Piccolo Simulator
Uploaded by
PaMe LiTaPiccolo Simulator
Uploaded by
PaMe LiTaPiccolo Simulator
March 31, 2011
Author:
Bill Vaglienti / Marius Niculescu / Jeff Hammitt
2621 Wasco Street / PO Box 1500 / Hood River, OR 97031
(541) 387-2120 phone / (541) 387-2030 fax
www.cloudcaptech.com / sales.cct@goodrich.com / support.cct@goodrich.com
Cloud Cap Technology, a Goodrich Company
www.cloudcaptech.com | sales.cct@goodrich.com | Tel. +1.541.387.2120 | Fax +1.541.387.2030
Table of Contents
1
Introduction............................................................................................................................. 5
1.1
Hardware-in-the-Loop .................................................................................................... 5
1.2
FlightGear ....................................................................................................................... 5
1.3
Software-in-the-Loop...................................................................................................... 6
Dynamics Model Overview .................................................................................................... 6
Creating Simulator Model Overview...................................................................................... 7
Aerodynamic Model ............................................................................................................... 7
4.1
AVLEditor Commands ................................................................................................... 8
4.2
Aircraft Editor................................................................................................................. 8
4.3
Surface Editor ................................................................................................................. 9
4.3.1
New Section .......................................................................................................... 11
4.3.2
Control Surfaces.................................................................................................... 12
4.3.3
Geometric Translation .......................................................................................... 14
4.3.4
Vortex Lattice ....................................................................................................... 15
4.4
Body Editor................................................................................................................... 16
4.5
XFOIL Analysis............................................................................................................ 17
4.6
AVL Analysis ............................................................................................................... 19
4.7
Control Surfaces............................................................................................................ 20
Inertia Model......................................................................................................................... 21
Propulsion Model.................................................................................................................. 22
6.1
Engine Models .............................................................................................................. 23
6.1.1
Piston Engine Model............................................................................................. 23
6.1.2
Electric Motor Model............................................................................................ 24
6.2
Engine Actuator Models ............................................................................................... 25
6.2.1
Fixed-Pitch Propeller Model................................................................................. 26
6.2.2
Simple Rigid Rotor ............................................................................................... 28
6.2.3
Helicopter Main Rotor .......................................................................................... 29
6.2.4
Helicopter Tail Rotor ............................................................................................ 37
Landing Gear Model ............................................................................................................. 39
Sensor Models....................................................................................................................... 42
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Actuator Models.................................................................................................................... 44
10
Launcher Model ................................................................................................................ 45
11
Initialization ...................................................................................................................... 46
12
Piccolo Parameters............................................................................................................ 46
13
Installation and Operation................................................................................................. 47
13.1
Installing FlightGear ..................................................................................................... 48
13.1.1
FlightGear Version 0.9.2....................................................................................... 48
13.1.2
FlightGear Version 0.9.4 / 0.9.8 / 0.9.9 / 0.9.10 .................................................. 48
13.2
Starting Simulator ......................................................................................................... 48
13.3
FlightGear View Options.............................................................................................. 49
13.4
Displaying Multiple Aircraft......................................................................................... 51
13.5
Displaying Custom 3-D Aircraft Models...................................................................... 52
14
Appendix........................................................................................................................... 53
14.1
Inertia Data.................................................................................................................... 53
14.2
Stability Derivative List................................................................................................ 53
14.3
Prop Example File......................................................................................................... 54
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Piccolo Simulator Change Log
March 31, 2011
Table 11: Added Swashplate Servo Mixing Table
December 23, 2009
Section 2: Added Simulator model graphic.
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1 Introduction
Piccolo is an avionics system for flying small unmanned aircraft. A cornerstone of Piccolos
development environment is the hardware-in-the-loop (HiL) and software-in-the-loop (SiL)
simulation system. The Simulator allows the aircraft control laws and mission functionality to be
tested without risking hardware in flight test. Although HiL/SiL simulation can not replace flight
testing, it measurably reduces the likelihood of failure by detecting bugs and deficiencies in the
lab. To facilitate this function, the Piccolo Developers Kit includes a Simulator that can be used
to test the performance of a Piccolo implementation.
1.1 Hardware-in-the-Loop
In HiL mode the Simulator uses an external CAN interface to connect to an avionics. Piccolo
sends servo control information over the CAN bus, and accepts external sensor data on the CAN
bus. The Simulator runs on a PC with a CAN interface card and closes the loop by reading the
actuator positions, applying them to an aircraft dynamics model, calculating new sensor data, and
putting that data on the CAN bus.
1.2 FlightGear
In order to visualize the state of the aircraft the Simulator sends UDP network packets to another
PC running the open source FlightGear Flight Simulator (FGFS) program. FlightGear accepts the
simulation state packets in favor of its own dynamics model, when properly configured for this.
This provides an attractive graphics interface for visualizing the performance of the aircraft.
Two Computer Configuration
with UDP Network Connection
FlightGear
PCC and Simulator
USB to CAN
Interface
Ground Station
Configuration
UHF Communication
Piccolo Autopilot
Configuration
Figure 1 - Hardware-in-the-Loop (HiL)
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1.3 Software-in-the-Loop
SiL is largely the same except the avionics is virtualized as an application on the PC
(PiccoloPC.exe) and the Simulator connects to that application over a TCP socket interface. This
is useful for cases where a full hardware laboratory is not available.
Piccolo
Command
Center
Flight Gear
Software
Location and
Orientation
Simulator
Software
Sensor Data
User
Commands
Telemetry
Actuator Data
Telemetry
User Commands
Piccolo Autopilot
Configuration
Ground Station
Configuration
Figure 2 - Software-in-the-Loop
2 Dynamics Model Overview
The heart of the Simulator is the dynamics model 1. It is the sum of all the components that affect
the dynamics and kinematics of the aircraft, including: aerodynamics, propulsion, ground contact
forces, and inertia effects. The dynamics model contains an integration method that estimates the
state of the aircraft based on the previous state and new control surface signals.
+Pitch
+Y
+Roll
+X
+Yaw
+Z
Figure 3 - Aircraft Body Axes used by Simulator
1
The Simulator is built with a modular architecture that allows third party force and moment models to be pluggedin. This document describes the standard dynamics model that Cloud Cap Technology provides.
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There are seven main components of the dynamics model. Each of these components are defined
or referenced in the main Simulator input text file.
Aerodynamics Model
Launcher Model.
Propulsion Model
Inertia Model
Sensor Model
Landing Gear Model
Actuator Model
3 Creating Simulator Model Overview
The following are the basic steps for developing an aircraft model for the Simulator:
1. Measure aircraft geometry, pull data
from 3-view / solid model
2. Determine CG location
3. Create AVL model
4. Refine AVL model with XFOIL data
5. Generate XML aerodynamics model
file
6. Model aircraft inertia data
7. Create prop model
8. Create Piccolo Simulator model
template
9. Set up Piccolo autopilot configuration
(control surfaces, tail configuration,
aircraft parameters)
10. Test with software-in-loop simulation
and FlightGear visualization
11. Verify manual control response,
required control surface limits
12. Generate autopilot gains
13. Load the aircraft file into the Simulator
14. The model is now ready for simulation
4 Aerodynamic Model
To create the aerodynamic model for the Piccolo Simulator, CCT leverages off a program called
AVL. AVL is a vortex lattice code developed by Prof. Drela of MIT that models linear
aerodynamics with a few nonlinear extras. It is useful for modeling unusual aircraft
configurations. So far Cloud Cap has used it to successfully model 20 aircraft. As with all
aerodynamic models, it is critical to compare models results with real world dynamics. One of
the draw backs of the AVL program is the text based interface. AVLEditor is a program
developed by Cloud Cap to visually simplify the modeling process by using a graphical user
interface (GUI).
Standard AVL models are generated using a keyword text based data input. AVLEditor replaces
this text based data input with a GUI based data entry system that generates a properly formatted
AVL data file for you. Cloud Cap modified the stock AVL code to output an XML file of the
stability derivatives representing a virtual wind tunnel angle of attack sweep. This XML file is
then used for the aerodynamics model in the Simulator. For more detailed information on the
specifics of AVL please reference the AVL documentation.
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4.1 AVLEditor Commands
AVLEditor breaks the aerodynamic
modeling process down into four major
groups: Aircraft data, Surface data,
Body data, and Airfoil data. These
options can be accessed from the
Model menu
in the AVL Model
Editor window or through the icon
menu bar.
Aircraft Editor Surface Editor Body Editor
Airfoil Editor
Figure 4 - AVL Editor Commands
The following depicts the various ways of navigating in the AVL Model Editor window:
Pan: Left click drag, direction keyboard arrows
Rotate: Right click drag, Ctrl + directional keyboard arrow
Zoom: GUI tool, mouse wheel, right click zoom in/out
4.2 Aircraft Editor
This section is used to define the basic aircraft
parameters used by AVL. The CG is used as the
reference point by which the moment and rotation
rates are defined. Typically, the CG point is
empirically measured from the aircraft being
modeled. If no CG is specified, then it is roughly
estimated by using an approximation from the
body and surfaces. The following reference
dimensions are used for calculation of the output
aerodynamic coefficients:
S is the reference area used to define all
the coefficients.
C is the reference chord used to demine
the pitching moment.
B is the reference span used to define roll
and yaw moments.
