Fuel Octane differences?

[awrabbit]

No was curious as to if the higher octane fuel was used for testing captured aircraft or if the performance numbers were from the country of origin of the aircraft.

I knew the allies used hotter fuel but, was unclear as to what was used or how the performance numbers were gathered.

 


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There was no rant at all intended.  Just curious and got some education. 

A lot of sharp people involved in this community.  <S>


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[FBKampfer]

It should be noted that the 190A3 and later models were required to use C3 fuel by their BMW 801D's. The chemical synthesis of the artificial C3 fuel was relatively straightforward, but the infrastructure was simply of limited capacity.

Pre war, intention had been to transition the Luftwaffe exclusively to synthetic C3 fuel, leaving refined B4 fuel for the Heer.  But production never managed to reach required levels, and so B4 continued to be used wherever possible, while C3 was for 190 units, and units operating high altitude interceptor variants of the 109, such as the G5, and G6,G14/As models.

Throughout the war, synthetic fuel had shown stability problems, but certainly nothing insurmountable. It was distributed on as-needed basis, and only in 1944 did fuel supply issues affect the Luftwaffe to any significant degree. And it's important to remember that it affected the entirety of the Luftwaffe, including units running B4 fuel.

Thought general logistics isn't my expertise, I would hazard a guess that it was in large measure related to the Allies targeting transportation hubs. Stop the fuel, stop the fighters.

[PR3D4TOR]

B4 is also synthetic. A3 and C2 are natural.

[Krusty]

Concerning testing of captured enemy planes on high octane US fuel...................

Yes the fuel is higher octane and better quality but it will not provide "extra horsepower" over the fuel the airplane was designed to run..............unless the "testers and technicians" who prepared the planes for flight deviated from the factory settings and advanced the ignition timing and raised boost pressure.

The only advantage likely seen by the testing would have been a safety margin concerning detonation.

You're not taking into account the Japanese engine development and wartime practices of the time.

Take, for example, an engine DESIGNED for 130 octane. Now add in such deplorable production quality and then top it off with lack of 130 octane gas. What are you going to do? Just... put some 87 octane in it and tell the pilots "don't run it above xxx inches"

Then what happens when the US (for example) gets a captured version, cleans it up and with no real changes other than making sure it all functions, puts 130 octane gas in it?

The Japanese engine development was full of pittfalls and setbacks and their ambitions surpassed their abilities by a lot. They had more engine teething problems and delays than most US planes had -- and we've had our share! Many of their fuel sources were contaminated, or thinned down with sap-based turpentine just to keep the fight going. It didn't matter if the quality was less, when pilots were still taking the fight to the US forces. Several tales from Zero pilots recount how they used poor fuel and could not meet even the factory specified numbers. The planes would belch and spit and sputter and even trail gray smoke streams at times during combat. This was the norm.

Now imagine that engine got a total overhaul and was fixed with perfect new seals, gaskets, clean oils, fresh gas of the best quality? Guess what -- it's going to behave a HELL of a lot better in the US tests than the Japanese tests.


Just saying...

[Devil 505]

Now imagine that engine got a total overhaul and was fixed with perfect new seals, gaskets, clean oils, fresh gas of the best quality? Guess what -- it's going to behave a HELL of a lot better in the US tests than the Japanese tests.

I doubt that any engine parts were overhauled unless absolutely necessary. Why risk damaging parts that are extremely difficult to get a hold of? And it's not like the plane came with an English language manual for tear-down and assembly procedures.

[PR3D4TOR]

All this speculation is pointless. If someone (and you know who you are) have documentation then post it.

[DaveBB]

Where's the famous KI-84 and KI-100 test documentation?

[Krusty]

Where's the famous KI-84 and KI-100 test documentation?

Oh you mean the documentation that showed that for a time 2/3 crashed on takeoff from the factory into the trees, making the people who built them sad? Or the ones where the engines would never output even at rated basline levels, so much that outdated Kis were faster and more reliable? Or the many reports where Ki-84s would take off but not make enough power to climb up to even mid-level attackers because their engines were struggling to run at all?

Plenty of documentation for all of that has been shown before.


>

[Krusty]

I doubt that any engine parts were overhauled unless absolutely necessary. Why risk damaging parts that are extremely difficult to get a hold of? And it's not like the plane came with an English language manual for tear-down and assembly procedures.

