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Watching videos of screw-propelled vehicles, I came across this one, where at some point (2:15 to 2:40) there's one weird steering/yaw reversal:

While driving forward in a swamp, thrust comes from left screw and right screw isn't spinning. Yet the vehicle steers to the left. Then left screw is stopped and forward thrust applied to the right screw, yet the vehicle yaws to the right.

how comes it does not turn left between 2:15 and 2:20? It's basically plowing straight forward rectilinear with one screw not spinning at all. that's what i don't get.

I fail to understand that particular behaviour, why does this happen?

for what it's worth, automatic subtitle english translation tells about early development steering issues that's solved only while driving in reverse.

Maybe watching the whole video and not focusing on that particular sequence highlights the nonsensical of that particular sequence.

It shouldn't be able to switch from reverse port thrust to reverse starbord thrust while still happily moving forward as a whole system. Drag should stop it almost instantly

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  • $\begingroup$ Is that screw reversing? $\endgroup$
    – Weather Vane
    Commented Dec 9 at 20:26
  • $\begingroup$ @WeatherVane yes probably. yet it looks like there's only forward thrust during that particular sequence. ( vehicle moves fwd on a straight path with one screw not spinning, even steering towards opposite direction) $\endgroup$
    – user721108
    Commented Dec 9 at 20:35
  • $\begingroup$ We can't see the the RH screw at that point, but because the craft is turning on a sixpence, suspect that it's in reverse thrust. Like you do in a canoe: you can pull with that paddle, or drag with it. $\endgroup$
    – Weather Vane
    Commented Dec 9 at 20:39
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    $\begingroup$ And also, bear in mind the "wagon wheels turning backwards" effect. And from the side, you can't really tell the direction of the craft very well. You'd need to be on it to appreciate its motion. $\endgroup$
    – Weather Vane
    Commented Dec 9 at 21:27
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    $\begingroup$ @WeatherVane thanks for your helpful insights btw $\endgroup$
    – user721108
    Commented Dec 9 at 21:58

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I can only offer some comments, which may or may not be useful. According to the offscreen voice in Russian, initially the vehicle's control was poor, but it improved when they started to use a screw with the "right" helix on the right and a screw with a "left" helix on the left. So I believe that, as a result, the total angular moment when moving forward became zero. If the angular moment is not zero, turning the vehicle to the left or to the right can become tricky due to conservation of the angular momentum.

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