Why didn't Allison quickly develop a one-stage 2 speed Supercharger for the P-40

[KiwiBiggles]

The Spit IX and later the Spit XVI were the main a/c used by the 2TAF in NE Europe. They could be dived up 60 degrees.

Careful, you're using facts to destroy a widespread article of faith. Everyone knows that the Spitfire was fragile; in fact, it's astonishing they ever made it into the air.

Tactical Spitfire squadrons in Italy, probably using Mk.Vs, used to dive-bomb at an angle of 85 degrees.

 

[Shortround6]

I think the Russians actually preferred the P-40K though with the Allison engine because they were fighting down low for the most part. They got about 100 P-40Fs but sent them right to PVO units (air defense). Allison engine P-40s seem to also have been preferred in the CBI.

One question I have is why weren't the Allison engined P-51s a bit more widely used in the Med? They did have them but were using them as dive bombers and recon planes mostly.

Production numbers and spare parts answer those questions. There were about 1560 P-40Fs built, that includes 250 Kittihawk IIs. This compares to the roughly 2900 P-40D&Es and 1320 (?) P-40Ks. The P-40L was built to the tune of about 700 compared to about 600 Ms (including lend lease) and then we get into the Ns starting in March of 1943. these run to around 5000.
There simply weren't enough Merlin P-40s to scatter around to too many different theaters. The US screwed up and only ordered around 20% spare engines (or equivalent spares?) instead of the more customary 50% spares. The British tore down around 600 used Merlin engines to provide the US forces in North Africa with spare parts.

sending a few squadrons of P-40F/Ls to lesser theaters without adequate spare parts (not just the engines, the Merlin and Allison needed different radiators and oil coolers) is going to result in a lot of effort for not much result.

The numbers tell the story of the Allison P-51/Mustang/A-36 too.
There were roughly 1580 Allison Mustangs built. The British got the first 620 (-2) the Americans got 500 A-36s with dive brakes and the rest were somewhat divied up. There simply weren't enough to go around to everybody who wanted them (British were still using two squadrons on VE day).
Now please note that there were 3 different Allison engines used in the P-51. The 500 A-36s got a special low altitude model engine that would have limited them more than the other Allison engines.

The 500 A-36s kept 3 fighter bomber groups (9 squadrons?) in action for quite some time, over a year?

 

[Shortround6]

British try using bombs as air to air weapons as Spitfires are too fragile for ground attack

Yes the Spitfire was not as desirable as some other aircraft for ground attack (Typhoons with hundreds of pounds of extra armor?) and P-51s were more susceptible to ground fire/battle damage than P-47s but both Spitfires and P-51s performed many ground attack missions.

 

[Schweik]

Power to weight is what makes an aircraft "0ver weight"
Once you get a Allison P-40 to 15,000ft or so you have an 1150hp engine in an 8,000lb plane and as you go higher it gets worse.

That's part of it (Power to Weight) and with the turbo, especially useful at high altitude - but there is another factor, wing loading, which is an issue at medium altitude and increasingly important as you get lower and lower. Seeing as how P-47s were used so much in the Fighter Bomber role and even P-38s were used that way as well (and therefore could be engaged by enemy fighters at low altitude), this was an issue.

This is one of the main reasons that neither the P-47 nor P-38 were particularly popular with our allies and saw little postwar service. I think the English accepted a few hundred P-47s which were immediately sent to Burma to be used as bombers in lieu of Hawker Hurricanes. The Soviets accepted a small number, which they evaluated. They appreciated the big engine and all the space and nice construction standards, but noted that at low altitude the aircraft performed aerobatics "reluctantly" and in the words of the Soviet Test pilot, while nice in many respects, the P-47 was "not a fighter". The UK had a similar opinion of the P-38 I believe.

With a leaden wing loading combined with a huge draggy fuselage and a weight of 12,700 lbs the P-47 is not the ideal candidate in a dogfight at low altitude, regardless of how much power that huge turbo has. Until they got the paddle blade props it didn't climb well either. Can you do impressive things with it anyway? Certainly, you can work around the weight - but I think that does qualify as overweight. At 53 lbs per square foot wing loading the P-38 was even less agile than a Thunderbolt at a low or medium altitude dogfight (at least P-47s had good roll), which is why they had so much trouble in the Med and ETO. Not even getting into the compressability, heating, engine, turbo, intercooler, etc. problems.

