The X-Planes

History of the X-Plane Program

The U.S. X-Plane Program has evolved from being the first rocket-powered airplane to break the sound barrier (the X-1 on October 14, 1947) and included over 30 different major research designs, although not all were developed into flying prototypes. As the program progressed, other non-rocket-powered experimental aircraft were built and tested. These aircraft included: a range of vertical takeoff and horizontal landing vehicles; smaller, propeller-driven reconnaissance vehicles; and a series of unmanned missile testbeds of both single and multistage designs. Although the program grew to include conventional propeller-driven aircraft, all designs had in common the aspect of being highly valuable research tools for advancement of aerodynamics and astronautics.

Accomplishments of the X-Plane family have been many. The program included: (1) the first aircraft to break the sound barrier; (2) the first aircraft to use a variable-sweep-wing in flight; (3) the first to fly at altitudes in excess of 30,000, 60,000, and 90,000 m (100,000, 200,000 and 300,000 ft); (4) the first to use exotic alloy metals for primary structure; (5) the first to test gimbaled jet and rocket engines; (6) the first to use jet-thrust for launch and landing; (7) the first to fly three, four, five, and six times the speed of sound; (8) the first to test boundary-layer-airflow control theories over an entire wing at transonic speeds; (9) the first to successfully complete a 180 degree turn using a post-stall maneuver; and (10) the first missile to reach an intercontinental flight range.

The majority of testing for the X-Plane family has occurred at Edwards Air Force Base (formerly known as Muroc Army Airfield). Hosts within Edwards include the Air Force Flight Test Center and Dryden Flight Research Center. Other sites which have served as X-Plane testing sites include: Langley Research Center and Ames Research Center; various Government owned ships; White Sands Missile Range, New Mexico; Wright-Patterson Air Force Base, Ohio; Cape Canaveral Air Station, Florida; Pinecastle Air Force Base, Florida; Buffalo, New York; and the National Aviation Facilities Experimental Center in Atlantic City, New Jersey. Edwards has seen more X-Plane programs and test flights than any other similar facility in the U.S.

As with every research program testing prototype equipment, the X-Plane Program has not been without technical glitches and equipment failures. Since the beginning of the program's manned flight operations in 1946, approximately 15 major accidents and 4 fatalities (pilots) have been associated with manned vehicle tests. Three of these fatalities were from the X-2 Program, flown between 1952 and 1956, and the remaining fatality happened in 1967 during an X-15 research flight. Stringent range safety controls have resulted in no civilian property damage losses or fatalities being reported as a result of any X-Plane Program accident. Given the overwhelming number of test flights, the small number of accidents which resulted in loss of aircraft or life can be considered a remarkable program achievement. Table 1 provides key information about each plane tested in the X-Plane series of vehicles.

Another member of the X-Plane Program would be the X-33. As a reusable spaceplane, the X-33 continues the research line developed by various components of the X-Program, such as the X-10 which tested cruise missile components; the X-12, the Atlas B missile which tested one-and-one-half propulsion staging and obtained the first intercontinental flight distance for a U.S. missile; the X-15 which explored the problems of space and reentry at high speeds (Mach 6) and altitudes; the X-17 which explored high Mach effects on reentry vehicles; and the X-23A which was the first maneuvering lifting reentry vehicle. The X-17 was a multistage rocket design which transported various reentry vehicle configurations to very high altitudes to examine their reentry characteristics. The X-23A was launched by a modified intercontinental ballistic missile and utilized a lifting body design to glide back to earth. Information acquired from the X-23A was instrumental in later development of the Space Shuttle.

 

