P-61 Without Turret

[KJ_Lesnick]

The P-61 was actually a surprisingly good design despite it's monstrous size

• Normal max g-load of 7.3g was similar to normal day fighters
  
• Turn rate was tighter than the DH Mosquito NF (roll rate was slower)
  

.
The turret appeared to be a major problem and an unnecessary feature as I see it

• It was designed for an illogical purpose
  
• It added unnecessary drag and volume
  
• It required an additional crew-member
  
• It probably cut down on range
  
• It had aerodynamic problems early on (later on it didn't matter as the technology was needed for the B-29)
  

I'm curious if the design would have won against the XA-26 if it didn't have the turet admittedly.

[sandiego89]

The P-61 was actually a surprisingly good design despite it's monstrous size

• Normal max g-load of 7.3g was similar to normal day fighters
  
• Turn rate was tighter than the DH Mosquito NF (roll rate was slower)
  

.
The turret appeared to be a major problem and an unnecessary feature as I see it

• It was designed for an illogical purpose
  
• It added unnecessary drag and volume
  
• It required an additional crew-member
  
• It probably cut down on range
  
• It had aerodynamic problems early on (later on it didn't matter as the technology was needed for the B-29)
  

I'm curious if the design would have won against the XA-26 if it didn't have the turet admittedly.

I am not sure why you say the purpose of the turret was illogical?  It was hoped that the turret could give 360 degree coverage and attack from below.  With a gun computing gun sight and being able to be controlled by either the gunner or the radio operator- it likely seemed like a desirable feature for the first clean sheet design for a night fighter- and seems logical- especially as they knew it would not be as nimble as a traditional fighter.  It just didn't work out well.  I would not be that harsh on the design team.  Even with the turret deleted it still flew with a crew of three.  Plenty for each to do. 

The P-61 did not have a bomb bay, so a major re-design would have been required to make it a "bomber" in the traditional sense, and would have required the quad 20's to be deleted, or moved back to the wings (which would cut fuel load).  Gondola was a bit skinny for a bomb bay.   Carrying a external bomb load similar in size to a B-26 or A-26 would have cut down on speed and range due to drag. 

Size and performance wise it does seem similar to the A-26.  It would be interesting to see how it could have been employed as a staffer against land targets or shipping. I think the 20mm would have been quite handy in that role.     

[KJ_Lesnick]

I am not sure why you say the purpose of the turret was illogical?  It was hoped that the turret could give 360 degree coverage and attack from below.

If you mean attack bombers from below by spraying gunfire up either head on or at angles off course, yeah it could.  It's still unnecessary for a variety of reasons

• It was surprisingly maneuverable despite it's size: I don't know what they demanded out of it, but it could pull 7.3g x 1.5 far as I know, and in a mock dogfight it beat a P-38
  
• The radar was used to acquire targets and maneuver into visual range for the kill: The radar usually could be used to place the aircraft around the correct elevation (provided it could climb fast enough) and heading (provided the turn can be made within the aircraft's maneuverability) so that only small corrections are needed once in visual range for the shot.
  

With a gun computing gun sight and being able to be controlled by either the gunner or the radio operator- it likely seemed like a desirable feature for the first clean sheet design for a night fighter- and seems logical- especially as they knew it would not be as nimble as a traditional fighter.

The airplane had a gyro-sight?  Wouldn't that make aiming easier for the pilot?

Even with the turret deleted it still flew with a crew of three.  Plenty for each to do.

The plane sometimes flew with three crew, other times with just two.

The P-61 did not have a bomb bay, so a major re-design would have been required to make it a "bomber" in the traditional sense, and would have required the quad 20's to be deleted, or moved back to the wings (which would cut fuel load).  Gondola was a bit skinny for a bomb bay.

Honestly for a couple of seconds I kind of was thrown for a loop: I didn't mean that it was supposed to do the A-26's mission -- what I commented on was the possibility that the A-26 would be selected over the P-61 if it had no turret.

Size and performance wise it does seem similar to the A-26.

True, though if the P-61 had been fitted with a turbocharger, it would have gone potentially around 50 mph faster and 10,000 feet higher

[kerick]

Actually, as the threat from German night bombers fell to nearly zero the P-61 was re-purposed into a strafer and IIRC some carried bombs or rockets. The turret was deleted due to the aerodynamic problems. Even the radar was removed to save weight on the strafing missions.

