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Aviation History
1987
1987 - 2292.PDF
I generators fail. By any aircraft's standards the USAF landing specification is tough, particularly in a big fast jet such as the F-15, so how will the pilot be aided? One of the main aims is to keep the pilot workload low, and a substantial amount of front-end effort in the design stage will ensure that Stol Eagle Project Pilot Larry Walker should not have a too-frantic time of it come the day. Macair has run through five devel opment cockpit simulations to achieve the standard now being adapted for hardware- in-loop simulation of the concept. An AN/APG-70 forward looking infrared (adapted from Martin Marietta's Lantirn system) will be pod-mounted and provide a 1:1 field-of-view match of the scene ahead on the pilot's wide field-of-view headup display. Also displayed will be present and target airspeed, thrust nozzle/vane position, and a pitch ladder. The pilot will make a radar sweep of the runway, freeze the picture, select a strip to land on, and designate it using the radar. If he picks too small a strip it will be rejected. When the strip is accepted the radar will interface with the Flir, INS and Hud via the central computer to project a view of the runway, shown in the correct pilot perspective, on the Hud, (Passive ground landing aids are allowed so that radar corner reflectors could be set up to deliniate a suitable strip). Once the Stol strip is locked into the system, the pilot will fly the Hud pipper on to the desired touchdown point and select full military power. The IFCS will then vary the nozzles and thrust reverse vanes to maintain 119kt. (The F-15's usual approach speed is 135kt) at a constant angle of attack. This is maintained until a positive touchdown (at up to 13-5ft/sec Right The 2-D nozzles demonstrate thrust vectoring in afterburner with (top) 20" nose-up pitch (centre) normal and (bottom) 20° nose- down pitch *m Above The Stol Eagle will equal or better the F-15C's air combat performance rather than the F-15's usual maximum of lift/sec) is achieved when 135° vane is selected by pulling the throttles back via a spring-loaded gate for full reverse thrust. Also, on positive touchdown of the main gear a weight-on-wheels switch triggers an IFCS programme to make the canards and tailplane dump lift, effectively "snow-ploughing" with both canard and tailplane working to get the nose down for full reverse thrust and anti-skid auto wheel-brake effectiveness. As the groundspeed falls off, the vanes schedule back automatically to avoid exhaust recirculation and subsequent reingestion. On the ground the F-15's rough-field gear will be able • to hit a Category E repaired runway at full speed with no adverse effects. Category E repairs to bomb craters allow a rough-edged bump or sag of some 80ft diameter every 200ft. (The rough-field gear might be retrofitted to all F-15s). When the Stol Eagle first flies it will be with the normal F-15 round-hole engines. The square-section thrust vectoring nozzles will not be fitted until the Stol tests start at Edwards AFB. The aircraft will have extensive telemetry fitted. This will monitor 55 aircraft motion points, 370 propulsion system parameters, 193 load points, and 190 control input points. In the overall envelope, windtunnel testing predicts some sparkling perform ance increases, compared with the standard F-15C. The take-off roll for Stol Eagle will be 29 per cent shorter, while the landing run is predicted as 72 per cent shorter. The pitch rate will be 33 per cent better and roll rate 53 per cent better (it is already neck-breaking). The maximum lift coefficient is up by 78 per cent, and deceleration rate improved by 72 per cent. Quite apart from all that, it retains the F-15's ability to shoot you down. B 34 FLIGHT INTERNATIONAL, 7 November 1987
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