Another Look At Fly By Wire


As aviation technology goes, nothing is quite so enduring as the steel cable or torque tube as a means of manipulating flight controls. Add hydraulics for big airplanes, but the basic idea has sustained for more than a century.

Is it time to revisit the idea? That’s being done commonly in the automotive world, with drive by wire, shift by wire and throttle by wire. Even ahead of that, fly by wire for military and commercial aircraft is more or less standard. As you may have seen in this video I shot at the University of Stuttgart last spring,the idea of fly by wire for light aircraft is on the horizon experimentally, if not commercially.

Is there a good reason to do it? Right now, I’d say no. As the video shows, the systems are too complex and too heavy and they don’t provide significant benefit over cable-driven controls manipulated by the pilot’s muscles and grey matter. There’s a halfway point here and we’re already there. The high-end digital autopilots that have become standard for new airplanes almost universally have envelope protection, to include bank, pitch and airspeed exceedance protection for the pilot who might be dozing or overwhelmed. There aren’t enough such systems out there to even hazard a guess if they have improved safety or prevented an accident. It may never be possible to have meaningful data on that, even if the idea of envelope protection itself is sound.

In the video, Rolf-Rekke Riebeling explained that one idea the university is exploring is what he called the easy-to-fly airplane. Think of it as an airplane with fly-by-wire controls that the pilot manipulates but which the underlying software is capable of overriding if the pilot gets into trouble, is about to run out of fuel or wanders into restricted airspace. From there, it’s easy to see an aircraft that could be flown by anyone, with very little training or knowledge of aeronautics. This is essentially what a remotely operated quadcopter drone is. It’s fundamentally self-stabilized; with minimal control input, the pilot can direct it where he wants it to go, where it will again park itself, awaiting the next command.

Is this a good thing? Good or not, it’s coming. Personally, I don’t get too wrapped around the axle about lost airmanship skills or the end of the romance of flight. When the internal combustion engine was struggling to replace horse-drawn transportation, I’m sure the hardcore Luddites decried the erosion of equestrian skills … before they bought their first automobiles. Progress has both benefits and a price, but in modern industrial economies, we have firmly decided progress is worth the price.

The larger challenge, in my view, is economic, not technical. As much as we like to whine about the death of general aviation, small airplanes powered by some means or another will always be with us. There may be fewer of them, but they’ll still be out there. If they’re to be some version of fly by wire, the systems will have to be orders of magnitude smaller, lighter and cheaper than they are now; otherwise, they simply won’t have the economic imperative to replace what works: cables and tubes. It’s questionable whether manufacturing volume can ever again support the R&D needed to bring such a system to market unless its costs are dramatically less than what we can envision now. Could be it will be driven by the mass market automation that will transform surface transportation. To a degree, you’ve already seen that. Automotive and consumer electronics volume has driven down the cost of MEMS devices used in GA glass cockpits. Without that volume, they would be either non-existent or unaffordable.