Figure 5 - Aircraft Editor
Cruise velocity is used to determine the Mach number in AVL and the Reynolds numbers in
XFOIL. AVL treats compressibility using the Prandtl-Glauert transformation. This
transformation is a function of Mach number, and is valid to Mach numbers of ~0.6-0.7. For
swept wings, the PG model should be judged using the wing-perpendicular Mach number.
XFOIL uses the cruise velocity and local chord lengths to calculate the Reynolds numbers for
Drag polar determination. The default profile drag value, CDp, is added to the geometry and
applied to the CG.
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4.3 Surface Editor
Figure 6 - Aircraft Surface Model
The first step in developing a model is to create the surfaces of the aircraft. This is done using the
Surface Editor tool. Surfaces are created using sections. Each section contains position,
chord, incidence and various other parameters. This allows you to create a wing with varying
chord, sweep, and di/anhedral. Sections also are used to define the beginning and ends of control
surfaces.
The main interface to the surface editor is in the lower left corner of the window. This allows
you to create new surfaces, add/delete sections to surface, or add/delete control surfaces on the
surface. After any type of modification, it is important to click the Apply button for the changes
to be saved.
To create a new surface, go to Model Surface Editor
or click the Surface Editor icon. Click the New
Surface button and enter the surface name. In this
example, we will create a basic wing. AVL creates a basic
wing made of two sections symmetric about the 2nd section.
To simplify the modeling process AVLEditor can model
symmetric surfaces.
Figure 7 - New Surface
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To edit the size or shape of the wing, use the surface editor tool. Positioning the cursor over each
section highlights the section in the AVL Model Editor window. When using the Y-symmetric
feature, both sections are highlighted.
Figure 8 - Editing a Surface
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4.3.1 New Section
Use the New Section tool to define a new section in a
surface. When inserting a new section, the tool will place a
new section in between the selected section and the section
after.
You can then alter those positions manually by using the
Position function under each section. In this example we
are going to add two new sections to capture the control
surfaces and the change of sweep angle.
Figure 9 - New Section
Figure 10 - Defining New Sections
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4.3.2 Control Surfaces
Control surfaces are defined in between at least two sections. A control surface can span multiple
sections. To add a control surface, use the New Control feature in the Surface Editor. When
defining a control surface on a symmetric surface, the control surface will also be duplicated.
Control surfaces are highlighted in yellow on the surface they are defined on.
In this example, we will add an aileron between Section 2 and Section 4.
Figure 11 - Adding a Control Surface
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The section that were selected now
have a control surface selection. To
make a control surface you must define
an endpoint to the control surface.
Simply create another control surface.
Defining a control surface consists of
the following elements: Name, Hinge
Vector,
Chord
Fraction,
Deflection, and Gain.
Figure 12 - Control Surface Selection
4.3.2.1 Hinge Vector
The Hinge Vector on the control surface is a non-functional piece of code in the AVL. It is
designed to allow control surfaces to be rotated at a different location from the defined control
surface leading edge.
4.3.2.2 Chord Fraction
Chord Fraction defines the size and location of the control surface. Positive values define the
control surface extending from Chordfaction/Chord to the tailing edge. Negative values define
the control surface extent from the LE to -Chordfraction/Chord.
(a)
(b)
Figure 13 - (a) Chord fraction value of -0.2. Control surface extends from the LE to .2/C down the
span. (b) Chord fraction value of 0.8. Control surface extends from 0.8/C to the TE of the surface.
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4.3.2.3 Deflection
Used when defining control surfaces on a symmetric surface. This allows the controls surface
rotations to be defined as symmetric (i.e. elevators) or asymmetric (i.e. ailerons).
4.3.2.4 Gain
The Control Surface gain is used to define direction of rotation of the control surface. The
direction of rotation is defined by the right hand rule based off the direction of surface definition.
Piccolo defines positive control surface motion as one that produces lift, i.e. aileron down is
positive rotation/rudder right, creating positive yaw motion.
Surfaces defined from left to right, result in a positive control surface rotation following the right
hand rule. Gain values should be set to 1 for this case. Surfaces defined from right to left result in
negative control surface rotation. The gain value should be set to -1.
4.3.3 Geometric Translation
When creating new surfaces it is easiest to define the leading edge of the surface at the 0,0,0
section position, and use the geometric transformation tool to position the surface in it proper
location. This allows you to easily modify the position of the surface without having to
recalculate and reenter all the surfaces section positions.
Figure 14 - Geometric Translation
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4.3.4 Vortex Lattice
The vortex lattice feature defines how many vortices are used to define the wing. There are four
parameters that define how the vortices are defined on the surface.
Chord/Span Vortices: Number of vortices in the chordwise/spanwise direction.
Chord/Span Spacing: A number from -3 to 3 defining either a linear, sine, or cosine
spacing of the vortices. An intermediate parameter will result in a blended distribution
between the two parameters, i.e. a value of 2.5 will result in a blend between sine and
equal spacing.
Table 1 -Chord/Span Spacing
Parameter
Spacing
Spacing Representation
3.0
equal
| | | | | | | | |
2.0
sine
|| | | |
1.0
cosine
|| |
equal
| | | | | | | | |
-1.0
cosine
|| |
-2.0
- sine
-3.0
equal
| | | | | | | | |
|
|
|
|
|
|
|
|
|
| ||
| ||
| | | ||
For optimum results, the following rules defined in the AVL documentation should be followed:
In a standard VL method, a trailing vortex leg must not pass close to a downstream
control point; else the solution will be garbage. In practice, this means that surfaces
which are lined up along the x direction (i.e. have the same or nearly the same y,z
coordinates), must have the same spanwise vortex spacing. AVL relaxes this requirement
by employing a finite core size for each vortex on a surface which is influencing a control
point in another surface (unless the two surfaces share the same INDEX declaration).
This feature can be disabled by setting the core size to zero in the OPER sub-menu,
Option sub-sub-menu, command C. This reverts AVL to the standard VL method.
Spanwise vortex spacings should be "smooth", with no sudden changes in spanwise strip
width. Adjust Nspan and Sspace parameters to get a smooth distribution. Spacing should
be bunched at dihedral and chord breaks, control surface ends, and especially at wing
tips. If a single spanwise spacing distribution is specified for a surface with multiple
sections, the spanwise distribution will be fudged as needed to ensure that a point falls
exactly on the section location. Increase the number of spanwise points if the spanwise
spacing looks ragged because of this fudging.
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If a surface has a control surface on it, an adequate number of chordwise vortices Nchord
should be used to resolve the discontinuity in the camberline angle at the hingeline. It is
possible to define the control surface as a separate surface entity. The optional X1, X2
parameters of the airfoil and aFile keywords are specifically intended for this purpose.
Cosine chordwise spacings then produce bunched points exactly at the hinge line, giving
the best accuracy. The two surfaces must be given the same index and the same spanwise
point spacing for this to work properly. Such extreme measures are rarely necessary in
practice, however. Using a single surface with extra chordwise spacing is usually
sufficient.
When attempting to increase accuracy by using more vortices, it is in general necessary
to refine the vortex spacings in both the spanwise and in the chordwise direction.
Refining only along one direction may not converge to the correct result, especially
locally wherever the bound vortex line makes a sudden bend, such as a dihedral break, or
at the center of a swept wing. In some special configurations, such as an unswept planar
wing, the chordwise spacing may not need to be refined at all to get good accuracy, but
for most cases the chordwise spacing will be significant.
4.4 Body Editor
AVL has the capability of modeling bodies, i.e. fuselages and nacelles, via source and doublet
filaments according to the slender body theory. AVL does not recommend modeling bodies if
they are expected to have little influence on the aerodynamics of the system. AVLEditor
provides a tool for quickly generating bodies. Bodies are saved as a separate text file. This file
needs to be located in the same directory as the AVL files.
To create a new body, select New Body from the pull down menu. Bodies are defined by using
the X position, Z position, and Area. As with the surfaces, the body can be scaled and translated.
The vortices spacing and distribution is also defined similarly to the surfaces.
Figure 15 - Body Editor
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4.5 XFOIL Analysis
XFOIL, also by Mark Drela et al., allows you to calculate airfoil properties. I has a sophisticated
model of low speed aerodynamics (low Reynolds number data can be generated). XFOIL
combines high-order panel methods with a fully-coupled viscous/inviscid interaction method.
XFOIL like AVL has its limitations, look out for lack of convergence (possibly Re too low or
airfoil data not smooth enough).
AVLEditor has created an interface to XFOIL to help analyze the CDCL distributions for the
airfoils. For more information regarding the specifics of XFOIL please reference the XFOIL
documentation.
For each surface, AVLEditor uses XFOIL to calculate the CDCL curves and Cla curve based off
the surface Reynolds number. When running XFOIL Analysis you have the option for specifying
Minimum Reynolds Number and Maximum Iterations. Specifying a minimum Reynolds number
helps XFOIL converge when actual Reynolds numbers are low. The Maximum iteration prevents
XFOIL from trying to solve a non-converting solution.
Figure 16 - XFOIL Options
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The menu in Figure 17 also has the option of manually specifying the CDCL and CLa curves for
each of the surfaces. This allows you to use empirical data to specify the curves.
