The purpose and content of this website is the description of a very unique airplane, The Lockheed Aero Space Trainer (AST), it's conception and performance and the flying experiences of the test pilots who took it to the edge of space. The AST was a major modification of the famous Starfighter, the first airplane to attain twice the speed of sound (Mach 2) in level flight. AST was designed to teach experienced test pilots to expand their capabilities into space at a time that both the Air Force and NASA were developing airplanes to journey into earth orbit and return to landing. The AST would allow a skilled test pilot to fly a rocket aircraft on the edge of our atmosphere, controlling only with rocket thrusters into a zone where it stopped operating as an airplane and became a space vehicle. It provided austere pilot training in space flight, during a very demanding and precise flight profile with an extended period of zero 'g', and with a reentry to the atmosphere similar in many ways to today's Shuttle reentry, and their "Drinkwater" approach to landing, named after the NASA engineer/pilot who developed the technique.
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Conception
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NF-104 with rocket mount |
This aircraft was conceived under a brilliant officer and pilot , Major McElmurray, who was the Deputy Commanding Officer of the Air Force Aerospace Research Pilots School, then under the command of Col. Robert 'Buck' Buchanan. ARPS Academic Instructor Mr. Chuck Schweikhard was also instrumental in the conceptual development. This school had been set up by the Air Force as a next step beyond Test Pilot School. Its graduates were especially prepared for the NASA and Air Force Space Craft, including winged vehicles, then being designed. The first class completed training in 1961 and its small class included three future famous astronauts, all of whom later flew to the moon: Frank Borman, Jim McDivitt, and Tom Stafford. Frank and Tom remained on as instructors for Class II, made up of 7 test pilots, one of who was an Air Force finalist for the first NASA Gemini astronaut group and later was the Air Force test pilot for the AST. Even before the first class, Buchanan's staff felt an advanced flight trainer for space was vital but recognized the impossibility of acquisition through standard processes for a new aircraft. The cost, the politics and the acquisition timeline would be prohibitive. It was a credit to their technical capabilities and foresight that they recognized the potential in the NF-104A airplanes assigned to the school. Maybe more importantly, the way they approached acquiring the aircraft was equally inventive. Every school F-104A had an "N" prefix, commonly used to designate "Non-Standard" on any Air Force Airplane. In the case of the school it normally addressed only the addition of a test instrumentation package for student training. Their idea was a big stretch as just another "N" model, but it solved the approval problems. It just happens that the modification were more than very substantial, beginning with the addition of a liquid rocket motor, AR2-3, which had powered the Bell X1-A on the first supersonic flight by Chuck Yeager. Next, the addition of a dozen monopropellant rockets to control flight outside the sensible atmosphere. In this case they chose small rockets being used to control the X-15 in the manner a space capsule is controlled. The "modifications" go on and on. A fully pressurized cockpit would be necessary since full-pressure suits, when inflated, were not compatible with normal pilot functions. An oxygen-pressurized cockpit would be explosive at high altitude, as later occurred on the Apollo launch fire, so pressurized nitrogen gas would be necessary but with drawbacks, one of which almost cost the life of one test pilot. Significant changes in flight instruments would be necessary for a pilot to control in near-space, and here again they conceived unique modifications of existing equipment. For example, the Navy's standard All-Attitude Control Display was adopted by changing the Instrument Landing System meters to aeronautic measures of angle of attack (alpha) and side-slip (beta), absolutely necessary to control the airplane when it became the spaceplane. The addition of a long nose probe with large alpha and beta vanes made this possible.
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Design and Construction
The school management and a small Lockheed team worked out the detailed concept and were able to convince Air Systems Command that a shoestring modification could be funded to design and convert three existing F-104s. The project was approved, and managed under the school, with testing to be accomplished by the Air Force Flight Test Center, Test Division, before the planned turn over of the 3 AST airplanes to the ARPS. The design and major modification of the standard airplanes into the AST configuration were accomplished by a small team of Lockheed Aircraft employees in the company's Burbank plant in California. Every pilot that ever went through the ARPS flew an NF-104A, but few had a chance to fly the Aero Space Trainer, because of its brief life. The first of three ASTs, 60756, made its maiden flight on July 9, 1963, flown by Lockheed test pilot Jack Woodman.
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Maximum Zoom
The
last two zooms
of the Joint Contractor/Air Force testing were
flown by Smith and Woodman on maximum zoom
profiles, to 118,860 and 118,400 feet
respectively. Thereafter, all zooms under
the Air Force testing were flown by Smith, plus
one by Rushworth, to 112,000 were maximum also.
The testing was declared complete and Yeager
made four attempted zooms, also intended to be
flown with maximum zoom profile, also achieving
a best somewhat over 103,000 feet. The
maximum zoom is represented by the chart pictured
below.
Maximum Zoom Profile
This overview explains the maximum zoom
mission from take-off to landing, including the
primary procedures and operations, from the
pilot’s point of view. The detailed procedures
for a pilot are available in the Partial Flight
Manual (PFM), Section II, except with
significant restrictions later imposed by the
Yeager Accident Board. Two of many vital
pre-flight checks, peculiar to AST were to set
16 degrees on the “alpha null selector”, which
would be the pitch attitude guide, and the final
and important pre-flight check was “ AARS erect
and heading slaved” which was very important to
assure that the most vital instrument during
zoom was slaved to actual headings and that the
critical horizontal reference was functional.
The take-off roll of AST was a bit longer
and all events occurred at a bit higher speed
than the standard fighter because AST was
heavier, even though lift was gained from the
added total of four feet in wingspan, due to the
additional wing tip segments housing roll
thrusters.
