If AE was flying with one tank of 100 octane because she had been told or led to believe she needed it for extra power on takeoff then why would she have that tank topped up with non 100 octane. She believed she had plenty of fuel, with ample reserve, for the trip to Howland.
She did know that Howland's airstrip had just been constructed and has no idea what shape it was really in. So saving any 100 octane for a "boosted" takeoff on a new runway on a small island would have been prudent. She didn't plan on getting lost and needing every tank to be 100% full. But she did need to plan her takeoff from Howland. If some of the arguments/inferences in this thread are true then why was she carrying two types of octane in the first place?
Because she was misinformed. High octane fuel is needed in
high compression engines to prevent detonation (knock) that can quickly damage the engine. Earhart's S3H1 engines are low compression engines with a compression ratio of only 6:1, designed to make full takeoff power with the 87 octane fuel available at Lae. One hundred octane fuel only became available,
in experimental quantities, in 1934. The S3H1 had been designed to use the existing 87 octane fuel because it takes a lot longer than the one or two years that 100 octane fuel was available, prior to the actual construction of her engines, to design a new aircraft engine. Only one of the 107 other versions of the Wasp engine, many designed during WW2 after 100 octane fuel was freely available, required the use of 100 octane fuel and even that one version only put out 600 hp, just like Earhart's engines. (That one engine type was fuel injected and had many other modifications.) Think about it, there was a lot of pressure and incentive for Pratt & Whitney to increase the power of these engines, ("don't you know, there's a war on") but they were unable to do so even when 100 octane and other even higher octane fuels were available, all the way up to 145 octane.
Ask all of your friends and I bet that they will all say the same thing, that putting high octane fuel in their cars, that have engines that use "regular," will make the car go faster and accelerate faster because the engine will make more power with the "high power," high octane fuel.
All of your friends will be wrong. Simply putting high octane fuel in your low compression engine that is not designed to use high octane fuel, that does not require the use of high octane fuel to prevent detonation, will
not allow the engine to make more power. Apparently, in 1937, this was also a common misconception but, since the 100 octane fuel was just newly available, perhaps this misconception can be forgiven. The power setting table for these engines proves this, using the higher octane 91/96 fuel produces the exact same power output as when using 80/87 octane, the higher octane does not produce more power and the same is true if using 100 octane fuel.
Another question presents itself, where did Earhart get the 100 octane fuel, did she tanker it all the way around the world?
gl
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