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 TFX | by Digital Image Design

TFX: by Digital Image Design

HUD (Heads Up Display) from TXX, 1993

APPENDIX SIX
THE SIMULATION
SOME NOTES ON TAKEOFF

In takeoff, the aim is to attain sufficient lift to leave the ground. For most airplanes, this is achieved by increasing the angle of attack (by raising the nosewheel from the ground) in order to increase lift. For safety's sake, takeoff speed is always significantly higher than stall speed, but there is another reason for this. When on the ground, the rolling force on the wheels acts not only to slow down the aircraft, but also to pitch the nose down. You can get the same effect, only exaggerated, by turning on the brakes at 60 kts. A major problem in shortening the takeoff distance is obtaining enough aerodynamic pitching moment to turn the nose skyward.

Although many fighters have more thrust available than weight, using engines instead of wings for lift is still very inefficient. The Harrier is capable of vertical takeoff due to its thrust vectoring nozzles, but in doing so uses fuel that could otherwise extend range significantly. For this reason, most Harrier missions start with a short, but not vertical takeoff. The F-22 uses thrust vectoring in a different way. Instead of assisting the wings with engine thrust, the F-22 diverts its vector nozzles upward.

THRUST VECTORING IN TAKEOFF

The down-thrust from the F-22 engines, as well as the downward force from the elevators, has the effect of turning the whole aircraft nose-up, increasing the angle of attack and gaining enough lift from the large wings, with flaps deployed, to more than counteract the downward thrust and lift the aircraft from the runway. This system makes the F-22 with thrust vectoring a short takeoff aircraft.

The Eurofighter 2000 solves the problem in a different way. In contrast to traditional tailplaned designs, the Eurofighter's foreplanes raise the nose from the ground at the same time as providing extra lift. As the rolling force is proportional on the total downward force through the wheels (i.e., weight - lift), this further decreases rolling force and helps the aircraft to get airborne.

TFX simulates ground forces by treating each wheel as a separate system, with suspension, shock-absorption, rolling forces and brake forces. "

From the manual