4–5 February 1929: At 5:37:30 p.m., Pacific Time, Monday, Frank Monroe Hawks took off from Metropolitan Field, Los Angeles, California, (now known as Van Nuys Airport, VNY) in a new Lockheed Model 3 Air Express transport, NR7955, serial number EX-2. Also on board was Oscar Edwin Grubb, the final assembly superintendent for Lockheed. The pair flew non-stop to Roosevelt Field, Long Island, New York, arriving there at 2:59:29 p.m., Eastern Time, on Tuesday. The duration of the flight was 18 hours, 21 minutes, 59 seconds.
The only previous non-stop West-to-East flight had been flown during August 1928 by Arthur C. Goebel, Jr., and Harry Tucker with their Lockheed Vega, Yankee Doodle, NX4769. Hawks cut 36 minutes off of Goebel’s time.
Hawks was a technical adviser to The Texas Company (“Texaco”), a manufacturer and distributor of petroleum products which sponsored the flight. On his recommendation, the company purchased the Air Express from Lockheed for use as a company transport.
On 17 January 1930, “Pilot Frank Hawks attempted a takeoff from a soggy field in West Palm Beach, Florida, destroying the aircraft christened ‘Texaco Five’ in a spectacular crash that catapulted it into a row of three parked aircraft. All three occupants were unhurt while the aircraft was destroyed.” —Bureau of Aircraft Accidents Archives
NC7955’s Department of Commerce registration was cancelled 31 January 1930.
The Lockheed Model 3 Air Express was a single-engine parasol-wing monoplane transport, flown by a single pilot in an open aft cockpit, and capable of carrying 4 to 6 passengers in its enclosed cabin. The airplane was designed by Gerard Freebairn Vultee and John Knudsen Northrop. It used the Lockheed Vega’s molded plywood monocoque fuselage.
The Model 3 received Approved Type Certificate No. 102 from the Aeronautic Branch, U. S. Department of Commerce.
The Lockheed Air Express was the first production airplane to use the “NACA Cowl,” an engine cowling for radial engines which had been designed by a team led by Fred Ernest Weick of the the National Advisory Committee for Aeronautics’ Langley Memorial Aeronautical Laboratory. The new cowling design tightly enclosed the engine and used baffles to control air flow around the hottest parts of the engines. The exit slots were designed to allow the air to exit the cowling at a higher speed than it had entered the intake. The new cowling design provided better engine cooling and caused significantly less aerodynamic drag. The addition of the NACA cowling increased the Air Express’s maximum speed from 157 to 177 miles per hour (253 to 285 kilometers per hour).
The day following Hawks’ transcontinental flight, Vultee sent a telegram to NACA:
COOLING CAREFULLY CHECKED AND OK. RECORD IMPOSSIBLE WITHOUT NEW COWLING. ALL CREDIT DUE TO NACA FOR PAINSTAKING AND ACCURATE RESEARCH. GERRY VULTEE, LOCKHEED AIRCRAFT CO.
The Lockheed Model 3 Air Express was 27 feet, 6 inches (8.382 meters) long with a wing span of 42 feet, 6 inches (12.954 meters) and height of 8 feet, 4½ inches (2.553 meters). The wing area was 288 square feet (26.756 square meters). The wing had no dihedral. The airplane had an empty weight of 2,533 pounds (1,149 kilograms) and gross weight of 4,375 pounds (1,984 kilograms).
The Model 3 was powered by an air-cooled, supercharged 1,343.804-cubic-inch-displacement (22.021 liter) Pratt & Whitney Wasp C nine cylinder, direct-drive radial engine. The Wasp C was rated at 420 horsepower at 2,000 r.p.m. at Sea Level. It was 3 feet, 6.63 inches (1.083 meters) long, 4 feet, 3.44 inches (1.307 meters) in diameter, and weighed 745 pounds (338 kilograms).
The Air Express had a cruising speed of 135 miles per hour (217 kilometers per hour), and maximum speed of 177 miles per hour (285 kilometers per hour). It’s service ceiling was 17,250 feet (5,258 meters).
