally confident that's right -- for a level pull-up: I'm pretty sure you'd use power-on stall, for turns things get murky because of the asymmetry in airflow. That said I have contemplated something like 1/4 to 1/2 between power-off and power-on. There is a more iron-clad method, but it requires you to know the co-efficient of lift figures. Like the actual ones, not something somebody guessed.

Regardless, I do remember in a book I read about the P-61 that after either flying it, or using it at night, that they would be quite comfortable taking it up in day time. I could only imagine what pilots who survived an encounter would find themselves saying "Mein Gott - Es ist wie ein Hauskampf!"

That said, the maneuverability figures I got were based on power-off stall. Some sources did say to use power on: For a level pull-up, I would probably use those figures, but the real best solution is to get the CL Max figures, which I don't have.

 

[MIflyer]

I read that P-61's in the Pacific were told NOT to engage enemy aircraft in daylight if they encountered some on the way back from their night patrols. But on at least one occasion a P-61 heading back to base at dawn sighted a Japanese fighter, and unable to get a response by radio, the pilot said, "Ah, t'hell with it." and shot the Japanese aircraft down.

And the Luftwaffe leadership was forced to tell its night fighter crews, "Yes, there are American P-61's operational in the area, but they are not THAT deadly so don't be scared of them." Earlier, the Luftwaffe night fighter pilots suffered from "Mosquitopanic"; if they scored a kill against an RAF bomber they immediately dove steeply for the ground, sure that a Mossie was in their Six and about to blow them away.

 

[Shortround6]

Zipper, please see page 603 of "AHT" but please note the P-61B-1 is listed at an absurdly low weight compared to the other aircraft. Like full crew, 1/2 /ammo, 1/2 oil and about 215 gal of fuel.

 

[Zipper730]

I read that P-61's in the Pacific were told NOT to engage enemy aircraft in daylight if they encountered some on the way back from their night patrols. But on at least one occasion a P-61 heading back to base at dawn sighted a Japanese fighter, and unable to get a response by radio, the pilot said, "Ah, t'hell with it." and shot the Japanese aircraft down.

Honestly, I can understand that mindset. Plus, if I shoot him down, he can't shoot me down.

And the Luftwaffe leadership was forced to tell its night fighter crews, "Yes, there are American P-61's operational in the area, but they are not THAT deadly so don't be scared of them." Earlier, the Luftwaffe night fighter pilots suffered from "Mosquitopanic"; if they scored a kill against an RAF bomber they immediately dove steeply for the ground, sure that a Mossie was in their Six and about to blow them away.

Both were quite dangerous actually. The Mosquito's areas of advantage were range, roll-rate, probably climb-rate, and dive. The P-61 had advantages in terms of firepower, rate of turn, and maximum g-load.

I would guess that the change to two hours at full throttle went away pretty quickly as no US aircraft engines were really rated that way, unless max continuous or "normal" power is what is meant by full throttle (it sure wasn't military power).

I'm guessing they mean enough endurance to run 2 hours on maximum continuous. That's still quite an impressive achievement in itself.

@ 24000' that would be around 440 gallons of fuel burned to do this. It seems to take about 65 gallons to climb from 0' to 22000' using military power and around 12-1/2 minutes (part of it has to do with a fuel consumption chart I have from a P-61 flight manual, and part of it came from another post, which had altitude in metric and required some guesswork to factor in conversions and fuel burns with altitudes) to do it. I don't know how long it takes to climb and accelerate another 2000' while reducing climb angle to get up to speed and stuff.

I also don't know how long a typical warm-up would be, what power-settings are used (and fuel burn to go with it), how much fuel would be allotted for loitering, and combat. With those in there, I don't think it'd cover it even with 646 gallons aboard (particularly loiter and combat).

I've only seen the Shrike in secondary sources, so I've no idea how it fit into the P-61 story.

Yeah, I'm not sure if it was a preliminary design for the P-61, or was a design that they'd been working on for another purpose, that ended up as the baseline for the P-61.

The USAAC did have some interesting aircraft concepts, particularly when it came to bomber-escort (when they entertained the concept at all), and some unorthodox ideas regarding patrol-interception: The YFM-1 Airacuda was designed for both (though predominantly as a bomber-destroyer/patrol interceptor).

For the latter, it was designed around the range and endurance to allow it to be able to follow the bomber, heavy firepower to bring it down, and the ability to carry 20 x 15 pound bombs to drop on formations from above (something the USN looked into as well); for the former, it carried a turret to act as a flying gunship to cover the bomber formation, and enough internal fuel to fly the escort-range without drop-tanks (something the USAAC did not want in escort aircraft).

It turned out to be a flop as it wasn't all that agile (3.4g normal, 5.1g ultimate), and couldn't fly as fast as desired.

While the Shrike seems like a reach for this, it did have a turret, a rear-gun. It didn't appear to be suitable as a bomber (it didn't seem to have a bomb-bay), and it seemed to be an oversized design like the YFM-1.

