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Aviation History
1958
1958 - 0745.PDF
761FLIGHT, 6 June1958 Rotodyne Flight Development STEADY PROGRESS WITH A UNIQUE FLYING MACHINE EXACTLY seven months ago the first Fairey Rotodyne tookto the air. Since then its flight programme has proceededin a highly satisfactory manner, more than 80 flights having been logged and a substantial proportion of the difficult task offlight development being satisfactorily completed. It is now possible to present a brief account of what has been done to date. The manufacture and flight development of a unique machinelike the Rotodyne—particularly on such a large scale—presup- poses a very great deal of testing in wind tunnels, ground rigsand other aircraft. The use of the Jet Gyrodyne and several of the ground rigs has already been extensively reported in Flight. Basicdevelopment—largely of an empirical nature—to determine the optimum type of tip jet unit was carried out on rigs at the com-pany's airfield at White Waltham, near Maidenhead, Berks. After static trials, tests were made on a single-blade rotating rig to studythe centrifugal effects in the air and fuel flows. When a good tip unit had been produced a complete rotor waserected at the Aeroplane and Armament Experimental Establish- ment, together with the two Napier Eland powerplants and theircomplete control system. Included in this rig are virtually all the untried and critical portions of the Rotodyne, and the rig wasfound invaluable in ensuring the safety of the aircraft during its early flight trials. At the main factory at Hayes the companyconstructed a rig for testing the rotor-head swashplate mechanism and hydraulic jacks. Superimposed on this work was the necessityfor conducting orthodox fatigue tests on all major aircraft com- ponents, the rotor blades being subjected to flight loads while freeto oscillate at their natural frequency. In most helicopters one of the most critical problems concernsground resonance, and for the Rotodyne a l/15th-scale model was built with the correct blade inertia and stiffness and with dyna-mically correct characteristics in the airframe and undercarriage. Extensive tests were made to check the behaviour of the modeland to correlate theory with the results obtained. Later, full-scale tests were conducted on the prototype itself. For the latter pro-gramme, the rotor blades were replaced by equivalent masses, and an out-of-balance force was fed in at the head, the airframeresponse at all critical points being measured between 0.5 and 3 c/s. Lift was simulated by slinging the aircraft to a jib and applying lift forces through air jacks (to give a soft suspensionat the low frequencies involved) up to the weight of the aircraft. These results were fed back into the model tests, and from thecomplete picture of ground resonance thus obtainable it could be deduced that, in one rather unusual combination of circumstances,ground resonance might be encountered. To avoid this trouble, a new retractable undercarriage wasdesigned. Pending delivery of the first set of legs to the revised design, the undercarriage of the prototype was temporarily fixedin the down position with rigid bracing struts. With these struts in place, the final full-scale ground resonance and complete power-plant clearance tests were successfully accomplished in five days. Ground-resonance testing of the complete aircraft, providedwith the temporary fixed undercarriage, began on October 25 last year. This was followed by the final functional checks on thepowerplants and control systems, which were completed on November 3. Finally, on November 6 the aircraft started its flighttrials, in the hands of S/L. Ronald Gellatly, A.F.C., senior heli- copter test pilot, and Lt-Cdr. John Morton. It must be appreciated that a great deal of the Rotodyne testflying has encompassed fields never before explored outside a tunnel. Initially the aircraft was flown as a simple helicopter,remaining within the confines of White Waltham airfield and rarely being airborne for more than about a quarter of an hour ata time. Each trip was concerned with a particular set of results, and these had to be analyzed before the next step could be takenon the long road to transitional flight, i.e., conversion to autogyro flight. Gradually the flight envelope was extended, according tothe predictions resulting from the extensive tunnel testing. Tunnel testing had indicated that change in trim due to inter-ference between the rotor and airframe would be small and well within available control power. It was also evident that the lossof lift at low speeds resulting from the rotor downwash on the airframe would be quite small. These facts have been borne outin practice, and the powered cyclic and collective-pitch controls have been found to be extremely crisp and precise. Indicative ofthe latter is the fact that no difficulty has been experienced in restricting the vertical velocity at landing to under 3ft/sec (dueto the temporary fixed undercarriage). Again confirming tunnel
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