P38 with Merlins

[drgondog]

Here is something I copied down years ago, after this same discussion on another forum.
It discusses both the proposed Merlin version and the single test example fitted with "paddle-blade" props, and the changes required for either (ideally, both at the same time).

It mentions the reason neither was actually done - the changes on the production line would disrupt production flow, which was NOT acceptable to the government. Note that the War Production Board had 100% control of what was produced, by whom, and when - and that many similar improvements to Government-contracted aircraft from many different manufacturers met exactly the same veto unless requested by the US military branch the aircraft were for, or the change could be implement with no appreciable effect on production rates.

Note the sections I have bolded:




So, the "paddle-blade" prop would have fixed the climb issue with the Merlin, and would have improved altitude performance as well - at the cost of a major redesign of the aircraft, and a significant disruption and delay in production.

As the saying goes: "Perfect is the enemy of good enough".

More "good enough" aircraft NOW and later as well is normally preferable to a "better" aircraft later AND fewer "good enough" aircraft in the interim.

What you failed to notice was the test weight of the P-38K compared to P-38J - which was 600 lbs under combat weight for the P-38K. Under similar conditions the P-51B-1-NA, at 8600 lbs GW, had a ROC of 4200 fpm and top speed of 450mph at 29000. (reference NAA test by Chilton May 1944)

 

[Reluctant Poster]

Allison was begging Material Command for new orders in fall of 1943 as its Mustang/Allison production forecast disappeared with the advent of the Merlin Mustang production orders in fall 1942. It was projected at 50% capacity for 1944 (which was real).

Yes. Allison was the only US engine builder to produce fewer engines in 1944 as compared to 1943. The others increased their outputs substantially.
Note that the V-1710 was cancelled shortly after VE Day while the V-1650 lasted until VJ Day.

 

[Admiral Beez]

Yes. Allison was the only US engine builder to produce fewer engines in 1944 as compared to 1943.

Perhaps they should have improved their product to make it competitive or superior to the Merlin?

 

[Shortround6]

Unfortunately Brodie could play just a little bit fast and loose with the timeline and a few technical details.

"The installation of Rolls Royce XX Merlins was seriously considered. Lockheed went as far as designing the installation package. The advantages of the Merlin engine were numerous. First and foremost was the elimination of the complex turbocharger system. This would also result in a much cleaner engine nacelle. The turbo intercoolers could be removed. That would have allowed for a for more aerodynamic package, closer in shape to that of the original XP-38."

The XP-38 had such nicely streamline looking nacelles, in part, because it's engines used the same long pointy reduction gears as the early P-40s. Once they went to the spur gear reduction gear the propshaft was raised 6in. No amount of turbocharger equipment removal was going to lower the propshaft back to or anywhere near the level of the XP-38.
Please note that the British 322 aircraft used the same long nose reduction gear.

These are the nacelles Brodie seems to have an issue with.

these Nacelles being used on all the early P-38s (British 322s excepted) and up until the J version.

At the time the Merlin XX was was under consideration there were no intercoolers in the cowl to remove. the intercoolers were in the wing leading edge.

" Another option was to remove the Prestone radiators and place them under the engine as in the P-40. This location had the additional advantage of reducing the length of the cooling system plumbing. This, in turn, reduced the risk of battle damage to the system. Either option would result in a significant reduction in drag and weight. "

Less battle damage yes, significant reduction in Drag???? I don't think so. You can't have it both ways, either the chin intercoolers were high drag or they were not, you can't shove radiators into the same space as the later intercoolers and claim low drag. Please not the existing radiators are well aft of the center of gravity, moving them up behind the propeller is gong play havoc with the CG. Reduction in weight is the weight of the cooling lines back and forth and the amount of coolant in them. 10-20lbs?




'A further benefit would be gained by the removal of intercooler ducting in the front portion of the outer wings. This volume could be utilized for increased fuel capacity. In fact, that is what was done when the P-38J was designed with revised intercooler cores that eliminated the ducting. This increased internal fuel capacity by 110 gallons."

Wait a minute, I thought (according to Brodie) that the turbo intercoolers were in the nacelle and by getting rid of them we could have a much more streamline nacelle? WOW, these early P-38s had double intercoolers?

"Service ceiling would also be reduced as the Packard Merlin XX made considerably less power above 30,000 feet than did the Allison V1710 "

30,000ft? try 27,000ft or so, it rather depends on which P-38. The D & E was rated at 1150hp at 25,000ft. The F was rated at 1240hp at 21,000ft and 1325hp at 15,000ft due to cooling problems. the G could make the same 1240hp at 21,000ft but was rated at 1425hp at 15,000ft. It could also make 1100hp at 24,000ft at max continuous (2600rpm/41in)
Now the G was limited by both the radiators and the intercoolers. But hey, ditch the stock radiators and use P-40 radiators up under the engine, right? the fact that the air is much less dense at 25,000ft than it is at 15-18,000ft you need bigger radiators (or at least more airflow) for the same power at higher altitudes doesn't matter, right?

The H used larger radiator ducts and cooled better and could use more power higher up, the J used the new intercoolers and made even more power.

Power between the Allisons used the early P-38s and Merlin XX is going to see saw back and forth a bit depending on what boost limits are available on which engine when.