Re-engined planes

[GrauGeist]

The SCR-720A radar system used in the P-61 was not only heavy as mentioned, but was also large in size. You would have to modify the fuselage quite a bit in order to fit that antenna assembly in the nose.

After all the modifications and refitting, you'd probably end up with something that looked alot like the XP-58

 

[tomo pauk]

Hopefully not

Here is the 'Swordfish', FWIW (from Wikipedia):

vs. plain vanilla P-38 (from mustangsmustangs.com):

 

[Elmas]

But there's a reason if engines designed about early-mid thirties gave the maximum power at low levels. As stated before they were designed for both civil and military use, so the flight level of airplanes could not exceed much more than ten thousand feet. No pressurised airframes and unpractical to make the passengers of a liner to breath pure oxigen....

 

[Shortround6]

Thanks for the link to the table rest of the stuff you've contributed here
The Japanese were able to make the Ki-45 going 357 mph at 18500 ft, on 2 x 960 HP. The wing area was some 10% greater than of the P-38, but the Ki-45 was significantly lighter.
I was not 'aiming' on the 1350 HP variant of the R-1830, but the 'usual' 1200 HP one. There is no doubt that a V-1710 powered version would've been faster.

Ki-45??

Or Ki-46?

Ki-46 later got more powerful engines (same ones as the Ki-100) but with the addition of guns (helpful for a fighter) speed only went to 391mph? No armor, no self sealing tanks? or minimal?
As a Recon plane was the Ki-46 stressed for fighter like maneuvers?

The P-38 NF should be available maybe a year earlier than the P-61, should compensate quite a bit for the lower performance of the radar. Lack of cooling system might allow for extra space for radar electronics, though it would've take a new central pod to offer both a powerful radar, space for 2nd crew member, armament and a bigger antenna - all at once. Something that would've appeared like the 'Swordfish' pod?

The problem, given even a slightly larger fuselage, isn't so much the space (cubic feet) occupied by the black boxes but the size of the radar antenna and radar dome. That parabolic dish in the photo in 29" (74cm) across and rotates 90 degrees to either side, 20 degrees down and 50 degrees up. and does several hundred times per minute in scan mode.
The earlier SCR 520 radar used in the P-70 was bulkier and heavier and there is part of the problem with using the "retrospectroscope"

You KNOW what the size of the finished radar units will be. When work started on the night fighters they had no idea how big/heavy the radars of the future (2-3 years down the road) would be. They might get smaller (they did) they may get longer ranged ( they did) but how much smaller for what range? or would a slightly bigger unit give even more range?

 

[GrauGeist]

Here's a couple "glass nosed" P-38s...

The first one was actually built for bombing (P-38J-15-LO 'Colorado Belle', 1943-1945), the second P-38 pictured was modified for civil land surveying.

The fuselage for the P-38 was actually quite small and an adaptation to fit such a large radar in it would require extensive work like I mentioned. And once the fuselage was been modified to shoe-horn the radar system in, where would the weapons go?

 

[tomo pauk]

Ki-45??
Or Ki-46?

Ki-45, at least going by this table.http://www.wwiiaircraftperformance.org/japan/japfighters-comp.jpg OTOH, Wikipedia gives only 336 mph.

The problem, given even a slightly larger fuselage, isn't so much the space (cubic feet) occupied by the black boxes but the size of the radar antenna and radar dome. That parabolic dish in the photo in 29" (74cm) across and rotates 90 degrees to either side, 20 degrees down and 50 degrees up. and does several hundred times per minute in scan mode.
The earlier SCR 520 radar used in the P-70 was bulkier and heavier and there is part of the problem with using the "retrospectroscope"

You KNOW what the size of the finished radar units will be. When work started on the night fighters they had no idea how big/heavy the radars of the future (2-3 years down the road) would be. They might get smaller (they did) they may get longer ranged ( they did) but how much smaller for what range? or would a slightly bigger unit give even more range?

We know that RAF fighters were using bow arrow antennae as early as in 1940. Granted, not as good solution as the late war stuff, but it shows that useful NF, with useful radar can be built much earlier than P-61.
Once the P-38 NF is in production (winter of 1942/43?), we can go for bigger 'badder' stuff.

Here's a couple "glass nosed" P-38s...

