X Planes

The United States has a long history of producing X-planes for aeronautical research and testing of new technologies. US X-planes were mostly military designs that didn't progress beyond the experimental stage. The modern X-plane series began with the Bell X-1 which became famous as the first plane to break the sound barrier in 1949. Other X-planes usually produced important research results but only the North American X-15 gained comparable fame. X-planes 7 through 12 were actually missiles and some later X-planes carried no pilot at all. Almost all modern X-planes were never intended to go into production. However the X-35 went on to become the Joint Strike Fighter.

X-20 Dynasoar

The X-20 Dynasoar was a US Air Force program to develop a reusable spacecraft that could be used for reconnaissance, bombing, rescue, satellite maintenance and anti-satellite attacks. The X-20 was designed to operate in much the same way as the Space Shuttle did. It would be launched vertically atop a Titan III rocket. The Dynasoar would perform it’s mission and then land on it’s skids like a conventional airplane. The development program began on October 1957 and was canceled in December 1963 just before testing was scheduled to begin. Had the program been allowed to continue, the X-20 would have been a far more advanced spacecraft than anything else at the time. This model shows an X-20 in the markings of a Strategic Air Command bomber.

X-20 Dynasoar

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Boeing  SAC 3

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The X-36 Tailless Fighter Agility Research Aircraft was a NASA designed and McDonnell Douglas built project to develop a 1/6th scale tailless research aircraft to reduce the weight, drag and radar cross section associated with traditional fighter aircraft designs. The X-36 first flew in the summer of 1996 and went through a flight test program making 31 flights. Initial tests focused on low speed, high angle-of-attack performance. The X-36 was remotely controlled by a pilot in a ground station cockpit. The flight tests demonstrated the feasibility of using new flight control technologies in place of vertical and horizontal tails to improve the maneuverability and survivability of future fighter aircraft. After completion of the flight test program in 1998, the two X-36 UAVs were stored in flyable condition at NASA Dryden. In 2003 one X-36 was moved to the National Museum of the United States Air Force and the other sent to the Air Force Test Flight Center Museum. The aircraft had flown a total of 31 flights, achieving speeds of up to 206 knots, an altitude of more than 20,000 feet and more than 40 degrees angle of attack.


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The X-45 is an Unmanned Combat Air Vehicle (UCAV) that was developed as a concept demonstrator by Boeing's Phantom Works division. Developed from data gathered from the Bird of Prey project the X-45 was designed to test technology for air to ground attacks using an unmanned vehicle. The X-45 first flew in September 2000 and on April 18, 2004, the X-45 conducted it’s first bombing run test at Edwards Air Force Base. After the completion of the flight test program, both X-45s were sent to museums, one to the National Air and Space Museum, and the other to the National Museum of the United States Air Force at Wright-Patterson Air Force Base.


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darpa  Boeing

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On October 14, 1947 the Bell X-1 became the first plane to fly faster than sound piloted by Chuck Yeager. The X-1, named Glamorous Glennis flew at Mach 1.06 at an altitude of 43,000 feet over the Mojave Desert near Muroc Dry Lake, California. Powered by a rocket engine the X-1, although originally designed to take off under it’s own power, was dropped from the belly of a modified B-29 Superfortress and glided to a landing on a runway. The X-1's fuselage was shaped like a .50 caliber bullet and the plane carried more than 500 pounds of flight test instruments. As a result of the X-1's supersonic flight, the National Aviation Association voted its 1948 Collier Trophy to be shared by Bell Aircraft, Chuck Yeager and NACA (later NASA). This record breaking plane was later transferred to the Smithsonian Museum.

Bell X-1

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Bell  NACA

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The Convair XF-92 was the first American delta-wing aircraft. The design was originally developed by Dr. Alexander Lippisch of Germany before and during World War II as the ramjet powered Lippisch P.13a, but progressed only to a powerless glider example. After moving to the US as part of Operation Paperclip, Lippisch managed to interest Convair in building the design with a jet engine as a point defense interceptor. When interest in point defense fighters waned, Convair continued development of the XF-92 as a research aircraft. In 1953 NACA's High-Speed Flight Research Station took over flight testing. NACA pilot Scott Crossfield flew all 25 of the XF-92 flights over the six month test period. Research from the XF-92 test program was used in the development of Convair's F-102 Delta Dagger and the F-106 Delta Dart, as well as the B-58 Hustler bomber. Also see the DM-1 for the WWII research glider.

