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Aviation History
1949
1949 - 1289.PDF
JULY 14TH, 1949 FLIGHT 53 ADJUSTING PIN PISTON the disc is mounted almost flush with the edge of thewheel, so that one side is fully exposed to the airstream to ensure a rapid dissipation ot heat. By positioning theoperating unit behind the undercarriage leg, its blanking effect is kept to a minimum and the maximum effectivecooling area exposed. An interesting feature on these brakes is thatno lining clearance adjustments are required, since these are effected automatically by. pneof two schemes. On the larger brakes the adjustment device is incorporated in theoperating unit. The piston carrying the lining pad is mounted on the head of an adjusting-pin, the stem of which passes through a pack- ing nut. The attachment allows a predeter-mined axial movement of the piston equal to the desired clearance. When the brake is operated the piston ispushed against the underside of the head of the pin, which is then pulled through the packing nut by an amount equalto the wear on the lining. Upon release of the brake the piston slackens off by an amount equal to the slope of theattachment. As the lining wears, so the adjusting pin is pulled farther through the packing towards the disc. It isthis operation which automatically takes up the wear on the linings and is progressive right through their life. Onrelease, when an adjustment has automatically taken place, the piston will again return only to the designed clearance. Testing for operating clearance with the aircraft on jacksis misleading, because the roll of the wheels over the ground immediately after releasing the brakes assists in the LININC UNINC The small Palmer brake assembled in a wheel: it is mounted on the outside to obtain maximum cooling effect from the slipstream. On the sight it is shown unmounted. recovery of clearance. The best test procedure is applied after the aircraft has rolled a few yards and before the brakes have again been used. No more than a brushing of the linings on the discs should then be felt. On the smaller brakes, the self-adjusting mechanism is incorporated in the master cylinder. On this, as the linings wear, the operating piston merely follows further through the cylinder, and the extra volume of hydraulic fluid to compensate for this extra travel of the piston is taken from a header tank by the master cylinder at the commencement of each working stroke. The reservoir pressure-head holds the linings in contact with the disc and this allows the omission of return springs. The pedal or lever travel thus remains constant throughout the life of the linings, the only effect of wear being that more oil is brought into the brake cylinder. This scheme does not give an initial clearance, but if the reservoir pressure is controlled no undue idling friction results. Two disc brakes which differ from those already reviewed are the Messier "Multi-spot" and the Bendix "Segmented Rotor" brakes. Embodying several unusual features is the Messier B 25 Goodyear automatic wear-adjuster : the loose fit of the piston on the adjusting-pin allows the linings to return to a predetermined clearance when the brake is released. On the right is the Goodyear single-disc brake. " Multi-spot," which is claimed to combine the advantages of early types of multi-disc brakes with the cooling of the exposed disc type. The linings are equally spaced around the disc in a metal carrier pierced with holes; circular lining pads are used for ease of manufacture. Multiple discs are fitted, each of relatively narrow section so that the tempera- ture gradient across each is reasonably flat, thus improving the instantaneous storage-capacity of the brake. The com- plete unit is housed inside the wheel and cooling of the discs is assisted by the forced circulation of air through the brake, due to the rotation of the spaced elements, which throws air radially outwards under centrifugal action. This cooling is not so effective as for exposed discs, but the multi-discs provide an ample storage capacity, so cooling is prolonged. The Bendix brake is sufficiently different from previous "multi - disc" types, both in de- sign and function of parts, to warrant a separate classific- tion, and the term ' 'segmented-rotor'' type is used. The rotating members or rotors are not thin plates, but are substantial discs of __m,,^^_.sizeable thickness. fW^^^Jf C HKKlIti I cient mass of metal B ff* Ww H sf ffi%ll 'is provided to func- tion as an effectiveheat-reservoir. This capacity for heatabsorption in- creases the possiblerate of energy ab- sorption of the Bendix segmented-rotor brake as fitted to the Lockheed Constellation. Rendix brake: detail of friction-lined stator between two segmented rotors.
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