P-61 alternatives

Koopernic said:

The R-2800 appears to be about 300lbs heavier than the R-2600 but I suggest it is within the capacity of the A20 to handle especially as the bomb bay would not be used.

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The two stage supercharged engines in the P-61 were 550lbs heavier than the R-2600s. the Single stage engines used with turbos were only about 300lbs heavier but then you need the weight of the turbos, the ducting, the larger intercoolers. You also have the larger, heavier propellers, without which there isn't much point in putting in the fancy high altitude engines.

And again, design work was being done on the A-26 through most of 1941. Doing design/engineering work on an R-2800 powered A-20 is only going to delay the A-26.

Something to consider when proposing bombers for night fighters (or fighter duties in general) was that MOST bombers were not stressed for fighter like maneuvers.
The B-25 for instance was rated at up to 3.8 Gs up to certain weight and under 3.0 (2.7 or 2.8 Gs? ) above that weight.
Granted most night fighters were not doing high G turns but there may be point on the gross weight scale you don't want to go above when doing hard maneuvers even if it is below "gross" weight.

The high weight airframe of the Ju 88 that was left over from the dive bomber requirement may have been a benefit when it was used as a fighter/night fighter.

jmcalli2 said:

Do you have a source for 400mph A-26? I've never seen it over 370.
Later versions of the P-61 were at 430mph.
And 370 is amazing at the altitudes it was designed to fly at, under 15,000.
The P-61 was designed for 15-20,000+ altitudes, thus the supercharger differences.

However, my point was replying to the idea that an A-20 with R-2800 engines would be better than the P-61. I just used the A-26 as an example of a more advanced aircraft (than the A-20) using those engines being roughly equal or slightly inferior to the P-61; therefore, the less advanced A-20 would not likely perform better. If it would, why build the A-26 at all?

I'm a fan of all three aircraft. Only the A-26 was still in combat 20 years after its first flight.

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Re the 400mph Invader

Douglas A-26 Invader
XA-26D but I believe a few 2800hp water injected engines made it into solid nose A-26. I remember reading that they went 'hunting' Luftwaffe fighters, I think on rec.aviation,military.

If the US need a night fighter in 1943 the A20 is the only game in town, else it's the B-26.

Imagine the scenario of Luftwaffe bombers attacking the US east coast at night.
1 In 1936 Luftwaffe's General Walter Weaver doesn't die in an aircraft crash.
2 He builds up a small force of Ju 89/Do 19 4 engine bombers, about 40, that are far more effective than Fw 200 in supporting the German Navy and also conduct nuisance raids all over the British Isle. They even attack the ships attacking Bismarck.
3 In 1939 When Ernst Heinkel approaches the German Air ministry warning of the problems in developing the He 177 as a two engine aircraft and Weaver agrees. The He 177 enters service in 1941 at the same time as the Manchester powered of 4 Jumo 211 engines. He 111 production is shut down.
4 His reputation growing and the Heinkel He 177 a great success he has Willy Messerschmitt develop the Me 264/6m, the 6 engine version of the Me 264 rather than the 4 engine version because he rejects waiting years for advanced engines to develop. Instead of the Me 264 flying in December 1942 the well supported Me 264/6m flies a few months earlier.
In October 1943 the first production Me 264/6m are coming of production lines. Soon Carrying copies of captured H2S radar they begin sewing mines of the US coast and attacking harbour and port targets.

Would the P-61 be ready?

Comparisons using the A-20 are not valid - you must compare using the P-70 which I suspect was somewhat slower due to the additional drag of the gun package below the belly and the aerodynamics of the gun installation. All those holes in the gun bulge for the barrels and spent brass and spent links degrade aerodynamics. Add to that the effects of the additional armour that late A-20 models carried which the actual P-70s did not and you lose more performance. Hanging an aerodynamic a***hole under the streamlined A-20 fuselage is definitely going to significantly degrade performance on an aircraft where speed is one of the prime requirements.

Redesigning the late A-20s to take 4 cannon in the nose and the ammo in the bomb bay as well as the R-2800s would have reduced these issues but there is no spare room under floor for the ammo ducts to these would cancel some of the gains. And it would lose the radar in the nose so could not be a night fighter. Diverting design staff from the multi-role A-26 to achieve the night fighter only super P-70 is going to make the A-26 even later into service and definitely be counterproductive.

I love the A-20. It is easy to work on for major operations and the major components are very easy to remove/replace which is great for field repairs but I do not think the claimed super P-70 performance is realistic and I also think the A-26 was a more important project.

