FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1953
1953 - 1024.PDF
i7« FLIGHT, 7 August 1953 SIKORSKY S-52 SERIES A Successful Little Helicopter and its Background A Sikorsky S-S2-2 three/four seater which carries full dual control. Note the two ventral fins and the tail-boom stabilizer. lIBi ALTHOUGH little known in Great Britain, the Sikorsky S-52-2 has earned for itself in the U.S.A. a well-deserved k. reputation for being a great little helicopter. It has been used extensively in Korea as a rescue machine for the evacuation of wounded, and as a command transport vehicle. In these capaci ties it has ably demonstrated that the comprehensive background of research behind its production has resulted in flight character istics of which its makers may be justly proud. Analogies have been drawn between the helicopter and the horse; it is not without precedent, therefore, that the pedigree of the S-52-2 should be examined in equestrian terms. Sired by the S-52-1, of 1948 vintage, it had its origins in the stable which produced a helicopter that was for a number of years the mainstay of rotating-wing flight, the Sikorsky R-4. In fact, it was the R-6A series which was born directly out of the R-4; but this series, although it achieved a high quality of rotor control, suffered numerous drawbacks—associated with maintenance—which made it clear that a re-design was necessary. Thus the S-52-1 emerged, incorporating all the lessons learned from the R-4 and R-6 series, together with many features of its own, and it showed its worth quite early in its development by establishing a new world helicopter speed record of 129.8 m.p.h. As may be expected, it is from improvements in rotor head design that the S-52 derives its pleasant handling characteristics. The basic change involves the location of the blade flapping hinges so that their action is coincident with the drag hinges. This results in a decreased control lag and also allows greater range of control. Movements of the stick are light and easy, and the response in the machine is lively and accurate. Shortly after gaining the speed record, the little two-seater demonstrated its manoeuvrability, during the course of a routine test flight, by performing a series of successive "loops," gaining height slightly after each in the approved manner. The pilot was Harry Thompson of Sikorsky's flight-test department, and the date was May 9th, 1949. Later he repeated the performance— carrying Ralph Alex, then project engineer, as passenger. From that time development proceeded steadily. A project was then already in hand to enlarge the cabin space to provide three/ four seats, and thus utilize the Franklin engine's 245 b.h.p. in a more practical manner. The enlarged version, designated S-52-2, was granted its C.A.A. certification in the early part of 1951. A few civil machines were built, but the main production up to the present has been for the U.S. Navy; the type has been designated HO5S-1. The machine is officially classified as a "three-place" helicopter but a fourth occupant can be carried on shorter flights. The large fuel-tankage capacity allows for 60 American gallons (50 Imp. gallons). With a pilot and three passengers aboard sufficient fuel can be carried for a flight of approximately one-and-a-half hours—or a distance of between 120 and 140 miles at the cruising speed of 95 m.p.h. With only three occupants the fuel tank may be filled, giving an endurance of 3\ hours and a range, with fuel reserves, of 330 miles. This "built-in alternative" increases the machine's versatility and has been proved to be of much practical value in the A stretcher case is loaded in Korea with rotors still turning. The port-side sliding door facilitates stretcher-loading. ;::':.:•:•::•: field. For delivery flights, auxiliary fuel tanks may be fitted to provide for a maximum distance of 800 miles with pilot only aboard. In its role as a rescue helicopter the S-52-2 normally carries two stretcher cases alongside the pilot. The canopy opens forward, in a manner reminiscent of the Bristol Freighter, to allow ease of loading and unloading. Improvements in stability have been effected by the addition of large ventral stabilizing fins to the tail boom. These fins are fixed surfaces, as they have recently been so made on the American S-55. In earlier versions of the S-55 the fins were adjustable by the pilot to provide fore-and-aft trimming in flight, but this is no longer necessary. Additional vertical fin area has also been pro vided by an extended fairing on the tail-boom elbow to compen sate for the increased keel surface forward of the rotor pylon with the longer nose. The use of a high-speed rotor allows a wide range of permissible rotor revolutions in flight, which is of particular advantage in the autorotative-landing case. Where an engine-off landing with zero forward speed is desired, it is possible, by using the kinetic energy stored in the rotor, to hover the machine momentarily in the flare-out before touching down. The touch-down itself is per fectly steady with the quadricycle landing gear. Of the many features embodied in this admirable little heli copter, the most important is undoubtedly the metal construction of the rotor blades. These blades were originally incorporated on the S-52-1 and now have had five years of flight experience on the series. The main spar is an alloy extrusion which is itself the lead ing edge of the blade. The trailing edge is made up in sections, each of which is attached to the spar individually. Thus the sec tions towards the blade tip are relieved of carrying the centrifugal load exerted on the inner sections, resulting in greater overall strength. The blades are fully interchangeable and their uni formity is a considerable contribution to the smoothness of the machine in flight. * The S-52-2 is a happy compromise in size between the small two-seater helicopter, the utilization of which is rather limited, and the somewhat larger 4/5-seater machine in the 500 h.p. class. The latter is often uneconomical for many charter operations. The current military versions are in use by the U.S. Army, Coast Guard and Marine Corps, but the series has now been re turned to the stable for another "breeding" spell while further power-plant research and development is carried out. When the new "filly" eventually emerges it is to be expected that it will uphold the reputation of its distinguished forbears. B.H.A.
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
