Lightening the P-40

[Clay_Allison]

I think most of us have seen pictures of the P-40 alongside the Bf-109 and the Supermarine Spitfire and most of us can agree that they are not that much different in size, unless I'm blind, the P-40 looks pretty small compare to the P-51 etc.

My question is: If they started in April 1939 systematically cutting weight off the P-40, could they have gotten it down to a loaded weight of 6,500 pounds, and could they have done it by January 1942? The P-40 had a lot of steel armor, probably two more guns than it really needed, and a lot of steel structure that could be replaced with Aluminum (maybe?).

I'm obsessed with the concept that the US should have had a true contemporary to the Bf 109 and the Spitfire and I wonder if there is any possibility that the P-40 could have been a real, legitimate short range interceptor capable of dogfighting with the real bad-asses in the early 1940s. I really feel like there is a legit dogfighter buried in all of that armor, It was by all accounts a maneuverable fighter for its limitations and one that handled itself well at high speeds.

 

[GrauGeist]

From what I've read and heard, the P-40 was a pretty capable fighter and was able to bring the hurt to a fight.

I think it got an undeserved reputation for being a dog, because it's performance in the Far East, PTO and MTO proves it was an excellent performer.

It wasn't good at high elevations, and that touches on the fact that they should have done better with the supercharger for the Allison engine.

At lower altitudes, it proved itself against the Bf109 and the M.C202 in North Africa and in the Pacific, it was able to use it's superior dive speed to avoid being a victim to the Zero while being superior to various other Japanese aircraft.

There were lightnened versions, the L and the N, but I'm not sure what thier weight specs were compared to the E's 6,350 (empty)/8,280 (loaded) other than they only had 4 .50s and a Packard Merlin.

A real good read on the P-40, would be "God is my co-pilot" by Col. Robert Scott which gives great details about his P-40 service with the AVG.

 

[Clay_Allison]

Before we start the same old supercharger talk, remember the 109 and the Spitfire started the war with single stage supers. Pretty sure the entire air war over north Africa was fought that way with German fighters having an advantage over Warhawks in altitude primarily because of weight. If the thing could be brought down (I mean with major enough changes to maybe deserve another model name (P-46 maybe) to a similar weight, it could put the pilot on even footing with any of the enemies.

 

[GrauGeist]

Well, here's an interesting idea:

The P-40's direct predecessor was the P-36. Perhaps a little modifying would bring the P-36 up to the Bf109 Spit's level easier than it would be to trim the P-40 down.

The P-36 was 5,650 pounds loaded. Perhaps replace the P&W R-1830-17 (1,050 horse) with a R-1830-92 (1,200 horse) or R-1830-94 (1,350 horse) and upgrade the armament?

 

[Clay_Allison]

Well, here's an interesting idea:

The P-40's direct predecessor was the P-36. Perhaps a little modifying would bring the P-36 up to the Bf109 Spit's level easier than it would be to trim the P-40 down.

The P-36 was 5,650 pounds loaded. Perhaps replace the P&W R-1830-17 (1,050 horse) with a R-1830-92 (1,200 horse) or R-1830-94 (1,350 horse) and upgrade the armament?

I've considered that and it sounds like a decent idea too.

 

[Shortround6]

I think most of us have seen pictures of the P-40 alongside the Bf-109 and the Supermarine Spitfire and most of us can agree that they are not that much different in size, unless I'm blind, the P-40 looks pretty small compare to the P-51 etc.

Perhaps you do need to see the eye doctor

P-40E wing span and area: 37.33 ft and 235.94 ft²
P-51D wing span and area: 37 ft 0 in and 235 ft²

P-40E length and weight: 31.67 ft and 6,350 lb
P-51D length and weight: 32 ft 3 in and 7,635 lb

Numbers are from Wiki and weights are empty. P-51s engine is several hundred pounds heavier.

My question is: If they started in April 1939 systematically cutting weight off the P-40, could they have gotten it down to a loaded weight of 6,500 pounds, and could they have done it by January 1942? The P-40 had a lot of steel armor, probably two more guns than it really needed, and a lot of steel structure that could be replaced with Aluminum (maybe?).