Figure 17 - Specifying Curves
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4.6 AVL Analysis
The final step in aero-modeling process is to run the AVL code. From AVL Model Editor
window menu, go to Model AVL Analysis. This brings up the AVL Output window. From
here you can run AVL analysis on your aircraft and review the results in the plotting functions.
Figure 18 - AVL Analysis
There are 3 basic options for running an AVL analysis that define the alpha sweep:
Minimum Alpha
Maximum Alpha
Increment amount
Note: Currently the Beta Sweep function is non-functional and should not be used.
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4.7 Control Surfaces
Specify an association between the control surfaces in PCC and the AVL control surfaces:
AVLEditor XML output
<surface_1> Laileron </surface_1>
<surface_2> Raileron </surface_2>
<surface_3> Rudder </surface_3>
<surface_4> Elevator </surface_4>
// Left Aileron
Channel_d1=0
// Right Aileron
Channel_d2=5
// Rudder
Channel_d3=3
// Elevator
Channel_d4=1
Figure 19 - Surface Calibration Window in PCC
Channel_dn is the AVL control surface. For assignments, look in the xml file. They are listed in
numerical order.
If using control surface mixing such as ruddervators (or elevons) you can specify the left and
right ruddervator channels. For example, aerosonde.avl implements separate ailerons and
ruddervators, and the Aerosonde.txt file assigns the AVL control surfaces d1..d4 to the
appropriate Piccolo channels:
// Right aileron
Channel_d1=5
// Left aileron
Channel_d2=0
//Right ruddervator
Channel_d3=8
//Left ruddervator
Channel_d4=3
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5 Inertia Model
The Piccolo Simulator can take in inertia data directly with the following parameters:
Roll_Inertia=
Pitch_Inertia=
Yaw_Inertia=
Roll_Yaw_Coupled_Inertia=
The inertia model includes the mass and rotational inertia of the whole airplane. The mass
depends on the initial mass and the amount of fuel that has been burned. Rotational inertia is
based on the inertias of the X, Y, and Z axis. Additionaly, one cross component, X to Z is
included.
Table 2 - Inertia Parameter Values
Value
Meaning
Default
Gross_Mass
Mass of the entire aircraft, including fuel, in kg.
Required
Empty_Mass
Mass of the aircraft with no fuel, kg
Required
Roll_Inertia
Required
Required
Inertia about the X axis in kg-m .
Pitch_Inertia
Inertia about the Y axis in kg-m .
Yaw_Inertia
Inertia about the Z axis in kg-m .
Required
Roll_Yaw_Coupled_Inertia
XZ inertia coupling in kg-m2.
0.0
In addition to mass and moments of inertia, the inertia model also includes the acceleration
effects due to the avionics being mounted at a certain distance from the aircraft CG, as well as
the frame transformations for inertial measurements due to misalignment between avionics and
aircraft body frame. The parameters are listed in Table 3.
Table 3 - Avionics (or IMU) Mounting Geometry
Value
Meaning
Default
IMU_Sensor_Roll_Angle
The roll angle of the avionics with respect to the body frame, in deg.
0.0
IMU_Sensor_Pitch_Angle
The pitch angle of the avionics with respect to the body frame, in
deg.
0.0
IMU_Sensor_Yaw_Angle
The yaw angle of the avionics with respect to the body frame, in
deg.
0.0
IMU_Sensor_Position_X
The X-axis component of the position vector of the avionics' center
with respect to the aircraft CG, in m.
0.0
IMU_Sensor_Position_Y
The Y-axis component of the position vector of the avionics' center
with respect to the aircraft CG, in m.
0.0
IMU_Sensor_Position_Z
The Z-axis component of the position vector of the avionics' center
with respect to the aircraft CG, in m.
0.0
An inertia by component spreadsheet is available in the AVLCCT.zip archive. It can handle Vtails and can be used as an empirical or exact model or it can calculate inertias with a basic point
mass + block model with the parameters found in the Appendix. (Values are in kg and m.)
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6 Propulsion Model
The propulsion model estimates the loads (three forces and three moments) generated by the
propulsion system on the simulated aircraft as a function of the throttle setting, engine data,
actuator data, and aircraft state. The Simulator supports left and right propulsion units. Each of
the parameter names given in the following sections should be preceded by either a Left_ or a
Right_ depending on which propulsion unit is intended.
Each of the left and right propulsion units consists of an engine and an actuator or combination
of two actuators (Figure 20). The engine produces mechanical work for the actuator(s) while
these generate forces and moments that are applied to the airframe.
Figure 20 - Propulsion Model Structure
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6.1 Engine Models
The engine is the component that transforms the internal energy (chemical or electrical) stored
on-board the aircraft into mechanical work used to drive the actuator. The Simulator propulsion
system is designed to support multiple types of engine models. The piston engine and the electric
motor engine are the models currently available in the Simulator.
Before defining the parameters for a specific engine model, the general engine parameters shown
in Table 4 should be included in the aircraft configuration file. After specifying the engine type,
the engine model will be completed with model-specific parameters.
Table 4 - General Engine Parameters
Value
Engine_Type
Meaning
Default
Index of the engine model to be used:
0 (piston engine)
0 = Piston engine
1 = Electric motor
6.1.1 Piston Engine Model
The piston engine model calculates the torque and power for a given engine based on the throttle,
RPM, and ambient pressure. It is based upon a simple one-dimensional look up table which
relates wide-open-throttle (WOT) power to RPM.
To calculate the power at each time step, the engine model uses the current RPM to calculate the
WOT power. That power number is then multiplied by the ratio of the ambient pressure to
standard sea level pressure, and also by the throttle position (which is a number from 0 to 1).
Fuel flow is calculated using a single number, the brake-specific fuel consumption, which relates
the fuel consumption to the amount of power produced.
The piston engine model suffices for purposes of simulation. More advanced models can be
constructed, but they require more detailed knowledge of the actual engine implementation.
Estimating the engine power by a look up table is done by reading in data from the file indicated
in the parameter list. This file must contain two columns of ASCII data. The first column is the
RPM, and the second column is the corresponding WOT power, in Watts. The RPM must be
given in ascending order. The following is a sample engine look-up table for a Honda Mini 4stroke engine:
Honda Mini 4-stroke GX-31
# Look-up Table
# Wide open throttle
# RPM Power[W]
0 0.00
1000 75.00
4000 730.00
5000 950.00
6000 1050.00
7000 1100.00
8000 1075.00
9000 950.00
10000 100.00
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The piston engine is a rotating engine. As such, the rotational acceleration of the engine is
calculated from the difference between the torque produced by the engine and the torque
consumed by the actuator(s), and the rotational inertia of the engine shaft, gearbox, and
actuator(s). The engine angular speed is obtain by time-integration of the angular acceleration.
In a rotating engine, the piston engine model incorporates an optional governor that is modeled
as a proportional-integral feedback loop that regulates the engine angular speed using throttle.
Table 5 - Piston Engine Parameter Values
Value
Meaning
Default
Engine_Channel
Throttle servo channel assignment
2 for left engine, 7
for right engine
Engine_CutOffThrottle
The throttle fraction at which the engine stops
running
0.0
Engine_Inertia
Moment of inertia of the engine rotor, in kg*m^2
0.0
Engine_FrictionTorque
Torque consumed by internal friction, in N*m
0.0
Engine_GovernorGainPro
RPM governor proportional gain. By default the
governor is disabled. To enable it, set this parameter
to non-zero value.
0.0 (governor
disabled)
Engine_GovernorGainInt
RPM governor integral gain
0.0
Engine_GovernorRPM
Governor engine RPM command
0.0
Engine_GovernorRPMWindow
Governor activation window (RPM regulation starts
when RPM > RPMcmd - RPMwindow
0.0
Engine_LUT
File name for the Look up table of the engine WOT
power (in Watts) versus RPM curve.
None, parameter is
required
Engine_BSFC
Brake specific fuel consumption for the engine, in
grams of fuel per hour per Kilowatt of power
0.0
6.1.2
Electric Motor Model
The electric motor model implements the DC motor equations that provide the motor torque as a
function of input voltage and shaft RPM. The model does not employ look-up tables, instead it
relies on the motor characteristics typically provided by the DC motor manufacturer. The motor
input voltage is assumed to be linear with the throttle input. Zero throttle results in a zero-voltage
input to the motor, and full throttle (=1) results in the nominal voltage input to the motor.
The electric motor is a rotating engine. It includes rotational acceleration based on produced
torque, load torque, and inertia of the rotating masses. It also includes an optional RPM governor
model.
Table 6 - Electric Motor Parameter Values
Value
Meaning
Default
Motor_Channel
Throttle servo channel assignment
2 for left engine, 7 for right
engine
Motor_Inertia
Moment of inertia of the engine rotor, in kg*m^2
0.0
Motor_GovernorGainPro
RPM governor proportional gain. By default the
governor is disabled. To enable it, set this
parameter to non-zero value.
0.0 (governor disabled)
Motor_GovernorGainInt
RPM governor integral gain
0.0
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Motor_GovernorRPM
Governor engine RPM command
0.0
Motor_GovernorRPMWindow
Governor activation window (RPM regulation
starts when RPM > RPMcmd - RPMwindow
0.0
Motor_NominalInputVoltage
The nominal voltage the motor batteries will
provide, in Volts (V).
0.0
Motor_TorqueConstant
Typically represented by Km or Ki, it is the
motor torque per coil current, in Newton-meters
per Ampere (N*m/A).
