The issue that we were initially discussing was the question: IF the 81 gallon tank that contained about 40.5 gallons of 100 octane fuel had been "topped off" with 40.5 gallons of 80/87 octane fuel, THEN would the distance to takeoff have been appreciably lengthened?

I guess you missed this, I put it on a different thread:

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"What Johnson said was correct for a 14,000 pound takeoff without flaps but was definitely NOT TRUE for a 15,000 pound takeoff which takes significantly more than 2,000 feet at standard conditions and even more at the 2,000 foot density altitude at Lae. According to report 487, it takes 2,600 feet to take off without flaps at 16,500 pounds at a sea level density altitude. Doing the same calculations we did before, we find that a takeoff at Lae at a density altitude of 2,000 feet and 15,000 pounds without flaps results in a ground run of 2,278 feet. Lest you think that this is all just theoretical mumbo-jumbo, this calculation agrees quite closely with Chatter's observation of 2,550 feet, a difference of only 272 feet, less than a 12% difference thus Chatter's observation confirms the accuracy of this calculation. (I accept Chatter's report as more accurate in all of it's detail compared to Collopy's short letter.)

It is interesting to look at what would have happened if Earhart had completely filled that tank, adding about 50 U.S. gallons weighing 300 pounds. A takeoff at 15,300 pounds without flaps would have taken 2,370 feet, only 92 feet longer. And if she had put the flaps down to the 30° position specified in report 487 the takeoff would have taken only 1,914 feet providing a 1,086 foot safety margin, 57% extra runway.

We know that Earhart did not fill that tank because she believed that she needed 100 octane fuel to get maximum power out of her engines but Pratt and Whitney documents show that the engines make full takeoff power of 600 horsepower using the 87 octane fuel available at Lae (Jeff Neville disputes this) so she could have filled that tank, made a safe takeoff, and then have an extra hour of flying endurance to find a safe place to land.

Just for the sake of argument, let's say that Neville is correct and that she could only get 550 horsepower from each engine using 87 octane fuel, how would this have affected the takeoff? The length of the takeoff run varies with the inverse of the ratio of the engine power. Report 487 shows 2,100 feet for standard conditions, 30° of flaps, and 16,500 pounds using the full power of 600 horsepower from each engine, a total of 1,200 horsepower so taking off with a total of 1,100 hp gives a takeoff distance 9% longer, 2,290 feet. We adjust this for the takeoff weight of 15,300 pounds as we did before and find 1,970 feet. We then increase this by 6% to account for the density altitude so the complete calculation gives 2,088 feet compared to 1,914 for 1,200 hp (we could have just multiplied the 1,914 by 1.09 too), only 174 feet longer and with 912 foot safety margin, 44% extra runway available. Doing the same calculation for the flaps up scenario produces a takeoff run of 2,585 but this would be cutting it close so Earhart would have to have remembered to set the flaps correctly.

So no matter how you figure it, Earhart unnecessarily left behind an hour's worth of fuel and this fuel could have made a significant difference in the end. "

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That should answer your question.

gl