There were two P-38F's converted into two seat night fighters and went into combat in the Pacific as early as Feb 1943. They installed an SCR-540 radar that operated in the VHF band, the American version of the British Mk IV radar, not the APS-4. They put a radar operator in the radio compartment behind the pilot and installed the regular radio equipment in a drop tank. They installed the radar antenna on the nose (like the one that comes for the MK II Mosquito in the Monogram kit) and had to move two of the .50 cal guns forward.

But Lockheed came out with what would have been a great nightfighter version of the P-38, called the Swordfish, which was designed to investigate the diving problems.

There was one P-51D converted into a two seat radar equipped fighter, using a spilt bubble canopy. They used it late in the ETO but not as a nightfighter; it was designed to enable enemy aircraft to be spotted in the daytime.

Pictures from Warren Bodie's book on the P-38.

The first photo was a 2seat conversion used by Lockheed for research. The wings are shown with built up airfoils and spray fittings on port side for iceing tests. Because of the second seat and recording gear, the center fuselage was lengthened which incidentally increased speed. I suspect if a different canopy were used, the increase would be greater.

special ed said:

The first photo was a 2seat conversion used by Lockheed for research. The wings are shown with built up airfoils and spray fittings on port side for iceing tests. Because of the second seat and recording gear, the center fuselage was lengthened which incidentally increased speed. I suspect if a different canopy were used, the increase would be greater.

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That should show that a two-seat, night fighter variant of the P-38 would not be too much of a stretch, and possibly a better path than the P-61.

Koopernic said:

The night fighter version of the Douglass A20 Havoc known as the P70 might have been fitted with PW R-2800 engines. With 18% more power and less drag due to the smaller diameter engines it should have a decent performance. I suspect 350mph. Fitting navy two stage supercharger engines even more. The A26 Invader seems a good candidate as well.

The Germans tried radar on the Me 109 and Fw 190. The pilot could tell range and approximately how far up/down left/right the target was but they found staring into an abstract oscilloscope destroyed his precious night vision. I really don't know how the USN got around this. The radar would have to be so good the pilot didn't need night vision.

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Red filters on the screen, and / or goggles with red lenses were used by the Navy to preserve night vision.

Below is a 1945 photo of Buck Dungan, USN Hellcat nightfighter ace, wearing an electrically heated leather flight suit. Note the red lens goggles carried for night vision adaption prior to takeoff and for use, when needed, in flight.

Dana Bell said:

I think the oft-quoted figures touting P-61 performance are slightly off. AAF Manual 45-59-1 Security Classification and Selected Data on AAF Aircraft and Equipment dated August 1945 was, itself, formerly classified Confidential. Page 23 describes the P-61A and P-61B with the unclassified max speed as "Over 375 mph." Critically, the classified max speed is listed as 363 mph 15,000 feet (formerly Restricted). What matters to me is that the P-61 was the only aircraft in the document to list a classified max speed lower than the unclassified max speed.

Another note explains that the P-61C will have the CH-5 turbo-supercharger for high altitude performance. No projected high speed is listed, but internal memos note that the P-61C's actual high speeds were dismally below projections.

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I'm curious if you have any data for fuel consumption at altitude. There was one here for the P-61A/B here, and I'm just curious how things would have worked out if the P-61A/B had been fitted with turbos.

Yes, there were NF versions of the BF-109. From the book "Confound and Destroy."

Where are the radar antennas? Both 109s and 190s did ground radar directed night intercepts.

Wilde Sau (German for wild boar) was the term given by the Luftwaffe to the tactic used from 1943 to 1944 during World War II by which British night bombers were engaged by single-seat day-fighter aircraft flying in the Defense of the Reich. It was adopted when the Allies had the advantage over German radar controlled interception.

The 109s equipped with Naxos Z could home in on the H2X/H2S transmissions of night bombers. (You can see the dorsal NAXOS dome aft of the canopy on the second aircraft (#9) in the illustrations above.

Cheers,



Dana

Zipper730 said:

I'm curious if you have any data for fuel consumption at altitude. There was one here for the P-61A/B here, and I'm just curious how things would have worked out if the P-61A/B had been fitted with turbos.

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Here are some notes on the P-61D's projected performance. Note that Wright Field didn't take Northrop's projections as gospel; experience would show that Wright Field was smart about this...

