Improve That Design: How Aircraft Could Have Been Made Better

[tomo pauk]

I don't know how big a difference there was in the thickness of the wings on th e109 and Zero where the guns (and ammo) were located. I mean actual thickness, not percentage as the Zeros wing was a lot bigger. Even a few inches might make a difference.
The MG FF and FF/M had the dual problems of low rate of fire and poor velocity. You need more than two to get a large number of shells in the air, and you have to get close or use angles of fire with little deflection. The long time of flight making deflection shooting difficult.

The FF fired at 540 m/s, vs. the FFM at 700 m/s for the M-shell, so I'd say that FFM will give pilots a good chance to hit. Three FFMs will not be too heavy - circa 80 kg worth of cannons + ammo weight. Granted, we must wait to DB 601N so the central cannon can be installed, the 601A was a show stopper in that regard.
WRT to Bf 109s wing thickness - Spanish managed to install the big HS 404 cannon on their Buchons, after fiddling a bit with wing internals.

Well, the Do 215 was rated at just about 500kph. Since the bombs are carried inside it doesn't take the performance hit that strapping bombs to the bottom of the 110 would cause so the actual attack speeds (30 minute rating?) would be a lot closer. Get rid of the "bug-eye" nose and put on something like the night fighter nose. Use DB 601N or E engines (mainly to get the altitude up higher than the DB601A and DB601Aa. You also have a more range than the 110. Possibility of trading bomb bay space for more fuel. Just do something about the idiotic gun array at the rear of the canopy.

It was rated by manufacturer at 500 km/h. And by the user? Granted, insisting on the slim nose might gain a few km/h.
It was also listed as capable for 20 x 50 kg of bombs only, again by manufacturer - less than 1/2 kg of bombs per HP installed, and 50 kg bombs will not impress with their destructive power. No dive bombing means less accuracy. Waiting for 601N, let alone 601E engines means it's already 1941? Perhaps it is better to have actual escort fighters for proper bomb trucks that can carry twice the bomb load, or more?
Trading of bomb bay space for more fuel is self-defeating here IMO.

It will never equal the Mosquito but since you could have them almost 2 years before the Mosquito shows up in any numbers it doesn't have to be quite as good.
The JU-88 was never going to equal the Mosquito either as by the time you get to the A-4 (very late 1940/early 41) you have plane weighing thousands of pounds more.

The Do 215 does not have to be as good as Mosquito, it needs to be that good so it can reliably evade RAF fighters. At 500 km/h for 5 minutes (say we believe manufacturer's figures) in mid 1940, it might evade Hurricane squadron that is about to take off, but probably not the other squadron that has 3000 ft advantage in height, let alone squadron of Spitfires. What happens once the 5 min limit is out, and Do 215s fly at 480 km/h?
Ju 88 as a bomber was an exercise in self-inflicted wounds, from the wrong position of wing/fuselage juncture onward.

 

[fliger747]

The comment was interesting about the B26 pilots needing to adapt to faster landing aircraft. I did the flight dynamics for a FSX B26 and was struck by this. The landing pattern and speeds were more like the ones that you might use flying the pattern in a light weight 737! Flying it as I would one of the jets, it was a quite pleasant plane to fly, if not having the jet like climb!

 

[Ivan1GFP]

As with all generalities there are some holes. However:
Who else in 1940 had a 1600hp radial engine in production (over 1900 built in 1940) ? with a two speed supercharger?
Who else was working on a 1700hp radial that would enter production in 1941?
Who else had an 1850hp engine going into production at the end of 1940 (2 speed)?
Who else had a two stage engine in production in 1940?
Wright was offering two speed engines in 1938.
Who else had turbo superchargers in production in 1940?

So I would say that the US was in pretty good shape in regards to engines compared to the rest of the world in the 1939-41 time period.

Hello Shortround6,
No question there was developed engine technology in the pre-war US, but with one notable exception: There wasn't a multi stage supercharged inline unless you used turbos which were not quite ready for service.
This was a strange oversight especially since the US Army was showing a preference for inline engines in the most recent designs and updates such as from P-36 to P-40.
One has to wonder how history would have changed had the Merlin engine not been made available for production in the United States.
There was a mad scramble after the war when the US was no longer able to produce Merlins without paying royalties to RR.

