<HTML>
<HEAD></HEAD>
<BODY>
<h1>What Aero-Matic does</h1><br>
<b>Engine Configuration</b><br>
Engine.php creates a configuration file for the JSBSim engine modules according to
the following table:<br><br>
<center>
<table width="50%" border>
 <tr align="left">
  <th width="50%">Engine Type</th>
  <th width="50%">JSBSim Module</th>
 </tr>
 <tr align="left">
  <td width="50%">Piston</td>
  <td width="50%">FGPiston</td>
 </tr>
 <tr align="left">
  <td width="50%">Turbine</td>
  <td width="50%">FGSimTurbine</td>
 </tr>
 <tr align="left">
  <td width="50%">Turboprop</td>
  <td width="50%">FGSimTurbine</td>
 </tr>
 <tr align="left">
  <td width="50%">Rocket</td>
  <td width="50%">FGRocket</td>
 </tr>
</table><br>
</center>
The user inputs are first converted to English units.  The header is
then printed, and user inputs are echoed as comments.  Now engine2.php
prints data specific to the engine type.  The only calculation done for
the piston engine is displacement, which is based on an assumed 0.625 hp per
cubic inch.  All other piston engine values are "typical".
<br><br>
The turbine engine is modeled with an assumed bypass ratio of 1.0 and a TSFC
of 0.8.  Other data needed by the module are filled with "typical" values.
Afterburning and water injection are enabled if so selected.
<br><br>
The turboprop engine is modeled as a turbine with a bypass ratio of 0 and
a TSFC of 0.55.  The maximum power value is converted to a maximum thrust
value using the rough approximation that 1 hp equals 2.24 pounds of thrust.  Thrust
is then set to decrease at high speeds, thus simulating a propeller.
<br><br>
The rocket engine is Jon Berndt's X-15 engine.
<br><br>
<b>Propeller Configuration</b><br><br>
Prop.php first converts user input to English units, then echoes the input
as comments.
The propeller is modeled by first estimating the total "linear blade inches",
i.e. sum of all blade lengths, needed to absorb the engine's power.  I use 5.3
times the square root of the horsepower, a formula based only on curve-fitting
a sample of engine/prop combinations.  No science here.  The number of blades
is estimated using the following chart:<br>
<center>
<table width="50%" border>
 <tr align="center">
  <th width="50%">Engine Horsepower</th>
  <th width="50%">No. of Blades</th>
 </tr>
 <tr align="center">
  <td width="50%">&lt; 400</td>
  <td width="50%">2</td>
 </tr>
 <tr align="center">
  <td width="50%">400 - &lt; 1400</td>
  <td width="50%">3</td>
 </tr>
 <tr align="center">
  <td width="50%">1400+</td>
  <td width="50%">4</td>
 </tr>
</table><br>
</center>
The mass of each blade is estimated to be 0.9317 slugs per foot.  The rest of
the values are "typical".
<br><br>
<b>Aero Configuration</b><br><br>
Aero.php first converts user input to English units.  The first calculation
is to estimate wing loading at maximum weight based on the aircraft type as
per this chart:<br><br>
<center>
<table width="80%" border>
 <tr align="center">
  <th width="50%">Aircraft Type</th>
  <th width="50%">Wing Loading (psf)</th>
 </tr>
 <tr align="center">
  <td width="50%">Glider</td>
  <td width="50%">7</td>
 </tr>
 <tr align="center">
  <td width="50%">Light Single</td>
  <td width="50%">14</td>
 </tr>
 <tr align="center">
  <td width="50%">Light Twin</td>
  <td width="50%">29</td>
 </tr>
 <tr align="center">
  <td width="50%">WWII Fighter, racer, aerobatic</td>
  <td width="50%">45</td>
 </tr>
 <tr align="center">
  <td width="50%">Single Engine Transonic/Supersonic Fighter</td>
  <td width="50%">95</td>
 </tr>
 <tr align="center">
  <td width="50%">Two Engine Transonic/Supersonic Fighter</td>
  <td width="50%">100</td>
 </tr>
 <tr align="center">
  <td width="50%">Two Engine Transonic Transport</td>
  <td width="50%">110</td>
 </tr>
 <tr align="center">
  <td width="50%">Three Engine Transonic Transport</td>
  <td width="50%">110</td>
 </tr>
 <tr align="center">
  <td width="50%">Four+ Engine Transonic Transport</td>
  <td width="50%">110</td>
 </tr>
 <tr align="center">
  <td width="50%">Multi-engine Prop Transport</td>
  <td width="50%">57</td>
 </tr>
</table><br>
</center><br><br>
