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X-35 JSF

Lockheed Martin Aeronautics · Concept demonstrator aircraft (CDA) · USA · Modern (1992–2009)

X-35 JSF — Concept demonstrator aircraft (CDA)
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The Lockheed Martin X-35 was the American technology demonstrator that won the Joint Strike Fighter competition — Lockheed Martin Skunk Works's prototype that became the F-35 Lightning II. Lockheed Martin developed the X-35 in 1996-2000 under the JSF Concept Demonstration Phase (CDP); first flight (X-35A) 24 October 2000. Two prototypes were built: X-35A (CTOL) + X-35B (STOVL). The JSF competition selected the X-35 over the Boeing X-32 on 26 October 2001 — the largest defence contract in US history (~$200 billion at award, $1.7 trillion lifetime).

The X-35 used 1 × Pratt & Whitney F119 afterburning turbofan (35,000 lbf, the F-22 Raptor's engine — modified for the JSF). Maximum speed Mach 1.6, length 15.4 m, wingspan 10.7 m. The X-35B STOVL variant used a unique lift-fan + main-engine + roll-post arrangement — the lift fan (driven by a shaft from the main engine) provides vertical thrust at the nose, while the main engine's vectoring nozzle provides vertical thrust at the tail + the two wing-mounted roll posts provide stability — a more-efficient STOVL system than the Boeing X-32's competing single-jet design. The lift-fan + vectoring-nozzle concept made the X-35B the first STOVL aircraft to demonstrate sustained vertical hover at full takeoff weight.

X-35 flight-testing 2000-2001 demonstrated three key milestones: (1) supersonic flight + STOVL transitions in the same airframe (the 'mission X' demonstration), (2) zero-rotation vertical landings, + (3) sea-level supersonic cruise. The Boeing X-32 — the competing prototype — had far larger thrust margin issues during STOVL testing + the X-35's lift-fan design was judged technically superior + lower-risk. The JSF win launched the F-35 Lightning II development programme; production F-35s incorporate the X-35's lift-fan, vectoring-nozzle, + general airframe configuration. Both X-35 prototypes are preserved — X-35A at the National Air and Space Museum (Udvar-Hazy Center) + X-35B at the Patuxent River Naval Air Museum.

For Kids — a shorter, friendlier version

The Lockheed Martin X-35 was the test plane that became the famous F-35 Lightning II fighter. The X-35 first flew in October 2000. Only 2 X-35s were built: the X-35A for normal takeoff, and the X-35B for vertical takeoff. In October 2001, Lockheed won the Joint Strike Fighter contest against the Boeing X-32.

The X-35 is 51 feet long with a 35-foot wingspan, longer than a school bus. One Pratt and Whitney F119 jet engine makes 35,000 pounds of thrust, the same engine used on the F-22 Raptor. Top speed is Mach 2, faster than a rifle bullet. The X-35B can take off vertically like a helicopter.

The X-35B has a unique vertical lift system. A lift fan behind the cockpit makes downward thrust at the front. A swiveling nozzle at the back makes downward thrust at the tail. Two small roll posts under the wings keep the plane stable in hover. This was the first plane to demonstrate vertical hover at full takeoff weight.

The Joint Strike Fighter contest was worth $200 billion at first, growing to over a trillion dollars over the lifetime of the F-35. That makes the JSF contract the largest defense deal in American history. The X-35 paved the way for the F-35 Lightning II, now serving with American forces and 15 or more allies.

Fun Facts

  • The X-35 was the test plane that became the F-35 Lightning II fighter.
  • Only 2 X-35s were built, in 2000.
  • The X-35 is 51 feet long, longer than a school bus.
  • Top speed is Mach 2, faster than a rifle bullet.
  • The X-35B can take off vertically like a helicopter.
  • Lockheed beat Boeing's X-32 in October 2001 for the JSF contest.
  • The JSF program is the largest defense contract in American history.

Kids’ Questions

How does the lift fan work?

The X-35B has a special fan behind the cockpit, driven by a shaft from the main engine. When the pilot wants to hover, the shaft spins the fan, which pushes air down to lift the front of the plane. The rear engine nozzle swivels down to lift the tail. Two roll posts under the wings keep balance. This system is more efficient than the Boeing X-32's single-jet approach.

Why win the JSF contest?

The Air Force, Navy, and Marines wanted one fighter to replace many older planes. The Joint Strike Fighter would be made in three versions: normal takeoff for Air Force, vertical takeoff for Marines, and carrier-landing for Navy. The X-35 won because its lift-fan vertical takeoff worked better than Boeing's X-32 design. The X-35 also had a smoother shape and better stealth.

How is the F-35 different?

The F-35 is the production version of the X-35, with many changes for combat use. The F-35 has stealth coatings, weapons bays, a real radar, helmet-mounted display, and many other systems the X-35 lacked. The F-35 is also slightly bigger and heavier than the X-35. Three versions exist: F-35A normal, F-35B vertical takeoff, F-35C carrier.

Variants

X-35A (CTOL)
Conventional takeoff + landing prototype. First flight October 2000.
X-35B (STOVL)
Short takeoff + vertical landing prototype. Lift-fan demonstration.
X-35C (CV)
Carrier-variant prototype. Larger wing for naval operations.

Notable Operators

Lockheed Martin / NASA / USAF / USN (2000-2001)
JSF Concept Demonstration. Selected for F-35 production October 2001.

Frequently Asked Questions

Why did the X-35 win over the Boeing X-32?

Three reasons. (1) Better STOVL design — the X-35B's shaft-driven lift fan + vectoring nozzle was more thrust-efficient + thermally manageable than the X-32's single-jet-with-vectoring approach (the X-32 had ground-thermal issues from its single nozzle + struggled to reach full vertical takeoff weight). (2) Cleaner airframe — the X-35's chin-mounted main inlet allowed a cleaner wing-fuselage blend than the X-32's distinctive shovel-shaped under-nose intake, giving better stealth signature + drag characteristics. (3) Programme management — Lockheed Martin's JSF programme team was judged more cohesive + more credible than Boeing's, which had to integrate the X-32 development team across multiple Boeing sites. The October 2001 JSF down-select was based on technical merit + programme execution risk; Lockheed Martin scored higher on both.

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