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The Edge of Knight

Forty-three years ago this month, USAF Major William F. “Pete” Knight made an emergency landing in X-15 No. 1 at Mud Lake, Nevada.   Knight somehow managed to save the hypersonic aircraft following a complete loss of electrical power as it passed through 107,000 feet during climb. 

The famed X-15 Program conducted 199 flights between June 1959 and October 1968.  North American Aviation (NAA) built three (3) X-15 aircraft.  Twelve (12) men from NAA, USAF and NASA flew the X-15.  Eight (8) pilots received astronaut wings for flying the X-15 beyond 250,000 feet.  One (1) aircraft and one (1) pilot were lost during flight test.

The X-15 flew as fast as 4,520 mph (Mach 6.7) and as high as 354,200 feet.   The basic airframe measured 50 feet in length, featured a wing span of 22 feet and had a gross weight of 33,000 pounds.  The type’s Reaction Motors XLR-99 rocket engine burned anhydrous ammonia and liquid oxygen to produce a sea level thrust of 57,000 pounds.  The X-15 used both 3-axis aerodynamic and ballistic flight controls. 

An X-15 mission was fast-paced.  Flight time from B-52 drop to unpowered landing was typically 10 to 12 minutes in duration.  The pilot wore a full pressure suit and experienced 6 to 7 G’s during pull-out from max altitude.  There really was no such thing as a routine X-15 mission.  However, all X-15 missions had one factor in common; danger.

On Thursday, 29 June 1967, X-15 No. 1 (S/N 56-6670) made its 73rd and the X-15 Program’s 184th free flight.  Launch took place at 1828 UTC as the NASA B-52B launch aircraft (S/N 52-0008) flew at Mach 0.82 and 40,000 feet near Smith Ranch, Nevada.  Knight, making his 10th X-15 flight, quickly ignited the XLR-99 and started his climb upstairs. 

The X-15 was performing well and Knight was enjoying the flight until 67.6 seconds into a planned 87 second XLR-99 burn.  That’s when the engine suddenly quit.  A couple of heartbeats later, the Stability Augmentation System (SAS) failed, the Auxiliary Power Units (APU’s) ceased operating, the X-15’s generators stopped functioning and the cockpit lights went out.  This was the total hit; a complete power failure.     

Pete Knight was now just along for the ride.  No thrust to power the aircraft.  No electrical power to run onboard systems.  No hydraulics to move flight controls.  Even the reaction controls appeared inoperative.  The X-15 continued upward, but it wallowed aimlessly in the low dynamic pressure of high altitude flight.  At this point, Knight considered taking his chances and punching-out.

The X-15 went over the top at 173,000 feet.  On the way downhill, Knight was able to get some electrical power from the emergency battery.  This meant that he now had some hydraulic power and could utilize the X-15’s flight control surfaces.   Knight next tried to fire-up the APU’s.  The right APU would not respond.  The left APU fired, but the its generator would not engage.

As the X-15 descended and the dynamic pressure built-up, Knight was able to maneuver his stricken X-15.  He headed for Mud Lake in a sustained 6-G turn.  As he leveled off at 45,000 feet, Knight instinctively knew he could now make the east shore of the Nevada dry lake.  But it was tough work to fly the X-15.  Knight ended-up using both hands to fly the airplane; one on the side stick and one on the center stick.

While Knight was trying to get his airplane down on the ground in one piece, only he and his Maker knew his whereabouts.  The X-15 flight test team certainly didn’t, since Knight’s radio, telemetry and radar transponder were now inop.  Further, the X-15 was not being skinned tracked at the time of the electrical anomaly.  Just before he touched-down at Mud Lake, Knight’s X-15 was spotted by NASA’s Bill Dana who was flying a F-104N chase aircraft.

Pete Knight made a good landing at Mud Lake.  The X-15 slid to a stop.  After a struggle with the release mechanism, he managed to get the canopy open.  Hot and soaked with perspiration, Knight somehow removed his own helmet.  A ground crewman usually did that for him.  But there were no flight support people at his X-15 landing site on this day.

As he attempted to get out of the X-15 cockpit, Knight pulled an emergency release.  To his surprise, the headrest blew off, bounced off the canopy and smacked him square in the head.  Undeterred, Knight got out of the cockpit and onto terra firma.  In the meantime, a Lockheed C-130 Hercules had landed at Mud Lake.  Wearily, Pete Knight got onboard and returned to Edwards Air Force Base.

