Helicopters come in all sorts of weird shapes and sizes. In the early days of mass-produced helicopters in the 1940s and 1950s, engineers experimented with strange designs and unique concepts, many of which never made it past the testing phase. The most incredible helicopter to meet such a fate was the Hughes XH-17 “Flying Crane.”
Built in the early ’50s at the behest of the U.S. Air Force to move heavy equipment quickly and easily out of strategically important locations, the XH-17 was spectacular for several reasons, most having to do with its absolutely gargantuan stature. It was three stories tall, and carried a rotor diameter of 130 feet—still the largest of any helicopter, ever.
The only thing more interesting than XH-17’s size was the way in which it got into the air. Instead of a normal helicopter, which uses an engine connected to a transmission and a driveshaft to spin the rotor by applying torque at the hub, the Hughes mega-copter used a “tip jet” design to get the rotors spinning. In this setup, compressed air is funneled out the ends of the rotor tips to create thrust, causing the blades to spin.
Like many of the wacky helicopter concepts of the ’50s, the Hughes XH-17 did not meet a heroic end, despite its amazing design and record-holding rotor span. Let me tell you all about it.
Dramatic Beginnings
It was in 1946, right after World War II, when the U.S. military began seeking proposals from manufacturers to build a large helicopter designed to carry particularly heavy cargo. According to Aviastar.org, the U.S. Army Materiel Command, the agency responsible for making sure the military has all the gear it needs to be effective, wanted a copter that could externally carry a piece of cargo measuring up to 8 feet tall, 8 feet wide, and 20 feet long. It also wanted a payload capacity of 10,000 pounds, a range of 100 miles, and a minimum operational time of 30 minutes per flight. From Aviastar:
It was intended for use in transfer of ordnance, equipment, supplies, and personnel, with loads to be lowered into or lifted out of areas in which even helicopter landings were impossible. Moreover, this sky crane helicopter had to be easily dismantled for transport on standard trailer trucks.
After reviewing proposals, the military awarded Kellett Autogiro Corporation a contract to construct a prototype. The Upper Darby, Pennsylvania-based aircraft firm had been around since the 1930s, designing weird propeller-driven vehicles for the military. But this would be its most ambitious project yet.
At first, things were going well for Kellett. The firm got as far as designing and building a powertrain for the helicopter, which was originally called the XR-17. Then, the company hit financial trouble. From OldMachinePress.com:
By 27 August 1947, the XR-17 design had progressed well, and Kellett was awarded a contract to produce a test rig of the helicopter’s rotor system. Kellett went to work constructing the test rig and tried to save money wherever possible by using components of other aircraft. The company was having financial issues, and the XR-17 project had an uncertain future.
It didn’t work out. Just two years into the project, Kellett’s finances were in such dire shape that it couldn’t complete the project. In June 1948, Hughes Aircraft—the company led by none other than aviation legend Howard Hughes—purchased the incomplete project, now called the XH-17, for $250,000, according to the Smithsonian Magazine.
Today, Hughes’ move into the helicopter business is looked back upon as a success, with several designs seeing thousands of units of production, most notably the AH-64 Apache attack helicopter and the MH-6 “Little Bird,” a lightweight helicopter used for special operations. But back in 1948, he hadn’t dabbled in the world of helicopters at all. An engineer for the XH-17 project, Nick Stefano, expressed his doubts to fellow engineer Ray Prouty in a letter about Hughes’s ability to get the project completed. From the Smithsonian Magazine:
“I can remember most of us saying, ‘Do something to get this Hughes guy out of the picture!’” Stefano said. Hughes had never built helicopters or mass-produced aircraft. He was known mainly for his flying boat, the H-4 Hercules, which had made its sole flight on November 2, 1947.
“All of a sudden we have this foisted upon us and we are now in the helicopter business,” said Hughes engineer Jim Crabtree at the 1983 AHS meeting.
Despite Stefano’s doubts, the incomplete XH-17 project and all of its components were moved from Pennsylvania to Hughes’s headquarters in Culver City, California, where testing and development would continue. But it wasn’t without a bit of drama
A Rotor Setup That Sounds Like Science Fiction
With a fuselage measuring in at 53 feet, 4 inches long, an empty weight of 41,700 pounds, and an overall height of 30 feet, it’s hard to understate just how big the XH-17 was. It was also very much a parts-bin special. To save on costs, many of the XH-17’s components were borrowed from other aircraft, including the cockpit, the landing gear, and much of the powertrain. From OldMachinePress.com:
The Hughes XH-17 consisted of a cockpit from a Waco CG-15 glider attached to a custom-built tube steel frame. Its steerable front landing gear was made using the main wheels from a North American B-25 Mitchell, and its rear landing gear was made using the main wheels from a Douglas C-54 Skymaster. The XH-17’s fuel tank was originally a 636-gallon (2,408-L) extended-range bomb bay tank for a Boeing B-29 Superfortress.
The main attraction, of course, was the 130-foot two-blade rotor system—25 feet longer than the rotor found on the Russian Mil Mi-26, the helicopter with the largest rotor system to enter production. The XH-17’s setup still holds the world record for the largest rotor system to take flight, and it was incredibly complex. As mentioned previously, the rotor wasn’t spun by torque applied at the hub via a driveshaft, but by a little-used method called tip jets. Instead of being mechanically attached to the rotors, the two modified General Electric J35 gas turbine engines mounted on the fuselage acted as huge air compressors that piped pressured air through the insides of the rotor blades.