Here's a couple of good articles
http://www.militaryfactory.com/aircraft/detail-page-2.asp?aircraft_id=78
https://en.wikipedia.org/wiki/Northrop_P-61_Black_Widow

[scooter]

With a gun computing gun sight and being able to be controlled by either the gunner or the radio operator- it likely seemed like a desirable feature for the first clean sheet design for a night fighter- and seems logical- especially as they knew it would not be as nimble as a traditional fighter.

The airplane had a gyro-sight?  Wouldn't that make aiming easier for the pilot?

Pilot's job was to just fly, and fire the fixed 20mms.  The gunner and radio operator had control of the turret.  And even without the turret, the gunner was still responsible for the radar and target acquisition.  Check out Northrop's Night Hunter P-61 Black Widow, by Jeff Kolln ISBN 978-1580071222

[KJ_Lesnick]

kerick

Actually, as the threat from German night bombers fell to nearly zero the P-61 was re-purposed into a strafer and IIRC some carried bombs or rockets. The turret was deleted due to the aerodynamic problems.

I know that by 1944 the Luftwaffe was on the decline, but when the plane was conceived that wasn't the case.  The point is that it would have been faster, and more maneuverable, and less complicated.

As for the use of bombs and rockets, it as a big plane and had the advantage of being able to lug them along without too much penalty

Even the radar was removed to save weight on the strafing missions.

Night attacks too?


scooter

Pilot's job was to just fly, and fire the fixed 20mms.

I would figure crew coordination would dictate that all of them would be working together to ensure the kill... after all the pilot flies the plane but doesn't operate the radar; the radar operator can work at night but cannot fly the plane; the gunner can shoot but without somebody to fly the plane...

The gunner and radio operator had control of the turret.  And even without the turret, the gunner was still responsible for the radar and target acquisition.

My position is that the gunner wasn't really needed: A fighter doesn't need a turret.  The plane would have been faster, lighter, and greatly simpler without it.

Check out Northrop's Night Hunter P-61 Black Widow, by Jeff Kolln ISBN 978-1580071222

I ordered quite a number of books, it'll take some time to get around to this...

[tomo pauk]

There is no doubt that turret pushed up the size & weight of the future P-61. Conversely, it was reducing the performance. The 'triple tandem' crew layout meant a long & heavy nacelle, and twin boom layout increased weight, complexity and production time. But even if we remain on twin boom design, not incorporating the turret, and pilot and radar operator seated much closer, if not side-to-side - the resulting aircraft would've been far smaller, lighter and of better performance.

[sandiego89]

My understanding is the P-61 was never going to be a smallish, light fighter.  Military aircraft are almost always built to customer requirements with certain performance specifications, and in some cases certain design requirements.  If I recall correctly for what ended up as the P-61 the United States largely used RAF specifications that called for a night figher with radar, turrets and very demanding endurance requirements. 

The US issued these specifications and Northrop responded.  The specifications drove the size of the design: large and heavy radar (big dish, lots of heavy black boxes), turrets, heavy armament, at least two engines to meet the performance requirements is going to give your a learge airframe- and on top of that perhaps the biggest driver of size was an 8 hour loiter requirement.  That much fuel is going to drive you to an even larger airframe.   

Northrop responded appropriately.  If he had replied, "Hey, I came up with something different, without turrets, smaller, less endurance, and 'better' than what you asked for" they would have said, no thanks, stick to what we asked for......

Now 70 years later it may be easy to say what they should have asked for, but for the first clean sheet design for a radar equipped nightfighter, I say they did pretty good.... 

       

[scooter]

Even with the demanding requirements that pushed it up to the size of a medium bomber, Northrop made a fast, maneuverable fighter.  IIRC, one of the test pilots, to show AAC pilots that it was just as maneuverable as a single seat fighter, threw it into all sorts of maneuvers on ONE[/i] engine.  Another test flight had both engines shut down, maneuvers done, and dead sticked into a landing.

Because of slipstream problems with the turret, P-61A-5s through B-10s did not have the turret installed.

[tomo pauk]

Don't think anybody was blaming Northrop, they indeed came out with what specification said. After all, He 177 was a 'fruit' of a specification, so was Defiant, so was the Su-2 - the design bureaus came out with what was wanted.

Sorry for not buying that P-61 was as maneuverable as 'normal' fighter, on any number of engines running.

[KJ_Lesnick]

sandiego89

My understanding is the P-61 was never going to be a smallish, light fighter.  Military aircraft are almost always built to customer requirements with certain performance specifications, and in some cases certain design requirements.

