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question

CaptMatto avatar image
CaptMatto asked CaptMatto edited

Getting airspeed correct at higher altitudes in the G36

I’ve started further editing of the bonanza’s engine.cfg for the G36 Improvement Mod.

When we first looked at it we set the aircraft to have 4 cylinders and tweaked accordingly. Our changes matched the POH but subsequent sim updates have made the aircraft slightly overpowered and have slightly less fuel burn than what is published.

I’ve started looking at editing the engines.cfg to bring it more in line with the POH but can’t seem to get the numbers right. I can get the TAS to be correct for low level flight but when we get up around 6000ft my numbers fall off faster than the anticipated. Fuel burn is within .5 / 1gph all the way up to 16000.

At the moment it looks like I can get it right at altitude and wrong down low, or vice versa.

Can anyone help? Or know what causes this? I presume it is a setting I have missed or not understood regarding fuel/air mixtures perhaps. I'm sorry bit I don't understand some of the complex math behind this, i'm of the tweak and test school.

This is the issue I'm having as shown in the graph below.

1636823657293.png

The orange line is my new 'tweaks' the grey line is our old engine.cfg but as a 4 cylinder, and the red line is the POH. As you can see my TAS falls off as altitude increases by 14000ft I am a good 4/5knts behind the POH. I've predominantly been changing values in the engine_mechanical_efficiency_table, fuel flow scalar, & thrust_scalar

I am testing at ISA conditions, over 5 runs to get a good average at 25"/full throttle & 2500rpm, 20°C rich of peak EGT then plan on 23/23 etc.


Below is my engine cfg as it stands.

[VERSION]
major = 1
minor = 0


[GENERALENGINEDATA]
engine_type = 0
fuel_flow_scalar = 1.075
min_throttle_limit = 0
master_ignition_switch = 0
starter_type = 0
max_contrail_temperature = -1
Engine.0 = 4, 0, 1.2
ThrustAnglesPitchHeading.0 = 0, 0


[PISTON_ENGINE]
power_scalar = 1
cylinder_displacement = 91.6
compression_ratio = 8.5
number_of_cylinders = 6
max_rated_rpm = 2700
max_rated_hp = 300 ; Max rated HP
min_cruise_rpm = 1800
max_cruise_rpm = 2700
max_indicated_rpm = 2700
fuel_metering_type = 0
cooling_type = 0
normalized_starter_torque = 0.3
starter_time = 1.5
turbocharged = 0
max_design_mp = 29.6
min_design_mp = 15
critical_altitude = 0
emergency_boost_type = 0
emergency_boost_mp_offset = 0
emergency_boost_gain_offset = 0
fuel_air_auto_mixture = 0
auto_ignition = 0
max_rpm_mechanical_efficiency_scalar = 1
idle_rpm_mechanical_efficiency_scalar = 1
max_rpm_friction_scalar = 1
idle_rpm_friction_scalar = 0.76
BestPowerSpecificFuelConsumption = 0.41
egt_tuning_constant = 1
egt_peak_temperature = 2100 ; typical peak EGT: 1200 degF + 460
egt_tc = 2
cht_tuning_constant = 1
cht_cooling_constant = 0.65
cht_heating_constant = 960
rpm_on_cht_table = 0.28:0.75, 0.9:1
cht_tc = 0.015
oil_press_tuning_constant = 1
oil_press_max = 6500 ; max oil pressure (psf)
oil_press_tc = 0.8
oil_temp_tuning_constant = 1
oil_temp_cooling_constant = 0.21
oil_temp_heating_constant = 700 ; max oil temperature degrees Rankine
oil_temp_tc = 0.03
radiator_temp_tuning_constant = 1
radiator_temp_cooling_constant = 0.015
radiator_temp_max = 670 ; max radiator temperature degrees Rankine
radiator_temp_tc = 0.02
fuel_press_tuning_constant = 1
fuel_press_max = 2376 ; max fuel pressure (psf)
fuel_press_tc = 2
number_of_magnetos = 2
two_stroke_cycle = 0
supercharged = 0
radiator_cooling_constant = 0.015
radiator_heating_constant = 670
radiator_tc = 0.02
radiator_tuning_constant = 1
magneto_order_left_right_both = 0
engine_mechanical_efficiency_table = 0:0.77, 1200:0.57, 2000:0.55, 2200:0.55, 2500:0.572, 2700:0.565
engine_friction_table = -300:-25, 300:25, 500:25, 2700:31
manifold_efficiency_table = 0:0.2, 1:0.985
rpm_to_oil_pressure_table = 0:0, 0.1:0.3, 0.2:0.9, 0.519:1, 0.74:1
rpm_to_fuel_pressure_table = 0:0, 500:0.3, 1400:1, 2000:1
oil_temp_factor_from_rpm = 0:0.5, 500:0.8, 2000:1
prop_lever_pos_to_oil_pressure_delta_table = 0:2160, 1:0
diesel = 0
induction_air_temp_tc = 0.7
carb_heat_delta_temp = 55
single_magneto_efficiency = 0.97
oil_temp_to_oil_pressure_table = 0:0, 500:-1, 700:-600
shaft_torque_tc = 2
recip_stop_arc_degrees = 90
recip_stop_arc_restitution = 0.8
recip_stop_arc_max_pct_rpm = 0.04
recip_stop_arc_friction_factor = 2
egt_factor_from_pct_power = 0:0.5, 0.5:0.894, 0.64:0.956, 0.75:0.98, 1:1
egt_delta_from_mixture_ratio = 0.043:-100, 0.05:-89.7, 0.067:-50, 0.07:0, 0.075:-4.9, 0.083:-80, 0.108:-120.5


