P-38 with Merlin Engines? Any such animal?

Messy1 · 06-24-2008, 04:51 PM

I was watching Showdown on the Military Channel this past weekend. The episode was the P-38 vs. Zero. A question came to mind. Did anyone ever experiment with replacing the Allison engines in the P-38 with RR Merlins? Was this ever done? Was or would there be any benefit? Just curious to see what the many fine minds on here thought or know about this?

HoHun · 06-24-2008, 05:13 PM

Hi Messy,

>Did anyone ever experiment with replacing the Allison engines in the P-38 with RR Merlins? Was this ever done? Was or would there be any benefit?

I believe there were some thoughts historically about such a conversion, but as far as I know no conversion ever resulted.

I once prepared a rough calculation of the effect of using mechanically supercharged Merlins instead of turbo-supercharged Allisons, and while the results vary with the exact subtypes of each engine model one might consider for installation, my conclusion was that the Allisons as installed in the P-38 were an excellent choice for the aircraft, and that the Merlins probably would not have improved general performance even if they could have fit into the same airframe with the same aerodynamic efficiency as the original Allisons.

This conclusion somewhat suprised me, as the Merlin for example enjoys the benefit of a substantial increase in effective power over the rated values from the thrust of its exhausts which the turbo-supercharged Allisons lack, but the greater full throttle height of the Allisons helped to make up for the diference, and possibly more.

This is nothing final of course, just my best guess at the time when I did said analysis a couple of years back.

Regards,

Henning (HoHun)

SoD Stitch · 06-24-2008, 06:17 PM

Not long after the P-38 entered service, Hal Hibbard and Clarence "Kelly" Johnson did propose installing Packard-built Merlins in the Lightning, which would've made the P-38 a world-beater; but the Army Materiel Command told Lockheed that all of the Packard-built Merlins were already slated to go to Mustangs. I have a book which discusses this episode in some detail, I'll see if I can track it down. The author of the book is fairly convinced that there were unknown forces working behind the scenes to deny installing superior engines in the P-38; sounds a little like a conspiracy theory to me, but you gotta wonder why it never happened. With improved high-altitude performance, the up-engined P-38 might've negated the need for the P-51D in the ETO, at least temporarily.

FLYBOYJ · 06-24-2008, 06:35 PM

The Merlin P-38 never happened because there were no guarantee it was really going to improve anything (look at the Merlin powered P-40s) and the engines were GFE - government furnished. It was at the government's request that the Allison was chosen and remained the powerplant of the P-38.

Besides introducing a mod like that was no easy task - the P-51 was way more adaptable to the Merlin than the P-38 - it's not a matter of "just bolting it on." Not only does the nacelle have to be re-designed but the whole QEC had to be re-engineered for ease of assembly and maintenance.

With or without the Merlin, the P-38L was the ultimate P-38 model.

SoD Stitch · 06-24-2008, 07:25 PM

Quote:

Originally Posted by FLYBOYJ

Besides introducing a mod like that was no easy task - the P-51 was way more adaptable to the Merlin than the P-38 - it's not a matter of "just bolting it on." Not only does the nacelle have to be re-designed but the whole QEC had to be re-engineered for ease of assembly and maintenance.

If I had to guess (and I do!), I would say the two-stage supercharger bolted to the rear of the Merlin would've caused major problems installing it on the P-38; the turbo-supercharger for the Allisons was behind the main landing gear on the P-38, in the boom. I think the supercharger on the Merlin would've intruded into the main wheel wells on the P-38, necessitating a complete redesign of the nacelles.

FLYBOYJ · 06-24-2008, 07:25 PM

Yep.....

Messy1 · 06-25-2008, 08:43 AM

Good Info! I was wondering about the engine fit myself. It would have been interesting to see a comparison between an Allison and a Merlin powered P-38.

KrazyKraut · 06-25-2008, 11:22 AM

The P-38 did pretty well with the Allison. In fact it was probably the best plane with that engine. People have to realize that engines aren't available at will. The avialable Merlins were probably put to better use in the P-51 especially with the mentioned modifications needed to the P-38 airframe. You can also speculate how good the Hs-129 could've been with a BMW 801, but these engines were needed elsewhere.

Marshall_Stack · 06-30-2008, 04:27 PM

I read in Warren Bodie's book that there may have been some politics involved with using Allison's over the Merlins. Something to do with an Army officer close to the project used to be an exec with GM (who owned Allison) and probably still had stock in GM.

Warren is pretty much of the opinion that the Merlin would have been a good idea. The turbocharging system was having a problem at high altitude in Northern Europe.

FLYBOYJ · 06-30-2008, 04:45 PM

Although I have a lot of respect for Bodie, I think that's just a myth. Again, the redesign for the installation of merlins would have been immense with no guarantee of substantiated performance.

Again, amazing that the same problems weren't that wide spread in the Pacific.

SoD Stitch · 06-30-2008, 06:09 PM

Quote:

Originally Posted by Marshall_Stack

I read in Warren Bodie's book that there may have been some politics involved with using Allison's over the Merlins. Something to do with an Army officer close to the project used to be an exec with GM (who owned Allison) and probably still had stock in GM.

Warren is pretty much of the opinion that the Merlin would have been a good idea. The turbocharging system was having a problem at high altitude in Northern Europe.

Yes, that's the same book I have; here's what Brodie has to say about the "Army officer close to the project":

"No real proof exists, but it must be a fact of life that Lt. Gen. Knudson was not going to do anything that would hurt General Motors (wartime manufacturer of the Allison engine). After all, he had been a top executive with that corporation for years until he had accepted his appointment to the Office of Production Management at the beginning of the new decade. It would be ludicrous to believe that he would throw more plums to competitor Packard (builder of the Merlins) at the expense of G.M., and it is also likely Knudsen held a large block of stock in the corporation. (In those days, it was not necessary to give up your stock holdings when a "conflict of interest" might occur)."

drgondog · 06-30-2008, 06:18 PM

Quote:

Originally Posted by FLYBOYJ

Although I have a lot of respect for Bodie, I think that's just a myth. Again, the redesign for the installation of merlins would have been immense with no guarantee of substantiated performance.

Again, amazing that the same problems weren't that wide spread in the Pacific.

Two reasons come to mind Joe. Both related

1. The fights in the PTO were so rarely above 15-20K and most were below that altitude - far more like MTO in summer.
2. The relative temps for altitude were higher in PTO versus ETO.

syscom3 · 06-30-2008, 08:30 PM

And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.

FLYBOYJ · 06-30-2008, 08:43 PM

Quote:

Originally Posted by drgondog

Two reasons come to mind Joe. Both related

1. The fights in the PTO were so rarely above 15-20K and most were below that altitude - far more like MTO in summer.
2. The relative temps for altitude were higher in PTO versus ETO.

Point taken and agree, but as we know corrected on the later models...

Quote:

Originally Posted by syscom3

And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.

Yep!!!

Marshall_Stack · 07-01-2008, 01:43 PM

Quote:

Originally Posted by syscom3

And the 11th AF in the Aleutions didn't have the same problems the 8th AF did.

As for that argument (and I am just relaying the info, not claiming to be an expert), I read that the P-38's in the Alaska weren't flying as high (since they were escorting low-flying bombers) and that the temps still weren't as cold as Northern Europe.

I have also read that they operated differently; in one theatre they had high RPMs but low manifold pressure and vice versa. Again I'm not a pilot or expert but that was claimed as a possible difference in performance. I'm interested in comments to this claim.....