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AirWrench
User Guide
Introduction
AirWrench is a user-friendly software tool for creating flight dynamics for Microsoft Flight Simulator.
AirWrench is not a traditional air file editor – it compiles a complete ‘air’ file, the binary file of aerodynamic
coefficients, used by the Microsoft Flight Simulator using the physical dimensions and performance
specifications of the real aircraft.
AirWrench Operation
The simulator loads two data files at the start of each flight that define the characteristics of the aircraft
selected by the user. These two data files are the text-based aircraft configuration file containing
parameters like the dimensions and weight, and the binary AIR file that contains aerodynamic coefficients.
Together, these files define the MSFS flight model. It is important to remember that these two files are a set
and that changes in either can affect the flight characteristics and performance of the simulated aircraft.
For computational efficiency, MSFS ‘compresses’ all the physical bits and pieces of a real-world aircraft into
a very simple virtual aircraft that consists of a mass, a wing and an engine. All of the aerodynamic forces
produced by the wings, body, stabilizers, ailerons, elevator and rudder of a real aircraft are calculated at runtime from the dimensions of the virtual wing and the aerodynamic coefficients in the AIR file.
The current flight simulator file container system originated with FS98. The data that defines the flight
dynamics for MS flight simulators are contained in two files: a binary file having the extension '.air', and a
text file named 'aircraft.cfg'. AirWrench considers these two files as a single flight dynamics file set.
In the older versions of MS flight simulator, most of the aircraft parameters were located in the binary 'air'
file, but as the simulator evolved from one version to the next, much of the air file content has migrated to
the text-based aircraft.cfg file.
Although the flight simulator needs both files to run, FS2004 aircraft.cfg files contain nearly all the aircraft
parameters AirWrench needs to compile a corresponding air file 'from scratch'.
AirWrench will generate flight dynamics for Microsoft FS2000, FS2002, FS2004, FSX, CFS1, CFS2 and
CFS3. At run time, each version of the sim looks in different places in the two flight dynamics files for
various parameters. The key to getting a single set of flight dynamics files that works across multiple
simulator versions is to ensure that all parameters in the air file and aircraft.cfg file are consistent with one
another.
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Flight Dynamics Analysis
AirWrench opens all flight dynamics files in 'read-only' mode. When you open a flight dynamics file set,
AirWrench searches through both the air file and the aircraft.cfg file for the parameters it needs to analyze
the flight dynamics. AirWrench gives the parameters found in the aircraft.cfg file precedence over
parameters found in an air file.
If any parameters are missing, AirWrench will substitute default values. The composite set of dimensions,
weights, power ratings, and aerodynamic coefficients are then analyzed and the estimated performance
characteristics - maximum speeds, climb rates, roll rates, etc. - are displayed on the Performance tab as
shown below:
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Before you edit flight dynamics with AirWrench...
Contact points and weight distribution are critical for modeling appropriate ground handling. Tricycle gear
aircraft will not rotate properly on takeoff or may even fall on the tail if the center of gravity and landing gear
contact points do not have appropriate geometric relations. Tail draggers are just as sensitive to the same
geometric relations.
AirWrench will compile the flight model without changing the balance of the original flight dynamics, and will
quite happily compile some very unflyable aircraft configurations. Please see the Repair Aerodynamic
Balance section to learn how AirWrench can automatically balance a flight model.
Airwrench displays a pictograph of the model on the Balance tab. The aircraft outline is scaled to the proper
length, but not the actual shape of the 3-D model. It is shown to give you an idea where the flight dynamics
file set has the CoG, CoL, MAC, landing gear, and tail surfaces located.
Note: The unlabeled ‘+’ symbols are contact point locations.
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Editing Flight Dynamics
To compile a new flight dynamics file set, find 'Edit Mode' on the Performance tab and click the 'Enabled'
radio button.
When Edit Mode is Enabled, AirWrench clears the air file and regenerates all aerodynamic coefficients using
the composite physical parameters found in the original flight dynamics file set - which includes the linear
dimensions, surface areas, weights, engine ratings - and the target performance characteristics - maximum
speeds, climb rates, roll rates, etc.
