P-61 or Reverse Lend Lease Mosquito

[Shortround6]

If the P-61 was designed without the turret and designated gunner & his cockpit, the resulting aircraft could've been both smaller and lighter. The central pod losses the superimposed gunner's quarters, meaning lowering the drag further. Hopefully the resulting aircraft would've been just a bit bigger than the F7F, with a turn of speed around 400 mph.

Alternatively, accept (X)P-65 proposal from Grumman, but with R-2800 engines and no turbo.

We are designing with hindsight.
Army didn't sign contract for the XP-65 (with R-2600s) until June of 1941. R-2600s were supposed to be turboed. Navy signs up for two prototypes 2 weeks later.
Army signed contract for XP-61s in Jan of 1941, signed contract for 13 YP-61s in March 41 and inspected mock up in April 41. 20mm guns were moved from the wing to the fuselage belly and fuel tanks enlarged from 540 gallons to 646. Radar at the time was evolving, initial radar was the SCR-520 but even that was not available during initial design stages.
P-61 got the SCR 720 radar for service use. The F7F didn't get SCR 720 radar until the -3N model which didn't fly until May 15 1945. Earlier F7F night fighters used the smaller radar from the wing pods of F4U and F6Fs.
F7F night fighters had 375 gallons of internal fuel, radar operator cockpit took the place of 80 gallons of fuel.
The F7F or something like it wouldn't have met the requirement for endurance in the early specifications.
In 1940-41 nobody actually know what size the future radar units would be.

F7F-3N with the same radar as the P-61. of course they had several years to figure out how to fit it to the airframe.

BTW a 150 gallon belly tank cost about 11mph using normal power, at 300 gallon tank costs 12mph .

 

[tomo pauk]

Thanks for the timeline.

We are designing with hindsight.
Army didn't sign contract for the XP-65 (with R-2600s) until June of 1941. R-2600s were supposed to be turboed. Navy signs up for two prototypes 2 weeks later.

I've already stated that -2600s were to be with turbo on the XP-65, for the AAF version; the USN version was supposed to be with R-2800s? So let's have R-2800 for the both.

F7F night fighters had 375 gallons of internal fuel, radar operator cockpit took the place of 80 gallons of fuel.
The F7F or something like it wouldn't have met the requirement for endurance in the early specifications.
In 1940-41 nobody actually know what size the future radar units would be.
F7F-3N with the same radar as the P-61. of course they had several years to figure out how to fit it to the airframe.
BTW a 150 gallon belly tank cost about 11mph using normal power, at 300 gallon tank costs 12mph .

Problem with F7F's fuel situation is that it did not housed a single gallon of fuel in it's wings, all 455 sq ft, or about the same area as in the Mosquito, so Grumman would've need to adress this by adding fuel tankage in the wings.

 

[Shortround6]

Thanks for the timeline.

You are welcome, just trying to that the P-61 was designed with a few unknowns.

I've already stated that -2600s were to be with turbo on the XP-65, for the AAF version; the USN version was supposed to be with R-2800s? So let's have R-2800 for the both.

That isn't the problem, it was part of the timeline.

Problem with F7F's fuel situation is that it did not housed a single gallon of fuel in it's wings, all 455 sq ft, or about the same area as in the Mosquito, so Grumman would've need to adress this by adding fuel tankage in the wings.

The wing roots have the 20mm guns in them, the ammo boxes are in the wings outboard of the cannon. oil cooler takes up space out board of cannon

Then we start to run into one of the reasons the Army canceled and allowed Grumman to dedicate the airframe to Navy needs.

Navy isn't going to want fuel tanks in the part of the wing that folds. you are starting to run out of wing.
Mosquito used a large part of the inner wing for fuel tanks.

The radiators and ducts only occupied space in front of the front spar.
Please also note that the F7F got part of it's performance from it's R-2800-22/W engines which were "C" series engines. Not available for the first few hundred P-61s at the very least.
Power may have been a bit closer to late B-26 engines than to the two stage engines used in the P-61 but they were about 120lbs lighter, had no inter-coolers and no inter-cooling ducting. They required less cooling air at the same power levels and so had less drag even for the basic engine.

Maybe Grumman or Northrop could have built a smaller night fighter but it may well have required giving up more than just the turret and four .50cal guns. Radar and tactics were evolving. Early radar had a minimum range and often the radar operator would look up from his screen/hood and try to get a visual once they had closed to minimum range. 2 pairs of eyes being better than one. Radars got shorter minimum ranges and better angle discrimination even as the prototype night fighters were being built. Short of throwing thousands of man hours out and starting over they were stuck with what they had.

