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Comment by lutusp | Hacker News Reader

> By the way, are there some kind of autopilots on modern amateur planes?

By "amateur planes" do you mean ultralights or experimental homebuilts? The answer depends on which -- an ultralight could hardly tolerate the extra weight that a decent autopilot would require. And most experimental homebuilt owners probably want the pleasure of actually flying their planes.

Autopilots are more attractive to people who fly long distances and not for pleasure. I had a Mooney 201 years ago that I would fly on business, and the flights tended to be long and a bit boring, so I had an autopilot installed.

Picture of me putting my bicycle in the backseat of my Mooney: http://i.imgur.com/R5qVo.jpg

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>an ultralight could hardly tolerate the extra weight that a decent autopilot would require

Where does most of the weight come from in an autopilot?

Equipment to move the control surfaces automatically, I'm guessing. (I think the most common setup is to have a motor move the trim controls, and I'm not sure ultralights even have trim.)

I would assume the actuators to actually control the plane. I doubt ultralights are fly by wire.

Oh, that makes sense, although I guess I'm a bit surprised that FBW isn't common with ultralights, given its advantages.

I'm not aware of of any aircraft costing less than the 8 figures equipped with FBW. It's a LOT of added complexity/cost for very little gain in anything that isn't either dynamically unstable (e.g. modern military aircraft) or so large that the flight controls can't be comfortably operated by hand, and is rare even in the bizjet and smaller airliner market.

On all small aircraft (and some larger older ones, DC-3s for instance), muscle is the only thing that moves the control surfaces. They're very well designed and counterweighted so that the required effort is quite minimal.

In the US an ultralight has to be under 254 pounds and does not require any training or licensing to fly. In most other countries an ultralight is more like the sport class in the US.

At 254 pounds you want light and simple. FBW requires actuators. And controllers. And sensors. And power. And then you have to double up everything for redundancy. You would easily eat up 50 lbs or more making a reliable FBW system and it would cost 3-4x what the entire aircraft cost.

Even with normal light aircraft a FBW system is both unneeded and overly complex. Cables and pulleys are extremely reliable. They are inspected every year (along with the engine and various other pieces of the aircraft).

This is completely destroying my sense of living in the future. I have no choice but to delete this discussion from my memory.

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