Effectiveness of the P-38 (2 Viewers)

[GregP]

Sadly, that means at just under 40 years old I'm sort of a youngster LOL. And the closest museum dedicated to aviation to me is the NMUSAF at Wright Patterson AFB in Dayton, and that's a 4 hour drive.

Also ironic is that I tend to collect physical media of (among other things) World War II aviation, though there I'm hoping to add to that digital stuff from some archives.

Talk to me BarnOwlLover.

Our museum sometimes has many things for sale in the giftshop. I recently got a fork and blade rod / piston from a Griffon from the gift shop, and they had pistons and rods from Merlins available for a long time.

Over time, I have a rod, wrist pin, and piston set from an Allison V-170, a backfire screen from an Allison, and the rods, bearings, and a piston from a Griffon. I'll likely get a Merlins set in the future and could likely snag one for you. They aren't plentiful, but come up every once in awhile. PM me if interested.

 

[BarnOwlLover]

Might be worth considering, but finances for me are hard to come by after bills and other commitments each month. But I'll considering sending a PM for more info soon.

 

[Reluctant Poster]

Not really. The Spitfire pilots were given a list of possible rpms and boost levels for the same speeds at different altitudes that would give the lowest fuel burns.
They were certainly instructed to fly faster as it took a Spitfire V a couple minutes to go from slow cruise to full speed.
Using a faster cruise speed at lower rpm and higher boost combination still allowed tactical flexibility while keeping the fuel burn either the same or lower.

Actual speed/s of the unit/formation were selected based on the expected threat level. High threat meant high speed (2650rpm and +5lbs ?) but a lower threat might call for 2000rpm and 3 3/4lbs instead of 2650rpm and 2lbs of boost. Same airspeed but less fuel burn. Getting from 280mph to 340mph + was going to take a while regardless of engine rpm at start but trying to go from 225mph to 340mph was going to be a lot slower even if the engine was doing 2650rpm at -3lbs.

Problem with the P-38s, especially once you get to the later versions was that the turbo maxed out at 26,300-26,400rpm.
If the plane was cruising at high RPM and low boost the turbo bypass (waste gate) was mostly open and the turbo was down the low teens (?). You are in real turbo lag land if you are flying higher than 20,000ft. You need the turbo to make high power. Without the turbo you are lucky to have 800hp per engine at 20,000ft. With the turbo, even if only turning in the high teens, you have more power even if the engine is not quite up to the full 3000rpm.

Per Morgan and Shacklady they were specifically told to use 2650 rpm and +5 lb boost when they might encounter FW 190s. Note that this is near maximum revs but no where near maximum boost. As you yourself pointed out if you want quick response in a car you drive in a lower gear i.e. keeping the revs up. This is the same concept. The down side is the increased fuel consumption at higher revs due to increased internal friction as well as throttling losses.

 

[Reluctant Poster]

To me it appears there were two fuel problems, and they were over 1 year apart.
The early problem (British 20% min and US 2% max) went away in late 1941 or early 42, before P-38s showed up in England.
The US had already agreed to use much higher amounts of aromatic compounds for 100/125 fuel and test batches should have been sent to all engine makers to try to catch problems.
The 100/125 joint specification didn't last long, a few weeks or months and was superseded by the first 100/130 specification.

