MEMORANDUM for Chief, Research Projects Office
Summary
Flight 2-43-75 was flown essentially as planned by Lt. Col. Rushworth on November 3, 1965 to: a. obtain handling qualities data with external tanks installed, b. evaluate external tank separation characteristics and, c. determine ejected external tank trajectories.
'The tanks-on handling qualities were very adequately predicted by earlier simulator studies and were satisfactory for all flight conditions.
The tanks separated cleanly from the aircraft for the ejection at the planned flight conditions. The rotation of the tanks, (nose down and out) was not exhibited to the degree expected. The tanks appear to fly in a horizontal attitude until the drogue parachutes are deployed.
The tanks were unstable with either the drogue or main parachute and because of the increased drag attendant with the instability, the tanks impacted short of the anticipated points. Only the ammonia tank was recovered in a repairable condition.
Flight Profile
The radar track and flight profile were very close to what was planned. Maximum altitude was approximately 70,000 feet (70,000 feet planned) and maximum velocity was approximately 2100 fps (2200 fps planned). The ground track was within one half mile of the planned track at the time of tank ejection. The planned and flight tank ejection conditions were:
Velocity 2,100 fps » 2,100 fps
Altitude 69,000 feet » 70,000 feet
Dynamic Pressure 300 psf » 300 psf
Angle of Attack 5° » 4.8°
Handling qualities with tanks on were essentially the same as had been predicted earlier by wind tunnel and simulator data. Pilot ratings for all conditions indicate satisfactory handling qualities and are as follows:
Condition Pitch Roll Yaw
Launch (3) 3 (3) 3 (3) 1.5
Acquiring a (2.5) 2.5 (4) 2.5 (2) 1.5
Holding q (2) 2.5 (3.5) 2.5 (2) 1.5
Tank ejection (3) 2.5 (3) 2 (3) 1.5
The launch transients were within the range of experience for previous X-15 flights. The transients at tank ejection were more severe in pitch and yaw and less severe in roll than have been experienced at launch. All transients were well damped. The maximum angular rates were:
Pitch rate 3.2°/sec. 5°/sec. to -13°/sec.
Roll rate 45°/sec. 20°/sec.
Yaw rate -1°/sec. 2°/sec.
Tank Separation Characteristics
The external tanks separated cleanly from the airplane when ejected under circumstances which were expected to be less favorable than at normal tank ejection. At normal tank ejection, some residual propellants will be retained in the tanks and this will result in the tanks having a more favorable center of gravity location for both separation and stability on the drogue chute.
Movies of the ejection and separation were of such poor quality that tank motion could not be accurately defined. These .movies do indicate, however, that the tanks did not rotate nose down and out to the extent expected. The tanks tended to fly straight and level while dropping away from the airplane. An increase in angle of attack to a value greater than 5° increases the risk of the tanks hitting the airplane. An increase in dynamic pressure may also increase this risk since it tends to accentuate the separation characteristics which are a function of angle of attack.
Future empty tank flights will investigate separation at higher dynamic pressure once better photo coverage is assured.
Tank Trajectories
The tanks were unstable during the descent on the drogue parachute. Tank center of gravity location with respect to the chute attach point and the size of the chute contribute to this instability. A need for a larger chute and a more aft center of gravity are indicated.
The drag produced by the unstable tank/drogue combination resulted in a decrease in the range of about 2.5 miles. Both tanks impacted well within the bounds of the bombing range with the NH3 tank landing 2.3 miles short and 0.6 miles left of its predicted point, and the LOX tank impacting 2.7 miles short and 1.6 miles left of its predicted point.
The NH3 tank was only slightly damaged at impact while the LOX tank was damaged beyond repair. The loss of the LOX tank was the consequence of a failure of an explosive bolt which secures the nose cone covering the parachute compartment. The bolt fired but did not separate, so that the parachute could not deploy.
Tank recovery was complicated by tank instability while being towed by the helicopter.
Instrumentation and Operational Discrepancies
Telemetered data showed transients and/or drop outs for critical times during the flight: launch, tank ejection, engine shutdown, ventral jettison and landing.
The pilot's vertical velocity indicator (H-dot) was backwards, indicating an upwards velocity when the airplane was, in fact, sinking.
The inertial velocity presentation to the pilot malfunctioned.
The ventral was dropped from very low altitude, and the parachute did not deploy.
The squat switch (SAS cutoff) was not armed for the landing, and SAS did not disengage at touchdown.
Strain gage #204 did not record properly on O-18-36C.
The center stick pitch CPT did not record properly on O-19-36C.
The processing of the film from O-19-36C was not satisfactory.
The Milliken camera
on the vertical tail had poor resolution, possibly because of frosting
of the lens.
Elmor J. Adkins, Head
X-15 Research Project Office