P-38 likewise a had a much better power to weight ratio at altitude due to the turbos. A late model P-38 had four times the power at 25,000ft that a P-40N did. It sure didn't weigh four times as much.

"At altitude" being the key phrase here. P-38 didn't even have an impressive HP to weight ratio (0.16) compared to say, a Spitfire Mk V (.22) - in fact it's about the same as a later model P-40.

A P-40 with a V-1650-7 might have been a very dangerous opponent but i.

I'll just skip the 'what-ifs' with you guys lol...

S

 

[Schweik]

British try using bombs as air to air weapons as Spitfires are too fragile for ground attack

Yes the Spitfire was not as desirable as some other aircraft for ground attack (Typhoons with hundreds of pounds of extra armor?) and P-51s were more susceptible to ground fire/battle damage than P-47s but both Spitfires and P-51s performed many ground attack missions.

You have an excellent command of the obvious, and of the literal.

I'm well aware Spits were used for ground attack - the whole DAF was, every aircraft type pretty much - I just said they were a bit too fragile for it, which is true. Not the ideal bird for that job. This was also the feeling of most Spit pilots. Spitfire was basically an interceptor, that was what it was best at.

S

 

[Schweik]

Production numbers and spare parts answer those questions. (snip) There simply weren't enough Merlin P-40s to scatter around to too many different theaters.

But production doesn't tell the whole story and in fact proves misleading. They may have built 5,000 P-40Ns but by the time the N came out, the urgency for using P-40s was over. The P-40F and L models, conversely, were available at the most critical moment. They had enough of them to be the main variant in use by no less than 5 USAAF fighter groups in the Med / Italian Theaters: 33 FG, 324 FG, 325 FG, 57 FG and 79 FG were all mainly using merlin engined P-40s, as well as some P-40K.

sending a few squadrons of P-40F/Ls to lesser theaters without adequate spare parts (not just the engines, the Merlin and Allison needed different radiators and oil coolers) is going to result in a lot of effort for not much result.

5 Fighter groups with 3 squadrons each = 15 squadrons, (that's a little more than 'a few'), operating during the most critical months on the war, they played a key role in finally and decisively securing the English supply route from India, taking one of the major Axis powers (Italy) out of the war and forcing vast amounts of German resources to be redirected to cover their southern flank, not a "lesser Theater" in my opinion, though I know some perceive it that way.

Conversely what, precisely, was happening in North West Europe in 1942 and early 1943?

The Theaters of significance in 1942 were Russia, the Pacific and the Med. Probably in that order. The Battle of Britain was a key battle but that was long over. I don't think Dieppe qualifies as "THE" major front line event of the war in that era. YMMV.

The numbers tell the story of the Allison P-51/Mustang/A-36 too.
There were roughly 1580 Allison Mustangs built. (snip)

The 500 A-36s kept 3 fighter bomber groups (9 squadrons?) in action for quite some time, over a year?

Actually again, not of that actually tells us much of anything. It's a large number of planes which they seemed to mostly use for recon - not that recon was unimportant - it was very important and recon planes seemed to almost always get shot down, so a fast one like the P-51 / A-36 certainly had an important role. I'm just wondering why they weren't using them more on fighter sweeps over German airfields like they did with the P-40s and Spit Vs.

S

 

[Schweik]

My guess on the P-51A / A-36 is that they didn't have too many of them in the Med or Italy and were probably using most of them for recon and "army cooperation" stuff from the UK.

 

[Milosh]

Spitfire fragile? The Spit had a higher dive speed than the Mustang.

The A-36's 1st mission was June 6 1943 attacking Pantelleria. The 27th and 86th FBG flew mission in the MTO. The 311th FBG flew in the Far East. They flew some 23,373 combat sorties and delivering over 8,000t of bombs. They shot down 84 e/as for the loss of 177 to all types of enemy action.

The P-51/Mustang Ia had a camera mounted but not the A-36.

 

[Shortround6]

I'll just skip the 'what-ifs' with you guys lol...

I like a good what if.
However when we start talking about 1943/44 engines in 1942 aircraft it starts getting strange.
The P-40 was going to be 20-40mph slower than P-51 using the same engine so it is a little hard to to figure out why they would take the best engine and put it in the 2nd best airframe.
The British did do this with the Hurricane II and the Spitfire but then it was a case of improving the Hurricane or facing a real fighter shortage in the winter of 1940/41. SPitfire production not being large enough. The Americans were not faced with such a production problem in the summer/fall of 1943 (or later?) when the V-1650-7 became available.