I don't know if some people in the US were using "British fuel" as a shorthand for the 100/130 fuel. Or were using "British fuel" as shorthand for a blend favored by the British. Agreements on fuel were not easy. USN and US Army didn't agree on amounts of certain compounds let alone agreeing with the British. The British were pushing aromatic amines to enhance rich mixture response. Shell (British) chose monomethyl amine to concentrate on, shortened to methyl amine. This worked well in for rich mixture but gave no benefit to lean mixture, in fact it sometimes degraded lean mixture. British in early work were more interested in better rich mixture performing fuel than increase production. US was interested in lean mixture cruise so there conflicts right away. Standard Oil of California wanted to use Xylidine instead of methyl amine.
The late 1942 fuel standard for 100/130 is always listed as going to 4.6cc per US gallon for lead but other changes are not given except to say that more heavy aromatics were allowed. It was this fuel that gave the problems with the P-38s and it was anticipated that the heavier aromatics would give problems and small batches of fuel were manufactured and give to engine makers to see what problems there might be. But in short histories of fuel they never say what these heavier aromatics are. Turns out the radials with their short intakes didn't have the same problems as the Allison and British problems or lack of problems are not recorded by the most popular writer.
It was found that this type of fuel would separate out and puddle in the intake manifolds of the Allison engines and the "Madam Queen" intakes were developed to counter it, on ALL Allison engines not just the P-38s although little or no trouble seems to have occurred in service.
P-38s only operated in England for a short period of time in 1942 before going to North Africa. They didn't go back to England until the Summer of 1943.

As I have said before, by this time the US 100 octane fuel with 2% is long gone. But there was a fuel that was going to give problems in 1942/43 and it was known and things were being done, maybe not fast enough. Depending on who was writing reports/letters there may certain blend/s of fuel that some people called "British fuel".

In the US there was quite a controversy over using Xylidine and the Navy wanted no part of it. They thought that water injection was better solution than using Xylidine in the fuel to push past the 100/130 fuel limit and finally refused to accept any fuel that had Xylidine in it. The Army wanted Xylidine for liquied cooled engines and in fact even the army was not in 100% agreement. Wright field was in favor of limited use but was opposed to general use. Xylidine was used in the 100/150 fuel but not 115/145?

I am not saying there were no letters talking about "British fuel". I am not saying there were no problems with the P-38s with some of the fuel the P-38s were using in England in 1943 (or even in other places in fewer incidents). I don't know if there are not some terse notes about "Army" and "Navy" fuels floating around in late 1943/early 1944.
But what was "British fuel"? and how did it differ, especially considering all the different possible blends that could be involved.
Any P-38s, P-39s or P-40s using WEP power in the fall of 1942 (or unauthorized in mid 1942) was using 100/130 or perhaps 100/125, they sure were not using 100/100 US 1940 fuel without blowing up the engines. I am not sure anybody got the 100 octane fuel from Burma, Malaya, DEI back to lab to be tested.

I am also unclear about how re-jetting fixed the problem. I may not have the needed knowledge but doesn't jetting simply mean either leaning the mixture or richening the mixture?
Perhaps the mixture was too rich for cruise allowing the puddling to happen? But changing the jets should not stop heavier compounds from separating out or cause lead to not separate out either?

The aromatic added in 1942 was Cumene (Isopropylbenzene) . Lots of Cumene

As you can see Cumene was responsible for a massive increase in US production of Aviation gasoline. Also note that conversion of the existing Houdry CAT cracking plants was significant as well. The base stock produced by those plants also contained aromatics. Toluene is another aromatic but it was mostly reserved for other purposes.
I have posted extensively on the subject. I suggest anyone interested in the subject look at the materials I have posted in the past.

Sam Heron from his book Development of Aviation Fuels:
"In lieu of suitable straight run gasolines, aromatics and the sensitive cat cracked gasolines (which largely owed their sensitive and rich mixture properties to aromatics) became desirable material for making Grade 100/130 in maximum quantity."
For non cat cracked gasoline the aromatic cumene (isopropyl benzene) was the solution to improving rich mixture response. "For every 1000 gallons of benzol which were allotted about 1,200 gallons of cumene could be produced; production soon reached about a quarter of a million gallons a day and it soon proved to be of considerable value in increasing the output of Grade 100/130."

125 became standard in July 1942 replaced by 130 in January 1943

Xylidine was used as a substitute for Cumene but was ultimately unsuccessful. It was produced in limited quantities and never used overseas. The Navy didn't want it as lost its Xylidine when it was stored over water in the avgas tanks. It was also a much more powerful solvent attacking rubber lined fuel tanks.