 

[pinehilljoe]

In one of the old Wings/Airpower articles on the Corsair night fighters in Korea a pilot was interviewed and said the F7Fs were not allowed to fly over North Korea, the Avionics were a step above the Corsair's and the Navy did not want to risk one going into enemy hands. I'll try and dig up the article.

 

[Glider]

I wouldn't be suprised the same thinking was very common with the RAF

 

[pinehilljoe]

I wouldn't be suprised the same thinking was very common with the RAF

Which RAF or Fleet Air Arm aircraft were not allowed to go over North Korea?

 

[fastmongrel]

Probably the only RAF aircraft worth sending to Korea was the Canberra. A MIG15 wouldn't get anywhere near a Canberra at altitude.

 

[Milosh]

Which RAF or Fleet Air Arm aircraft were not allowed to go over North Korea?

I think Glider is thinking about the Meteor over Europe in WW2, tho they were eventually allowed.

 

[Milosh]

Probably the only RAF aircraft worth sending to Korea was the Canberra. A MIG15 wouldn't get anywhere near a Canberra at altitude.

MiG15
Service ceiling: 15,500 m (50,853 ft)

B-57B
Service ceiling: 45,100 ft (13,745 m)

 

[Shortround6]

US B-57Bs didn't enter service until over a year after the cease fire in Korea. The US planes had more equipment (including guns in the wing) and different engines.
British Canberra's started with 6500lb thrust Avons in the B2 and used higher powered engines on later versions. Many later versions were rebuilds of early ones.
While an early Canberra set a world altitude record it was an engine test bed aircraft fitted with Bristol Olympus engines that wee hardly standard.

 

[GregP]

The Canberra was WAY more maneuverable than a MiG-15 at most altitudes where they would encounter one another. They usually wouldn't see a MiG in the landing payttern and didn't stay low for long.

The Canberra had a wing loading at normal takeoff of some 42 lbs./ sq. ft., with THICK wings of high lift (relative to the MiG-15 bis anyway) and the MiG-15-bis had a wing loading at normal takeoff of about 50 lbs. sq. ft.

The difference at height would make the Canberra easily out-turn the MiG and, if he dropped his ordnance, it would be a "no contest." Break into the MiG and he overhsoots every time, much like US PR aircraft did for years operating near service ceiling versus Soviet fighters. Then again, MOST PR aircraft are more lightly loaded than fighters are. They don't have to have the offensive armament and attendant ammunition, for one thing.

 

[tomo pauk]

...
The wing roots have the 20mm guns in them, the ammo boxes are in the wings outboard of the cannon. oil cooler takes up space out board of cannon
Then we start to run into one of the reasons the Army canceled and allowed Grumman to dedicate the airframe to Navy needs.
Navy isn't going to want fuel tanks in the part of the wing that folds. you are starting to run out of wing.
Mosquito used a large part of the inner wing for fuel tanks.
The radiators and ducts [on Mosquito] only occupied space in front of the front spar. .

[my edit]

The Army does not need a folding wing. Thus move also the carb air intake to the inboard of nacelles (also to be used on the Navy aircraft), and there is a better part of the outer wing available for fuel tanks. The P-38 acquired 2x55 gals using just a small part of the outer wing, in front of the main spar.
But then, the fuselage on the historical F7F does not look like devoted to maximizing fuel tankage (my red 'oval'):

Please also note that the F7F got part of it's performance from it's R-2800-22/W engines which were "C" series engines. Not available for the first few hundred P-61s at the very least.
Power may have been a bit closer to late B-26 engines than to the two stage engines used in the P-61 but they were about 120lbs lighter, had no inter-coolers and no inter-cooling ducting. They required less cooling air at the same power levels and so had less drag even for the basic engine.

If the 2-stage R-2800s can be installed, the performance would've surpased the historical F7F even in B series engines are used. If not - let's recall that early A-20s were clocked at 349 mph on the low powered R-2600 engines, and F7F was with thinner wing. The turn of speed of in-between A-20 and historical F7F - 380-390 mph - would not be so outrageous to expect.

Maybe Grumman or Northrop could have built a smaller night fighter but it may well have required giving up more than just the turret and four .50cal guns. Radar and tactics were evolving. Early radar had a minimum range and often the radar operator would look up from his screen/hood and try to get a visual once they had closed to minimum range. 2 pairs of eyes being better than one. Radars got shorter minimum ranges and better angle discrimination even as the prototype night fighters were being built. Short of throwing thousands of man hours out and starting over they were stuck with what they had.

