- •Builds performance from geometry and airfoil/engine characteristics, not control/stability derivatives
- Uses Prandtl-Glauert rule for subsonic, compressible flow lift from 2-D airfoils
- Models forces and moments over every airfoil surface (including propellers) more than 15 times per second
- Allows modifications for low Reynolds number applications
- Facilitates rapid evaluation of new designs
- Integrates results from disparate sources into a single "experimental" environment with vast "instrumentation"
Building the Plane
The Powerplant
- •X-Plane allows the user to select horsepower, fuel consumption, maximum engine rpm, and useable rpm range
The Wings
- X-Plane models all lifting surfaces the same way – as 2-D airfoil data modified to account for real-world effects
Modifications
- X-Plane starts with airfoil sloped based on a 2-D section of an infinite airfoil
- Low Reynolds number data is imported from
high-fidelity tools to improve accuracy
- This corrects artificially low drag and high lift in default airfoils
- Wing, tail, and propeller airfoils were changed to better match real low Reynolds number performance
 |
 |
Less Than Infinite
- •Compressibility and vortex effects are simulated by combining the Prandtl-Glauert rule with empirical geometric effects related to aspect ratio, taper ratio, and the specific airfoil to produce a new lift slope from 2-D data:
- This slope is finally combined with wing
area and atmospheric qualities to produce lift:
- Fortunately, X-Plane does this for us many times each second…
Experiments in X-Plane
- Created a mock course to simulate the DBF mission, including standard-rate and steep turns, as well as takeoff, landing, and straight-and-level flight
- •Varied maximum weight and motor power with
a fixed propeller/airframe combination
- •Tracked power settings, engine power,
thrust, and distance (in 3-space) at short time intervals
- Flight results show virtually
the entire mission is flown at maximum power, and that aircraft weight and thrust are the two
most significant performance parameters for a given geometry
- Demonstrated the poor handling qualities of
the “Flying T-Shirt” prototype