The afterburner was always used for zoom
takeoffs, with nominal indicated airspeeds in
knots of 185 at nose wheel lift-off and take-off
at 210 CIAS. Wing flaps were raised at 260 and
level acceleration to 400 knots was the point of
terminating afterburner and start of climb in
full military power. Acceleration was continued
to 450 in the early climb to retain that climb
speed until an indicated Mach number, after
which climb rate was established to maintain
0.86 Mach to mission altitude.
We climbed west out over the Pacific then
turned around for our run-in at 35,000 on an
easterly heading, calculated to reach the
pull-up in a position north of the base, in
event of inability to restart, necessitating a
dead-stick landing. During this period the RCS
was checked, and preparations for ignition of
the rocket motor were completed.
The run-in to pitch up started with military
power going to full afterburner at the
appropriate point to achieve precise pull-up
location. The necessary checks are presented in
the chart above. At Mach 1.8, the final pitch
alignment of the AARS was set. For maximum
performance, it was beneficial to get as much of
the acceleration from the unassisted jet engine
which could go all the way to Mach 2.2 depending
on environmental conditions at altitude, saving
the rocket time for vertical flight! It was
also ideal to be at only 1200 pounds of jet fuel
at pull-up, for a lighter AST, thus higher
altitude.
The rocket engine was ignited at full thrust
while still in level flight and the 3.5 g
pull-up was initiated at the 2.2 Mach point.
(The exception was my highest zoom with a
pull-up at Mach 2.4.) All of these
preliminaries to the climb, especially the
exactness of the pull-up, were crucial to best
performance.
In order to provide safe conditions upon
reentering after zoom, re-trim from the level
position, before pull-up was not permitted.
That did add difficulty to retaining constant
pitch angle thus to the frequency of monitoring
the AARS, but that gage would be the most vital
throughout the zoom in any event.
Upon achieving a precise 70 degree pitch
angle before giving up any of the 3.5 g’s,
maintaining that precise angle became the most
imperative task for maximum altitude,
thereafter.
Pitch angle, being the airplane’s
longitudinal reference to the horizon was very
near its flight path angle at the end of the
pull up, with the very high Mach, thus low angle
of attack. However to maintain that 70 degree
climb path as the speed began to dissipate,
required a gradual increase in angle of attack
to supply lift, so the pilot was sitting at 84
degrees and more, his back virtually horizontal,
because the ejection seat was installed to cant
back 14 degrees to the airplane. The pressure
suits fixed helmet and visor provided a limited
field of view straight ahead. Consequently,
from pull until descending all flight control
was on instruments, since reference-free sky was
the only sight, and the flying job allowed
virtually no time to view it.
The climb to apogee was a true straight path
70 degree climb until airspeed got too low.
During that straight but challenging effort to
maintain a perfect climb, there were
distractions and vital chores. The distractions
were the necessary checks of vital instruments
and system functions. The chores which resulted
included throttling the afterburner to stay
within limit as jet exhaust gas temperature was
monitored, until it had to be shut off to avoid
damage at around 75,000 feet. In the range of
85,000 that procedure was followed from full
military all the way to idle power, which was
maintained until EGT was exceeded, then engine
was shut off.
Then a curved flight path was formed from
the tangent between the fixed 70 degree pitch
and the increasing alpha (relative wind) until
alpha reached 16 degrees. At that point,
aerodynamics was virtually out of the situation
and a ballistic AST had arrived on its parabolic
path. Gravity would control that path, but the
pilot had the toughest job, just ahead, which
was to maintain proper attitude on a path he
could not alter.
The pilot could not change the path again
until the AST had reached its apogee and fallen
back, well into aerodynamics region. But he
had his most vital and difficult job just to
assure that the AST would be properly aligned
with that path in all three axes throughout that
space journey.
It was especially challenging in the pitch
axis, where rapid control changes were
necessary, with a unique space control and
stability, to assure the reentry would occur at
16 degrees with near zero yaw and roll.
Maintaining alpha was always the most
important and demanding task, especially in the
space adventure but even in the resulting dive
to earth. A risk reduction during reentry was
made possible, after our early testing, by a
modification to speed brakes which made their
use possible during recovery from zooms,
removing a coffin corner from the profile.
Final descent, short the occasional
dead-stick landing if relight failed, was
routine and was the time in which you realized
just how hot that suit became
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AST Use for Student Training
Limited use of the remaining two ASTs
was the only flying ever permitted after Major
Smith completed all the tests required by the
Yeager Accident Board and the remaining two ASTs
were finally returned to the ARP School for student training, as directed, with the restricted profile to assure that the aircraft were always within the aerodynamic control region.
It should be noted that all of the data in the
partial Flight Manual reflect only the
restricted flight regime, not the maximum
performance. This greatly reduced the likelihood of entering uncontrolled flight during a zoom by lowering the maximum altitude, decreasing the climb angle, increasing the minimum airspeed, and decreasing the angle of attack limit to 12 degrees. These safety features assured remaining outside the zone in which true space control could be experienced, but in so doing offered little, if any, spacecraft training and experience not offered by the ordinary F-104A zooms. It became an expensive "Gee Whiz" ride and possibly a confidence builder. Another AST flight accident occurred later from an explosion in a rocket oxidizer tank that resulted in safe recovery of the instructor pilot in one of the school staff's checkouts. A similar ground incident resulted in un-repairable damage to the aircraft, ending the life of the Aerospace Trainer Program, with one becoming a static display on a pedestal at Edwards, AFB. Even that last airplane suffered ravages when its special nose section was allowed to be borrowed by Mr. Daryl Gruenmeyer to further modify a civilian F-104 in which he had set a
low altitude speed record, and the aircraft was
destroyed in a crash.
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