Okay, I mis-used the word "overhaul" -- you're right. But they often did have to do a lot of work on these captured airframes. One they found flipped on its back after force-landing on a tiny island in the middle of the ocean. It had been days before a sub spotted it and more before they could get in there, remove the dead pilot, and figure out how to cart it off. All while sitting on a salt-sprayed beach. Doesn't lend itself to keeping an engine in good keep. They'd try to replace some seals and gaskets if they were brittle and worn, and in some cases (not specific to IJN captures) they had to do a lot of work and were best-guessing what they should do. RAF captured Fw190 tests were pretty well botched because they had unbalanced the trim and weren't running the engine properly. Just one example.

[Zimme83]

But all this is of course irrelevant when we talks about AH as long as mechanical errors and production issues are not modeled. ALL our planes have better performance and reliability than the real world fighters had. Production issues, rushed development, poor fuel and a bad day decreased the performance for most fighters.

We all know that a lot of fighters had a lot of mechanical issues but no one would accept having random engine failures etc just because it happened in the real world..

[PR3D4TOR]

Okay, I mis-used the word "overhaul" -- you're right. But they often did have to do a lot of work on these captured airframes. One they found flipped on its back after force-landing on a tiny island in the middle of the ocean. It had been days before a sub spotted it and more before they could get in there, remove the dead pilot, and figure out how to cart it off. All while sitting on a salt-sprayed beach. Doesn't lend itself to keeping an engine in good keep. They'd try to replace some seals and gaskets if they were brittle and worn, and in some cases (not specific to IJN captures) they had to do a lot of work and were best-guessing what they should do. RAF captured Fw190 tests were pretty well botched because they had unbalanced the trim and weren't running the engine properly. Just one example.

Then wouldn't it be a safer bet to say that the crashed and jury-rigged IJN/IJAAF aircraft in the U.S. tests probably performed worse than in Japanese service, just like the RAF Fw 190. Way to go on shooting down your own argument.

[PR3D4TOR]

Found the report on the U.S. Zeke test:

They had problems with the propeller not allowing maximum RPM.

the propeller on this particular Zero airplane is not set to permit maximum allowable r.p.m. (maximum obtainable r.p.m. was 2075)

They did not use the best available U.S. fuel and recognized that the engine had timing issues and thus had reduced performance during the tests.

91 octane fuel was used in the conduct of all tests, and at full throttle at 10000 feet no detonation was experienced. This indicates that timing was probably slow, insomuch as engine is reportedly designed to operate on 100 octane fuel; normal performance probably was still further reduced thereby.

They did not understand the mixture controls, or the controls themselves were not in working order.

Mixture control - Use of this control is not fully understood, as in the rear position of this lever, mixture control is automatic. Movement of the lever to any forward position at any altitude causes no perceptible change in engine operation.

So they tested a crashed Zeke that they repaired without having spare parts or factory documentation. They did not use any higher grade fuel than what the Japanese were using, they couldn't figure out the mixture controls, the engine timing was off and the propeller governor did not allow maximum RPM. I think it is pretty safe to assume this Zeke performed rather poorly compared to its brethren in Japanese service at the time.

[Krusty]

According to many Japanese pilots that flew it in combat, not so much. Again, you need to get a wider sampling and look at actual war-time records.

It wouldn't be safer to say that it performed better than the test. As a total "system" of combat there were many considerations including the fuel and oil flowing through the engine. It would be safe to say it gave the US a data point when they had none at all. It was SOMEthing for them to look at to use, but it could be better, and it could be worse. For example, the Ta-152-H-0 test flown did about what ours does on WEP but without any "go-juice" because the H-0s and most of the 152s got a mid-life engine retuning to run hotter without actually needing additive boosts. They had factory engineers make the rounds and effect minor changes and this had real world effects on the plane's combat performance that aren't quite reflected in-game. Kind of like the Spit12 got for the fuel flow constrictor in the carbuerator.

[MiloMorai]

Kind of like the Spit12 got for the fuel flow constrictor in the carburetor.

???

[Krusty]

The Spit12 had a gravity-fed carb that would sputter in low-Gs. They put a restrictor on the feed so that it would pool and feed in, so that in moments of low-G it wouldn't sputter out and die. See Miss Shilling's orifice.

EDIT: Not important. Just an example of an comprehensive modification that changed performance for the better.