Quote:
Originally Posted by Old Tele man
Cross-country race planes back in the 1930-40's would fillup with COLD fuel and takeoff in the morning because as the day warmed up, so did the fuel, which then expanded in volume...essentially allowing a 100 gallon fuel tank to contain MORE than 100 gallons.
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The thermal expansion coefficient for gasoline is 0.00053, so if the pilot filled his tanks with 100 gallons of gas at 60 degrees F in the morning, that pilot's tanks would be holding 101.59 gallons of gas when the temps got up to 90 degrees F later on that day. But, pilots flying distances cross country usually climb to a high altitude for more efficient flying and the air temps at 25,000 feet certainly aren't going to be at 90 degrees F.
The temperature lapse rate is 3.56 degrees F /1000 feet. If the pilot took off from an airfield at 1000 feet above sea level on a 90 degree F day and leveled off for his cruise at 25,000 feet above sea level, his outside air temp would be 5 degrees F, so the fuel wouldn't remain at a temp of 90 degrees F for very long. Since the big radial engines used by air racers in the 1930's typically had fuel burn rates in the 20 to 30 gallons per hour range, even if that pilot had a 1.59 gallon increase in fuel on board, that increase would only translate into a few minutes of additional run time. I guess every little bit of advantage they could get helped.