After he graduated from Purdue, Armstrong decided to try to become an experimental, research test pilot. He applied at the National Advisory Committee for Aeronautics High-Speed Flight Station at Edwards Air Force Base, which had no open positions and forwarded the application to the
Lewis Flight Propulsion Laboratory in
Cleveland, Ohio. Armstrong began working at Lewis Field in February 1955; he took a position at Edwards five months later.
On his first day at Edwards, Armstrong flew his first assignments, piloting
chase planes on drops of experimental aircraft from converted bombers. He also flew the converted bombers, and on one of these missions had his first flight incident at Edwards. Armstrong was in the right-hand seat of a
B-29 Superfortress on
March 22,
1956, which was to air-drop a
Douglas Skyrocket D-558-2. As the right-hand seat pilot, Armstrong was in charge of the payload release, while the left-hand seat commander, Stan Butchart, flew the B-29.
As they ascended to 30,000 ft (9 km), the number four engine stopped and the
propeller began windmilling in the airstream. Hitting the switch that would stop the propeller spinning, Butchart found the propeller slowed but then started spinning again, this time even faster than the other engines; if it spun too fast, it would fly apart. Their aircraft needed to hold an airspeed of 210 mph (338 km/h) to launch its Skyrocket payload, and the B-29 could not land with the Skyrocket still attached to its belly. Armstrong and Butchart nosed the aircraft down to pick up speed, then launched the Skyrocket. At the very instant of launch, the number four engine propeller disintegrated. Pieces of it careened through part of the number three engine and hit the number two engine. Butchart and Armstrong were forced to shut down the number three engine, due to damage, and the number one engine, due to the
torque it created. They managed to make a slow, circling descent from using only the number two engine, and they landed the aircraft safely.
Armstrong's first flight in a rocket plane was on
August 15,
1957, in the Bell X-1B, to an altitude of 11.4 miles (18.3 km). He broke the
nose landing gear when he landed, which had happened on about a dozen previous flights of the aircraft due to the aircraft's design. He first flew the North American X-15 on
November 30, 1960, to a top altitude of 48,840 ft (14.9 km) and a top speed of Mach 1.75 (1,150 mph or 1,810 km/h).
In November 1960 Armstrong was chosen as part of the pilot consultant group for the
X-20 Dyna-Soar, a program to develop a military space plane. On
March 15, 1962 he was named as one of six pilot-engineers who would fly the space plane when it got off the design board.
Armstrong was involved in several incidents that went down in Edwards folklore and/or were chronicled in the memoirs of colleagues. The first was an X-15 flight on
April 20, 1962, when Armstrong was testing a self-adjusting control system. He first rocketed to a height of 207,000 ft (63 km), (the highest he flew before Gemini 8), but he held the nose of the aircraft up too long as he descended, and the X-15 literally bounced off the atmosphere back up to 140,000 ft (43 km). At that altitude, the atmosphere is so thin that aerodynamic surfaces have no effect on the attitude of the aircraft. He flew past the landing field at Mach 3 (2,000 mph, or 3,200 km/h) and over 100,000 ft (30.5 km) in the air. He ended up 45 miles (72 km) south of Edwards (legend at the base has that he flew as far as the
Rose Bowl). After he descended enough, he turned and headed back to the dry lake beds, and barely managed to land without crashing into
Joshua trees at the south end. It was the longest X-15 flight in both time and distance of the ground track.
A second incident happened when Armstrong flew for the first and only time with
Chuck Yeager, four days after his X-15 adventure. Flying a
T-33 Shooting Star, their job was to test out Smith Ranch Dry Lake in case it needed to be used as an emergency landing site for an X-15 flight. In his autobiography, Yeager wrote that he knew the lake bed was unsuitable for landings after recent rains, but Armstrong insisted on flying out anyway. As they made a "
touch and go", the wheels became stuck and they had to wait for rescue. Armstrong tells a different version of events, where Yeager never tried to talk him out of it and they made a first successful landing on the east side of the lake. Then Yeager told him to try again, this time a bit slower. On the second landing they became stuck and according to Armstrong, Yeager was in fits of laughter.
Many of the test pilots at Edwards highly rated Armstrong's engineering ability.
Milt Thompson said he was "the most technically capable of the early X-15 pilots."
Bruce Peterson said Armstrong "had a mind that absorbed things like a sponge." Those who flew for the
Air Force tended to have a different opinion, especially people like Chuck Yeager and
Pete Knight who did not have engineering degrees. Knight said that pilot-engineers flew in a way that was "more mechanical than it is flying," and gave this as the reason why some pilot-engineers got into trouble; their flying skills didn't come naturally.
In the final episode on
May 21, 1962, Armstrong was involved in what Edwards' folklore called the "Nellis Affair." He was sent up in a F-104 to inspect Delamar Lake, again in case of emergency landings. He misjudged his altitude, and also did not realize that the plane's landing gear had failed to fully extend – so as he touched down, the landing gear began to retract. Armstrong applied full power to abort the landing but the
ventral fin and landing gear door came into contact with the ground, which damaged the radio equipment and released
hydraulic fluid. Without radio communication, Armstrong flew to
Nellis Air Force Base, past their control tower, and waggled his tail, the signal for a no-radio approach. The loss of hydraulic fluid caused the emergency tail-hook to release, so when he landed, he caught the arresting wire attached to an anchor chain. He was not prepared for this, and careened down the runway dragging chain links with him. Thirty minutes were needed to clear the runway and rig a makeshift arresting cable. Meanwhile, Armstrong telephoned Edwards and asked that they send someone to pick him up. Milt Thompson was sent in a F-104B, the only two-seater available but a plane Thompson had never flown. With great difficulty, Thompson made it to Nellis, but a strong crosswind on landing caused a hard landing and the left main tire suffered a blowout. The runway was once again closed to clean it of debris.
Bill Dana was sent to Nellis in a T-33 Shooting Star, but he almost landed long. The Nellis base operations office decided that it would be best to find the three NASA pilots some transport back to Edwards, to avoid any further problems.
Armstrong made seven flights in the X-15. He reached a top altitude of 207,500 ft (63.2 km) in the X-15-3, and a top speed of Mach 5.74 (4,000 mph or 6,615 km/h) in the X-15-1, and he left the Dryden Flight Research Center with a total of 2,450 flying hours in more than 50 types of aircraft.