Granted the US had a few clangers, or more than few, The Wright Tornado and early R-3350s come to mind. But the US had enough different engines that proved powerful and reliable to supply power for most of their needs. The French, Italians, Russians and Japanese weren't even in the same league (in part due to fuel but two row radials without a center bearing weren't going anywhere) and it took the Germans several years to get a radial up to the power of the early US radials (R-2600 A series).

The R-3350 did eventually become a mostly reliable and dependable power plant but that didn't happen until after the was was over. Every country seemed to have its share of "clangers" for whatever reason.

- Ivan.

 

[Ivan1GFP]

If only there was a 1-stage V-1710 with the critical altitude of 20000 ft - the best in-service version went to 15500 ft (for 1125 HP) by late 1943/early 1944.

Hello Tomo Pauk,
The problem was that those V-1710 with the higher altitude ratings were the two speed supercharged versions and didn't have the same ridiculously high emergency ratings at sea level.

Thing with C3 injection was that it worked under 1.5 km of altitude. What BMW 801D needed, apart from reliability in 1st 6 months of service use, was a better supercharger from mid-1943, that eventually was in service by late 1944 with 801S - too late, that is.
The (un)reliability of DB 605As was not so acute as with BMW 801s in the first ~15 months of service with Fw 190s, that acute that it almost killed the whole Fw 190 program with engine itself. Let's note that DB 605A still have had no restrictions on 30-min regime, or any other lower regime, while restrictions on the BMW 801D were applied for all regimes.

With the BMW 801, eventually it was able to achieve about the same power without C-3 injection or any other power adder.
No argument with the your other discussion. The BMW 801 was hardly trouble free initially.
One has to wonder if the Germans were being overly cautious though. Faber's captured FW 190A apparently was one of the de-rated versions but was flown in testing as if it were not and did not seem to run into any problems as a result. One would assume that a captured aircraft would not have particularly good supply chain for maintenance purposes.

- Ivan.

 

[Shortround6]

The FF fired at 540 m/s, vs. the FFM at 700 m/s for the M-shell, so I'd say that FFM will give pilots a good chance to hit. Three FFMs will not be too heavy - circa 80 kg worth of cannons + ammo weight. Granted, we must wait to DB 601N so the central cannon can be installed, the 601A was a show stopper in that regard.
WRT to Bf 109s wing thickness - Spanish managed to install the big HS 404 cannon on their Buchons, after fiddling a bit with wing internals.

You are comparing the velocity for different weight shells. Always a problem for German 20mm guns
Some sources say 600m/s for the MG/FF but in any case it was for 134 gram projectile.
The 700m/s was for the 92 gram mine shell but the mine shell lost velocity much quicker. actual time of flight to 300 meters was much closer than the muzzle velocity would suggest. At some point short of 300 meters the heavier shell would have passed the lighter one with the higher velocity. This is at sea level, at higher altitudes things aren't quite so bad.

The 92 gram shell lost (at sea level) 38% of it's velocity by 300 meters. The 7.9mm AP round lost 33% but since it had a higher velocity to begin with it actually reached 300 meters about 0.1 seconds quicker. the US. 50 cal only lost about 15% of it's velocity in the first 300 meters.
As the infamous mine shell will not carry either tracer or incendiary the Germans had to come up with a "standard" shell that would function with the same weight of recoiling parts and mainspring as the mine shell used. the result was a 115-115 gram projectile at 585 m/s that lost around 23% velocity (or bit less) at 300meters.

This set up may work perfectly well against 1939-42 bombers (at least most of them) but may be a bit lacking in fighter vs fighter combat. The MG 151 15mm lacked "punch" but it was a lot easier to hit with.

It was rated by manufacturer at 500 km/h. And by the user? Granted, insisting on the slim nose might gain a few km/h.
It was also listed as capable for 20 x 50 kg of bombs only, again by manufacturer - less than 1/2 kg of bombs per HP installed, and 50 kg bombs will not impress with their destructive power. No dive bombing means less accuracy.

The Bf 110 couldn't really dive bomb either. It was claimed that the do 17z could do 600kph in a dive. So strength and control; was already there for at least a steep glice bomb attack.
Bomb loads are iffy, If you have any manuals please post? Some sources claim two or four 250kg bombs and few claim or hint at two 500kg bombs. Depending on how they are hung 20 50kg bombs can take up a fair amount of room (B-26 would only hold 30 equivalent bombs even using the rear bomb bay). Unfortunately photos are rare?