[PROPELLER]
thrust_scalar = 1.25
propeller_type = 0
propeller_diameter = 6.6
propeller_blades = 3
propeller_moi = 5
beta_max = 31
beta_min = 12
min_gov_rpm = 0
prop_tc = 0.01
gear_reduction_ratio = 1
fixed_pitch_beta = 0
low_speed_theory_limit = 0
prop_sync_available = 0
prop_deice_available = 1
prop_feathering_available = 0
prop_auto_feathering_available = 0
min_rpm_for_feather = 0
beta_feather = 0
power_absorbed_cf = 1.3
defeathering_accumulators_available = 0
prop_reverse_available = 0
minimum_on_ground_beta = 0
minimum_reverse_beta = 0
prop_reverse_max_vel = 2
prop_governor_p = 20
prop_governor_i = 2
prop_governor_d = 20
prop_governor_iboundary = 5
prop_governor_dboundary = 50
prop_efficiency_table = 0.000000:0.000000:0.200000:0.400000:0.600000:0.800000:1.000000:1.200000:1.400000:1.600000:1.800000:2.000000:2.200000,15.000000:0.150000:0.400000:0.710000:0.860000:0.720000:0.500000:0.340000:0.230000:0.150000:0.110000:0.080000:0.060000,20.000000:0.100000:0.300000:0.670000:0.810000:0.800000:0.740000:0.550000:0.420000:0.300000:0.190000:0.120000:0.090000,25.000000:0.080000:0.230000:0.490000:0.720000:0.820000:0.870000:0.820000:0.600000:0.410000:0.280000:0.180000:0.130000
prop_power_cf = 0.000000:0.000000:0.200000:0.400000:0.600000:0.800000:1.000000:1.200000:1.400000:1.600000:1.800000:2.000000:2.200000:2.400000,15.000000:0.032000:0.029000:0.025000:0.022000:0.009000:-0.057000:-0.188000:-0.338000:-0.522000:-0.705000:-0.915000:-1.092000:-1.220000,20.000000:0.084000:0.075000:0.066000:0.058000:0.045000:0.010000:-0.074000:-0.188000:-0.338000:-0.525000:-0.726000:-0.942000:-1.120000,25.000000:0.098000:0.094000:0.088000:0.080000:0.070000:0.050000:0.020000:-0.040000:-0.134000:-0.272000:-0.468000:-0.717000:-0.933000,30.000000:0.138000:0.132000:0.128000:0.120000:0.110000:0.099000:0.078000:0.040000:-0.017000:-0.110000:-0.248000:-0.468000:-0.741000,35.000000:0.206000:0.198000:0.188000:0.178000:0.163000:0.150000:0.130000:0.105000:0.070000:0.023000:-0.074000:-0.254000:-0.510000,40.000000:0.250000:0.242000:0.233000:0.223000:0.214000:0.204000:0.190000:0.175000:0.150000:0.118000:0.072000:0.019000:-0.059000
use_propeller_rpm = 1
beta_cruise = 31 ; usual beta in cruise (full torque) used to setup prop Cx (degrees)
prop_cx_min = 0.06 ; Value of the propeller Cx when beta = 0
prop_cx_at_cruise_beta = 0.21 ; Value of the propeller Cx when beta = beta_max


[DISABLED_CONTROLS]
DisableFuelValveControls = 0 ; Disable fuel valve controls
DisableMixtureControls = 0 ; Disable mixture controls
DisableParkingBrakeControls = 0 ; Disable parking brake controls
DisablePropellerControls = 0 ; Disable propeller controls



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