 

[Shortround6]

But production doesn't tell the whole story and in fact proves misleading. They may have built 5,000 P-40Ns but by the time the N came out, the urgency for using P-40s was over. The P-40F and L models, conversely, were available at the most critical moment. They had enough of them to be the main variant in use by no less than 5 USAAF fighter groups in the Med / Italian Theaters: 33 FG, 324 FG, 325 FG, 57 FG and 79 FG were all mainly using merlin engined P-40s, as well as some P-40K.



5 Fighter groups with 3 squadrons each = 15 squadrons, (that's a little more than 'a few'), operating during the most critical months on the war, they played a key role in finally and decisively securing the English supply route from India, taking one of the major Axis powers (Italy) out of the war and forcing vast amounts of German resources to be redirected to cover their southern flank, not a "lesser Theater" in my opinion, though I know some perceive it that way.

The P-40Fs were sent to the NA/Med in 1942 as that was, as you say, the most important theater at the time, at least for the US. They were not used in Europe (England) at all.
They were also not used (at least in any numbers) in the CBI or Pacific theaters, which for supply purposes are different. Those are the lesser theaters I was referring to. The CBI and Pacific using different supply routes and depots for the most part.

Actually again, not of that actually tells us much of anything. It's a large number of planes which they seemed to mostly use for recon - not that recon was unimportant - it was very important and recon planes seemed to almost always get shot down, so a fast one like the P-51 / A-36 certainly had an important role. I'm just wondering why they weren't using them more on fighter sweeps over German airfields like they did with the P-40s and Spit Vs.

As I said, there weren't enough of them. The British kept the vast majority of the Mustang Is in England and while they called it reconnaissance, many of them engaged in low level strafing from the beginning. The next batch was the P-51/Mustang IA with 20mm cannon and there were only 150 of them. 93 go to England and 57 stay in the US, 55 of which become F-6A photo-recon planes. Then comes the A-36 production batch. Deliveries start (at the factory) In Oct of 1942 which is a bit late for operation Torch, at least the initial stages. The 310 P-51As are what is left after the initial order for 1200 is cut in Dec of 1942 with the 890olane difference to be delivered as P-51Bs with Merlin engines. However that cut was made before the first P-51A rolled out the factory door. It takes until May of 1943 to complete the 310 P-51As and a P-51 sitting on a ramp In Los Angles is weeks/months away from seeing combat in any theater. 50 of the P-51As are supplied to the British as replacements for the 57 P-51s taken by the US.
Timing of aircraft into service squadrons took a while. The British had four squadrons of Mustang Is at Dieppe and it took until Jan 1943 to get 15 squadrons into service. The British operated a peak of 21 squadrons of Mustang Is. But notice that the last Mustang I was delivered/accepted at the factory in July of 1942, so 618/620 planes accepted by July of 1942 but only 4 squadrons in service at the beginning of Aug.

 

[P-39 Expert]

The AAF made their decision in '42 that the P-38 and P-47 would be the main combatants and the P-39, P-40 and P-51 would be mainly for export to our allies and help out with ground support.
Neither the Lightning nor Thunderbolt panned out as superplanes for the AAF.
The P-38 had the obvious flaws of poor diving characteristics and below average maneuverability which put it at a disadvantage in Europe where the opposition was just as fast. It excelled in the PTO because of a 70mph speed advantage.
The Thunderbolt didn't want to climb or turn and had the endurance of a Spitfire.
Both were enormously expensive compared to other fighters and neither was available in 1942 (except for the P-38 at the very end).
Why in the world didn't the AAF prioritize two stage Allison production for the P-39, P-40 and P-51? Turn these planes into high altitude planes and their utility to the AAF goes through the roof.
But the big question is why the AAF insisted on making the P-39, P-40 and P-51 so damn heavy when the engine they were designed around only produced 1150-1200HP at TO? At 6# per HP those planes should have weighed 7200# when they actually weighed 7650, 8400 and 8600#.
Either a two stage engine or a significant weight reduction program would have turned those planes into tigers.

 

[Shortround6]

The Thunderbolt didn't want to climb or turn and had the endurance of a Spitfire.

We have been over this before, the P-47 had much greater endurance than Spitfire, roughly double on internal fuel.