A P-40 C (deliveries start April of 1941) weighed 5812lb empty equiped and 7549lbs loaded. Two .50s with 380 rounds per gun and four .30s with 490 rounds per gun. It did carry 160 US gallons of fuel?. .30 cal ammo wieghs about 1/4 of what .50 cal ammo does. .30 cal guns weigh about 1/3 of a .50.

you need to cut about 1000lbs from the P-40C. you could cut some armament (not a lot) , you could cut fuel and range/endurance.
If you cut structure you loose the ruggedness the P-40 was known for. Cutting armour makes the plane vulnerable to Japanese 7.7mm MGs.

 

[Clay_Allison]

Perhaps you do need to see the eye doctor

P-40E wing span and area: 37.33 ft and 235.94 ft²
P-51D wing span and area: 37 ft 0 in and 235 ft²

P-40E length and weight: 31.67 ft and 6,350 lb
P-51D length and weight: 32 ft 3 in and 7,635 lb

Numbers are from Wiki and weights are empty. P-51s engine is several hundred pounds heavier.




A P-40 C (deliveries start April of 1941) weighed 5812lb empty equiped and 7549lbs loaded. Two .50s with 380 rounds per gun and four .30s with 490 rounds per gun. It did carry 160 US gallons of fuel?. .30 cal ammo wieghs about 1/4 of what .50 cal ammo does. .30 cal guns weigh about 1/3 of a .50.

you need to cut about 1000lbs from the P-40C. you could cut some armament (not a lot) , you could cut fuel and range/endurance.
If you cut structure you loose the ruggedness the P-40 was known for. Cutting armour makes the plane vulnerable to Japanese 7.7mm MGs.

It performed adequately against the Japanese, but in North Africa that famous ruggedness was less effective versus German cannon. The toughness aspect of early war US planes is under-appreciated but it seems to me that the key is not getting shot in the first place. Replacing steel structure with aluminum and dropping a lot of the armor (all but the pilot's back plate).

Actually, it seems like the P-40N is exactly what I'm talking about. If they had started in 1939 with a "hot rod" P-40 in mind rather than having to wait until the summer of 1943 to decide they needed it. The 'N' got down to 7400 pounds in seemingly only a few months and without appearing to interrupt delivery schedules. Shedding another 400 pounds with a year and a half to work on it should have been quite possible.

 

[Vincenzo]

we can put out no more that all the .30 and half fuel for ~700 pounds no more

w/o wing weapon we have also manuvreability benefit

original p-40 weight ~6800 pounds i think no armour no ss tanks

 

[Clay_Allison]

we can put out no more that all the .30 and half fuel for ~700 pounds no more

w/o wing weapon we have also manuvreability benefit

original p-40 weight ~6800 pounds i think no armour no ss tanks

I'd only be willing to part with the SS tanks if you could feed exhaust into them to prevent fire. (several planes used this system, it seems to have worked well)

 

[davebender]

M2 Browning machine gun - Wikipedia, the free encyclopedia
.50cal MG weighs 38kg
6 x .50cal MG weigh 228kg

MG 151 cannon - Wikipedia, the free encyclopedia
MG151/20 cannon weighs 42kg
2 x MG151/20 cannon weigh 84kg.

Replacing the 6 x .50cal MGs with a pair of decent 20mm cannon would probably save weight and also increase overall firepower. However the weight savings is small potatoes compared to overall aircraft weight.

 

[Clay_Allison]

M2 Browning machine gun - Wikipedia, the free encyclopedia
.50cal MG weighs 38kg
6 x .50cal MG weigh 228kg

MG 151 cannon - Wikipedia, the free encyclopedia
MG151/20 cannon weighs 42kg
2 x MG151/20 cannon weigh 84kg.

Replacing the 6 x .50cal MGs with a pair of decent 20mm cannon would probably save weight and also increase overall firepower. However the weight savings is small potatoes compared to overall aircraft weight.

2x20mm H.S.404 cannon would be probably an ideal armament. We should have put more emphasis on getting that gun working from the beginning, so adding that to the lightening project is a wise move. (it would also have the effect of better arming our other fighters. imagine a 6x20mm battery on the thunderbolt or 4 on the lightning).

