Directory of U.S. Military Rockets and Missiles|
Appendix 4: Undesignated Vehicles
|Liberty Eagle (Bug)|
|Copyright © 2005 Andreas Parsch|
Other than the U.S. Navy, which became interested in using unmanned aeroplanes as "aerial torpedoes" as early as 1915 (see Sperry "Flying Bomb"), the U.S. Army was more reluctant to enter this field. However, this changed after an Army Major General watched a demonstration of a Curtiss N-9 flying several miles under automatic control in November 1917. Inventor Charles F. Kettering, member of a board which had been tasked with evaluating the possibilities of the "aerial torpedo" concept, argued in favour of building and testing a flying bomb design. With the help of others, Kettering designed such a machine, which was to be built by the Dayton Wright company. In January 1918, the Army ordered 25 examples of the aircraft. It was officially named the Liberty Eagle, but was generally referred to as the Kettering "Bug". The performance goal was to carry a 90 kg (200 lb) high-explosive payload over a distance of 80 km (50 miles).
|Photo: U.S. Air Force Museum|
|Liberty Eagle ("Bug")|
The Kettering Bug was a small biplane of decidedly cheap construction. It used a wooden framework, which was covered with pasteboard on the fuselage and tail surfaces, and with doped paper and muslin on the wings. The wings had 10° of dihedral, which was intended to improve stability on take-off. Flight distance was measured by counting air-impeller revolutions, and when the preset distance was reached, the engine was cut, the wings detached, and the Bug fell to the ground. For testing purposes, a slightly larger manned version of the aircraft was flown a few times, beginning in July 1918. The unmanned Bug had no undercarriage, and was launched on a four-wheel dolly running on a track. The first flight attempt on 2 October failed, but a second try two days later was more successful. The Bug remained in the air for about 45 minutes, but did fly in large circles instead of the intended straight line. The flight was impressive enough to secure an order for 75 additional Bugs.
|Photo: Greg Goebel|
|Liberty Eagle ("Bug")|
After the end of the war, the Army continued the experiments with the Kettering Bug, but the overall results were disappointing and the program was terminated in late 1919. Out of a total of 24 attempts at unmanned flights, only 7 could be considered at least partially successful. In the end, these early flying bombs failed because of the limited reliability of key components (engine and automatic pilot) as well as the incomplete knowlegde of aerodynamics at that time. The Army nevertheless continued experimenting with unmanned flight during the 1920s, using manned aircraft fitted with improved gyrostabilizers and radio-control systems.
Note: Data given by several sources show slight variations. Figures given below may therefore be inaccurate!
Data for Liberty Eagle (Kettering "Bug"):
|Length||3.8 m (12 ft 6 in)|
|Wingspan||4.6 m (15 ft)|
|Weight||240 kg (530 lb)|
|Speed||185 km/h (115 mph)|
|Ceiling||3650 m (12000 ft)|
|Range||> 100 km (60 miles)|
|Propulsion||Wills/DePalma 4-cyl. piston engine; 27 kW (37 hp)|
|Payload||80 kg (180 lb) high-explosive|
 Kenneth P.Werrell: "The Evolution of the Cruise Missile", Air University Press, 1985
 Laurence R. Newcome: "Unmanned Aviation: A Brief History of Unmanned Aerial Vehicles", AIAA, 2004
 Frederick I. Ordway III, Ronald C. Wakeford: "International Missile and Spacecraft Guide", McGraw-Hill, 1960
 Bill Gunston: "The Illustrated Encyclopedia of Rockets and Missiles", Salamander Books Ltd, 1979
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