Simple Flying provides a round-up of some of US military aviation's most notable experimental aircraft. These X-planes have forever changed flying!
Close 1 X-1: First aircraft to break the sound barrier.
The Bell X-1 left an indelible mark on both the history of aviation and the history of America. Chuck Yeager became the first human being to break the sound barrier on October 14, 1947 when he piloted "Glamorous Glennis" to her moment in the sun. The X-1, developed by Bell Aircraft for the US Air Force and the National Advisory Committee for Aeronautics (NACA) which would later be absorbed by NASA. It was the first rocket-powered research aircraft designed to explore transonic speeds and break the sound barrier. The X-1 flights demonstrated that humans could exceed the speed of sound, leading to significant advancements in aviation technology, including new wing designs and control systems.
"It wasn't that the X-1 would kill you, it was the systems in the X-1 that would kill you." - Chuck Yeager
Three X-1 aircraft were built. The first flew unpowered in 1946, with powered flights starting the same year. The X-1A and X-1B were follow-on variants featuring design enhancements that allowed for higher speeds and altitudes. The X-1A reached Mach 2.4 and 90,000 feet in 1953. The X-1B conducted further high-speed research until its retirement in 1958. Additional variants, the X-1C (canceled) and X-1D (destroyed), were also planned, with the final variant, X-1E, modified for exclusive NACA use from 1955 to 1958.
Photo: Wikimedia Commons 2 X-15: Set the world record for fastest manned aircraft.
The X-15 was a hypersonic research program in collaboration between NASA, the US Air Force and the Navy. The program spanned nearly a decade and set unofficial records of 4,520 mph (Mach 6.7) and 354,200 feet altitude. The goal was to explore piloted hypersonic flight and the flight tests provided vital data that influenced the Mercury, Gemini, Apollo, and Space Shuttle programs. North American built three X-15 aircraft that completed 199 flights. The aircraft were launched from a B-52 at high altitude, so high that their designs included reaction control systems (RCS) for maneuvering in space. The program yielded over 765 research reports that contributed to a long list of technological innovations but primarily focused on hypersonic theory and application, reaction controls, and the physiology of pilots.
Photo: Wikimedia Commons 3 X-29: Forward-swept wings and advanced aerodynamics.
The X-29 was built by Grumman for NASA and featured a radically unconventional design - forward-swept wings and canards. It was flown at NASA Ames-Dryden from 1984 to 1992 to investigate advanced aeronautical technologies. The wings, mounted behind the fuselage, and forward canards enhanced maneuverability and performance at high angles of attack. The program yielded an extensive engineering database for future aircraft design, with the X-29 completing 422 research missions. The X-29 was also built using advanced composites, variable camber wing surfaces, and a computerized fly-by-wire system to manage its inherent instability. Phase 1 focused on demonstrating the benefits of the forward-swept wing design, while Phase 2 explored high-angle-of-attack capabilities, revealing superior control characteristics. In 1992, the X-29 was modified for vortex flow control studies, successfully demonstrating enhanced control at high angles of attack. Overall, the X-29 significantly contributed to the understanding of flight dynamics and the development of new materials used in aviation construction today.
Anywhere & Anytime: A Closer Look At US DARPA's ANCILLARY UAV X-Planes
In sci-fi pop culture, you have "The X Files." In the real world, you have the X-planes, courtesy of DARPA.
Photo: Wikimedia Commons 4 X-37B: High endurance unmanned spaceplane.
The BoeingX-37, also known as the Orbital Test Vehicle (OTV), is a reusable robotic spacecraft operated by the US Air Force and the Space Force, designed for experimental missions to showcase reusable space technologies. Initially developed by NASA in 1999, it is capable of autonomous landings, a feature it shares with the Space Shuttle and the Soviet Buran. The X-37 is a 120-percent scaled version of the X-40 and has successfully completed several orbital missions since its first launch in 2010, with the latest, OTV-7, occurring in December 2023. Over te course of its missions, the X-37 has spent a total of 3,774 days in space. All while testing advanced technologies like experimental avionics and propulsion systems. Most of its missions are classified, but in general, the aim is to evaluate equipment for future military and civilian space operations. However, there is speculation about its use as a reconnaissance platform - that remains unconfirmed.
The X-37 B's on-orbit duration will vary based on flight requirements, but it can perform flights lasting up to 270 days.
Close 5 X-47B: First unmanned aircraft to conduct carrier-based takeoffs and landings.
The X-47B is an unmanned combat air system (UCAS) developed by Northrop Grumman for the U.S. Navy, specifically designed for carrier operations. The UCAS program aimed to demonstrate the deployment of fighter-sized, unmanned aircraft from aircraft carriers to fly alongside manned strike fighters of the Naval Aviation community (much like the USAF program, the Collaborative Combat Aircraft). The X-47B features a wingspan of 62.1 feet, a payload capacity of 4,500 pounds, and advanced navigation systems. It is powered by a Pratt & Whitney F100-PW-220U engine, achieving high subsonic speeds and a range of approximately 2,100 nautical miles. Both X-47B aircraft have undergone extensive testing, most notably deck handling trials and launch/recovery operations aboard the USS Harry S. Truman.
"I'm a believer that this is only the beginning," said Don Blottenberger, deputy program manager for the Navy UCAS Program Office (PMA-268). "We're taking UCAS-D into next year with what we learned aboard [USS] Truman. We are planning to get it back on a carrier to complete catapult launches, arrested landings and aerial refueling tests. There is a lot ahead for our program and a lot of hard work behind us. I look at Truman as the beginning of future unmanned integration with the fleet."
Its first autonomous aerial refueling took place in April 2015 with an Omega Air KC-707 tanker. The aircraft was developed under the UCAS-D program at an estimated cost of $813 million, with its initial test flight in July 2012 and integration with manned naval aircraft in August 2014. The Navy deemed the project a very strong success at conclusion and the successor to program is eagerly awaited to debut.
"We proved that the X-47B air system is mature and can perform flawlessly in the most hostile electromagnetic environment on Earth -- a Nimitz-class Navy aircraft carrier," said Mike Mackey, UCAS-D program director for Northrop Grumman Aerospace Systems.
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