Rounding-up our review of tiny 'ram jet' helicopters (prompted by LOZZ's wonderful photographs from Dunsborough House in the late 50's on the previous page) we should also mention the developments across the Atlantic which were taking place at the same time if not slightly before:
The Hiller YH-32 Hornet (company designation HJ-1) was an American ultralight helicopter built by Hiller Aircraft in the early 1950's. It was powered by two Hiller 8RJ2B ramjet engines mounted on the blade tips and which weighed 13lbs each and produced an equivalent of 45 hp delivering a total of 90 hp. Versions of the HJ-1 Hornet were built for the United States Army and the United States Navy in the early 1950's.
Stanley Hiller flies a Hornet testbed in California in 1952 (Photo: John Gutmann)
Stanley Hiller (with a more conventional helicopter prototype) gives his wife, Carolyn, a lesson in hovering in 1946
Another development of the era was the American Helicopter Co. XH-26 Jet Jeep (also known as the XA-8) which was an experimental tip jet helicopter developed in 1951 to meet a United States Army and Air Force (USAF) request for a collapsible and air-droppable observation helicopter.
The XH-26 was constructed of aluminum (except for the aft fuselage which was laminated fiberglass) and possessed a well-glazed, pyramidal-shaped cockpit. When collapsed, its five-by-five foot by fourteen foot container fit on a trailer that could be towed by a military Jeep. If stripped for an air drop the Jet Jeep, which weighed less than 300 pounds, could be assembled by two men in just 20 minutes.
The American Helicopter Co's XH-26 Jet Jeep undergoing flight testing
In my notes further up the page I mentioned the Dutch 'Kolibri' ram-jet helicopter incorrectly citing this as the industry's first Kolibiri and which, upon reflection, was woefully incorrect (my apologies). The industry's first Kolibiri is (I am reasonably confident) the well-known Fletner FL282 which was developed by Anton Fletner in 1940.
The Fletner FL282 Kolibri of the German Luftwaffe during seaborne trials in the early 1940's
The intended roles of FL282 included ferrying items between ships and submarines as well as seaborne and land-based reconnaissance. However, as the war progressed, the Luftwaffe began considering converting the FL282 for battlefield use. The craft originally had accommodation for a single pilot but, a position for an observer was added at the rear of the craft resulting in the B-2 version.
During the Battle of the Bulge a formation of five of Kolibris conducted the world's first helicopter strike against armour. Operating low over the Ardennes Forest they destroyed two American tanks at a loss of two Kolibris. One to a British Spitfire the other to groundfire. Later the B-2 proved useful as an artillery spotting aircraft and in 1945 an observation unit was established comprising of three FL282's and three FA223 (Focke-Achgelis) helicopters.