USAAF procures P-51 with V-1650-1 instead of the A-36

[tomo pauk]

Aircraft looks like A-36 (under-wing racks, 4 .50s) on the outside, except the ram air intake that is now under the engine section instead over it. What might be the benefits and shortcomings to the Allied air war of 1943 and on? Expected performance and range? Impact on other Allied fighters' modifications and use? Possible earlier switch of the Dallas factory to the P-51?
The 'P-51+' enters service some time in early 1943, being produced from October 1942 on; no P-51A as we know it.

(The USAAF buys the 'A-40' from Curtiss, so we have funds in ballance. The reduction in V-1650-powered P-40s is obvious.)

 

[Shortround6]

I am not sure the dates line up for any significant change in air force capabilities?

P-40F production (1561 planes) starts in Jan 1942, This includes 250 planes for the British or export.
The A-36 starts production in Oct 1942. 500 planes
The P-40L starts production in Jan 1943 700 planes including 100 for the British.
The P-51A starts production in March of 1943, 310 planes
April 28th 1943 is last Merlin powered P-40L completion date.
The P-51B production starts in May of 1943.

Trying to sort out month by month production of P-40s by engine type may be rather hard. P-40Ks, Ms, and Ns were being built at the same time, side by side, with the Fs and Ls.

You may be able to do it but I don't think there is going to be a major change in capability. You get around 800 P-51s with V-1650-1s but you get around 500 A-40s with Allison -87 engines, better have some good top cover for them
Perhaps Allison can switch the supercharger gears and give you more -73 engines in the last few months of fall 1942 (More P-40Ks) and convert to -81 engine in winter of 1942 for more Ms and Ns?

You still need to fix the ailerons and you can't fit much of a rear tank into the plane as while the V-1650-1 is heavier than the V-1710 is isn't that much heavier.
You also need to redo the radiators and oil coolers and probably the whole ventral scoop. The P-40F used different radiators and oil coolers than the Allison powered planes as the Merlin dissipated a different amount of heat to the oil and coolant than the Allison did.
You might not speed up the development of the P-51B but rather hinder it. NA was working on the P-51B with two stage Merlin in July of 1942, taking time out to figure out the V-1650-1 engine installation with it's different combustion air requirements and different cooling requirements and different weight/s may very well slow down the introduction of the P-51B when you have to do it all over again.

 

[tomo pauk]

...
You may be able to do it but I don't think there is going to be a major change in capability. You get around 800 P-51s with V-1650-1s but you get around 500 A-40s with Allison -87 engines, better have some good top cover for them

800 P-51s with V-1650 is excellent. My intention is to use them in the ETO, one of effects is that hundreds of extra Spitfires can now be shipped in the MTO.

You still need to fix the ailerons and you can't fit much of a rear tank into the plane as while the V-1650-1 is heavier than the V-1710 is isn't that much heavier.

I will certainly not advise installing anything like the 85 gal rear tank until the 2-stage Merlin is installed.

You also need to redo the radiators and oil coolers and probably the whole ventral scoop. The P-40F used different radiators and oil coolers than the Allison powered planes as the Merlin dissipated a different amount of heat to the oil and coolant than the Allison did.
You might not speed up the development of the P-51B but rather hinder it. NA was working on the P-51B with two stage Merlin in July of 1942, taking time out to figure out the V-1650-1 engine installation with it's different combustion air requirements and different cooling requirements and different weight/s may very well slow down the introduction of the P-51B when you have to do it all over again.

The 2-stage Merlin will still have to wait until Packard hits the stride with 2-stage Merlins, I don't expect that P-51s powered by a 2-stage engine will be in service in England before 1944.

With all this said - how the air war of 1943 might unfold differently in this scenario? Effects on further Allied and Axis developments, wins and losses?

 

[swampyankee]

I think the A-36 and P-51A are two of the unsung successes of US industry. While these aircraft weren't world-beaters, as was the P-51B and later (putting a fighter at least as good as the Bf109 and FW190 on top of Berlin would cause a lot of Luftwaffe planners to wee themselves), having another high-performance aircraft, especially one with longer range, would be suitably annoying to the Luftwaffe.

