Le Douglas X-3 Stiletto era un aereo a reazione sperimentale statunitense del 1950 con una fusoliera snella e un lungo muso affusolato, prodotto dalla Douglas Aircraft Company. La sua missione principale era quella di studiare le caratteristiche di progettazione di un velivolo adatto a velocità supersoniche sostenute, che includeva il primo uso del titanio nei principali componenti della cellula. Douglas progettò l'X-3 con l'obiettivo di una velocità massima di circa 2.000 m.p.h, ma era, tuttavia, gravemente sottodimensionato per questo scopo e non poteva nemmeno superare Mach 1 in volo di livello. Sebbene l'aereo da ricerca sia stato una delusione, i progettisti della Lockheed hanno utilizzato i dati dei test X-3 per il Lockheed F-104 Starfighter che ha utilizzato un simile design dell'ala trapezoidale in un caccia Mach 2 di successo.
Le Douglas X-3 Stilettowas perhaps the most visually striking experimental aircraft of the 1950s. Designed to test the effects of sustained supersonic flight, it featured a slender fuselage, a long, tapered nose, and tiny, trapezoidal wings. While the X-3 failed to reach its intended design speeds due to being severely underpowered, it became an invaluable research tool for structural engineering, pioneering the use oftitaniumin aircraft construction and providing the data that made the Lockheed F-104 Starfighter possible.
Attribute
Technical Specification (Douglas X-3)
Ruolo
Experimental High-Speed Research Aircraft
Equipaggio
1 (Pilot)
First Flight
October 15, 1952
Motopropulsore
2 × Westinghouse J34-WE-17 afterburning turbojets
Thrust
3,370 lbf (15.0 kN) each / 4,850 lbf with afterburner
Velocità massima
Mach 1.21 (Reached) / Mach 2.0 (Design Goal)
Apertura alare
22 ft 8 in (6.91 m)
Lunghezza
66 ft 9 in (20.35 m)
Design Innovations and Challenges
High Fineness Ratio:The X-3 had an incredibly high “fineness ratio” (length vs. width), designed to pierce the “sound barrier” with minimal drag. Its nose was so long that the pilot sat far back from the tip, necessitating a specialized downward-ejection seat.
The First Titanium Jet:The X-3 was the first aircraft to make extensive use of titanium in its major airframe components. This was necessary to handle the “thermal thicket”—the intense heat generated by air friction at speeds above Mach 2.
Underpowered Reality:The original plan called for Westinghouse J46 engines, which failed to materialize. The substitute J34 engines were so weak that the X-3 could barely exceed Mach 1 in a level flight, usually requiring a dive to reach supersonic speeds.
Trapezoidal Wings:The wings were tiny, thin, and straight (non-swept). This design offered low drag at supersonic speeds but made takeoffs and landings extremely dangerous, with a landing speed of roughly 200 mph (322 km/h).
Inertial Coupling and Legacy
Inertial Coupling Discovery:During a test flight in 1954, pilot Joseph Walker experienced “inertial coupling”—a violent, uncontrollable roll/yaw maneuver caused by the mass distribution of the long fuselage. This data was critical in redesigning the tail surfaces of the F-100 Super Sabre.
The “Starfighter” Connection:The thin, stubby wing data from the X-3 was directly applied by Kelly Johnson at Lockheed to create theF-104 Starfighter, often called the “Missile with a Man in It.”
Tire Technology:Because of its exceptionally high takeoff and landing speeds, the X-3 forced engineers to develop entirely new high-pressure tire compounds and heat-resistant wheel assemblies.
Preservation:The sole surviving X-3 Stiletto is currently on display at theNational Museum of the United States Air Forcein Dayton, Ohio.