Τετάρτη, 15 Ιουνίου 2016

Made from parts from B-25s, B-29s & a Waco glider, we give you the ‘Flying Crane’




Great image here for the scale of the 'flying crane'. source
Great image here for the scale of the ‘flying crane’. source
OK, it looked ugly and strange but it worked – kind of. Made from parts from various WWII warbirds the Hughes XH-17 “Flying Crane”  was by far ,the most impressive of all rotor-craft in the early 1950s was a strange monster designated XH-17. This was planned and taken through the design process by Kellett, but hardware trials were transferred to Hughes Aircraft at Culver City. Already the aircraft firm of billionaire Howard Hughes had a reputation for being quite undeterred by the most formidable development problems, and certainly the XH-17 made sense on paper. In any case, it was part-funded by the USAF. It was a flying crane, the specialized category pioneered by the German Fa 284 and intended to lift cargo weighing up to 27,000 lb more than ten times as much as any other rotorcraft of its day. To do so it had a radically new form of lift power.



Howard Hughes (second from left) standing under the blade of the XH-17, Flying Crane with L-R: Rea Hopper, Director of the Aeronautical Division, Hughes Aircraft Company; Hughes; Clyde Jones, Director of Engineering, Hughes Tool Company Aeronautical Division; Warren Reed, Assistant; Colonel Carl E. Jackson, Air Research and Development Headquarters; Gale. J. Moore, Pilot; Chal Bowen?, Flight Engineer/Co-Pilot; unidentified pilot. source
Howard Hughes (second from left) standing under the blade of the XH-17, Flying Crane with L-R: Rea Hopper, Director of the Aeronautical Division, Hughes Aircraft Company; Hughes; Clyde Jones, Director of Engineering, Hughes Tool Company Aeronautical Division; Warren Reed, Assistant; Colonel Carl E. Jackson, Air Research and Development Headquarters; Gale. J. Moore, Pilot; Chal Bowen?, Flight Engineer/Co-Pilot; unidentified pilot. source

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The prototype was finished in 1949, ahead of schedule and one of the reasons being that it was made from parts poached from WWII warbirds.  The XH-17 was a heavy-lift rotorcraft that was designed to lift loads in excess of 15 metric tons.
To speed construction, parts of the XH-17 were scavenged from other aircraft. The front wheels came from a B-25 Mitchell and the rear wheels from a C-54 Skymaster. The fuel tank was a bomb bay-mounted unit from a B-29 Superfortress. The cockpit was from a Waco CG-15and the tail rotor from a Sikorsky H-19 was used for yaw control.
In the late 1940s, Hughes developed an interest in helicopters. In August 1947, helicopter manufacturer Kellett sold his design for the giant XH-17 Sky Crane to Hughes, who commissioned the development of the XH-17 Flying Crane research vehicle. In 1948, the XH-17 began to take shape. The giant helicopter was tested in Culver City, California over a three-year period beginning in 1952. The XH-17 flew in 1953 at a gross weight in excess of 50,000 pounds (23,000 kg). It still holds the record for flying with the world’s largest rotor system. Only one unit was built, since the aircraft was too cumbersome and inefficient to warrant further development.


Engines: two GE J35 turbojets Weight fully loaded: 52,000 lb Cruising speed: 60 mph Range: 40 miles Number of seats: 2. source
Engines: two GE J35 turbojets
Weight fully loaded: 52,000 lb
Cruising speed: 60 mph
Range: 40 miles
Number of seats: 2. source
The propulsion system was unusual. Two General Electric J35 turbojet engines were used, sending bleed air up through the rotor hub. The blades were hollow, and the hot compressed air traveled through the blades to tip jets where fuel was injected. In flight, the rotors spun at a sedate 88 rpm. Since the rotor was driven at the tips rather than the hub, little torque compensation was required.

The XH-17 employed an unusual gas-turbine and rotor-tip combustion combination to provide power to spin the gigantic rotors. sourceThe XH-17 employed an unusual gas-turbine and rotor-tip combustion combination to provide power to spin the gigantic rotors.
Thus, the XH-17 had a very small tail rotor compared to its main rotor. This drive system was inefficient, limiting the test aircraft to a range of only 40 miles. Finally, having received the Air Force serial 50-1842, the XH-17 was first flown by Gale Moore at Culver City on 23 October, 1952. That flight, however, had to be cut short after the XH-17 had been airborne for barely a minute as directional control forces were excessive. While correction of this deficiency could be made quickly, difficulties uncovered later in the trials required more time. In particular, high vibratory stresses in the main rotor blades were difficult to correct and the XH-17 was repeatedly grounded while modifications were incorporated. The off and on test programme ended when the rotor blades reached their design life in December 1955 writes aviastar.org


Hughes experimental helicopters XH-17 at the front XH-28 mock up at the rear. source
Hughes experimental helicopters XH-17 at the front XH-28 mock up at the rear. source
By the end of the test program the XH-17 had proved its concept, that it could fly, and that it could carry a considerable payload – exceeding the original requirement. However it fell short, well short, of the Air Force’s range requirement. Mainly due to its appalling fuel consumption, and there was little which could be done to improve it.
In the end it became a bit of an engineering cul-de-sac. One derivative, the XH-28, an even larger version, was proposed. But it never got further than a wooden mock-up. The sole XH-17 prototype was eventually scrapped, and sadly nothing remains of this unusual giant except for photos and some video footage.

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