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Aviation History
1980
1980 - 0027.PDF
FLIGHT International, 5 January 1980 25 206B LIVE SYSTEM LIVE SYSTEM INTERNAL DESIGN LIQUID CHAMBER- INNER CYLINDER- OUTER CYLINDER- RUBBER SPRING- -PYLON ATTACHMENT -FUSELAGE ATTACHMENT Left The Bell Liquid Inertia Vibration Eliminator (LIVE) uses a heavy liquid to cancel rotor vibration. Right The liquid is pumped from end to end of the sealed chamber formed by an elastomeric seal between two metal sleeves ing rotor which primarily shows pro mise of allowing on-condition main tenance and eliminating all conven tional hearings. Though it has been flown without powered control, it is better with a fairly large degree of power boost. The test JetRanger has been flown through a full flight en velope including 152 m.p.h. in a dive, 3,2001b gross weight, 40 m.p.h. side ways, 35 m.p.h. rearwards and yaw rates at the hover up to 63°/sec and yaw decelerations up to 128°/sec/sec. The rotor has proved to be stable and to run outside fatigue limits and to be able to accept cambered aerofoils. In- plane balance counterweights have been used to reduce control forces and prevent self-cancelling pitch reactions. The new rotor has plastic blades mounted on a flexible hub strap attached to the shaft with graphite elastomer bearings. Bell is still con cerned about lightning strike. Another area of product improve ment is in numerically controlled machining of gearing and the adop tion of double helical tooth forms. Bell reports that noise from a spur gear is reduced by 15-6dB by virtue of the much larger contact area be tween gears covering three to four teeth at a time. Silicon carbide bear ings are being used. The new trans mission is 20 per cent lighter, promises twice the mean time between re movals and saves 20 per cent of the recurring cost of manufacture. Bell is very active in applying com posites, particularly carbon fibres, to various helicopter structural parts. The US Army will shortly choose a manufacturer to produce a major por tion of an airframe in composites. Bell would offer a section of the 222. For Nasa, Bell is making and fitting 45 Kevlar cabin and baggage doors to LongRangers to be flown in commer cial service in three different parts of the USA and then retested after ser vice. The cabin doors save nearly 51b. Another LongRanger has been fitted with a graphite epoxy tail fin incor porating a lightning-protection mesh. Even the little tail-skid is carbon fibre. The company expects to gain civil certification for the fin in mid- 1980 and then to place a few of them with operators for service testing. An important area of carbon fibre application is in flying control tubes, which are normally slow and expen sive to manufacture and vulnerable to corrosion and bullet strike. Bell has discovered how to machine-wind not only the cylindrical section of the tube, but the tapered end-fittings into which the adjustment and attachment lugs are fitted. Twenty-three of these tubes will now be used in each pro duction 214ST. About 40 per cent of the weight of earlier swaged alumin ium tubes is saved. The JetRanger will also be fitted later. This technique could be used to manufacture tail- rotor shafts with integral couplings. In the 222, Bell is providing a simple energy-absorbing crew seat using various combinations of plastics and aluminium honeycomb. The pan of the seat directly beneath the pilot has a dished glass fibre shape filled with foam. Over it is stretched a rubber/nylon membrane forming the cushion surface. The pan is mounted on a sub-structure, or bucket, made of Kevlar facing round aluminium "flex- core" filling. In a crash at a vertical velocity of 30ft/sec, which would normally subject the pilot to a fatal 2S0g load, the seat is free to travel down its main mounting tubes and compresses a graphite epoxy tube end-wise, and reducing the vertical load experienced by the pilot to an easily survivable 18g. In the electronic controls field, Bell intends in future to provide either stability augmentation (Seas) or auto pilot for all its helicopters. The 214ST already has an electrically controlled tailplane which adjusts fuselage attitude for best cruise performance, damps the natural phugoid and re duces attitude response to power changes. The signalling and sensing channels are triplexed. A further advance is a digital adaptive Seas in which an airspeed sensor causes the system to adapt its responses to air speed. E Left Bell's new bearingless tail rotor, using a plastic flexible-strap hub, promises on-condition maintenance. Centre Bell can now wind both barrel section and end fitting of a control rod in carbon fibre. Right Carbon control rods in the 2I4ST
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