Summary

Flight 2-50-89 was flown by Major William J. Knight on November 18, 1966, to obtain handling qualities data with and without full external tanks installed, to evaluate external tank separation characteristics, for evaluation of ablatives located on the lower fixed vertical stabilizer, to obtain optical degradation data with the Maurer camera, to obtain data on local flow conditions in the proposed ramjet location, to obtain base pressure data, and to evaluate the ablation effect on glass.

The maximum velocity attained was 6250 feet per second (4261 mph and a Mach number of 6.33) at an altitude of 96,800 feet. The maximum altitude during the flight was 98,900 feet.

The objectives of the flight were accomplished as planned with the exception of the Maurer camera experiment. The pilot considered the handling qualities of the aircraft to be satisfactory. The external tanks separation was satisfactory. The external tank recovery system worked properly, however, the tanks have not been returned to FRC due to the unavailability of the helicopter. The ablative material covering the speed brakes ablated away during the flight. The material on the remaining part of the ventral showed some charring. Adherence of the ablative fog or smoke to glass was observed on the ventral test window glass.

Profile

The flight was flown essentially as planned. Immediately after launch the aircraft rolled left to a 28-degree bank angle resulting in the left heading change observed on the ground track shown in figure 1.

A 2-degree shift in the value of the ball nose angle of attack resulted in lower than planned values of angle of attack during the flight. This shift was first noted during pre-launch when the pilot reported the angle of attack to be 5 degrees rather than the normal value of 2 to 3 degrees. After the nose-down trim change at tank release, the pilot planned to maintain zero "g", however, internal data indicates that the normal acceleration was -0.25 "g". Because of this negative "g" and the lower actual angle of attack prior to tank release, the aircraft leveled off at an altitude approximately 3000 feet lower than planned.

The pilot's velocity had indicated approximately 300 fps lower than normal prior to launch. The cockpit film shows the pilot shut down the engine at an indicated velocity of 6000 fps and after engine "tail-off" a maximum indicated velocity of 6050 fps was observed. From internal records engine shutdown occurred after 136.2 seconds total engine time with 135 seconds occurring at full 100 percent thrust. The planned engine burn time was 132 seconds.

The pilot reported the launch transients were no more difficult than a normal X-15 launch. A time history of the flight is shown in figure 2.

The higher roll command required by the pilot after launch resulted from a higher rolling moment induced by the increased lift at the higher angle of attack with the lateral center of gravity offset to the left because of the heavier liquid oxygen tank.

During the rotation, the angle of attack varied between 9 to 12 degrees and probably averaged 10 to 11 degrees which was lower than planned because of the angle of attack calibration shift. The maximum normal acceleration observed was 2.2 "g" versus a planned 1.8 "g" maximum. The maximum dynamic pressure during rotation was 730 psf. A value of 600 psf was expected for simulation.

As planned, the pilot pushed over to an indicated angle of attack of 5 degrees at 59 seconds to set up for the tank ejection, however, the actual angle of attack was again 2 degrees low.

During the descent and deceleration to Edwards, a higher than planned energy condition existed and the speed brakes were not retracted as planned at 3800 fps at 60 nautical miles but rather at approximately 1500 fps within 15 nautical miles of high key position.

Handling Qualities

The pilot felt that the handling qualities of the aircraft during the tank flight were quite good. The following pilot ratings were given for the listed tasks.
 

Task	Pitch Rating	Roll Rating
Acquiring a	3	3 1/2
Maintaining a	2	2 1/2
Acquiring q	2	2
Maintaining q	2	2

No ratings were given to the yaw axis because the angle of sideslip presented no problem and no control task was required. An angle of sideslip oscillation was observed on the data that started before tank drop and persisted until the speed brakes were extended and angle of attack increased. The pilot did not observe or feel the oscillation which was less than ±1 degree.

The pilot performed the requested rudder pulses with the dampers on during the deceleration.

External Tank Ejection Characteristics

The conditions at tank ejection were:
 

	Planned	Final
Velocity, fps	2100	2170
Mach Number	2.17	2.27
Altitude, ft	69,000	69,700
Dynamic Pressure, psf	320	340
Angle of Attack, deg	5	3.5

 
 
 

The transients induced to the aircraft were similar to the empty tank flight (2-43). At tank ejection the angle of attack instantaneously increased to +4.2 degrees, then during the trim change, angle of attack went to -1.7 degrees. The normal acceleration dropped to -0.35 "g" immediately after tank separation and the maximum excursion observed was +1.3 "g". Both tanks separated cleanly from the airplane but the LOX tank separated 0.12 seconds before the NH3 tank.

Good photo coverage of tank separation and recovery system performance were obtained by three ground-based telescopic cameras at the Tonopah Test Range located approximately 7 to 10 miles from the tank release point. During descent, under the drogue chute, the tanks appeared to rotate in a similar manner as previously observed but at a slower rate.

From radar tracking of the NH3 tank it appears that impact under no wind conditions would have been approximately 2 miles from the release point. The idealized predictions had indicated that the tank would travel down range 6 miles. This difference is attributed to the drag coefficient of the tumbling tank with a slightly larger drogue chute being higher than that used in the idealized conditions.

The actual tank impact is shown in figure 3. The NH3 tank landed within restricted area 4809 at an elevation of approximately 6700 feet. The LOX tank landed on the boundary between restricted areas 4809 and 4807 at an elevation of 5700 feet. It is felt that some adjustment can be made to the launch point and planned heading for the next tank flight to allow impact in a more accessible area.