Why in the world didn't the AAF prioritize two stage Allison production for the P-39, P-40 and P-51? Turn these planes into high altitude planes and their utility to the AAF goes through the roof.

Because the early Allison two stage was a piece of crap. Talking about the early test rig/s. You can "prioritize" whatever you want, without sufficient engineers and a good basic design you have crap for output. The first proposal/development contract was in Dec 1940 and used an auxiliary stage supercharger using the smae sized impeller as the main engine and used a fixed speed (single) supercharger drive to the auxiliary supercharger. At the time Allison was building about 250 engines a month and desperately trying to increase production of engines for P-38s, P-39s, P-40s (all different models) and work on a few other experimental projects. What gets DE-prioritized ? weight given is 1545lbs and output is whopping 1150hp at 21,000ft. I think we can see why they weren't jumping all over this thing.
The F9R engine was proposed to the Navy with a weigh of 1510lbs and 1125hp at 18,000ft using a two stage supercharger.

But the big question is why the AAF insisted on making the P-39, P-40 and P-51 so damn heavy when the engine they were designed around only produced 1150-1200HP at TO? At 6# per HP those planes should have weighed 7200# when they actually weighed 7650, 8400 and 8600#.
Either a two stage engine or a significant weight reduction program would have turned those planes into tigers.

In part because the US believed in self sealing tanks and pilot protection, in part because US strength standards were higher than some other countries and in part because the US was saddled with the .50 cal machine gun and it's ammo. A P-40D with four guns and 250rpg was carrying 621lbs of guns, ammo and gun equipement. A Spit with two 20mm and four .303s was carrying about 650lbs of guns/ammo, extra equipement unknown.
How much below four .50 cal do you want to go? Please note the Spit was carrying 243bs of ammo, 1000 rounds of .50 cal weighs 300lbs.
Yes the US planes were over armed but their is a limit as to how low you can go.

 

[Barrett]

Just FWIW: The JSF program is now in its 21st year, coming up on 11 since first flight. Contrary to what L-M, the services and DoD claim, not one F35 is FMC (that's fully mission capable.) The marines have been lying about its status forever, beginning with the first one that rolled into the chocks with the training squadron at Yuma. The AF recently had to announce that none of the first block (a coupla hundred airframes) will ever be FMC because they were delivered AND ACCEPTED as-was. Costs too much to upgrade them.

A few years ago the AF secretary expressed a revelation when she said "Maybe we shouldn't buy airplanes until they're finished testing." Yathink? That's why F35 remains in low-rate production: the law requires successful completion of operational test & development, and the thing is nowhere close.

JSF is a prime example of corporate welfare, which is no accident because subcontractors are strewn across more than 80% of congressional districts. (Same with F22, as I recall.)

I could go on & on & on, but being naval-centric I'll note that the USN's C model spent 2 1/2 years getting the tailhook to engage a wire. A test pilot told me that it only had a 10% arresting rate during land-based "roll in" tests. That's on the most expen$ive Fighterjet of all time, and we've been hanging hooks on airframes since 1922!

What should we do? Aside from massive fines and maybe prison time, cut back JSF to sustainable levels and buy upgraded "legacy" jets like F15/18, AND INVEST IN ECM. But the AF has sacrificed EW on the Stealth Altar, leaving only the navy and marines with that capability. Still, it should be a no-brainer: you cannot add on stealth (which gets degraded just flying around, let alone basing in blowing sand & dirt--and heavy rain--and in-flight refueling.) ECM is much-much-much less expensive, which is probably why we don't have enough of it!

I'm a taxpayer. I want a refund...

 

[P-39 Expert]

We have been over this before, the P-47 had much greater endurance than Spitfire, roughly double on internal fuel.

Because the early Allison two stage was a piece of crap. Talking about the early test rig/s. You can "prioritize" whatever you want, without sufficient engineers and a good basic design you have crap for output. The first proposal/development contract was in Dec 1940 and used an auxiliary stage supercharger using the smae sized impeller as the main engine and used a fixed speed (single) supercharger drive to the auxiliary supercharger. At the time Allison was building about 250 engines a month and desperately trying to increase production of engines for P-38s, P-39s, P-40s (all different models) and work on a few other experimental projects. What gets DE-prioritized ? weight given is 1545lbs and output is whopping 1150hp at 21,000ft. I think we can see why they weren't jumping all over this thing.
The F9R engine was proposed to the Navy with a weigh of 1510lbs and 1125hp at 18,000ft using a two stage supercharger.