You'll also notice that the display windows labeled 'Performance Goals' are no longer grayed out. You can
now enter your own performance goals in these windows. When the performance goals are changed,
AirWrench re-evaluates the flight dynamics and updates the display windows accordingly. (To get
AirWrench to accept inputs immediately, press carriage return after entering the data.)
A note on performance limits: The estimated performance limits displayed are based on the current set of
aircraft parameters and performance goals. Aircraft parameters and goals can change during an editing
session, and as a result the estimated performance limits may also change. Therefore, AirWrench will let
you enter goals that are outside the limits shown; however, it will not allow you to save the flight dynamics if
the limits are exceeded.
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When the compiled flight dynamics files are saved, AirWrench does not modify the original files. The
original aircraft.cfg and AIR files are always renamed and are not overwritten. For example, if AirWrench is
used to update the flight dynamics for the original FS Boeing 747, the original files are renamed boeing747400_000.air and aircraft_000.cfg. Each time AirWrench saves the flight dynamics files, the files opened are
renamed using new file names, so after the next update, backup files named boeing747-400_001.air and
aircraft_001.cfg will be present.
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Repair Aerodynamic Balance
Aerodynamic balance is extremely important in a flight model. As noted previously, AirWrench does not
normally change the parameters that affect the balance of a flight model, which gives the user complete
freedom to locate components anywhere. However, the parameters that affect aerodynamic balance may
not be obvious, and establishing a balanced flight model can be a difficult and frustrating task, particularly
for newcomers.
The Repair Aerodynamic Balance button, located on the Balance tab, may be used to automatically
establish an aerodynamically balanced flight model. This option ensures that the weight and aerodynamic
centers are collocated. Depending on their initial values, the following parameters may be changed:
Empty Weight Center of Gravity
Center of Lift
Nose Position
Horizontal stabilizer longitudinal position
Vertical stabilizer longitudinal position
Station load longitudinal positions
Fuel tank longitudinal positions
Landing gear longitudinal positions
Note: The 3D visual model and the flight model dimensions are independent, and use of the Repair
Aerodynamic Balance option may cause misalignment of the landing gear with the visual model.
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Notes on Repair Aerodynamic Balance
This is a fairly complicated problem and many things are changed in the aircraft.cfg file, which subsequently
results in air file changes.. AirWrench uses the following algorithm to repair the aerodynamic balance:
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reset the wing position (wing_pos_apex_lon, wing_pos_apex_vert)
reset the CoG (empty_weight_CG_position_lon, etc.)
reposition the station loads and fuel tanks
use reasonable numbers for main gear contact point locations
estimate nose position
if tricycle gear, keep the center gear aft of the nose
reset the tail surface locations (vtail_pos_lon, htail_pos_lon)
the reference_datum_position_lon, so the engines, and remaining scrape points, and lights are
unchanged
move engines to vertical center
use AirWrench MOI values (empty_weight_pitch_MOI, etc.)
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Editing Flight Dynamics with AirWrench
AirWrench has tabs for aircraft Dimensions, Systems, Dynamics, Engine, Fuel, Weight, Balance, Contacts,
Tuning, and Air Foils that show the information AirWrench found in the flight model files. In Edit Mode, you
can change many of these parameters directly in AirWrench.
If a set of flight dynamics files has not been edited with AirWrench, the performance goals are initially set to
the estimated performance. When AirWrench saves the flight dynamics files, it saves the current
performance goals in the aircraft.cfg file, and in subsequent editing sessions, AirWrench will remember the
last set of performance goals you entered.
Critical Dimensions
The physical characteristics on the Dimensions tab are critical to getting an accurate virtual representation
of the aircraft being modeled. All linear measurements and surface areas are critical. If the values are
wrong, the flight dynamics will not represent the aircraft you're attempting to model, and may not perform at
all as expected in the simulator.