If the user did not supply a wing area, then the wing loading and
maximum weight are used to estimate one.  If the user <i>does</i>
supply a wing area, then the actual wing loading is calculated and
is used in lieu of the charted value.<br><br>
Once wing area has been established, it is divided by wing span to
give the mean aerodynamic chord.  The areas of the tail surfaces are
estimated by multiplying wing area by a factor depending on aircraft
type.  The moment arms of the tail surfaces are similarly estimated
from the aircraft length and type.<br><br>
The airplane's moments of inertia about three axes are estimated using
Roskam's formulae and constants for various airplane types. Presently I'm
increasing the moments by 50% to make up for a lack of feel in the
control stick.<br><br>
The aircaft's ZFW, zero-fuel weight, is estimated by multplying the maximum 
weight by a factor according to aircraft type.  This value is named "empty
weight" in the JSBSim configuration.<br><br>
Next the aircraft's center of gravity, CG, location is estimated.  The
longitudinal (x axis) location was already assumed when the horizontal
stablizer moment arm was estimated, so this distance is used to get the
longitudinal location of the CG from the nose, in inches.  The CG is located
on the intersection of the x and y axes, under the assumtion that the 
aircraft is laterally symetric, so the y location is zero.  I've put the
vertical (z) location of the CG a bit below centerline.  The location of
the aerodynamic center is, for simplicity, the same as the CG, except it 
is a bit above the CG to help with stability.<br><br>
The location of the pilot's eyepoint is then estimated based on aircraft
type.<br><br>
The landing gear location is based on the CG location.  Tricycle main wheels
are placed slightly behind the CG, and taildragger main wheels slightly ahead.
The lateral spread of the main gear is a function of wing span and airplane 
type.  The z-position of the main gear is based on the airplane's length. 
This is the distance in inches from the centerline to the bottom of the tire
when the gear is extended and hanging freely.  Note that the glider presents
a problem in that JSBSim presently supports three ground contact points,
whereas a glider needs five (main wheel, nose skid, tail wheel, and two
wing tip skids).  The locations of the nose or tail wheels is estimated from
the airplane length and the location of the main gear.<br><br>
The engines and thrusters are positioned according to the user-selected engine
layout, and some assumptions on engine spacing and location.  There are N+1 
fuel tanks for an N-engined airplane.  All fuel tanks are located at the aircraft 
center of gravity and contain 500 pounds of fuel.<br><br>
The FCS, flight control system, is the same for every airplane, except for the
yaw damper, which is only added if desired by the user.<br><br>
The lift force is based on a lift-vs-alpha curve made from four points, using
the assumed CL_0, CL_alpha and CL_max for the aircraft type.  Additional lift
due to flaps is estimated based on aircraft type.  Some types will have a lift
decrement due to speedbrakes (or spoilers).  All types have a lift contribution
due to elevator deflection, based on aircraft type.<br><br>
The drag force consists of CD0 (drag at zero-lift), CDi (induced drag), CDmach
(drag due to compressibility), CDflap, CDgear, CDsb (speedbrakes), CDbeta (drag
due to side slip), and CDde (drag due to elevator deflection).<br><br>
The only side force used is the force due to yaw angle (sideslip).<br><br>
Roll moments used are Clbeta (roll due to sideslip), Clp (roll damping), Clr (roll
due to yaw rate), Clda (roll due to ailerons), and Cldr (roll due to rudder
deflection).<br><br>
Pitch moments used are Cmalpha (pitch due to angle-of-attack), Cmde (pitch due to
elevator deflection), Cmq (pitch due to pitch rate), and Cmadot (pitch due to alpha
rate).<br><br>
Yaw moments are Cnbeta (yaw due to sideslip), Cnr (yaw damping), Cndr (yaw due to
rudder deflection), and Cnda (adverse yaw).<br><br>


<br><br><hr>
David Culp, 30 June 2003, (davidculp2 at comcast.net)<br>
update: 16 Oct 2003
</BODY>
</HTML>
