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Aviation History
1956
1956 - 0214.PDF
212 FLIGHT, 24 February 1956 A model of the Aerotecnica AC-]2 two-seater helicopter (Lycoming 0-320 engine of 150 h.p.). Two prototypes are being built by A.I.S.A. with transmissions made by E.N.H.A.SA. Twelve machines have been ordered by the Spanish Government. MADE IN SPAIN . . Among the last-named was the HM-2, a tandem two-seat low-wing monoplane with retractable undercarriage, made of wood and covered with fabric. Designed as a trainer, it is poweredby an E.N.M.A.S.A. Tigre of 125 h.p. Another was a develop- ment of this machine, the HM-5, similarly laid out and con-structed, but having a single open cockpit and fixed undercarriage. It is a single-seat aerobatic trainer for die same role as the BiickerJungmeister. Finally there was the HM-7, a four-seater with an enclosed cabin and retractable undercarriage powered by aGerman Argus inverted vee-eight engine similar to that of the Fiesler Storch. This machine was still being evaluated as a com-munications and touring aircraft. The A.I.S.A. AVD-12 and the Dornier Do25 have already been described in previous articlesin this series. I.N.T.A. is to some extent hampered at the moment becausesome of the buildings are as yet incomplete; but when the new installations are finished the country will have at its disposal acomprehensive research and test establishment of considerable capacity yet of manageable size. Aerotecnica S.A. The helicopter design work originallycarried out by Jean Cantinieau in France was transferred some time ago to the Aerotecnica company in Madrid, andM. Cantinieau and his two sons are now continuing development work under a Spanish Government contract. The company hasbuilt no factory and therefore all production is lodged with the existing organizations, and particularly with A.I.S.A. andE.N.H.A.S.A., the national airscrew company. Aerotecnica is, at the moment, the only Spanish company engaged in helicopterdesign. Before it took up such work Aerotecnica was the Spanish agent for the American Piper company and was concerned inaerial photography and crop-spraying. The original Cantinieau helicopter prototype, with a 135 h.p.Lycoming engine mounted above the pilot, close to the rotor hub, has been designated AC-11. This machine was purelyexperimental and has been superseded by several other types— namely, the AC-12, with two seats and a 150 h.p. Lycomingengine; the AC-13, with three seats and a 260 h.p. Turbom&a Artouste I; and the AC-14, with five seats and a Turborne"caArtouste II of 350-400 h.p. A further development, the AC-21, an 8/10-passenger machine powered by two Artouste Ills, willmake full use of the gyrodyne principle described below. Two prototypes of die AC-12 are being built by A.I.S.A. witha transmission and reduction gear designed on motor-car prin- ciples and made by E.N.H.A.S.A. Twelve of them have beenordered by the Spanish Government. The main features of the AC-12 are the high mass-concentration achieved and the balancedrotor system with fully articulated blades controlled by rods pass- ing through the hollow rotor pylon. The blades themselves arebuilt up from a solid, machined-metal nose section and a thin "Flight" photograph metal trailing-edge member connected by sheet-metal ribs. Thespace between the ribs is filled with a plastic foamed synthetic resin compound called Klegecell and the whole blade is thencovered with resin-impregnated glass-fibre sheet. The contour accuracy and structural strength thus achieved are quite excep-tional for helicopters, and static tests carried out by Breguet in France showed that under a tension of 59,200 lb and the vibra-tion for normal, and then over-speed conditions, the blade itself did not break even after specially prolonged tests. The rootattachment was the first section to fail. An unintentional test came when the rotor of the AC-13 was accidentally brought intocontact with the ground during a test flight. Though such a mishap normally spells complete destruction, the blades in thiscase shed some of the covering and a good deal of the Klegecell filling, but did not break up. A similar structure is used for thetail rotor of the AC-12. The next development in the Cantinieau series was the AC-13,a shaft-drive helicopter powered by an Artouste I. In this case the engine was mounted behind the passengers instead of abovethem and an extra reduction gear was incorporated to reduce the engine's 34,000 r.p.m. to the rotor's fairly high 340 r.p.m.The same rotor controls were used, and the same blade structure. Two prototypes were built for Aerotecnica by S.N.C.A.N. inFrance, to whom the licence rights have been sold. The AC-13 is not able to absorb the available power of the Artouste and usesonly some 160 h.p. at the transmission case and 136 h.p. at the rotor. Some 132 lb of residual thrust are passed along a straighttail-pipe inside the tail-cone and vented against a bifurcated nozzle. The final portion of this tail-pipe can be swung laterallyunder control of the rudder pedals so that varying proportions of the residual thrust are deflected to port or starboard to counter-act torque and to give directional control. The swinging nozzle is connected by a linkage to the two vertical fins which supplementdirectional control either at high cruising speeds or during autorotation. It has been observed that this anti-torque system uses some80 h.p., which is four times the power normally needed for a tail rotor doing the same work. But the company points outthat the power-wastage decreases as the dead weight of the machine increases, so that for a large helicopter an anti-torque jetis quite reasonably efficient. The great advantage lies in sim- plicity and safety since it is claimed that the majority of helicopteraccidents are caused by failure of the tail-rotor system, either in the transmission or control or through the rotor striking a groundobject. The use of an anti-torque jet dierefore gives greater safety and reliability, less vibration and weight, lower maintenance costand—particularly—better autorotational qualities, since the main rotor is not coupled to a tail rotor. Better handling qualities arealso claimed for the system. Finally, the company plans to arrange the tail nozzle so that at the higher forward speeds all residualthrust—some 110 1b in the AC-13—can be vented directly rear- wards to provide forward thrust, only the fins being used fordirectional control. I flew as passenger in the AC-13 from Torrejon airfield withCapt. Rochon, Aerot6cnica's French test pilot. He showed me several noteworthy characteristics of the machine. Firstly, thecontrol linkage includes no damping or boosting features, so the rotor is directly connected to the control column. The forceshave been balanced in such a way that, widi the slight friction which exists in the runs, the machine can be hovered with collec-tive pitch "hands-off", using only the rudder pedals and cyclic- pitch stick. Furthermore, the turbine and rotor are both runat constant r.p.m. and all flight conditions are controlled by rotor pitch changes alone. This makes the machine very much moresimple to fly and, incidentally, results in steady noise level. By virtue of small weights in the tips of the blades, the AC-13'srotor has very high inertia, the benefits of which were proved when the prototype suffered a fuel-stoppage during a test flightsome time ago. The rotor was turning at 400 r.p.m. and Capt. The second prototype Aerotecnica AC-12 in the A.I.S.A. factory. Cool- ing air is drawn through two oil-coolers and blown over the cylinders.
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