X-15 OPERATIONS FLIGHT REPORT



FLIGHT NO: 2-34-57 DATE OF REPORT: October 1, 1964

PILOT: L/C Rushworth DATE OF FLIGHT: September 29, 1964

CARRIER AIRCRAFT: B-52 #008 LAUNCH LAKE: Mud Lake

PURPOSE OF FLIGHT: Stability & Control Evaluation and ENGINE S/N: 108

Advanced X-15 Landing Dynamics

I. Discussion of Previous Operations

A. Preliminary conclusions given in the last flight report (2-33-56) for extension of the nose gear during that flight were proved correct by the heating facility tests conducted on September 1 & 2. These conclusions are:
  1. Uplock hook yield is caused by excessive loads imposed by the door when it "warps" due to aerodynamic heating.

2. Uplock hook yield, when combined with inadequate "hot" compensation in the gear actuating cable, will cause the gear to unlock and extend in flight under relatively high aerodynamic heating.
 

 The following fixes were incorporated:
  1. A stronger uplock hook was installed.

2. The actuating cable "hot" compensation was increased from nominal 1-1/2 inches to 3-1/2 inches.

3. Spring loaded door brackets were installed to reduce uplock hook loads by allowing the door to deflect approximately 3/16" under thermal loading.
 

 Inspection after this flight showed no bending of the uplock hook although aerodynamic heating was similar to that experienced during the last flight. It therefore appears that these fixes adequately prevent unlocking of the nose gear. However the uplock system for the scoop door is still inadequate since that door did open during flight at approximately the point of highest aerodynamic heating. A redesigned scoop door uplock will be incorporated prior to next flight. (See Section IV for more detail.)

B. A bright blue "hot spot" which appeared on the rear bulkhead of the RH tunnel after 2-32-55 continued to enlarge slightly on 2-33-56. It did not show any further enlargement during flight 2-34-57.

A titanium test panel was installed inside the compartment for this flight, just forward of the base bulkhead and spaced 1/4~ from the bulkhead. No evidence of heat was shown by this test panel. It therefore seems likely that the origin of the heat is outside of the tunnel compartment.

It is thought that this hot spot is caused by the close proximity of the RH tunnel base bulkhead to the engine turbine exhaust. Further temperature data on this "hot spot" will be gathered on subsequent flights.

 II. Configuration Changes A. Nose gear uplock fixes were incorporated as listed in I. A. above.

B. Two base pressure orifices were installed in the engine flame shield to obtain research data on base drag.

C. Internal recording of speed brake position was added to one of the oscillographs.

D. Hycon cameras were installed in the C.G. bay for this flight.

E. A titanium test panel was installed as described in I. B. above.

 III. Preflight Events A. Engine S/N 106 was replaced by engine S/N 108 because of a leaking governor seal.

B. Canted bulkhead #131 developed a crack in the flange at the inner skin joint resulting in excessive cabin leakage, at approximately the 8 o'clock position. A patch angle was installed over this joint after drilling stop holes in the cracks. The entire area was resealed and a cabin leak check performed. 46 C.F.M. leakage was recorded.

C. New seat booms were received and installed Saturday, September 19.

D. Engine run on engine S/N 108 was completed Tuesday, September 22. APU runs planned for that same day were postponed until Thursday, September 24, due to a failed transformer rectifier unit which was replaced.

E. Personnel from Hycon Corporation arrived Thursday afternoon (9/24) to install and checkout the Hycon cameras. Checkout was completed with no significant trouble and the cameras were serviced for flight Thursday evening.

F. A failure of the solid state commutator caused a breakdown in the T/M system the night prior to flight. Third shift time was used to repair this system and the flight was rescheduled from 0900 to 1200 on Tuesday, September 29, 1964.
 
 

 IV. Flight Events A. Servicing was normal. A ground jettison check of the propellant jettison system was made.

B. Cabin altitude was marginal during captive flight varying between 35,000 and 41,000 feet until the point at which the "Aux Cabin Pressure" system was initiated. It appears that #l mixing chamber was not feeding LN2 properly since its controlled temperature indicated approximately -35°F instead of -34°F. (This mixing chamber has since been removed for bench check).

C. During flight at approximately Mach 4.5 and 88,000 ft altitude the N.G. scoop door popped open. The pilot decelerated the X-15 and descended to Edwards for a landing. When "landing gear down" was selected, the main gear cycled down normally but the nose gear was slow in moving to the down and locked position. The actual landing was completed without further incident, the tires remained inflated and rollout was approximately 6,000 feet. Postflight inspection, including two cycles of the nose gear from the stowed and serviced position, revealed no mechanical deficiencies responsible for the slow cycle experienced during the flight. It is thought that this slow cycle was caused by one or more of the following:
 

1. Adverse air loads due to the scoop door position, bent backwards from its normal "scoop" position.

2. Loss of the pyrotechnic initiator due to possible premature firing earlier during the flight, triggered by aerodynamic heating from the opened scoop door

3. Possible temporary mechanical binding or interference caused by aerodynamic heating from the opened scoop door.
 

 As to failure of the scoop door uplock system, two possible alternate redesigns are being considered:
  1. Elimination of the scoop door (except for inspection and servicing). The door would be bolted shut during flight, and to retain redundancy a second initiator would be installed to actuate the gear to approximately a 30° position where airloads would act on the main nose gear door.

2. A new uplock design for the scoop door featuring positive retention of the door roller on the uplock hook.

 Both of these ideas are being studied and whichever one is selected will be incorporated in all X-15s. Approve By: Prepared by:

Perry V. Row William P. Albrecht

X-15 Senior Project Engineer X-15 Project Engineer