Air was bled off from the compressor section of the modified engines and was ducted through the hollow rotors. The 400°F (204°C) air was exhausted from each rotor via four pressure-jets in the tip’s trailing edge. The jet of air emanating from the rotor tips caused the rotors to turn. This propulsion system was referred to as cold-cycle pressure-jet, because the air from the engine’s compressor section was much cooler than the air from the engine’s exhaust.
Each blade, according to the Smithsonian Magazine, weighed an incredible 5,000 pounds and measured nearly six feet wide and 12 inches thick. Because there was no counterforce from the blades applying torque to the airframe, the XH-17 could get away with no tail rotor (but it still had a small one borrowed from a Sikorsky S-55 that was used for yaw control, according to ThisDayInAviation.com)
To squeeze even more power from the setup, fuel was sprayed and ignited into the pressurized air as it was exiting the rotor tips. With the jet tip ignition activated, combined power was estimated to be around 3,480 horsepower, according to Avistar. This proved to be incredibly loud, according to people on the ground:
After about three months of testing, the rotor burners were fired for the first time on 22 December 1949. This created a very a loud whop-whop-whop noise that coincided with the passing of each set of lit burners on the rotors’ tips. The noise was so loud that it could be heard eight miles (13 km) away, and the XH-17 caused numerous noise complaints to be filed against Hughes.
Despite the noise complaints, Hughes’s new helicopter division forged on and eventually felt confident enough in the design to begin real-world testing a few years later.
Leaving The Ground During The Fall Of 1952
The XH-17’s first official flight was planned for October 23, 1952. But it actually left the ground for the first time over a month earlier, on September 16. On both occasions, it was piloted by Gale Moore, a pilot for Los Angeles Airways who left his job flying Sikorsky S-51 helicopters to take on a new challenge with Hughes. This excerpt from the Smithsonian Magazine describes what that first September liftoff was like:
On September 16, 1952, he had hovered the aircraft, technically its first flight. It rose only a foot, but when Moore slowly pulled collective pitch, the machine lurched into the air, almost uncontrollably. He lowered the pitch lever, then raised it again, all without calming the erratic movements, before settling on the ground with a solid thud. Flight test data revealed the controls were much more sensitive than those of the S-51. “The flight was like riding a pogo stick in a sitting position—up, down, up, down,” Moore said.
Moore got used to the controls enough for the official October 23 demonstration, which had media, including journalists, photographers, and news cameramen present. Even Hughes himself made an appearance to see his company’s first helicopter flight in action.
“I felt very conspicuous as I stepped out of my car,” Moore recalled at an American Helicopter Society meeting in 1983, where XH-17 personnel reminisced about the project. “I hoped this wouldn’t be the day we made any big mistakes. Howard Hughes himself would be in the audience. I had to admit to a little bit of stage fright.”
When the blade-tip jet engines on the helicopter fired up, flames shot from the ends of the rotor blades. “The whoosh-whoosh of the whirring blades sounded like hundreds of artillery shells in flight,” the Los Angeles Times reported. “You could hear it seven or eight miles away,” Moore said.
Video of the event survives to this day, and shows the XH-17 rising into the air as its rotor spins at 88 rotations per minute:
The demonstration involved a vertical ascent and a nine-minute hover, before Moore flew forward, backward, and made full rotations in both directions before safely landing. Everything had gone as the company planned.
Too Big To Succeed
After that successful first test flight, Hughes continued to perform tests, including some where the helicopter actually lifted cargo into the air, until 1955. By then, pilots had reached a top speed of 70 mph and a maximum altitude of 350 feet. Its last test flight involved lifting an 8,000-pound trailer, which, according to OldMachinePress.com, pushed the helicopter’s gross weight over 50,000 pounds. Here’s a test flight video from 1953:
By December of 1955, the rotors had reached the end of their recommended operating lifespan, which was just 10 flight hours. The XH-17 was grounded and never flew again.
The short flight life of those blades, plus the booming sounds from their tips, and the helicopters’ woefully short 30-minute range meant the XH-17 would never make it out of the prototype phase. The Air Force cut funding for the project, and the only example was later scrapped.
The XH-17’s dismantling is a sad end to one of the most fascinating 1950s helicopter designs to make it to real-world testing. It’s a shame Hughes didn’t tuck the XH-17 into some hangar and leave it there for a museum to unearth a few decades later, though I sort of understand why you might not want to deal with a 40,000-pound hunk of unairworthy metal with rotors that span more than half the length of a football field. So it’s not terribly surprising that it’s gone. So long as we have the photos, video, and recountings from people like Moore, I’m happy.
Top graphic image: Wikimedia Commons
In order to fully comprehend large scale sizes, I usually put it in a “football field” frame of reference. The rotor span on this was nearly half the length of a football field. Wild!
they make a 2,500 lb lift drone with 4 blade, I am kind of surprised an 8 blade design that can do closer to 5K has not happened yet.
Hop in my chopper, it’s as big as a whale, and it’s about to set sail.
Being hellaciously loud is a well known issue for helicopters. The Fairey Rotodyne failed because of noise complaints too. I guess the chopper falls under the “Ambitious but rubbish” classification. The more conventional Sikorsky S-64 succeeded at the job and is still in limited production
100 Passengers (oof)
I really admire the optimism of that time.
Hold my beer – Spirit Airlines
Watching that thing fly is disturbing, like a big Amazonian bug that you don’t swat but rather knock out of the sky with a baseball bat. It just doesn’t look like it has any business mid-air.
Yeah. It’s hard to believe those rotors are spinning slow enough to easily see with your eyes and yet it can lift a crazy payload. 10 hr service life on the blades sure seems like a dealbreaker though. At those RPMs it means they’re good for just under 53,000 rotations. I’m guessing you don’t normally measure blade durability like that.