Waiting for 601N, let alone 601E engines means it's already 1941? Perhaps it is better to have actual escort fighters for proper bomb trucks that can carry twice the bomb load, or more?
Trading of bomb bay space for more fuel is self-defeating here IMO.

The Do 215 certainly could not replace the He 111 or even the JU 88 for some missions. But since the 215 could outrun a JU 88A-4 it would seem that some use might be found for it.
If you go the four 250kg bomb route there may be room in the top of the bomb bays for fuel tanks. five 50 kg bombs stacked on top of each other take up vertical space. Or the ever popular aux tanks out board of the engines.
Maybe the bomb doors would need to be bulged? In any case the Mosquito was pretty much limited to four 500lbs until 1944 and even then not all bombers carried much more on every mission.
It might give you an airplane to use all those engines that were supposed to go into Me 210s
I am sure they found a use for them.

The Do 215 does not have to be as good as Mosquito, it needs to be that good so it can reliably evade RAF fighters. At 500 km/h for 5 minutes (say we believe manufacturer's figures) in mid 1940, it might evade Hurricane squadron that is about to take off, but probably not the other squadron that has 3000 ft advantage in height, let alone squadron of Spitfires. What happens once the 5 min limit is out, and Do 215s fly at 480 km/h?
Ju 88 as a bomber was an exercise in self-inflicted wounds, from the wrong position of wing/fuselage juncture onward.

While it may have to evade British fighters (Spitfires) over England, what it has to evade in the Balkans, and NA in 1941 are rather different, not to mention what it has to evade in Russian in 1941/42. Not the best the Russians have but the Average that the Russians have. With DB601Ns or DB601Es it might only be 15-25mph slower than the PE-2?

 

[tomo pauk]

Hello Tomo Pauk,
The problem was that those V-1710 with the higher altitude ratings were the two speed supercharged versions and didn't have the same ridiculously high emergency ratings at sea level.

Several problems, actually. The V-1710s with the higher altitude ratings were the 2-stage supercharged versions, no 2-speed supercharged V-1710 ever entered service. Then, 2-stage V-1710s were used by a redundant aircraft - the P-63. Too late in the game, too - Autumn of 1943, in what time the Allies have had a firm grip on the things aircraft-related (plus, we have Germany sufferign crushing defeats on all fronts and in retreat by that time). The 2-stage V-1710s with water injection have had even greater emergency ratings at low altitudes, going to 1850 HP.

With the BMW 801, eventually it was able to achieve about the same power without C-3 injection or any other power adder.
No argument with the your other discussion. The BMW 801 was hardly trouble free initially.
One has to wonder if the Germans were being overly cautious though. Faber's captured FW 190A apparently was one of the de-rated versions but was flown in testing as if it were not and did not seem to run into any problems as a result. One would assume that a captured aircraft would not have particularly good supply chain for maintenance purposes.

- Ivan.

No doubt that BMW 801 earned it's place in aircraft history. What it lacked in early service was reliability, and later (mid/late 1944 on) it lacked a better supercharger. We also have a thing that 801 was not not contributing to the Axis cause for the 1st 20-22 (24?) moths of the war - 'my' RLM would've supported BMW staying in V12 business even after they acquired Bramo.

 

[Shortround6]

Hello Shortround6,
No question there was developed engine technology in the pre-war US, but with one notable exception: There wasn't a multi stage supercharged inline unless you used turbos which were not quite ready for service.
This was a strange oversight especially since the US Army was showing a preference for inline engines in the most recent designs and updates such as from P-36 to P-40.
One has to wonder how history would have changed had the Merlin engine not been made available for production in the United States.

Hello Tomo Pauk,
The problem was that those V-1710 with the higher altitude ratings were the two speed supercharged versions and didn't have the same ridiculously high emergency ratings at sea level.

