History of X-Planes

X-planes are a series of experimental airplanes, helicopters, and rockets used to test and evaluate new technologies and aerodynamic designs. Most of the X-planes have been operated by the  National Aeronautics and Space Administration (NASA) and its predecessor National Advisory Committee for Aeronautics (NACA), often in conjunction with the United States Air Force.

X-37b returning in September 2014 after a 2-year, classified mission (unmanned).

X-37b returning in September 2014 after a 2-year, classified mission (unmanned).

After WWII, experimental aircraft experienced a golden era as new designs and technology combined with cold war urgency. The United States was the only country at the time to possess the funds and technical talent for such an aggressive experimental program. The X-1, for instance, was the first piloted aircraft to break the sound barrier.

But X-planes were not the only driving force on the frontier of aeronautical innovation.  Six months after the X-1 success, in April 1948, test pilot George Welch flew the swept-wing XP-86 beyond the sound barrier in stable flight. Much the same happened at Mach 2. The test pilot Scott Crossfield was the first to reach this mark, flying the experimental Douglas Skyrocket in November 1953.  Simultaneously, Alexander Kartveli of Republic Aviation was well along in crafting the XF-105. In June 1956 an F-105 reached Mach 2.15. It too was an opera­tional fighter, in contrast to the Skyrocket.

Beginning in the 1950s, ramjet-powered craft excelled beyond jet engine limitations. The Navaho cruise missile flew near Mach 3. An even more far-reaching prospect was in view at Republic Aviation, where Alexander Kartveli was working on the XF-103. It was designed to fly at Mach 3.7 with its own ramjet, nearly 2,500 miles per hour (mph), with a sustained ceiling of 75,000 feet.   While not an official x-plane, the XF-103 demonstrates the important contributions made by designers working on practical, manned aircraft.

The Bell X-2 proved to be the fastest and highest-flying of the "round one" X-planes and the most tragic, with the two X-2s logging only 20 glide and powered flights between them. Nevertheless, Captain Iven C. Kincheloe, Jr., managed to take one of the airplanes to 126,200 feet on 7 September 1956. Twenty days later, Captain Milburn G. Apt was killed during his first X-2 flight after he reached Mach 3.196 (1,701 mph), becoming the first person to fly at three times the speed of sound, albeit briefly.

The first combat type designed from the start as a supersonic fighter—Kartveli's XF-91 "Thunderceptor"—made its maiden flight only 19 months after Yeager's flight. How much the X-1 experience contributed to Alexander Kartveli's design is unknown.   Kartveli continued to design interceptors capable of reaching Mach 3+ speeds as the lead designer at Republic Aircraft. 

Here is a list of all the x-planes. 

X-1

Bell Aircraft
USAF, NACA

January 19, 1946High-speed and high-altitude testing.
First aircraft to break the sound barrier in level flight.
Proved aerodynamic viability of thin wing sections.


X-2 "Starbuster"

Bell Aircraft

USAF

June 27, 1952High-speed and high-altitude testing.
First aircraft to exceed Mach 3.


X-3 Stiletto
USAF, NACA

October 27, 1952

Titanium alloy construction; low aspect ratio wings.
Planned to test long-duration high-speed flight.
Incapable of reaching design speed, but provided insights into inertia coupling.


X-4 Bantam

Northrop
USAF, NACA

December 15, 1948

Evaluated handling characteristics of tailless aircraft in the transonic speed region.


X-5

Bell Aircraft
USAF, NACA

June 20, 1951First aircraft to fly with variable geometry wings.



X-7 "Flying Stove Pipe"

Lockheed
Tri-service

April 1951

High-speed testbed for ramjet engines.


X-8 Aerobee

Aerojet
NACA, USAF, USN

Upper air research vehicle and sounding rocket.


X-9 Shrike

Bell Aircraft
USAF

April 1949

Guidance and propulsion technology testbed.
Assisted development of GAM-63 Rascal missile.


X-10

North American Aviation
USAF

October 13, 1953

Testbed for SM-64 Navajo missile.


X-11 Convair
USAF
June 11, 1957

Testbed for SM-65 Atlas missile.


X-12 Convair
USAF

July, 1958

Advanced testbed for SM-65 Atlas missile.


X-13 Vertijet

Ryan Aeronautical
USAF, USN

December 10, 1955

Vertical takeoff and landing (VTOL) testbed.
Evaluated tailsitting configuration for VTOL flight.


X-14

Bell Aircraft
USAF, NASA

February 19, 1957

VTOL testbed.
Examined the vectored thrust configuration for VTOL flight.


X-15

North American Aviation
USAF, NASA

June 8, 1959

Hypersonic (Mach 6.7), high-altitude (350,000 feet (110,000 m)) testing.
First manned hypersonic aircraft; capable of suborbital spaceflight.


X-16

Bell Aircraft
USAF

Never flew - High-altitude reconnaissance aircraft project.
"X-16" designation used as cover story.


