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Aviation History
1948
1948 - 0179.PDF
FEBRUARY 1548 FLIGHT 155 American Helicopter Development Amazing Range of Rotor Configurations Tested : Progress with Jet-driven Blades WOBBLE PUT-; AT the meeting of the Helicopter Asso- r\ ciation of Great Britain on January -*• -^- 24th the lecturer was Major J. C. Siltanen, who was introduced by Dr. J. A. J. Bennett. Dr. Bennett said that Major Siltanen has been for the past four years in the Rotary-wing Branch at Wright Field, first as project officer in charge of the ^particular military version of the Sikorsky helicopter from which the S-51 has been derived, and later as assistant chief of the Rotary-wing Branch. He has been assigned recently for duty over here as Air Technical Liaison Officer in the office of the U.S. Mili- tary Attache in London, and is the first rotary-wing officer to hold this position. Dr. Bennett announced that, in recognition of this appointment, and to show their esteem, the Helicopter Association had elected Major Siltanen an honorary member. Major Siltanen's lecture was really a talk about the many lantern slides he showed rather than the reading of a formal paper. The first slides showed early Sikorsky development, but as this is already well known to our readers there is little need to repeat it here. Major Siltanen then dealt with the first variation from the three well-known Sikorsky models, a rotor head designed and built by Doman-Frasier. It is in- stalled on a standard R-6, and consists of four non-articu- lated rotor blades mounted on a gimbal joint. It has hy- draulically operated controls, and there has been a total of approximately 15 hours of flying on this head so far. It is claimed by Doman that the four-bladed rotor is smoother because not only are the lift variations on the blade effectively cancelled, but the twice-per-revolution blade moment variations about the blade feathering axis balance each other to produce zero stick shake. One of the illustrations is a schematic diagram of the j. Doman-Frasier rotor head. The blades are rigidly attached t to the steel hub. The controls are all inside the rotor head. The rotor blades are made of laminated birch .spars with plywood covering and stainless steel leading-edge strip. They are made very flexible in order to have the natural bending frequencies fall well below any of the normal blade exciting frequencies which occur in flight. The con- trols are hydraulic, but in the event of a ""PUSH ROD 1 FIXED STRUCTURE A Doman-Frasier rotor head mounted on a Sikorsky R-6 for development testing. All controls are housed inside the rotor head. (Left) Diagram of the controls of the Doman-Frasier rotor. The blade thrust bearings are unloaded in flight by hydraulic oil pressure. MAIN AXIS OF ROTATION TO COCKPIT CONTROL failure an independent stand-by system, which is normally used to trim the helicopter in forward flight, can be used in emer- gency. Major Siltanen explained that it was not flying at any of the times he was at Doman-Frasier, but motion pictures seemed to show that it handled very well in gusts. This is explained by Doman as being one of the important advantages of having a gimbal-mounted rotor. One of the original innovations of Doman-Frasier is to mount on the rotor head a pump with a small accumulator reservoir for the purpose of unloading the Made cyclic-pitch bearing so as to lighten the load forces, although, of course, with this hydraulic system there is not much need to reduce the blade forces except that if they could be unloaded in this manner, which they intend to go ahead with in *he (Right) An interesting fea- ture of the Kellett XR-IO rotor-blade construction is the laminated tension-rod attachment, which fulfils the same function as the sectoral scheme in the Bristol helicopter; INCIDENCE ARM PIN OUTER ANCHOR TENSION-TORSION BARS s NNNER ANCHOR STAINLESS STEEL COLL SPOTWELDED TO SPAR' AND RIVETED TO RIB OO7O IN PLYWOOD AOE SURFACES The Sikorsky S-52 has now received its C.A.A. certificate for both day and night flying. SOLID SPRUCE TRAILINC EDCE-
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