X-15
Adventures:
Flight 1(1-1-5) -- June 8, 1959
X-15's first flight
...
A glide to a
challenging landing
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Flight statistics
| Maximum altitude |
37,550 feet |
| Maximum speed |
Mach 0.79
522 mph |
| Flight duration |
4 min. 56.6 sec. |
| Rocket burn |
0 sec |
Scott Crossfield
already had years of experience with the X-15 before piloting its first
flight. He left NACA to join North American Aviation specifically to
contribute a rare combination of skills to shaping the X-15. He
offered the
perspective of an aeronautical engineer who already was one of the most
experienced test pilots of rocket powered aircraft, as well as early
jets.
One of the control effectiveness issues that he raised during design
would unexpectedly show itself on the first flight, challenging his
piloting skills and threatening to end the flight with a crash instead
of a landing. By June, 1959 the X-15 had completed several
captive-carry flights under the wing of a B-52. Some were deliberate,
testing system X-15 systems, B-52 systems, and aerodynamic
characteristics of both aircraft. Others were aborts, intended to be
the first free flight but terminated due to a variety of problems. They
ranged from APUs (auxiliary power units) that incinerated themselves to
a torn glove on Crossfield's pressure suit. The program was well behind
its expected schedule, everyone felt the need for a successful
free flight.
On the morning of June 8, 1959 the B-52 and X-15 went aloft again.
The objective was to do a simple glide to a landing, checking the
X-15's flying characteristics for the first time. All systems
looked good except that the pitch mode of the SAS (stability
augmentation system) didn't work. On a hypersonic flight this would
have been grounds for yet another abort, but this was to be an easy
subsonic flight. The decision was to go ahead as planned.
After takeoff the B-52 flew a spiral pattern around Edwards Air Force
Base, staying within X-15 glide range of a landing area in case of an
early drop. Rogers Dry Lake was the primary landing site,
Rosamond Dry Lake was available as a backup for the western part of the
climb pattern.
The first objective was to confirm that the X-15 would drop away from
the B-52 cleanly at launch. On the B-52's pylon the X-15 rode in air
flow disturbed by the carrier aircraft's wing and engine nacelles, as
well as by the X-15 itself. Because the B-52 has swept wings, the
X-15's left and
right wings experienced different airflow before launch. There was very
limited
room to avoid damage to both aircraft if the X-15 would pitch up or
down,
yaw left or right, or roll left or right at the moment of release.
Aerodynamic analysis and wind tunnel tests predicted that the X-15
would roll to the right after release but would drop away cleanly if
its pitch trim was set correctly. Crossfield set the trim to 1
degree nose-up in preparation for launch. The B-52 completed its turn
onto heading 040 magnetic and quickly closed on the launch point over
Rosamond Dry Lake at an altitude of 37,550 feet. With a short
countdown, B-52 pilot Charlie Bock pulled the release -- A hydraulic
ram in the pylon disengaged three shackles, dropping the X-15 for the
first time at 8:38 a.m. and 40 seconds.
The X-15 pitched down and rolled to the right, more than Scott
Crossfield expected but little enough to produce clean separation.
Following the flight plan, he quickly checked out the new aircraft's
handling qualities before retrimming and slowing. Two more "getting the
feel" phases followed -- first slowing to near-stall airspeed, then
diving a bit more to accelerate to
190 knots. Here he dropped the flaps for a quick check of flying
qualities as they would be on approach, shortly before touchdown.
Raising the flaps, he accelerated again to perform the last planned
handling tests and to enter the landing pattern. The pilot had to be a
quick learner on this flight
-- With a glide ratio of about 4:1, the X-15 had only about 5 minutes
of
flying time available.
Crossfield found that the X-15 handled nicely, though a bit sensitive
in pitch due to the inoperational SAS mode. Rounding the turn to final
approach, he jettisoned the ventral fin, which parachuted down for
recovery.
Preparing for touchdown, he dropped the flaps. Unexpectedly, the nose
rose. Trying to recover, Crossfield found sluggish and late response to
his pitch inputs. The X-15 entered a PIO (pilot-induced
oscillation), porpoising through large pitch excursions. Crossfield's
challenge was to
learn in a matter of seconds how to arrest the instability or to time
the
motion well enough to set down without crashing. The solution had to be
found
before the X-15's airspeed bled off so far that it would stall,
dropping
abruptly into the lakebed. Crossfield tamed his bucking aircraft just
in
time, touching down on the lakebed at about 145 knots (160 m.p.h.).
North
American's design had anticipated a normal touchdown speed of about 200
knots.
Postflight analysis showed that the horizontal stabilizers couldn't
move quickly enough to track the pilot's control inputs -- once the PIO
started the pilot and the aircraft were out of synch with each other.
The stabilizers were driven by hydraulic actuators with only enough
power to move the control surfaces up to 25 degrees per second.
Changing valving in the hydraulic systems raised this limit to 35
degrees per second, and the problem never recurred in the 198 X-15
flights that followed.
Related materials:
Flight summary form as a web
page (html)
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Draft
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Final
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Scans of flight summary
form
from NASA flight log files:
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Radio communications transcript
Flight plan for
X-15 pilot as a web page (html)
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Draft
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Final
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Scans of flight plan form
for X-15 pilot
from NASA flight log files:
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Planned flight path
Note
by Milt Thompson on flight 1 (1-1-5)
Scott Crossfield, Bob White, and Neil Armstrong flew the X-15 for
North American Aviation, USAF, and NASA. On flight 1 (1-1-5)
Crossfield flew the X-15, White flew the F-104 chase plane.
Send comments or questions by email to Paul Raveling
Note
by Milt Thompson on flight 1 (1-1-5)