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Scale drawings are probably the best source of the necessary dimensions, but some of the required data
can also be found in aircraft manuals and reference books.
The following measurements are critical for AirWrench to generate accurate flight dynamics:
Wingspan - The distance from wing tip to wing tip.
Length - The distance from the tip of the nose to the tip of the tail.
Wing Surface Area - Includes the area 'shadowed' by the fuselage.
Wing Root Chord - The distance from the wing's leading edge to trailing edge where the wing meets
the fuselage.
Vertical Wing Position - The distance from the vertical center line to the center of the wing.
Wing Dihedral - The angle formed by the left and right wings.
Horizontal Stabilizer Area - The surface area of the horizontal stabilizer, including the area
'shadowed' by the fuselage. Does not include the elevator area. Be careful here, some books
include the elevator area.
Elevator Area - The surface area of the elevator.
Horizontal Stabilizer Longitudinal Position - The distance from the leading edge of the wing to the
leading edge of the horizontal stabilizer.
Vertical Stabilizer Area - The surface area of the vertical stabilizer. Does not include the rudder
area. Be careful here, some books include the rudder area.
Rudder Area - The surface area of the rudder .
Vertical Stabilizer Longitudinal Position - The distance from the leading edge of the wing to the
leading edge of the vertical stabilizer.
Wing Configuration
The number of wings in FS is actually always one, but AirWrench determines a 'virtual' number of wings by
dividing the wing area by the product of the wing span and the root chord. If the result is less than one, it's a
'monoplane'. Between 1 and 2 is a biplane, and larger than two is a triplane.
For a monoplane with a normal tapered wing, the wing area will always be less than the 'footprint' defined by
the wing span multiplied by the root chord. If the wing area is larger than this footprint, then there must be
more than one wing.
Many existing flight models use the mean chord as the root chord, and round-off errors can often cause the
wing’s ‘footprint’ to be slightly less than the wing surface area. The solution is to use a larger (and more
likely correct) value for the root chord.
AirWrench was designed with the assumption that the aircraft's wing is tapered and that the root is wider
than the tip. If this is not the case, then use the maximum chord width as the root chord.
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Estimate Control Surface Dimensions
AirWrench uses the stabilizer and control surface parameters to estimate the stability and control
coefficients for the air file. The Estimate Control Surface Dimensions feature may be useful when the
actual parameter values are unknown, or when the actual aircraft is tail-less.
The Estimate Control Surface Dimensions button, located on the Dimensions tab, may be used to
estimate values for the stabilizer and control surface parameters. The current values of aircraft length,
wingspan, and wing surface area are used to automatically update the following aircraft parameters:
Horizontal stabilizer area
Horizontal stabilizer span
Horizontal stabilizer longitudinal position
Horizontal stabilizer vertical position
Horizontal stabilizer incidence
Horizontal stabilizer sweep
Vertical stabilizer area
Vertical stabilizer span
Vertical stabilizer longitudinal position
Vertical stabilizer vertical position
Vertical stabilizer sweep
Elevator area
Rudder area
Aileron area
Using the Estimate Control Surface Dimensions button will automatically set the control surface deflection
limits to the following values:
elevator_up_limit
elevator_down_limit
aileron_up_limit
aileron_down_limit
rudder_limit
elevator_trim_limit
25.0
25.0
20.0
20.0
30.0
20.0
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Engine Setup
There are three different tabs for engine specifications: Piston, Jet, Turboprop. The specific engine tab
displayed will match the engine type selected on the Dimensions tab.
Piston Engine Tab
Propeller Design Altitude
Propeller power coefficients are determined by the following equation:
power_coef = 550.0 * max_hp / (rho * (engine_rpm /(60.0 * gear_reduction_ratio)^3) * propeller_diameter^5)
Air density (rho) changes with altitude, which in turn, affects the ability of a propeller to absorb engine power
as altitude changes. Constant speed propellers compensate for both changes in altitude and air speed;
however, fixed pitch propellers operate best at one speed and one altitude. 'Propeller Design Altitude' sets
the best overall operating altitude for a fixed pitch prop, and by default is set to 5,000 ft (a compromise value
that works quite well for most general aviation flight models).
