Early Mustangs-performance/experience?

[IdahoRenegade]

The success of the 2-stage/2 speed Merlin equipped P-51Bs and later models is well documented and justifiably famous. I'm fairly familiar with it's combat success from December '43 on, as are most casual aviation enthusiasts. I believe most know the plane was developed as a result of a British purchase order. This order was somewhat out of desperation, with the British being desperate for more fighters, most any fighters, with the original contact with NAA being a request to build P-40s-in spite of its limited performance. NAA engineers offered to develop what became the P-51 instead and the results are history.

While I'm pretty familiar with the results of the Merlin Mustangs, what I haven't found is a great deal of discussion of the early, Allison equipped British birds (MK-1s?) equipped with single stage superchargers. Does anyone have any sources discussing the use/performance of this plane by the British and how it fared against the opposition, as well as how it compared to its British contemporaries? What theaters did it operate in? I understood (anecdotally anyway) that it performed well at lower altitudes compared to the Spit in terms of speed, being significantly faster at the same power level due to the low drag airframe (true or am I mistaken?). I also believe that even in the early variations with no rear fuselage tank that it had a considerable range advantage over the Spit due to it's lower drag airframe. Did it also carry significantly more fuel even in this variation, and was it used to a significant extent over occupied Europe?

Similar questions concerning the US utilized P-51A model. Where was it utilized and how did it well did it succeed at it's missions. I know virtually nothing about the A-36 dive bomber version. "Version" perhaps not being accurate-was this basically a '51 with dive flaps or were the changes more extensive? How did it perform in that roll? It seems like a plane with a single liquid cooled engine would be pretty susceptible to loss in that role, given the susceptibility of the cooling system to damage. Was the A-36 produced due to it's performance, or more as a way to keep the NAA production line in operation?

Finally-the story of the Mustang being re-engined at Rolls with the Merlin is well known-but I know nothing of the details. Any information on the backstory? Who's idea was it, when did it happen, reviews of the test flights? Other than the prototypes retrofitted at Rolls, were any production Mustangs built for the British before the US P-51B model went into production?

Sorry about all the basic questions. Compared to the vast amount of knowledge so many here have, I'm just a rookie. Thanks.

 

[Greyman]

Interesting US report on British Mustang I use over at wwiiaircraftperformance E-GEH-16

 

[tomo pauk]

Bill (drgondog) will cover the origins of the idea to install Merlin on Mustang. There was also a short-lived proposal to re-engine the Mustang with 1-stage 2-speed Merlin, but it was skipped.
USAF used P-51A in CBI (China, Burma, India) thatre, and in the MTO. IIRC RAF also got a handful of those.
A-36 was an useful dive bomber, the losses were nothing extravagant. It was also used as escort fighter in the MTO, to escort medium bombers. It have had dive brakes installed, flaps were not changed for that version. Production of the A-36 was a way to keep the NAA production line open. Susceptibility of liquid cooling to enemy fire is over-exgagerated IMO.
British operated the Mustang I/Ia exclusively in the ETO*. Range was excellent, but Spitfire was also able to carry a drop tank that gave SPitfire a comparable rage, or better range if the 170 gal tank was used. Tests of the Allison-engined Mustangs: link.
The Mustang I was well liked by the RAF and operated as long as 1944, though it's main use was of recon.

*ETO, not MTO here

 

[drgondog]

Don't have much time today:

Early Merlin - NAA Kindleberger had a knock down fight with Allison beginning in early December 1941, went as far as getting Mossie engine mount drawings, engine specs from Packard for Merlin 28 (1650-1) and preliminary estimates to convert from Schmued. The meeting occurred in January 1942 with two GM Board members including Breech and Allison CEO. Ronnie Harker, Test pilot for RR, made recommendation to install new Merlin 61 in Mustang I on May 1, 1942. Hives, Managing Director of RR/Hucknall approved on May 4, and set up meetings with Ministry and RAF Air Staff - project go-ahead on 5/19/142 with Mustang I AG518 allocated to project.