Francis Monroe Hawks was born at Marshalltown, Iowa, 28 March 1897. He was the son of Charles Monroe Hawks, a barber, and Ida Mae Woodruff Hawks. He attended Long Beach Polytechnic High School, Long Beach, California, graduating in 1916. He then studied at the University of Southern California, in Los Angeles.
Frank Hawks was an Air Service, United States Army, pilot who served during World War I. He rose to the rank of Captain, and at the time of his record-breaking transcontinental flight, he held a commission as a reserve officer in the Army Air Corps. Hawks transferred to the U.S. Naval Reserve with the rank of Lieutenant Commander. His date of rank 27 May 1932.
His flying had made him a popular public figure and he starred in a series of Hollywood movies as “The Mysterious Pilot.”
On 28 December 1920, Miss Amelia Earhart took her first ride in an airplane at Long Beach Airport in California. The ten-minute flight began her life-long involvement in aviation. The airplane’s pilot was Frank Monroe Hawks.
Francis M. Hawks married Miss Newell Lane at Lewiston, Montana, 7 August 1918. They had a daughter, Dolly. They later divorced. He next married Mrs. Edith Bowie Fouts at St. John’s Church, Houston, Texas, 26 October 1926.
Frank Hawks was killed in an aircraft accident at East Aurora, New York, 23 August 1938. He was buried at Redding Ridge Cemetery, Redding, Connecticut.
25 January 1946:¹ Near Pinecastle Army Airfield in central Florida, Bell Aircraft Corporation Senior Experimental Test Pilot Jack Woolams made the first unpowered glide flight of the XS-1 supersonic research rocketplane, 46-062.
46-062 was the first of three XS-1 rocketplanes built by Bell for the U.S. Army Air Corps and the National Advisory Committee for Aeronautics (NACA) to explore flight at speeds at and beyond Mach 1, the speed of sound. The airplane had been rolled out of Bell’s plant at Buffalo, New York, on 27 December 1945. The rocket engine, which was being developed by Reaction Motors, Inc., at Franklin Lakes, New Jersey, was not ready, so the experimental aircraft was carrying ballast in its place for the initial flight tests.
The XS-1 was to be air-dropped from altitude by a modified heavy bomber so that its fuel could be used for acceleration to high speeds at altitude, rather than expended climbing from the surface. Bell manufactured B-29B Superfortresses at its Atlanta, Georgia, plant and was therefore very familiar with its capabilities. A B-29, 45-21800, was selected as the drop ship and modified to carry the rocketplane in its bomb bay.
Pinecastle Army Airfield was chosen as the site of the first flight tests because it had a 10,000 foot (3,048 meter) runway and was fairly remote. There was an adjacent bombing range and the base was a proving ground for such aircraft as the Consolidated B-32 Dominator. (Today, Pinecastle A.A.F. is known as Orlando International Airport, MCO.)
The B-29 carrying the XS-1 took off from Pinecastle at 11:15 a.m., and began its climb to altitude. Woolams was in the forward crew compartment. As the bomber reached approximately 10,000 feet (3,048 meters), he entered the bomb bay and climbed down into the cockpit of the research aircraft. At the drop altitude, the B-29 was flying at 180 miles per hour (290 kilometers per hour) with the inboard propellers feathered and flaps lowered to 20°.
The XS-1 dropped away smoothly. Woolams flew the rocketplane to a maximum 275 miles per hour (443 kilometers per hour), indicated air speed, during this first glide test. He described the rocketplane as, “solid as a rock, experiencing absolutely no vibration or noise. At the same time, it felt as light as a feather during maneuvers due to the lightness, effectiveness and nice balance between the controls.” Woolams described the visibility from the cockpit as “not good, but adequate.”
The duration of the first glide flight was about ten minutes. Woolams misjudged his approach to Pinecastle and landed slightly short of the runway, on the grass shoulder, but the XS-1 was not damaged.
The conclusion of Woolams’ flight report is highly complementary of the experimental airplane:
11. Of all the airplanes the writer has flown, only the XP-77 and the Heinkle [sp] 162 compare with the XS-1 for maneuverability, control relationship, response to control movements, and lightness of control forces. Although these impressions were rather hastily gained during a flight which lasted only 10 minutes, it is the writer’s opinion that due to these factors and adding to them the security which the pilot feels due to the ruggedness, noiselessness, and smoothness of response of this airplane, it is the most delightful to fly of them all.
