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NASA - Dryden History - Historic Aircraft - X-1 Technical Data
October 9, 2008

Technical Data

Bell Aircraft developed the X-1 largely based on specific NACA design criteria. The aircraft measured 30 feet 11 inches in length and 10 feet 10 inches in height. Wing surface area was 130 square feet. Total gross weight empty was 6,784 lbs. and loaded, 13,034. Official rollout of the #1 aircraft was December 27, 1945. The #1 and #2 aircraft were initially painted saffron (yellow-orange) to aid aerial visibility. The #1 aircraft had a "Glamorous Glennis" logo added in the fall 1947. The #2 aircraft's color was changed to white with a black NACA logo on its vertical tail after its transfer to NACA control in October 1947. The #3 airplane was painted white after its completion in 1951. Its visible differences from the first two aircraft included its turbine pump dump ports and its lack of restraining straps on the cockpit canopy.

The X-1 body was a semimonocoque, aluminum-alloy, stressed skin construction and shaped like a .50 caliber bullet. Based on NACA data, its maneuver load factor was constructed at an unheard of 18 times the force of gravity (18g). (For many contemporary fighter aircraft it was 12g). This decision to provide the X-1 with such a margin of safety proved a classic case of overdesign. However, at that time there were no computer aided design or flight simulators to help NACA in assessing such questions and the decision was made to err on the side of caution due to concerns about potential transonic stresses-a decision that must have given the Air Force added confidence as the aircraft approached Mach 1 speeds.

During project design, the NACA initially requested an aircraft with a wing chord thickness of 12%. (Conventional aircraft possessed 15%-18%). This would allow the aircraft to encounter severe compressibility effects very low in the transonic zone. However, NACA researcher Robert R. Gilruth proposed a thinner wing to provide a higher level of safety farther into the transonic region (through less problematic stability and control characteristics). The AAF mandated a 10% wing. Bell Aircraft believed that a very thin 8% wing was possible, although difficult to anufacture. The final agreement was to develop the thinner wings. After its initial flights at Pinecastle, the XS-1 #1 had an 8-percent-thick wing and a 6-percent-thick horizontal tail. The #2 aircraft had wings and tail that were each 2 percent thicker. The thicker 10-percent wing meant that the #2 airplane would always have a lower top speed than the #1 aircraft.

The moveable horizontal stabilizer was developed from data supplied by NACA based on its tests on the XP-42. The unit had a deflection of 5 degrees up and 10 degrees down. It was fitted with a screwjack operated, ultimately, by a pneumatic motor. The stabilizer was initially capable of one-degree, later three-degree, and finally two-degree per second adjustments.

The need for a movable stabilizer became critical in the upper transonic speed range when the XS-1 #1 reached an indicated Mach number of 0.94 and its elevators lost their effectiveness. So important was this discovery that nearly every transonic and supersonic aircraft since that time has had an all-movable horizontal stabilizer, although the Air Force managed to keep the information about it classified for about five years. This was long enough to give the later versions of the U.S. F-86 used by American pilots in the Korean War a decided advantage over the MiG-15s used by their opponents, because the F-86s had all-movable stabilizers and the MiGs did not.

The X-1 planes were equipped with an array of internal NACA flight data recorders. Pilot instrumentation was conventional with the exception of the Machmeter, an adjustable stabilizer switch, and the rocket engine controls. The cockpit was pressurized to a maximum of 3 lbs/square inch by nitrogen gas. An H-shaped control wheel rather than a conventional stick was provided to allow the pilot to use both hands in controlling X-1 flight in the expected turbulence of the transonic range.

The 210 lbs. weight RMI XLR-11 motor was a four-chamber unit providing a nominal 6,000 pounds of thrust at sea level. The engine was not throttleable although each chamber could be fired individually. Propellants for the #1 and #2 aircraft's engines were 311 gals. of liquid oxygen and 293 gals. of diluted ethyl alcohol. Capacity for the #3 aircraft was respectively, 437 gals. and 493 gals.

The #1 and #2 aircraft used a high-pressure nitrogen gas system to force the liquid oxygen and alcohol into the rocket engine. The 17.5 cubic feet of nitrogen was stored inside the airplane in twelve pressurized tanks. Due to the weight of the nitrogen tanks, the fuel supply for the two aircraft was severely restricted. Although the aircraft was initially designed to possess 8,160 pounds of fuel, the changes required by the nitrogen dropped fuel capacity to only 4,680 pounds. This allowed a maximum of about 2.5 minutes of powered flight time. The restricted flight time severely hampered efforts to reach the desired 35,000 feet altitude where supersonic testing was planned and led to the decision to use an airlaunch system.

Bell Aircraft initially used a Renton model Boeing B-29 (#45-21800) mother ship to carry the X-1 aloft to approximately 25,000 feet for airlaunch powered flight testing. The decision to employ a mother ship to carry the X-1 to launch altitude was strictly based on the X-1's limited flight time. The X-1 #3 used a B-50A (#46-006) mother ship for its flights, and B-50s were also used to launch the #1 and #2 aircraft on occasion.

No ejection seat was included in the construction of the X-1 because of weight and questions of its utility in high-speed escape. Nor was there any proven method of exit through the cockpit hatch due to the close proximity to the wing leading edge and the necessity to unhinge the pilot control wheel.

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