As with any modern aircraft the Typhoon is reliant on many systems for flight. Of greatest importance here is the Flight Control System. However are several other systems of note including various utilities and navigation systems as well as the integrated health monitoring system.
The design of the Typhoon is such that without input to any control surfaces the aircraft will pitch up during flight extremely quickly. Although this improves the agility of the aircraft it also requires a system to enable controlled flight to be maintained. This is achieved through the Fly By Wire (FBW) Flight Control System (FCS) developed by a number of companies from the partner nations. With this system the pilot has no direct link to any of the aircraft's control surfaces. Instead, all movements of the throttle, stick or pedals are interpreted by the FCS and an appropriate control response taken. There is no manual reversion in case of FCS failure and thus it must be extremely robust.
The FBW FCS is a quadruplex Active Control Technology (ACT) fully digital system. Each of the four (quadruplex) FBW units comprises eight 68020 CPUs. In addition to these processors there are a number of additional ASICs (Application Specific Integrated Circuits) which handle the more critical tasks. Each box has a STANAG-3910 high-speed optical databus for connection to the main avionics systems, a STANAG-3838 bus for connection to the UCS bus as well as proprietary high speed links to each of the other boxes. The FCS software itself is a combination of SPARK ADA with the more time critical elements utilising 68K assembler. Self diagnosis software is included. Each of the four FBW units weighs just 10kg including all necessary interfaces. The physical Fly By Wire system is the responsibility of ENOSA, GFSA and Bodenseewerk Geratetechnik (BGT) under the leadership of BAe Systems.
The FCS software is now the responsibility primarily of BAe with involvement from DASA. This follows earlier BAe, DASA and CASA efforts on the first version software which resulted in delays and problems. The system achieves its job through a complex model simulating the Eurofighter's dynamics. The model takes a number of external and internal parameters such as static and pitot air pressure and temperature (via the Air Data Transducers) as well as the aircraft's pitch, yaw, roll and velocity. When the pilot makes a control input, say pulling the stick back, the software computes the optimal flight control surface response given all the current data. The resulting signal is then fed to the appropriate servo actuator. The Typhoon is the first production aircraft to use Direct Drive Actuators for hydraulic control. Instead of requiring separate power and control signals these instead use the high current control signal to provide power.
Benefits of FBW
One of the benefits of such a system is the ability to program the aircraft's flight envelope characteristics directly into the FCS. By doing this the pilot is prevented (without manually overriding the system) from pushing the plane outside its stress/strain limits, e.g. by pulling to sharp a climb or too tight a turn. This capability has become known as care-free handling and it removes the need from the pilot to constantly monitor their own flight actions. In a similar way it is possible via the FCS to compensate for external factors such as gusting which can suddenly lead to loss of aircraft control. In an aircraft with a low wing loading like the Typhoon this can be a particularly important issue. A very useful function built into the Eurofighter is a single button push Return To Level feature. Upon pushing this button, part of the VTAS function set, the aircraft is automatically returned to nose-up, wings level flight with the throttles set at an intermediate position.
As well as providing what may be thought of as direct flight controls the FCS also provides for automation of flight. Of course the typical function is a simple wings level, constant air speed auto-pilot. The Typhoon however adds substantially to this thanks to the level of integration between systems. So in addition to the standard auto-pilot the Typhoon incorporates the following other automates; auto-throttle, auto-approach, auto-attack, auto-waypoint (or auto-CAP) and auto-track. Of these the most interesting is probably auto-attack. When in this mode the FCS will attempt to fly the aircraft towards the currently tracked target.
Future of the Typhoon's FCS
When the first Eurofighter's are delivered to the airforces of the four partner nations the FCS they contain will be a preliminary edition. To this end the software will be upgraded in three stages between 2001 and 2005. The first, Tranche-1 deliveries of Typhoon will be fitted with Production Software Package 1 (PSP 1). This is primarily aimed at enabling enough aircraft facilities for training and conversion of pilots. This will be followed by PSP-2 which will enable the MIDS datalink and various aspects of DASS. The final installment, PSP-3 should become available as the first squadrons form in 2005. This will see full sensor and sensor fusion capabilities in addition to the remaining DASS and cockpit modes. For the RAF models additional software will be made available, also by 2005 to enable full air to ground modes. Beyond this additional flying time will no doubt open up further refinement and upgrade possibilities.
Any modern fighter operating both day and night and in all weathers needs an accurate way to determine its position. To this end the Eurofighter contains several such systems to ensure an accurate position can always be calculated. The most common method for navigating aircraft relies on accelerometers and gyroscopes, so called Inertial Navigation Systems (INS). The Typhoon is equipped with a Litton Italia LN-93EF laser gyro INS (or LINS) and accelerometer package with an accuracy better than 1nm/hr (one nautical mile per hour of flight). In addition military specification Global Positioning System equipment is fitted enabling the aircraft to determine its position within several meters anywhere on Earth. By cross referencing the INS with the GPS data it will be very hard to get lost in a Eurofighter.
To prevent a Eurofighter pilot from having un-timed (and typically hazardous) contact with the ground the aircraft is fitted with two additional systems. A microwave altimeter (effective through one or two thousand feet) provides highly accurate data on the Eurofighter's exact height above the ground. In addition the latest generation of BAe's flight proven TERPROM system, TERPROM® II, or TERrain PROfile Matching system is to be fitted which provides digital terrain elevation maps of the Earth's surface. The TERPROM software via either continuous or discontinuous updates from the aircraft's LINS, GPS and radar altimeter provides drift-free navigation. Perhaps more importantly TERPROM can provide automatic terrain following and terrain elevation prediction without the continuous use of the radar altimeter (which may give away the aircraft's position). For example, should a pilots request to bank result in the aircraft hitting a cliff face TERPROM will give audible warning of the danger.