Post-flight investigation revealed that the most probable source of the X-15’s electrical failure was arcing in a flight experiment system.  This system had been connected to the X-15’s primary electrical bus.  The solution was to connect flight experiments to the secondary electrical bus.

Reflecting on Knight’s amazing recovery from almost certain disaster, long-time NASA flight test manager Paul Bickle claimed the fete was among the most impressive of the X-15 Program.  Indeed, it was Pete Knight’s clearly uncommon piloting skill and calmness under pressure that gave him the edge.

Posted in Aerospace, History

X-5 First Flight

Fifty-nine years ago this month, the No. 1 USAF/Bell X-5 variable-sweep-wing aircraft testbed took to the air for the first time with Bell test pilot Jean “Skip” Ziegler at the controls.  The X-5 holds the distinction of being the first aircraft capable of changing its wing sweep while in flight.

The ability to change wing sweep during flight allows an aircraft to be flown more optimally throughout its flight envelope.  For instance, low wing sweep enhances low-speed lift characteristics while high wing sweep reduces wave drag at high speeds.  Unfortunately, these aerodynamic gains come at the price of increased structural weight and mechanical complexity.

During World War II, the Third Reich developed the Messerschmitt P.1101 aircraft which was configured with a ground-adjustable variable-sweep wing. The P.1101 was captured in 1945 by the United States as part of the spoils of war.  The aircraft was subsequently transported to Wright Field in Ohio for detailed examination by American aeronautical experts.

The Bell Aircraft Corporation ultimately came into possession of the P.1101 in August of 1948 after it had been examined by the Air Force and subsequently declared as surplus by the service.  After an abortive attempt to re-engine the aircraft, Bell abandoned its effort to fly the P.1101.  The company then made a decision to develop a completely new variable-sweep-wing aircraft.

Bell secured a contract from the Air Force in February of 1949 to build a pair of experimental variable-sweep-wing aircraft.  The new airplane joined the young X-plane family as the X-5.  The tail numbers assigned by the Air Force were 50-1838 and 50-1839.

The X-5 wing sweep could be varied between 20 and 60 degrees in flight.  This resulted in a wing span that varied between 33.5 feet at 20 degrees of sweep and 20.75 feet at 60 degrees of sweep.  The X-5 measured 33.5 feet in length and had a gross take-off weight of 9,875 pounds.  The aircraft was powered by a single Allison J35-A-17A turbojet rated at 4,900 pounds of sea level thrust.

The X-5 was a nimble aircraft.  It flew as fast as Mach 0.95 and as high as 45,000 feet.  In fact, the X-5 was used at various times as a chase aircraft in support of other flight test programs at Edwards.  On the other hand, the X-5 was less than docile in terms of handling qualities.  It was particularly unruly in a spin. 

On Wednesday, 20 June 1951, the No. 1 X-5 (50-1838) took-off from Edwards Air Force Base on its first contractor flight.  This aircraft would eventually accumulate 153 flights, the last of which occurred on Tuesday, 25 October 1955.  A dozen men from Bell, USAF and NACA flew the X-5 during that period.  The last man to fly the X-5 was none other than Neil Armstrong.

While the No. 1 X-5 (50-1838) survived the flight test program, the No. 2 aircraft (50-1839) did not.  The aircraft first flew on 10 December 1951 and was lost following an unrecoverable spin on Wednesday, 14 October 1953.  USAF Major Raymond Popson lost his life when he was unable to eject from the stricken aircraft.  The flight was Popson’s first and last in the X-5.  It is not clear how many flights 50-1839 made during its service life.

The Bell X-5 provided a wealth of performance, stability and control and handling qualities data relative to variable-sweep-wing flight.  The aircraft served as the progenitor to a number of famous operational aircraft including the General Dynamics F-111 Aardvark, Grumman F-14 Tomcat, and Rockwell B-1B Lancer.

The surviving X-5 (50-1838) is currently on display at the United States Air Force Museum at Wright-Patterson Air Force Base in Dayton,Ohio.

Posted in Aerospace, History

The Flying Stove Pipe

Fifty-seven years ago this month, NACA test pilot A. Scott Crossfield piloted the United States Navy/Douglas D-558-I transonic research aircraft on the last of the type’s 230 flights.  The flight was conducted on Wednesday, 10 June 1953 at Edwards Air Force Base, California. 