—PILOT’S REPORT, Flight #1, by Jack Woolams
Jack Woolams made ten glide flights with 46-062, evaluating its handling characteristics and stability. The aircraft was returned to Bell to have the rocket engine installed, and it was then sent to Muroc Army Airfield in the high desert of southern California for powered flight tests. (Muroc A.A.F. was renamed Edwards Air Force Base in 1949.)
Bell XS-1 46-062 was later named Glamorous Glennis by its military test pilot, Captain Charles E. Yeager, U.S. Army Air Corps. On 14 October 1947, Chuck Yeager flew it to Mach 1.06 at 13,115 meters (43,030 feet). Today the experimental aircraft is on display at the Smithsonian Institution National Air and Space Museum.
The Bell XS-1, later re-designated X-1, was the first of a series of rocket-powered research airplanes which included the Douglas D-558-II Skyrocket, the Bell X-2, and the North American Aviation X-15, which were flown by the U.S. Air Force, U.S. Navy, NACA and its successor, NASA, at Edwards Air Force Base to explore supersonic and hypersonic flight and at altitudes to and beyond the limits of Earth’s atmosphere.
The X-1 has an ogive nose, similar to the shape of a .50-caliber machine gun bullet, and has straight wings and tail surfaces. It is 30 feet, 10.98 inches (9.423 meters) long with a wing span of 28.00 feet (8.534 meters) and overall height of 10 feet, 10.20 inches (3.307 meters).
46-062 was built with a thin 8% aspect ratio wing, while 46-063 had a 10% thick wing. The wings were tapered, having a root chord of 6 feet, 2.2 inches (1.885 meters) and tip chord of 3 feet, 1.1 inches (0.942 meters), resulting in a total area of 130 square feet (12.1 square meters). The wings have an angle of incidence of 2.5° with -1.0° twist and 0° dihedral. The leading edges are swept aft 5.05°.
The horizontal stabilizer has a span of 11.4 feet (3.475 meters) and an area of 26.0 square feet (2.42 square meters). 062’s stabilizer has an aspect ratio of 6%, and 063’s, 5%.
The fuselage cross section is circular. At its widest point, the diameter of the X-1 fuselage is 4 feet, 7 inches (1.397 meters).
46-062 had an empty weight is 6,784.9 pounds (3,077.6 kilograms), but loaded with propellant, oxidizer and its pilot with his equipment, the weight increased to 13,034 pounds (5,912 kilograms).
The X-1 was designed to withstand an ultimate structural load of 18g.
The X-1 was powered by a four-chamber Reaction Motors, Inc., 6000C4 (XLR11-RM-3 ) rocket engine which produced 6,000 pounds of thrust (26,689 Newtons). This engine burned a 75/25 mixture of ethyl alcohol and water with liquid oxygen. Fuel capacity is 293 gallons (1,109 liters) of water/alcohol and 311 gallons (1,177 liters) of liquid oxygen. The fuel system was pressurized by nitrogen at 1,500 pounds per square inch (103.4 Bar).
The X-1 was usually dropped from the B-29 flying at 30,000 feet (9,144 meters) and 345 miles per hour (555 kilometers per hour). It fell as much as 1,000 feet (305 meters) before beginning to climb under its own power.
The X-1’s performance was limited by its fuel capacity. Flying at 50,000 feet (15,240 meters), it could reach 916 miles per hour (1,474 kilometers per hour), but at 70,000 feet (21,336 meters) the maximum speed that could be reached was 898 miles per hour (1,445 kilometers per hour). During a maximum climb, fuel would be exhausted as the X-1 reached 74,800 feet (2,799 meters). The absolute ceiling is 87,750 feet (26,746 meters).
The X-1 had a minimum landing speed of 135 miles per hour (217 kilometers per hour) using 60% flaps.
There were 157 flights with the three X-1 rocket planes. The number one ship, 46-062, Glamorous Glennis, made 78 flights. On 26 March 1948, with Chuck Yeager again in the cockpit, it reached reached Mach 1.45 (957 miles per hour/1,540 kilometers per hour) at 71,900 feet (21,915 meters).
