Lockheed XV-4 Hummingbird

Vertical take-off lift was obtained by exhausting the engine flow downward through multiple nozzles, augmented by a secondary flow of cold air.[1] But the performance was far below estimates with only a 1.04 thrust-to-weight ratio, and the prototype crashed on 10 June 1964, killing the pilot. The second aircraft was converted to lift jets instead, yet also crashed after several tests.

Rockwell's XFV-12 would be even less successful at producing lift by using engine exhaust to entrain cold air, in this case through flaps on the wings.

None of the early American V/STOL designs would result in a production aircraft. The British Hawker Siddeley Harrier used vectoring nozzles, while the Russian Yakovlev Yak-38 Forger attack jet used lift jets in conjunction with rotating rear nozzles. The Lockheed F-35 Lightning II would later employ a shaft-driven lift fan located in the fuselage.

On 4 June 1968, the second prototype of the XV-4B Hummingbird rolled out. Just like the XV-4A, the XV-4B used vertical takeoff and landing systems (VTOL) as well as conventional flight methods. Upon takeoff the aircraft weighed 5706 kg. The wingspan was 7.8m, and it had a top speed of 883 km/h with a cruising speed of 630 km/h (.68 mach). It had a range of 965 km and was able to climb at a rate of 3660m/minute. The XV-4B was 10.36m long. The heaviest part of the plane was the propulsion system, which weighed in at 1466 kg. The initial service life of the aircraft was intended to be 500 hours, but the aircraft was destroyed in 1969 during testing, long before the designated goal. The fuel tanks were located internally, with boost pumps and jet ejectors, along with the associated valves. The tanks were located in the front of the fuselage and could hold a total of 740 gallons of aviation turbine fuel. Because of the forward position of the tanks, fuel had to be consumed evenly. An unbalance in the fuel tanks of over 100 gallons ran the risk of destabilizing the aircraft.

The XV-4B was significantly different than the XV-4A in its internal design. The differences were found in the wings, fuselage, landing gear, power plant installations, hydraulics and controls. XV-4B contained two reaction control valves as a failsafe for the engine. One major change was the addition of 4 turbo jet engines faced vertically on the fuselage. This provided massive amounts of vertical thrust for VTOL flight. The addition of a stability augmentation system (SAS), along with hydro-mechanical clutches and feel springs, gave the pilot a good feel on the controls and more ability to control the SAS. The rudder included a new centering spring above the feel spring to reduce friction on the rudder. The Primary Flight Control System (PFCS) was a hybrid fly-by-wire system along with conventional flight controls as a back up. No fuel was carried in the wings, even though the wings had the basic box-beam structure. It had 2° of freedom in the pitch and sideslip, whereas the rolls only had 1° of freedom.

Each engine contained a diverter valve. These valves either ducted longitudinally into the horizontal thrust nozzles of the aircraft, or inward to the lift nozzles located in the fuselage. The lift/cruise engines provided forward thrust when faced horizontally and lift when faced vertically. This was through the use of the diverter valves. All 6 tail pipes had 10° of freedom in order to direct thrust. The fuselage engines were used when initiating VTOL flight but were turned off when the aircraft was sufficiently in flight.

The XV-4B was faced with its fair share of electronic challenges, largely due to improper wiring. Otherwise the power system performed quite well, with a reduced number of electrical system components giving good reliability. One electronic stage was located at the end of the wiring sequence with the other at the opposite end in the electrohydraulic power actuators. Electrohydraulics simply replaced the hydraulically operated systems in the aircraft with purely electrical systems that do the same job. This reduced weight along with adding simplicity and reliability. It was driven by a set of two 300 amp generators powered by the engines. These fed 9 volt DC power into the main bussing and power distribution system.

Data from Lockheed Aircraft since 1913[2]

General characteristics

• Crew: 2
• Length: 32 ft 8 in (9.96 m)
  

XV-4B 32.66 ft (10 m)

• Wingspan: 25 ft 8 in (7.82 m)
  

XV-4B 25.66 ft (8 m)

• Height: 11 ft 9 in (3.58 m)
  

XV-4B 12.25 ft (4 m)

• Wing area: 104.00 sq ft (9.662 m²)
• Empty weight: 4,995 lb (2,266 kg)
  

XV-4B 7,463 ft (2,275 m)

• Gross weight: 7,200 lb (3,266 kg)
  

XV-4B 12,580 ft (3,834 m)

• Powerplant: 2 × Pratt & Whitney JT12A-3LH turbojet, 3,300 lbf (15 kN) thrust each take-off thrust[3]
• Powerplant: 6 × General Electric J85-GE-19 turbojets, 3,015 lbf (13.41 kN) thrust each XV-4B only, 4 for lift,2 for horizontal flight

Performance

• Maximum speed: 518 mph (833 km/h, 450 kn) at 10,000 ft (3,048 m)
  

XV-4B 463 mph (745 km/h)

• Cruise speed: 390 mph (628 km/h, 339 kn)
• Range: 600 mi (965 km, 521 nmi) normal
  
• VTO range: 600 mi (966 km)
• Rate of climb: 12,000 ft/min (61 m/s)
• Wing loading: 69.2 lb/sq ft (338 kg/m²)
• Thrust/weight: 1.176
  

XV-4B 1.43

Aircraft of comparable role, configuration, and era

• Hawker P.1127
• Rockwell XFV-12
• Ryan XV-5 Vertifan

Related lists

• List of military aircraft of the United States
• List of Lockheed aircraft
• List of VTOL aircraft

• X-Planes and Prototypes by Jim Winchester

Wikimedia Commons has media related to Lockheed XV-4 Hummingbird.

• VSTOL.org Wheel