Convair XF-92

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Convair  NACA

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XF-91 Thunderceptor

The Republic XF-91 Thunderceptor was a swept wing jet and rocket propelled interceptor based on the F-84 Thunderjet. The choice of jet and rocket propulsion was inspired by the WWII German ME-163 and the ME-262 C. The wings were also a unique feature of the XF-91. Swept wing designs of the late 1940s and early 1950s tended to cause a stall at low speed and high angles of attack. The Thunderceptor's wings were built to have considerably more chord at the tip than root correcting this problem. A side effect of this was that the wing tips had more internal room so the landing gear was mounted to retract outward with the wheels lying in the wingtips. The wings were also designed to vary the angle of incidence, tilting it up for low speed flight and leveling off for high speed flight. The first prototype flew on May 9, 1949 and broke the sound barrier in December 1951. When using both the jet and rockets the Thunderceptor could reach Mach 1.71. A second prototype was created and they completed 192 test flights over the course of five years. Both prototypes were modified several times during testing. Ultimately the XF-91 did not have the performance or armament capability to meet the needs of the USAF. It's extremely short flight time of about 25 minutes and inability to carry radar and fire control systems for night and all weather operation caused the programs cancellation. The first prototype is on display at the National Museum of the United States Air Force in Dayton, Ohio.

Republic XF-91 Thunderceptor



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XP-55 A Ascender Fighter

In November 1939 the US Army Air Force issued a request for aircraft with an unconventional design in an attempt to produce fighter planes that would have a top speed, rate of climb, maneuverability, armament, and pilot visibility superior to those of any existing fighter. By the end of 1940 the Curtiss designed XP-55 was selected as one of four designs the merited further work. With its swept wings, rear mounted engine, forward mounted canards and wing tip fins, the XP-55 Ascender was the most unconventional of the four finalists. First flying on July 19, 1943 the 3 XP-55 prototypes went through an extensive series of flight tests and suffered several crashes. The XP-55 never achieved it’s promised performance specifications and testing was halted in 1945. The Ascender was to have been armed with four .50 cal. machineguns. The sole surviving XP-55 is at the National Air and Space Museum.

Curtiss XP-55 Ascender Experimental Fighter

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XP-77 A Fighter

The Bell XP-77 was designed as a simplified lightweight fighter aircraft using non-strategic materials such as wood. It was a single engine, low wing monoplane with a wood structure and a metal laminate skin and equipped with a bubble canopy and tricycle landing gear. Design was started in 1941; however the prototype did not fly until April 1, 1944 due to problems with the development of the engine. While it was an innovative design, the first flights revealed vibration problems and poor pilot visibility. The XP-77 was difficult to fly and even though it flew without guns or armor it did not meet the expected performance estimates. The second prototype crashed during testing and the development program was terminated in December 1944. The XP-77 was to have been armed with two 20 mm Hispano-Suiza HS.404 cannons, two .50 cal. M2 machineguns with 200 rounds each and either one 300 lb. bomb or one 325 lb. depth charge.

Bell XP-77 Experimental All Wood Fighter

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XV-5 A Vertifan Experimental VTOL Plane

The Ryan XV-5 Vertifan was a jet powered VTOL experimental aircraft commissioned by the US Army. The XV-5 had a 5 ft diameter fan in each wing with covers the looked like half-garbage can lids which flipped up for vertical flight to provide vertical lift. A smaller fan in the nose in front of the two person cockpit gives pitch control and additional lift. The fans provided a total vertical thrust of 16,000 lb and were driven by the exhaust gases of two 2,650 lb thrust GE J85-GE-5 turbojets. With a 7,000 lb empty weight, and a 12,200 lb gross weight, the Vertifan had 31% excess power. Two aircraft were built; the first one flew from May 25, 1964 until it crashed the following April, killing the pilot during a transition attempt. First hover was in June 1964 and first transition in November 1964. The second aircraft flew until it crashed in October 1966 (also killing the pilot), but was rebuilt as an XV-5 B. The main drawbacks of the Vertifan were the large volume and weight occupied by the lift system, slow control response, and the narrow transition corridor.

Ryan XV-5 Vertifan Experimental VTOL Plane

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X-15 A

The North American X-15 was probably the most famous of the United States X Plane series. Operated by NASA and the USAF, the X-15 set many speed and altitude records during the 1960s. It still holds the official world record for the fastest speed ever reached by a manned aircraft. The design was based on a concept study by Walter Dornberger with the airframe built by North American and the engines by Reaction Motors. The X-15 became the world's first operational spaceplane, reaching space in 1962. The first X-15 flight was an unpowered test flight by Scott Crossfield, on June 8, 1959 and the last flight was on October 24, 1968. During the testing program there were two accidents. On November 15, 1967 test pilot Major Michael J. Adams was killed when X-15 number 3 broke apart at 60,000 ft. X-15 number 2 was rebuilt after a landing accident. It was lengthened 2.4 feet, a pair of auxiliary fuel tanks attached underneath its fuselage and wings and a heat resistant ablative coating was added. During the X-15 program 13 flights by eight pilots met the spaceflight criterion by exceeding 50 miles altitude and thereby qualifying the pilots for astronaut status. X-15 number 1 flew 82 powered flights, X-15 number 2 flew 53 powered flights and X-15 number 3 flew 64 powered flights. X-15 number 1 is on display in the National Air and Space Museum Milestones of Flight gallery in Washington, D.C. and X-15 number 2 is on display at the National Museum of the United States Air Force at Wright-Patterson Air Force Base. This model shows X-15 number 2 before its rebuild.