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Jet Engine Tab
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Turboprop Tab
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Flight Dynamics – Roll, Climb, and Turn Rates
AirWrench also estimates roll, climb and turn rates throughout the entire speed range and shows these
estimates in graphical form on the Dynamics tab:
This tab is also used to adjust aileron performance. Roll rates are a function of airspeed. At low speeds, roll
rates are more or less linear and increase proportionally with airspeed. However, as the airspeed increases,
ailerons become less effective due to many physical factors, and this causes the roll rate to flatten out and
eventually decrease at very high speeds.
The low speed roll rate is a function of several aircraft parameters; but with respect to the ailerons
themselves, the total aileron area and deflection angle limits are the critical parameters.
In order to match a specified roll rate, the critical aileron parameters have to be large enough to generate
the desired roll response. If the aileron dimensions are insufficient to generate the desired roll response,
AirWrench will highlight the data entry cells that need to be updated to correct the problem.
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Control Tuning
This tab has a number of radio buttons and control sliders designed to tailor the dynamic performance and
feel of the flight model.
The 'Aircraft Type' radio buttons allow you to select Warbird, General Aviation, Aerobatic, Commercial Jet,
Military Jet, or SST types. These buttons change the assumptions AirWrench makes about how to estimate
the aerodynamic parameters for the flight model.
The WWI Warbird type causes the most drastic changes in control response and feel. The WWII Warbird
type assumes the flight model is for a high performance subsonic aircraft with mechanical control linkages.
The General Aviation type is assumed to have a low to medium speed range and higher stability. Aerobatic
aircraft are assumed to have a speed range similar to the General Aviation type with very positive responses
and marginal stability. Commercial jets are assumed to highly stable and operate at speeds just short of
mach 1. Military jets are assumed to operate across a broad speed range. The SST type enables air file
parameters introduced with the FS2000 Concorde. General Aviation v2 has minimal stability coefficient
changes with speed and angle of attack.
Use the control sliders can be used to adjust the flight dynamics and control feel for any selected aircraft
type to match the pilots' flight notes, or to suit your own experiences or tastes.
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Air Foil Data
The flight model's lift characteristics are defined using a look up table in MSFS. Lift coefficients (CL) are
defined as a function of angle of attack from -180 to +180 degrees. The Air Foils tab displays the air foil's lift
coefficients in graphic format.
The Air Foil tab also contains a stall speed calculator that can be used to generate a reasonable estimate if
the clean stall speed (Vsi) is unknown. This calculator has no effect on the flight dynamics.
The CL vs AoA curve is responsible for many flight characteristics that AirWrench attempts to match, for
instance the Clean Stall Speed and Pitch Attitude at Cruising Speed both depend on the values found in the
CL vs AoA curve. The only way for AirWrench to match these performance figures is to discard the original
air file's lift curve (CL vs AoA) and generate it's own.
CLmax is determined by solving the lift equation at stall speed:
CLmax = 391 * W /(V^2 * S)
V = airspeed in mph
S = wing surface area in square feet
W = weight in pounds
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Make sure the stall speed, weight and wing surface area are correct. If you believe you know the correct
value of CLmax, the Air Foils tab has a built-in calculator that calculates the corresponding stall speed for
the current aircraft parameters. To generate an air foil curve with a specific value of CLmax, enter the value
of cl_max in the calculator, then copy the calculated Clean Stall Speed (Vsi) value to the Specs tab. (The
calculated value of Vsi can be copied from tab to tab using Ctrl-C and Ctrl-V.)
The slope of the CM vs AoA curve depends on Static Margin (Specs tab) and the slope of the CL vs AoA
cyurve. The overall envelope of the CM vs AoA curve depends on the Aircraft type selected on the Tuning
tab.