Finally to enable landings in all weathers both day and night the aircraft is fitted with standard microwave Instrument Landing System equipment.
As with any aircraft there is of course an essential requirement for communications equipment. The Typhoon features an integrated system termed CAMU, Communications and Audio Management Unit. This single sub-system comprises not only the major off-board communications equipment but also integrates the DVI and audio synthesis modules as well.
In terms of off-board communications the Typhoon features the normal systems you would expect to find in a modern aircraft. In June 1999 an order for radio equipment was placed with Germany's Rohde and Schwarz leading a consortium of companies including BAe Systems, ELMER and Enosa. The systems they will supply, having been specifically designed for the Typhoon will enable open and encrypted VHF/UHF communications. The units have been designed for NATO interoperability and feature the latest techniques in Low Probability of Detection and Exploitation via the SATURN, Second-generation Anti-jam Tactical UHF Radio for NATO system and NATO based encryption algorithms.
Perhaps of more interest though are the DVI and audio modules. DVI provides for direct voice interaction between the pilot and the aircraft's systems (covered in more detail on the Cockpit page). As well as the pilot being able to verbally interact with the systems the aircraft can also respond verbally, similar to the so called "Bitchin' Betty" (or "Naggin' Nora in the UK) present in many aircraft for some time. This is achieved through a series of modules supplied by Spain's Enosa. The system contains around 200 stored warning messages which can be replayed in either a female or male voice upon request via the integrated avionics system.
The Eurofighter is the first military aircraft to incorporate a true health monitoring system. The airframe of the aircraft incorporates twenty stress monitoring sensors. These sensors collect information every 1/16th of a second and send it to a central processing and data storage apparatus. The data from the airframe sensors is augmented with additional data from the EJ200 propulsion systems own sensors. This system cuts maintenance times considerably by allowing the ground crew to spot potential problems long before they become serious. In the event of a serious accident a BAE Systems supplied crash survivable unit is present along with a CDC supplied voice/video recorder allowing data analysis of the event to be carried out.
As well as incorporating extensive self monitoring systems the Typhoon is also built for fast turnaround. A typical groundcrew of 4 personnel can change-out a single EJ200 engine in only 45 minutes. A typical operational turn-around can be performed in 25 minutes with 6 personnel.
In keeping with the level of integration present in the other Typhoon systems the utilities components are also tightly combined and highly automated. The suite of utilities is combined under the Utilities Control System, or UCS, the primary contractor being Italy's Alenia. The UCS can however be broken down into several sections.
The Typhoon has essentially two electrical systems, the primary power generation and distribution system and the secondary systems (including the auxiliary power unit). Primary power is supplied via the engine turbines through a LucasVarity/BAe Systems supplied distribution and rectification system. Using this electrical power can be supplied at a number of voltages and AC phases as well as supplying a DC output. The DC system is fully redundant with two back-up rectifier units in case the two primaries fail. Additionally a DC battery source is available in emergencies as well as to power up the APU.
The secondary system provides a back-up using air-driven turbines in case of total engine (or engines) failure or partial (gearbox, turbine, etc.) failure. Since the Typhoon is designed for autonomous operation the aircraft includes an Auxillary Power Unit, or APU as part of the secondary system. Before the engines are started the APU generates all the AC/DC power required to operate the aircraft's systems. The engine start systems, supplied by AlliedSignal and Microturbo are also powered by the APU.
Hydraulics are of course essential to the integrity of an aircraft. In the Eurofighter's case there are eight separate systems requiring hydraulic supply, they are; flight control surface actuators, undercarriage, brakes, nose wheel steering system, air intake (moveable lower cowl) control, cockpit canopy, air-refuelling probe and the the Mauser BK27 cannon.
Since the loss of hydraulic power would render the flight control surfaces inoperable (let alone preventing undercarriage deployment and retraction) the Typhoon includes two, fully redundant hydraulic systems each of which incorporate flight control isolation valves. Therefore a failure in one of the other systems should not lead to the loss of hydraulic power for the control surfaces. Both systems are supplied by engine driven gearboxes.
There are several storage areas for fuel in the Typhoon, these include two centre fuselage mounted tanks as well as tanks within the wings. In addition external tanks can be carried on three hardpoints (one on each wing and one on the centreline position of the fuselage). To enable long range continual flight a retractable fuel probe (for drogue and probe compatible refuelling, i.e. non-USAF NATO airforces) is incorporated in a small compartment just below the cockpit on the starboard side. Regulation, monitoring and control of the fuel system pumps is handled automatically. The current remaining fuel can be graphically displayed via any one of the MHDDs.
In common with the other utility systems the environmental controls are also designed with autonomous operation in mind. To this end the Typhoon is equipped with its own oxygen generation system based on molecular sieve (fed by engine bleed air) technology and supplied by Microturbo. This unit provides all the filtered air required allowing operation in situations where NBC (Nuclear, Biological, Chemical) agents may be present. Since the system uses engine bleed air operation of the O2 generator before engine start relies instead on the APU for air supply.
On top of supplying breathing air both to the pilot and the anti-G suit the Environmental Control Services also provide for systems cooling and conditioning. For example the the ECR-90, FLIR sensor and the conditioned anti-g suit must all be cooled. In addition the avionics bay systems must also be conditioned to maintain proper operation. To provide for this liquid refrigerant systems are present with the planes fuel acting as the primary heat sink.
The webmasters would like to express their thanks to BASE and particularly Chris Tear for providing information on TERPROM.
 : BAE Systems, UK