North American X-15 A




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X-3 Stiletto

Although the Douglas X-3 Stiletto was the fastest looking X Plane, it was a total failure in it's intended role as a high speed research plane. The Stiletto was designed to take off from the ground under its own power, climb to high altitude, maintain a sustained cruise speed of Mach 2 and then land under its own power. It was also to be used to test low aspect ratio wings and titanium in aircraft structures. Construction of two X-3s was approved on June 30, 1949 with the first plane delivered to Edwards Air Force Base, CA on September 11, 1952 and it's first flight made on October 15, 1952. Due to the poor performance of the engines, the X-3 was never able to reach Mach 1 in level flight. It was only able to break the sound barrier in a 30 degree dive. Despite it's poor performance, the X-3 did provide valuable information on roll inertia coupling, low aspect ratio high speed unswept wings (later used in the F-104), titanium structures and high speed tires. Due to the poor performance of the first plane, the partially completed second aircraft was canceled and was used for spare parts. The X-3 Stiletto is on display in the Research & Development Gallery at the National Museum of the United States Air Force at Wright-Patterson Air Force Base, Ohio.

X-3 Stiletto




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XF2Y-1 Sea Dart Seaplane

The Convair XF2Y-1 Sea Dart was designed to take off and land on water. It was a delta winged, turbojet powered seaplane that first flew on January 14, 1953. In the late 1940s and early 1950s the navy had doubts about launching and landing high performance aircraft on aircraft carriers so they asked for designs that could operate on water. Convair's proposal was given an order for two prototypes in 1951. The Sea Dart was a delta winged fighter with a watertight hull and twin retractable hydro-skis for takeoff and landing. When stationary or moving slowly in the water, the Sea Dart floated with the trailing edge of the wings touching the water. The skis were not extended until the aircraft reached about 10 mph. Unfortunately, the engines that were to be used in the Sea Dart were not ready in time and lower powered engines were fitted. This caused the performance of the aircraft to fall far below what was expected. Testing continued at San Diego Bay but the underpowered engines made the fighter sluggish and the hydro-skis were not as successful as hoped. While the skis were improved, the engines prevented the Sea Dart from going supersonic except in a dive. The second Sea Dart disintegrated in mid-air over San Diego Bay on November 4, 1954 All further production orders were canceled, the remaining 2 test aircraft were completed but never flown and the original prototype was used for testing until 1957. The Convair XFY2-1 Sea Dart is the only seaplane to exceed Mach 1. When the designation system for navy planes was changed in 1962, the Sea Dart was designated YF-7A The Sea Dart was to be armed with four 20mm cannons and two air to air missiles. This model shows the second Sea Dart in early 1954.

XF2Y-1 Sea Dart Seaplane




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Curtiss XP-37 Fighter

First flying in April 1937 the XP-37 was the result of a request from the USAAC to Curtiss to see if the performance of the P-36 could be increased. Curtiss took the Model 75 prototype and fitted it with a 1150 hp Allison V-1710-11 turbo supercharged engine. They also added three Prestone cooling radiators immediately behind the engine. The cockpit was moved far back to make room for the radiators and to balance the aircraft. The rest of the airframe was essentially unchanged from the P-36. The XP-37 was plagued by problems from the beginning. The supercharger was extremely unreliable, the performance fell short of the expectations and there was very poor visibility from the cockpit during takeoff and landing. In spite of all this the USAAC continued to believe that the idea had potential and they ordered 13 test aircraft. Although improvements were made, the design still suffered from the same problems. By the end of 1942 all of the XP-37s were out of service or retired to mechanics' schools. The last XP-37 survived at the NACA until January 1946. The XP-37 was armed with one .30 cal. and one .50 cal. machinegun mounted in the fuselage and synchronized to fire through the propeller arc. This model shows a XP-37 used for cold weather testing in Alaska during early 1940.  Also see the Curtiss Hawk 75 and the P-36 A Hawk the P-40 B Warhawk and the P-40 E Warhawk and the Hawks group.

XP-37 Fighter

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Avro 606 B Fighter

Avro Aviation in Canada became interested in circular wing aircraft in the mid 1950s. Although only on circular wing project made it to the prototype stage (the VZ-9 Avro Car), dozens of others made it to the project study stage. Project 606 started out as a high speed reconnaissance plane whose circular wing was supposed to make it less visible to enemy radar.  Project 606-B was a VTOL fighter concept featuring a raised section in the middle over the six engines with the intake covered with a series of louvers that would be closed in forward flight.  Performance estimates for the concept were for Mach 3.5 at 100,000 ft. The project got as far as wind tunnel testing with a variety of scale models. In 1955 an article appeared in Look magazine that speculated that current UFO sightings were Soviet built saucers. The article went on to describe such an aircraft with diagrams that were clearly influenced by the Avro design.

Avro 606 B Fighter

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