Table 1. Summary of the X-Plane Program.
Model Manufacturer No. of Vehicles Built Years of Operation No. of Flights Primary Testing Facility Research Goals Program Achievements No. of Major Accidents Causes of Accidents No. of Fatalities Civilian Involvement
X-1 Bell Aircraft 3 1946-51 157 Edwards AFB Investigate flight characteristics at greater than sonic velocities. Structural, physiological phenomena within transonic speed envelope First Mach 1+ flight; Maximum altitude of 71,902 ft 1 Defueling Explosion 0 None
X-1A Bell Aircraft 1 1953-55 25 Edwards AFB Continue X-1 goals at higher speeds and altitudes Obtained speed of Mach 2.44; Maximum altitude of 90,440 ft 1 Explosion during captive flight; vehicle jettisoned 0 None
X-1B Bell Aircraft 1 1954-58 27 Edwards AFB Exploratory aerodynamic heating tests; experimental reaction control system First reaction controlled flight 0 Not applicable Not applicable Not applicable
X-1D Bell Aircraft 1 1951 1 Edwards AFB Continue X-1 goals at higher speeds and altitudes No major milestones 1 Explosion during captive flight; vehicle jettisoned 0 None
X-1E Bell Aircraft, Stanley Aircraft (wings) 1 1955-58 26 Edwards AFB High-speed wing performance Mach 2.24, altitude 73,458 ft; first flight with ventral fins 0 Not applicable Not applicable Not applicable
X-2 Bell Aircraft 2 1952-56 20 Edwards AFB Swept-wing performance; higher speeds and altitude than X-1 New altitude record of 126,200 ft; new speed record of Mach 2.87 2 Gasket explosion destroys first X-2; second aircraft lost to inertial coupling 3 None
X-3 Douglas Aircraft 1 1954-56 20 Edwards AFB High speed aerodynamic phenomenon; titanium construction; take off, land under its own power Led to understanding of inertia coupling 0 Not applicable Not applicable Not applicable
X-4 Northrop Aircraft 2 1950-53 82 Edwards AFB Test tailless, semi-tailless configuration at transonic speeds Showed tailless craft not suited for transonic flight 0 Not applicable Not applicable Not applicable
X-5 Bell Aircraft 2 1952-55 133 Edwards AFB Investigate aerodynamics of variable-seep-wing design Successful sweep-wing operation 0 Not applicable Not applicable Not applicable
X-6 Convair Division, General Dynamics 1 shield-test aircraft (modified B-36H) 1955-57 47 Convair Testing Facility Test feasibility of nuclear propulsion Program terminated before prototypes constructed 0 Not applicable Not applicable Not applicable
X-7A, X-7A-3, X-7B, X-Q5 (unmanned) Lockheed Missiles 61 1951-60 130 New Mexico Test viability of ramjet engines for anti-aircraft missiles; modified to testing of powerplants Obtained Mach 4.31, first air-breathing full-scale research aircraft designed as Mach 3 testbed 0 Not applicable Not applicable Not applicable
X-8A, X-8B, X-8C, X-8D Aerobees (unmanned) Aerojet Engineering 108 (X-8 designation) 800+ (Aerobees) 1947-56 Unknown White Sands, Holloman AFB Upper air research, parachute recovery system Peak altitude of 121 miles 0 Not applicable Not applicable Not applicable
X-9 (unmanned) Bell Aircraft 31 1949-53 28 Holloman AFB Test air-to-surface missiles; guidance systems, etc. First chemical warhead test vehicle to test supersonic clusterable dispersion 9 unsuccessful flights Servo system failures 0 Not applicable
X-10 (unmanned) North American Aviation 13 1955-59 15 Edwards AFB Testbed for cruise missile components Established technology base for remote control; first Mach 2-capable target drone 3 unsuccessful flights Communications disruption; miswiring; autopilot malfunction 0 Not applicable
X-11 (unmanned) Convair Astronautics Division 8 1956-58 8 Cape Canaveral Provide flight data for Atlas missile First ICBM prototypes 0 Not applicable Not applicable Not applicable
X-12 (unmanned) Convair Astronautics Division 5 1958 5 Cape Canaveral Test 1½-propulsion-staging guidance system, nose reentry configuration First intercontinental range mission of 6,325 miles 0 Not applicable Not applicable Not applicable
X-13 Ryan Aeronautical Company 2 1955-57 Unknown Edwards AFB Test pure-jet vertical takeoff and landing First successful VTOL flight on jet thrust alone 0 Not applicable Not applicable Not applicable
X-14, X-14A, X-14B Bell Aircraft 1 1957-81 Unknown Moffet Field Test VTOL technology First VTOL aircraft using jet thrust diverter system for vertical lift 0 Not applicable Not applicable Not applicable
X-15, X-15A-2 North American Aviation 3 1959-68 199\ X-15 High Range (Wendover, UT, to Edwards AFB) Explore problems of space and atmospheric flight at very high speeds and altitudes First manned hypersonic flight vehicle; altitude of 354,200 ft obtained; Mach 6.33 reached 4 Mid-flight explosions (2); loss of control (1); collapsed landing gear (1) 1 Not applicable
X-16 Bell Aircraft Canceled None None None High-altitude, long-range reconnaissance aircraft Not applicable Not applicable Not applicable Not applicable Not applicable
X-17 (unmanned) Lockheed Missiles 26 1955-57 26 Holloman AFB Explore reentry characteristics High Mach effects on reentry vehicles 0 Not applicable Not applicable Not applicable
X-18 Hiller Aircraft 1 1959-61 20 Edwards AFB Explore large VTOL vehicles First tilt-wing usage for VTOL 0 Not applicable Not applicable Not applicable
X-19 Curtiss-Wright 2 1964-65 50 Caldwell; NAFEC, NJ Test VTOL technology using radial lift Dual-tandem tilt propeller use 1 Equipment failure 0 Not applicable
X-20 Boeing Canceled None None None Piloted orbital flight Provided heat materials testing Not applicable Not applicable Not applicable Not applicable
X-21A Northrop Corporation 2 1963-64 Unknown Edwards AFB Test full-scale boundary control on large aircraft Proved Laminar Flow Control viable 0 Not applicable Not applicable Not applicable
X-22A Bell Aerospace 2 1966-84 501 Bell, Calspan Test Facilities Research dual-tandem-ducted propeller configuration; research V/STOL handling using variable stability system design Ducted fan viability, advancement of VTOL technology 1 hydraulic system failure 0 None
X-23A (unmanned) Martin Marietta 4 1966-67 3 Vandenberg AFB/Pacific Ocean Test configurations, control systems, and ablative materials for hypersonic reentry vehicles First maneuverable reentry vehicle 0 Not applicable Not applicable Not applicable
X-24A, X-24B Martin Marietta 1 1969-75 64 Edwards AFB Research of aerodynamics, flight characteristics of manned vehicle with FDL-7 configuration Verified theoretical advantages of lifting body configuration for hypersonic transatmospheric aircraft 0 Not applicable Not applicable Not applicable
X-25, X-25A, X-25B Bensen Aircraft 3 1968   Raleigh, NC Test discretionary descent vehicle designs Insight on pilot training 0 Not applicable Not applicable Not applicable
X-26A, X-26B Schweizer Aircraft, Lockheed Missiles 6 1967-88 Unknown Vietnam Develop ultra-quiet surveillance aircraft Use as training vehicle; contributions to stealth designs 3 Training exercises 0 Not applicable
X-27 Lockheed-California Canceled None None None Advanced, lightweight fighter None Not applicable Not applicable Not applicable Not applicable
X-28A George Pereira, Osprey Aircraft 1 1971 Unknown Philadelphia Naval Base, PA Explore usefulness of small, single-place seaplane for civil police patrol in Southeast Asia Unique contribution as home-built aircraft in X-Plane program 0 Not applicable Not applicable Not applicable
X-29A Grumman Aerospace 2 1984-90 Unknown Edwards AFB Test forward-swept wing design, advanced composites, other aerodynamic advances First FSW aircraft to fly supersonically in level flight 0 Not applicable Not applicable Not applicable
X-30 None selected None
(Cancelled)
None None None Serve as testbed for sustained hypersonic speeds within atmosphere or as space vehicles for orbital payload delivery Not applicable Not applicable Not applicable Not applicable Not applicable
X-31A Rockwell International, Deutsche Aerospace 2 1990-95 523 Edwards AFB Break "stall-barrier," examine angles of attack 180 degree turn post-stall maneuver 1 Failure of the pitot-static system: erroneous total pressure data 0 None
X-32 Boeing         Joint Strike Fighter          
X-33 Lockheed-Martin Skunk Works 1
(Cancelled)
1999-2000 15 Edwards AFB Develop reusable single-stage-to-orbit transportation vehicle Not applicable Not applicable Not applicable Not applicable Not applicable
X-34   (Cancelled)       Reusable, unmanned suborbital spacecraft       Not applicable  
X-35 Lockheed-Martin 2 2000-2001 66 Palmdale, CA
Edwards AFB
Joint Strike Fighter Developed into the
F-35 Joint Strike
Fighter
       