Required, if RPMConstant
not defined
Motor_RPMConstant
Typically represented as Kv, it is the no-load
shaft speed per input voltage, in rotations per
minute per Volt (rpm/V).
Required, if
TorqueConstant not
defined
Motor_NoLoadCurrent
Also known as idle current (I0) it is the coil
current when running with no shaft load, in
Amperes (A).
Required
Motor_TerminalResistance
Typically represented as Ri, it is the resistance
of the armature, given in Ohms ().
Required
Motor_ThermalResistance
The characteristic value of the thermal transition
resistance from winding to housing and from
housing to ambient, in degrees Kelvin per Watt
(K/W).
0.0
If the aircraft model is using an electric motor, fuel consumption displayed in the Simulator
dialog is represented by the coil current shown in amperes.
The following is an example of the configuration parameters for a Kohler Actro 32-4 electric
motor:
// Electric motor Kohler Actro 32-4
Left_Engine_Type=1
Left_Motor_Channel=4
Left_Motor_Inertia=0.03
Left_Motor_NominalInputVoltage=42.0
Left_Motor_RPMConstant=415
Left_Motor_NoLoadCurrent=1.21
Left_Motor_TerminalResistance=0.055
Left_Motor_ThermalResistance=1.2
6.2 Engine Actuator Models
By engine actuator we are referring to the engine subsystem that creates loads (three forces and
three moments) on the airframe. Each of the left and right engines will have a corresponding left
or right actuator, respectively. Each engine may have a single actuator (propeller or helicopter
rotor) or a predefined combination of main actuator and slave actuator (helicopter main rotor and
helicopter tail rotor). In the case of a combo actuator, both the main and the slave actuator will
rotate at fixed distinct ratios of the engine angular speed.
The RPM displayed in the Simulator dialog is from the actuator, not the engine. In the case of a
combo actuator, the RPM displayed is from the main actuator (the main rotor on a helicopter
combo, for example).
Before defining the parameters for a specific actuator model, the parameters in Table 7 should be
included in the aircraft configuration file.
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Table 7 - General Actuator Parameters
Value
Meaning
Default
Actuator_Type
Index of the actuator model to be used:
0 (propeller)
0 = Fixed-pitch propeller
1 = Simple rigid rotor
2 = Helicopter main rotor
3 = Helicopter tail rotor
4 = Helicopter combo main+tail (geared to the same engine)
After specifying the actuator type, the actuator model will be completed with model-specific
parameters.
6.2.1 Fixed-Pitch Propeller Model
The propeller model calculates the thrust and torque of the propeller based on the RPM, and
forward speed of the aircraft. It uses a propeller look up table that gives the coefficient of thrust
and coefficient of power as a function of the advance ratio.
The Simulator calculates the advance ratio, and uses the look up table to determine Ct and Cp. Ct
is used to calculate the thrust from the propeller. Cp is used to calculate the power absorbed by
the propeller.
Estimating the propeller performance by look up table is done by reading in data from the file
indicated in the parameter list. This file must contain three columns of ASCII data. The first
column is the advance ratio, and the second column is the coefficient of power, and the third
column is the coefficient of thrust. The advance ratio must be given in ascending order. A sample
look-up table for an APC 20x8 propeller is shown in the Appendix.
The torque consumed by the propeller is applied to the propulsion system rotational dynamics.
The thrust produced by the propeller is transformed to forces and moments in aircraft body axes,
at aircraft CG location. A propeller definition includes the parameters in the aircraft
configuration file shown in Table 8.
Table 8 - Propeller Parameter Values
Value
Meaning
Default
Prop_X
The x-axis location of the actuator. Positive if actuator is ahead of
aircraft CG, in meters (m).
0.0
Prop_Y
The y-axis location of the actuator. Positive if actuator is to the
right of aircraft CG, in meters (m).
0.0
Prop_Z
The z-axis location of the actuator. Positive if actuator is below the
aircraft CG, in meters (m).
0.0
Prop_Tilt
Aircraft-to-actuator frame transformation pitch angle, in deg.
Positive if actuator is pitched up from aircraft axes, or negative if
actuator is pitched down.
0.0
Prop_Pan
Aircraft-to-actuator frame transformation yaw angle, in deg.
Positive if actuator is yawed to the right of the aircraft axes, or
negative if the actuator is yawed to the left.
0.0
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Prop_Diameter
Propeller diameter, in m.
Required, if
Prop_Radius not
defined
Prop_Radius
Propeller radius, in m.
Required, if
Prop_Diameter not
defined
Prop_Inertia
Propeller moment of inertia, in kg*m^2.
0.001
Prop_GearRatio
Engine-to-propeller gear ratio. Ratio is greater than 1 if prop
rotates slower than the engine (gear reduction).
1.0
Prop_Sense
Propeller sense of rotation (set to 1 for clockwise X-axis rotation,
or to -1 for counter-clockwise X-axis rotation). Propeller always
rotates about its X-axis.
Prop_LUT
File name for the Look up table of the propeller performance.
Required
Several parameters that define the actuator position and orientation are graphically represented in
Figure 21.
Figure 21 - Propeller Actuator Position and Orientation
The following tools are available to help with propeller modeling:
CreatingPropModels.pdf
PropModelling.zip
The Creating Prop Models document contains a method for approximating prop inertia as wells
as a small database of estimated prop inertias. A reasonable prop inertia value has proven
important for determining altitude controller gains.
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6.2.2 Simple Rigid Rotor
The simple rigid rotor model uses momentum theory to calculate the induced velocity and thrust
of a variable-pitch rotor. The rotor blades are assumed to have no twist and constant chord. The
induced velocity calculation accounts for ground effect.
The rigid rotor model user-configurable parameters are shown in Table 9.
Table 9 - Rigid Rotor Parameter Values
Value
Meaning
Default
Rotor_X
The x-axis location of the actuator. Positive if
actuator is ahead of aircraft CG, in meters (m).
0.0
Rotor_Y
The y-axis location of the actuator. Positive if
actuator is to the right of aircraft CG, in meters (m).
0.0
Rotor_Z
The z-axis location of the actuator. Positive if
actuator is below the aircraft CG, in meters (m).
0.0
Rotor_Tilt
Aircraft-to-actuator frame transformation pitch
angle, in deg.
0.0
Rotor_Pan
Aircraft-to-actuator frame transformation yaw
angle, in deg.
0.0
Rotor_Diameter
Rotor diameter, in m
Required, if
Rotor_Radius not
defined
Rotor_Radius
Rotor radius, in m
Required, if
Rotor_Diameter not
defined
Rotor_Inertia
Rotor moment of inertia, in kg*m^2
0.001
Rotor_GearRatio
Engine-to-rotor gear ratio
1.0
Rotor_Sense
Rotor sense of rotation (set to 1 for clockwise Xaxis rotation, or to -1 for counter-clockwise X-axis
rotation). Rotor always rotates about its X-axis.
Rotor_NumberOfBlades
Number of blades
Rotor_BladeLiftSlope
Slope of the coefficient of lift for the blade airfoil,
per rad.
Rotor_BladeProfileDrag
Profile drag coefficient of the blade airfoil
0.0
Rotor_BladeChord
Blade chord, in m
0.0
Rotor_GroundEffect
Factor that defines the magnitude of ground effect,
KGE, empirical
0.05
Rotor_IsVariableCollective
1 if rotor has variable collective controlled by a
servo, or 0 if the rotor collective pitch angle is fixed
Rotor_CollectivePitch
If rotor collective is fixed, this defines the blade
pitch angle, in deg.
0.0
Rotor_CollectiveChannel
If rotor has variable collective, this defines the
collective input servo channel
3 for left rotor, 8 for
right rotor
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6.2.3 Helicopter Main Rotor
The helicopter main rotor model is derived from the simple rigid rotor model, but adds the
following parameters:
First-order flapping dynamics
Secondary rotor representing the flybar with its own flapping equations
2-axis variable cyclic
An assumed vertical orientation with respect to the aircraft
The main rotor model user-configurable parameters are shown in Table 10.
Table 10 - Helicopter Main Rotor Parameter Values
Value
Meaning
Default
MainRotor_X
The x-axis location of the actuator. Positive if
actuator is ahead of aircraft CG, in meters (m).
0.0
MainRotor_Y
The y-axis location of the actuator. Positive if
actuator is to the right of aircraft CG, in meters (m).
0.0
MainRotor_Z
The z-axis location of the actuator. Positive if
actuator is below the aircraft CG, in meters (m).
0.0
MainRotor_Diameter
Rotor diameter, in m
Required, if
MainRotor_R
adius not
defined
MainRotor_Radius
Rotor radius, in m
Required, if
MainRotor_Di
ameter not
defined
MainRotor_GearRatio
Engine-to-rotor gear ratio
1.0
MainRotor_Sense
Rotor sense of rotation (set to 1 for positive X-axis
rotation, or to -1 for negative X-axis rotation). This
controls the sense of the main rotor torque.
MainRotor_NumberOfBlades
Number of blades
MainRotor_BladeLiftSlope
Slope of the coefficient of lift for the blade airfoil,
per rad.
