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I am trying to determine the plausibility of a larger, broad question using a modified plane equipped with a modified E-fan and external electric ultra light weight rail. The power would be collected from the rail by Laser Induced Plasma Channel. The problem is to stay a safe 3-7 meters from the sky rail during flight because of turbulence.

Is there a plane or guidance system that can ensure a smooth and straight line of flight without any shift in position because of turbulence?

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    $\begingroup$ Short answer, no. You will never be able to guarantee 3-7 metres unless you have some physical restraint. A heavier than air machine generates lift by moving through an airmass and must move with that airmass. If you encounter a downward moving column of air, then you must move down with it because the angle of attack, and therefore the lift, is reduced. $\endgroup$
    – Simon
    Sep 12, 2016 at 17:07

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There are currently no production anti-turbulence devices or control systems that I know of. It should however be noted that auto-pilot (to an extent) will hold a course in turbulence within a margin but will or may constantly be auto-correcting. However there is some research going on at RMIT into the matter and it looks like they have at least a small working prototype. The issue you have in the matter is positive control, to avoid turbulence and/or be ready to correct for it before it happens you need to be able to see it/predict it ahead of time. There is some more research going into Laser based Radar systems for detecting clear air turbulence but as far as I know nothing has made it to market. So yes it may be/is almost possible but the systems are still in research and development at best.

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    $\begingroup$ +1 also the FBW of the 787 has Gust Suppression, it gives smoother ride but doesn't cancel out the effects. The direct-lift control of the L-1011 may also have been used for a similar thing in addition to its main function in holding the attitude steady during approach. $\endgroup$
    – user14897
    Sep 13, 2016 at 15:28
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I can only answer the second half about guidance systems from a controls system approach. Turbulence is movement through the air and constitutes a disturbance to the system. It's like trying to walk in a straight line when the ground is moving. Any control system can mitigate the impact of the changes by noticing a deviation from the desired attitude or path and correcting, but it can't do so until the deviation occurs. Perfect tracking always requires seeing the future (a non-causal controller, in technical terms) to tell how you're going to have to adjust to stay 100% on course.

If you can't track the target perfectly, you could do a decent job of compensating for errors, also called "disturbance rejection" in control system theory. The biggest issue here is that the disturbances are very big, enough to knock airplanes hundreds of feet off path in a matter of seconds. We can always reduce the maximum deviation from course by making the controller more aggressive, but we run into the limitations of control systems very quickly:

  • there are physical limits to the system like mechanical reaction time and corrective force available
  • the more aggressive a controller is, the difficult it is for it not to be unstable and go out of the desired bounds under certain conditions
  • more aggressive controllers traditionally have increased overcorrection (overshoot) and bouncing back and forth (ringing).

In summary, you'll never achieve perfect tracking without seeing the future, but you can reduce the amount of bumps from turbulence with a very well designed and very aggressive control system. In my opinion 3-7 m tracking would be very difficult in turbulence. Typical modern auto pilots barely achieve 50 m tracking of altitude in turbulent conditions in my experience.

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  • $\begingroup$ What if you had a rail to follow above the aircraft. Like flying just off the ground, but just under the rail? Air speed would be at 500 mph to 1500mph. Also after researching the margin can be from 2ft to 10 meters. $\endgroup$
    – user20435
    Sep 13, 2016 at 19:23
  • $\begingroup$ I'm giving all low rep users +3 for giving an effort on answering my low quality questions. $\endgroup$
    – user20435
    Dec 18, 2017 at 2:44

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