I would note that the British didn't get a multi stage supercharged inline into service until 1942. They weren't even working on it in 1940 so blaming the US for not pursuing that avenue seems a bit harsh. Especially considering that the British were not pursuing the turbo option at all. The P & W Two stage radial went into production about 2 years before RR got the the two stage Merlin into production.
The RR single stage superchargers were better than what the US using. Much better after Hooker worked on them.
The Allisons that had the 15,500ft altitude rating were single speed engines. Allison didn't get a two speed engine built until either the end of the war or just after, quantity was minuscule with four being intended for an Allison powered DC-4 plus a few test engines.

One does wonder what would have happened without Packard. Packard was initially contracted to build 9000 single stage , two speed engines, this contract was fulfilled in the beginning of March of 1943. But Packard didn't totally change over to two stage engines, further contracts saw them build almost 7200 single stage engines in 1944 of which the US got none, This is added to the over 10,000 single stage engines they built in 1943 of which the US got none.

I do believe that one or two Short Stirlings were trialed with Wright R-2600s and perhaps they could have been used on the Halifax?

 

[Shortround6]

my' RLM would've supported BMW staying in V12 business even after they acquired Bramo.

I don't have any details on a large BMW V-12 but the BMW 116 wasn't going to do the job
BMW 116 - Wikipedia

There may have been nothing wrong with it except being of the same size and power as the Jumo 210 and Kestrel, which means either starting over or unpacking the pantograph and scaling it up.

 

[tomo pauk]

You are comparing the velocity for different weight shells. Always a problem for German 20mm guns
Some sources say 600m/s for the MG/FF but in any case it was for 134 gram projectile.
The 700m/s was for the 92 gram mine shell but the mine shell lost velocity much quicker. actual time of flight to 300 meters was much closer than the muzzle velocity would suggest. At some point short of 300 meters the heavier shell would have passed the lighter one with the higher velocity. This is at sea level, at higher altitudes things aren't quite so bad.

The 92 gram shell lost (at sea level) 38% of it's velocity by 300 meters. The 7.9mm AP round lost 33% but since it had a higher velocity to begin with it actually reached 300 meters about 0.1 seconds quicker. the US. 50 cal only lost about 15% of it's velocity in the first 300 meters.
As the infamous mine shell will not carry either tracer or incendiary the Germans had to come up with a "standard" shell that would function with the same weight of recoiling parts and mainspring as the mine shell used. the result was a 115-115 gram projectile at 585 m/s that lost around 23% velocity (or bit less) at 300meters.

I can't compare M-shell data for the FF since it could not fire it, unlike the FFM.

This set up may work perfectly well against 1939-42 bombers (at least most of them) but may be a bit lacking in fighter vs fighter combat. The MG 151 15mm lacked "punch" but it was a lot easier to hit with.

German pilots were managing to kill a sizable number of Allied fighters even with the FF in 1939-40, the FFM will give them better chances. As long as they fire under 300-350m (just like RAF did, once the data was collected).

The Bf 110 couldn't really dive bomb either. It was claimed that the do 17z could do 600kph in a dive. So strength and control; was already there for at least a steep glice bomb attack.
Bomb loads are iffy, If you have any manuals please post? Some sources claim two or four 250kg bombs and few claim or hint at two 500kg bombs. Depending on how they are hung 20 50kg bombs can take up a fair amount of room (B-26 would only hold 30 equivalent bombs even using the rear bomb bay). Unfortunately photos are rare?

Curiously enough, unlike with Do 17s, only 50 kg bombs are listed (20 of them). Manual is here: link
The Bf 110C was rated for 650 km/h in dive.

The Do 215 certainly could not replace the He 111 or even the JU 88 for some missions. But since the 215 could outrun a JU 88A-4 it would seem that some use might be found for it.
If you go the four 250kg bomb route there may be room in the top of the bomb bays for fuel tanks. five 50 kg bombs stacked on top of each other take up vertical space. Or the ever popular aux tanks out board of the engines.
Maybe the bomb doors would need to be bulged? In any case the Mosquito was pretty much limited to four 500lbs until 1944 and even then not all bombers carried much more on every mission.
It might give you an airplane to use all those engines that were supposed to go into Me 210s
I am sure they found a use for them.

Granted, the previous Do 17s were able to carry 250 kg bombs, so perhaps that could be shoehorned in the 215s? All/any of the extra DB 601 engines will end up in Fw 190s or Italian fighters, the Me 210 program is axed come 1941.
Mosquito (bomber version) was slower by perhaps 2-3% than fastest LW interceptors? As above - Ju 88 was an exercise how to un-make fast bomber.

