def pwr2ff(pwr, rpm, mixture='pwr', ff_units='gph'):
"""
Returns fuel flow. Defaults to mixture for best power ("pwr"), but may
also be used with mixture for best economy ("econ"). Fuel flow units
default to USG/hr, but pounds per hour ("lb/hr") and litres per hour
("l/hr") may also be selected.
"""
if mixture == 'pwr':
if rpm >= 2600:
rpm1 = 2600
rpm2 = 2700
elif rpm >= 2400:
rpm1 = 2400
rpm2 = 2600
elif rpm >= 2200:
rpm1 = 2200
rpm2 = 2400
else:
rpm1 = 2000
rpm2 = 2200
ff1 = _pwr_ff_best_power(rpm1, pwr)
ff2 = _pwr_ff_best_power(rpm2, pwr)
elif mixture == 'econ':
if rpm >= 2600:
rpm1 = 2600
rpm2 = 2700
elif rpm >= 2400:
rpm1 = 2400
rpm2 = 2600
elif rpm >= 2200:
rpm1 = 2200
rpm2 = 2400
elif rpm >= 2000:
rpm1 = 2000
rpm2 = 2200
else:
rpm1 = 1800
rpm2 = 2000
ff1 = _pwr_ff_econ(rpm1, pwr)
ff2 = _pwr_ff_econ(rpm2, pwr)
else:
raise ValueError('mixture must be one of "econ" or "pwr"')
# else:
# raise ValueError('Invalid value for mixture.')
ff = ff1 + (ff2 - ff1) * (rpm - rpm1) / (rpm2 - rpm1)
if ff_units == 'lb/hr':
pass
elif ff_units == 'gph':
ff = unit_conversion.avgas_conv(ff, to_units='USG')
elif ff_units == 'l/hr':
ff = unit_conversion.avgas_conv(ff, to_units='l')
else:
raise ValueError('Invalid fuel flow units')
return ff
def test_02(self):
# 200 lb of nominal fuel at -40 deg C to USG
# truth value from Canada Flight Supplement
Value = U.avgas_conv(200., from_units='lb', to_units='USG', temp=-40)
Truth = 200. / 6.41
self.assertLessEqual(RE(Value, Truth), 5e-4)
def test_01(self):
# 10 USG of nominal fuel at nominal temperature to lbs
# truth value from Canada Flight Supplement
Value = U.avgas_conv(10, from_units='USG', to_units='lb')
Truth = 60.1
self.assertLessEqual(RE(Value, Truth), 5e-4)
def test_03(self):
# 200 lb of 100LL grade fuel at 15 deg C to Imperial Gallons
# truth value from Air BP Handbook of Products - 715 kg/m**3
Value = U.avgas_conv(200.,
from_units='lb',
to_units='ImpGal',
grade='100LL')
Truth = (((200. / 2.204622622) / 715) * 1000) / 4.54609
self.assertLessEqual(RE(Value, Truth), 5e-4)
def test_05(self):
# 200 l of 80 grade fuel at -40 deg C to kg
# truth value from Air BP Handbook of Products - 690 kg/m**3 at 15 deg C
Value = U.avgas_conv(200.,
from_units='l',
to_units='kg',
grade='80',
temp=-40)
Truth = (200. / 1000) * 690
# correct for temperature, using ratio given in Canada Flight Supplement
Truth *= 6.41 / 6.01
self.assertLessEqual(RE(Value, Truth), 5e-4)
def test_04(self):
# 200 kg of 100 grade fuel at 30 deg C to l
# truth value from Air BP Handbook of Products - 695 kg/m**3 at 15 deg C
Value = U.avgas_conv(200.,
from_units='kg',
to_units='l',
grade='100',
temp=30)
Truth = (200. / 695) * 1000
# correct for temperature, using ratio given in Canada Flight Supplement
Truth *= 6.01 / 5.9
self.assertLessEqual(RE(Value, Truth), 5e-4)
def power_lop(ff, n, ff_units='USG/h'):
"""
Alternate, very simplified and approximate method to determine power, for
lean of peak operations. Optimized for operations at 50 deg F lean of
peak on Lycoming IO-360A series engines. This was a trial, and initial
testing suggests this function is not adequately accurate.
"""
ff_units = ff_units[:-2]
ff = unit_conversion.avgas_conv(ff, from_units=ff_units, to_units='USG')
a, b, c, d, e, f, g, h, i = [
4.61824610e+00, -7.90382136e-01, -4.09623195e-03, 7.58928066e-04,
-3.51093492e-05, -1.87325980e-07, 8.64253036e-09, 3.65001722e-02,
1.02174312e-06
]
sfc = a + b * ff + c * n + d * ff * n + e * ff**2 * n + \
f * ff * n**2 + g * ff**2 * n**2 + h * ff**2 + i * n**2
pwr = ff * 6.01 / sfc
return pwr
def power(ff,
ff_at_pk_EGT,
rpm,
CR=8.7,
displacement=360,
ff_units='USG/h',
fric_power_factor=1):
"""
Returns engine power, based on fuel flow data. Based on an internal
Lycoming document, apparently for use during flight test programs.
ff = fuel flow
ff_at_pk_EGT = fuel flow at peak EGT
rpm = engine speed
CR = compression ratio. Allowable values are 6.75, 7, 7.2,
7.3, 8, 8.5, 8.7 or 9 (10 to be implemented later).
displacement = engine displacement in cubic inches. Allowable values are
235, 320, 360, 480, 480S, 540, 540S, 541 or 720.
The suffix S denotes GSO or IGSO engines.
# type = type of fuel delivery system. Allowable values are
# 'port_injection', 'carb', and 'single_point' (i.e fuel
# injected at a single point, prior to the intake tubes).
# This input is not yet implemented, as it is only needed
# for an alternate method, for high power conditions where
# it is not safe to lean to peak EGT.
ff_units = fuel flow units. Allowable values are 'USG/h', 'ImpGal/h',
'l/h', 'lb/h', and 'kg/h'
"""
ff_units = ff_units[:-2]
ff = unit_conversionavgas_conv(ff, from_units=ff_units, to_units='lb')
ff_at_pk_EGT = unit_conversion.avgas_conv(ff_at_pk_EGT,
from_units=ff_units,
to_units='lb')
ff_best_mixture = ff_at_pk_EGT / .849
SFC_best_mixture = iSFC(CR)
best_mixture_pwr = ff_best_mixture / SFC_best_mixture
ihp = best_mixture_pwr * pwr_ratio_vs_ff_ratio(ff / ff_best_mixture)
try:
imep = piston.BMEP(best_mixture_pwr,
rpm,
displacement,
power_units='hp',
vol_units='in**3')
disp_numeric = displacement
except TypeError:
disp_numeric = int(displacement[:3])
imep = piston.BMEP(best_mixture_pwr,
rpm,
disp_numeric,
power_units='hp',
vol_units='in**3')
if imep < 140:
imep_best_pwr = imep
for n in range(10):
SFC_best_mixture = iSFC(CR, imep_best_pwr)
best_mixture_pwr = ff_best_mixture / SFC_best_mixture
imep_best_pwr = piston.BMEP(best_mixture_pwr,
rpm,
disp_numeric,
power_units='hp',
vol_units='in**3')
# print('iSFC = %.4f' % SFC_best_mixture)
ihp = best_mixture_pwr * pwr_ratio_vs_ff_ratio(ff / ff_best_mixture)
bhp = ihp - friction_hp(displacement, rpm) * fric_power_factor
return bhp