 

[Kevin J]

Honestly, I can understand that mindset. Plus, if I shoot him down, he can't shoot me down.
Both were quite dangerous actually. The Mosquito's areas of advantage were range, roll-rate, probably climb-rate, and dive. The P-61 had advantages in terms of firepower, rate of turn, and maximum g-load.

I'm guessing they mean enough endurance to run 2 hours on maximum continuous. That's still quite an impressive achievement in itself.

@ 24000' that would be around 440 gallons of fuel burned to do this. It seems to take about 65 gallons to climb from 0' to 22000' using military power and around 12-1/2 minutes (part of it has to do with a fuel consumption chart I have from a P-61 flight manual, and part of it came from another post, which had altitude in metric and required some guesswork to factor in conversions and fuel burns with altitudes) to do it. I don't know how long it takes to climb and accelerate another 2000' while reducing climb angle to get up to speed and stuff.

I also don't know how long a typical warm-up would be, what power-settings are used (and fuel burn to go with it), how much fuel would be allotted for loitering, and combat. With those in there, I don't think it'd cover it even with 640 gallons aboard (particularly loiter and combat).

Yeah, I'm not sure if it was a preliminary design for the P-61, or was a design that they'd been working on for another purpose, that ended up as the baseline for the P-61.

The USAAC did have some interesting aircraft concepts, particularly when it came to bomber-escort (when they entertained the concept at all), and some unorthodox ideas regarding patrol-interception: The YFM-1 Airacuda was designed for both (though predominantly as a bomber-destroyer/patrol interceptor).

For the latter, it was designed around the range and endurance to allow it to be able to follow the bomber, heavy firepower to bring it down, and the ability to carry 20 x 15 pound bombs to drop on formations from above (something the USN looked into as well); for the former, it carried a turret to act as a flying gunship to cover the bomber formation, and enough internal fuel to fly the escort-range without drop-tanks (something the USAAC did not want in escort aircraft).

It turned out to be a flop as it wasn't all that agile (3.4g normal, 5.1g ultimate), and couldn't fly as fast as desired.

While the Shrike seems like a reach for this, it did have a turret, a rear-gun. It didn't appear to be suitable as a bomber (it didn't seem to have a bomb-bay), and it seemed to be an oversized design like the YFM-1.

Looks like the YFM-1 could have had some potential as a night fighter if it wasn't for the fact that it was so damned slow. Even the Blenheim If could have been faster with two speed Pegasus engines at the altitudes that the He 111 flew, the YFM-1 wouldn't have been.

 

[MIflyer]

One on one, an experienced pilot in a fighter Mossie Mk VI, operating in daylight, was in serious trouble if he encountered an FW-190 alone and was not in a position to outrun it. One of the RAF's most experienced night fighter pilots was shot down that way. I think that under the same circumstances a P-61 would be somewhat better off, assuming it had the turret and an experienced 3 man crew, the radar operator acting as a lookout.

The Mossie was a much more useful airplane than the P-61 overall, but it was not designed as a fighter. Of course a Beaufighter or a P-70 would have been in even worse trouble in that scenario.

 

[XBe02Drvr]

I seem to recall reading something many years ago about the P-61 having an excellent sustained turning radius, as good or better than many single-engine fighters

A pilot who did a lot of P-61 test flying said that with a trained crew and the top turrent operational he thought he could take on any four single engine fighters and win.

In a Wings/Airpower article back in the '60s, this pilot was interviewed. He was an AAF acceptance test pilot and P61 OTU instructor on the west coast where many USN/AAF fighter OTUs were based. He and his gunner (no RO for daylight ops) routinely tackled four plane flights of F6Fs, FM2s, P51s, P47s, and P38s flown by combat veteran OTU instructors, and got guncam tags on all four without getting tagged themselves. He often resorted to gyrations he didn't recommend nugget pilots attempt until they had a lot more experience in the bird. Apparently the combat setting for the flaps had a very quick extend/retract response, and with a sudden application of asymmetric thrust and a sharp pull on the yoke combined with a quick poke of flap and a stomp on the rudder, the beast would do an impossibly tight snap roll out of the sights of an attacking fighter which would shoot right past and into the kill zone of his 20MMs. Restore full thrust, flaps up, pitch down, center the target, and start running film. Nose down, with 4,000 ponies pulling, the speed deficit from the snap roll would be quickly erased.
The spoiler-aided lightning roll and tight turning radius could be used to force overshoots, giving the alert gunner a shot as the attacker slides past or pops up into a yo-yo. If the opponent goes yo-yo, a quick reversal of turn gives the gunner an overhead shot. Quite a different environment for a gunner trained to defend bombers. Needless to say, the classic Thach weave would not work against an agile target with four .50s protecting it's tail.
Somebody upthread mentioned the difficulty of an RO staying alert staring at the scope on an all night patrol. Not a problem. The Widow was not an AWACS and didn't have a 360° search radar. Its narrow beam AI radar was nearly useless at searching the entire sky for targets. It depended on guidance from ground radar to put the bandits in the relatively narrow cone of its radar, and then when in range, it depended on visual aiming of its guns. It wasn't precise enough to put the guns on target by radar alone.
Cheers,
Wes

 

[MIflyer]

Yes, that is the article I have somewhere.