MainRotor_BladeProfileDrag
Profile drag coefficient of the blade airfoil
0.0
MainRotor_BladeChord
Blade chord, in m
0.0
MainRotor_GroundEffect
Factor that defines the magnitude of ground effect,
KGE, empirical
0.05
MainRotor_IsVariableCollective
1 if rotor has variable collective controlled by a
servo, or 0 if the rotor collective pitch angle is fixed
MainRotor_CollectivePitch
If rotor collective is fixed, this defines the blade
pitch angle, in deg.
0.0
MainRotor_CollectiveChannel
If rotor has variable collective, this defines the
collective input servo channel
3 for left
rotor, 8 for
right rotor
MainRotor_BladeHingeOffset
Blade flapping hinge offset from rotor hub, in m
0.0
MainRotor_BladeMass
Blade mass, in kg
0.0
MainRotor_BladeTwist
Blade tip twist angle, in deg.
0.0
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MainRotor_TeeterDamping
Rotor teeter damping coefficient
0.0
MainRotor_MaxTPPTilt
Maximum tilt angle of the rotor tip path plane, in
deg. applies to both main rotor and flybar flapping
angles.
30 deg.
MainRotor_MaxAdvanceRatio
Maximum rotor advance ratio
0.2
MainRotor_FlybarRadius
Flybar radius in m.
0.0 (no flybar)
MainRotor_FlybarLiftSlope
Flybar blade airfoil lift curve slope, per rad.
MainRotor_FlybarBladeChord
Flybar blade chord, in m
0.0
MainRotor_FlybarBladeSpan
Flybar blade span (outer radius inner radius), in
m.
0.0
MainRotor_FlybarBladeInertia
Flybar blade flapping inertia about its hinge, in
kg*m^2
0.0
MainRotor_FlybarCyclicGain
Cyclic pitch of flybar per cyclic pitch of main rotor
blade.
0.0
MainRotor_CyclicFlybarTPPGain
Cyclic pitch of main rotor blade per flybar tip path
plane tilt.
0.0
MainRotor_LatCyclicChannel
Servo channel for direct control of main rotor
lateral cyclic.
0 left, 5 right
MainRotor_LonCyclicChannel
Servo channel for direct control of main rotor
longitudinal cyclic.
1 left, 6 right
MainRotor_SwashplateType
Swashplate mixing type:
0 (no mixing)
0 = no mixing
1 = SWH2 mixing
2 = SWH2-reversed mixing
3 = SWH4 mixing
4 = SR3 mixing
5 = SR3-reversed mixing
6 = SN3 mixing
7 = SN3-reversed mixing
MainRotor_Servo1Channel
First mixed servo channel (see Table 11 Swashplate Servo Mixing Table)
0 left, 5 right
MainRotor_Servo2Channel
Second mixed servo channel (see Table 11 Swashplate Servo Mixing Table)
1 left, 6 right
MainRotor_Servo3Channel
Third mixed servo channel (see Table 11 Swashplate Servo Mixing Table)
4 left, 9 right
MainRotor_Servo4Channel
Fourth mixed servo channel (see Table 11 Swashplate Servo Mixing Table)
3 left, 8 right
MainRotor_CyclicSwashplateGain
Deflection of main rotor blade per deflection of
swashplate.
0.0
MainRotor_BladeGripArm
Blade grip arm length, length units consistent with
linear servo pushrod deflection calibrated in the
avionics (cm typical).
0.0
MainRotor_SwashplateRadius
Swashplate radius at servo pushrod connection,
length units consistent with linear servo pushrod
deflection calibrated in the avionics (cm typical).
0.0
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Table 11 - Swashplate Servo Mixing Table
Name
Description
Diagram
Servo 3
Front
SWH2
Roll cyclic and collective are mixed on
servos 1 and 2, pitch cyclic is
independently controlled by servo 3.
Servo 1
Left
Nose
Servo 2
Right
Tail
Nose
SWH2
Reversed
Roll cyclic and collective are mixed on
servos 1 and 2, pitch cyclic is
independently controlled by servo 3.
Servo 1
Left
Servo 2
Right
Tail
Servo 3
Rear
Servo 3
Front
SWH4
Two servos for pitch, two for roll, and all
four servos used for collective.
Servo 1
Left
Nose
Servo 2
Right
Tail
Servo 4
Rear
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Nose
Servo 1
Left
SR-3
Servo 2
Right
Each servo is 120 degrees from its
neighbor.
Tail
Servo 3
Rear
Servo 3
Front
SR-3
Reversed
Nose
Each servo is 120 degrees from its
neighbor.
Servo 1
Left
Servo 2
Right
Tail
Nose
Servo 1
Front
SN-3
Rotor heads look like the following diagram:
Servo 3
Left
Servo 2
Rear
Tail
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Nose
Servo 1
Front
SN-3
Reversed
Servo 3
Right
Rotor heads look like the following diagram:
Servo 2
Rear
Tail
Nose
H4X
Servo 3
Front
Servo 2
Front
Servo 4
Rear
Servo 1
Rear
Two pairs of diagonally-opposed servos.
Tail
Several of the main rotor and flybar geometry parameters can be represented graphically on a
simple top-view drawing of the main rotor shown in Figure 22.
Figure 22 - Main Rotor and Flybar Geometry, Top View
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A side view of the typical Bell-Hiller mixer is shown in Figure 23. The following dimensional
elements are needed for the Simulator model:
a and b = the mixer arm lengths from blade arm to flybar pushrod and to swashplate
pushrod respectively;
m = the main blade grip arm, see MainRotor_BladeGripArm parameter;
n = the flybar blade grip arm or offset of the swashplate pushrod link to Hiller bridge
from main rotor shaft center axis.
p = radius of the Hiller bridge or offset of the mixer arm pushrod link from main rotor
shaft center axis.
r1 = the offset of mixer arm pushrod link from main rotor shaft center axis.
r2 = the offset of Hiller bridge pushrod link from main rotor shaft center axis.
R = the outer swashplate radius, or offset of servo pushrod from main rotor shaft center
axis, see MainRotor_SwashplateRadius parameter.
Figure 23 - Bell-Hiller Mixer Diagram
The aircraft model parameter MainRotor_BladeGripArm is element m shown in Figure 23. The
parameter
MainRotor_SwashplateRadius
is
element
R.
The
parameter
MainRotor_FlybarCyclicGain represents the change in flybar cyclic pitch angle per unit
change of the main rotor cyclic pitch angle. It can be calculated from the dimensional elements
in the diagram using the following formula:
FlybarCyclicGain
a b m r2
a
n r1
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The parameter MainRotor_CyclicFlybarTPPGain represents the change in main rotor blade
cyclic angle per unit change of the flybar tip path plane angle. It can be calculated from the
parameters in the diagram using the following formula:
CyclicFlybarTPPGain
b
p
ab m
The parameter MainRotor_CyclicSwashplateGain which represents the change in main rotor
blade cyclic angle per unit change of swashplate tilt angle, can be calculated from the parameters
in the diagram using the following formula:
CyclicSwashplateGain
r
a
1
ab m
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Figure 24 - Maxi-Joker 2 Rotor Head Example
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The following is an example of the geometry parameters for the Maxi-Joker 2 rotor head shown
in Figure 24.
Rotor head
parameter
Value (on MaxiJoker 2), in mm
20.00
b
m
n
p
r1
r2
R
14.00
34.15
18.00
54.15
24.50
29.00
35.22
Using the formulas presented earlier, listed below are the following gains for the Maxi-Joker 2:
FlybarCyclicGain 3.8177
CyclicFlybarTPPGain 0.6529
CyclicSwashplateGain 0.422
The typical R/C helicopter rotor see Maxi-Joker 2 example in Figure 24 is not hingeless but
not fully-articulated. The flapping hinge consists of an elastomer fitting that allows a limited
amount of angular displacement of the rod connecting the two blade roots, acting both as a
spring and as a damper.
Because the rotor model implemented in the Simulator assumes an articulated rotor, some tuning
of the MainRotor_BladeHingeOffset parameter would be required in order to improve the
fidelity of the rotor flapping dynamics.
6.2.4 Helicopter Tail Rotor
The helicopter tail rotor model is derived from the simple rigid rotor, but it adds a proportional
yaw damper, it removes the ground effect, and it assumes an orientation orthogonal to the
aircraft's X-axis (90 deg. pan angle).
The tail rotor model has the following user-configurable parameters:
Table 12 - Helicopter Tail Rotor Parameter Values
Value
Meaning
Default
TailRotor_X
The x-axis location of the actuator. Positive if
actuator is ahead of aircraft CG, in meters (m).
0.0
TailRotor_Y
The y-axis location of the actuator. Positive if
actuator is to the right of aircraft CG, in meters (m).
0.0
TailRotor_Z
The z-axis location of the actuator. Positive if
actuator is below the aircraft CG, in meters (m).
0.0
TailRotor_Diameter
Rotor diameter, in m
Required, if
Rotor_Radius
not defined
TailRotor_Radius
Rotor radius, in m
Required, if
Rotor_Diamet
er not defined
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TailRotor_Inertia
Rotor moment of inertia, in kg*m^2
0.001
TailRotor_GearRatio
Engine-to-rotor gear ratio
1.0
TailRotor_Sense
Rotor sense of rotation (set to 1 for positive X-axis
rotation, or to -1 for negative X-axis rotation). This
controls the sense of the tail rotor thrust force.
