def cp2bhp(Cp,
rpm,
density,
dia,
power_units='hp',
density_units='lb/ft**3',
dia_units='in'):
"""
Returns the bhp, given propeller power coefficient (Cp), revolutions per
minute (rpm), and propeller diameter.
The power units may be specified as "hp", "ft-lb/mn", "ft-lb/s", "W"
(watts) or "kW" (kilowatts), but default to "hp" if not specified.
The density units may be specified as "lb/ft**3", "slug/ft**3" or
"kg/m**3", but default to "lb/ft**3" if not specified.
The diameter units may be specified as "in", "ft", or "m", but default
to inches if not specified.
"""
# bhp = U.power_conv(bhp, from_units = power_units, to_units = 'W')
density = U.density_conv(density,
from_units=density_units,
to_units='kg/m**3')
dia = U.length_conv(dia, from_units=dia_units, to_units='m')
bhp = Cp * (density * ((rpm / 60.)**3) * dia**5)
bhp = U.power_conv(bhp, from_units='W', to_units=power_units)
return bhp
def BMEP(bhp, rpm, disp, power_units=default_power_units, vol_units=default_vol_units, press_units=default_press_units):
"""
Return brake mean effective pressure, given brake power, rpm and displacement.
Rpm is revolutions per minute.
"""
bhp = U.power_conv(bhp, power_units, 'hp')
disp = U.vol_conv(disp, vol_units, 'in**3')
bmep = 2 * bhp * 33000. * 12 / (rpm * disp)
return bmep
def eff2thrust(eff, bhp, TAS, power_units="hp", speed_units="kt", thrust_units="lb"):
"""
Returns thrust, given prop efficiency, true airspeed and brake power.
Matches the results from the Hartzell prop map program fairly closely.
"""
TAS = U.speed_conv(TAS, from_units=speed_units, to_units="m/s")
bhp = U.power_conv(bhp, from_units=power_units, to_units="W")
thrust = eff * bhp / TAS
return U.force_conv(thrust, from_units="N", to_units=thrust_units)
def eff2thrust(eff,
bhp,
TAS,
power_units='hp',
speed_units='kt',
thrust_units='lb'):
"""
Returns thrust, given prop efficiency, true airspeed and brake power.
Matches the results from the Hartzell prop map program fairly closely.
"""
TAS = U.speed_conv(TAS, from_units=speed_units, to_units='m/s')
bhp = U.power_conv(bhp, from_units=power_units, to_units='W')
thrust = eff * bhp / TAS
return U.force_conv(thrust, from_units='N', to_units=thrust_units)
def BMEP(bhp,
rpm,
disp,
power_units=default_power_units,
vol_units=default_vol_units,
press_units=default_press_units):
"""
Return brake mean effective pressure, given brake power, rpm and displacement.
Rpm is revolutions per minute.
Example:
>>> BMEP(200, 2700, 360, vol_units="in**3")
162.96296296296296
"""
bhp = U.power_conv(bhp, power_units, 'hp')
disp = U.vol_conv(disp, vol_units, 'in**3')
bmep = 2 * bhp * 33000. * 12 / (rpm * disp)
return bmep
def bhp2Cp(bhp, rpm, density, dia, power_units="hp", density_units="lb/ft**3", dia_units="in"):
"""
Returns the propeller power coefficient, Cp, given power, revolutions per
minute (rpm), and propeller diameter.
The power units may be specified as "hp", "ft-lb/mn", "ft-lb/s", "W"
(watts) or "kW" (kilowatts), but default to "hp" if not specified.
The density units may be specified as "lb/ft**3", "slug/ft**3" or
"kg/m**3", but default to "lb/ft**3" if not specified.
The diameter units may be specified as "in", "ft", or "m", but default
to inches if not specified.
"""
bhp = U.power_conv(bhp, from_units=power_units, to_units="W")
density = U.density_conv(density, from_units=density_units, to_units="kg/m**3")
dia = U.length_conv(dia, from_units=dia_units, to_units="m")
Cp = bhp / (density * ((rpm / 60.0) ** 3) * dia ** 5)
return Cp
def test_04(self):
Value = U.power_conv(0.74569987, from_units='kW',
to_units='ft-lb/s')
Truth = 550
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_03(self):
Value = U.power_conv(550, from_units='ft-lb/s', to_units='kW')
Truth = 0.74569987
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_02(self):
Value = U.power_conv(33000, from_units='ft-lb/mn', to_units='hp'
)
Truth = 1
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_01(self):
Value = U.power_conv(1, from_units='hp', to_units='ft-lb/mn')
Truth = 33000
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_04(self):
Value = U.power_conv(0.74569987, from_units='kW', to_units='ft-lb/s')
Truth = 550
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_03(self):
Value = U.power_conv(550, from_units='ft-lb/s', to_units='kW')
Truth = 0.74569987
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_02(self):
Value = U.power_conv(33000, from_units='ft-lb/mn', to_units='hp')
Truth = 1
self.failUnless(RE(Value, Truth) <= 1e-5)
def test_01(self):
Value = U.power_conv(1, from_units='hp', to_units='ft-lb/mn')
Truth = 33000
self.failUnless(RE(Value, Truth) <= 1e-5)