The first one was actually built for bombing (P-38J-15-LO 'Colorado Belle', 1943-1945), the second P-38 pictured was modified for civil land surveying.

The fuselage for the P-38 was actually quite small and an adaptation to fit such a large radar in it would require extensive work like I mentioned. And once the fuselage was been modified to shoe-horn the radar system in, where would the weapons go?

'Swordfish' featured the accommodation for two, in a longer and overall bigger nacelle.

 

[GrauGeist]

'Swordfish' featured the accommodation for two, in a longer and overall bigger nacelle.

This is true, the fuselage was "bigger" in the fact that it was lengthened. The radar system used, was a fixed antenna unlike the SCR-720, which was an articulated or "sweeping" type. To place the SCR-720 system in the P-38, you would have to increase the height of the fuselage and widen it, to the same dimensions the P-61 and the A-20 used for their installations.

You'll note that the P-38 nightfighter had a under-nose mounted radar assembly while retaining their upper nose armament, but in a situation where a SCR-720 is stuffed into a heavily modified P-38, you'll have to consider not only relocating the armament, but make the radar mount sufficient far enough forward to clear the nose-gear assembly.

After all that work, you'll end up with something that looks alot like this!

 

[Shortround6]

The thing is to be built by Northrop, instead of the P-61, it has to do what the P-61 was supposed to do. The US was fooling about with A-20s as night fighters (P-70s).

Douglas P-70 Nighthawk

and although not spelled out, even more different radar fits were used than are mentioned in this article. Even the A-20 resorted to belly packs of guns in order to fit in some of the different radar types. Or to preserve pilots night vision

If you have trouble putting certain models of radar inside an A-20 the the P-38 doesn't offer much hope. The later P-38s may have been moderately successful but carried a much lower capability radar than the P-61.

 

[Nivek]

P-36 with R-2600

 

[Shortround6]

Maybe I am missing something but it looks like you are mounting an engine that weighs 535lbs more than a P-36 engine roughly 6in further forward than the existing engine?
Seems like a lot of faith is being placed on the longer, larger rear fuselage to balance things out?
I would note that lowering the thrust line by 3.5 inches might not be the best idea either unless longer landing gear is used to regain prop clearance. And longer landing gear pushes the wheel/tires further to the rear of the wing into a thinner part. Bulges over the wheel wells?

This also assumes you can get a prop with a similar diameter to absorb the extra power. Douglas A-20 uses an 11ft 3in prop for their R-2600 engines.

 

[GregP]

How about a Reggiane Re.2005 with an R-2800 out of a Corsair?

Lots more power, and reliable. 500 more pounds, but farther back on the airframe.

 

[swampyankee]

It's probably easier to re-engine with engines out on the wings -- there were prototypes of the B-17 with Allison V-12s and of the B-29 with Allison W-24s, and there were production Lancasters, Beaufighters, and Halifaxes built with both Merlins (the majority) and Hercules.

Sources
British WW2 Bomber Aircraft (1939-1945)

 

[Nivek]

Maybe I am missing something but it looks like you are mounting an engine that weighs 535lbs more than a P-36 engine roughly 6in further forward than the existing engine?
Seems like a lot of faith is being placed on the longer, larger rear fuselage to balance things out?
I would note that lowering the thrust line by 3.5 inches might not be the best idea either unless longer landing gear is used to regain prop clearance. And longer landing gear pushes the wheel/tires further to the rear of the wing into a thinner part. Bulges over the wheel wells?

This also assumes you can get a prop with a similar diameter to absorb the extra power. Douglas A-20 uses an 11ft 3in prop for their R-2600 engines.

Those are good points. My thoughts: The R-2600 is about 7" larger diameter and I wanted to keep the pilot to top of engine cowl relationship the same. So the engine thrust line is lower than the thrust line of the R-1830 while the top of the engine is about the same place. I used the firewall as a base line for engine installation and the R-2600 is about 3 inches longer than the R-1830. The larger engine will most likely need a larger propeller hub so the front of the engine from the firewall is about 3-6 " farther out. To compensate for the increased front weight I added structure to the rear of the fuselage by increasing its vertical cross section and lengthening the fuselage as much as might be necessary. I think this would also clean up the airflow on the bottom of the fuselage. I don't know how much that would be so I just guessed at a minimum of 12 inches. Moving the battery and radio farther aft along with increasing the strength and weight of the rear fuselage may be enough? ....I supposed more length could be added as necessary.