TailRotor_NumberOfBlades
Number of blades
TailRotor_BladeLiftSlope
Slope of the coefficient of lift for the blade airfoil,
per rad.
TailRotor_BladeProfileDrag
Profile drag coefficient of the blade airfoil
0.0
TailRotor_BladeChord
Blade chord, in m
0.0
TailRotor_IsVariableCollective
1 if rotor has variable collective controlled by a
servo, or 0 if the rotor collective pitch angle is fixed
TailRotor_CollectivePitch
If rotor collective is fixed, this defines the blade
pitch angle, in deg.
0.0
TailRotor_CollectiveChannel
If rotor has variable collective, this defines the
collective input servo channel
3 for left rotor,
8 for right
rotor
TailRotor_GyroGain
Proportional gain for yaw rate feedback to tail rotor
collective, in rad/(rad/s)
0.0
6.2.4.1 Helicopter Combo Main Rotor + Tail Rotor
The helicopter combo unit models a typical helicopter configuration in which the main rotor and
the tail rotor are driven by the same engine, but with different gear ratios. This model makes use
of the main rotor and the tail rotor models discussed in the previous subsections.
The aircraft configuration file should define the parameters of the main rotor and of the tail rotor.
The following example is a configuration for the Maxi-Joker 2 helicopter:
// Main rotor + tail rotor system
Left_Actuator_Type=4
// Main rotor definition
Left_MainRotor_X=0.0
Left_MainRotor_Y=0.0
Left_MainRotor_Z=-0.335
Left_MainRotor_Radius=0.8754
Left_MainRotor_GearRatio=9.25
Left_MainRotor_Sense=-1
Left_MainRotor_NumberOfBlades=2
Left_MainRotor_BladeLiftSlope=5.44
Left_MainRotor_BladeProfileDrag=0.0135
Left_MainRotor_BladeChord=0.0593
Left_MainRotor_GroundEffect=0.05
Left_MainRotor_IsVariableCollective=1
Left_MainRotor_BladeHingeOffset=0.0522
Left_MainRotor_BladeMass=0.230
Left_MainRotor_BladeTwist=0.0
Left_MainRotor_TeeterDamping=0.0
Left_MainRotor_MaxTPPTilt=20
Left_MainRotor_MaxAdvanceRatio=0.2
Left_MainRotor_FlybarRadius=0.3415
Left_MainRotor_FlybarLiftSlope=3.0
Left_MainRotor_FlybarBladeChord=0.045
Left_MainRotor_FlybarBladeSpan=0.128
Left_MainRotor_CyclicFlybarTPPGain=0.6529
Left_MainRotor_SwashplateType=5
Left_MainRotor_Servo1Channel=0
Left_MainRotor_Servo2Channel=1
Left_MainRotor_Servo3Channel=2
Left_MainRotor_CyclicSwashplateGain=0.422
Left_MainRotor_BladeGripArm=3.415
Left_MainRotor_SwashplateRadius=3.522
// Tail rotor definition
Left_TailRotor_X=-1.065
Left_TailRotor_Y=0.057
Left_TailRotor_Z=-0.16
Left_TailRotor_Radius=0.1725
Left_TailRotor_GearRatio=2.2
Left_TailRotor_Sense=1
Left_TailRotor_NumberOfBlades=2
Left_TailRotor_BladeLiftSlope=3.2
Left_TailRotor_BladeProfileDrag=0.01
Left_TailRotor_BladeChord=0.0295
Left_TailRotor_IsVariableCollective=1
Left_TailRotor_CollectiveChannel=3
Left_TailRotor_GyroGain=0.1
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Left_MainRotor_FlybarBladeInertia=0.00412
Left_MainRotor_FlybarCyclicGain=3.8177
7 Landing Gear Model
The landing gear model provides the forces and moments that are applied to the airframe when a
specific set of points on the aircraft come in contact with the ground. This includes not just the
landing gear itself, but also other parts of the airframe that may come in contact with the ground.
The ground contact points are each modeled with coefficients for stiffness, damping, and
longitudinal/lateral friction. There are two types of contact points: simple, and wheels. They
differ through the coefficients listed above. The longitudinal friction of a wheel is actually a rollfriction type (resisting force proportional to the velocity). The wheels can also steer the friction
forces are computed in the local frame of the wheel and rotated back to the aircraft frame.
The user can specify the location (with respect to the aircraft CG) of three wheels and nine other
contact points. The entire set is represented in the following two figures.
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Figure 25 - Top and Bottom View of Ground Contact Points and Wheels
Table 13 - Wheel Contact Points
Value
Meaning
Default
NoseWheel_Position_X
The X-axis component of the position vector of the nose
wheel or tail wheel ground contact point with respect to the
aircraft CG, in m. (positive if ahead of CG)
0.0
NoseWheel_Position_Y
The Y-axis component of the position vector of the nose
wheel or tail wheel ground contact point with respect to the
aircraft CG, in m. (positive to the right)
0.0
NoseWheel_Position_Z
The Z-axis component of the position vector of the nose wheel
or tail wheel ground contact point with respect to the aircraft
CG, in m. (positive if below the CG)
0.0
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NoseWheel_RudderWheelRatio
If nose wheel is mechanically linked to the rudder, this is the
ratio of steering angle to rudder deflection angle (negative for
nose wheel, positive for tail wheel, leave at 0.0 for nonsteerable)
0.0
NoseWheel_Steering_Channel
The Piccolo servo channel number for the steering actuator.
RightWheel_Position_X
The X-axis component of the position vector of the right wheel
of the main gear with respect to the aircraft CG, in m. (positive
if ahead of CG)
0.0
RightWheel_Position_Y
The Y-axis component of the position vector of the right wheel
of the main gear with respect to the aircraft CG, in m. (positive
to the right)
0.0
RightWheel_Position_Z
The Z-axis component of the position vector of the right wheel
of the main gear with respect to the aircraft CG, in m. (positive
if below the CG)
0.0
LeftWheel_Position_X
The X-axis component of the position vector of the left wheel
of the main gear with respect to the aircraft CG, in m. (positive
if ahead of CG)
0.0
LeftWheel_Position_Y
The Y-axis component of the position vector of the left wheel
of the main gear with respect to the aircraft CG, in m. (positive
to the right)
0.0
LeftWheel_Position_Z
The Z-axis component of the position vector of the right wheel
of the main gear with respect to the aircraft CG, in m. (positive
if below the CG)
0.0
Table 14 - Other Contact Points
Value
Meaning
Default
ContactPoint_Top_Position_X
The X-axis component of the position vector of the topmid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Top_Position_Y
The Y-axis component of the position vector of the topmid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Top_Position_Z
The Z-axis component of the position vector of the topmid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Bottom_Position_X
The X-axis component of the position vector of the
bottom-mid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Bottom_Position_Y
The Y-axis component of the position vector of the
bottom-mid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Bottom_Position_Z
The Z-axis component of the position vector of the
bottom-mid fuselage point w.r.t aircraft CG, in m.
0.0
ContactPoint_Nose_Position_X
The X-axis component of the position vector of the
fuselage nose point w.r.t aircraft CG, in m.
0.0
ContactPoint_Nose_Position_Y
The Y-axis component of the position vector of the
fuselage nose point w.r.t aircraft CG, in m.
0.0
ContactPoint_Nose_Position_Z
The Z-axis component of the position vector of the
fuselage nose point w.r.t aircraft CG, in m.
0.0
ContactPoint_Tail_Position_X
The X-axis component of the position vector of the
fuselage tail endpoint w.r.t aircraft CG, in m.
0.0
ContactPoint_Tail_Position_Y
The Y-axis component of the position vector of the
fuselage tail endpoint w.r.t aircraft CG, in m.
0.0
ContactPoint_Tail_Position_Z
The Z-axis component of the position vector of the
fuselage tail endpoint w.r.t aircraft CG, in m.
0.0
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ContactPoint_LWing_Position_X
The X-axis component of the position vector of the left
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_LWing_Position_Y
The Y-axis component of the position vector of the left
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_LWing_Position_Z
The Z-axis component of the position vector of the left
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_RWing_Position_X
The X-axis component of the position vector of the right
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_RWing_Position_Y
The Y-axis component of the position vector of the right
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_RWing_Position_Z
The Z-axis component of the position vector of the right
wingtip w.r.t aircraft CG, in m.
0.0
ContactPoint_LStab_Position_X
The X-axis component of the position vector of the left
horizontal stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_LStab_Position_Y
The Y-axis component of the position vector of the left
horizontal stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_LStab_Position_Z
The Z-axis component of the position vector of the left
horizontal stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_RStab_Position_X
The X-axis component of the position vector of the right
stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_RStab_Position_Y
The Y-axis component of the position vector of the right
stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_RStab_Position_Z
The Z-axis component of the position vector of the right
stabilizer tip w.r.t aircraft CG, in m.
0.0
ContactPoint_Fin_Position_X
The X-axis component of the position vector of the top
of the vertical tail w.r.t aircraft CG, in m.
0.0
ContactPoint_Fin_Position_Y
The Y-axis component of the position vector of the top
of the vertical tail w.r.t aircraft CG, in m.
0.0
ContactPoint_Fin_Position_Z
The Z-axis component of the position vector of the top
of the vertical tail w.r.t aircraft CG, in m.