While it may have to evade British fighters (Spitfires) over England, what it has to evade in the Balkans, and NA in 1941 are rather different, not to mention what it has to evade in Russian in 1941/42. Not the best the Russians have but the Average that the Russians have. With DB601Ns or DB601Es it might only be 15-25mph slower than the PE-2?

It will not need to evade anything in Balkans, since even historical LW bombers have had easy task there due to Yugoslavs and Greeks having radar-less and otherwise obsolete air defences.
NA and Eastern front in 1941 might get me Fw 190s - long range, rate of roll and all of that...

 

[tomo pauk]

I don't have any details on a large BMW V-12 but the BMW 116 wasn't going to do the job
BMW 116 - Wikipedia

There may have been nothing wrong with it except being of the same size and power as the Jumo 210 and Kestrel, which means either starting over or unpacking the pantograph and scaling it up.

Wrong BMW - this one was in my mind: BMW 117 - a 36 L engine.
Unless they make something of ~45L with know-how and technology of mid/late 1930s.

To move a bit from Luftwaffe.
- Hurricane & Sea Hurricane: beard radiator, better carbs, props and exhausts, a bit thinner wing from the get go. Also even more firepower. Folding wings for the S-H.
- MiG-3 with proper canopy, AM-38 (later AM-39) and two cannons
- Zero and Oscar with Kinsei from day one
- Ki-61 with Ha-109, later with Homare

 

[Shortround6]

First thanks for the link to the manual

I can't compare M-shell data for the FF since it could not fire it, unlike the FFM.

No but the Germans had some problems coordinating fire. If we are going to trouble of designing ideal aircraft why are we using 2nd rate armament?

German pilots were managing to kill a sizable number of Allied fighters even with the FF in 1939-40, the FFM will give them better chances. As long as they fire under 300-350m (just like RAF did, once the data was collected).

The MG FFM had a few problems, yes it was better than A machine (or even two) but you have the drum feed problem and the mixed ammo load problem, sometimes only 40% of the ammo was the mine shell. Bigger drums are not a real problem for the fuselage mounted gun but more of a problem with the wing mounted guns. Japanese may have shifted to some sort of box magazine? details/translations are not good. When you are dealing with 1000-1200hp there is only so much you can do, but when better engines are available (and faster targets) it doesn't give quite the return for investment.

Curiously enough, unlike with Do 17s, only 50 kg bombs are listed (20 of them). Manual is here: link
The Bf 110C was rated for 650 km/h in dive.

My German is practically non existent. In the early part of that manual is some reference to 650kph but I don't what it refers to.

Blatt 4 (?) near the end of the first paragraph?

Granted, the previous Do 17s were able to carry 250 kg bombs, so perhaps that could be shoehorned in the 215s? All/any of the extra DB 601 engines will end up in Fw 190s or Italian fighters, the Me 210 program is axed come 1941.

The manual shows a picture of a bomb rack/dispense for 80 10 kg bombs. Later there are loadouts and diagrams for a dispenser(?) for 40 10 kg bombs. and/or 400kg of light bombs.

Mosquito (bomber version) was slower by perhaps 2-3% than fastest LW interceptors?

The 215 cruised 100-140kph faster than the Do 17z, with better engines? Not the immunity of a Mosquito but would present interception difficulties for an enemy without an integrated air defense.
Nobody cruised at top speed. early Mosquitoes cruised at about 310mph max weak mixture at about 14,000ft.

It will not need to evade anything in Balkans, since even historical LW bombers have had easy task there due to Yugoslavs and Greeks having radar-less and otherwise obsolete air defences. .

Sorry, Balkans would include Greece/Crete with British intervention but still no radar.


BTW the manual shows some rather strange drawings of a Zerstorer near the end. it appears to have a single cannon firing through each prop hub and no other changes to armament.
Unsold proposal? Magazines under the gun? notes seem to indicate Oerlikon FFS guns which used the same ammo as Allied AA guns (very comparable to the Hispano.
Export to Sweden?

 

[gjs238]

Okay, my input is simple.

Have a Rolls-Royce design a supercharger for the V1710, then update it it regularly as they made advances on the Merlin.

