Forty Years Ago in the X-15 Flight Test Program, May 1962 |
At the beginning of May 1962, Major
Robert Rushworth was preparing to fly an airframe heating
investigation with the X-15-2, but first it would be carried
across the country by the NB-52A to appear at the Eglin Air Force
Base airshow. Major Bob White was planning to evaluate the
performance of the Alternate Stability Augmentation System (ASAS)
of the X-15-1 at high angle of attack.
The X-15-2 was displayed at an airshow at Eglin Air Force Base in Florida over the first weekend of May 1962. Major Jack Allavie piloted the NB-52A across the country with the X-15-2 on the pylon on May 2. Major Bob White went along as co-pilot. That was the only occasion on which an NB-52 landed with an X-15 away from Edwards. They returned the X-15-2 to Edwards Air Force Base on May 5.
One of the main parameters that aerospace engineers are concerned with is called dynamic pressure. The dynamic pressure that an airplane encounters is directly related to the speed of the airplane and the density of the atmosphere through which it is flying. The effectiveness of aerodynamic control surfaces and the rate of airframe heating from aerodynamic friction are both related to the value of the dynamic pressure. Engineers use the letter q to represent dynamic pressure. The value of q at typical X-15 launch conditions (45,000 feet altitude and an airspeed of 450 miles per hour) is about 145.
After Major White endured two aborts of the X-15-1 airframe heating flight in April, Major Robert Rushworth was assigned to fly the twenty-second flight of the X-15-1.
The flight plan called for Major Rushworth to make a 20 degree climb at full throttle to an altitude of 54,000 feet, followed by a pushover to zero-g flight. Rushworth was to level off at 73,000 feet and throttle back to 30% thrust, adjusting the speed brakes to keep the speed of the X-15-1 at about 3,400 miles per hour. During this period, the value of dynamic pressure (q) would exceed 2,000 for the first time during an X-15 flight. The engine would burn out after about 103 seconds. After burnout Rushworth would make a 5-g turn to the right. As the X-15 decelerated, he was to turn off the channels of the SAS, one at a time, to evaluate the response of the ASAS.
Major Rushworth was scheduled to fly the X-15-2 on May 7, but overcast skies postponed the launch for a day. The NB-52B took off on May 8 with Major Allavie and Major Russell Bement at the controls. Jack Russel occupied the launch panel operator's station behind the pilots. The number four J57 jet engine malfunctioned and was shut down. The flight progressed on the power of the Stratofortress' other seven engines.
Rushworth triggered the drop of the X-15-2 over Hidden Hills Lake and started climbing at full throttle. He leveled off at 70,000 feet and throttled the XLR-99 engine to 30% thrust. This was the first time that the XLR-99 had flown at less than 50% thrust. Rushworth extended the speed brakes 16 degrees to maintain a speed of mach 5 for 33 seconds. The edges of the speed brake panels were heated to a tempertature of 1,250 degrees Fahrenheit by aerodynamic friction. The pressure in the cockpit of the X-15 dropped, and Rushworth's pressure suit inflated just as the rocket engine consumed the last of its fuel. The X-15 was traveling mach 5.34 (3,524 miles per hour) at engine burn out. Rushworth rolled the X-15 ninety degrees to the right and pulled back on the stick until he was subjected to 4.5 gs. Rushworth was impressed by the "snap, crackle, and pop" sounds emanating from the X-15 as it glided back to Edwards Air Force Base.
The 1962 Edwards Air Force Base Open House was held on May 20. Major Allavie and RAF Squadron Leader Harry Archer piloted the NB-52B as it participated in the rehearsal for the aerial display on May 19. The X-15-3 was mounted on the wing of the NB-52A and they were placed on static display on the flightline during the airshow. Major Miles Burganheim occupied the co-pilot's seat of the NB-52B as Major Allavie flew it past the crowd on May 20.
NB-52A displayed with the X-15-3 suspended from
the pylon at the Edwards AFB Open House on May 20, 1962. Photo by
Tom Brewer via Greg Spahr.
Rushworth was assigned to fly the twenty-eighth flight of the X-15-1 two days after the open house. The X-15-3 was removed from the pylon of the NB-52A and the X-15-1 took its place. The primary purpose of the flight was an investigation of boundary layer flow around the airframe of the X-15. The flight plan called for Rushworth to pull up to a climb of 30 degrees at full throttle, then push over to zero-g flight until leveling out at an altitude of 90,000 feet. He was to shut down the engine after 77 seconds . After shutting down the engine, he was to pitch the nose up and down in steps of 5 degrees between 10 degrees nose up and ten degrees nose down three times.
