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Aviation History
1981
1981 - 1235.PDF
FLIGHT International, 2 May 1981 1245 simplicity was not to rely on thrust reversers. It reasoned that since the 146 would have a touchdown speed of only 90kt, and because reversers are not normally used below about 60kt, their effectiveness would be limited. Reverse thrust also would have subjected each engine to an extra cycle/flight. Instead, the 146 has two large airbrakes below the rudder. Total area of the airbrakes is 40ft2, and each deflects through up to 60°. The airbrakes may be used at any time during flight to increase descent rate without any trim change, but are mainly intended for use during approach. BAe says that the airbrakes will bs more than twice as effective as those on the McDonnell Douglas D09 or Boeing 737. Maximum descent rate achievable with the airbrakes is 7,000ft/min and at speeds of less than 250kt and be^ low 10.000ft, there is still 4.000ft/ min available. By comparison, a typical airliner descent rate on the approach is around 2,000ft/min. BAe 146 operators may also use airbrakes during the landing roll. One of BAe's early design decisions was to limit 146 maximum operating speed to 310kt/Mach 0-7. It was able to do this because the block time on a 1501 n.m. sector is not sensitive to speed. A big advantage of this com paratively low design speed, is that it allows manually operated flying controls. The aileron and elevators are moved as a result of tab deflections on each control surface, the tabs being operated by traditional cable runs. Each half of the aileron and elevator circuits is independent, and will continue to work even if the other side jams or becomes discon nected. To protect against overstress- ing at high speeds, artificial feel is built into the elevator and rudder controls in the form of pneumatic units. Rudder operation is by two hyd raulic jacks, which are mainly neces sary to offset the comparatively heavy surface if an engine fails. Roll con trol is aided by the outer spoiler on each wing, which is called into play when the aileron next to it moves downward beyond a preset limit. The spoiler would normally be of most use during an approach, when speed is low. There is a slot in the part of the flap directly behind each outboard spoiler to avoid airflow separation from the flap. Three other spoilers on each wing act purely as lift-dumpers, and are joined in this role by the outboard spoilers. All the spoilers are hyd- raulically powered and can be set for automatic operation at touchdown. BAe has opted for a conventional flightdeck, judging that the latest digital avionics and cathoderray tube displays do not justify their cost for such an aircraft. The avionics options are conventional, allowing for HF and U4b n The 146 is intended for two-pilot operation and has an uncluttered cockpit, as this mockup shows. Note the Garrett thrust management system to the right of the cautionjwarning lights, and the glareshield-mounted autopilot VLF/Omega where required. The RCA colour weather-radar is centrally mounted, flanked by the control boxes for the Edo-Aire radios. Area- navigation equipment may be fitted on a side console, or on the pedestal, displacing the radio control-boxes to the side console. The automatic flight guidance sys tem comprises a Smiths Industries SEP-10 autopilot, a Sperry flight direc tor and a Garrett thrust management system (TMS). Certification will be for category 1 landings, but category 2 will be available with a dual installa tion. Built to BAe specifications, the TMS is a limited-authority auto- throttle which helps to reduce the workload arising from the four engines, while giving a 1-2 per cent fuel saving. The TMS gives correct engine settings for take-off with the throttles in the fully forward position, automatically ensuring equal thrust from each engine. For take-off, maxi mum thrust, cruise or flight-idle, the TMS can trim the throttles to a pre set engine r.p.m. or turbine gas temperature. One of BAe's main goals in design ing the 146 structure was to keep down production and maintenance man-hours—>and hence their cost. It has done this by reducing the number of separate parts as well as the num ber of joints. The wingbox is a good example of parts reduction, each half featuring a single-piece front spar, rear spar, upper skin, and lower skin. The 146 wing is Hatfield's second design with underwing pylons—it had the experience' of the A300 wing on which to draw. Stringer/skim Redux bonding plays an important part in the 146 wing, as it did on the Trident. The upper skin has top hat stringers that double as fuel vents, while the lower skin avoids corrosion-traps with I-section stringers. Like the spars, each of the ribs is integrally machined, helping to simplify assembly and keep parts-count low. Avco Aerostructures of Nashville, Tennessee, is a risk-sharing partner in the 146 wing (Flight, April 19, 1980). Avco has invested in tooling and materials to make the wing, but de- sign responsibility belongs to Hatfield. Avco had not previously carried out Redux bonding, but it has now pro duced several wing skins with stringers to Hatfield's specifications. Access panels in the lower wing skin are a traditional part of most airliners—they allow inspection of the structure as well as fuel system main-
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