P-38 with Roll-Royce Merlins

MIflyer · Jul 8, 2019

The V-1710 of the P-38J/L weighed 1395 lb not including the turbo and intercooler and was rated at 1,475 hp at 30,000 ft. The turbo and intercooler probably weighed no more than 100lb.

The V-1650-3 of the P-51 weighed 1640 lb and was rated at 1390 hp at 20,000 ft.

As for putting the Merlin in the P-51, the Allison Mustang/Apache was an outstanding aircraft but was not in much use by the USAAF. Stopping P-51A production to start building the P-51B was not a problem, while stopping P-38 production to build a Merlin powered version would have been a problem. I talked to a friend of mine who was a P-38 maintenance chief in WWII and he said that putting a Merlin in would not have been all that easy. The air intake for the downdraft carb would have interfered with the structure.

Milosh · Jul 8, 2019

Didn't Merlins have an updraft carb?

syscom3 · Jul 8, 2019

The War Production Board decided that the production line would have had to be shutdown for a while, and it was not worth it to get a marginal increase in performance. The P51 was where the AAF had its money on and they didn't want to squander the Merlins on a so-so fighter.

wuzak · Jul 8, 2019

Milosh said:
Didn't Merlins have an updraft carb?

Yes.

Shortround6 · Jul 9, 2019

MIflyer said:
As for putting the Merlin in the P-51, the Allison Mustang/Apache was an outstanding aircraft but was not in much use by the USAAF. Stopping P-51A production to start building the P-51B was not a problem,

We all know that the US took quite a while to acknowledge that the Allison Mustang was a very good airplane. We also know that the Apache/A-36 was a funding trick to keep the production line open. The contract for 500 A-36s was awarded April 16th 1942 but actual development wasn't started until June, FIrst flight of an A-36 was in Sept 1942.
With start of a new fiscal/budget year June 23rd 1942 saw a contract for 1200 Allison powered P-51As placed. This was later changed to 310 aircraft the remainder changed to P-51Bs with Melrins.
To put a few other things into the timeline (and try to tie it back to the P-38) the last Mustang I left the production line in July of 1942 and was followed by the P-51 no letter.

Packard only hits the 800 engines a month production goal (of single stage engines) in July of 1942 (contract signed in Sept of 1940) and won't build a two stage engine until Nov of 1942 and won't build their 10th (yes 10th) two stage engine until May of 1943.

Getting back to the P-38, the first G with 1325hp engines is delivered in July of 1942 (a very busy month) and the first H with 1425hp engines was delivered in March of 1943. Obviously orders hand been placed months earlier with development of the engines going on both before and after the order dates (in some cases the "orders" were changes to existing airframe orders)

There are few Packard Merlins to be had in 1942-43(Packard's 1943 production was double what it's 1942 production was and it's 1944 production was over what the 1942 and 1943 combined production was.)

Trying to squeeze the Merlin P-38 into that is going to be hard, Which Merlin was going to be available when and in what numbers? And this is as the P-38 is going through several engine and turbo combinations, each one getting more powerful/capable even if there were a few hiccups along the way.

IdahoRenegade · Jul 9, 2019

MIflyer said:
The V-1701 of the P-38J/L weighed 1395 lb not including the turbo and intercooler and was rated at 1,475 hp at 30,000 ft. The turbo and intercooler probably weighed no more than 100lb.

The V-1650-3 of the P-51 weighed 1640 lb and was rated at 1390 hp at 20,000 ft.

According to this source: P-51 Mustang Performance the Merlin was at 1075hp at 30,000 ft., about 27% less than the V-1710 at that altitude per your spec.

b0ned0me · Jul 9, 2019

MIflyer said:
The turbo and intercooler probably weighed no more than 100lb.

Believe the P-38 used the B-13 turbo, which was 135lb including wastegate but excluding intercooler, ducting, and any extra items such as oil lines, mountings heat shields etc.

Deleted member 68059 · Jul 9, 2019

MIflyer said:
The turbo and intercooler probably weighed no more than 100lb.

The bare B2 turbo-unit itself weighs 135 lbs, according to the official cataloge, although when the Germans weighed one they
reckoned 153 lbs in actual practical form (the catalogue weight probably ignores some flanges and fittings etc). Thats without
the coolers, pipes, controllers, fluids, and so on for which read a very considerable increase.

The German report reckoned the approximate installation weight for a B2 turbo system was 150kg per engine (330lbs), so 300kg = 660lbs
for a twin engine aircraft.

