Flying-by-Wire: How Computers Revolutionised Flight

Digital technology has revolutionised the skies with aircraft using their digital brain to aid the skill of pilots. However, getting there was a long and complicated road.


The Hai Lung SS-793 diesel-electric submarine emerges from underwater during a during a drill near Yilan naval base, Taiwan April 13, 2018.
The Hai Lung SS-793 diesel-electric submarine emerges from underwater during a during a drill near Yilan naval base, Taiwan April 13, 2018.
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LONDON (Bywire News) - This month we heard that the UK’s next generation submarines will be benefitting from fly-by-wire technology already being used in the air. It’s the latest development in a long history in which automatic technology has made the life of pilots easier and most importantly, safer. 

Flying by wire 

Fly-by-wire uses computer technology to interpret the inputs of the pilot. If a pilot decides he wants to pitch to the right, he moves the control stick. The computer will then calculate the changes to the aerodynamic structures on the wing and tail required to make that movement. 

It’s a major step forward from the early aircraft in which flight control was entirely mechanical. Aircraft relied on a mess of wires, pulleys and rods directly linking the pilot’s control stick and peddles to control surfaces on the wings and tail.

They were heavy and unwieldy. Aircraft had to be designed in a way which was inherently stable so it could revert to a level flight path after the pilot’s input. With even the best pilot, reaction speeds are slow for the demands of flight. This need for stability governed everything from the placement of the fuselage to the wings and tail. With this approach manoeuvrability was strictly limited. 

In other words, every aircraft suffered with the human bit in the middle. 

Electrical flight control

The solution was to find an electrical alternative which could automatically monitor and control aspects of the aircraft in a way which humans could not. They aimed to remove the physical connection between the pilot and control surfaces. Instead, a computer would process signals from the aircraft surface making minute adjustments to aerodynamics of the aircraft. Meanwhile it would respond to the pilot’s inputs by interpreting the desired outcome and putting it into effect. 

This would allow designers to create aircraft designed for manoeuvrability rather than stability. The computer would handle swift calculations to keep it in the air. 

In the 1930s the Soviets tested servo electrically operated control surfaces on the Tupolev Ant 20. Wires and electric servos replaced mechanical and hydraulic connections. This was a step in the right direction but it wasn’t until 1969 and the arrival of Concorde that the world’s first fly by wire airliner became a reality.

This analogue fly by wire system was a big reason why the flying experience was so special and helped set it up in a class of its own in the aviation world. Electrical signals responded to movements on the control panel and rubber pedals to control the flight. 

It also had a back up mechanical system in case anything should go wrong with the fly by wire system. 

Going digital 

Concorde’s system was analogue, but at the same time, NASA were making their way towards digital fly by wire technology. They had been looking at various projects ever since the Apollo program. 

When Neil Armstrong stepped out onto the lunar surface on the moon, he did so thanks to a computer driven with a fly by wire system. 

When Armstrong became deputy Associate Administrator for Aeronautics, he accelerated NASA’S drive for a fly by wire system for its fighter jets. At the agency’s Flight Research centre, they tested a digital flight control system on an F-8C Crusader, which had been stripped down and modified with a computer control system evolved from the Apollo Program.

Their previous experiences shaped the DFBW program but the F-8C did not come with a mechanical back up system. If anything went wrong with the digital brain the pilot would be in trouble. Fortunately, on the first test flight on May the 25th 1972 everything clicked. Search pilot Gary Krier popped up and down with no problems at all. 

Over the course of its 210 flights the DFBW program proved that a digital computer coupled with an electronic flight control system could put right all the wrongs of mechanical flight control. The technology it produced would be embraced by the military and laid the foundations for future projects. 

Commercial fly by wire 

Digital fly by wire proved popular with the military, but it wasn’t until the 80s that Airbus brought it right into the world of commercial aviation. The benefits were clear. They hoped to use fly by wire as a main point of difference in the fight against Boeing to become lighter, more efficient and safer. 

The new digitally driven  fly by wire systems replaced the pilot’s column with a simple side stick control. Movements on the wings and the tail would now be controlled by the computer rather than the pilot. 

As it launched its massive A320, Fly By Wire had become its biggest selling point. They produced a system which was supposedly immune to pilot error. While previous fly by wire systems produced artificial feed back to create an intuitive sense on control Airbus did away with feedback altogether. 

The pilot could move the stick as much as he or she wished, but the computer would limit the degree of movement to what it felt was safe. So, for example a pilot could move the stick all the way to the right, but the computer would only roll up to 67 degrees which was the limit it determined was safe. 

The system was as ground breaking as it was controversial. It effectively acknowledged an uncomfortable truth: most air accidents were caused by pilot error rather than a problem with the aircraft. This aimed to eliminate human error by putting the computer firmly in control. Even if the pilot made an error, the computer would correct it. 

Pilots disliked it. They wanted to feel as if they were fully in control of the aircraft at all times. Not least for emergencies. Customers also distrusted a system so reliant on computers. Controversy was fuelled by the crash of Air France Flight 296 as it performed a fly by at an air show. Critics leapt on the incident suggesting the fly by wire system had prevented the pilots climbing away from the runway. 

An investigation later showed the system had performed as expected. The crash had been down to pilot error, but it highlighted a major concern with fly by wire technology: redundancy. What happens if the computerised brain fails? The Airbus system was notable for not having a back up mechanical system in case the fly by wire failed. 

Today’s redundancy systems either focus on multiple back up systems which kick in if one fail or a failsafe mechanical back up allowing the pilot to take over. 

The modern age 

For all the controversies, Airbus’ fly by wire system laid the foundations for the industry. It has now become the standard with most aircraft being fly by wire. As aviation moves into the future, the technology will continue to evolve becoming smaller and lighter. 

Its use will be crucial to the proposed future of electric aircraft. These will require smarter and more integrated controls which are flexible enough to fit into aircraft of all sizes, from small two seater ‘air taxis’ to large airliners. 

With BAE taking fly by wire technology into their submarines it takes on a whole new dimension. Both in the air and in the sea, computers are taking control from humans, making life simpler for pilots and safer for everyone else. 

 

(Written by Tom Cropper, editing by Michael O'Sullivan)

 

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