Airfoils Expert Mode
This section explains the effect of the Expert Mode parameters on the Airfoils tab. This is not intended to
explain what values should be used or what flight dynamics effects to expect from any particular
combination of values. If in doubt, leave these parameters set to the default values.
When Expert Mode is enabled on the Airfoils tab, five additional air foil parameters appear below the air foil
data displays. These parameters define the shape of the post-stall lift curve. The data fields are labeled
AoA, Width, Offset, Step, and Final.
The purpose of each parameter is as follows:
AoA - nominal critical angle of attack
Width - number of degrees CL remains high post-stall
Offset - number of degrees CL takes to decrease post-stall
Step - initial value CL drops to post-stall
Final - final value CL drops to post-stall
The following figure shows the default parameter values for a typical lift curve:
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The following figure shows the effect of increasing the width parameter to 10:
The width of the lift coefficient peak, post-stall, is increased to 10 degrees.
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Systems – Flaps, Spoilers, Landing Gear, Brakes
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Automatic flap configurations with drag and pitch tuning sliders
Automatic spoiler configuration with with lift, drag, and pitch tuning sliders
Landing gear drag and pitch tuning sliders
When the Flap Modifications Enabled box is checked, the new automatic flaps configuration feature allows
you to select none, plain, split, or slotted flaps, how many stops to use, the extention time, and the maximum
deflection angle. Whenever the flaps type is changed, AirWrench automatically resets the pitch and drag
sliders to values appropriate for the type selected, and will output all the necessary parameters in the air file
and aircraft.cfg file when the flight dynamics files are updated. The drag and pitch sliders can also be used
to override the values AirWrench selects.
If you don't want AirWrench to change the current flap configuration in the aircraft.cfg file, just leave the Flap
Modifications Enabled box unchecked. You'll still be able to adjust the drag and pitch settings, but the flaps
configuration in the aircraft.cfg file will not be changed when the flight dynamics files are updated.
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Fuel – Tank and Engine Locations
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Tabulated display of all fuel tank locations and capacities
Tabulated display of all engine locations
The Fuel page allows you to display and edit all the fuel tank locations and capacities for your flight model.
This page allows you to adjust the effects of fuel on the center of gravity location without leaving AirWrench.
The Fuel page also allows you to display and edit all the engine locations for your flight model. Since
engine location can affect many aspects of flight model performance, it's important to review the engine
locations to be sure they make sense.
All of the parameters on the Fuel page can be edited and saved without changing any other aspect of your
flight model by using the button labeled 'Save this page to Aircraft.cfg file'. AirWrench has to be in 'Edit
Mode' in order for this feature to work, and be sure to answer 'No' when you exit AirWrench if you don't want
any other aspect of your flight model updated.
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Weight
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Tabulated display of 16 station load weights and locations
The Weight page allows you to display and edit all the station load weights and locations for your flight
model. This page allows you to adjust the effects of station loads on the location of the center of gravity
without leaving AirWrench.
All of the parameters on the Fuel page can be edited and saved without changing any other aspect of your
flight model by using the button labeled 'Save this page to Aircraft.cfg file'. AirWrench has to be in 'Edit
Mode' in order for this feature to work, and be sure to answer 'No' when you exit AirWrench if you don't want
any other aspect of your flight model updated.
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Contacts
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Tabulated display of up to 16 contact points
Estimated and current Static CoG Height
Estimated and current Static pitch
The Contacts page allows you to display and edit up to 16 contact points for your flight model. The contact
points can be edited and saved without changing any other aspect of your flight model by using the button
labeled 'Save this page to Aircraft.cfg file'. This feature is very useful for fine tuning the in-game alignment
of the landing gear with the ground.
AirWrench has to be in 'Edit Mode' for the save page feature to work - just be sure to answer 'No' when you
exit AirWrench if you don't want any other aspect of your flight model updated.
You may notice that AirWrench does not allow direct edit of the landing gear compression ratio. AirWrench
calculates the landing gear compression ratio using the specified static compression and maximum
compression values. See the paper at www.mudpond.us for further details on how these landing gear
parameters.