Thanks to active interest by Maj Tommy Hitchcock, who was extremely well connected to not only Ambassador Winant but also Roosevelt, His constant prodding enabled NAA to invest preliminary cycles to look further into converting to both the Merlin XX (16501-) and Merlin 61 (1650-3 with longer dimension because of supercharger) in June 1942. Despite foot dragging by AAF Mat'l Command (Echols and others) contract NA-101 dated 7-25-1942 was executed for two prototype Mustang/Merlin (as yet not determined which one) as XP-78. It allocated two P-51-1 to the project.

David Burch's Rolls Royce and The Mustang is THE book for the narrative from RR point of view.

The RAF loved the Mustang I, and IA for its range and speed and overall maneuverability - They used it quite effectively as Armed Recon and intruder into Germany, shooting up rail and barge traffic as well as airfields.

The biggest issue with the Mustang I as far as AAF concerned is that it a.) wasn't requested by Material Cmd, b.) It was a drain on Allison's capacity to produce engines, and c.) the political intrigue was almost Not overcome. Echols was a friend of Arnold and did have a degree of influence, but at the end of the day, the Arnold/Fairchild connection, after the A-36 proposal and contract was let, was STILL required to keep Echols from not proceeding with the follow on P-51A contract immediately after A-36 run completed/

The period April, 1942 through May, 1943 was characterized by Echols trying to keep the P-51 bottled up, which did not help him later career wise when the reports of the Mustang X, then Xp-51B, then P-51B-1 emerged from other sources than Material Command - particularly as the Eglin Field tests emerged.

IMO the P-51B could not possibly have been operational in ETO before they actually began Dec 1, 1943 - simply because the ability of Packard to take the RR Merlin 61 and tool for it, produce a couple in October, lose two to engine failures and actually delay the first flight of the Xp-51B by six weeks - pointed to the real critical path. Packard simply couldn't get functional engines in the hands of NAA until late June/early July, 1943.

 

[pbehn]

As far as I know the RAF were interested in putting a Merlin in the Mustang as soon as they test flew it, some may have been interested as soon as they found out its internal fuel load.

The first air victory and loss of Mustangs was in the Dieppe raid, a mustang pilot downed a FW190 who had just downed his wingman. The victory was by American Holis Hills flying with RCAF 414 Sqrn while the "loss" flt Clarke was picked up and survived ditching being picked up by a landing craft.

Some useful info here.
P-51 Mustang - History, Pictures, and Specs

 

[davebender]

ability of Packard to take the RR Merlin 61 and tool for it
Lancaster bomber was competing for those engines.
When did British made Lancaster bombers start using Packard made Merlin engines?

 

[tomo pauk]

Don't have much time today:

Early Merlin - NAA Kindleberger had a knock down fight with Allison beginning in early December 1941, went as far as getting Mossie engine mount drawings, engine specs from Packard for Merlin 28 (1650-1) and preliminary estimates to convert from Schmued. The meeting occurred in January 1942 with two GM Board members including Breech and Allison CEO.
...

Talk about missed oportunity - the Mustang with V-1650-1. Ready to hit Luftwaffe in 1943 above Germany proper.

ability of Packard to take the RR Merlin 61 and tool for it
Lancaster bomber was competing for those engines.
When did British made Lancaster bombers start using Packard made Merlin engines?

Lancester never used Merlin 61, the two-stage supercharged Merlin. Only Merlin 20s (1-stage), those were in good supply from early 1941 on, plus Packard started producing them from late 1941 on.

 

[wuzak]

ability of Packard to take the RR Merlin 61 and tool for it
Lancaster bomber was competing for those engines.
When did British made Lancaster bombers start using Packard made Merlin engines?

Since the original contract specified 2/3 (6000/9000 IIRC) of Packard production was to go to the British, I imagine Lancasters received the V-1650-1/Merlin 28 as soon as the factory started making them. Similarly for the Mosquito and Canadian Hurricanes.

The issue for the P-51B was the change at Packard to also build the V-1650-3/Merlin 61/63. It was the production of the -3 which was problematic for the Mustang program.

