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Aviation History
1958
1958 - 0259.PDF
CRUISE PITCH STOP WITHDRAWAL FLIGHT, 28 February 1958 VISCOUNT 810 ... 273 TAKE-OFF H.P. COCK OPEN | / H.P.COCK CLOSED hydraulic pressure from the "up" side of the actuating jack and theairstep can then be pushed out by hand. An over-centre lock ensures the rigidity of the steps in the down position, but theyare pivoted at the door sill and carry casters at the base of the lowest tread to accommodate variations in fuselage attitude. There are now two rear doors aft, disposed port and starboardto meet C.A.A. evacuation requirements. The port door may be used for passenger loading and the starboard door can serve asuseful access for loading pantry stores. Aircraft that come under C.A.A. jurisdiction have escape hatches on the forward windowon the starboard side and on windows 6, 7 and 8 over the wings on both sides of the fuselage. Where a rear lounge replaces the rearupper freight hold (as on the 812) two more small windows are provided and new intercostal members above and below thewindow carry the additional loads. The rear freight door is not fitted when a lounge is installed. Most of the additional strengthening concerns details only; thetail cone area has been stiffened to carry increased tail loads and small structural changes have been made to accommodate variousaerials and flashing beacon lights at the top and bottom of the fuselage. The corrugated skin of the luggage bay floor has beenchanged for a sandwich construction with a smooth floor surface which makes it easier to handle the luggage and also to keep thebay clean. A modification has also been made to the nosewheel doors and bay, which have been extended 1.9in to accommodatethe longer stroke undercarriage. In order to cater for a maximum landing weight of 60,000 lb(that is, an increase of 1,500 lb over the Viscount 800 series) changes have been made to the wing structure and main under-carriage. The most important of these is an all-round dimensional increase in the T-section spar booms. Local modifications havealso been made to leading and trailing edge members, spanwise members and their respective attachments. As shown upon thecutaway drawing, the Vickers-designed undercarriage has been stiffened for the Viscount 810 and the geometry slightly revised.To cater for the increased landing loads a longer stroke under- carriage has been fitted and the main chassis ribs have beenstrengthened. Structural provision has been made such that the Dart 541 can be installed without further structural alteration. To meet C-A.A. requirements for water/methanol injection,larger (55 Imp gal) water/methanol tanks, similar to those needed on 700 series Viscounts, are provided in each wing. Rather lesswater-methanol will be needed with the Viscount 840 since there is a higher power reserve in the engine fitted. The four-tank fuelsystem comprises 20 Marlite nylon fuel cells with a total capacity of 1,900 Imp gal—a few gallons less than the 800 series aircraftdue to the water-methanol system. A fuel jettison system has been provided for Continental aircraft—once again a C.A.A.requirement—similar to the system evolved for Capital's Viscount 745s; it consists essentially of two pumps and an electrically-con-trolled dumping valve for jettisoning the required amount of fuel. Provision is also made for mounting two 145 Imp gal slippertanks externally on the wings, as an optional extra. Flying Controls. To cater for the higher tail loads, the tailplane—identical in appearance with earlier Viscounts except for an asymmetric tab configuration—has been strengthened by thicken-ing the skin and increasing the dimensions of the spar webs, chordwise sections and local attachments. Other modificationsto the flying controls also result directly from their adaptation to a higher performance aeroplane. Some local strengthening to thecontrol rods has been made and improvements have been made to the tab stiffness by fitting honeycomb-foam filled tabs. The spring-loaded cable which actuates the control lock plunger The rear lounge, with small additional windows, is an attractive feature of the Viscount 812. Behind the curtain is a passenger wardrobe. NORMAL'. ,' V» .ENERGISING . '• DISARM CRUISE PITCH STOP ISOLATION SWITCH DISENGAGE / //^-FLIGHT FINE-PITCH SELECTOR LEVER DOUBLE-POLE SELECTOR SWITCHES CONTROL (CF. P.)CIRCUIT TWIN MICRO-SWITCHES CONTROL RELAYS, AND ISOLATE THE ELECTRO-HYDRAULIC PITCH STOP(19')CIRCUIT WHEN- FLIGHT FINE-PITCH LEVER IS AT "DISENGAGE" Undercarriage micro-switch selection of ground fine pitch has been replaced—on the 812—by a manual (ever. Its operation, and that of the gust-lock control, is discussed in the text. from the cockpit has been replaced by a double wire run with apositive return. The flying control runs have also been modified so that the servo motors of the Bendix PB 10 autopilot are nowsituated directly under the tail surface torque tubes, where the inevitable small amounts of friction, break-out force and backlashin the control circuit are eliminated—the result should be a much better standard of control than is possible with the autopilot servosunder the pilot's floor. (The Bendix PB 10 autopilot, coupled with the Collins FD 105 Integrated Flight System, is fitted to theViscount 812; the standard Viscount 810 installation is the Smiths Flight System with S.E.P.2 autopilot.) The Bendix autopilot includes a torque-limiting device on theelevator which causes a break link to operate against a pre- determined spring force if the autopilot torque exceeds a certainvalue. Operation of the break link also trips a micro-switch which cuts out the autopilot servo motor and hence prevents excessiveloads being transferred to the control surfaces; if the condition passes, the break link springs back and the autopilot resets. Propeller and Engine Controls. Introduced on the 810, is thenew Rotol 2-step lock propeller with trapezoidal plan-form blades and an activity factor of about 160. This propeller is controlledby a revised control lever layout in the cockpit, with a manual selector for ground fine pitch in place of the undercarriage-trippedmicro-switches used in the past; this is again a requirement of the C.A.A. The layout is shown diagrammatically in the accompany-ing sketch. Also shown is the improved control gust-lock arrange- ment that mechanically prevents selection of flight fine pitch withthe aircraft on the ground and the gust-lock in, although in this condition any two engines may be run-up to take-off power forground-testing purposes. Four positive propeller-pitch positions are provided: Feather,"high stop" cruise pitch lock (35 deg blade angle), flight fine "low stop" pitch lock (23 deg) and ground fine pitch (19 deg) for enginestarting and minimum drag on the ground. The new lock position —for cruise pitch—has been added to cater for the additional powerof the Dart 525 and higher speed of the 810. Should a hydraulic (Overleaf is a double-page drawing of the Viscount; and this description is continued on page 280) \
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