AirWrench also estimates values for the static CoG height above the ground and the static pitch. The
simulator uses these aircraft.cfg parameters to position the aircraft when it loads the model on the runway.
Using accurate values for these parameters eliminates drops and bounces at the start of a new flight.
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Landing Gear Compression in MSFS
Maximum Compression
Gear Fully Extended
Gear Fully Compressed
Landing gear position
at gMax frame 200
(Full compression)
Landing gear position
at gMax frame 100
(Full extension)
Maximum Compression (feet)
Maximum Compression is the total distance the wheel can travel from fully extended to fully compressed.
This distance is determined by the animation frames in the visual model.
The fully extended position is visible when the wheels are down in the air, but the fully compressed
position will almost never be visible.
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Static Compression
Position of Gear on Runway
Gear Fully Extended
Runway Surface
Static Compression (feet)
When an aircraft is loaded, it is positioned on the runway with the landing gear compressed by an amount
specified by the Static Compression parameter for each contact point.
Static Compression should be set to a value less than Maximum Compression.
At run time FS calculates a spring constant for each landing gear using Static Compression and the weight
supported by the gear. The lower the value of Static Compression, the stiffer the spring.
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Compression Ratio
Gear Fully Extended
Position of Gear on Runway
Gear Fully Compressed
Runway Surface
Maximum Compression
Static Compression
Static Compression and Compression Ratio values are required for each landing gear contact point in the aircraft
configuration file. Static Compression can be set to any value less than Maximum Compression, and the
Compression Ratio can be calculated using the following formula:
Compression Ratio = Maximum Compression / Static Compression
Note: If Static Compression is changed, Compression Ratio must be recalculated.
If the values of Static Compression and Compression Ratio for a model are correct, Maximum Compression can
be found using the following formula:
Maximum Compression = Static Compression * Compression Ratio
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Contact point lights
With just a few mouse clicks, you can add and remove white navigation lights wherever you have a contact
point. This shows you where your contact points are in-the-sim and helps you align the visual model with
your flight model.
To add contact point lights, follow these steps:
1) Put a check mark in the ‘Add Light’ box for each contact point where you want to add a light
2) Click the ‘Add/Delete Contact Point Lights’ button
3) AirWrench will update the [lights] section of the aircraft.cfg file
Click check
boxes to
add or
remove
contact point
lights
To remove contact point lights, follow these steps:
1) Remove the check mark in the ‘Add Light’ box for each contact point where you want to remove a
light
2) Click the ‘Add/Delete Contact Point Lights’ button
3) AirWrench will update the [lights] section of the aircraft.cfg file
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Base Aerodynamic Stability and Control Coefficients
The AirWrench 'Coef' tab displays the base aerodynamic stability and control coefficients. The coefficient
values are displayed as both real numbers and as legacy fixed binary point integers. The values shown are
determined automatically by AirWrench and can not be edited directly.
The aerodynamic coefficients determine the dynamic performance and stability of the flight model. These
coefficients are used by MSFS to calculate the linear and rotational acceleration, velocity and position of the
model.
A number of the aerodynamic coefficients used by MSFS are ‘stability derivatives’. Stability derivatives are
simply numbers used to scale the effectiveness of the horizontal and vertical stabilizers relative to the span,
area and chord of the main wing.
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The aerodynamic coefficient symbols used by MSFS are derived from the following definitions:
CL
Cd
Cm
Cl
Cn
q
P
R
A (alpha)
adot
B (beta)
ih
da
de
dr
df
dg
ds
lift coefficient (lift/qS)
drag coefficient (drag/qS)
pitching-moment coefficient about the quarter-chord point of the MAC
rolling-moment coefficient
yawing-moment coefficient
pitch rate, deg/sec or rad/sec
roll rate, deg/sec or rad/sec
yaw rate, deg/sec or rad/sec
angle of attack, deg or rad
angle of attack change rate, deg/sec or rad/sec
angle of sideslip, deg or rad
horizontal stabilizer incidence, deg or rad
aileron deflection, deg or rad
elevator deflection, deg or rad
rudder deflection, deg or rad
flap deflection, deg or rad
gear deflection, deg or rad
spoiler deflection, deg or rad
Lift Coefficients
The aerodynamic lift coefficients are defined as follows:
CL spoilers
CL flaps
CLih
CLde
Coefficient of lift for spoiler deflection, per radian of deflection.