The P-51A was better, in many ways, than the P-40. I also think that the USAAF should have purchased more A-36s; it was a better aircraft for CAS than any of the two-engine bombers.

 

[Shortround6]

800 P-51s with V-1650 is excellent. My intention is to use them in the ETO, one of effects is that hundreds of extra Spitfires can now be shipped in the MTO.

What were the A-36s doing in Sicily and Italy, could it be done by the P-40/Spitfire combo? Will Spitfires, even with drop tanks, have the needed range/radius for some of the missions?
And what do the Merlin A-36s get you in Europe? Are they able to escort 8th air force bombers or not?
You are trading around different countries aircraft here, not replacing American fighters with a different kind of fighter but trading American fighters for British fighters.
Please remember that a Merlin powered A-36 is going to be almost 1 ton heavier (clean) than a Spitfire V and over 1/2 ton heavier than a clean Spitfire IX.
It may have speed, but climb and sustained turn are certainly suspect.
How many Spitfires do you need in Italy to take over the high cover (or medium cover) rolls from the P-40F/Ls you don't have?

The 2-stage Merlin will still have to wait until Packard hits the stride with 2-stage Merlins, I don't expect that P-51s powered by a 2-stage engine will be in service in England before 1944.

Will the deployment of these single stage Merlin powered fighters in the spring of 1943 make up for the delay in deploying the 2 stage Mustangs for several months in 1944?

 

[tomo pauk]

What were the A-36s doing in Sicily and Italy, could it be done by the P-40/Spitfire combo? Will Spitfires, even with drop tanks, have the needed range/radius for some of the missions?
And what do the Merlin A-36s get you in Europe? Are they able to escort 8th air force bombers or not?
You are trading around different countries aircraft here, not replacing American fighters with a different kind of fighter but trading American fighters for British fighters.
Please remember that a Merlin powered A-36 is going to be almost 1 ton heavier (clean) than a Spitfire V and over 1/2 ton heavier than a clean Spitfire IX.
It may have speed, but climb and sustained turn are certainly suspect.

Yes, the intention is very much that the 'P-51+' are used above German-held Europe.
The A-36 as-is was useless as escort over 10000 ft.

How many Spitfires do you need in Italy to take over the high cover (or medium cover) rolls from the P-40F/Ls you don't have?

Probably far less than 800.

Will the deployment of these single stage Merlin powered fighters in the spring of 1943 make up for the delay in deploying the 2 stage Mustangs for several months in 1944?

Why would the delay happen? NAA still has months to tweak the P-51 for 2-stage Merlins.

 

[Shortround6]

Why would the delay happen? NAA still has months to tweak the P-51 for 2-stage Merlins.

Because installing the two stage Merlin instead of the single stage Merlin isn't a tweak.
The two stage engine is 190lbs heavier, it needs a prop that is about 100lbs heavier, it needs a bigger radiator, it needs bigger oil coolers, it needs the intercooler radiator.
It needs the whole new ventral scoop worked out for the P-51B except the engineers weren't working on that scoop, they were working on a scoop that would work for the single stage Merlin.
People seem to be under the idea that fitting the basic Merlin in was the hard part. It wasn't. You could stuff a single stage Merlin in fairly easy. The engine (as made by Packard) was about 190lbs heavier than the Merlin but the prop was about the same weight (or within 10-15lbs) and while you need different sized radiators and oil cooler the radiator and coolant weights wer about the same (or within 10-20lbs?) I forget which way it goes but one engine needed a bigger radiator than the other but smaller oil cooler/s and the other engine needed bigger oil coolers but smaller radiator. The Engines did need close to the total airflow for cooling, P-40F air scoop got bigger, in part because they also added the carb air intake to the scoop.
On the P-51B the cooling system was about 300lbs heavier than on a P-40F.
Parts of a P-51B fuselage are 7in deeper top to bottom to fit the two stage engine and radiator/intercooler set up.
Sticking a single stage Merlin in a P-51A airframe won't require any where near that kind of surgery.

Basically you have do all of the engineering all over again, after you have spent thousands of engineering hours in the summer and fall of 1942 setting the plane up to take the single stage Merlin engine. You are not going to get the P-51B done on time.