Were the turrets a requirement or a specification?  I know the range was a requirement.

If I recall correctly for what ended up as the P-61 the United States largely used RAF specifications that called for a night figher with radar, turrets and very demanding endurance requirements. 

The US issued these specifications and Northrop responded.  The specifications drove the size of the design: large and heavy radar (big dish, lots of heavy black boxes), turrets, heavy armament, at least two engines to meet the performance requirements is going to give your a learge airframe- and on top of that perhaps the biggest driver of size was an 8 hour loiter requirement.  That much fuel is going to drive you to an even larger airframe.

Northrop responded appropriately.  If he had replied, "Hey, I came up with something different, without turrets, smaller, less endurance, and 'better' than what you asked for" they would have said, no thanks, stick to what we asked for......

1. Who ever said anything about reducing range?

• The removal of the turret would have eliminated their protrusion and lowered drag
  
• The requirement of the turret eliminated have allowed the crew compartment to be less boxy, and the elimination of the gunner would have allowed for a smaller compartment, both of which would improve aerodynamics
  

This would not reduce range, but increase it

2. Sometimes corporations submit alternate designs: Consider they already removed one turret already (the specification called for two); an alternate proposal with the proposed weight, and drag reductions listed; the projected increases in range and endurance, and; the necessity for only two crew members listed sound like good arguments for removing the turrets (especially if the wing-design & maneuverability were already known).  Admittedly, with all the secrecy: I'm not sure if Jack Northrop or any of the engineering/design team even knew what the radar and the turrets were for (and as a result could determine what was needed), and I'm not sure how the USAAF had reacted and whether it'd be approved or not, and what prospects this would have for it's competition against the A-26 (which had a NF variant)

Now 70 years later it may be easy to say what they should have asked for, but for the first clean sheet design for a radar equipped nightfighter, I say they did pretty good....

Of course



scooter

Even with the demanding requirements that pushed it up to the size of a medium bomber, Northrop made a fast, maneuverable fighter.

Yeah, most people don't even know that it was rated for 7.3g x 1.5 ultimate load.  It was surprising for such a big fuzzy bunny to be able to maneuver that well.

IIRC, one of the test pilots, to show AAC pilots that it was just as maneuverable as a single seat fighter, threw it into all sorts of maneuvers on ONE engine.

Did it have counter-rotating props?

Another test flight had both engines shut down, maneuvers done, and dead sticked into a landing.

Now that takes cojones...

Because of slipstream problems with the turret, P-61A-5s through B-10s did not have the turret installed.

I know that they often flew without it, however the design would probably have been lighter had it never had one to begin with: The canopy could have been greatly smaller (no need to handle the turret) and a crew requirement of two would have helped.


tomo pauk

There is no doubt that turret pushed up the size & weight of the future P-61. Conversely, it was reducing the performance.

Yeah, and you really only needed the pilot and radar operator.

The 'triple tandem' crew layout meant a long & heavy nacelle

The length of it might have reduced drag as it's generally best to have the fairing of the gondola extend aft of the wing though I'm not sure if they knew this.

and twin boom layout increased weight, complexity and production time.

I thought the twin-booms were good for weight

But even if we remain on twin boom design, not incorporating the turret, and pilot and radar operator seated much closer, if not side-to-side - the resulting aircraft would've been far smaller, lighter and of better performance.

Tandem seems to have worked fine for the F7F

Don't think anybody was blaming Northrop, they indeed came out with what specification said.

Of course, however I want to point out that Northrop could have submitted an alternative: I want to point out that the de Havilland Mosquito night-fighter was to have a turret too, they were eventually persuaded it wasn't needed.  I don't know if this would have been as acceptable for US contracting practices, or what Northrop's attitude was on these matters in those days, but submitting an alternate with no turret would have been more streamlined (the canopy wouldn't have had to be so boxy) and faster, though I don't know what the specified maneuverability requirements were, and what Northrop thought he could achieve, but if he thought he could really achieve the 7.3g x 1.5 requirement: I think he should have submitted it as an alternative at the very least

Admittedly, I don't know if they realized the A-26 was being developed into a night fighter, and to be honest, if it would have won if Northrop had no turret in its design.

[wuzak]

Even with the demanding requirements that pushed it up to the size of a medium bomber, Northrop made a fast, maneuverable fighter.

Yeah, most people don't even know that it was rated for 7.3g x 1.5 ultimate load.  It was surprising for such a big fuzzy bunny to be able to maneuver that well.

