In 1961, the U.S. Army awarded Lockheed a contract for a radical VTOL surveillance aircraft that didn't tilt rotors, didn't tilt wings, didn't deflect thrust, and didn't even use lift fans. The Lockheed XV-4 Hummingbird hovered using a principle that almost no aircraft since has tried at scale: jet ejector augmentation. And it worked — until it didn't.

The concept, championed by Lockheed-Georgia engineer John Wimpress, was elegant. Two Pratt & Whitney JT12A-3 turbojets, mounted on the fuselage sides, normally provided forward thrust like any conventional jet. For hover, valves redirected their exhaust into a network of 20 mixing nozzles buried inside the fuselage. These nozzles fired downward into ejector ducts running the length of the aircraft's belly. The high-velocity jet exhaust entrained ambient air at roughly a 3:1 ratio, theoretically multiplying thrust by ~1.4× — enough to lift the 7,200-lb aircraft using engines that produced only 3,300 lbf each.

Prototype XV-4A first hovered on 7 July 1962 at Dobbins AFB. Test pilot Jack Gordon transitioned from hover to forward flight on 20 November 1963 — a milestone. But the ejector system was marginal. Real-world augmentation came in closer to 1.2× than the predicted 1.4×, leaving almost no thrust margin. On 10 June 1964, the XV-4A crashed during transition testing, killing pilot John Reichert. The cause was traced to control problems during the handoff between hover and wing-borne flight.

The Army wasn't ready to give up. Lockheed rebuilt the second airframe as the XV-4B, abandoning the ejector concept entirely. It instead used six J85 engines — four dedicated lift engines mounted vertically in the fuselage, plus two cruise engines. It was a different aircraft pretending to be the same one. The XV-4B flew in 1968 and crashed on 14 March 1969. Pilot ejected safely. Program canceled.

Why it died: The ejector physics were right, but 1962 metallurgy and CFD couldn't optimize the mixing geometry. The internal ducting added weight and consumed fuselage volume that should have held fuel and sensors. The control system used analog hydromechanics with no authority to manage the violent thrust transients during transition. And the Army's competing VTOL programs (XV-5 Vertifan, X-22, XC-142) saturated the budget.

Why it's viable now: Ejector augmentation has quietly become a hot topic again. Aurora Flight Sciences' XV-24A LightningStrike (DARPA, 2016–2018) used 24 ducted fans driven by a turbogenerator — a different solution to the same problem. But the pure ejector concept benefits enormously from modern tools:

• Additive manufacturing can print the complex internal nozzle/diffuser geometry as a single titanium part — Lockheed welded theirs from sheet metal with brutal weight penalties.
• CFD on GPU clusters can optimize the mixing-section aerodynamics to push augmentation ratios past 1.6×, validated experimentally by Georgia Tech and ONERA in the 2010s.
• Fly-by-wire with model-predictive control eliminates the transition-instability that killed Reichert. The XV-4's control problem is trivial for a modern flight computer.
• High-bypass cores (think F135 lift fan, but driven by ejector entrainment instead of a shaft) could combine the two approaches.

The Hummingbird's real legacy: it proved you could hover a fixed-wing fighter with no tilting parts, no exposed fans, and no jet blast scouring the runway. That's still a hugely valuable property — and we now have the manufacturing and control technology to actually make it work.