Hey everyone,
I'm currently doing a case study for a uni course on Digital Fly-By-Wire (DFBW). Whilst researching I began wondering what the pilot's community view would be on the technology. Firstly a couple of facts for those who haven't a clue what I'm talking about:
1) In a DFBW aircraft, the stick/yoke (I'll use stick) is not connected to the controls directly, but rather acts as an input to a series of computers which take into account a range of parameters including (but not limited to) the airspeed, altitude and vertical acceleration (g's) and decides on an appropriate control surface position that would satisfy the pilot's request.
2) The stick now takes on a different role in the aircraft. When the stick is moved sideways, the computer interprets this as a request for a particular roll rate rather than a control surface position like in traditional mechanical/hydraulic control systems. The only exception is when the stick is centralised, this is interpreted as wings level and the computers will again solve complex differential equations to determine suitable control surface positions which will accomplish this. If you've ever watched any fast jet coming into land, you will have seen this illustrated. The elevators (which also act as ailerons) appear to 'twitch' as the plane is coming in to land. This is not because of the pilot, but rather a perfect example of the DFBW computers constantly chasing 'wings level' by adjusting control surfaces. All the while the pilot may be sitting there with the stick centralised.
3) As far as vertical (pitch) control goes, the stick is a 'g' setting, with centralised as obviously 1g and max aft position may be the maximum rated g for the airframe, or a little bit more. Depends on the aircraft. It should also be noted that this negates the need for elevator trim in the aircraft. Once a nose attitude is set and the stick centralised, it will maintain that position until the next input from the aircraft.
4) Power-By-Wire is also known as Full-Authority-Digital-Engine-Control (FADEC) this is where the throttle takes on the role of a power setting rather than a butterfly valve position. Mixture, Propeller setting and throttle setting are all computed by the computers to find the optimum settings for the requested power from the pilot.
The first (and rightly so) concern most pilots will have is system reliability. Typically these DFBW systems are quadruplex systems, meaning that 4 independent computers all create the same data independently. If one computer creates erroneous data (due to any number of reasons) that disagrees with the other 3, then it is 'voted out' by the others and disregarded completely.
The benefit of such systems are typically; reduced dry weight, ease of transition between similar types (using DFBW, it should be possible to make all the Tecnams, Jabirus etc 'feel' the same) and a reduction in pilot workload (due to the lack of need for things like trim inflight)
Also, usually the computers used for FADEC are separate to DFBW, but I may be wrong about this.
My main reason for asking is, with computers getting smaller and more powerful at an exponential rate, it is only a matter of time before this technology is possible in light aircraft. The Liberty XL-2 already has the world's first FADEC system in a light aircraft; the Embraer Phenom 100 (a 6 seat very-light-jet) has a some-what limited DFBW system as well as FADEC. It is coming.
I can't wait to see how this technology is currently percieved by the pilot community.
Cheers,