Granted, the proposed changes would've needed to be done when the whole project is in early 'paper' stage.
BTW - the radar operator will have his night vision hampered due to glaring in the radar scopes, unlike what was the case with pilot.

 

[fastmongrel]

MiG15
Service ceiling: 15,500 m (50,853 ft)

B-57B
Service ceiling: 45,100 ft (13,745 m)

Canberra B2 service ceiling with bombload was 45,000 and 48,000 without

Mig15bis at the same height was barely controllable and was at Coffin Corner and any big control movement either put it in a spin which was 99% impossible to get out of or meant it exceeded safe Mach speed pitched up and stalled which put it into a tail spin which was 100% impossible to get out of.

 

[swampyankee]

Is the Vmc related to the stall speed?

Only indirectly. Vmc is determined by engine power and placement, yaw stability, and rudder authority. Obviously, you'll want lower Vmc as stall speed decreases, but they're not directly related.

 

[Shortround6]

The Army does not need a folding wing. Thus move also the carb air intake to the inboard of nacelles (also to be used on the Navy aircraft), and there is a better part of the outer wing available for fuel tanks. The P-38 acquired 2x55 gals using just a small part of the outer wing, in front of the main spar.
But then, the fuselage on the historical F7F does not look like devoted to maximizing fuel tankage (my red 'oval'):

actual space on the P-38 was larger than you might think.

30-40% of the volume of the outer wing (not counting ailerons and flaps?

If the 2-stage R-2800s can be installed, the performance would've surpased the historical F7F even in B series engines are used. If not - let's recall that early A-20s were clocked at 349 mph on the low powered R-2600 engines, and F7F was with thinner wing. The turn of speed of in-between A-20 and historical F7F - 380-390 mph - would not be so outrageous to expect.

The expected speed depends on altitude and time the estimate is made. The first production contract for the P-61 was placed in Sept of 1941. The P-61s engines were not fitted with water injection (and rated for WER) until the end of 1943 or the beginning of 1944.

Photo of P-61 air inlets:

out board 3 slots (right of the heavy divider) are for the oil cooler. the rest of the outer slots and all the inner opening are for the carb and intercoolers. There was an intercooler on each side of the engine nacelle or partially in the wing/nacelle junction.
Two stage engines cannot be swapped in and out of designs as whim may take the design staff or purchasing agent. If you make the design tight like an F7F you may not have room for the intercoolers and ducting. Take them out of an existing design and you have empty wing/nacelle space (larger airframe than needed. Two stage engines can help considerably with performance at around 15-20,000ft and up. they hurt performance at lower altitudes, also note the 12 ft 2 in propeller. Without a doubt heavier than the 3 blade prop on the F7F.
P & W started work on the "C" series engine in 1940. the first flight of an F7F was in Nov of 1943, 17 months after the first flight of the P-61. At what point was P & W advanced enough in work on the "C" series to offer it as a viable engine to Grumman for the F7F project?

Granted, the proposed changes would've needed to be done when the whole project is in early 'paper' stage.
BTW - the radar operator will have his night vision hampered due to glaring in the radar scopes, unlike what was the case with pilot.

The first gets to the heart of things as to the original question, what was known when design started and what was desired (like how many hours of endurance and take-off landing speeds).
As to the second, perhaps night vision was impaired a bit but but then F4U and F6F night fighter pilots would have been in real trouble.

 

[Glider]

I think Glider is thinking about the Meteor over Europe in WW2, tho they were eventually allowed.

I was also thinking of the use of new AI sets. Mk IV sets were delayed before they could fly over Eurpe and later they were for a period, the only sets allowed over Europe.

There were many examples of the Canberra being used for PR missions over europe during the cold war and attempted intercepts by Mig 15s always failed.

A few years ago there was a fascinating programme on this where a number of RAF pilots were interviewed. The one that stuck in my mind was a pilot who could see the mig 15's close but unable to get up to his altitude. However the Russian pilot was close enough to try a long range shot, He tried but when he fired, his aircraft stalled and he lost height allowing the Canberra to get away. Another mission was to take photos of a Russian site, close to Moscow in daylight. They were sure this would be a step too far but they got away with it.