Faster and better performing P-40s, P38s, P-39s and P-51As...

The follow up would be what could you do performance wise with Merlin type power at altitude with those aircraft?

My input would be for the original design of the V-1710 to be more modular, in particular, the supercharger.
The V-1710 was advertised as being designed with what they felt was great modularity: see Allison V-1710 - Wikipedia
But I wonder if perhaps a sidewinder supercharger arrangement would have increased modularity, allowing one of two superchargers to be installed without a major rework of the engine or resorting to a remote shaft driven 2nd stage supercharger.
In effect, the supercharger(s) would be accessorie(s) bolted to the engine.

PS: If nothing else, plan for a multi-speed supercharger from the get-go.

 

[Kevin J]

Wrong BMW - this one was in my mind: BMW 117 - a 36 L engine.
Unless they make something of ~45L with know-how and technology of mid/late 1930s.

To move a bit from Luftwaffe.
- Hurricane & Sea Hurricane: beard radiator, better carbs, props and exhausts, a bit thinner wing from the get go. Also even more firepower. Folding wings for the S-H.
- MiG-3 with proper canopy, AM-38 (later AM-39) and two cannons
- Zero and Oscar with Kinsei from day one
- Ki-61 with Ha-109, later with Homare

Like but disagree:-
Mig-3. No change. Discarded as unsuccessful design for Eastern Front.
Sea Hurricane I from 1939 for service on carriers not Sea Gladiator. No folding wings ever as interim type pending arrival of Seafire. Sea Hurricane Ib (1939), IIb (1940), IIc (1941). Replaced by Seafire in 1942.
Spitfire III to form basis for Seafire to be put into production by Westland in 1941. Maybe Seafire Ic (c for carrier version) not Spitfire I's in 1941 for training, hook only and Merlin 20. Seafire IIc as per Spitfire III without folding wings in 1942 with late Merlin 20 series, but with hook and catapult spools. Seafire LIII as per Spitfire III with folding wings service intro early 1943 using Merlin 32, first deliveries late 1942. Cunliffe Owen to build Seafire XV based on Spitfire IV with Griffon engine service intro 1943, limited edition. Seafire FR 17 to appear in 1944. Should all be feasible. Supermarine leads the way for land based versions with Castle Bromwich being the mass producer. Westland uses their design skills to turn the Spitfire III/IV into World beating carrier fighters.
Zero and Oscar with Kinsei from 1943 on.
Ki-100 service intro 1944. No Ki-61-II. Replaces Shoki phased out of production in favour of Ki-84. Performance not quite as high as Raiden but more reliable. Better range and dive speed.

 

[Shortround6]

Everything is trade-offs.
Sidewinder superchargers require right angle drives.
upside down Jumo 211

Not a great supercharger to begin with, it doesn't make for a shorter engine, especially as the supercharger gets bigger. Germans with fuel injection didn't have to worry about where to the carburetor.
Right side up

Now try to fit the ducting from one supercharger to the other and hopefully an intercooler between the superchargers. Or even an after cooler between the last supercharger and the intake duct/manifold.
I am not saying it won't work, only that it takes a lot to really improve on what they were doing

The post war R-2800 used in the F4U-5 was a different beast.

The primary supercharger was still on the back of the engine and the TWO sidewinder superchargers ran in parallel, not series, they were driven by a variable speed drive with both impellers turning at the same speed. Photo does not show the ducting and intercoolers needed. that outlet on the right had side needs to go to the intercooler and then come back to the engine to the inlet for the main supercharger.

 

[swampyankee]

Getting back to the "make it better" bit in the original post.

I think the P-61, with the intrinsic weight and drag added by the (imho) superfluous turret and gunner has the most obvious fix. Since I tend to think that turrets are fighters are nearly always completely superfluous, we could easily improve the Boulton-Paul Defiant and Blackburn Roc by getting rid of that monstrosity in both of them. Of course, the Roc has many more problems, starting with having too little engine.