The third X-1, 46-064, made just one glide flight before it was destroyed 9 November 1951 in an accidental explosion.
The second X-1, 46-063, was later modified to the X-1E. It is on display at the NASA Dryden Research Center at Edwards Air Force Base. Glamorous Glennis is on display at the Smithsonian Institution National Air and Space Museum, next to Charles A. Lindbergh’s Spirit of St. Louis.
Jack Valentine Woolams was born on Valentine’s Day, 14 February 1917, at San Francisco, California. He was the second of three children of Leonard Alfred Woolams, a corporate comptroller, and Elsa Mathilda Cellarius Woolams. He grew up in San Rafael, California, and graduated from Tamalpais School in 1935.
After two years of study at The University of Chicago, in 1937 Woolams entered the Air Corps, U.S. Army, as an aviation cadet. He trained as a pilot at Kelly Field, San Antonio, Texas. On graduation, 16 June 1938, he was discharged as an aviation cadet and commissioned as a second lieutenant, Air Reserve. He was assigned to Barksdale Army Air Field, Louisiana, where he flew the Boeing P-26 and Curtiss P-36 Hawk.
On 10 February 1939, Lieutenant Woolams was one of three Air Corps officers thrown into the waters of Cross Lake, near Shreveport, Louisiana, when the boat, owned by Woolams, capsized in 4 foot (1.2 meters) waves. Woolams and Lieutenant J.E. Bowen were rescued after 4 hours in the water, but the third man, Lieutenant Wilbur D. Camp, died of exposure.
Lieutenant Woolams transferred from active duty to inactive reserve status in September 1939 in order to pursue his college education at The University of Chicago, where he was a member of the Alpha Delta Phi (ΑΔΦ) fraternity. While at U. of C., he played on the university’s football and baseball teams, and was a member of the dramatic society. Woolams graduated 18 July 1941 with a Bachelor of Arts (A.B.) degree in Economics.
Jack Woolams married Miss Mary Margaret Mayer at the bride’s home in Riverside, Illinois, 16 June 1941. They would have three children. Miss Mayer was also a 1941 graduate from the University of Chicago. She had been Woolams’ student in the Civilian Pilot Training Program.
Woolams became a production test pilot for the Bell Aircraft Corporation at Buffalo, New York. He tested newly-built Bell P-39 Airacobra fighters. As he became more experienced, he transitioned to experimental testing with the P-39, P-63 King Cobra, and the jet-powered P-59 Airacomet.
On 28 September 1942, Jack Woolams flew a highly-modified Bell P-39D-1-BE Airacobra, 41-38287, from March Field, near Riverside, California, to Bolling Field, Washington, D.C., non-stop. The duration of the flight was approximately 11 hours. The modifications were intended to allow P-39s to be flown across the Pacific Ocean to Hawaii and on to the Soviet Union for delivery under Lend Lease.
During the summer of 1943, Woolams flew the first Bell YP-59A Airacomet, 42-108771, to an altitude of 47,600 feet (14,508 meters) near Muroc Army Air Field in California.
On 5 January 1945, Woolams was forced to bail out of a Bell P-59A-1-BE, 44-22616. He suffered a deep laceration to his head as he left the airplane. He lost his flight boots when the parachute opened, and on landing, had to walk barefoot through knee-deep snow for several miles to reach a farm house. The deep snow prevented the company’s ambulance from getting to Woolams. Bell Aircraft president Lawrence D. Bell sent the company’s second prototype Bell Model 30 helicopter, NX41868, flown by test pilot Floyd Carlson, to transport a doctor, J.A. Marriott, M.D., to the location. Another Bell test pilot, Joe Mashman, circled overhead in a P-63 King Cobra to provide a communications link. Later in the day, an ambulance was able to get through the snow to take Woolams to a hospital.
Woolams was scheduled to make the first powered flight of the XS-1 during October 1946.
Jack Woolams was killed Friday, 30 August 1946, when his red Thompson Trophy racer, Cobra I, a modified 2,000-horsepower Bell P-39Q Airacobra, crashed into Lake Ontario at over 400 miles per hour. His body was recovered by the U.S. Coast Guard four days later.