In part because the US believed in self sealing tanks and pilot protection, in part because US strength standards were higher than some other countries and in part because the US was saddled with the .50 cal machine gun and it's ammo. A P-40D with four guns and 250rpg was carrying 621lbs of guns, ammo and gun equipement. A Spit with two 20mm and four .303s was carrying about 650lbs of guns/ammo, extra equipement unknown.
How much below four .50 cal do you want to go? Please note the Spit was carrying 243bs of ammo, 1000 rounds of .50 cal weighs 300lbs.
Yes the US planes were over armed but their is a limit as to how low you can go.

A clean Thunderbolt (as all were until August '43) had barely the same range as a clean Spitfire especially in the ETO where they had to operate at max continuous.
Regarding the two stage Allison, 1180HP at 21500' was a tremendous increase over single stage models that would develop less than 700HP at that altitude. The Merlin 61 only developed 70HP more at 23000'.
Regarding weight, the Germans (and British) were able to manufacture fighters with self sealing tanks, armor and heavy firepower at much better P/W ratios. What is the use of pouring resources into a fighter if it can't climb high enough to engage the enemy?

 

[tomo pauk]

My guess on the P-51A / A-36 is that they didn't have too many of them in the Med or Italy and were probably using most of them for recon and "army cooperation" stuff from the UK.

P-51As and A-36s flew about zero combat sorties from the UK. A-36s were used exclusively in the Med, P-51As in the Med and CBI.

 

[Shortround6]

A clean Thunderbolt (as all were until August '43) had barely the same range as a clean Spitfire especially in the ETO where they had to operate at max continuous.

Do you have some documentation of this? Comparing endurance, range, radius and combat/escort radius is very difficult unless you are sure you are comparing the same things. I would note however that a clean P-47 rarely had to cruise at max continuous (rich mixture) as that is 2550rpm and 42in map. At low level the P-47 could suck down a lot of fuel but at 25,000ft &altitude used for figuring escort radius it could do 360mph at 2500rpm and 38in map. Since that is about 30mph faster than US planners figured on (they figured 210mph IAS) you can drop down to 225mph IAS at 25,000ft at 2350rpm and 36in MAP and still be going faster than the planners need and drop fuel burn from 190gph tp 145gph. Max lean is 2250 and 32in MAP (105 gallons per hour) , The chart is missing a column but at 200mph IAS at 25,000ft the P-47 was supposed to need 2150rpm and 31in map and burn 95 gallons an hour.
Do you have any figures for the Spitfire when cruising at those altitudes and speeds?

Regarding the two stage Allison, 1180HP at 21500' was a tremendous increase over single stage models that would develop less than 700HP at that altitude. The Merlin 61 only developed 70HP more at 23000'.

Yes 1180hp at 21500 was a very large improvement however you have underated the Merlin considerably. The Merlin 61 was good for 1390hp at 23,500ft.
So Allison power is down to 84% and 2000ft lower rather than the 94% and 1500ft you are claiming.
I would note that the V-1650-1 in the P-40F was rated at 1120hp at 18,500ft with it's single stage supercharger which basically comes down to the early two stage Allison going to a lot of complication and trouble for 2500-3000ft of altitude. Later ones got better.

 

[Schweik]

While we are on the subject of superchargers, how did the Germans manage to get such good high altitude performance with the DB 601 series, just a lighter plane? Multi speeds? Something different about the impeller? I know water injection came a bit later (I think) and they didn't use two stage superchargers.

 

[wuzak]

While we are on the subject of superchargers, how did the Germans manage to get such good high altitude performance with the DB 601 series, just a lighter plane? Multi speeds? Something different about the impeller? I know water injection came a bit later (I think) and they didn't use two stage superchargers.

They used a variable speed drive for the supercharger, and improved the supercharger itself over time. The supercharger may have even got bigger in later versions.

 

[Milosh]

They used a variable speed drive for the supercharger, and improved the supercharger itself over time. The supercharger may have even got bigger in later versions.

I thought everyone knew that.

 

[Schweik]

I thought everyone knew that.

Forgive my ignorance I'm not really into Luftwaffe planes that much. When it comes to the Axis kit I've always been more drawn to the Japanese and Italian planes, though granted some of the nicer of theirs also used the DB 601.

S