Coefficient of lift for flap deflection, per radian of deflection.
Coefficient of lift due to horizontal stabilizer incidence. CLih is multiplied
by horizontal stabilizer incidence; lift will be zero if stabilizer incidence is
zero.
Coefficient of lift due to elevator deflection, per radian of deflection.
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Drag Coefficients
The aerodynamic drag coefficients are defined as follows:
CDo
CD flaps
CD gear
CD spoilers
Parasitic drag for total airframe.
Parasitic drag for flaps deflection, per radian of deflection.
Parasitic drag for landing gear in the down position.
Parasitic drag for spoiler deflection, per radian of deflection.
Pitch Coefficients
The aerodynamic pitch coefficients are defined as follows:
CMih
CMde
CMde due to propeller
wash
CLq
CL adot
CM adot
CMq
CMq due to propeller
wash
CMo
CM flaps
CM delta trim
CM gear
CM spoilers
Pitching moment due to horizontal stabilizer incidence. CMih is
multiplied by horizontal stabilizer incidence; moment will be zero if
stabilizer incidence is zero.
Pitch moment due to elevator deflection, per radian of deflection.
Determines how much leverage the elevator has to pitch the aircraft up
and down.
Effect of propeller wash on Elevator Control. Determines how much
elevator leverage is increased when propeller wash increases.
Lift due to pitch velocity. A lift coefficient that controls transient lift
changes in proportion to pitch velocity.
Lift due to pitch acceleration. A lift coefficient that controls transient lift
changes in proportion to pitch acceleration.
Pitch moment due to pitch acceleration. Pitch damping coefficient that
controls resistance to pitching motions in proportion to pitch
acceleration. Resists pitching motions in either direction, and adds to
the stability of the aircraft.
Pitch moment due to pitch velocity. Pitch damping coefficient that
controls resistance to pitching motions in proportion to pitch velocity.
Resists pitching motions in either direction, and adds to the stability of
the aircraft.
Pitch damping due to propeller wash. Pitch damping coefficient that
controls resistance to pitching motions in proportion to propeller wash.
Resists pitching motions in either direction, and adds to the stability of
the aircraft.
Reference moment at zero angle of attack. Pitching-moment coefficient
at zero lift. Positive values cause nose to pitch up.
Pitching moment due to flap extension, per radian of deflection.
Pitching moment due to pitch trim, per radian of trim deflection.
Pitching moment due to landing gear extension in the down position.
Pitching moment due to spoiler deflection, per radian of deflection.
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Side Force Coefficients
The aerodynamic side force coefficients are defined as follows:
CyB
CyP
CyR
Cy Delta Rudder
Side force due to yaw angle. Determines how much the aircraft sideslips
in proportion to yaw angle.
Side force due to roll velocity. A side force coefficient that controls
transient changes in side force in proportion to roll velocity.
Side force due to yaw velocity. A side force coefficient that controls
transient changes in side force in proportion to yaw velocity.
Side force due to rudder deflection. Determines how much the aircraft
sideslips in proportion to rudder deflection, per radian of deflection.
Roll Coefficients
The aerodynamic roll coefficients are defined as follows:
ClB
ClP
ClR
Cl Delta Spoiler
Cl Delta Aileron
Cl Delta Rudder
Roll moment due to yaw angle. Dihedral effect - the tendency of the
aircraft to roll level in proportion to the yaw angle.
Roll moment due to roll velocity. Roll damping coefficient that controls
resistance to rolling motions in proportion to roll velocity. Resists rolling
motions in either direction, and adds to the stability of the aircraft.
