def test_03(self):
# Truth values from NASA RP 1046
Value = SA.alt2press_ratio(20000, alt_units='m')
Truth = 5474.87 / 101325
self.assertLessEqual(RE(Value, Truth), 1e-5)
def test_02(self):
# Truth values from NASA RP 1046
Value = SA.alt2press_ratio(-1000)
Truth = 2193.82 / 2116.22
self.assertLessEqual(RE(Value, Truth), 1e-5)
def prop_eff(prop,
bhp,
rpm,
tas,
altitude,
temp='std',
power_units='hp',
alt_units='ft',
temp_units='C',
speed_units='kt',
dia_units='in'):
"""
Returns propeller efficiency based on engine power provided to the propeller.
"""
press_ratio = SA.alt2press_ratio(altitude, alt_units=alt_units)
if temp == 'std':
temp = SA.alt2temp(altitude,
temp_units=temp_units,
alt_units=alt_units)
temp_ratio = U.temp_conv(temp, from_units=temp_units,
to_units='K') / 288.15
density_ratio = press_ratio / temp_ratio
density = density_ratio * SA.Rho0
Cp = bhp2Cp(bhp,
rpm,
density,
prop.dia,
power_units=power_units,
density_units='kg/m**3',
dia_units=dia_units)
J = advance_ratio(tas,
rpm,
prop.dia,
speed_units=speed_units,
dia_units=dia_units)
blade_tip_mach = tip_mach(tas,
rpm,
temp,
prop.dia,
speed_units=speed_units,
temp_units=temp_units,
dia_units=dia_units)
prop_eff = cp2eff(prop, Cp, J, blade_tip_mach)
if N.isnan(prop_eff):
raise ValueError('Out of range inputs')
return prop_eff
def blade_angle2bhp(prop,
blade_angle,
rpm,
tas,
altitude,
temp='std',
power_units='hp',
alt_units='ft',
temp_units='C',
speed_units='kt',
dia_units='in'):
"""
Returns returns engine power, given blade angle, rpm and flight conditions.
"""
press_ratio = SA.alt2press_ratio(altitude, alt_units=alt_units)
if temp == 'std':
temp = SA.alt2temp(altitude,
temp_units=temp_units,
alt_units=alt_units)
temp_ratio = U.temp_conv(temp, from_units=temp_units,
to_units='K') / 288.15
density_ratio = press_ratio / temp_ratio
density = density_ratio * SA.Rho0
# Cp = bhp2Cp(bhp, rpm, density, prop.dia, power_units = power_units, density_units = 'kg/m**3', dia_units = dia_units)
J = advance_ratio(tas,
rpm,
prop.dia,
speed_units=speed_units,
dia_units=dia_units)
blade_tip_mach = tip_mach(tas,
rpm,
temp,
prop.dia,
speed_units=speed_units,
temp_units=temp_units,
dia_units=dia_units)
Cp = blade_angle2cp(prop, blade_angle, J, blade_tip_mach)
bhp = cp2bhp(Cp,
rpm,
density,
prop.dia,
power_units=power_units,
density_units='kg/m**3',
dia_units=dia_units)
return bhp
def blade_angle(prop,
bhp,
rpm,
tas,
altitude,
temp='std',
power_units='hp',
alt_units='ft',
temp_units='C',
speed_units='kt',
dia_units='in'):
"""
Returns propeller blade angle.
"""
press_ratio = SA.alt2press_ratio(altitude, alt_units=alt_units)
if temp == 'std':
temp = SA.alt2temp(altitude,
temp_units=temp_units,
alt_units=alt_units)
temp_ratio = U.temp_conv(temp, from_units=temp_units,
to_units='K') / 288.15
density_ratio = press_ratio / temp_ratio
density = density_ratio * SA.Rho0
Cp = bhp2Cp(bhp,
rpm,
density,
prop.dia,
power_units=power_units,
density_units='kg/m**3',
dia_units=dia_units)
J = advance_ratio(tas,
rpm,
prop.dia,
speed_units=speed_units,
dia_units=dia_units)
blade_tip_mach = tip_mach(tas,
rpm,
temp,
prop.dia,
speed_units=speed_units,
temp_units=temp_units,
dia_units=dia_units)
blade_angle = cp2blade_angle(prop, Cp, J, blade_tip_mach)
return blade_angle
def prop_data(prop,
bhp,
rpm,
tas,
altitude,
temp='std',
power_units='hp',
alt_units='ft',
temp_units='C',
speed_units='kt',
dia_units='in',
thrust_units='lb'):
"""
Returns advance ratio, power coefficient, thrust coefficient, blade tip
mach number, propeller efficiency and thrust.
Validated against Excel spreadsheet provided by Les Doud (Hartzell).
"""
press_ratio = SA.alt2press_ratio(altitude, alt_units=alt_units)
if temp == 'std':
temp = SA.alt2temp(altitude,
temp_units=temp_units,
alt_units=alt_units)
temp_ratio = U.temp_conv(temp, from_units=temp_units,
to_units='K') / 288.15
density_ratio = press_ratio / temp_ratio
density = density_ratio * SA.Rho0
Cp = bhp2Cp(bhp,
rpm,
density,
prop.dia,
power_units=power_units,
density_units='kg/m**3',
dia_units=dia_units)
J = advance_ratio(tas,
rpm,
prop.dia,
speed_units=speed_units,
dia_units=dia_units)
blade_tip_mach = tip_mach(tas,
rpm,
temp,
prop.dia,
speed_units=speed_units,
temp_units=temp_units,
dia_units=dia_units)
prop_eff = cp2eff(prop, Cp, J, blade_tip_mach)
try:
Ct = cp2ct(prop, Cp, J, blade_tip_mach)
except BaseException:
Ct = cp2ct_alt(prop,
Cp,
bhp,
rpm,
tas,
altitude,
temp=temp,
power_units=power_units,
alt_units=alt_units,
temp_units=temp_units,
speed_units=speed_units)
if prop_eff > 0.1:
thrust = eff2thrust(prop_eff,
bhp,
tas,
power_units=power_units,
speed_units=speed_units,
thrust_units=thrust_units)
else:
thrust = ct2thrust(Ct,
density,
rpm,
prop.dia,
thrust_units=thrust_units,
density_units='kg/m**3',
dia_units=dia_units)
# data_block = 'J = ' + str(J) + '\nCp = ' + str(Cp) + '\n Tip mach = ' + str(blade_tip_mach) + '\n Ct = ' + str(Ct) + '\n Thrust = ' + str(thrust) + ' ' + thrust_units + '\n Prop efficiency = ' + str(prop_eff)
print(' prop = ', prop.prop)
print(' J = %.3f' % J)
print(' Cp = %.5f' % Cp)
print(' Tip Mach = %.3f' % blade_tip_mach)
print(' Ct = %.3f' % Ct)
print(' Thrust = %.2f' % thrust, thrust_units)
print('Prop efficiency = %.4f' % prop_eff)
print(' Thrust HP = %.2f' % bhp * prop_eff)
return
def test_01(self):
PR = SA.alt2press_ratio(0)
self.assertEqual(PR, 1)