 

[tomo pauk]

Because installing the two stage Merlin instead of the single stage Merlin isn't a tweak.
The two stage engine is 190lbs heavier, it needs a prop that is about 100lbs heavier, it needs a bigger radiator, it needs bigger oil coolers, it needs the intercooler radiator.

Agreed.

It needs the whole new ventral scoop worked out for the P-51B except the engineers weren't working on that scoop, they were working on a scoop that would work for the single stage Merlin.
People seem to be under the idea that fitting the basic Merlin in was the hard part. It wasn't. You could stuff a single stage Merlin in fairly easy. The engine (as made by Packard) was about 190lbs heavier than the Merlin but the prop was about the same weight (or within 10-15lbs) and while you need different sized radiators and oil cooler the radiator and coolant weights wer about the same (or within 10-20lbs?) I forget which way it goes but one engine needed a bigger radiator than the other but smaller oil cooler/s and the other engine needed bigger oil coolers but smaller radiator. The Engines did need close to the total airflow for cooling, P-40F air scoop got bigger, in part because they also added the carb air intake to the scoop.
On the P-51B the cooling system was about 300lbs heavier than on a P-40F.
Parts of a P-51B fuselage are 7in deeper top to bottom to fit the two stage engine and radiator/intercooler set up.
Sticking a single stage Merlin in a P-51A airframe won't require any where near that kind of surgery.

Agreed again. This will mean that NAA can have the V-1650-1-powered P-51 in production after a short notice.
BTW - the undescored word is a typo? V-1710, not Merlin?

Basically you have do all of the engineering all over again, after you have spent thousands of engineering hours in the summer and fall of 1942 setting the plane up to take the single stage Merlin engine. You are not going to get the P-51B done on time.

NAA received the contract for 2-stage Merlin powered P-51 on 25th July 1942, the 1st such P-51 took flight at 30th Nov 1942 - 4 moths later. After changes to cooling system, it again flew in December 1942 (5 moths after the contract).
So let's say that they 1st fly the 2-stage Merlin powered P-51 in February of 1943. You still have to wait for the 2-stage Merlins from Packard whole spring and summer - that is not something NAA can change, and that was one of reasons the P-51B program was delayed into start of 1944 to make effect to the air war in the ETO.

With that said - what about the effects of hundreds of 'P-51+' from early 1943 in ETO, both for operations and development/modification of other fighters?

 

[Shortround6]

You still have to wait for the 2-stage Merlins from Packard whole spring and summer

No, as of July 1943 NA had received 173 engines and completed 534 airframes.

May 16 engines
June 56 engines
July 184 engines
Aug 371 engines
Sept 475 engines

These numbers are completed at the Packard factory and since the engines probably went by rail to NA there may have been a 1-2 week delay (if you were lucky) in a completed engine getting to the NA factory. But is seems packard caught up.
There is also a difference between fly prototype airplanes and having production drawings done and new jigs/fixtures in place for volume production. In the Spring of 1943 NA was making about 120 planes a month.

 

[tomo pauk]

No, as of July 1943 NA had received 173 engines and completed 534 airframes.

May 16 engines
June 56 engines
July 184 engines
Aug 371 engines
Sept 475 engines
These numbers are completed at the Packard factory and since the engines probably went by rail to NA there may have been a 1-2 week delay (if you were lucky) in a completed engine getting to the NA factory. But is seems packard caught up.

Yes, you're right.

There is also a difference between fly prototype airplanes and having production drawings done and new jigs/fixtures in place for volume production. In the Spring of 1943 NA was making about 120 planes a month.

That would be 120 P-51s a month (all of them from Inglewood)?

 

[tomo pauk]

For the sake of discussion: let's say that AAF deploys 4 groupsof 'P-51+' (~200 fighters) in April and May, and another two groups in June and July of 1943. How to use them, and what can be expected vs. Fw 190s predominantly? Best-case and worst-case for the bomber units (reduction of losses etc)? Expected German reaction, both in tactics and tech?

 

[Kevin J]

For the sake of discussion: let's say that AAF deploys 4 groupsof 'P-51+' (~200 fighters) in April and May, and another two groups in June and July of 1943. How to use them, and what can be expected vs. Fw 190s predominantly? Best-case and worst-case for the bomber units (reduction of losses etc)? Expected German reaction, both in tactics and tech?

