By Nathan Pfau, Army Flier Staff WriterJanuary 12, 2018
FORT RUCKER, Ala. -- Experimentation is an important aspect of creating revolutionary advances in Army Aviation, but sometimes the only good result is to gain the knowledge that an idea doesn't work.
That's the legacy of the American Helicopter Company's XH-26 Jet Jeep, which was an experimental aircraft designed to meet the needs of light observation, according to Bob Mitchell, U.S. Army Aviation Museum curator.
"The Jet Jeep was one of those ideas that had to be tried if for no other reason than to make sure it wasn't a good idea," said the curator, adding that the U.S. Army Aviation Museum has three of the experimental aircraft in storage.
The notable stand-out feature of the Jet Jeep, aside from its size and weight -- weighing less than 300 pounds -- was the way the aircraft was powered, which was done by utilizing two 6 and 3/4-inch pulse jet engines that were mounted on the end of each of the rotor blades.
"In the early 1950s, the Army and the Air Force were looking at something that could be used for light observation, and could also be air dropped into remote regions," said Mitchell. "They started looking at the concept of a pulse jet rotor system because that eliminated the need for an engine and a transmission, which reduced the weight considerably."
Also, since the aircraft was powered by pulse jets rather than an engine, it eliminated the need for a tail rotor system for anti-torque capability. The experimental aircraft did, however, still utilize a tail rotor to provide the pilot with the ability to turn the aircraft left or right.
The Jet Jeep was designed in two different models -- a single-seat aircraft and a two-man version -- and although the aircraft was able to be constructed to be extremely light weight, the disadvantages of the aircraft couldn't be overlooked as testing began.
Because of the pulse jets, the aircraft sounded exactly as jet engines sound -- extremely loud, said the museum curator. Additionally, since the rotor blades were using jet propulsion, the visible signature at night made it impossible for the aircraft to go undetected.
"They (first) evaluated the single-man version and determined that it wasn't feasible for a couple reasons -- it was extremely loud and at night time it looked like a UFO," said the museum curator. "You couldn't do any sneaking and peeking with that thing -- the whole world knew you were there."
After these initial findings, the project was scrapped and deemed impracticable.
In addition to having little-to-no feasibility, the aircraft was terribly unsafe, said Mitchell. The fuel tank in the aircraft was located under the pilots, who would find themselves sitting on the tank, and the fuel lines ran directly behind the pilots up into the rotor blades, which were exposed on the exterior of the aircraft.
"In the event of a crash sequence, you can see there is very little attenuation in anything on this that is going to help cushion the impact and keep the pilot from sustaining serious injury," he said. "It was a very rigid design and it doesn't afford itself with any real crash survivability -- you'd have to be really desperate to fly this thing."
Another drawback was in the event that one of these pulse jets failed, the aircraft had very limited autorotation ability, which Mitchell said means that it pretty much doesn't have any, so the odds for survival are almost nil.
Additionally, the range of the aircraft was abysmal -- it was only able to sustain flight for about 20 minutes. "It just gobbled up fuel," said the curator.
Despite all the hang ups, the Army revisited the two-man version again because they were still looking for something that could be used for light observation, said Mitchell.
"Back in the early 50s, we're looking at this kind of technology here, and the engines and the transmissions weighed so much that you had very little payload to operate with," he said. "So, they were trying to come up with some other concept where you could eliminate that excessive weight and still do the mission."
After further testing, the Army found that the concept was still unworkable and scrapped the project altogether.
Although the Jet Jeep was a failure, Mitchell said that experimentation, even if the end result wasn't practical, was a necessary part of research and development.
"I like to say that there is nothing new under the sun, only ideas that have been tried and put back on the shelf," he said. "You have to experiment with different concepts and different ideas to expand and to promote new technologies.
"Sometimes during that exploration and experimentation process, you come across a design that absolutely does not work," he continued. "But in the discovery of that, you'll find that maybe the application that you're using can be applied to something else."
If nothing else, the Jet Jeep provides a glimpse into the world of Aviation experimentation that molded Army Aviation into the fighting force it is today, he added.