¹ This article was originally dated 19 January 1946. There were known discrepancies as to the date of the first flight from various reliable sources. Recently discovered test flight reports, provided to TDiA by Mr. Roy T. Lindberg, Historian of the Niagara Aerospace Museum, Niagara Falls, New York, have confirmed that the date of the first flight was actually 25 January 1946. The article has been been revised accordingly, as well as to incorporate new information from these reports.
TDiA is indebted to Mr. Lindberg for providing this and other documentation.
29 December 1941: The first North American Aviation XP-51 fighter prototype, Air Corps serial number 41-038, arrived at the National Advisory Committee for Aeronautics Langley Memorial Aeronautical Laboratory, Langley Field, Hampton, Virginia, for flight testing. This airplane was the fourth production Royal Air Force Mustang Mk.I, RAF serial AG348 (North American serial number 73-3101).
The test program resulted in an improved aileron design which significantly improved the Mustang’s maneuverability. The new aileron was used on all production models.
41-038 was returned to Wright Field on 2 November 1942. The second XP-51, 41-039, arrived at Langley in March 1943 for continued testing.
The Mustang Mk.I (NAA Model NA-73) was a single-place, single-engine fighter of all metal construction. It was 32 feet, 3 inches (9.830 meters) long with a wingspan of 37 feet, ½-inch (11.290 meters) and overall height of 12 feet, 2½ inches (3.719 meters). The airplane’s empty weight was 6,280 pounds (25,848.6 kilograms) and loaded weight was 8,400 pounds (3,810.2 kilograms).
The Mustang Mk.I/XP-51 was powered by a liquid-cooled, supercharged 1,710.60-cubic-inch-displacement (28.032 liter) Allison Engineering Company V-1710-F3R (V-1710-39) single overhead cam 60° V-12 engine, with a compression ratio of 6.65:1 and a single-stage, single-speed supercharger. This was a right-hand tractor engine (the V-1710 was built in both right-hand and left-hand configurations) which drove a 10 foot, 6 inch (3.200 meter) diameter, three-bladed, Curtiss Electric constant-speed propeller through a 2.00:1 gear reduction.
The V-1710-39 had a Normal Power rating of 880 horsepower at 2,600 r.p.m. at Sea Level; Take Off Power rating of 1,150 horsepower at 3,000 r.p.m. at Sea Level, with 44.5 inches of manifold pressure (1.51 Bar), 5 minute limit; and a War Emergency Power rating of 1,490 horsepower at 3,000 r.p.m., with 56 inches of manifold pressure (1.90 Bar). The V-1710-F3R was 3 feet, ¾ inches (0.934 meters) high, 2 feet, 5-9/32 inches (0.744 meters) wide and 7 feet, 1-5/8 inches (2.175 meters) long. It had a dry weight of 1,310 pounds (594 kilograms).
The XP-51 tested at Wright Field had a maximum speed of 382.0 miles per hour (614.8 kilometers per hour) at 13,000 feet (3,962 meters) at wide open throttle, and cruise speed of 300 miles per hour (483 kilometers per hour).
Below 20,000 feet (6,096 meters), the Mustang was the fastest fighter in the world. The Mk.I was 30 m.p.h. (48 kilometers per hour) faster than its contemporary, the Curtiss P-40 Warhawk, though both used exactly the same engine. Below 15,000 feet (4,572 meters), the Mustang was also 30–35 m.p.h (48–56 km/h) faster than a Supermarine Spitfire, which was equipped with the more powerful Roll-Royce Merlin V-12.
The service ceiling was 30,800 feet (9,388 meters) and range was 750 miles (1,207 kilometers).
Armament consisted of two synchronized Browning AN-M2 .50-caliber machine guns mounted in the nose under the engine and firing through the propeller, and two more .50-caliber and four Browning .303 Mk.II machine guns in the wings.