The length of the prop may need to be a little longer if the increase power cannot be utilized by changing the design of the propeller width/cord. The wing has a cord that could be lengthened to the rear as it extends farther out from the fuselage. This would allow for an increase in landing gear length. Also this would add a little weight to the rear of the center of gravity. It also would increase the wing area a little. This would minimize the wing loading change with the added weight.

But as someone said, The R-2600 had early development issues and seems to not have been super reliable until 1942-43? Still, it is fun to play around with ideas of re-engining these old airplanes.

 

[Nivek]

Re-engined Yak for racing:

Czech Mate

 

[Nivek]

Those are good points. My thoughts: The R-2600 is about 7" larger diameter and I wanted to keep the pilot to top of engine cowl relationship the same. So the engine thrust line is lower than the thrust line of the R-1830 while the top of the engine is about the same place. I used the firewall as a base line for engine installation and the R-2600 is about 3 inches longer than the R-1830. The larger engine will most likely need a larger propeller hub so the front of the engine from the firewall is about 3-6 " farther out. To compensate for the increased front weight I added structure to the rear of the fuselage by increasing its vertical cross section and lengthening the fuselage as much as might be necessary. I think this would also clean up the airflow on the bottom of the fuselage. I don't know how much that would be so I just guessed at a minimum of 12 inches. Moving the battery and radio farther aft along with increasing the strength and weight of the rear fuselage may be enough? ....I supposed more length could be added as necessary.

The length of the prop may need to be a little longer if the increase power cannot be utilized by changing the design of the propeller width/cord. The wing has a cord that could be lengthened to the rear as it extends farther out from the fuselage. This would allow for an increase in landing gear length. Also this would add a little weight to the rear of the center of gravity. It also would increase the wing area a little. This would minimize the wing loading change with the added weight.

But as someone said, The R-2600 had early development issues and seems to not have been super reliable until 1942-43? Still, it is fun to play around with ideas of re-engining these old airplanes.

I am not an engineer, just a mechanic/technician. It appears one way change the propeller to use an increase in power is to change propeller area with width rather than length.

 

[swampyankee]

I am not an engineer, just a mechanic/technician. It appears one way change the propeller to use an increase in power is to change propeller area with width rather than length.

More diameter is always better, but it may be constrained by aircraft geometry or tip speed, then, yes, you start increasing activity factor, by adding blades or increasing chord. Either would require changes to the hub and pitch-change mechanism or, at an absolute minimum, new structural analysis of the hub and to see if there's enough force and power from the pitch change mechanism.

 

[wuzak]

Those are good points. My thoughts: The R-2600 is about 7" larger diameter and I wanted to keep the pilot to top of engine cowl relationship the same. So the engine thrust line is lower than the thrust line of the R-1830 while the top of the engine is about the same place. I used the firewall as a base line for engine installation and the R-2600 is about 3 inches longer than the R-1830. The larger engine will most likely need a larger propeller hub so the front of the engine from the firewall is about 3-6 " farther out. To compensate for the increased front weight I added structure to the rear of the fuselage by increasing its vertical cross section and lengthening the fuselage as much as might be necessary. I think this would also clean up the airflow on the bottom of the fuselage. I don't know how much that would be so I just guessed at a minimum of 12 inches. Moving the battery and radio farther aft along with increasing the strength and weight of the rear fuselage may be enough? ....I supposed more length could be added as necessary.

The length of the prop may need to be a little longer if the increase power cannot be utilized by changing the design of the propeller width/cord. The wing has a cord that could be lengthened to the rear as it extends farther out from the fuselage. This would allow for an increase in landing gear length. Also this would add a little weight to the rear of the center of gravity. It also would increase the wing area a little. This would minimize the wing loading change with the added weight.

But as someone said, The R-2600 had early development issues and seems to not have been super reliable until 1942-43? Still, it is fun to play around with ideas of re-engining these old airplanes.

A similar example to what you want to do is the Spitfire XIV.

In order to improve the pilot's view the Griffon in the XIV was canted down a small amount. This reduced ground clearance, and resulted in the XIV having a smaller diameter prop than the Merlin powered IX. The solution was to add blades and run it at higher speed.

