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wdolson -> RE: Jap "Heavy" bombers (8/6/2014 12:23:40 AM)
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The octane rating is the rating on how fast the fuel burns. The higher the rating the slower the burn. With low octane fuel, the fuel burns quickly and hammers the piston with a quick jolt. With high octane fuel, the fuel continues to burn as the piston moves so there is a constant push to the cylinder throughout the stroke. The engine has to be tuned to take best advantage of this which is why putting high octane fuel in an engine tuned for lower octane fuel is a waste of money, though it doesn't really do harm to use higher octane fuel than the engine needs.
With the higher octane fuel and the engine tuned right, you can get more power out of the displacement. Modern engines do some sort of electronic magic to get massive performance out of small engines. My SOs new Subaru's engine has almost the same power and torque out of its 4 cylinder engine as I get out of my 90s vintage 350 cu inch V-8. My expertise is in embedded processors which do that sort of thing, and I'm still massively impressed. But that's 21st century technology. In the mid-20th century, one of the few options to get better performance out of the displacement you had was to boost the octane.
American engine technology was also better than the Japanese, but that point had already been made. The Japanese surprised the west with the quality of their airframes, but their best engines at the start of the war were licensed copies from other countries. The Sakae engine that powered the Zero was a copy of a Gnome Rhone engine from the French.
The US started the war with the P&W 2800 just going into production. It powered the B-26, P-47, F6F, F4U, and A-26. At the time it was one of the world's largest radial engines and there were two others even bigger in development. The Japanese had lost access to quality foreign engine designs except from Germany and the lifeline to get that technology involved a perilous and long journey. The Japanese had to step up their engine designs on their own and they did develop larger engines and put them into production by the end of the war, but they were still working out the bugs when the war ended.
The US was about 4 years ahead of Japan in engine designs.
The B-26 had a lot more horsepower to work with than any contemporary medium bomber with 2X 2000 HP engines. The B-25 used smaller engines, but it was an excellent and versatile design. It became the predominant skip bomber because it handled like a fighter. North American had some of the best American aircraft designs of the era. Three of the most common WW II vintage planes still flying are NA aircraft: The AT-6, B-25, and P-51.
I can't tell you for sure why the B-25 did have better load carrying capability than similarly powered Japanese aircraft. I've never looked into it. However, if you consult reliable sources that compare the different designs using the same criteria, you will find the load values for the B-25 are generally more than other aircraft with similar horsepower available.
I do know that by mid war at least most B-25s were flying on 140 octane fuel. My father said that a favorite trick guys he knew would do was to fill their cigarette lighters with 140 octane fuel from a small drain on the engine of the B-25 then go into town (this was stateside before he shipped out to New Guinea in late 1943). They would wait until someone put a cigarette in their mouth and offer to light it for them. They would get a flame about a foot long. I would think the lighter would get very hot too. He never did it because he never smoked and never had a lighter, he just witnessed other people do it.
Bill
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