 

[Shortround6]

It performed adequately against the Japanese, but in North Africa that famous ruggedness was less effective versus German cannon. The toughness aspect of early war US planes is under-appreciated but it seems to me that the key is not getting shot in the first place. Replacing steel structure with aluminum and dropping a lot of the armor (all but the pilot's back plate). .

I am not sure how much steel structure there was and I certainly don't know exactly why they used it. I will offer up this however. Wright changed from forged aluminium crankcases on the R-1820 to forged steel crankcases on the later models because not only were the steel ones stronger, they were lighter than a new forged aluminium one would have been to handle the same load. Depending on exactly where in the structure the steel was you might have to use twice or more aluminium by volume to get the same strength as the steel and so your weight saving may diminish rapidly. Toughness in North Africa might be a goos thing depending oin which 109 is shooting at you. Until the G model with the 13mm guns shows up the two cowl 7.9mm mgs aren't that hot an armament if the cannon jams or goes dry.

Actually, it seems like the P-40N is exactly what I'm talking about. If they had started in 1939 with a "hot rod" P-40 in mind rather than having to wait until the summer of 1943 to decide they needed it. The 'N' got down to 7400 pounds in seemingly only a few months and without appearing to interrupt delivery schedules. Shedding another 400 pounds with a year and a half to work on it should have been quite possible.

Part of the "hot rod" P-40s lighter weight came from aluminium radiators and oil coolers which didn't exist in 1939-40. While the "combat" weight dropped almost 700lbs the empty weight dropped only 500lbs. Resticting ammo for the 4 remaining guns and leaving out the forward fuel tank are some of the other differences.

The XP-40 was converted from the 10th production P-36A airframe so we might assume there was little difference in structure aside from what was needed for the engine change.

P-40 production aircraft (no letter) had a normal gross weight of 6,787lbs in the spring/summer of 1940. Two .50 cal MGs with 200rpg. no armour, no bullet proof wind screen and no self sealing tanks.

to blatantly steal from Anthony Williams and Dr. Gustin's book "Flying Guns of World War II" page 315:

"...Comparisons of gun weight need to be regarded with caution, as the installed weight could be much higher than these figures indicate. For example, the US Hispano AN-M2 weighed 46kg as a bare gun, but the muzzle brake and adaptor weighed 5kg, the electric trigger and the hydraulic charger totalled3.5kg, and the ammunition feed weighed 10kg (60-round drum) or 8.5kg (belt drive), giving a total weight of 60-65kg, plus the mounintg or cradle, plus ammunition."
Any other gun accessories woud have to be included also, like gun heaters.

 

[davebender]

I agree. However .50cal machineguns also need accessories and ammunition. I suspect that including weight for these items simply tilts the advantage even more in favor of using a pair of 20mm cannon.

 

[Shortround6]

I agree. However .50cal machineguns also need accessories and ammunition. I suspect that including weight for these items simply tilts the advantage even more in favor of using a pair of 20mm cannon.

It might.

But I am just trying to point out that the weight change, up or down, from a change in armament is more than just the bare weight of the guns and ammo.

 

[Clay_Allison]

seems like making the airframe smaller and reducing internal fuel capacity (replaced by drop tanks) would help.

 

[Shortround6]

Well, if you make the airframe smaller you have an XP-46.

The stripped prototype did 410mph at 15,000ft but the version with guns, armour and self seaing tanks only mangaged 355 at 12,200ft.

How many fewer guns, how much less armour and how much less protected fuel would get you to a a "Half-way point" say 380mph I don't know.
XP-46 also had an intial climb rate of about 2,460fpm.

It did weigh 5625lb empty and grossed 7,322lb.

 

[Clay_Allison]

Well, if you make the airframe smaller you have an XP-46.

The stripped prototype did 410mph at 15,000ft but the version with guns, armour and self seaing tanks only mangaged 355 at 12,200ft.

How many fewer guns, how much less armour and how much less protected fuel would get you to a a "Half-way point" say 380mph I don't know.
XP-46 also had an intial climb rate of about 2,460fpm.

It did weigh 5625lb empty and grossed 7,322lb.

