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Aviation History
1947
1947 - 0346.PDF
218 FLIGHT MARCH 13TH, 1947 ICE on the VIKING Important Flying Tests : Results and Remedies : Resumption of Services AFTER four months of inactivityr-\ Vikings have now, as we briefly A. JL recorded last week, regained.A.R.B. approval for operation in icing conditions on all B.E.A.'s routes. Theirprecautionary withdrawal from service was a severe blow, but it may also wellprove indirectly to have been of great ad- vantage to the British aircraft industry.The findings of what must be the most extensive series of flying tests in severeicing conditions, which have been con- ducted as a result of their withdrawal,are to be made available to all manufac- turers by the Vickers-Armstrong com-pany. Three things are required of a modernaircraft should icing be encountered ; the ability to fly and be handled nor-mally;;—perhaps with some increase of power—with ice on surfaces; theability, with the aid of its de-icing equipment, to get rid of any ice whichhas formed and, in anticipation, the power again through the de-icingequipment, to prevent ice from form- ing at all. Being the most important problemthe aerodynamic one was tackled -first. It had been known for some time thatthe elevators of the Viking, though satisfactory in effect, left something tobe desired in their feel. The woolli- ness had been assumed to be a matter (Below) Elevator modifications.Quite distinct asymmetry results. concerning the fore and aftstability of the whole air- frame; icing problems haveshown that it was caused by too closely balanced eleva-tors. It'centres around the B2 coefficient—the rate ofchange of hinge moment with elevator angle—andwas to a great extent cured as soon as the negative valueof B 2 was increased. Shouldthe B, coefficient, through icing or ©ther causes, be-come positive, tiie elevators would be overbalanced;there must, therefore, be PORT TAILPLANES „ OVERHANG 1 Oi STARBOARD TAILPLANES 1O" Proposed y of additional tanks for de-icing fluid in the Viking wing root (starboard side). A nacelle fuel tank will be used pending modification. SERVO TAB1-48" UPS DOWN 3 CORDTOP&BOTTOM SURFACESHORNCUT/Wii TRIM TAB Possible effect of insufficient flowof de-icing fluid. The next stage may be a build-up of upper and lower icesections to a three-pronged formation. HORN INCREASED I__L. r, «Q ^^ H+18MIN Stages in the removal of ice from tailplanes by the T.K.S. system with increased rates of flow. sufficient negative margin to prevent this occurring. A second factor which bears on the aerodynamic problem is the asymmetry of slipstream resulting from airscrews rotating in the same direction. Handed airscrews are not a practical proposition, chiefly because of the duplication of spare engines and components which would be entailed. The port horn balance on the Viking has from the start been smaller than the starboard one because the destabilizing effect of the slipstream acts on the port side only. On the modified Vikings, which will go back into service with B.E.A., a quite pro- nounced asymmetry will exist. This is the first time that the slipstream problem has been countered in this way, but the Vickers-Armstrong Com- pany regard it as a simple and logical step, which may well be adopted by others. In attacking the Viking elevator overbalance condition several mea- sures were considered: (1) Spring tab modification. (2) Cusped trailing edges. (3) Built-up trailing edges. (4) Modified horn balances Longer-term preparation was also made to increase the size of tailplane and to set back the elevator hinges, but other measures have proved successful and this will not now be necessary. Chief modifications at once adopted for the elevators were; (1) A reduction in size of portelevator horn to 62 per cent of the original. It is now shielded and is,in effect, only a mass balance. (2) Addition of 3ft 6in lengths of 'sintube above and below the trailing edges. (See diagram.) (3) Gearing-up of servo tabs to 1.5111each way instead of lin. (4) Addition of a spring compensator(bungee) to give a 25 lb down-load at the controls. Tests with an increase in size of the starboard horn of 10 per cent were tried and found successful, and a 40 per cent increase is to be adopted. When the large horn is added the in- terim spring compensator will be dis- carded. The effect of the fsvn tube on the handling of the elevator controls is to make them heavier, while the increased gearing of the tabs has rather the reverse effect under normal conditions. The aim, successfully achieved, has been to obtain less balance but the same stability under all conditions. r One effect of the modifications to the tail units has been to the stick load in the event of an overshoot. From a powered approach to a balked landing the load is rather less than 30 lb, and from the glide at 90 to 95 kt it may be as high as 60 to 70 lb. This last case would be exceptional, and in that the trimmers are very accessible the
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