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I understand the function of the cyclic and collective, and I am specifically wondering if anyone has a good image/video showing the mechanism of how the flight control "mixer" works! I can't seem to find many good illustrations of the mechanisms themselves, even a simple example.

Perhaps something like this but clearer, or something filmed in real life?

A simple mechanical helicopter

Edit: I circled the area in question in the picture below. Basically I understand how the cyclic and collective sticks move, and how the swash plate moves, but how do the stick movements move the swash plate actuators correctly?

I think I generally understand what is going on, and I understand what the swash plate is supposed to do, and which direction the swashplate actuators are supposed to move for a given maneuver. But what does this look like in real life? Is it typical to have just two actuators to the swash plate? And in this system it seems like adjusting the collective would make the pilot's control column move? Is it common?

Area in question circled in red

For example, I can understand in this picture that the cyclic stick can move forward and aft (circled in blue), which moves a control rod around a pivot, which lifts the forward actuator on the swash plate. I guess I am mostly confused as to how the collective plays in, and would like other diagrams or images to understand.

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This is an image of a mirrored cyclic linkage as I understood it from @Pilothead: enter image description here

Thanks!

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  • $\begingroup$ Are you talking about the linkage below the rotor in the middle? Can you draw a circle on the area you are talking about on the posted image? $\endgroup$
    – John K
    Jan 30, 2020 at 1:20
  • $\begingroup$ Hey John K, I've added some edits and circled some parts of the drawing! Basically I understand how the cyclic and collective sticks move, and how the swash plate moves, but how do the stick movements move the swash plate actuators correctly? $\endgroup$
    – Gerry
    Jan 30, 2020 at 17:46

3 Answers 3

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The required motion of the swashplate in order to achieve a desired motion of the helicopter is not as simple as your illustration supposes. Due to gyroscopic precession, tilting the swashplate forward does not tilt the helicopter forward but to one side. This video explains how. The principle that pitch and roll can be controlled by tilting the swashplate to get differential lift is also explained.

The collective controls climb and descent. This is achieved by increasing pitch on all blades simultaneously, or collectively, explained towards the end of the video.

enter image description here

In your diagram, lifting the collective uses linkage to raise the swashplate without tilting it as shown by the arrows.

enter image description here

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  • $\begingroup$ Hi Pilothead, thanks for the explanation! So if I understand, the actuators on the static portion of the swash plate are placed 90 degrees from where they should be in the image, correct? Also, as far as I understand if the pilot uses the collective, will he/she feel a change in pitch in the cyclic stick that he would need to correct? Is it a flaw in this diagram, or is it how typical helicopters work? $\endgroup$
    – Gerry
    Jan 30, 2020 at 22:05
  • $\begingroup$ @Gerry Yes, roughly 90deg off. Use of collective does not affect cyclic, though your simplified diagram looks like it would. It does not show any offsetting force which could be provided in multiple ways, as by a mirrored cyclic linkage. $\endgroup$
    – Pilothead
    Jan 30, 2020 at 22:40
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    $\begingroup$ Would you happen to have a better diagram, or one that shows a mechanism where the collective does not affect the cyclic? By a mirrored cyclic linkage, you mean that for this diagram's system, there is a linkage missing that would push the cyclic down at the stick level if the collective is raised? $\endgroup$
    – Gerry
    Jan 30, 2020 at 22:51
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    $\begingroup$ I don't have a diagram, but it is simple. Take the longitudinal cyclic linkage right in front of the collective linkage in your diagram, and mirror it to the rear so that it works opposite to the front linkage. When the collective raises the swashplate, the opposing cyclic linkages cancel out any force because they only move opposite to each other. $\endgroup$
    – Pilothead
    Jan 31, 2020 at 23:30
  • $\begingroup$ I think I understood, and I added a drawing of my understanding to my original post. Thanks! $\endgroup$
    – Gerry
    Feb 1, 2020 at 0:58
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The mixer is mainly found in larger helicopters where their expense is not such a large part of the purchase price. This answer explains more of the function of the flight control mixer: it de-couples degrees of freedom from the control inputs.

The helicopter in OP picture shows unmixed inputs into the swash plate: tilt swashplate forward for longitudinal control, sideways for lateral control, pedals connected to tail rotor only. Picture below is from Principles of Helicopter Aerodynamics by Leishman, and shows a schematic of the cyclic longitudinalenter image description here

Three actuators are connected to the Non-Rotating Plate, which can be tilted and lifted. The Rotating Plate follows the fixed plate, and cyclically pitches the rotor blades so that they adjust their circular path up/down. The swash plate arrangement is quite complicated, as shown in the photo below, from the same book.

enter image description here

The mechanical linkage from the cyclic and collective sticks to the main rotor actuators does have some input summation involved, as the picture below shows (from this source, which indeed calls it a mixer).

enter image description here

There are always three swashplate actuators. The collective stick always deflects all three simultaneously so that the swashplate lifts, while cyclic stick movement deflects one or two in such a way that the swashplate tilts.

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    $\begingroup$ Thanks Koyovis! I guess I had not realized that the term "mixer" specifically referred to a system where the swash plate is not mechanically connected to the flight control stick. I should clarify my question to reflect that I am trying to understand how an unmixed helicopter swashplate receives commands from the control sticks. $\endgroup$
    – Gerry
    Jan 30, 2020 at 18:51
  • $\begingroup$ @Gerry Mixers can be mechanical as shown in your diagram. All this means is that multiple control inputs, like cyclic and collective, are 'mixed' together to get a different set of outputs, like swashplate height and angle. The horizontal bars in your large blue oval are the mixers, actuated on one end by the cyclic and the other by the collective. $\endgroup$
    – Pilothead
    Jan 30, 2020 at 20:07
  • $\begingroup$ Makes sense! So if the pilot uses the collective, will he/she feel a change in pitch in the cyclic stick that he would need to correct? I do not fly helicopters so I don't know if that is normally the case. $\endgroup$
    – Gerry
    Jan 30, 2020 at 22:01
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    $\begingroup$ There is some interaction between the flight controls, not very seriously. Particularly noticeable in large helicopters with long linkages from stick to swashplate - when collective is pulled, some feedback force can be felt in the cyclic, easy to overrule. Never the other way around. $\endgroup$
    – Koyovis
    Jan 31, 2020 at 0:52
  • $\begingroup$ Well that was a revelation to me! I had no idea that the controls were not completely "decoupled" and was really shocked. I suppose that despite that, the helicopter is still controllable. Thanks for clarifying Koyovis! $\endgroup$
    – Gerry
    Jan 31, 2020 at 16:38
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Video worth watching

YOUTUBE - hydraulic system test of Mi-24 rotor hub

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