=======
"Des gesamtgewicht einer Anlage mit Abgasleitung, rohrleitung und allen sonstigen dasugehörigen Teilen kann mit 150kg im durschnittangesetz werden."
======
Ergebnisse der Beuteauswertung #34 - 1st July 1944 (Conclusions from Examination of Enemy Equiptment)

This shouldnt be very surprising as even putting one extra blower with a chargecooler on the Merlin-60
increased its weight by 265lbs (120kg) from 1375 to 1640lbs. (Merlin III vs Merlin-61)

(snipped attached is from a photo taken by me)

MIflyer · Jul 10, 2019

Intersting! I saw a video of two troops lifting a turbo unit off of a P-38. It did not look like it weighed more than maybe 50 pounds. I wonder what that 135 lb weight includes?

wuzak · Jul 10, 2019

Using Google Translate I get the following:

turbine runner (complete with shaft) - 10.60kg (23.37lb)
loader impeller - 3.02kg (6.66lb)
bearing housing (completely with pump) - 8.80kg (19.40lb)
turbine housing (with radiation protection) - 28.10kg (61.95lb)
loader volute casing - 17.00kg (37.48lb)
loader rear wall - 2.15kg (4.74lb)
---------------------------------
Total weight of the turbocharger - 69.67kg (153.60lb)

Deleted member 68059 · Jul 11, 2019

wuzak said:
Using Google Translate I get the following:
loader impeller - 3.02kg (6.66lb)
loader volute casing - 17.00kg (37.48lb)
loader rear wall - 2.15kg (4.74lb)

FYI Lader = Compressor

thats not google translates fault really, its one of those funny words
which was used at the time but has since passed out of use in that context in German.

pbehn · Jul 11, 2019

Snowygrouch said:
FYI Lader = Compressor

thats not google translates fault really, its one of those funny words
which was used at the time but has since passed out of use in that context in German.

Like LADING in English, I have never heard it used in conversational English. It is used all the time in shipping where "a clean bill of lading" is required for most shipments. and trucks have a laden and unladen weight.

K5083 · Jul 12, 2019

On the issue of weight a couple of hundred pounds would make little difference. Losing the turbo would free up space for fuel, but you probably need more fuel for the Merlin anyway.

The things that were wrong with the P-38 would not be fixed by the Merlin. The wing section. The lack of internal space. The complete dedication of the airframe design to turbo requirements, cooling, ducting, heat and so on. Prop clearance. To use much more power you need a bigger prop, and/or four blades. Look at the props on Spit 9 or P-51B-D. More clearance needs an undercarriage change. None of it is easy.

And of course, that Brit fuel. The same fuel that worked in every other warplane based in the UK, including turbo-charged B-17, B-24s and P-47s.

MIflyer · Jul 12, 2019

Actually, I quoted those V-1710 and Merlin figures to Warren Bodie back around 1992 and he replied that he had a copy of the Lockheed analyses that showed putting two stage Merlins in the P-38 would have been a good idea.

Note that later in the war Packard built Merlins were being used in Lancasters, Mosquitoes, and Spitfire XVI, as well as the P-82, so it probably would have been feasible to build enough engines for the P-38 at some point.

K5083 · Jul 12, 2019

But a P-38 capable of compressibility on the level would not have been an improvement. And that means only 440mph at altitude. The engines weren't a major problem, or at least it got fixed. The baked-in problems were not fixable without major airframe mods. Also, if you look for what could be done with two late Merlins on a single-seater, try the DH Hornet. That reached speeds that no 38 could hope for. It missed the war but a version with merlin 61s was technically possible in 1942-3, had they not been building Mosquitoes instead. What-ifs can't improve the P-38 easily. And with the P-47 better at ground attack and the P-51 better at air-to-air, why pay extra to get worse.

An aside, when comparing power don't forget the Merlin 60series gets around 200hp equivalent at high speeds from exhaust thrust.

Another question though, what assumptions were made in the Merlin P-38 paper exercise as far as propellers were concerned. It seems to me you need more prop.

drgondog · Jul 18, 2019

MIflyer said:
Actually, I quoted those V-1710 and Merlin figures to Warren Bodie back around 1992 and he replied that he had a copy of the Lockheed analyses that showed putting two stage Merlins in the P-38 would have been a good idea.

