def induced_velocity(diskload_lb_ft2, dens_alt_ft, atm=None):
"""
Computes the induced velocity at the rotor plane.
:param diskload_lb_ft2: diskloading, lb/ft2
:param dens_alt_ft: density altitude [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: induced velocity at the rotor plane, in ft/s
"""
if atm is None:
atm = uat.stdatm1976(0.0)
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
iv = (diskload_lb_ft2 / (2* rho_slugcf)) ** 0.5
return iv
def dimensionalize_prop_cp(cp_prop, rpm, radius_ft, dens_alt_ft, atm=None):
"""
Converts propeller cp into power ft-lb/s
:param prop_cp: power coefficient
:param rpm: revolutions per minute
:param radius_ft: radius [ft]
:param dens_alt_ft: density altitude [ft]
:param atm: atmosphere object (optional, 1976 used if None)
:return: power [ft-lb/s]
"""
if atm is None:
atm = uat.stdatm1976(0.0)
n = rpm * uu.rpm2n
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
diameter_ft = radius_ft*2.0
power_ftlbs = cp_prop*(rho_slugcf*n**3.0*diameter_ft**5.0)
return power_ftlbs
def dimensionalize_cp(cp, rpm, radius_ft, dens_alt_ft, atm=None):
"""
Converts cp into power ft-lb/s
:param cp: power coefficient
:param rpm: revolutions per minute
:param radius_ft: radius [ft]
:param dens_alt_ft: density altitude [ft\
:param atm: atmosphere object (optional, 1976 used if None)
:return: power [ft-lb/s]
"""
if atm is None:
atm = uat.stdatm1976()
rho_slugcf = atm.rho(dens_alt_ft*uu.ft2m)*uu.kgcm2slugcf
area_ft2 = np.pi * radius_ft**2.0
omega = rpm * uu.rpm2rad_s
power_ftlbs = cp*rho_slugcf*area_ft2*(omega*radius_ft)**3.0
return power_ftlbs
def prop_ct(thrust_lb, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes propeller thrust coefficient
:param thrust_lb: thrust [lb]
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: thrust coefficient
"""
if atm is None:
atm = uat.stdatm1976(0.0)
n = rpm*uu.rpm2n
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
diameter_ft = radius_ft*2.0
ct_prop = thrust_lb/(rho_slugcf*n**2.0*diameter_ft**4.0)
return ct_prop
def prop_cp(power_ftlb_s, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes propeller power coefficient
:param power_ftlb_s: power [ft-lb/s]
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: power coefficient
"""
if atm is None:
atm = uat.stdatm1976(0.0)
n = rpm * uu.rpm2n
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
diameter_ft = radius_ft*2.0
cp_prop = power_ftlb_s/(rho_slugcf*n**3.0*diameter_ft**5.0)
return cp_prop
def cq(torque_ft_lb, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes torque coefficient
:param torque_ft_lb: torque [ft-lb]
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: torque coefficient
"""
if atm is None:
atm = uat.stdatm1976(0.0)
omega_rads = rpm * uu.rpm2rad_s
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
area_ft2 = np.pi*(radius_ft**2.0)
cq = torque_ft_lb/(rho_slugcf * area_ft2 * radius_ft * (omega_rads * radius_ft)**2)
return cq
def prop_torque(prop_cq, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes torque from a torque coefficient
:param prop_cq: propeller torque coefficient
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: torque [ft-lb]
"""
if atm is None:
atm = uat.stdatm1976(0.0)
n = rpm * uu.rpm2n
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
diameter_ft = radius_ft*2.0
torque_ft_lb = prop_cq*rho_slugcf*n**2.0*diameter_ft**5.0
return torque_ft_lb
def thrust(ct, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes thrust from a thrust coefficient
:param ct: thrust coefficient
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: thrust [lb]
"""
if atm is None:
atm = uat.stdatm1976(0.0)
omega_rads = rpm * uu.rpm2rad_s
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
area_ft2 = np.pi*(radius_ft**2.0)
thrust_lb = ct * rho_slugcf*area_ft2*(omega_rads*radius_ft)**2.0
return thrust_lb
def hover_power_calc(thrust_lb, fom, density_alt_ft, radius_ft, atm=None):
"""
Compute hover power in watts
:param thrust_lb: required thrust
:param fom: figure of merit
:param density_alt_ft: density altitude in feet
:param radius_ft: rotor radius in feet
:param atm: atmosphere object, if None use the 1976 standard atmosphere
:return: power [watts]
"""
if atm is None:
atm = uat.stdatm1976(0.0)
area_m2 = np.pi*(radius_ft*uu.ft2m)**2.0
rho_kgcm = atm.rho(density_alt_ft*uu.ft2m)
thrust_N = thrust_lb * uu.lb2n
power_watts = thrust_N/(fom*np.sqrt(2.0*rho_kgcm/(thrust_N/area_m2)))
return power_watts
def cp(power_ftlb_s, dens_alt_ft, rpm, radius_ft, atm=None):
"""
Computes power coefficient
:param power_ftlb_s: power [ft-lb/s]
:param dens_alt_ft: density altitude [ft]
:param rpm: revolutions per minute of the rotor [rpm]
:param radius_ft: radius [ft]
:param atm: atmosphere object, if None the 1976 standard atmosphere will be used
:return: power coefficient
"""
if atm is None:
atm = uat.stdatm1976(0.0)
omega_rads = rpm * uu.rpm2rad_s
rho_slugcf = atm.rho(dens_alt_ft * uu.ft2m) * uu.kgcm2slugcf
area_ft2 = np.pi*(radius_ft**2.0)
cp = power_ftlb_s/(rho_slugcf*area_ft2*(omega_rads*radius_ft)**3.0)
return cp