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So, I was looking at an image of a Bell UH-1N, and noticed that the top if the rotor has a little stick or rodthis image

What is this rod for? I also see this rod on a RC helicopter.

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lpydawa
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1 Answers1

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It is a stabilizer bar used on some two blade helicopters. The spinning weights want to stay in one plane and are used in conjunction with the cyclic to control changes in pitch and roll. Depending on how it is designed, it counters these changes making the helicopter more stable (less maneuverable).

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Pilothead
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  • Means its less input needed on the pilots side? – lpydawa Sep 01 '18 at 14:26
  • @lpydawa Means slower response, so less twitchy. – Pilothead Sep 01 '18 at 18:46
  • is it to reduce the chance of pilot induced oscillation? – lpydawa Sep 01 '18 at 22:55
  • @lpydawa PIO results from overcontrolling, so a slower response from the aircraft probably makes PIO worse. – Pilothead Sep 02 '18 at 00:31
  • why would they want a slower response then? – lpydawa Sep 02 '18 at 00:32
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    The bar is a gyro which wants to remain level. Its action on the rotor blade pitch angle mechanism causes the rotor itself to tend to seek a level plane of rotation, absent any input from the pilot's linkage, giving the helicopter's rotor a bit of stability it wouldn't normally have. You could call it a "self-leveling servo" device. So as Pilothead says, less twitchy, and a bit less tendency to wander off in any direction at any time. In the Huey Cobra, which is based on the same machine, the bar was done away with because responsiveness was a priority. – John K Sep 02 '18 at 00:53
  • @lpydawa What John said. It is a design choice, like how trucks handle differently than race cars. If you let go of the steering wheel of a truck it will go straight until it runs out of gas. If you let go of a formula1 wheel, the first crack in the pavement will send it into the weeds. – Pilothead Sep 02 '18 at 01:04
  • @lpydawa To avoid over-controlling the helicopter. To provide more generic in flight stability. See this answer about stability versus maneuverability. – KorvinStarmast Sep 02 '18 at 15:20
  • @JohnK that looks like a separate answer – Federico Sep 03 '18 at 08:29