Just because it had high stress loadings does not make it agile.

Don't think anybody was blaming Northrop, they indeed came out with what specification said.

Of course, however I want to point out that Northrop could have submitted an alternative: I want to point out that the de Havilland Mosquito night-fighter was to have a turret too, they were eventually persuaded it wasn't needed.

The second fighter prototype was fitted with a functioning turret (the first Mosquito prototype, W4050,  was fitted with a dummy turret for a time). It was not, at that time, a night fighter.

Tests showed that the turret was unnecessary.

[tomo pauk]

...
The length of it might have reduced drag as it's generally best to have the fairing of the gondola extend aft of the wing though I'm not sure if they knew this.

IMO, the necessity for 3 crew members drew both the size & weight up, while the rearmost (radar/radio operator) was probably supposed to be also checking out the rear hemisphere, despite the glare of the screens destroying it's night vision. Hence the twin boom; Northrop's design team knew their job alright.

I thought the twin-booms were good for weight

Don't think so. The design & weight analysis of similarly-sized and outfitted P-38 and DH Hornet are available on the internet, as well as for the Mosquito. The P-38's weight of booms+nacelle+pod is much greater than of Hornet's fuselage+naceles weight. This drives weight, size and drag spiral up, while driving down speed and RoC.
 

Tandem seems to have worked fine for the F7F

Modifying the F7F for the side-a-side seating will be to costly in time and post war resources. The side a side crew layout was preferred in post war dedeicated NFs of the USN.

Of course, however I want to point out that Northrop could have submitted an alternative: I want to point out that the de Havilland Mosquito night-fighter was to have a turret too, they were eventually persuaded it wasn't needed.

The Mosquito was already in pipeline when the turret idea surfaced. Northrop can offer what is wanted, or gamble with 'we know better than the costumer' approach.
BTW, five US aircraft producers were approached with USAF request to produce the (then recon) Mosquito under license. All five rejected the offer, so let's give the USAF some credit here.

[sandiego89]

Just to comment on the side by side, vs tandem seating debate, it must be remembered that the early radar scopes required a very dark compartment, or a viewing hood, to see the scope.  Side by side makes for a wider, draggier fuselage, and draggier canopy.  No way a F7 Tigercat could be side by side without a completely new fuselage. The F7 is really, really, skinny.   

I think having the radar operator in tandem, or even within another part of the fuselage, worked fine. Both arrangements have pros and cons.     

[KJ_Lesnick]

tomo pauk

IMO, the necessity for 3 crew members drew both the size & weight up

Of course

the rearmost (radar/radio operator) was probably supposed to be also checking out the rear hemisphere, despite the glare of the screens destroying it's night vision.

I thought the instrumentation was deliberately dull to minimize loss to night vision?  Regardless depending on how the canopy was shaped, some rear visibility would be allowed..

Don't think so. The design & weight analysis of similarly-sized and outfitted P-38 and DH Hornet are available on the internet, as well as for the Mosquito.

I did not know that: All this time

I thought it was better for the following reasons

• Aerodynamically-efficient engine-mounting: The P-38 for example, had an inline engine, turbochargers, the intake for the engine, the oil-coolers and radiators for the engine; I was under the impression that two huge engine-nacelles to mount that stuff with a single fuselage would have more drag than a twin-boomed aircraft with a small gondola in between.
  
• A location to mount the landing-gear: The ability to flip the gear back into the booms avoid having to fold them into the wings, which in turns allows more fuel to be carried in the wings; the P-38 carries fuel in the booms.
  
• Improved aerodynamic of efficiency of the wing and tail area in between the booms as they'd produce an endplate effect, plus you'd only need one elevator.
  

The P-38's weight of booms+nacelle+pod is much greater than of Hornet's fuselage+naceles weight.

Fascinating...

Modifying the F7F for the side-a-side seating will be to costly in time and post war resources.

Plus the F7F is very skinny...

The side a side crew layout was preferred in post war dedeicated NFs of the USN.

Good point, though you should realize that jets produce more power at high speed.

The Mosquito was already in pipeline when the turret idea surfaced.

As a recon bird...

Northrop can offer what is wanted, or gamble with 'we know better than the costumer' approach.

It's generally best to go with the customer's request: However, sometimes good has come from a company offering an alternative proposal.

five US aircraft producers were approached with USAF request to produce the (then recon) Mosquito under license. All five rejected the offer, so let's give the USAF some credit here.

I think that the 5 companies were idiotic to do this...