0.0
8 Sensor Models
The Simulator supports sensor models that can be used to alter the sensor information sent to the
avionics. The sensor data are included in a separate file, which is referenced from the main file
using the flag Sensors= followed by the path name to the sensors file. The sensors that are
modeled are given in Table 15.
Table 15 - Sensor Names For Simulator Sensor Model
Value
Meaning
Latitude_Sensor_
Latitude of the vehicle from the GPS
Longitude_Sensor_
Longitude of the vehicle from the GPS
Height_Sensor_
Height of the vehicle from the GPS
VNorth_Sensor_
North component of ground speed from the GPS
VEast_Sensor_
East component of ground speed from the GPS
VDown_Sensor_
Down component of ground speed from the GPS
PDynamic_Sensor_
Dynamic pressure sensor
PStatic_Sensor_
Static pressure sensor
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Roll_Rate_Sensor_
Avionics axis roll rate sensor
Pitch_Rate_Sensor_
Avionics axis pitch rate sensor
Yaw_Rate_Sensor_
Avionics axis yaw rate sensor
X_Accel_Sensor_
Avionics x-axis acceleration sensor
Y_Accel_Sensor_
Avionics y-axis acceleration sensor
Z_Accel_Sensor_
Avionics z-axis acceleration sensor
Each parameter in the file is formed by concatenating the sensor name with the parameter name.
Each sensor can be modeled according to the parameters in Table 16.
Table 16 - Sensor Modeling Parameters
Value
Meaning
Units
Offset
Sensor output when the signal being sensed is at zero
Output
Order
Order of the butterworth low pass filter that the sensor output is passed through. Use
0 for no filter
N/A
Bandwidth
Cutoff frequency in Hz of the low pass filter.
Hz
Gain
Gain of the sensor signal.
N/A
Resolution
Resolution of the sensor signal
Output
Noise
Sensor noise, used to scale random number added to the sensor output before
going through the low pass filter
Output
Min
Minimum saturation limit.
Output
Max
Maximum saturation limit.
Output
Drift_Rate
Maximum offset drift rate.
Output/s
Max_Drift
Maximum offset drift value.
Output
Drift_Hold
Amount of time to spend at a specific offset drift value before allowing the sensor to
drift again.
In addition to the individual sensor parameters, there are also global sensor parameters
controlling the GPS update rates (Table 17).
Table 17 - Sensor Modeling Parameters
Value
Meaning
Units
GPS_Period
The update rate of the GPS This value should 1000 for the M12 GPS and 250
for the uBlox GPS (used in Piccolo II)
ms
GPS_Position_Lag
The time lag of the position output, prior to the velocity projection. This should
be 500 for the M12 and 125 for the uBlox
ms
GPS_Velocity_Lag
The time lag of the velocity output. Should be 1100 for the M12 and 250 for the
uBlox.
ms
The Sensor models can be loaded, saved, or modified from the Actuator interface in the
Simulator. SensorPerfect and SensorPoor are the two default sensor models that are
provided in the Piccolo Developers Kit.
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Figure 26 - Sensor Models
9 Actuator Models
The Simulator supports actuator models that can be used to limit the responsiveness of the
control surface actuators. The actuator data are included in a separate file, which is referenced
from the main file using the flag Actuators= followed by the path name to the actuators file.
The actuators that are modeled are shown in Table 18.
Table 18 - Actuator Names for Simulator Actuators Model
Actuator
Channel number
Output units
Left_Aileron_
Radians
Left_Elevator_
Radians
Left_Throttle_
0-1
Left_Rudder_
Radians
Left_Flap_
Radians
Right_Aileron_
Radians
Right_Elevator_
Radians
Right_Throttle_
0-1
Right_Rudder_
Radians
Right_Flap_
Radians
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Each parameter in the file is formed by concatenating the actuator name with the parameter
name. The actuators can be modeled according to the parameters in Figure 19.
Table 19 - Actuator Modeling Parameters
Value
Meaning
Units
Defaults
Bandwidth
Bandwidth of the actuator
Hz
Rate_Limit
Maximum rate of actuator
output/s
4.189
Min_Limit
Minimum deflection of the actuator
output
-1
Max_Limit
Maximum deflection of the actuators
output
Error
Output error of the actuator
output
Backlash
Backlash error of the actuator
output
Scale Factor
Multiplier
NA
Each actuator model in the Simulator includes a 2nd order bandwidth limiter, position limiter, rate
limiter, backlash, and Scale Factor.
The actuator models can be loaded, saved, or modified from the Actuator interface in the
Simulator. The following five actuator models are provided in the Piccolo Developers Kit:
Fast, Sloppy, Slow, Standard, and Very Slow.
Figure 27 - Actuator Models
10 Launcher Model
The Simulator supports a rail launcher. The rail launcher simulation is intended to model simple
catapult launch systems where the vehicle is accelerated along a fixed rail. The rail length, force,
heading, and pitch angle can be controlled with parameters in the dynamics file.
Table 20 - Launcher Parameters Values
Value
Meaning
Defaults
Launcher_Length
The length of the launch rail in meters
10.0
Launcher_Initial_Force
The force applied to the vehicle in the direction of the rail, a the
start of the launch
160.0
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Launcher_Final_Force
The force applied to the vehicle in the direction of the rail, at the
end of the launch. Between the beginning and the end of the
launch the force applied is scaled linearly from the initial force to
the final force
160.0
Launcher_Heading
The heading of the launch rail in degrees. This determines the
direction the vehicle will move as it accelerates on the rail
0.0
Launcher_Pitch
The pitch angle of the launch rail in degrees. This determines how
steeply the vehicle will be climbing when it leaves the rail.
20.0
11 Initialization
After a model is loaded the Simulator will initialize all the state variables with zero. The
initialization can be overridden using inputs available on the screen. The state of the model can
be saved to a file and loaded later as initialization data. The form of the file is similar to the
dynamics model files, i.e each variable is named in the file. A list of the state variables that can
be initialized is shown in Table 21.
The State file can be loaded or saved from the Simulator interface from the File Load
State or File Save State.
Table 21 - State Initialization File
Value
Meaning
Alpha
Angle of attack of the model, in degrees
Beta
Angle of sideslip of the model, in degrees
Roll
Euler roll angle, in degrees
Pitch
Euler pitch angle, in degrees
Yaw
Euler heading angle, in degrees
Body axis roll rate, in degrees per second
Body axis pitch rate, in degrees per second
Body axis yaw rate, in degrees per second
TAS
True air speed in meters per second
Latitude
Latitude in degrees
Longitude
Longitude in degrees
Altitude
Altitude in meters
Left_Engine_RPM
RPM of the left engine
Right_Engine_RPM
RPM of the right engine
12 Piccolo Parameters
Piccolo flight control laws are based on the aircraft parameters. For typical applications, once the
aerodynamic parameters are defined, the default set of gains should fly the aircraft. The
Simulator has the ability to generate an aircraft parameters file from the Simulator input file.
From the Simulator menu select Vehicle Data Fixed Wing Gen 2. This will create an
XML file with all the vehicle parameters defined in the Vehicle tab of the Controller
Configuration window in PCC (Figure 28).
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Figure 28 - Controller Configuration
13 Installation and Operation
The Simulator works as a standalone executable. No special installation is required, however the
CAN interface driver must be installed. This is done using the USBCanModule driver disc. In
addition when starting the Simulator the USB to CAN module must be plugged in. The
Simulator will detect that it is plugged in and configures itself to use it as its source of control
surface data. If the CAN module is not connected, the Simulator will attempt to connect to a
software simulation source. If it fails to connect to a software simulation source, it will use any
installed joysticks for the control surface data.
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13.1 Installing FlightGear
The current version of the Simulator supports FlightGear versions 0.9.2, 0.9.4, 0.9.8, 0.9.9, and
0.9.10.
13.1.1 FlightGear Version 0.9.2
FlightGear version 0.9.2 should be installed by unzipping its archives. First, make sure that the
directory C:\FlightGear on your computer does not exist already. If it exists and you would like
to keep that version, rename that directory. Otherwise, delete it before installing the newer
version.
Unzip the file fgfs-base-0.9.2.zip to the root directory of your C: drive. This will
create a new directory called FlightGear and its directory tree. This archive contains most
of the FlightGear data.
Unzip the file fgfs-win32-msvc-bin-0.9.2.zip to the root directory of your C:
drive. This will add more files to the FlightGear directory and its tree. This archive
contains the binary executables of FlightGear.
Copy the two batch files runfgfsnet-c172.bat and runfgfsnet-j3cub.bat to the
C:\FlightGear directory. These two batch files can be used to launch the FlightGear
program in "external flight dynamics" mode, which is exactly what we want for
interfacing with our Simulator. The only difference between the two files is that they load
different visual models - one of them loads a Cessna 172, and the other one a Piper Cub.
Optionally, unzip the files wXXXnXX.tar.gz to C:\FlightGear\Data\Scenery. The four
files included provide scenery and airports for the west coast of the United States.
13.1.2 FlightGear Version 0.9.4 / 0.9.8 / 0.9.9 / 0.9.10
The newer versions of FlightGear for Windows platform come as a self-installing archive. Run
the fgsetup0.9.4.exe program. The Setup will guide you through the installation. When
completed, copy the two batch files runfgfsnet-c172.bat and runfgfsnet-j3cub.bat to the
directory where FlightGear was installed. These two batch files can be used to launch the
FlightGear in the correct mode.
