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The Monster Jet Engined Air Crane XH-17 Wrote Aviation History Exactly 70 Years Ago

Seventy years ago to the day, one of the biggest flying machines ever to take to the skies made its inaugural flight. The XH-17 experimental helicopter, built by Howard Hughes’s company, still holds the record for the largest-spanning rotor system to take off.
The XH-17 had a rotor blade span of 130 feet 16 photos
Photo: www.smartage.pl
The XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feetThe XH-17 had a rotor blade span of 130 feet
Initially, the helicopter wasn’t a helicopter at all, but a simple – read “non-flying” – test bench for tip-jet rotors. Drastically simplified, this concept means a helicopter with jet burners mounted inside the propeller blades at the far ends. This design would allow – in theory – for extensive cargo lifting capabilities.

You might have guessed that the client for such a fantastic machine was none other the Uncles Sam himself. Or, more accurately, the US Air Force wanted an air crane with outstanding capabilities: lifting and transporting an external payload of 8x8x20 feet (2.4x2.4x6.10 m) weighing up to 10,000 lbs. (4,536 kg) at a top speed of 56 knots (65 mph, 105 kph).

Moreover, the heavy hauler needed to hover at an altitude of 3,000 feet (915 m), have a tactical range of 87 nautical miles (100 miles / 160 km), and have 30 minutes of autonomy. The military wanted the new aircraft to move several types of payloads – from radar trucks to troops, supplies, ammo, or equipment – to and from areas where even a conventional helicopter would not be able to land. And finally, the flying lifter had to be easy to assemble and dismantle to be transported with relative ease using standard military air, land, and sea equipment.

Such unseen or unheard braveries could not have passed unnoticed by Howard Hughes, the eccentric aviator and billionaire, so in 1949 he got the contract to build the experimental helicopter. A scaffolding-like landing gear – duly borrowed from two airplanes, Douglas C-54 and a North American B-25 – provided the frame which would accommodate the cargo.

The XH\-17 had a rotor blade span of 130 feet
Photo: www.smartage.pl
Since crew comfort wasn’t a priority of the project, a Waco CG-15 military glider cockpit was deemed suitable for the job. However, the fuel came from the other end of the avionics spectrum: a 635-gallon (2,404-liter) B-29 Superfortress tank was fitted to the XH-17. (If you need a scale of things, know this: “Enola Gay” had the same fuel cell when it flew over Hiroshima on August 6, 1945).

The most critical aspect of this heli-monster was, undoubtedly, its engine and rotor assembly. Twin General Electric modified J35 turbojets turned the 130-feet-long (40 meters!) dual-blade propeller. The burners would also send bleed air to the rotor hub from the compressors. This air jet traveled through the hollowed-out blades and fed the fuel’s combustion at the tips.

The jet engine duo would thrust 3,480 hp at the nominal rotor RPM of 88 (half of the typical helicopters of the day), but it was enough to meet the requirements of the Air Force. Work on the XH-17 began in 1949, but some financial difficulties of Hughes’ associate postponed the project for two years. Finally, in 1952, on October 23, the massive Frankensteinian aircraft was ready (you can admire it in the gallery).

With the newly licensed tail number 50-1842, the XH-17 made its maiden flight with pilot Gale Moore at the stick. The event occurred in Culver City, California, but lasted for a bare minute because of overwhelming directional control forces. Hughes engineers ran into more challenges while trying to fix the initial mishaps, and the project never made it past the prototype stage.

The XH\-17 had a rotor blade span of 130 feet
Photo: www.smartage.pl
However, in 1953, it took off again and proved its worth (watch it in the videos). At that time, it was the heaviest rotor-flown aircraft in the world, with a combined weight of over 50,000 lbs (23 tons). But there was a fatal drawback: fuel consumption was devastatingly exceeding all estimates, and the XH-17 couldn’t fly for more than 26 nautical miles (30 miles / 48 km).

It was far less than what the Air Force required, and no technological solution managed to overcome this issue. So, in December 1955, the project was scrapped, but it did serve an essential purpose: it demonstrated that an airlift of enormous proportions was possible and practical.

At the time of its construction, the XH-17 had quite impressive specs: 53 feet long (16 m), 30 feet tall (9.2 m), and an empty weight of 28,562 lb (13 tons). Three crew (pilot, mechanic, and in-flight engineer) operated the massive flying machine.

Although never tested, the XH-17’s calculated performance was impressive: a top speed of 78 knots (90 mph, 140 kph) at 8,000 ft (2,438 m). Cruise speed was a steady 74 knots - 85 mph (137 kph), and it could climb to 13,100 ft (4,000 m) at a rate 1,650 ft/min (8.4 m/s). While it never passed the test stage, the XH-17 remains one of the most illustrious aircraft ever to honor the flying forces of the world.


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About the author: Razvan Calin
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After nearly two decades in news television, Răzvan turned to a different medium. He’s been a field journalist, a TV producer, and a seafarer but found that he feels right at home among petrolheads.
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