Originally Posted by
Patrick Illner
Hello there,
I am trying to calculate the Ground Roll Distance for a Learjet 35, however I am having some difficulties getting to the correct result.
I attached a PDF with my calculation.
Maybe somone can find my mistake.
Thanks to all.
Patrick
I don't think I ever could, but out of curiosity, where did you find this formula?
And seeing as you have Vlof, wouldn't it be easier to assume constant acceleration?
F=M*a , so: 31.000 = 8200 * a , so a = 3.8m/s^2
t=(v2-v1)/a , so t = (73 - 0)/3.8 , so t = 19s
(142 kts = 73m/s)
s = 1/2at^2 , so s = 1/2 * 3.8 * 19^2 , so s = 685m or around 2,250 feet, acceleration probably isn't constant so your number could be right for a sea level departure at ISA on a Lear with all engines running.
Don't know where you get the 1700m from, but no-way you would take 1700m for ground roll a Lear. The numbers I see are 5,000ft so around 1700m for TODR, and that includes climbing to 50 feet with one engine failed at V1, at max gross.