The X-15-1 on the wing of the NB-52A. This photo may have been
taken during the preparation for launch of mission 1-28-49 on May
22, 1962. Note the multi-probe pressure rakes mounted around the
nose of the X-15. The probes measured the airspeed at several
distances from the skin of the X-15 simultaneously. The air
closest to the skin of the rocket plane (called the boundary
layer) moves slower than the air farther away. A special X-15
silhouette, pointing to the left, was added to the scoreboard on
the side of the NB-52A to commemorate the return flight from
Eglin Air Force Base on May 5. It appears at far right on the
bottom. Photo courtesy NASA.
Major Allavie and Captain John Campbell were at the controls of the NB-52A on the morning of May 22. Jack Russel managed the systems of the X-15 using the launch panel controls, observing the rocket plane on the twin television monitors that occupied the space between his station and the pilot's seats.
After Rushworth launched the X-15-2 over Hidden Hills Lake, he was immediately aware that its roll stability was not as good as expected. He had to constantly counteract its tendency to roll to the left through the entire flight. At an altitude of 96,000 feet, an overspeed of the turbopump of the XLR-99 triggered an early shut down of the engine after a burn of 75.3 seconds, when the X-15-1 was going mach 5.03 (3,450 miles per hour). It was still climbing and reached a peak altitude of 100,400 feet, over 10,000 feet higher than planned. Rushworth dropped the nose slightly to get it back on profile, then pitched the nose up and down in controlled increments to collect the desired boundary layer flow data.
Major BobWhite was scheduled to make the twenty-third flight of the X-15-2 on May 24. The primary purpose of the flight was to evaluate the performance of the ASAS at an angle of attack of 23 degrees. The flight plan called for White to pull up to a climb angle of 30 degrees at full throttle to an altitude of 56,000 feet, then push over to zero-g flight for forty seconds. Seventy-five seconds into the flight he was to pull up so that the X-15 was pulling 2 gs for the last eighteen seconds of powered flight. After the XLR-99 engine consumed the last of its propellants, White was to pull up to an angle of attack of 23 degrees, disengage the roll channel of the primary Stability Augentation System (SAS) and observe the behavior of the X-15 as the ASAS kicked in. Then he would re-engage the SAS and roll the X-15 thirty degrees to the right while holding the angle of attack at 20 degrees for twenty seconds during the ascent. The X-15 should reach a peak altitude of 162,000 feet three minutes after launch.
Bad weather on the morning of May 24 resulted in a postponement of the flight until the next day. Major Fitzhugh Fulton and Major Russell Bement took the NB-52B aloft with White in the cockpit of the X-15-2 on May 25. As Jack Russel was setting up the inertial navigation system, the stable table overheat light came on, causing the mission to be rescheduled for May 28. It was postponed again to May 29, but the stable table malfunctioned again that day. This was the fourth consecutive launch abort for Major White.
The NB-52B taxis out with the X-15-2 on May 25,
1962. The launch was aborted when the stable table overheat light
came on. The last mission mark on the fuselage represents mission
1-27-48, flown on April 30. Photo courtesy AFFTC/HO
Major Rushworth scheduled to fly the fifth flight of the X-15-3 on May 29. The primary purpose of the flight was to familiarize Rushworth with the operation of the MH-96 adaptive gain flight control system that equipped X-15-3 and to evaluate its control of the reaction control system (RCS) while the X-15 was above the atmosphere. The flight plan called for him to ignite the XLR-99 engine at 75% thrust, then throttle up to 100% thrust and pull up to a climb angle of 32 degrees. He would shut down the rocket engine 77 seconds into the flight, at an altitude of 117,000 feet while the X-15 was going mach 5.15. During the ascent to the peak altitude of 206,000 feet he would roll the X-15 from side to side and then pitch the nose up in 5 degree increments to an angle of attack of 20 degrees. During the descent, he would keep the nose up to pull 4 gs as he reentered the atmosphere.
Major Rushworth was grounded by the flight surgeon on May 29 and again on May 30. The X-15-3 flight was reassigned to Major White, but he was still occupied with the twenty-third flight of the X-15-2. He was scheduled to fly the X-15-2 on June 1 and Joe Walker was on the roster to fly the twenty-ninth flight of the X-15-1 on June 7. The fifth flight of the X-15-3 would wait until later in June.
Books about
the X-15 available from 
X-15 (The Nasa Mission Reports)
Angle of Attack : Harrison Storms and the Race to
the Moon by Mike Gray. The biography of Harrison Storms, who
was instrumental in the development and operation of the X-15.
At the Edge of Space : The X-15 Flight Program
by Milton O. Thompson. The story of test flying the X-15 from the
point of view of the pilot.
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