I don't have access to Lockheed analysis. That said there is a world of difference between "good idea" and actually redesigning the P-38 wing and booms to accommodate a Merlin 61. Just considering the difference between Cooling/Aftercooling radiator required for the 1650-3 from the Allison V-1710-39 and -81 for the Allison Mustangs leads to approximately 50% more radiator system and must consider placement of carb updraft plenum as well as radiator and oil cooler in the P-38 boom. If the turbo system is removed aft of the engine what does a radiator/aftercooling matrix look like to get the volume of cooling fins in the matrix and what config intake scoop? Place somewhere in front and co-exist with carb updraft system for the Merlin? Place aft of the engine (Mustang type), place dual radiators imbedded in the wings w/o interfering with 55 gal LE tanks?

What are the drag considerations? What are performance considerations recalling that late V-1710s actually delivered 1325 and then 1475 BHP with Turbos when all the issues were ironed out in late model J? At 29000 feet the 1650-3 @3000 RPM and delivered ~1200 Hp. So, the reason for a Merlin 2sp/2st engine point to better reliability than was available for P-38H through J-10 at high altitude, not HP delivered

The reason that a new wing was needed for high altitude (and dives) was early onset drag rise and compressibility. Cranking up the HP Available would have been beneficial in all cases but the benefits above 0.6M for the P-38 were quickly obviated by the total Drag.

Note that later in the war Packard built Merlins were being used in Lancasters, Mosquitoes, and Spitfire XVI, as well as the P-82, so it probably would have been feasible to build enough engines for the P-38 at some point.

Although fumbling and bumbling was evident in Material Command thinking in summer 1943 (like some knucklehead moving an order for 1000 spare 1650-1s for FY 1944 P-40L at the sacrifice of 1650-3 deliveries), AAF finally stated that Packard's 1st Priority was to deliver to the NAA demand for the P-51B/C/D. Packard Never met the actual demand as required until the very end of the war. Prior to that time RAF by agreement was to receive 50% of Packard output - which was easily met for the 1650-1/Merlin XX/28 but never for the 1650-3/-7.

Col Cass Hough, Chief of VIII ATS in 1944, pulled two P-38Js in March/1944 and issued orders to have them modified for the Merlin - but was firmly denied permission to execute the conversion. That was the last gasp for the mythical Merlin P-38.

MIflyer · Jul 18, 2019

Lt Col Ward Duncan (9th PHOTO RECON SQUADRON) responded to my bringing up the idea of the Merlins replacing the Allisons with a description of all kinds of things that would have to be changed, just as described above. And perhaps the most important aspect would have been that to use Merlins would have required two different engines for the P-38 (as it did the P-82). V-1710's could be switched from right to left hand prop rotation by changing a single gear, and since the Allisons could have the gearcase removed, that could even be done in the field. For the V-1650-3 half the engines would be unique to P-38's or P-82's (all 20 of them). No doubt it would have been a harder job than on the P-40 or Mustang.

Here is a scan of Warren Bodie's letter to me:

pbehn · Jul 18, 2019

MIflyer said:
And perhaps the most important aspect would have been that to use Merlins would have required two different engines for the P-38 (as it did the P-82). V-1710's could be switched from right to left hand prop rotation by changing a single gear, and since the Allisons could have the gearcase removed, that could even be done in the field. For the V-1650-3 half the engines would be unique to P-38's or P-82's (all 20 of them). No doubt it would have been a harder job than on the P-40 or Mustang.

The Hornet had "handed" Merlins, this was achieved with an idler gear in the reduction casing.

wuzak · Jul 18, 2019

pbehn said:
The Hornet had "handed" Merlins, this was achieved with an idler gear in the reduction casing.

Not only that, Spitfire VIIIs and XIVs were trialled with contra-props in early 1944.

Kevin J · Jul 18, 2019

drgondog said:
Although fumbling and bumbling was evident in Material Command thinking in summer 1943 (like some knucklehead moving an order for 1000 spare 1650-1s for FY 1944 P-40L at the sacrifice of 1650-3 deliveries), AAF finally stated that Packard's 1st Priority was to deliver to the NAA demand for the P-51B/C/D. Packard Never met the actual demand as required until the very end of the war. Prior to that time RAF by agreement was to receive 50% of Packard output - which was easily met for the 1650-1/Merlin XX/28 but never for the 1650-3/-7.

Col Cass Hough, Chief of VIII ATS in 1944, pulled two P-38Js in March/1944 and issued orders to have them modified for the Merlin - but was firmly denied permission to execute the conversion. That was the last gasp for the mythical Merlin P-38.

I imagine something like 15,000 Packard produced Merlins must have been produced for the Avro Lancaster B.3'.

P-38 with Roll-Royce Merlins

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