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1.15 Tests and Research
The aircraft handbook for the Sabre Mark 5 contains the following performance data for the conditions at the time of the accident:
| Nosewheel lift-off speed | 110 knots |
| Takeoff speed | 130 knots |
| Takeoff distance | 3,200 feet |
| Distance to clear S0-foot obstacle | 4,600 feet |
An 8-mm movie of the takeoff was analyzed by making a series of 8 x 10 inch enlargments of every eighth frame, counting backward from the initial fireball. Various stationary landmarks in the background of each photograph were used to determine the angular displacement of the aircraft from the camera location, and also the distance the aircraft moved along the runway. The deck angle of the aircraft in each photograph was then measured and corrected for the distortion of that particular viewing angle. The groundspeed, based on camera frame speed and distance traveled, was calculated and the speeds were averaged for every three frames to minimize the effects of sighting errors, Finally, the height of the aircraft was established by calculation or estimated in relation to other photographs where calculations could not be made.
In summary, the initial lift-off occurred between 2,800 and 2,900 feet from the end of the runway at an airspeed of 124 knots. The deck angle was approximately 11° Aircraft Noseup (ANU). The airspeed and deck angle continued to increase to 130.5 knots and 15.5° ANU, respectively, At this time the deck angle kept increasing, but the acceleration stopped and the speed began decreasing. The aircraft was 2 feet above the ground, measured from the bottom of the main landing gear. The aircraft settled back to the runway at approximately 3,700 feet, as the nose attitude lowered to about 10° ANU and the velocity dropped to 128 knots. Within a few seconds the speed began increasing again and eventually reached a maximum of approximately 137 knots. However, the deck angle also increased markedly to over 16.5° ANU and remained in that attitude. During the same interval, the aircraft was approximately 5 feet above the runway. The aircraft touched down again 5,005 feet from the takeoff end of the runway and disappeared from the camera view.
The nose attitude of another Sabre Mark 5 aircraft was calculated from film made during a takeoff. Although the aircraft was not equipped with external fuel tanks, the initial lift-off attitude would not vary significantly from that of N275X. The attitude during the test takeoff was approximately 5° ANU.
