MSFS2020 - Cessna 172 Improvement Mod - V.1.13.16.1


Flight model modification version 1.13.16.0, date 2021-02-18:

The book "Quest for Performance: The Evolution of Modern Aircraft" tells about the C172 Skyhawk: "The zero-lift drag coefficient of the Skyhawk is 0.0319 as compared with 0.0358 for the Cherokee, and the maximum lift-drag ratios for the two aircraft are 11.6 and 10.0, respectively."
With MSFS 2020 the zero-lift drag coefficient CD,0 has the parameter name drag_coef_zero_lift and has the value 0.03270. With the MSFS 2020 build-in development tools Aircraft Editor, Debug, Sim Polar VhVs I measured maximum lift-drag ratio (L/D)max as 13.5.
The CD,0 values are close, but the (L/D)max values are not. I assume that the actual 3D model of the airplane determines how CD,0 gets mapped to (L/D)max. I got a (L/D)max value of 11.5 with a CD,0 value of 0.0411.

MSFS 2020 has no propeller drag and no ground effects. As workaround I use increased flaps drag with the drag_coef_flaps parameter. Airplane behavior feels "right" for me if the airspeed drops to 67% in flaps landing position compared to no flaps. A drag_coef_flaps value 0.0822 works fine.

[AIRPLANE_GEOMETRY]
wing_incidence = 0 ; const
oswald_efficiency_factor = 0.77 ; const
htail_incidence = 1.5 ; const

[FLIGHT_TUNING]
cruise_lift_scalar = 1 ; const
parasite_drag_scalar = 1 ; const
induced_drag_scalar = 1.5 ; 1.2 (sailplane, low power airplane) to 1.5 (piston, turboprop)
flap_induced_drag_scalar = 1.5 ; see induced_drag_scalar
pitch_stability = 0.04 ; const
roll_stability = 0.04 ; const
yaw_stability = 0.04 ; const

[AERODYNAMICS]
drag_coef_zero_lift = 0.0411 ; 0.01 (sailplane), 0.035 (GA plane), 0.05 (aerobatics plane)
compute_aero_center = 0 ; const
aero_center_lift = 0 ; const
lift_coef_at_drag_zero = 0.1 ; const
lift_coef_at_drag_zero_flaps = 0.1 ; const

cruise_speed = 124 ; Knots True (KTAS)
thrust_scalar = 1.3 ; 1.15 ; Propeller thrust scalar
After changing the polar, changing of thrust is needed, too. I give the airplane thrust for 124 KIAS maximum level flight airspeed at sea level.

fuel_flow_scalar = 0.76 ; 0.88 ; Fuel flow scalar
Set fuel consumption to 5h at 80% LVR.

empty_weight = 1691 ; Empty weight, (LBS)
empty_weight_pitch_MOI = 3089 ; 2410 ; Empty pitch moment of inertia, Jxx (SLUG SQ FEET)
empty_weight_roll_MOI = 2357 ; 2536 ; Empty roll moment of inertia, Jzz (SLUG SQ FEET)
empty_weight_yaw_MOI = 4400 ; 4270 ; Empty yaw moment of inertia, Jyy (SLUG SQ FEET)
empty_weight_coupled_MOI = 10 ; Empty transverse moment of inertia, Jyz (SLUG SQ FEET)
Increase moment of inertia (MOI) to make airplane less "jumpy".

empty_weight_CG_position = -3.23, 0, 0 ; -3, 0, 0 ; Position of airplane empty weight CG relative to reference datum (FEET), z, x, y
Move center of gravity to 25% MAC

flaps-position.0 = 0, -1, 0
flaps-position.1 = 10, -1, 1 ; 10, -1, 0.5
flaps-position.2 = 20, -1, 1 ; 20, -1, 0.75
flaps-position.3 = 30, -1, 1
The flaps drag results from sub-parameter Drag Coeff and flaps angle. Therefore 0 for 0° flaps and 1 for other settings gives linear progression of drag with flaps angle.

lift_scalar = 1 ; 1.9 ; Scalar coefficient to ponderate global flap lift coef (non dimensioned)
drag_scalar = 1 ; 1.9 ; Scalar coefficient to ponderate global flap drag coef (non dimensioned)
pitch_scalar = 1 ; Scalar coefficient to ponderate global flap pitch coef (non dimensioned)
lift_coef_flaps = 0
drag_coef_flaps = 0.0822 ; 0.04700
I control flaps lift/drag via [AERODYNAMICS] parameters.

wing_pos_apex_lon = -3.9 ; -2.75 ; Longitudinal (z) position of wing apex w.r.t reference datum (FEET)
Adjust to 3D model.

wing_incidence = 0 ; 1.5 ; Wing incidence (DEGREES)
htail_incidence = 2 ; 1 ; Horizontal tail incidence (DEGREES)
Adjust for level flight at cruise speed without elevator input.

fuselage_length = 22.1 ; -1 ; Nose to vtail/htail apex (FEET)
fuselage_diameter = 3.5
fuselage_center_pos = -7.5, 0, 0.3 ; -6, 0, 0.3
Adjust for good Aircraft Editor, Debug, Sim Forces display.

elevator_up_limit = 35 ; 28 ; Elevator max deflection up angle (DEGREES)
elevator_down_limit = 29 ; 23 ; Elevator max deflection down angle (absolute value) (DEGREES)
The elevator effect is increased for better inverted flight behavior.

elevator_trim_neutral = 0 ; 1 ; Elevator trim max angle (absolute value) (DEGREES), for indicators only (no influence on flight model)
This is a green area in the non-cockpit elevator trim display.

cruise_lift_scalar = 1
parasite_drag_scalar = 1
drag_coef_zero_lift = 0.0411 ; 0.03270
I control wings lift/drag via [AERODYNAMICS] parameters.

lift_coef_flaps = 0 ; 0.33790
lift_coef_spoilers = 0.00000
drag_coef_zero_lift = 0.0411 ; 0.03270
drag_coef_gear = 0 ; 0.00500
drag_coef_spoilers = 0.00000
Airplane has flaps, but no rectractable gear and no spoilers.

0/Post a Comment/Comments

Previous Post Next Post
Facebook Page Follow

Ads