Two Mustang Mk.Is, AG348 and AG354, were taken from the first RAF production order and sent to Wright Field for testing by the U.S. Army Air Corps. These airplanes, assigned Air Corps serial numbers 41-038 and 41-039, were designated XP-51. They would be developed into the legendary P-51 Mustang. In production from 1941 to 1945, a total of 16,766 Mustangs of all variants were built.
North American XP-51 41-038 was transferred to the Smithsonian Institution National Air and Space Museum. It was restored in 1976. It is now in the collection of the EAA AirVenture Museum, Oshkosh, Wisconsin. It has a current FAA registration number, N51NA.
20 December 1968: After 199 flights, the National Aeronautics and Space Administration cancelled the X-15 Hypersonic Research Program. A 200th X-15 flight had been scheduled, but after several delays, the decision was made to end the program. (The last actual flight attempt was 12 December 1968, but snow at several of the dry lakes used as emergency landing areas resulted in the flight being cancelled.)
The X-15A rocketplane was designed and built for the U.S. Air Force and the National Advisory Committee for Aeronautics (NACA, the predecessor of NASA) by North American Aviation, Inc., to investigate the effects of hypersonic flight (Mach 5+). Design work started in 1955 and a mock-up had been completed after just 12 months. The three X-15s were built at North American’s Los Angeles Division, at the southeast corner of Los Angeles International Airport (LAX), on the shoreline of southern California.
The first flight took place 8 June 1959 with former NACA test pilot Albert Scott Crossfield in the cockpit of the Number 1 ship, 56-6670.
While earlier rocketplanes, the Bell X-1 series, the the Douglas D-558-II, and the Bell X-2, were airplanes powered by rocket engines, the X-15 was a quantum leap in technology. It was a spacecraft.
Like the other rocketplanes, the X-15 was designed to be carried aloft by a “mothership,” rather than to takeoff and climb to the test altitude under its own power. The carrier aircraft was originally to be a Convair B-36 intercontinental bomber but this was soon changed to a Boeing B-52 Stratofortress. Two B-52s were modified to carry the X-15: NB-52A 52-003, The High and Mighty One, and NB-52B 52-008, Balls 8.
From 8 June 1959 to 24 October 1968, the three X-15s were flown by twelve test pilots, three of whom would qualify as astronauts in the X-15. Two would go on to the Apollo Program, and one, Neil Alden Armstrong, would be the first human to set foot on the surface of the Moon, 20 July 1969. Joe Engle would fly the space shuttle. Four of the test pilots, Petersen, White, Rushworth, and Knight, flew in combat during the Vietnam War, with Bob White being awarded the Air Force Cross. Petersen, Rushworth and White reached flag rank.
One pilot, John B. (“Jack”) McKay, was seriously injured during an emergency landing at Mud Lake, Nevada, 9 November 1962. Another, Michael James Adams, was killed when the Number 3 ship, 56-6672, went into a hypersonic spin and broke up on the program’s 191st flight, 15 November 1967.
Flown by a single pilot/astronaut, the X-15 is a mid-wing monoplane with dorsal and ventral fin/rudders and stabilators. The wing had no dihdral, while the stabilators had a pronounced -15° anhedral. The short wings have an area of 200 square feet (18.58 square meters) and a maximum thickness of just 5%. The leading edges are swept to 25.64°. There are two small flaps but no ailerons. The entire vertical fin/rudder pivots for yaw control.
Above 100,000 feet (30,840 meters) altitude, conventional aircraft flight control surfaces are ineffective. The X-15 is equipped with a system of reaction control jets for pitch, roll and yaw control. Hydrogen peroxide was passed through a catalyst to produce steam, which supplied the control thrusters.
The forward landing gear consists of a retractable oleo strut with steerable dual wheels and there are two strut/skids at the rear of the fuselage. The gear is retracted after the X-15 is mounted on the NB-52 and is extended for landing by its own weight.
The rocketplane’s cockpit featured both a conventional control stick as well as side-controllers. It was pressurized with nitrogen gas to prevent fires. The pilot wore an MC-2 full-pressure suit manufactured by the David Clark Company of Worcester, Massachusetts, with an MA-3 helmet. The suit was pressurized below the neck seal with nitrogen, while the helmet was supplied with 100% oxygen. This pressure suit was later changed to the Air Force-standardized A/P22S.