13.2 Starting Simulator
1. Start FlightGear by using one of the supplied batch files. This will start FlightGear in
external flight dynamics mode. The program accepts aircraft state data (position, velocity
and attitude) from a UDP network connection on port 5500. If you prefer to use the
default start batch file, the command line for launching FlightGear in external dynamics
mode is:
runfgfs.bat --native-fdm=socket,in,30,,5500,udp --fdm=external
2. On the Simulator computer, launch the Simulator application. Select File Open to
open the text file that contains the simulation model.
3. From the top menu, select External/FlightGear Type the network name of the
computer running FlightGear in the dialogue box. The aircraft in FlightGear should now
be exactly at the location that it is set in the Simulator.
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4. The aircraft states can now be initialized properly in the Simulator, after which you can
start the simulation anytime by pressing the Start button. The Stop button halts the
simulation but maintains the aircraft states to the last computed values. The Reset button
resets the aircraft states to the program defaults.
13.3 FlightGear View Options
This section covers the view options in FlightGear. The Cockpit View (Figure 29) is the first
view shown upon startup.
Figure 29 - FlightGear Cockpit View
Most of the instruments in the cockpit view are not useful for a UAV simulation since they are
designed for manned aircraft and are not connected to any external flight dynamics model. To
remove the cockpit clutter use the S key (Figure 30). The cockpit can be enabled by pressing the
S key again.
Figure 30 - Forward View Cockpit Removed
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The forward-looking pilot view is one of multiple views available in FlightGear. Views are fully
configurable, so any view is theoretically possible. For more information about configuring
views, see the FlightGear viewer document.
To navigate between different views use the V key. There is a set of default views that are
already configured when FlightGear is started. There are also two external views: fixed
orientation with respect to the airplane, and fixed orientation with respect to the ground (inertial
frame). An example of the external view is shown in Figure 31.
Figure 31 - External View
For the external views, change the location of the camera with respect to the airplane using the
SHIFT + arrow keys. The zoom can be adjusted using the X key (zoom in) and SHIFT+X keys
(zoom out).
Another type of view is the ground/tower view Figure 32. This is particularly useful for flying
UAVs/RPVs under manual control.
Figure 32 - Tower View
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13.4 Displaying Multiple Aircraft
If there are multiple Piccolo Simulators running on the local network, all the aircraft can be
displayed in a single FlightGear window Figure 33. Each instance of the Simulator application
should be connected to individual FlightGear computers, but with the appropriate command line
parameters. On the client FlightGear computer, run FlightGear with the following command line
parameters:
runfgfs.bat --aircraft=j3cub --native-fdm=socket,in,30,,5500,udp
--fdm=external --multiplay=out,10,XXX.XXX.XXX.XXX,5501 allsign=player1
On the server FlightGear computer (where all aircraft will be displayed) run FlightGear with the
following command line parameters:
runfgfs.bat --aircraft=j3cub --native-fdm=socket,in,30,,5500,udp
--fdm=external --multiplay=in,10,XXX.XXX.XXX.XXX,5501 -callsign=player2
Note: XXX.XXX.XXX.XXX is the IP address of the server.
Figure 33 - Multiple Aircraft
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13.5 Displaying Custom 3-D Aircraft Models
FlightGear can accept models in various 3-D formats. For more information regarding aircraft
modeling see the FlightGear modeling documentation.
In this example, we will use the Predator FS2000 model.
1. Copy the predator.md 3-D model file to the C:\FlightGear\data\Models\ directory.
2. In the same directory create a small XML file that defines the path property to the 3-D
model file. For this example, the file should contain the following:
<?xml version="1.0"?>
<PropertyList>
<path>Models/predator.mdl</path>
</PropertyList>
3. Save the file as predator.xml.
4. In the batch file that was used to start FlightGear, add a new command line parameter:
--prop:/sim/model/path=. This path points to the newly created predator.xml file. The
new batch file should contain the following:
%TOP_ROOT%\BIN\WIN32\FGFS.EXE
--prop:/sim/model/path=%FG_ROOT%\Models\predator.xml
--native-fdm=socket,in,30,,5500,udp --fdm=external
5. Launching FlightGear with this new batch file will result in loading the Predator FS2000
model as shown in Figure 34.
Figure 34 - Predator FS2000 Model
Piccolo Simulator 3-31-11
Page 52 of 54
Goodrich ISR Systems
www.cloudcaptech.com | sales.cct@goodrich.com | Tel. +1.541.387.2120 | Fax +1.541.387.2030
14 Appendix
14.1 Inertia Data
Some of these parameters may be omitted or se to zero (many of them default to 0), but all 3
axes must have non-zero inertias or the Simulator will declare it an invalid model. An inertia
spreadsheet is available (included in the AVL archive) which does a better job at modeling V-tail
aircraft, and allows you to interactively adjust the model. It also calculates CG location from
components.
Gross_Mass=
Empty_Mass=
Left_Engine_Mass=
Left_Prop_X=
Left_Prop_Y=
Left_Prop_Z=
Right_Engine_Mass=
Right_Prop_X=
Right_Prop_Y=
Right_Prop_Z=
Fuse_Z=
Tail_Mass=
Tail_Area=
Tail_Span=
Tail_X=
Tail_Z=
Left_Fin_Mass=
Left_Fin_Area=
Left_Fin_Span=
Left_Fin_X=
Left_Fin_Y=
Left_Fin_Z=
Right_Fin_Mass=
Right_Fin_Area=
Right_Fin_Span=
Right_Fin_X=
Right_Fin_Y=
Right_Fin_Z=
Wing_Mass=
Wing_Area=
Wing_Span=
Wing_X=
Wing_Z=
Fuselage_Mass=
Fuse_X=
14.2 Stability Derivative List
These are the stability derivatives that are used by the Simulator (and are output by AVL). This
ability to import XML data could be the basis for wind tunnel data support in the CCT Simulator.
Note: The drag used by the current AVL Simulator aerodynamics module is CDff+CDvis.
All of these derivatives can be tables vs. angle of attack.
Label
Description
CDff
Trefftz plane induced drag coefficient
CDvis
Profile drag + CDo drag coefficient
CY
Side force coefficient
CL
Lift coefficient
Cl
Roll moment coefficient
Cm
Pitch moment coefficient
Cn
Yaw moment coefficient
CLb
Variation of lift coefficient with sideslip angle (or use beta sweep)
CYb
Variation of side force coefficient with sideslip angle (or use beta sweep)
Clb
Variation of roll moment coefficient with sideslip angle (or use beta sweep)
Cmb
Variation of pitch moment coefficient with sideslip angle (or use beta sweep)
Cnb
Variation of yaw moment coefficient with sideslip angle (or use beta sweep)
Piccolo Simulator 3-31-11
Page 53 of 54
Goodrich ISR Systems
www.cloudcaptech.com | sales.cct@goodrich.com | Tel. +1.541.387.2120 | Fax +1.541.387.2030
CLp
Variation of lift coefficient with roll rate
CYp
Variation of side force coefficient with roll rate
Clp
Variation of roll moment coefficient with roll rate
Cmp
Variation of pitch moment coefficient with roll rate
Cnp
Variation of yaw moment coefficient with roll rate
CLq
Variation of lift coefficient with pitch rate
CYq
Variation of side force coefficient with pitch rate
Clq
Variation of roll moment coefficient with pitch rate
Cmq
Variation of pitch moment coefficient with pitch rate
Cnq
Variation of yaw moment coefficient with pitch rate
CLr
Variation of lift coefficient with yaw rate
CYr
Variation of side force coefficient with yaw rate
Clr
Variation of roll moment coefficient with yaw rate
Cmr
Variation of pitch moment coefficient with yaw rate
Cnr
Variation of yaw moment coefficient with yaw rate
CDffd1
Variation of induced drag coefficient with control surface 1 deflection (deg)
(note replace 1 with control surface # 1..n for this and all other d1 derivatives)
CLd1
Variation of lift coefficient with control surface 1 deflection (deg)
CYd1
Variation of side force coefficient with control surface 1 deflection (deg)
Cld1
Variation of roll moment coefficient with control surface 1 deflection (deg)
Cmd1
Variation of pitch moment coefficient with control surface 1 deflection (deg)
Cnd1
Variation of yaw moment coefficient with control surface 1 deflection (deg)
14.3 Prop Example File
Sample PRD file for an APC 20 x 8 propeller.
# Prop: 20x8
# RPM 4700 [m/s]
# Number of panels 0
# J Cp Ct %
-1.0000 0.0200 0.0600
0.2000 0.0250 0.0515
0.2441 0.0248 0.0508
0.3000 0.0245 0.0478
0.3800 0.0234 0.0422
0.4386 0.0216 0.0352
0.5000 0.0187 0.0262
0.5414 0.0160 0.0196
0.5883 0.0122 0.0110
0.6000 0.0111 0.0085
0.6083 0.0103 0.0068
0.6221 0.0089 0.0029
0.6331 0.0078 0.0000
0.7000 0.0000 -0.0050
0.8000 -0.0050 -0.0156
0.9000 -0.0097 -0.0203
1.0000 -0.0180 -0.0295
1.2000 -0.0273 -0.0400
2.0000 -0.0737 -0.1115
Piccolo Simulator 3-31-11
Page 54 of 54
Goodrich ISR Systems
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