X-17

Lockheed
USAF, USN

April 1956

Tested the effects of high Mach number reentry.


X-18

Hiller Aircraft
USAF, USN

November 24, 1959

VTOL/Short take-off and vertical landing (STOVL) testbed.
Evaluated the tiltwing concept for VTOL flight.


X-19

Curtiss-Wright
Tri-serviceNovember 1963Tandem tiltrotor VTOL transport testbed.
XC-143 designation proposed.


X-20 Dyna-Soar

Boeing
USAF

Never built

Reusable spaceplane for military missions.


X-21

Northrop
USAF

April 18, 1963

Boundary layer control testbed.


X-22

Bell Aircraft
Tri-service

March 17, 1966

Quad ducted fan tiltrotor STOVL testbed.


X-23 PRIME

Martin Marietta
USAF

December 21, 1966

Maneuvering atmospheric reentry effects testbed.
Designation never officially assigned.


X-24

Martin Marietta
USAF, NASA
August 1, 1973

Low-speed lifting body handling testbed.
Lifting body aerodynamic shape trials.


X-25

Benson
USAF

December 6, 1955

Light autogyro for emergency use by downed pilots.



X-27

Lockheed Never flew High performance fighter prototype.


X-28 Sea Skimmer

Osprey Aircraft
USN

August 12, 1970

Inexpensive aerial policing seaplane testbed.


X-29

Grumman
DARPA, USAF, NASA

1984

Forward-swept wing testbed.


X-30 NASP

Rockwell
NASA, DARPA, USAFNever built

Single stage to orbit spaceplane prototype.


X-31

Rockwell
DARPA, USAF, BdV

1990

Thrust vectoring super maneuverability testbed.
ESTOL testbed.


X-32

Boeing
USAF, USN, RAF

September 2000

Joint Strike Fighter prototype.


X-33 Venture Star

Lockheed Martin
NASA

Prototype never completed.  Half-scale reusable launch vehicle prototype.


X-34

Orbital Sciences
NASA

Never flew.  Reusable unmanned space plane testbed.


X-35

Lockheed Martin
USAF, USN, RAF

2000

Joint Strike Fighter prototype.


X-36

McDonnell Douglas/Boeing
NASA

May 17, 1997

28% scale tailless fighter testbed.


X-37

Boeing
USAF, NASA

April 7, 2006 (drop test)
April 22, 2010 (orbital flight). Reusable orbital space plane.


X-38

Scaled Composites
NASA

1999

Lifting body Crew Return Vehicle demonstrator.


X-39

Unknown
USAF

Classified - Unknown Purpose

Future Aircraft Technology Enhancements (FATE) program.
Designation never officially assigned.


X-40

Boeing
USAF, NASA

August 11, 1998

80% scale Space Maneuver Vehicle testbed.
X-37 prototype.


X-41
USAF

Classified Unknown

Maneuvering re-entry vehicle.


X-42
USAF

Classified Unknown

Expendable liquid propellant upper-stage rocket.


X-43 Hyper-X

Micro Craft
NASA

June 2, 2001

Scramjet hypersonic testbed (Mach 9.68) (110,000 ft).


X-44 MANTA

Lockheed Martin
USAF, NASA

Cancelled

F-22-based Multi-Axis.  No-Tail Aircraft thrust vectoring testbed.


X-45

Boeing
DARPA, USAF
May 22, 2002

Unmanned combat air vehicle (UCAV) demonstrator.


X-46

Boeing
DARPA, USN

Cancelled

Naval UCAV demonstrator.


X-47A Pegasus & X-47B

Northrop Grumman
DARPA, USN

February 23, 2003

Naval UCAV demonstrator.


X-48

Boeing
NASA

July 20, 2007

Blended Wing Body (BWB) testbed.


X-49 Speedhawk

Piasecki Aircraft
US Army

July 29, 2007

Compound helicopter
Vectored Thrust Ducted Propeller (VTDP) testbed.


X-50 Dragonfly

Boeing
DARPA

24 November 2003

Canard Rotor/Wing testbed.


X-51 Waverider

Boeing
USAF

26 May 201

Hypersonic scramjet demonstrator.


X-52

Number skipped to avoid confusion with B-52.


X-53

Boeing Phantom Works
NASA, USAF

November 2002

Active Aeroelastic Wing testbed.



X-55

Lockheed Martin Skunk Works
USAF

June 2, 2009

Advanced Composite Cargo Aircraft (ACCA).
Molded composite fuselage and empennage testbed.


X-56

Lockheed Martin Skunk Works
USAF/NASA

2012

Active flutter suppression and gust load alleviation technology for potential use in future high-altitude, long-endurance (HALE) reconnaissance aircraft



SOURCES:

Wikipedia

"The X-15: Extending the Frontiers of Flight" by Dennis Jenkins 2009