One P-61 unit in the ETO, lacking a operational turret on its airplanes, got rid of the gunner and moved the radar operator and his equipment forward into the gunner's position. This added coordination between the pilot and RO, and enabled both of them to search the skies for a target they had identified on radar.

 

[Zipper730]

In a Wings/Airpower article back in the '60s, this pilot was interviewed. He was an AAF acceptance test pilot and P61 OTU instructor on the west coast where many USN/AAF fighter OTUs were based. He and his gunner (no RO for daylight ops) routinely tackled four plane flights of F6Fs, FM2s, P51s, P47s, and P38s flown by combat veteran OTU instructors, and got guncam tags on all four without getting tagged themselves.

Quite an achievement for the P-61, though I would imagine those F6F, FM-2, P-51, and P-47 pilots would got some serious egg in their face.

He often resorted to gyrations he didn't recommend nugget pilots attempt until they had a lot more experience in the bird. Apparently the combat setting for the flaps had a very quick extend/retract response, and with a sudden application of asymmetric thrust and a sharp pull on the yoke combined with a quick poke of flap and a stomp on the rudder, the beast would do an impossibly tight snap roll out of the sights of an attacking fighter which would shoot right past and into the kill zone of his 20MMs. Restore full thrust, flaps up, pitch down, center the target, and start running film. Nose down, with 4,000 ponies pulling, the speed deficit from the snap roll would be quickly erased.

You know, I remember hearing it's diving characteristics were similar to the P-70. That said, I don't know how good the P-70 dived (it wasn't that fast an airplane though, but it was heavy).

 

[XBe02Drvr]

You know, I remember hearing it's diving characteristics were similar to the P-70. That said, I don't know how good the P-70 dived (it wasn't that fast an airplane though, but it was heavy).

In a 1 V 4 against single engine fighters a diving escape is not in the cards for a confident aggressive Widow driver with an alert turret gunner. What does matter is downhill acceleration pursuing a diving target before it can pull out of range. That the Widow could do. This is photo war, not bullet war. By the time you've reached your dive speed limits and he pulls away, he's "dead".
The combination of lots of power, innovative flight controls, a potent turret, and unorthodox tactics went a long way to overcoming the weight problem. IIRC, the P61 had combat flaps, speed brakes, roll control and lift dump spoilers, and ailerons that drooped with approach and landing flaps, allowing it to operate from surprisingly small fields. Its Achilles heel, IIRC, was its tire footprint pressure, which made soft fields a no-no.
The pilot quoted in the aforementioned article ranted about the pilots sent to the P61 OTU as instructors being from the bomber community. He wanted P38 pilots: "This thing's a fighter. You don't fly it like a bomber!"
Cheers,
Wes

 

[Zipper730]

In a 1 V 4 against single engine fighters a diving escape is not in the cards for a confident aggressive Widow driver with an alert turret gunner. What does matter is downhill acceleration pursuing a diving target before it can pull out of range. That the Widow could do. This is photo war, not bullet war. By the time you've reached your dive speed limits and he pulls away, he's "dead".

I was simply basing it on what you said about the tactic he pulled. Asymmetric thrust with, either a snap or high-g roll (the latter seems more likely as snap-rolls involve inducing a stall, and generally one adds flaps to lower AoA...), with flaps popped out followed by symmetricalizing (not sure if that's a word) thrust, pulling in the flaps, and dropping the nose.

Depending on the term "dropping the nose" could either mean simply leveling out to get a shot, or dropping into a dive. The latter part might not be necessary depending on how the opponent acts. When forced into an overshoot, some people are stunned, others try and climb/dive/turn to get away.

The combination of lots of power, innovative flight controls, a potent turret, and unorthodox tactics went a long way to overcoming the weight problem. IIRC, the P61 had combat flaps, speed brakes, roll control and lift dump spoilers, and ailerons that drooped with approach and landing flaps, allowing it to operate from surprisingly small fields.

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.

Its Achilles heel, IIRC, was its tire footprint pressure, which made soft fields a no-no.

I didn't actually even know that...

The pilot quoted in the aforementioned article ranted about the pilots sent to the P61 OTU as instructors being from the bomber community. He wanted P38 pilots: "This thing's a fighter. You don't fly it like a bomber!"

I'm surprised they'd have done that. Most all the pilots who flew the P-61 came from the P-70 -- I would have figured they'd have been P-70 drivers. I agree, I'd prefer a P-38 driver instead -- far more aggressive in piloting stile.