FlightGlobal.com
Home
Premium
Archive
Video
Images
Forum
Atlas
Blogs
Jobs
Shop
RSS
Email Newsletters
You are in:
Home
Aviation History
1981
1981 - 0938.PDF
964 FLIGHT International, 4 April 1981 Electronic controls from Dowty-Smiths DOWTY and Smiths Industries formed a joint engine-control com pany called Dowty and Smiths Indus tries Controls (DSIC) in 1977. DSIC combines the hydromechanical fuel- control capability of Dowty Fuel Sys tems with the electronics knowledge of Smiths Industries and Ultra, which Dowty acquired at about that time. The company was formed because it was realised that digital electronics was about to bring about a watershed in engine control technology—the ad vent of full-authority electronic engine controls. DSIC uses the term Fadec for full- authority digital electronic control, which means exactly what it says— the pilot's throttle demand is fed into a computer which controls the fuel valves, taking into account sensor readings which ensure that engine limits are not exceeded. There is no hydromechanical link between the throttles and the fuel valves. Pre vious electronic engine controls were only limiters acting on the primary hydromechanical control system. Fadec has several advantages, one being the replacement of large, heavy hydromechanical units by electronic devices which are reliable and need little or no maintenance or in-service adjustments. Unit cost of the elec tronic systems is also claimed to be lower, and built-in test equipment is incorporated easily. Pilot workload is reduced because the electronics prevent overspeeding or over- accelerating, which the pilot himself has to take into account with hydro mechanical systems. Lastly, fuel con sumption is reduced because the more precise control helps to elimin ate waste. DSIC is involved in three Ministry of Defence (MoD) demonstration pro grammes, the principles of which read over to civil engines. They com prise controllers for a helicopter engine, a VTOL engine like Pegasus and an advanced military engine like RB.199. DSIC is producing the definitive design for a Gem Fadec, which is due for tethered flight trials late this year. Already proven on a Gem testbed, this Fadec has been under development since DSIC was formed, the MoD contract being awarded in 1979. The helicopter Fadec gives a constant acceleration regardless of temperature and type of fuel, says DSIC, as well as avoid ing regimes which give high engine wear. The torque between coupled engines is also matched. Since Fadec is aimed at multi-engined helicopters, there are only two electronic control lanes (primary and backup) for each engine, and there is no reversionary hydromechanical system. Fuel is used to cool the electronics. DSIC lists Lvnx, WG.30, EH.101 (Sea King re placement). Agusta A.129 and PAH-2 as possible Fadec applications. DSIC estimates that the Pegasus programme will stretch over 50 years, and that a Fadec will be desirable after around 25 years of flying—in 1985. Pegasus clearly presents some special problems in engine control, and DSIC cites one—the Harrier can not be held on its brakes when the engines are developing more than 55 per cent thrust, so a Sea Harrier will fall off the ship if the engine con troller falters after this point. DSIC demonstrated the generic controller in 1978, working up to a full system testbed demonstration last year. Flight-tests are to start this summer. In the Pegasus, an automatic transfer to the backup channel occurs if the primary fails. The backup is designed to fail frozen, an emergency hydro mechanical system being available as a last resort. DSIC estimates that a primary failure would happen to a pilot once in roughly 12 years of flying, while he would be "very un likely ever to experience" a double failure. DSIC hopes to supply Fadecs for AV-8Bs, and the Harrier GR.5 if it is built, as well as for retrofitting to Harriers and AV-8As. An advanced military engine is de fined by DSIC as having high thrust/ weight ratio, two or three spools, re heat, and variable guide vanes, com pressor blow-off valves and nozzle. This points to engines such as the RB.199, and implies about nine variables to control. Operation at the limits of temperature, pressure, and r.p.m. are commonplace, and a range of incidences and Mach numbers must be accommodated. A test at Pyestock is proposed for this year, a Spey being used initially because of the non-availability of RB.199s. A further demonstrator programme is aimed at reducing system cost by 40 per cent and weight by 20 per cent. Tornado RB.199s currently use ana logue electronic controls, but DSIC is confident that its digital controller will have an application here. The DSIC afterburner control features the new vapour-core high-speed centrifugal pump and plug-in-hole electronic flow controller. DSIC is proposing a Fadec for future airliners such as the A310 and Boeing 757 and 767, Ultra having been responsible for the analogue unit on Concorde, which also had a digital fault-interrogation module. A civil microprocessor-based monitor is undergoing 50,000hr of environmental cycling tests, and four British Air ways RB.211-powered aircraft are testing the system in service. The main emphases for DSTC's future development are airframe-mounted electronics, more sophisticated control laws, hybrid-circuit work and enlarg ing the software-base. The digital electronics revolution which is sweeping the aircraft indus try promises much in decreasing cost and increasing payload, and full- authority digital aircraft and engine controls are part of this. There are inevitable reliability questions—pilots are bound to feel uneasy about re moving well-tried mechanical and hydraulic control altogether. It is for electronic engineers at companies like DSIC to prove the worth and relia bility of their devices. DSIC engineers work on a Pegasus full-authority digital engine control installed on the Dowty 30,0001b testbed at Staverton. The engine may be controlled from a Harrier cockpit next to the test cell for realism. Thrust can be increased from 55 to 100 per cent in 2-5sec
Sign up to
Flight Digital Magazine
Flight Print Magazine
Airline Business Magazine
E-newsletters
RSS
Events