I'll go with the way things actually went, was much better. P-51's in North Africa, A-36's in Italy, P-51A's around the World being used for fighter recon and counter air. It gives North American time to develop the P-51B and our forces time to wring the bugs out of the original design and add the knobs and whistles. You know like bomb racks, drop tanks, better ailerons.

 

[tomo pauk]

I'll go with the way things actually went, was much better. P-51's in North Africa, A-36's in Italy, P-51A's around the World being used for fighter recon and counter air. It gives North American time to develop the P-51B and our forces time to wring the bugs out of the original design and add the knobs and whistles. You know like bomb racks, drop tanks, better ailerons.

Lo and behold, the 1942-vintage A-36 was outfitted with bomb racks and drop tanks.

 

[Peter Gunn]

Interesting question, using the single stage Merlin for a P-51+. A couple of thoughts:

1). I had a short discussion with drgondog a year or so ago about getting the P-51B into combat 6 months earlier, between design and development and a certain AAF officer perhaps getting hit by a beer truck, it seems with a ton of fore-site and luck, the B might have gotten into combat MAYBE 4-6 month earlier. I'm in agreement with SR6, I think you're now delaying the arrival of the B to 8AF ops by several months when they needed it the most to begin to turn the strategic bombing campaign around and get it back on track so to speak.

2). Not sure what the 8AF would do with these, 9AF would certainly put them to some use, but I think the person that would REALLY want them isn't Eaker but George Kenney, better range than the Thunderbolt, faster with possibly the same or better range than the Lightning and flat out superior to the P-40. I read somewhere that one of the gripes Kenney had was the short range of the fighters he was getting, probably in reference to the Thunderbolt and he wasn't getting enough P-38's so this might be a God send to him.

Just my $.02 for what that's worth.

 

[Shortround6]

My problem with the "stick the -1 Merlin" in the P-51 airframe idea is that it sucks up engineering time.
The A-36 sucked up time but the engine compartment was essentially untouched. They changed the gear ratio on the supercharger, and changed it again on the P-51A. They modified the wing to take the bomb racks and plumbing, they added the dive brakes. Sounds simple but somewhere I ran across the the number of drawings that had to changed on the F4F WIldcat to go from 4 guns to 6 guns, it was hundreds.

Edit, found it, http://www.steampoweredradio.com/pd...rcraft/history of eastern aircraft part 1.pdf
page 42, not hundreds of drawings but 4,000 engineering changes, which could be simple dimension change on an existing drawing.

I would advise reading the whole thing, yes there is some self promotion, patting one's self on the back kind of stuff going on (and a few snipes ar rivals like Ford) but is does give a picture of what was being done and how it needed to be done to "convert" car plants to aircraft plants.


An experimental shop is a bit like a hot rod car builder. If they need to mount something to a firewall or bulkhead they just drill a couple of holes and bolt it on. The problem comes later when they try to "productionize" it. Somebody has to draw up the bracket, stress analyze it (it won't break/bend when dong a 6-7 G pullout) specify the bolts AND redraw the firewall/bulkhead with the new holes properly located and even specify in what order the holes should be drilled in the sequence of all the other holes being drilled in the same firewall/bulkhead.
Now do this with all the things that have to be changed to swap the Allison for the single stage Merlin. Oil tank, coolant header tank, control linkages, fuel, oil and coolant lines (and their brackets). Hot rodders will tell you that getting the engine into the car is easy, hooking everything up to have it actually run and run right takes a lot of time

And once you do this for the -1 Merlin you have to do it all over again (or most of it) for the -3 Merlin. Installing the -1 engine is not a shortcut in fitting the -3 engine. Maybe the basic engine mount is the same, maybe it isn't as you need to shift the engine to account for the difference in weight of the engine and the difference in length of the two stage supercharger.

Tactical/operational impact is another post.