Flight near and beyond the speed of sound is characterized by large variations in flowfield density.  Variable density flow is known as compressible flow.  A key compressible flow phenomenon is the formation of shock waves.  These fluid dynamic flow features are the result of locally supersonic flow being deflected or turned.   

As every aircraft has a distinct shape, it also has its own distinct shock wave system.   The topology and strength of this 3-dimensional shock wave system significantly affects aircraft flight performance, stability and control, handling qualities, airframe buffet characteristics and airloads.

Following World War II, the United States initiated a sustained flight research effort in the realm of transonic and supersonic flight.  In league with the US military and the National Advisory Committee For Aeronautics (NACA), the American aeronautical industry designed and built a variety of aircraft used to conduct flight research during the 1940’s and 1950’s.  These experimental aircraft were the first of the fabled X-planes.

In June of 1945, the Douglas Aircraft Company was awarded a contract by the United States Navy (USN) to build a total of six (6) flight research aircraft.  These vehicles would be used in a two phase flight research program.  Phase I was devoted to transonic flight testing while Phase II would investigate supersonic flight.  The Phase I aircraft was known as the D-558-I Skystreak while the Phase II airplane was called the D-558-II Skyrocket.

The USN/Douglas D-558-I Skystreak measured 36-feet in length and had a wingspan of 25-feet.  The straight-winged aircraft weighed a bit over 10,000 pounds and was powered by an Allison J35 turbojet rated at 5,000 pounds of sea level thrust.  The aircraft was single place and employed ground take-off.  Three (3) copies were made; BuAer tail numbers 37970, 37971 and 37972.

Later painted white to improve visibility, each Skystreak was originally painted a stunning red.  This led to the type’s nickname of the “Crimson Test Tube”.  Other nicknames included the “Flying Stove Pipe” and the “Supersonic Test Tube”.  This last moniker is misleading in that the aircraft could only go slightly supersonic and only in a dive.

Along with its D-558-II companion, the D-558-I helped write the book on transonic aircraft aerodynamics.  The D-558-I Skystreak acquired vital flight data relative to aircraft stability and control, handling qualities, airframe buffet and airloads.  Those data are used to support aircraft design efforts down to the present day.

Pilots reported that the D-558-I exhibited generally favorable handling qualities.  However, the Skystreak had its share of peculiar transonic aerodynamic attributes as well.  Wing drop due to asymmetric shock-induced separation was one such phenomenon.  Reduced control effectiveness and severe lateral-directional oscillations, both due to shock wave-induced flow separation at high Mach number, were exhibited as well.   

Beyond 0.94 Mach number, the D-558-I experienced a phenomenon known as “Mach Tuck”.  This condition is attributable to an aftward shift in the aircraft transonic center-of-pressure location as the pressure pattern over the aircraft changes with Mach number.  This is equivalent to an increase in nose down pitching moment.  Taken to extremes, the “Mach Tuck” flight condition is unrecoverable due to an exceedance of pitch control authority.

Approximately 15 men flew the D-558-I Skystreak 230 times between April of 1947 and June of 1953.  One aircraft and one pilot was lost during the type’s flight research program.  NACA  test pilot Howard Lilly died and aircraft 37971 was destroyed when a J35 turbojet compressor blade failed during take-off on Tuesday,  25 November 1947.

Today the surviving aircraft are publically displayed in tribute to the Skystreak’s contributions to aeronautics.  Tail No 37970 is displayed at the Naval Air Museum in Pensacola, Florida while Tail No. 37972 can be viewewd at the Carolinas Avaiation Museum in Charlotte, North Carolina.

Posted in Aerospace, History

The Angry Alligator

Forty-four years ago this month, NASA astronauts Thomas P. Stafford and Eugene A. Cernan became the 7th two-man Gemini crew to orbit the Earth.  Known as Gemini 9A, the mission was the 13th manned spaceflight flown by the United States.

The Gemini Program was absolutely critical to the success of America’s lunar landing effort.  A total of 10 Gemini missions was flown during a 20-month period between 1965 and 1966.  Gemini demonstrated the key capabilities of rendezvous and docking, orbital maneuvering, long duration spaceflight and extra vehicular activity.   

Each Gemini mission had its share of difficulties which arose and had to be overcome during flight.  Gemini 9A was arguably the most ill-fortuned and technically frustrating of the series.  Mission goals included rendezvous and docking with an Agena Target Vehicle (ATV), maneuvering the combined Gemini-Agena combination and demonstration of the first manned rocket pack; the United States Air Force Astronaut Maneuvering Unit (AMU).

