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FSXA Engine and propeller dynamics

MEPaquette

MEPaquette

Messages
235
Country
ca-ontario
Hello All
I am working on a boat model and I would like to know which parameter in either the “aircraft.cfg” or the “Klondike.air” file I would need to revise to achieve the following goals:
  1. I would like to have high thrust at low RPM, but keep the max speed to about 14 knots.
  2. It would be nice to have reverse, but up to now all attempts at changing constant speed prop parameters has failed.
First, I am working with a piston engine and at the moment it’s a fixed pitch prop, but I am willing to change the prop.
I know that going to a turbo prop I could get reverse, but I have tried it and I find it too sensitive to get neutral and I don’t like the delayed reaction to the throttle.

Michel E Paquette
 
You may be interested in the following extract from the cfg of a boat model I did - the propellor section is the main one. Forward/reverse is controlled by moving the prop pitch to opposite extremes. To limit speed, try increasing the parasite drag scalar in the flight_tuning section to something really large, like 40.

These tricks never work exactly the same way for every model - it depends on the airfile etc - but this gives the general idea as a base for further tinkering.

[piston_engine]
power_scalar=1//0.5
cylinder_displacement=300.00000
compression_ratio=8.00000
number_of_cylinders=9
max_rated_rpm=1800//2800.00000
max_rated_hp=1475.00000
fuel_metering_type=1
cooling_type=0
normalized_starter_torque=0.5//1//0.03359
turbocharged=1
max_design_mp=35//25//54.50000
min_design_mp=0.00000
critical_altitude=21500.00000
emergency_boost_type=3
emergency_boost_mp_offset=0.00000
emergency_boost_gain_offset=0.00000
fuel_air_auto_mixture=0
auto_ignition=0
max_rpm_mechanical_efficiency_scalar=1.00000
idle_rpm_mechanical_efficiency_scalar=1.00000
max_rpm_friction_scalar=1.00000
idle_rpm_friction_scalar=1.00000
emergency_boost_duration=0.00000

[propeller]
thrust_scalar=1//0.5
propeller_type=0
propeller_diameter=11.00000
propeller_blades=3
propeller_moi=42.27484
beta_max=10//45.00000
beta_min=-10//5.00000
min_gov_rpm=50//700.00000
prop_tc=0.10000
gear_reduction_ratio=1.00000
fixed_pitch_beta=0.00000
low_speed_theory_limit=80.00000
prop_sync_available=1
prop_deice_available=1
prop_feathering_available=1
prop_auto_feathering_available=0
min_rpm_for_feather=0//700.00000 //to enable reversing at low RPM
beta_feather=-10//82.50000 // negative pitch for reverse
power_absorbed_cf=0.2//0.90000 // reduce to stop engine cutout in reverse
defeathering_accumulators_available=0
//1//
prop_reverse_available=2 //scalar for reverse enabled
minimum_on_ground_beta=0//0.00000
minimum_reverse_beta=0//0.00000
 
Haeqri

I have revised as follow using what you gave me as a guideline:

[GeneralEngineData]
engine_type = 0 //0=Piston, 1=Jet, 2=None, 3=Helo-Turbine, 4=Rocket, 5=Turboprop
Engine.0 = -6.0, 0.0, 0.0 //(feet) longitudinal, lateral, vertical distance from reference datum
ThrustAnglesPitchHeading.0 = 0,0 //Thrust pitch and heading angles in degrees (+pitch down, +heading right)
fuel_flow_scalar= 0.88 //Fuel flow scalar
min_throttle_limit = 0.0 //Minimum percent throttle. Generally negative for turbine reverser


[piston_engine]
power_scalar = 2.0 //Piston power scalar
cylinder_displacement= 90 //Cubic inches per cylinder
compression_ratio= 8.5 //Compression ratio
number_of_cylinders=4 //Number of cylinders
max_rated_rpm= 1800 //2000 //Max rated RPM
max_rated_hp= 180 //Max rated HP
fuel_metering_type= 1 //0 //0=Fuel Injected, 1=Gravity Carburetor, 2=Aerobatic Carburetor
cooling_type= 0 //0=Cooling type Air, 1=Cooling type Liquid
normalized_starter_torque= 0.3 //Starter torque factor
turbocharged= 1 //0 //Is it turbocharged? 0=FALSE, 1=TRUE
max_design_mp= 35 //0 //Max design manifold pressure, (inHg)
min_design_mp= 0 //Min design manifold pressure, (inHg)
critical_altitude= 21500.0000 //0 //Altitude to which the turbocharger will provide max design manifold pressure (feet)
emergency_boost_type= 3 // 0 //0=None, 1=Water Injection, 2=Methanol/Water injection, 3=War Emergency Power
emergency_boost_mp_offset= 0 //Additional manifold pressure supplied by emergency boost
emergency_boost_gain_offset= 0 //Multiplier on manifold pressure due to emergency boost
fuel_air_auto_mixture= 0 //Automixture available? 0=FALSE, 1=TRUE
auto_ignition= 0 //Auto-Ignition available? 0=FALSE, 1=TRUE
max_rpm_mechanical_efficiency_scalar= 1.0 //Scalar on maximum RPM mechanical efficiency
idle_rpm_mechanical_efficiency_scalar= 1.0 //Scalar on idle RPM mechanical efficiency
max_rpm_friction_scalar= 1.0 //Scalar on maximum RPM friction
idle_rpm_friction_scalar= 1.0 //Scalar on idle RPM friction
BestPowerSpecificFuelConsumption=0 //0.49 //SFC at Best Power mixture ratio

