The American Helicopter XH-26 Jet Jeep (known as the XA-8 by its manufacturer) was an experimental

tip jet A tip jet is a jet nozzle at the tip of some helicopter rotor blades, used to spin the rotor, much like a Catherine wheel firework. Tip jets replace the normal shaft drive and have the advantage of placing no torque on the airframe, thus not re ...

helicopter A helicopter is a type of rotorcraft in which lift and thrust are supplied by horizontally spinning rotors. This allows the helicopter to take off and land vertically, to hover, and to fly forward, backward and laterally. These attributes ...

developed in 1951 by the American Helicopter Company to meet a United States Army and Air Force (USAF) request for a collapsible and air-droppable observation helicopter.

Design and development

The design of the original Model XA-8 single-seat lightweight helicopter began in 1951 under the sponsorship of the US Army Transportation Corps and the USAF. The Army's specification in 1950 called for a lightweight, one-man unarmed helicopter that was collapsible, capable of aerial delivery to troops in rugged terrain, and assembled quickly with simple tools. The helicopter was to be used for both light observation and as an air-droppable rescue vehicle for downed aircrews. After a review of all proposals American Helicopter was awarded the development contract in June 1951, based on its XA-8 design proposal. The first of five prototype XH-26s flew in January 1952. The XH-26 was constructed of

aluminum Aluminium (aluminum in American and Canadian English) is a chemical element with the symbol Al and atomic number 13. Aluminium has a density lower than those of other common metals, at approximately one third that of steel. It has ...

, except for the aft fuselage, which was laminated fiberglass, and possessed a well-glazed, pyramidal-shaped cockpit. When collapsed, its container fit on a trailer that could be towed by a military Jeep. If stripped for air drop, the Jet Jeep weighed less than . It could be assembled by two men in 20 minutes. The XH-26 did not use any gears, or an internal engine like other helicopters. Rather, the Jet Jeep was powered by two XPJ49

pulse jet engine 300px, Diagram of a pulsejet A pulsejet engine (or pulse jet) is a type of jet engine in which combustion occurs in pulses. A pulsejet engine can be made with few or no moving parts, and is capable of running statically (i.e. it does not need ...

s mounted on the end of each rotor blade tip as

s. Also designed by American Helicopter, each pulse jet weighed and produced of thrust, and were started with an internal compressed air system. Since the engines did not have to be warmed up, the XH-26 could take off in 30 seconds. The pulse jets produced no torque, and the tiny, belt-driven tail rotor was used only to improve directional control. The only mechanical item that had to be replaced after so many hours of flight was the intake air vanes, which were small and inexpensive and could be replaced with a small tool in minutes. American Helicopter chose the name "Jet Jeep", because the XH-26 could be used like a Jeep, but in the air. It could be transported by a Jeep, and even used the same fuel. The XH-26 could be dropped by air and assembled and be ready for flight in 20 minutes.

Operational history

Both the Army and USAF evaluated the five prototype Jet Jeeps. They proved to be rugged and durable vehicles with a top speed of and a ceiling of . Unfortunately, the pulse jets produced an unacceptable amount of noise and the drag of the engines in the event of power loss would prevent safe landings by

autorotation Autorotation is a state of flight in which the main rotor system of a helicopter or other rotary-wing aircraft turns by the action of air moving up through the rotor, as with an autogyro, rather than engine power driving the rotor. Bensen, Ig ...

. For these two reasons the Army found the pulse jet helicopters unsuitable as it had those with ramjets. Finally, cost considerations forced the cancellation of the program. The replacement of the XH-26's pulse jets with

ramjet A ramjet, or athodyd (aero thermodynamic duct), is a form of airbreathing jet engine that uses the forward motion of the engine to produce thrust. Since it produces no thrust when stationary (no ram air) ramjet-powered vehicles require an as ...

s was suggested but never undertaken; however, the

Hiller YH-32 Hornet The Hiller YH-32 Hornet (company designation HJ-1) was an American ultralight helicopter built by Hiller Aircraft in the early 1950s. It was a small and unique design because it was powered by two Hiller 8RJ2B ramjet engines mounted on the roto ...

helicopter was built using blade tip ramjets.

Operators

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United States Air Force The United States Air Force (USAF) is the air service branch of the United States Armed Forces, and is one of the eight uniformed services of the United States. Originally created on 1 August 1907, as a part of the United States Army Signal ...

United States Army The United States Army (USA) is the land service branch of the United States Armed Forces. It is one of the eight U.S. uniformed services, and is designated as the Army of the United States in the U.S. Constitution.Article II, section 2, cla ...

Surviving aircraft

* 50-1840 – XH-26 in storage at the

United States Army Aviation Museum The United States Army Aviation Museum is an aviation museum located on Fort Rucker near Daleville, Alabama. It has the largest collection of helicopters held by a museum in the world.Phillips 1992, p. 37.Purner 2004, p. 204. The museum feature ...

Ozark, Alabama Ozark is a city in and the county seat of Dale County, Alabama. As of the 2010 census, the population of the city was 14,907. Ozark is the principal city of the Ozark Micropolitan Statistical Area, as well as a part of the Dothan-Ozark Combi ...

* 50-1841 – XH-26 on static display at the

National Museum of the United States Air Force The National Museum of the United States Air Force (formerly the United States Air Force Museum) is the official museum of the United States Air Force located at Wright-Patterson Air Force Base, northeast of Dayton, Ohio. The NMUSAF is the ...

Dayton, Ohio Dayton () is the sixth-largest city in the U.S. state of Ohio and the county seat of Montgomery County. A small part of the city extends into Greene County. The 2020 U.S. census estimate put the city population at 137,644, while Greater Day ...

Specifications (XH-26)

References