GB552154A - Apparatus for testing the aerodynamic balance of airscrews - Google Patents

Abstract

552,154. Testing balance of rotary apparatus. DE HAVILLAND AIRCRAFT CO., Ltd., and HALFORD, F. B. Aug. 21, 1941, No. 10691. [Class 106 (ii)] Apparatus for testing the aerodynamic balance of air screw blades comprises an air screw hub 15 arranged for the reception of one or more production blades P to be tested against a master blade or blades M, driving means 11 for the hub being mounted therewith so as to be free to oscillate about an axis transverse to the hub, means 17, 19, 18, 16 for adjusting the pitch of at least one blade and means 23 for indicating the oscillations of the assembly. The motor 11 is supported by links 13, 14 on a rigid stand 10 and drives the hub 15 through reduction gear 16. Extending back from the motor is an arm 20 held central by springs 24, 25 and a stylus 21 thereon influences an electrical pick-up 22 connected to indicating and/or recording apparatus 23. The hub is faired by a spinner 26 and the remainder of the apparatus by a cowling 27. The driven wheel 28 of the reduction gear is fast on the shaft 29 on which the hub 15 is splined. The shafts 30, 31 are normally stationary, the shaft 30 being keyed to the end plate 32. The shaft 31 may be rotated by bevel gear and worm gear 33, 34 from the hand-operated shaft 19. Toothed annuli 35, 36 normally rotate with the air screw, the pinions 37 idling. If the sun wheel 39 on shaft 31 is rotated relative displacement of annulus 35 with respect to the air-screw takes place, and this rotates the gears 41, 42, Fig. 4, and the oppositely-threaded screws 43, 44 which abut against lugs 47, 48 on the boss of the adjustable blade to cause its pitch to be varied. To unseat the blade, the drive shaft 15 is provided with projecting studs 49 and the spider arm 50 is placed over the stud and forced home by a differential screw 51. The blade P is placed on the spider arm and secured by caps 57 threaded on to barrel projections 58 the usual packing being provided. In operation, the production blade is set by hand to the nominal pitch and the apparatus run up to resonance speed. The pitch of the master blade is then adjusted so that there is minimum vibration. The amount and direction of pitch adjustment being found, the blade P is marked in such a way that by reference to a standard marking it can be mounted in a production air screw hub in the best condition for aerodynamic balance. Where a hub is intended for three blades, two master blades are employed against a single production blade for test.