Question

The predator uav has the following characteristics: has the following characteristics: wingspan = 14.85 m, wing area = 11.45 m2, maximum weight = 1020 kgf, and fuel weight = 295 kgf. the power plant is a rotax four-cylinder, four-stroke engine of 85 horsepower driving a two-blade, variable-pitch pusher propeller. assume that the oswald efficiency factor 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 kgf of fuel per horsepower per hour. calculate the following:

1: maximum velocity at sea level.

2: the maximum range

3: the maximum endurance

Answer 1

Maximum Velocity:
The maximum velocity at sea level can be found using the following equation:

V_max = sqrt((2 * W) / (rho * S * CL_max))

where:

W = maximum weight = 1020 kgf
rho = air density at sea level = 1.225 kg/m^3
S = wing area = 11.45 m^2
CL_max = maximum lift coefficient = (2 * W) / (rho * V^2 * S)

To find CL_max, we need to assume a value for the velocity V and iterate until convergence. Let's start by assuming V = 70 m/s:

CL_max = (2 * 1020 kgf) / (1.225 kg/m^3 * (70 m/s)^2 * 11.45 m^2) = 1.87

Now we can use this value to find the maximum velocity:

V_max = sqrt((2 * 1020 kgf) / (1.225 kg/m^3 * 11.45 m^2 * 1.87)) = 35.5 m/s

Therefore, the maximum velocity of the Predator UAV at sea level is approximately 35.5 m/s.

Maximum Range:
The maximum range can be found using the following equation:

R = (L/D) * (1/OE) * ln(Wi/Wf)

where:

L/D = lift-to-drag ratio = CL / CD
CL = lift coefficient = W / (0.5 * rho * V^2 * S)
CD = drag coefficient = CD_0 + (CL^2 / (pi * e * AR))
CD_0 = zero-lift drag coefficient = 0.03
e = Oswald efficiency factor = 0.7
AR = aspect ratio = (wingspan)^2 / S
OE = overall efficiency = propeller efficiency * engine efficiency
propeller efficiency = 0.9
engine efficiency = 0.85 (assuming 85 horsepower for the engine)
Wi = initial weight = maximum weight + fuel weight = 1020 kgf + 295 kgf = 1315 kgf
Wf = final weight = maximum weight

We can start by assuming a value for the velocity V and iterating until convergence. Let's start with V = 25 m/s:

CL = 1315 kgf / (0.5 * 1.225 kg/m^3 * (25 m/s)^2 * 11.45 m^2) = 1.67
AR = (14.85 m)^2 / 11.45 m^2 = 19.3
CD = 0.03 + (1.67^2 / (pi * 0.7 * 19.3)) = 0.071
L/D = 1.67 / 0.071 = 23.5
OE = 0.9 * 0.85 = 0.765
R = 23.5 * (1/0.765) * ln(1315 kgf/1020 kgf) = 393 km

Now we can try a different value for V, let's say V = 30 m/s:

CL = 1315 kgf / (0.5 * 1.225 kg/m^3 * (30 m/s)^2 * 11.45 m^2) = 1.24
AR = (14.85 m)^2 / 11.45