How to find range and endurance

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Homework Statement


The Predator UAV has the following characteristics: wingspan = 14.85 m,
wing area = 11.45 m2
, maximum mass = 1020 kg, and fuel mass = 295 kg. Note the
weights are given in kg. You should covert them to weight force W in N. The power
plant is a Rotax four-cylinder, four-stroke engine of 85 horsepower driving a two-blade,
variable pitch pusher propeller. Assume the Oswald efficiency is 0.7, the zero-lift drag
coefficient is 0.03, the propeller efficiency is 0.9, and the specific fuel consumption is 0.2
kg(note this mass, not weight) of fuel per horsepower hour


Homework Equations


1.calculate the maximum range.
Hint) Please make sure you use the correct weight of the fuel (Wf=m*g= W0- W1
Also, please compute the correct value of c (SFC) in the SI unit, N/(second*Nm/s).
You have to convert 0.2kg/(hour*hp).
2. calculate the maximum endurance at sea level and


The Attempt at a Solution


1.I think when TR(thrust required) is at min, R(range) is at max, and when CD,0(zero-lift-drag)=CD,i(induced drag), TR is at min.
By doing in this way, I get 7.91*10^6meters, which is much larger than what wikipedia says about the Predator's range.
2.I think when PR(Power required) is at min, E(endurance) is at max, and when CD,0(zero-lift-drag)=1/3*CD,i(induced drag), PR is at min.
By doing in this way, I get 2.674*10^5s, which is much larger than what wikipedia says about the Predator's endurance.

Am I using a wrong method or making a mistake in calculation?
 

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