The US aircraft I'd start with would be the P-39 and the P-38
For the P-39

1. The M-4 cannon was not particularly useful. Replace it with something like the 20 mm HIspano (its production problems were due to idiocy within the Army's bureaucracy, not intrinsic flaws in the manufacturing process).
2. The car-doors were dumb. I know they were fashionable (iirc, the Tempest started with the same arrangement). Sliding canopies were definitely the way to go.
3. One of the problems of the mid-engined layout is that it puts the engine, a big, heavy lump, exactly where one wants to put the fuel. While moving the engine would, in essence, change the P-39 to the P-40, fuel tankage could be increased by a small increase in wing span, and putting tanks in the wing roots.
4. The original XP-39 had such a poor turbocharger installation that it actually impaired performance at altitude by increased drag. I think this could be fixed by lengthening the fuselage to permit a proper installation.

For the P-39:

1. You have liquid-cooled engines. I believe that the automotive industry had figured out how to heat a passenger compartment by the addition of a tiny radiator with air blown through it. I suspect some engineer or another at Lockheed would have been smart enough to get this to work.
2. Using the wing leading edge for cooling. Use a real heat exchanger.
3. There wasn't much to be done about the compressibility issue short of major redesign, so that's not an issue.

Of course, the real problem with the P-38 was inadequate pilot training. It was a large, complex airplane and was, insofar as I can remember, the first large twin-engined aircraft the USAAF operated without a co-pilot and possibly even a flight engineer.

Looking in hindsight, every single aircraft put into service in WW2 had problems of one level or another. For example, a couple of USN aircraft had manually retracted landing gear. The elegant, iconic, elliptical wing of the Spitfire was a bitch to manufacture. The Ju-87 had a remarkably draggy radiator installation.

 

[Kevin J]

Getting back to the "make it better" bit in the original post.

I think the P-61, with the intrinsic weight and drag added by the (imho) superfluous turret and gunner has the most obvious fix. Since I tend to think that turrets are fighters are nearly always completely superfluous, we could easily improve the Boulton-Paul Defiant and Blackburn Roc by getting rid of that monstrosity in both of them. Of course, the Roc has many more problems, starting with having too little engine.

Yes, get rid of the Roc, even though the Roc in Sinbad the Sailor was an apex predator. Other than that I disagree. The Defiant was right for its timescale service and the P-61 was designed around that time, so the concept was okay for its role as a night patrol interceptor. In service of course, the turret was useless as it was a predator not an interceptor.

 

[swampyankee]

Yes, get rid of the Roc, even though the Roc in Sinbad the Sailor was an apex predator. Other than that I disagree. The Defiant was right for its timescale service and the P-61 was designed around that time, so the concept was okay for its role as a night patrol interceptor. In service of course, the turret was useless as it was a predator not an interceptor.

We're all 20/20 in hindsight

The RN could have had a decent fighter without having to buy from the Americans; the real problem with the Roc is that the people who wrote the spec were not sufficiently knowledgeable to write good specs, and the Roc was the result. The Defiant may be more defensible, but I think its turret was the result of a poorly-conceived specification, although there were actually some two-seat biplanes, with a rear gunner, that were competitive, in air combat, with contemporary fighters.

As for the need for the turret on a night fighter: these were not used on, for example, Mosquito, Beaufighter, or P-70 night fighters. Why a turret was seen as necessary on the P-61, after it was shown unnecessary by successful radar-equipped night fighters, mystifies me.

 

[PAT303]

Can I ask why each manufacturer worked on different planes instead of the ones that they new worked?. Look at the Spitfire and Hurricane, they both worked as designed, why didn't someone higher up say to Boulton Paul/Fairey/DH/Wessex/Shorts your planes are rubbish, make Spitfires instead, likewise Rover/Austin/SS (Jaguar) make Merlins, is this idea feasible?.

 

[wuzak]

Can I ask why each manufacturer worked on different planes instead of the ones that they new worked?. Look at the Spitfire and Hurricane, they both worked as designed, why didn't someone higher up say to Boulton Paul/Fairey/DH/Wessex/Shorts your planes are rubbish, make Spitfires instead, likewise Rover/Austin/SS (Jaguar) make Merlins, is this idea feasible?.

MAP told Fairey to make a navalised Spitfire. Fairey said NO!

 

[Shortround6]

Using the Defiant as a night fighter was a waste of a target tug.

Now if somebody can list the air to air kills it made over the winter of 1940/41, from October to May, and if they come up to more than 16 (two per month average) I will retract that statement.