Cheers,



Dana

I've been organizing my notes on the P-61 for an article on America's WW2 search for a night fighter. The following are synopses of the complete documents - I hope they help with the continuing discussion:


5 Jun 42 2,000 hp – R-2880-25 (sic)

19 Sep 42 P&W reps to install oil jet in camshaft of two production R-2800-10s for XP-61 to eliminate failures encountered in previous two engines

17 Nov 42 P&W R-2800-10 not designed to provide 1800hp at 21,000' or 1875hp at 14,000' at normal rated power. "In fact, it will not deliver these horsepowers if at military rated power."

11 May 43 Request dash number of R-2800 2-stage B and C engines to be used in P-61; also what is approx date of change from B to C type engine?

13 May43 No dash number assigned to 2-stage C engine. The R-2800-10 2-stage B engine will be used in all P-61 production

26 May 43 Flight characteristics note R-2800-10

7 Jun 43 Reports two R-2800-10s

7 Sep 43 R-2800-10s will continue to use cast ignition harnesses until GE ignition systems can be provided and approved by P&W

11 Nov 43 Request Aircraft Lab estimate high speed and rate of climb curves using water injection with present engines, and also using military and war emergency power with type C engine

12 Nov 43 Recommend replacing current engines with R-2800-C with water injection, or adding water injection to present R-2800-B engines

23 Nov 43 Repeat 12 Nov 43

26 Nov 43 HISTORY - BuAer allowed to take over entire production of R-2800-10; Army not to receive more of this engine until Mar 1944

2 Dec 43 R-2800-10 will not be available for proposed increase in P-61 production

17 Dec 43 Performance curves provided for R-2800-B with water injection, since C-type engine cannot be fitted to the aircraft without major redesign of nacelles because of greater engine length

30 Dec 43 Orders test of one P-61 with R-2800-C with single stage, single speed, turbosupercharger.

1 Jan 44 Discussion of automatic speed shift for R-2800-10 – does not appear desirable at this time

7 Jan 44 report on P-61 with water injection, calculated

27 Jan 44 Test of water injection in 2-stage, 2-speed to commence this date. Incorporation of turbocharged 1-stage, 1-speed R-2800-C is continuing and awaiting letter of quotation

12 Feb 44 Water injection R-2800-B ground testing ended 5 Feb; flight testing to begin approx 16 Feb

11 Mar 44 There is a shortage of R-2800-10 engines. Studies have been made of water injection addition to both R-2800-C and R-2800B. Action initiated to install R-2800-57 with CH-5 turbos; this is favored by Materiel Command over R-2800-18 (2-stage type C)

17 Jun 44 Desire every effort to establish production of R-2800-C in P-61, Two P-61As have been delivered to Goodyear to incorporate R-2800-C 1-stage, 1-speed engines and CH-5 turbos. First modification expected to be complete in Sept 1944. Now studying 2-stage 2-speed R-2800-C in case 1-speed, 1-stage doesn't work out.

1 Aug 44 Water injection appeared on the production line on P-61 41-556 (the 96th a/c) and all subsequent articles

12 Aug 44 Desire R-2800-C with CH-5 turbo ASAP.

25 Aug 44 Installation of C engine has been a very slow process. Not expected to be available until next May or June - by that time it will be outclassed by other fighters, and not capable as a day fighter

28 Aug 44 Performance report lists powerplant as R-2800-65-W. Water/alcohol injection caused failure of exhaust stacks

1 Mar 45 Cold weather tests note that water injection system froze on every test flight (no alcohol used)


Cheers,



Dana

Milosh said:

Where are the radar antennas? Both 109s and 190s did ground radar directed night intercepts.

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The Fw190 profile number 5 shows the horizontal dipole antennas of the FuG 218 radar under the port wing. This was the "Neptun III V1" for single-seaters, the "V2" version for multi-seat aircraft was used on the Me 262 night fighters and also on some Ju88 night-fighters, with about 500 sets of both variants delivered. The set had a power of 2 kW, maximum range was 5 km (just over 3 miles) and minimum range 120 m (400 ft). Earlier single-seat NFs were equipped with the FuG 217 "Neptun II J I" with a range of 3500 m (3800 yds).



Picture on lower right shows the FuG 218 installation on a Fw190; lower left shows the display, replacing the SZKK ammunition counter. Upper right shows the display picture of FuG217, with one blip at a range of 1,3 km straight ahead and one blip at 2,2 km slightly to the left. Upper left shows the FuG 217 antennae on the Fw190 (for those who can't understand the German captions).

Koopernic said:

Re the 400mph Invader

Douglas A-26 Invader
XA-26D but I believe a few 2800hp water injected engines made it into solid nose A-26. I remember reading that they went 'hunting' Luftwaffe fighters, I think on rec.aviation,military.

