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Aviation History
1931
1931 - 0354.PDF
FLIGHT, APRIL 17, 1931 centre line by two inverted Veesof steel tube, hinged to the top longerons of the fuselage,' andoutboard by parallel struts at- tached by pivot joints to thelower longerons via adjustable members. The supporting struc-ture forms, in fact, a deformable parallellogram, the amount of de-formation permitted being limited by yet another member which islinked with the dynamometer. This member slopes downward andforward from the rear spar to a crank under the fuselage deck.This crank is, in turn, connected to the dynamometer by a hori-zontal fore-and-aft tube. The de- gree of free movement permittedto the wing is provided in this link between the crank and the dvnamo-meter. The general scheme of the cradle suspension of the wing isindicated in the perspective dia- grammatic sketch. Fig. 1. The reading obtained on thedynamometer from one setting of the wing determines the magnitudeof the air force on the wing, but not its direction. To obtain this, and from it the componentsof lift and drag, a second reading is necessary. This is obtained by altering the points of attachment of the wingbracing struts on the fuselage. The way in which this is done is illustrated diagrammatically in Figs. 1, 2, and 3. Althoughtwo positions only are necessary, three positions have actually been provided in order to afford a check reading. Certain wings, and in particular wings fitted with slots orother artificial aids to high lift, require the forces to be mea- sured up to quite high angles of incidence. To enable this tobe done an alternative series of wing attachment positions has been provided. These are shown diagrammatically inFigs. 4 and 5. All these changes in the positions of the strut attachments can be easily and quickly carried out with theform of structure used in the Parnall Parasol Monoplane. The mechanism of the dynamometer is illustrated in thepart-sectioned perspective view, Fig. 6. This sketch is self- explanatory, but attention should, perhaps, be drawn to themethod adopted for limiting the movement of the wing. The lower end of the dynamometer has two rollers, one on each Side View of the Parnall Parasol Monoplane,the form of a deformable parallelogram. Photograph.) The wing bracing struts are in (Crown Copyright, R.A .F. Official side, constrained by quadrant-shape cams. These cams canbe rotated through approximately 90 degrees by a lever in the pilot's cockpit. The width of the cams varies along thelength, one end fitting the roller, while the other end has a maximum clearance of 6 millimetres. This, therefore, repre-sents the amount of " play " of the wing, and is sufficient to get a reading, while at the same time failure of any partof the dynamometer mechanism will not affect the safety of the machine in any way. The control of the dynamometer is in the front cockpit,which is occupied by the observer, In the pilot's cockpit there is, in addition to the usual equipment, a lever whichactuates a hydraulic brake on the airscrew. By means of this brake the engine can be stopped and the dynamometer read-ings taken while the machine is in gliding flight, i.e., without the comphcations resulting from having a portion of the wingin the slipstream. An R.A.E. Gas Starter, Mark II, is fitted by means of which the engine can be started again when theglide has been completed. The engine fitted in the Parnall Parasol Monoplane is an Fig. 2 I'nslotteiJ Winj;.v Position OIK- Fig. 4 Slotted Om> Fig.3 Viu.lotted \N'mti-'> - Two. Fig, 5 Slotted Witnr:; - 1 tuition Two. ^ 330
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