The external tank recovery system worked properly, however, the drop tank "manhole cover" drain valves failed to open. The external tanks have not been returned to FRC due to the unavailability of the helicopter to retrieve the tanks.

Thermal Protection System

This flight completed the sixth flight of the MA-25S ablative material on the fixed portion of the ventral. Because the thermocouple system in the 29-inch extension area was inoperative for this flight, temperature data from the ventral were not obtained. Visual inspection of this area revealed the ablative material covering the speed brakes had charred away completely. This is believed to have been a result of the lengthy period the speed brakes were extended. Some buckles were noted in the outer speed brake skin. The remaining ablative material will be removed from the fixed ventral prior to the next flight.

The test to evaluate the effect of ablative smoke or fog on canopy glass was completed during this flight. The glass previously utilized in the Hycon camera experiment had been installed in the ventral prior to flight 2-45. Previous tests by the Martin Company had indicated a tendency of the ablative smoke to adhere to glass. This test was conducted to determine if the smoke would be expected to attach to the X-15 canopy glass during the flight, blocking pilot's vision during the approach. Following the flight the Hycon camera glass was removed and one-half of the glass was cleaned. The results of the test are shown in figure 4. The test installation will not be flown again.

Several temperature levels experienced during previous flights to Mach 6 were exceeded during this flight. Sample temperatures from the flight are compared with temperatures from previous flights in table I. Calculated temperatures agreed well with the measured data.

Data were not obtained from the ventral speed brake area. The thermocouple system located in the 29-inch compartment does not function properly and data recorded from this system were not obtained. Temperatures calculated for the speed brake area, which have shown good agreement during previous Mach 6 flights, show a possible maximum temperature of about 1550°F on the lower speed brakes. Prior to flight 2-45, the speed brakes were covered with a thin coating of ablative material and this coating was still intact for this flight. The coating may have had some effect in reducing speed brake temperatures but its effect was not significant. Previous Mach 6 flights have yielded speed brake temperatures to 1250°F.

Because of the moderate angle of attack experienced at the high Mach numbers, the aerodynamic heating on the upper surfaces of the airplane were no more severe than experienced during numerous other occasions.

Hycon Camera, Phase II (Exp. No. 27)

The Maurer camera system was installed and a satisfactory preflight performed in September. Prior to closing out, the preflight check indicated the camera mount would not erect in the pitch mode. At this time it was not possible to determine the cause of the malfunction and the camera mount was pinned such that the camera would be restricted to a vertical position for the flight. After the flight, the weight-shifter motor was found to be malfunctioning. This motor has been removed for repairs.

After shutdown the pilot established the required attitudes for photographing the ground target with the Maurer camera, however, because the aircraft was to the left of the planned track it is likely that target acquisition was not achieved. Following the flight the camera film was returned to the experimenter for development and for analysis.

The tape recorder required for recording of the vibration data from the camera mount accelerometers did not function properly. The tape recorder is located in the 29-inch extension area with the Maurer camera. The heater required for satisfactory operation of the tape recorder in this environmental area was not operating for the flight. The tape recorder operation will be checked during the next flight of X-15-2.

Ramjet Local Flow Conditions

Data were obtained as planned. Analysis of the data is continuing.

Base Pressure Data

Data for this program are being obtained during each flight of X-15-2.

Instrumentation Discrepancies

The thermocouple system located in the 29-inch extension did not function during the flight. Additional effort to correct the heating problems with this system are scheduled to be conducted prior to the next flight.

The Maurer camera shutter pulse and slit-width traces were off-scale during the flight. The Maurer camera clutch signal failed to record.

Two channels of the P-800 channels of engine data were not recording properly. The X-B-U channel was off-scale during the flight and P-C-D channel was not operating properly.

The airspeed and altitude recorder traces were extremely light.

The inertial velocity recorded on 0-l9-36C did not function.

The helium flow indication system for the ammonia drop tanks did not function. This malfunction had been expected prior to the flight.

Operational Discrepancies

The drop tank "manhole cover" drain valves failed to open. It is believed that a design change of the squibs is required.

The paddle switches installed in the propellant lines to detect positive flow from the external tanks worked properly. The pilot reported switching to internal flow at 64 seconds. At the planned tank drop time of 66 seconds, the pilot pushed for the eject button but made contact with the rim of the circular guard. The second attempt was successful and tank ejection occurred at 67.5 seconds.

The LOX helium flow indicated full flow; however, as suspected, the NH3 helium flow indicator did not operate.

At 66.1 seconds after engine light, the NH3 discharge pressure was observed to decrease and caused a momentary decrease in chamber pressure which recovered in 2 seconds. This characteristic can be expected if the time between external propellant depletion and switching to internal or tank ejection is too long. The pilot actuated the internal switch approximately 5 seconds after external exhaustion as planned, however, it was not known until after the flight that this procedure can result in an engine shutdown.

At approximately 5500 fps, during the boost, the pilot reported observing the fuel line low light was on. It is most likely that the light came on at 66 seconds, when the fuel pressure decrease described above occurred, but was not noted until later.

The pilot went to jettison at the normal place approaching high key, however, propellant jettison did not occur. The aircraft was approximately on downwind before the pilot discovered that the jettison switches were in the stop jettison position. After the switches were placed in their proper position jettison began and continued through the final approach to landing. A time history of aircraft weight is shown in figure 5.

Because of a hydrogen peroxide fire the ventral recovery chute did not deploy and, therefore, the ventral suffered damage on ground impact. The landing appeared normal although more than normal trapped propellants probably existed.

E. J. Adkins, Chief

X-15 Research Planning Office