 

[tomo pauk]

We might take a look at what Luftwaffe have had in their inventories by May 1943, from here (scroll almost to the bottom for May 1943).
Fw 190s: ~300 in the 'West', + ~90 in Germany & Denmark
Bf 109s: ~30 in the West, + ~110 In Germany and Denmark
Those are isted under 'serviceable' category. There was a lot of night fighters and bombers, obviously, but those are not going to matter much for the B-17s needed protection. NFs can be dealt easily by escorts provided the escorts are at least decent and available in good numbers.

So our escorts need to 1st move aside or destroy what they can from the 'West' Luftwaffe fighters (~330 of them), then to do same with ~200 of the fighters located in Germany proper, and then to protect the bomber stream on the way back. Those 200 fighters (or whatever the number was later in 1943) located in Germany are what historical Allied fighters were not able to touch in a meaningful way before late 1943 historically. This is what 'P-51 plus' need to mess with mostly, the Spitfires can provide escort until Ardenes roughly.
How far might that fighter range? The P-51B/C/D, without fuselage tank and with 2x75 gal drop tanks was supposed to have 460 miles radius at 25000 ft and on 210 mph IAS (~310 mph TAS at that altitude). That radius means it can cover Germany up until Hamburg or Frankfurt when deploying from East Anglia, or up until Stuttgart if deployed from Kent ( in know that USAAF rarely if ever was deployed from there).

 

[tomo pauk]

A bit about other WAllied aircraft that might try to prevent the 'P-51 plus' stealing their thunder.
P-47 - make a firm deal with the British for their 90 imp gal (108 US gal) drop tank to be supplied. See what 5th AF was doing (metallic tank that can be pressurized, made by Ford in Australia). Wing drop tanks. These are all historical improvements, just need to be done in a much more timely manner. Escort radius can grow to 375-425-475 miles for the razorback P-47. To be a proper long-range fighter, the P-47 needs the increase of 'fixed' fuel tankage, too.
P-38 - already has the good/great radius, but in this scenario it will be probably based away from ETO?
Spitfire - best bet are Spitfire VII and VIII, with another fuel tank behind the pilot. The low production numbers might be a problem, since these versions were also used extensively in the MTO. Perhaps Spitfire IX with extra fuel tankage might be shipped to MTO so more of the Mk.VII and VIII can be based in the UK?

These are short-term fixes that still lack coverage of Germany beyond ~470 mile limit, the air war of early 1944 will need more substantial improvements both for P-51 and other fighters.

 

[Kevin J]

A bit about other WAllied aircraft that might try to prevent the 'P-51 plus' stealing their thunder.
P-47 - make a firm deal with the British for their 90 imp gal (108 US gal) drop tank to be supplied. See what 5th AF was doing (metallic tank that can be pressurized, made by Ford in Australia). Wing drop tanks. These are all historical improvements, just need to be done in a much more timely manner. Escort radius can grow to 375-425-475 miles for the razorback P-47. To be a proper long-range fighter, the P-47 needs the increase of 'fixed' fuel tankage, too.
P-38 - already has the good/great radius, but in this scenario it will be probably based away from ETO?
Spitfire - best bet are Spitfire VII and VIII, with another fuel tank behind the pilot. The low production numbers might be a problem, since these versions were also used extensively in the MTO. Perhaps Spitfire IX with extra fuel tankage might be shipped to MTO so more of the Mk.VII and VIII can be based in the UK?

These are short-term fixes that still lack coverage of Germany beyond ~470 mile limit, the air war of early 1944 will need more substantial improvements both for P-51 and other fighters.

Problem with your extra fuel in the Spitfire VII/VIII idea is that the biggest drop tank you can put beneath the Spitfire's belly is 90 IG. I've never seen anywhere, drop tanks under their wings, only fuel in their wings or 250 lb bombs under on the Vc/IXc with outer LMG removed. So fuel used is going to be wing fuel for take off climb to height say 28 IG, 90 IG used for flight to target leaving your fuselage fuel of 94 IG for combat and return to home. So adding more fuel in the rear fuselage doesn't get you any further. Longest raids were: Spitfire VII, SW England to La Pallice, France, 455 miles each way; Spitfire VIII, Darwin to East Timor, 400 miles each way. Both flights were over water, not overland, nor contested airspace. Halve those figures for flying over the English Channel and back as you'll have to keep your cruise speed up.