MiG Alley: Designers Notes II
by Andrew McCrae
Click the image for a larger shot..
In Mig Alley you will be able to fly the following aircraft:
- North American F86 Sabre versions A, E and F.
- Mikoyan Gurevich MIG 15 and MIG15bis.
- Republic F84 E Thunder Jet.
- Lockheed F80 C Shooting Star.
- North American F51 D Mustang.
- North American F82 G Twin Mustang.
The aircraft in Mig Alley are capable of realistically simulating many characteristics such as flic rolls, spins, aileron reversal, adverse yaw, slipstreaming, stalling etc. Many aerodynamic and inertial effects such as aeroelasticity, wing sweepback, dynamic coupling, compressibility are modelled. Real life aerodynamic data has been used to correctly couple all six degrees of freedom. In each case the characteristics of the aircraft have been carefully adjusted to reproduce real life performance.
With respect to the Mig Alley software the job of the flight model is to receive player inputs, then output aircraft position, velocity, feedback and instrumentation data. The model is executed every 30 milliseconds, independently of the display frame rate. Within each execution the following processes occur:
- Receive player inputs
- Obtain ambient atmospheric conditions including wind and gust vectors
- Perform propulsion calcs (thrust, engine speed, reaction torque)
- Calculate aerodynamic forces and moments
- Calculate inertial moments (caused by aircraft rotating, mass distribution, gyroscopic effects)
- Integrate to get new velocity and position
- Calculate instrument parameters
On the ground, undercarriage tire and leg suspension forces are modelled to make the aircraft's attitude, speed and position respond realistically to terrain geometry, engine thrust, player brake, steering and control surface inputs. You will observe the aircraft in Mig Alley tilting in response to acceleration, braking, turning and even wind gusts. In Mig Alley, if you taxi too fast and turn hard you will find you lose control as the aircraft skids.
Propulsion has two modes of operation. You can control the engines throttle setting, as a real pilot does. Or, you may simply control the engines thrust output. For prop aircraft, blade element theory is used to determine thrust/braking and reaction torque produced by the propeller. Engine reaction torque is passed to the airframe.
Atmospheric conditions vary from day to day in Mig Alley. Obviously pressure and temperature change with height. Wind and gusts are modelled three dimensionally. All these effects are included in the aerodynamics and propulsion calculations. Try landing a shot up Sabre on a dodgy airfield in a heavy, gusty crosswind without skidding down the runway sideways.
In three further articles I plan to discuss, in detail, the aerodynamics, propulsion, undercarriage, mass/inertia and atmospheric aspects and effects of the Mig Alley flight model and the aircraft modelled.
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Last Updated June 25th, 1997