- #1

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## Main Question or Discussion Point

Hi - I just want to know if I'm approaching this correctly. I'm trying to calculate the equilibrium velocity of a propeller-driven aircraft when supplied a given amount of power. I'm iterating:

min_velocity = 0.01

max_velocity= 200

aircraft_velocity = 5

for i in range(steps):

That is: calculate drag at the current speed, figure out how bad the efficiency would need to be for the given power level to overcome it, calculate the rotation rate, use it to get the advance ratio, lookup the advance ratio in an efficiency table (which I found on some random website), and then either A) increase the speed if the needed efficiency is less than what the propeller should get at that advance ratio, or B) decrease the speed if the needed efficiency is greater than what the propeller should get.

Is this a reasonable way to approach this? Also, I'm calculating a rough wake velocity as:

wake_velocity = 0.5 * (aircraft_velocity + sqrt(4 * force + air_density * square(aircraft_velocity)) / air_density))

.. based on

F = rho * V_wake * (V_wake - V_free)

Does this seem correct? I haven't done much work with airfoils before, so please excuse me if I'm tackling this poorly ;)

min_velocity = 0.01

max_velocity= 200

aircraft_velocity = 5

for i in range(steps):

force = 0.5 * air_density * aircraft_velocity^2 * drag_coefficient

torque = force * propeller_diameter

calculated_efficiency = force * aircraft_velocity / power_in

rotation_rate = power_in / (2 * pi * torque * calculated_efficiency)

advance_ratio = aircraft_velocity / rotation_rate / propeller_diameter

real_efficiency = lookup_efficiency(advance_ratio, efficiency_table)

if real_efficiency < calculated_efficiency:

torque = force * propeller_diameter

calculated_efficiency = force * aircraft_velocity / power_in

rotation_rate = power_in / (2 * pi * torque * calculated_efficiency)

advance_ratio = aircraft_velocity / rotation_rate / propeller_diameter

real_efficiency = lookup_efficiency(advance_ratio, efficiency_table)

if real_efficiency < calculated_efficiency:

min_velocity = aircraft_velocity

aircraft_velocity = aircraft_velocity * 0.5 + max_velocity * 0.5

else:aircraft_velocity = aircraft_velocity * 0.5 + max_velocity * 0.5

max_velocity = velocity

aircraft_velocity = aircraft_velocity * 0.5 + min_velocity * 0.5

aircraft_velocity = aircraft_velocity * 0.5 + min_velocity * 0.5

That is: calculate drag at the current speed, figure out how bad the efficiency would need to be for the given power level to overcome it, calculate the rotation rate, use it to get the advance ratio, lookup the advance ratio in an efficiency table (which I found on some random website), and then either A) increase the speed if the needed efficiency is less than what the propeller should get at that advance ratio, or B) decrease the speed if the needed efficiency is greater than what the propeller should get.

Is this a reasonable way to approach this? Also, I'm calculating a rough wake velocity as:

wake_velocity = 0.5 * (aircraft_velocity + sqrt(4 * force + air_density * square(aircraft_velocity)) / air_density))

.. based on

F = rho * V_wake * (V_wake - V_free)

Does this seem correct? I haven't done much work with airfoils before, so please excuse me if I'm tackling this poorly ;)