Roll due to yaw velocity. A roll moment coefficient that controls transient
changes in roll force in proportion to yaw velocity. Opposes the dihedral
effect.
Roll moment due to spoiler deflection. Determines how much leverage
the spoilers have to roll the aircraft, per radian of deflection.
Roll moment due to aileron deflection. Determines how much leverage
the ailerons have to roll the aircraft, per radian of deflection.
Roll moment due to rudder deflection. Determines how much leverage
the rudder has to roll the aircraft, per radian of deflection.
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Yaw Coefficients
The aerodynamic yaw coefficients defined are as follows:
CnB
CnP
CnR
CnR due to propeller
wash
Cn Delta Aileron
Cn Delta Rudder
Cn Delta Rudder due to
propeller wash
Yaw moment due to yaw angle. Weathervane effect - the tendency of the
aircraft to yaw in proportion to the yaw angle.
Yawing moment due to roll velocity. Adverse yaw caused by wing to wing
lift differences when rolling.
Yaw moment due to yaw velocity. Yaw damping coefficient that controls
resistance to yawing motions in proportion to yaw velocity. Resists
yawing motions in either direction, and adds to the stability of the aircraft.
Yaw damping due to propeller wash. Yaw damping coefficient that
controls resistance to yawing motions in proportion to propeller wash.
Resists yawing motions in either direction.
Yaw moment due to aileron deflection. Adverse yaw caused by aileron
drag.
Rudder Control coefficient. Determines how much leverage the rudder
has to yaw the aircraft, per radian of deflection.
Rudder Control due to propeller wash. Determines how much rudder
leverage is increased due to propeller wash.
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AirWrench
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Stability and Control Coefficient Modifiers
The AIR file sections displayed on the 'Mach' and 'NonLinear' tabs modify the base aerodynamic stability
and control coefficients. These parameters are used to model the non-linear variation of the base
aerodynamic stability and control coefficients due to distance above ground, control linkage, airframe
elasticity, load factor, angle of attack, and mach number. The ground effect, control input parameter, and
angle of attack modifiers are scalar multipliers, while the mach effect modifiers are additive.
Mach Modifier Tables
This tab presents a graph of the data found in the selected Mach modifier table, a list of the values
contained in the table, and a list of all available Mach modifier tables. The values shown are determined
automatically by AirWrench and can not be edited directly.
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AirWrench
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Non-linear Modifier Tables
This tab presents a graph of the data found in the selected non-linear modifier tables, a list of the values
contained in the table, and a list of all available non-linear modifier tables. The values shown are
determined automatically by AirWrench and can not be edited directly.
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AirWrench
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Power System Coefficient Tables
This tab presents a graph of the data found in the selected power system coefficient table, a list of the
values contained in one row of the table, and a list of all available power system coefficient tables. The list
of available power system coefficient tables varies depending on the engine type, the tables used by a
turboprop aircraft in this example. The values shown are determined automatically by AirWrench and can
not be edited directly.
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AirWrench
User Guide
AirWrench Terms of Use:
AirWrench, Copyright (C) 2004-2015, GWBeckwith. AirWrench is protected by copyright laws and
international copyright treaties, as well as other intellectual property laws and treaties. AirWrench is
licensed, not sold.
By installing, copying, or otherwise using the AirWrench, you agree to the following Terms of Use. If you do
not agree to these Terms of Use, do not install or use AirWrench.





You may install and use AirWrench on one computer.
You may not use AirWrench for developing commercial products.
You may not sell flight dynamics files created with AirWrench.
You may not charge third parties for creating flight dynamics files with AirWrench.
You may not reverse engineer, decompile, or disassemble AirWrench.
Disclaimer:
AirWrench is supplied on an as-is basis. The author offers no warranty of its fitness for any purpose
whatsoever, and accepts no liability whatsoever for any loss or damage incurred by its use. The author
accepts no commitment or liability to address any problems that may be encountered in using this program.
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