The Lockheed S-3A Viking
Lockheed S-3A development followed a similar path to that for the McDonnell Douglas T-45A. That is, corrections for deficiencies found in the 1973 flight tests of the fourth S-3A airplane were stretched out over the next ten years. The original S-3A design had the same problem in carrier approaches as did the original T-45A Goshawk. With jet bypass engines delivering enough thrust at low engine rotation speeds to stay on the final approach path, “If all of a sudden you’re starting a settle coming into the carrier, you add power to regain altitude but nothing happens because of the delay in getting the engines to respond” (Wilson, 1992).
In the case of the S-3A, the belated fix was the direct lift control system described previously. Another belated stability and control fix to the S-3A for carrier suitability is thrust trim compensation. The S-3A’s low-slung engines produce longitudinal trim changes when power is used to adjust the final approach path angle, upsetting the desired constant angle of attack condition. The compensation moves the elevators automatically when the pilot adjusts the throttle position.