[propeller]
propeller.0 = -8.0, 0.0, -3.0 //parameter to locate propeller offset (longitudinal, lateral and vertical) in feet from the engine that is driving it.
thrust_scalar = 2.0 //Propeller thrust scalar
propeller_type= 0 //1 //0=Constant Speed, 1=Fixed Pitch
propeller_diameter= 11.0000 // 6.3 //Propeller Diameter, (feet)
propeller_blades= 3 //2 //Number of propeller blades
propeller_moi= 42.27484 //5.0 //Propeller moment of inertia
beta_max= 10 //0 //Maximum blade pitch angle for constant speed prop, (degrees)
beta_min= -10 //0 //Minimum blade pitch angle for constant speed prop, (degrees)
min_gov_rpm= 50 /0 //Miminum governed RPM
prop_tc= 0.10000 //0 //Prop time-constant
gear_reduction_ratio= 1.0 //Propeller gear reduction ratio
fixed_pitch_beta= 0.0000 //20 //Fixed pitch angle of fixed pitch prop, (degrees)
low_speed_theory_limit= 80 //Speed at which low speed theory becomes blended in (feet/second)
prop_sync_available= 1 //0 //Prop synchronization available? 0=FALSE, 1=TRUE
prop_deice_available= 1 //0 //Prop de-icing available? 0=FALSE, 1=TRUE
prop_feathering_available= 1 //0 //Prop feathering available? 0=FALSE, 1=TRUE
prop_auto_feathering_available= 0 //Prop auto-feathering available? 0=FALSE, 1=TRUE
min_rpm_for_feather= 0 //Minimum RPM for prop feathering
beta_feather= 10 //0 //Feathering pitch angle (degrees)
power_absorbed_cf= 0.2 //0 //Coefficient of friction for power absorbed by propeller
defeathering_accumulators_available= 0 //Defeathering accumulators available? 0=FALSE, 1=TRUE
prop_reverse_available= 2 //0 //Prop reverse available? 0=FALSE, 1=TRUE
minimum_on_ground_beta= 0 //Miminum pitch angle on ground, (degrees)
minimum_reverse_beta= 0 //Minimum pitch angle in reverse, (degrees)

When I rev up engine with feather control to max, my boat goes backwards (I just thought of something. I have located my prop at the back, hopping it would act as a pusher prop, but maybe that is why it is going backwards. I will change and see if that makes a difference)
Now if I feather back to 0, engine revs down and boat stops.

Michel
 
Reverse at fine pitch setting is as expected, and so is the boat stopping if you move to rough pitch. Are you able to rev up the engine at this setting? In my model, the boat needs high revs to get it going initially, then pulled back to half throttle to maintain about 10-12 knots.

Obviously you are using a different airfile, and therefore the effect of the parameters in the cfg will not be exactly the same. One possible way of getting more thrust at less rpm may be to increase the number of propellor blades - but again, what works in one case may not work in others.
 
Here's the same sections for another working model. Again, fine pitch = reverse and rough pitch forward, both at about half throttle. According to my comments - it's a long time since I did this and I can't remember! - beta_max and beta_min seem to affect ahead and reverse respectively.

The first cfg was for the Deltasim fs9 tug, and the second for the Hama fs9 Stalwart amphibian, both to work in FSX. If you have these models or can download them, and pm me an e-mail address, I could send you the cfg files for each (aircraft.cfg and airfile) for you to experiment with.

[piston_engine]
power_scalar=1.0
cylinder_displacement=87.000000
compression_ratio=8.500000
number_of_cylinders=6
max_rated_rpm=2600.000000
max_rated_hp=125.000000
fuel_metering_type=1
cooling_type=0
normalized_starter_torque=1.100000
turbocharged=1//0
max_design_mp=50//0.000000
min_design_mp=0.000000
critical_altitude=0.000000
emergency_boost_type=0
emergency_boost_mp_offset=0.000000
emergency_boost_gain_offset=0.000000
fuel_air_auto_mixture=1
auto_ignition=0
fuel_flow_scalar=1.000000
max_rpm_mechanical_efficiency_scalar=1.000000
idle_rpm_mechanical_efficiency_scalar=1.000000
max_rpm_friction_scalar=1.000000
idle_rpm_friction_scalar=0.500000
power_scalar=1.215

[propeller]
propeller_type=0
propeller_diameter=7.833
propeller_blades=4
propeller_moi=10//41.400
beta_max=60 //ahead
beta_min=-40 //reverse
min_gov_rpm=0//2000//1500.000 //? effects forward not reverse behaviour
prop_tc=0.01//0.1//0.010
gear_reduction_ratio=1.850
fixed_pitch_beta=65.000
low_speed_theory_limit=80.000
prop_sync_available=0
prop_deice_available=0
prop_feathering_available=1
prop_auto_feathering_available=0
min_rpm_for_feather=0.000
beta_feather=-1//0.000
power_absorbed_cf=0.000
defeathering_accumulators_available=0
prop_reverse_available=1
minimum_on_ground_beta=1.000
minimum_reverse_beta=0//-14.000//0
thrust_scalar=1//1.215
 
Last edited:
Haeqri
I have the Deltasim Gemini 94. I have tried in the past to used the engine and prop setup from there in combination with the .air file and for some reason it was not working.
But I just made another test today, and ist's working fine. But it's using a turboprop engine. I would prefer to stay with piston engine, but if all else fails, I guess I can go with the turboprop engine configuration.

I just tried copying what you have above and the boat does not move no mater what I do with throttle of feather. It have a feeling that it has something to do with the .air file not matching engine and propeller specs.

As for sending a PM, how would I do that? I have not done this before.

Michel
 
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