The X-15 is 50.75 feet (15.469 meters) long with a wing span of 22.36 feet (6.815 meters). The height—the distance between the tips of the dorsal and ventral fins—is 13.5 feet (4.115 meters). The stabilator span is 18.08 feet (5.511 meters). The fuselage is 4.67 feet (1.423 meters) deep and has a maximum width of 7.33 feet (2.234 meters).
Since the X-15 was built of steel rather than light-weight aluminum, as are most aircraft, it is a heavy machine, weighing approximately 14,600 pounds (6,623 kilograms) empty and 34,000 pounds (15,422 kilograms) when loaded with a pilot and propellants. The X-15s carried as much as 1,300 pounds (590 kilograms) of research instrumentation, and the equipment varied from flight to flight. The minimum flight weight (for high-speed missions): 31,292 pounds (14,194 kilograms) The maximum weight was 52,117 pounds (23,640 kilograms) at drop (modified X-15A-2 with external propellant tanks).
Initial flights were flown with a 5 foot, 11 inch (1.803 meters)-long air data boom at the nose, but this would later be replaced by the “ball nose” air sensor system. The data boom contained a standard pitot-static system along with angle-of-attack and sideslip vanes. The boom and ball nose were interchangeable.
The X-15s were built primarily of a nickel/chromium/iron alloy named Inconel X, along with corrosion-resistant steel, titanium and aluminum. Inconel X is both very hard and also able to maintain its strength at the very high temperatures the X-15s were subjected to by aerodynamic heating. It was extremely difficult to machine and special fabrication techniques had to be developed.
Delays in the production of the planned Reaction Motors XLR99 rocket engine forced engineers to adapt two vertically-stacked Reaction Motors XLR11-RM-13 four-chamber rocket engines to the X-15 for early flights. This was a well-known engine which was used on the previous rocketplanes. The XLR11 burned a mixture of ethyl alcohol and water with liquid oxygen. Each of the engines’ chambers could be ignited individually. Each engine was rated at 11,800 pounds of thrust (58.49 kilonewtons) at Sea Level.
The Reaction Motors XLR99-RM-1 rocket engine was throttleable by the pilot from 28,500 to 60,000 pounds of thrust (126.77–266.89 kilonewtons). The engine was rated at 50,000 pounds of thrust (222.41 kilonewtons) at Sea Level; 57,000 pounds (253.55 kilonewtons) at 45,000 feet (13,716 meters), the typical drop altitude; and 57,850 pounds (257.33 kilonewtons) of thrust at 100,000 feet (30,480 meters). Individual engines varied slightly. A few produced as much as 61,000 pounds of thrust (271.34 kilonewtons).
The XLR99 burned anhydrous ammonia and liquid oxygen. The flame temperature was approximately 5,000 °F. (2,760 °C.) The engine was cooled with circulating liquid oxygen. To protect the exhaust nozzle, it was flame-sprayed with ceramic coating of zirconium dioxide. The engine is 6 feet, 10 inches (2.083 meters) long and 3 feet, 3.3 inches (0.998 meters) in diameter. It weighs 910 pounds (413 kilograms). The Time Between Overhauls (TBO) is 1 hour of operation, or 100 starts.
The XLR99 proved to be very reliable. 169 X-15 flights were made using the XLR99. 165 of these had successful engine operation. It started on the first attempt 159 times.
The highest speed achieved during the program was with the modified number two ship, X-15A-2 56-6671, flown by Pete Knight to Mach 6.70 (6,620 feet per second/4,520 miles per hour/7,264 kilometers per hour) at 102,700 feet (31,303 meters). On this flight, the rocketplane exceeded its maximum design speed of 6,600 feet per second (2,012 meters per second).
The maximum altitude was reached by Joe Walker, 22 August 1963, when he flew 56-6672 to 354,200 feet (107,960 meters).
The longest flight was flown by Neil Armstrong, 20 April 1962, with a duration of 12 minutes, 28.7 seconds.
North American Aviation X-15A-1 56-6670 is on display at the Smithsonian Institution National Air and Space Museum. X-15A-2 56-6671 is at the National Museum of the United States Air Force.
