- #1
KarenRei
- 100
- 6
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 ;)