One pilot posted to a joint USAF/RAF unit and he recalled that although none were shot down there were a couple of examples where the Russians were able to get close. I cannot remember the name of these aircraft but they had four engines and had rear guns. The main problem was the USAF aircraft could only operate from approx 36,000 ft whereas the Canberra used to operate at 54,000 ft

Another RAF pilot because of his experience was assigned to a USAAF unit flying the RB-47 and on at least one occaision the Russians got close enough for the crew to fire back at intercepting Migs. A story which he admitted might have grown with the telling, was a co pilot who fired back was told later that he had disobayed orders. His reply was that he would rather live to face the charge than die obaying them.

 

[fastmongrel]

B45 is the one I think you mean. Long straight wing and 4 engines

 

[tomo pauk]

...
The expected speed depends on altitude and time the estimate is made. The first production contract for the P-61 was placed in Sept of 1941. The P-61s engines were not fitted with water injection (and rated for WER) until the end of 1943 or the beginning of 1944.

The 349 mph speed figure for the A-20 is for altitude of 12050 ft (with ram), at 1400 HP per engine.
Without ram, the rated altitude was 10800 ft. The R-2800-5 was supposed to do 1500 HP at 14000 ft, no ram; R-2800-27 was with 1600 HP at 13500 ft.

Photo of P-61 air inlets:
<snip>
out board 3 slots (right of the heavy divider) are for the oil cooler. the rest of the outer slots and all the inner opening are for the carb and intercoolers. There was an intercooler on each side of the engine nacelle or partially in the wing/nacelle junction.
Two stage engines cannot be swapped in and out of designs as whim may take the design staff or purchasing agent. If you make the design tight like an F7F you may not have room for the intercoolers and ducting. Take them out of an existing design and you have empty wing/nacelle space (larger airframe than needed. Two stage engines can help considerably with performance at around 15-20,000ft and up. they hurt performance at lower altitudes, also note the 12 ft 2 in propeller. Without a doubt heavier than the 3 blade prop on the F7F.

Grumman was offering the turbo R-2600 owered XP-65 to the Army, so I'd say that a 2-stage R-2800 would've been an easier fit for it. The ram air inlet can be located above the nacelle.
The 1st two-stage R-2800 with Army dash number was the -3, supposed to make 1700 HP at 10000 ft, 1600 HP at 20000 ft, seems that Army never bough those actually. Props can be 3-bladed 13ft 2 in - 2 in shorter than on the F4U anyway

P & W started work on the "C" series engine in 1940. the first flight of an F7F was in Nov of 1943, 17 months after the first flight of the P-61. At what point was P & W advanced enough in work on the "C" series to offer it as a viable engine to Grumman for the F7F project?

I'm not championing the C series engine, it is way too late for this. Once available, use them by all means.

...
As to the second, perhaps night vision was impaired a bit but but then F4U and F6F night fighter pilots would have been in real trouble.

Don't know - peraps it was easier for their night vision to take a peek every 5 or 10 seconds, rather than to look at the screeen(s) during the better part of the mission?

 

[Glider]

B45 is the one I think you mean. Long straight wing and 4 engines

Thats it, a slightly odd looking aircraft in my eyes

 

[pinehilljoe]

I was also thinking of the use of new AI sets. Mk IV sets were delayed before they could fly over Eurpe and later they were for a period, the only sets allowed over Europe.

There were many examples of the Canberra being used for PR missions over europe during the cold war and attempted intercepts by Mig 15s always failed.

A few years ago there was a fascinating programme on this where a number of RAF pilots were interviewed. The one that stuck in my mind was a pilot who could see the mig 15's close but unable to get up to his altitude. However the Russian pilot was close enough to try a long range shot, He tried but when he fired, his aircraft stalled and he lost height allowing the Canberra to get away. Another mission was to take photos of a Russian site, close to Moscow in daylight. They were sure this would be a step too far but they got away with it.

One pilot posted to a joint USAF/RAF unit and he recalled that although none were shot down there were a couple of examples where the Russians were able to get close. I cannot remember the name of these aircraft but they had four engines and had rear guns. The main problem was the USAF aircraft could only operate from approx 36,000 ft whereas the Canberra used to operate at 54,000 ft

Another RAF pilot because of his experience was assigned to a USAAF unit flying the RB-47 and on at least one occaision the Russians got close enough for the crew to fire back at intercepting Migs. A story which he admitted might have grown with the telling, was a co pilot who fired back was told later that he had disobayed orders. His reply was that he would rather live to face the charge than die obaying them.

Did the RAF operate the long winged RB-57?