X-36 McDonnell
Douglas
2 1997 31   Tailless fighter
agility research
      Not applicable  
X-37 Boeing 3 2006-     Unmanned orbital
test vehicle
Underwent orbital
test from 22 April
to 3 December 2010
       
X-38 Scaled Composites (Cancelled)
2 prototypes
1999-2002     Develop technology for a prototype Crew Return Vehicle for the ISS       Not applicable  
X-39
(unassigned)
                     
X-40A Boeing Phantom Works 1 1998-2001     Space maneuver vehicle       Not applicable  
X-41 Air Force / DARPA / Sandia National Labs / NASA         Common Aero Vehicle / Hypersonic Technology Vehicle Classified        
X-42           Pop-up upper stage Classified        
X-43A     2001-2004   Dryden/Edwards AFB Hyper-X, program to demonstrate hypersonic air-breathing scramjets       Not applicable  
X-44                      
X-45A Boeing 2 2002-06     Scaled down proof of concept demonstrator of an unmanned combat air vehicle          
X-45B/C Boeing Cancelled
(3 planned)
      Concept demonstrator of an unmanned combat air vehicle          
X-46 Boeing         Naval unmanned combat air vehicle          
X-47 Northrop   2003-     Concept demonstrator of an unmanned combat air vehicle          
X-48 Boeing         Blended wing body concept          
X-49 (unassigned)                    
X-50 Boeing         Technology demonstrator for the Dragonfly Canard Rotor/Wing          
Key to Acronyms:

AFB = Air Force Base

FDL-7 = Flight Dynamics Laboratory-7 (a prototype test craft of the Air Force's Flight Dynamics Laboratory, a predecessor to the X-24B).

FSW = forward swept wing

ICBM = intercontinental ballistic missile

V/STOL = vertical/short takeoff and landing

VTOL = vertical takeoff and landing

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Times accessed: 2049

An American X-Plane History, from NASA.

(NASA receives credit for the information contained on this page)