X-15 OPERATIONS FLIGHT REPORT



FLIGHT NO: 2-36-63 DATE OF REPORT: February 23, 1965

PILOT: Maj. R. Rushworth DATE OF FLIGHT: February 17, 1965

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

ENGINE: S/N 108

PURPOSE OF FLIGHT: (1) Stability & Control

(2) Advanced X-15 Landing Dynamics

(3) Star Tracker Checkout

I. Discussion of Previous Operations

A. Investigation of the "toe in" failure of the main gear strut lower clevis and skid pivot pins resulted in two conclusions:
  1. Inadequacy of the gear snubber to properly decelerate the gear at the end of its down cycle, resulting in high drag link load.

2. A "rebound" effect caused by bouncing of the skid bungee resulting in excessive peak loading in the drag links.
 

 These high peak loads in the drag link are concluded to be responsible for bending the lower clevis and partial shearing of the skid pivot pins.

Extensive testing at the contractors plant (H. W. Loud, Co.) produced a new snubber with higher damping, and in addition the rubber bumper in the skid bungee was replaced with expendable honeycomb inserts which absorb energy in the snubber piston without causing a rebound.

These two "fixes" were tested during two captive flights (2-C-61 and 2-C-62) on Monday, February 15, 1965. Drag link loads and snubber loads were well within limits for gear cycles at 260 knots indicated. Main gear "down" time was approximately 1.8 seconds, and nose gear time was 2.7 seconds. This new snubber and bungee combination was inadvertently subjected to a very severe test during flight 2-36-63 when the RH main gear was cycled down at approximately Mach 4.3 at 84,500 foot altitude, and about 620 "Q." Subsequent measurements show no deformation of the strut clevis, or toe-in resulting from this extreme test.

B. As a result of several NASA complaints regarding material and heat treat deficiencies in several parts received from NAA, the Air Force directed an inspection of the X-15-2 airframe by a task force composed of representatives of USAF, NAA and NASA. This inspection took place during the week of December 14, 1964. Selected items of structure were tested for hardness and proper alloy. Parts of the pylon structure of B-52 #008 were also inspected. No major defects were discovered although several minor (but acceptable) deviations were noted. The inspection was concluded on Friday, December 18, 1964.

 II. Configuration Changes A. Installed insulating cap on 20" helium sphere to reduce chill-down of source at altitude.

B. Installed new main gear snubber and new skid bungee with honeycomb energy absorber in place of rubber absorber.

C. Installed skid pivot pin with heavier wall thickness.

D. Relocated engine transducers from engine frame mounting to a new bracket in the aft fuselage. This should eliminate need for recalibration at every engine change.

E. Installed 2" altimeter in pilot's panel to make room for sensitive attitude indicator for Startracker missions. This attitude indicator replaced the "Q" meter which in turn was installed in place of the former large altimeter.

F. Installed additional 36 channel oscillograph (0-18). Landing gear data channels were shifted from the tape system to this oscillograph.

G. Vibration pick-ups and amplifiers were installed to record environmental data for design of the "Hycon II" induced turbulence experiment proposed for X-15-2.

 III. Preflight Events A. The new landing gear snubber system was received and installed during the week of February 8, 1965.

B. Engine and APU runs were made without incident on Monday, February 8. System preflights were conducted without major difficulty.

C. As mentioned in Part I, two captive flights were made on Monday, February 15, 1965. Only one was planned (for Monday morning) but due to a communications failure in the chase plane, no photographs (16mm movies) were obtained of the gear cycle and the captive flight was repeated in the afternoon. Photo coverage was excellent on the second attempt.

 IV. Flight Events A. Flight 2-36-63 was made as scheduled on Wednesday, February 17, 1965. During flight the RH main gear deployed at approximately Mach 4.3 and 84,500 feet altitude. The X-15 was landed without further incident. The RH main gear drag brace sustained severe discoloration due to aerodynamic heating. Subsequent inspection showed that the RH uplock hook was bent slightly open and, while further analysis is being made, it is presently thought that "bowing" of the strut in the stowed position, caused by aerodynamic heating of the outer surface of the strut, is responsible for overloading the hook and permitting the RH gear to "cam open" the bent hook. This theory will be tested by the NASA Heating Facility as soon as practical.

Other discrepancies observed during this flight were:
 

1. Inertial altimeter failure

2. Main engine pump oscillation

3. Radio receiver intermittent failure during latter portion of flight
 

 The engine (S/N 108) has since been removed for inspection of the pump control system, and the radio receiver has been replaced. The failure of the inertial altimeter is still under investigation.
 
  Approve By: Prepared by:

Perry V. Row William P. Albrecht

X-15 Senior Project Engineer X-15 Project Engineer