The original Gemini 9 prime crew was Elliot M. See and Charles A. Bassett.  However, both men died on Monday, 28 February 1966 as they attempted to land their T-38 aircraft during a rain storm in St. Louis, Missouri.  The Gemini 9 back-up crew of Stafford and Cernan somehow managed to land their T-38 aircraft during that same storm.  The men were appointed as the prime crew with the devastating loss of See and Bassett.

On Tuesday, 17 May 1966, an ATV was launched ahead of Gemini 9.  The Agena vehicle never made it to orbit due to a problem with its Atlas booster.  McDonnell engineers hurriedly conceived and built a substitute for the ATV known as the Augmented Target Docking Adapter (ATDA).  While Stafford and Cernan could rendezvous and dock with the ATDA, they could not change their orbital path since the ATDA had no propulsion system.

With the loss of the ATV and the introduction of the ATDA, Gemini 9 now came to be known as the Gemini 9A mission.  The ATDA was successfully fired into orbit on Wednesday, 01 June 1966.  However, the ATDA’s nose shroud had failed to jettison.   Thus, Gemini 9A would not be able to dock with the ATDA.

The launch window for Gemini 9A was only 40 seconds on the day that the ATDA was launched.  That window came and went when computer problems arose at a most inopportune moment.  Having been denied the opportunity to launch, Stafford and Cernan unstrapped and waited to fly another day.

On Friday, 03 June 1966, Gemini 9A lifted-off from LC-19 at Cape Canaveral, Florida.  Lift-off time was 1339 UTC.  Within 5 hours, the crew caught up with the ATDA.  What they saw did not inspire hope.  The ATDA’s shroud indeed had not jettisoned properly.  Commander Stafford radioed to Mission Control:  “It looks like an angry alligator out here rotating around.”

The Gemini 9A crew asked for permission to use the nose of their spacecraft to nudge the recalcitrant shroud from the ATDA.  Permission denied.  The Gemini spaceraft might be damaged.  How about performing an EVA and having Cernan cut the shroud attachment lanyards?  No way.  Sharp-edged debris might pierce Cernan’s EVA suit.

Making the best of the situation, Stafford and Cernan moved away from the ATDA and then rendezvoused with it again.  They did this a number of times to gain practice.  They also performed stationkeeping with the ATDA to learn the nuances of that flight mode.

Cernan’s much anticipated EVA with the AMU took place on Sunday, 05 June 1966.  That particular experience deserves an article all its own.  Suffice it to say that things did not go well.  Working outside the spacecraft was much more physically demanding and functionally non-intuitive than expected.

Cernan found that any movement of his limbs resulted in unwanted reactions on his body.  It was exceedingly difficult to remain still and perform useful work.  He had to continually fight to maintain body position.  Further, the Gemini spacecraft did not have enough hand-holds.  Cernan’s exertions were such that his heart rate peaked at 195 beats per minute.  Perspiration fogged his visor.  Now he was blind.

Cernan struggled to get to the AMU which was stored in the Gemini’s aft adapter.  He prepared the unit for free-flight, but continued to labor.   He ultimately came to the conclusion that free-flying the AMU was infeasible on this mission.  Dishearted and still blinded by the perspiration-induced fog on his visor, Cernan managed to safely return to the spacecraft cabin and secured the hatch.  Total EVA time was 128 minutes.

Stafford and Cernan completed their demanding mission with reentry and splashdown in the Atlantic Ocean on Monday, 06 June 1966.  They excuted a computer-controlled entry and landed less than one-half mile from the prime recovery ship; the USS Wasp.  Official mission elapsed time was 72 hours, 20 minutes and 50 seconds.

It is worth noting that Gemini 9A, like all Gemini missions, was a test flight.  The ATDA and AMU experiences were certainly frustrating, but not without merit from a learning standpoint.  That learning was put to good use as evidenced by the accomplishments of Gemini’s 10, 11 and 12. 

Rendezvous, docking and orbital maneuvering with the ATV all went extremely well on the last trio of Gemini missions.  And on Gemini 12, the most vexing of early manned spaceflight problems was solved; that of EVA.  Indeed, with the aid of techniques and equipment developed from Gemini 9A lessons-learned, one Edward E. “Buzz” Aldrin convincingly demonstrated the feasibility of an astronaut performing meaningful work in space.

Posted in Aerospace, History