 

[wuzak]

Lancester never used Merlin 61, the two-stage supercharged Merlin. Only Merlin 20s (1-stage), those were in good supply from early 1941 on, plus Packard started producing them from late 1941 on.

Not in quantity, anyway.

The Mk VI had later versions of the 61.

 

[MIflyer]

There's an Osprey book "Allison Engined P-51 Mustang" that covers the airplane pretty well. I also read in a book about Canadian airmen, "All The Fine Young Eagles" that while it was ostensibly a "army cooperation aircraft" the RAF used the Mustang Mk 1 as a long range intruder, even popping in at Luftwaffe basic training airfields to give the students a rude shock. Even though the Mk1 was not equipped to carry drop tanks, it still had a 1000 mile range with a full internal fuel load.

There was an issue of Air Enthusiast that covered the Allison Mustangs' service pretty well. Last known kill by an RAF Mk1 was on 1 Jan 1945, when one shot down a Ju88 that was one of the navigational aircraft used for Operation Bodenplate

The book "Straight Down" covers the A-36A quite well. The RAF wanted to use the Mustang Mk1 in the Med for low altitude recon but had none available. They did borrow one or two A-36A's from the USAAF to use for that role and found out that for long range low altitude missions the Spitfires they tired to provide as escorts could not hack it. The Apaches could throttle back and cruise along so much faster and longer than the Spitfires that escort was impossible. The book "Those Were the Days" was written by an A-36A pilot and is one of the few to cover personal experiences of those pilots. And it turns out that some P-51-1's, the USAAF version of the Mustang Mk 1A, with four 20MM cannon were used by the A-36A units as well.

A friend of mine who was in the CBI said that they found that while the P-47 could carry much larger bombloads, the P-51A's were better at carrying bombs out of short jungle strips. The P-51A's were also found to be better than the RAF fighters at CAS in Burma because they were still equipped with HF radios that could talk to the ground troops and thus get some FAC help. The RAF fighters had switched over to VHF, could not talk to the ground troops and asserted that, "We don't need to talk to the troops because we thoroughly brief our pilots on the targets they are to attack." Of course, everyone eventually figured out that "Target is 200 yards west of the red smoke" was a much better way to do things.

 

[Shortround6]

According to "AHT" the British were using 5 squadrons of Allison powered Mustangs at the time of D-day and were still using 2 squadrons of them at VE day. Which is certainly not too shabby considering the last Allison powered Mustang left the factory in May of 1943 . The last 310 Allison Mustangs are P-51As and the British got 50 (?) and called them Mustang IIs. These were "pay back" for the 57 P-51s (with 20mm cannon) the Americans had held back from the lend-lease contract for the Mustang-IA.

They were probably running into a spare parts problem keeping them in service at that point. They had gotten 93 of the Mustang IA (P-51) with four 20mm cannon.
21 British squadrons operated Mustang Is at the peak of use, but the last Mustang I left the production line in July of 1942.

 

[MIflyer]

By the way, the roll rate of the early Mustangs was not that great and the Farnborough people worked to develop better ailerons for the later airplanes. They did come up with a aileron design that improved the roll, and Capt Eric Brown said it was better in that regard than the new ones North American used on the Merlin engined models. I don't know if the P-51A got the new ailerons or if they were retrofitted to earlier models the way the new metal ailerons were on the Spitfires; I would guess not.

So the Allison engined models were much lighter than the Merlin models, among other things the Allison engine was 400 lb lighter than the Merlin 61. But the Merlin engined models had a better roll rate.

Oh, and the Allison engined models did not have a cockpit floor; the seat was simply bolted to the wing. The Merlin engined models had a plywood cockpit floor.

 

[drgondog]

I'm still trying to find the production break between the old/original aileron and the sealed aileron, that for sure was installed in B-1 and all succeeding Mustangs. Chilton tested both A-36 and P-51A for Roll rate so it is entirely possible that both received the improved aileron.

 

[davebender]

Lancester never used Merlin 61
Perhaps not that exact model but they were competing for Packard made Merlin engines along with the P-51, some makes of the P-40 etc.