If the US need a night fighter in 1943 the A20 is the only game in town, else it's the B-26.

Imagine the scenario of Luftwaffe bombers attacking the US east coast at night.
1 In 1936 Luftwaffe's General Walter Weaver doesn't die in an aircraft crash.
2 He builds up a small force of Ju 89/Do 19 4 engine bombers, about 40, that are far more effective than Fw 200 in supporting the German Navy and also conduct nuisance raids all over the British Isle. They even attack the ships attacking Bismarck.
3 In 1939 When Ernst Heinkel approaches the German Air ministry warning of the problems in developing the He 177 as a two engine aircraft and Weaver agrees. The He 177 enters service in 1941 at the same time as the Manchester powered of 4 Jumo 211 engines. He 111 production is shut down.
4 His reputation growing and the Heinkel He 177 a great success he has Willy Messerschmitt develop the Me 264/6m, the 6 engine version of the Me 264 rather than the 4 engine version because he rejects waiting years for advanced engines to develop. Instead of the Me 264 flying in December 1942 the well supported Me 264/6m flies a few months earlier.
In October 1943 the first production Me 264/6m are coming of production lines. Soon Carrying copies of captured H2S radar they begin sewing mines of the US coast and attacking harbour and port targets.

Would the P-61 be ready?

Click to expand...

Well, the A-20 in its P-70 version wasn't up to the task; too slow, too low a rate of climb. And as others have said, redesigning it for the R-2800 would have delayed the A-26.

Thanks for that XA-26D info!

MiTasol said:

Comparisons using the A-20 are not valid - you must compare using the P-70 which I suspect was somewhat slower due to the additional drag of the gun package below the belly and the aerodynamics of the gun installation. All those holes in the gun bulge for the barrels and spent brass and spent links degrade aerodynamics. Add to that the effects of the additional armour that late A-20 models carried which the actual P-70s did not and you lose more performance. Hanging an aerodynamic a***hole under the streamlined A-20 fuselage is definitely going to significantly degrade performance on an aircraft where speed is one of the prime requirements.

Redesigning the late A-20s to take 4 cannon in the nose and the ammo in the bomb bay as well as the R-2800s would have reduced these issues but there is no spare room under floor for the ammo ducts to these would cancel some of the gains. And it would lose the radar in the nose so could not be a night fighter. Diverting design staff from the multi-role A-26 to achieve the night fighter only super P-70 is going to make the A-26 even later into service and definitely be counterproductive.

I love the A-20. It is easy to work on for major operations and the major components are very easy to remove/replace which is great for field repairs but I do not think the claimed super P-70 performance is realistic and I also think the A-26 was a more important project.

Click to expand...

It appear the first P-70A, being derived from the Havoc light bomber, didn't have a superchargers at all, zilch. These versions apparently still managed 329mph. Latter versions, equipped with superchargers seemed to achieve 339mph despite the draggy modifications you refer to. This obviously at a higher altitude. They may even have been slower at lower altitude.

With plain PW R-2800 offering 300 more hp (18%) I would estimate 6% (20.4mph) more speed ie 360mph, maybe more due to abut 3% less drage.

Intercooled two stage R-2800 would probably be too heavy but single stage would add only 300lbs of weight.

Koopernic said:

It appear the first P-70A, being derived from the Havoc light bomber, didn't have a superchargers at all, zilch.

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The engines used in the P-70, the P-70A and the P-70B had single stage two speed superchargers. power in high gear was 1400hp at about 11-12,000ft no RAM.

2nd model Engines used the Martin B-26 bomber gave 1600hp at 13,500ft no Ram. Used 4 bladed props about 1 ft in diameter bigger than the 3 blade props on the A-20/P-70.

Koopernic said:

It appear the first P-70A, being derived from the Havoc light bomber, didn't have a superchargers at all, zilch.

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Every version of the R-2600 ever built had a supercharger just like every version of the Allison V-1710 used by the USAAF had a supercharger.

MiTasol said:

Every version of the R-2600 ever built had a supercharger just like every version of the Allison V-1710 used by the USAAF had a supercharger.

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These superchargers were internal, built right into the engine casing, thus easily overlooked by uninformed individuals in the information chain. I was astounded in mech school, when tearing down and reassembling radial engines, to find a supercharger and planetary reduction gear neatly tucked into each nose case. My previous experience with direct drive flat fours and sixes hadn't prepared me for that at all.
When I first saw the articulated counterweights in a Wright engine, I realized why they always sounded and felt like they were trying to clatter themselves to death at idle. A T28, C1, S2, or C117 could shake your fillings out idling on the ground.