They put 8(!) 30 cals and two 50s and 65 pounds of armor on the XP-46, in addition to 65 pounds of armor and self-sealing tanks.

I'd be willing to go with 4x.50MG or 2x20mm and exhaust-suppressed fuel tanks rather than self-sealing. The XP-46 was working with an 1150 horse version of the Allison, it could have continued to get better as they kept adding horsepower to the design.

 

[Shortround6]

They put 8(!) 30 cals and two 50s and 65 pounds of armor on the XP-46, in addition to 65 pounds of armor and self-sealing tanks.

I'd be willing to go with 4x.50MG or 2x20mm and exhaust-suppressed fuel tanks rather than self-sealing. The XP-46 was working with an 1150 horse version of the Allison, it could have continued to get better as they kept adding horsepower to the design.

See above posts about weight of guns.

Keep the two .50s in the cowl. a single .30 weighs about 10kg while a .50 weighs about 29kg. so by changing the four 30s in each wing to a single .50 you save about 22kg.
.30 cal ammo weighs about 3kg per hundred rounds. The .50 cal ammo weighs about 11.36kg per hundred. So 200 rounds of .50 weighs almost as much as 800rounds of .30 or 300rnd/.50 to 1200rnds/.30
So what are you saving on ammo? 12 to 24kg per wing? call it 48kg total for ammo weight. say you can save another 15kg on mounts, charging equipment, ammo trays,etc. per side.

120kg total=264lbs?

Now how much armour to you want to take out?
65lbs sure doesn't sound like much. either for protection or for an increase in performance. An F4F-4 had 162.5lb of armour plate. A piece of armour 2 feet high, 18in wide and 1/3 of in thick will weigh 40lbs. How big a back plate do you want your pilots to have?

While the exhaust gas trick does work it is not weightless. you do need a duct or pipe to bring the exhaust gas to the tank/s. you need a way to cool the exhaust gases before they enter the tank. you need a pressure regulator or pop valve to keep from over pressurizing the tank/s and you need a control valve to admit the gases to the tank/s under pilot control.

So what are you going to save in total? 350-400lbs?

Keeping four .50 cal guns with 250rpg means you added about 550lbs to the weight f the unarmed prototype.

 

[Clay_Allison]

So what are you going to save in total? 350-400lbs?

Yes, and that gets the plane down to 7.000 pounds, 1200 pounds lighter than the P-40E. You probably have a 375 MPH top speed with room to add later dash numbers of the Allison engine and "high activity" Hamilton Standard props (like the P-47) as the war progresses.

More importantly, rate of climb and high altitude performance would be decent enough to let you hold out for better (two stage) supercharging.

 

[michaelmaltby]

"I'm obsessed with the concept that the US should have had a true contemporary to the Bf 109 and the Spitfire and I wonder ...."

Clay - stop being obsessed. The USA in the '30's and pre-war '40's was NOT England or Germany. For starters - only in the US did you have such an open disagreement between the USAAF and USN over aircraft engines - radial vs inline. The RN used navalized Spits and Hurricanes with inlines - would the USN have done the same? Never Same with the Germans .. if they had ever got an aircraft carrier in operation - it would have carried Stukas and Me-109's.

If the USN and USAAF had set the same general requirements for fighter aircraft - perhaps you would have had a slightly different outcome. Personally - both the P-40 and P-39 were solid performers that had serious shortcomings. Same with the Wildcat. The only fighter in service on December 7-41 was the P-38 - and it had the hot fighter performance you're seeking but that came with limitations of other sorts.

It is a testament to the wealth of the US - even in the late Depression - that the military had as many options to produce competitive designs. Look at the Seversky Lancer for example - and what it evolved into, the Jug.

Personally Clay, I think most problems with the P-40 rest with the manufacturer - Curtiss Aircraft. They never got it together in wartime the way Bell, Douglas, North American, Grumman, Republic and Boeing did - the Directors were more influenced by short-term profit and loss figures. Consider the planes they built besides the P-40. The Helldiver was seriously flawed as was the C-46 Commando. Plus a few twin-engine trainers and catapult-launched naval observation aircraft.

Curtiss was complacent - not hungry - and the P-40 shows it.

My opinion

MM