Your re-engined P-36 would likely have to do the something similar.

Changing the wing and landing gear sounds like a lot of extra work.

Also, the P-36 did have the R-1820 installed in at least one version:

The Norwegian government had issued an order for 36 Hawk 75A-8 export versions of the P-36 just before the German occupation. These aircraft were powered by the export-model 1200 hp Wright R-1820-G205A Cyclone radial. Since Norway was under German occupation at the time these aircraft were completed in January of 1941, they were impounded by the US government.

Curtiss P-36G

The R-1820 was the same diameter as the R-2600.

 

[Nivek]

Comparison between Lavochkin LA-5 and Curtiss P-36.
P-36 introduced 4 years before LA-5.
Similar physical dimensions except for Horse Power.
Suggest performance potential with re-engined P-36.

 

[Shortround6]

We have to remember that the P-40 was a re-engined P-36 and any scheme to use the R-2600 in a P-36/P-40 airframe has to be compared to the P-40 and not the P-36.

The R-2600 made a lot of power at low altitude, at high altitude ( and here we are talking about 10,000ft as high altitude) things don't look so good. There were also 3 different R-2600 engines so lets not confuse those either.

Radial engine installations got much better with time. A 1944 radial installation was much better from a drag standpoint than a 1938 radial installation, they also learned to use exhaust thrust much better. Even the F4U-1 didn't make use, if any of exhaust thrust.

Having said all that as background the early R-2600 made 1600hp/2400rpm for take-off on 91 octane fuel, it made 1600hp/2400rpm at 1,000 ft ( yes, 1,000ft) in low gear military power and 1400hp/2400 at 10,000ft.

Using early American 100 octane fuel allowed no increase in power but did change the altitude ratings. 1600hp up to 1500ft and 1400hp to 11,500ft.

The XP-40 was fiddled with until it had 22% less drag than an P-36. SO an early P-40 with 1090hp at 13,200 ft compares to R-2600 with about 1345hp at that altitude. But the R-2600 powered plane needs about 1330hp IF it had the same drag as as P-36. Which it won't due to the larger size of the engine and the greater cooling air flow through the cowl needed to cool it.

Design work on the R-2600B (the 1700hp version with 1450hp at 14,1000ft ) was started in Nov 1938, the first experimental engine ran in Nov 1939 and the 5th production engine ran in June of 1941. Or about one month different than the P-40D going into production and the first flight of the XP-40F with Merlin engine.

Wright never seemed to get it's act together concerning superchargers until it was too late to really matter.

Sticking a R-2600 in a P-36/P-40 airframe seems like a lot of work for very little return.

P&W did get a radial engined P-40 to almost match the P-40 in drag (8% more drag) but not until late 1941 at best and more likely 1942.
How much of the difference may be exhaust thrust is questionable

GO to
P-36 Flight Tests

P-40 Performance Tests

For some test that show the amount of power used at different speeds (including cruise) for the P-36 and P-40 for confirmation of the much lower drag of the P-40.

An R-2600 powered Curtiss just didn't offer anything the Allison powered plane couldn't do.

 

[Nivek]

Yes, I agree with you. the Allison V12 in that air frame was the best idea and it worked out well. It did the job when needed. The P-40 made sense.

Just from curiosity, I still wonder what the big engine results would have been.

(1,450 hp (1,080 kW) at 2,600 rpm at 15,000 ft (4,575 m) military power)

Not an altitude engine but not a bad number for 1942. How much HP was the Allison making at 15K ft in 1942?

A lot of effort and time went into put the XP-37.

(XP-37: The aircraft flew in April 1937, reaching 340 mph (550 km/h) at 20,000 ft (6,100 m). Although the turbo-supercharger was extremely unreliable and visibility from the cockpit on takeoff and landing was virtually nonexistent, the USAAC was sufficiently intrigued by the promised performance to order 13 service test YP-37s. Featuring improved aerodynamics and a more reliable turbo-supercharger, the aircraft first flew in June 1939. However, the powerplant remained unreliable and the project was cancelled in favor of another Curtiss design, the P-40.)

R2600 in P-36/P40 air frame I guess would not be much more effort than they put into the various versions of the XP-37 and XP-42.

We will never know.