 

[tomo pauk]

Lancester never used Merlin 61
Perhaps not that exact model but they were competing for Packard made Merlin engines along with the P-51, some makes of the P-40 etc.

Hopefully this will not be turned into an anti-Lancaster tirade
The P-40 with Packard Merlin V-1650-1 was barely passable fighter in 1942 (imagine a slower Spitfire V that also climbs slower, has better range and rolls better), and by 1943 it was a waste of crucial engines. On the other hand, Lancaster was prossecuting a crucial bomb war that was far costlier for Germany to pay for defences, damage and lost work hours than it was for the UK to wage that war. There was no competition for engines between Lanc and P-51 - Packard was producing plenty of both -1 engines from Spring of 1942, let alone in 1943 when they also started manufacturing the production of 2-stage supercharged -3 and, swithching to -7 engines in 1944.

 

[MIflyer]

Yes, a point I have made elsewhere and been criticized for it. The V-1650-1 started production at the same time the Mustang Mk1 started production. If those engines had gone into Mustangs rather than P-40's you would have had a far more useful airplane. The P-51A as delivered had basically the same top speed as a Spitfire Mk IX at 20,000 ft. With an engine that enabled two critical altitudes, one at 15,000 and one at 20,000 ft, it would have run away from a Spitfire Mk IX and had an improved climb rate as well.

No, it would not have been nearly as good as a P-51B. But it would have been better than just about anything else around at the time.

Now, there was no earthly reason that Allison could not have built a two speed supercharger to bolt onto the V-1710 crankcase. Unlike the Merlin the V-1710 came in three main pieces, the gearcase, crankcase, and rear accessory section with supercharger. Building another version of the accessory section would have not affected the rest of the production. They probably could have even gotten another company to build the new accessory case and supercharger; it would have been simple.

Imagine getting Continental or GM or someone to build the new two speed V-1710 accessory section and telling Fisher to stop fooling around with that ridiculous XP-75 and start building Mustangs. Mustangs over Berlin in March of 1943 rather than 1944. And the two speed supercharger could have gone into the P-40 and P-39 as well.

 

[tomo pauk]

Yes, a point I have made elsewhere and been criticized for it. The V-1650-1 started production at the same time the Mustang Mk1 started production. If those engines had gone into Mustangs rather than P-40's you would have had a far more useful airplane. The P-51A as delivered had basically the same top speed as a Spitfire Mk IX at 20,000 ft. With an engine that enabled two critical altitudes, one at 15,000 and one at 20,000 ft, it would have run away from a Spitfire Mk IX and had an improved climb rate as well.

To be fair to the Spitfire IX, the engines in service in 1943 made it go more than 400 mph at 25000 ft and above, the P-51A can't compete. Especially once the wing racks are accounted for, cost was 12 mph on the P-51A/B/C (improved racks came with P-51D, cost was 4 mph). Spitfire's sigle drop tank facility was barely noticeable speed-wise. Rate of speed was firmly Spitfire's territory, P-51A is even less able to compete here.
More about critical altitudes in a second.

No, it would not have been nearly as good as a P-51B. But it would have been better than just about anything else around at the time.

The main benefit with going with Merlin early on is that there is a very useful long range fighter, without vices, in mass production, before 1943. Use it in 1943 as escort fighter in the ETO and LW can be hit hard above Germany proper.

Now, there was no earthly reason that Allison could not have built a two speed supercharger to bolt onto the V-1710 crankcase. Unlike the Merlin the V-1710 came in three main pieces, the gearcase, crankcase, and rear accessory section with supercharger. Building another version of the accessory section would have not affected the rest of the production. They probably could have even gotten another company to build the new accessory case and supercharger; it would have been simple.

Imagine getting Continental or GM or someone to build the new two speed V-1710 accessory section and telling Fisher to stop fooling around with that ridiculous XP-75 and start building Mustangs. Mustangs over Berlin in March of 1943 rather than 1944. And the two speed supercharger could have gone into the P-40 and P-39 as well.