Always Another Dawn: The Story of a Rocket Test Pilot, by A. Scott Crossfield and Clay Blair, Jr., The World Publishing Company, Cleveland and New York, 1960
At The Edge Of Space, by Milton O. Thompson, Smithsonian Institution Press, 1992
X-15 Diary: The Story of America’s First Spaceship, by Richard Tregaskis, E.F. Dutton & Company, New York, 1961; University of Nebraska Press, 2004
X-15: Exploring the Frontiers of Flight, by David R. Jenkins, National Aeronautics and Space Administration http://www.nasa.gov/pdf/470842main_X_15_Frontier_of_Flight.pdf
The X-15 Rocket Plane: Flying the First Wings into Space, by Michelle Evans, University of Nebraska Press, Lincoln and London, 2013
20 November 1953: At Edwards Air Force Base, California, NACA’s High Speed Flight Station research test pilot Albert Scott Crossfield, Jr., rode behind the flight crew of the Boeing P2B-1S Superfortress as it carried the Douglas Aircraft Company D-558-II Skyrocket supersonic research rocketplane to its launch altitude. As the four-engine bomber climbed through 18,000 feet (5,486 meters), Crossfield headed back to the bomb bay to enter the Skyrocket’s cockpit and prepare for his flight.
The Douglas D-558-II was Phase II of a United States Navy/Douglas Aircraft Company/National Advisory Committee on Aeronautics joint research project exploring supersonic flight. It was a swept-wing airplane powered by a single Reaction Motors LR8-RM-6 four-chamber rocket engine. The Skyrocket was fueled with alcohol and liquid oxygen. The engine was rated at 6,000 pounds of thrust (26.69 kilonewtons) at Sea Level.
There were three Phase II aircraft. Originally, they were also equipped with a Westinghouse J34-W-40 turbojet engine which produced 3,000 pounds of thrust (13.35 kilonewtons). The Skyrockets took off from the surface of Rogers Dry Lake. Once the D-558-II reached altitude, the rocket engine was fired for the speed runs.
As higher speeds were required, the program shifted to an air launch from a B-29 (P2B-1S) drop ship. Without the need to climb to the test altitude, the Skyrocket’s fuel load was available for the high speed runs.
The D-558-II was 42.0 feet (12.80 meters) long, with a wingspan of 25.0 feet (7.62 meters). The leading edge of the wing was swept at a 35° angle and the tail surfaces were swept to 40°. The aircraft weighed 9,421 pounds (4,273 kilograms) empty and had a maximum takeoff weight of 15,787 pounds (7,161 kilograms). It carried 378 gallons (1,431 liters) of water/ethyl alcohol and 345 gallons (1,306 liters) of liquid oxygen.
The mothership, NACA 137, was a Boeing Wichita B-29-95-BW Superfortress, U.S. Air Force serial number 45-21787. It was transferred to the U.S. Navy, redesignated P2B-1S and assigned Bureau of Aeronautics number 84029. Douglas Aircraft modified the bomber for its drop ship role at the El Segundo plant.
Going above the planned launch altitude, the Superfortress was placed in a slight dive to build to its maximum speed. At the bomber’s critical Mach number (Mcr), the Skyrocket was just above its stall speed. At 32,000 feet (9,754 meters), Crossfield and the Skyrocket were released. The rocketplane fell for about 400 feet (122 meters) until the rocket engine ignited and then it began to accelerate.
Crossfield climbed at a steep angle until he reached 72,000 feet (21,946 meters), and then leveled off. Now in level flight, the D-558-II accelerated, quickly passing Mach 1, then Mach 1.5. Crossfield pushed the nose down and began a shallow dive. The Skyrocket, still under full power, built up speed. As it passed through 62,000 feet (18,998 meters) the Skyrocket reached its maximum speed, Mach 2.005, or 1,291 miles per hour (2,078 kilometers per hour).
Scott Crossfield was the first pilot to fly an aircraft beyond Mach 2, twice the speed of sound. During his career as a test pilot, he flew the Douglas D-558-II, the Bell X-1, Bell X-2 and North American X-15. He made 112 flights in rocket-powered aircraft, more than any other pilot.