Having a gearbox with more SC speeds can't help the V-1710, at least not in the vein that it can improve much the altirude power. The impeller was too small - 9.5 in, vs. 10.25 in on most of the Merlin 1-stage engines, V-1650-1 and Merlin included. The V-1710 with 'faster' geared impeller was still lacking 3000-3500 ft worth of rated (or critical) altitude vs. V-1650-1 or the Merlin 45 that was an 1-speed supercharged engine. Or some 12% lack in power above 15000 ft.
Without going to a 2-stage supercharger, the V-1710 will never hope to match what 2-stage Merlin was offering.

 

[Shortround6]

Lancester never used Merlin 61
Perhaps not that exact model but they were competing for Packard made Merlin engines along with the P-51, some makes of the P-40 etc.

You had 3 basic types of Merlins.
1, single speed-single stage. Never made by Packard.
2. two speed-single stage, Made by Packard as shown in the chart posted by Tomo. In ten versions although some were NOT massed produced.
3. Two speed-two stage, also made by Packard as shown in the chart posted by Tomo.

Now please note that the initial contract for Packard Built Merlins was for 9,000 two speed single engines and at a max delivery rate of 800 engines a month. The US was to get 3000 engines and the British 6000 engines. Please note that the initial contract was completed some time in March of 1943.
Obviously a number of contracts were placed to cover the additional 17,759 singe stage engines and the over 20,000 two stage engines (chart above only goes to Dec 1944, not the entire war)

There seem to have been a grand total of NINE Lancasters using two stage engines ( Merlin 85/87s), any other "Lancasters" using two stage Merlins got different wings and were called Lincolns.

Also note that it took until the summer of 1942 for NA to complete the first 620 Mustang Is which, I believe, the British had paid for cash, and had purchased the Alison engines for (also cash?) so trying to swap engines around gets somewhat difficult.

Curtiss was turning out over 300 P-40s a month for most of 1942, NA would not exceed 150 fighters per month until Dec of 1943. For most of 1942 they didn't go over 90 fighters a month. Without some SERIOUS revamping of production facilities, engine allocations, and hundreds of subcontractor contracts you are simply not going to get large numbers of single stage Merlins all that early. Please consider that the XP-40F first flew on June 30th 1941 but it took until Jan 3rd 1942 for the first production example to leave the factory The last of 1561 P-40Fs leaves the factory in Jan of 1943, Curtiss built over 5000 Allison powered P-40s in the same time period.

I would note that the Curtiss factory was only about 215-220 miles from Packard if you cut through Canada ( Lake Erie is in the way) but it is just under 2000 air miles from Packard to NA in Los Angles. The engines have to go by train, not air, though. Forget cross country truck in 1941

 

[wuzak]

Having a gearbox with more SC speeds can't help the V-1710, at least not in the vein that it can improve much the altirude power. The impeller was too small - 9.5 in, vs. 10.25 in on most of the Merlin 1-stage engines, V-1650-1 and Merlin included. The V-1710 with 'faster' geared impeller was still lacking 3000-3500 ft worth of rated (or critical) altitude vs. V-1650-1 or the Merlin 45 that was an 1-speed supercharged engine. Or some 12% lack in power above 15000 ft.

Without changing the supercharger, a second speed would add power at lower altitudes and not increase the critical altitude.

Though, for the V-1710 it could have allowed the 9.6:1 gears for HI gear and 8.8 (?) for LO gear, so as gaining some altitude performance without losing low altitude performance.

Apparently there was a 2 speed V-1710 prototype model at some stage, but it did not make it into production.

Regarding supercharger impeller sizes, the V-3420 used a single 10" impeller. Which would seem to be way undersized.

For comparison, the Vulture (2600ci) had a 12" impeller, the Griffon (2240ci) had ~13" impeller.

 

[Shortround6]

Without changing the supercharger, a second speed would add power at lower altitudes and not increase the critical altitude.

Though, for the V-1710 it could have allowed the 9.6:1 gears for HI gear and 8.8 (?) for LO gear, so as gaining some altitude performance without losing low altitude performance.

Or the Allison could have used 7:48 gears or lower for low and kept the 9.6 gear for high,not enough change between 8.8 and 9.6 to be worthwhile.