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new design

My friend and I recently prototyped this radical new design for a helicopter. In this design, instead of using the main rotor to control the pitch of the helicopter, there are two other auxiliary motors at the tail rotor. This means that the main rotor doesn't tilt in any way to control the helicopter, it only controls the altitude. For the yaw, there would be another motor at the tail rotor area. Is this even feasible? Even at a model scale?

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  • $\begingroup$ Why two vertical tail rotors? One would surely be sufficient? $\endgroup$
    – Sanchises
    Dec 26, 2022 at 12:30
  • $\begingroup$ This is technically a tandom rotor en.wikipedia.org/wiki/Tandem_rotors with the second rotor on a long lever arm and scaled down. It can probably work in scale model but as drawn is will lack roll/lateral control. $\endgroup$ Dec 26, 2022 at 12:53
  • $\begingroup$ You'll be relying entirely on the "pendulum effect" to keep it upright, it appears (much like this -- youtube.com/watch?v=f4cAylbWvmU ) $\endgroup$ Dec 26, 2022 at 13:36
  • $\begingroup$ Roll control is missing. There is no pendulum effect with fixed rotors. $\endgroup$
    – U_flow
    Dec 26, 2022 at 13:37
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    $\begingroup$ Not as drawn. There is a fundamental problem that would make directional flight impossible. It looks to me like one of your design goals is to simplify the main rotor hub by eliminating the complexity of the cyclic mechanism by having a fixed hub, and you modulate only rotor RPM. This helicopter could theoretically hover, but once in directional flight (presumably forward) an entirely fixed main rotor hub without any cyclic mechanism would have no means to compensate for the difference in lift produced by the advancing and retreating blades. It will roll into the retreating blade. $\endgroup$
    – Max R
    Dec 26, 2022 at 14:52

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It should be feasible (with some modifications). And unfortunately is not radical nor new: Any RC helicopter toy without swashplate is controlled in a similar way, like the one in this picture (source):

enter image description here

Here the two contra-rotating main rotors produce the thrust to lift the helicopter and they balance their own torques.

To make the thrust pointing forward and give the helicopter a forward speed, the small rotor on the tail is activated so that it generates an upward thrust: this produces a nose-down pitch which makes the helicopter and the main thrust tilt forward, producing therefore also a forward force. If the rotor on the tail is activated to generate an downward thrust, it makes the helicopter and the main thrust tilt backward producing this time a backward force. This part is similar to your idea.

Yaw is controlled making the two main rotors rotate with a slightly different speed. In your case the yaw is controlled via a third rotor, much like a conventional helicopter.

Obviously there's no means to tilt the helicopter with its thrust to the right or left, so lateral movements are not possible.

As also pointed out in some comments, stability might be an issue. Thanks to the rotors on the tail, you might be able not only to manoeuvre but also to keep it stabilised in yaw and pitch but only if its own proper movements around those axes are not faster than your reflexes. Anyway, as already said, in roll there's no way you can control and stabilise it. A mechanical stabilising bar like the one in the picture is therefore necessary.

Another problem is the dissymmetry of lift that would make the helicopter tip over as soon as it moves somewhere horizontally. To avoid this, the blade shouldn't be rigidly connected to the rotor head but free to flap either via an hinge or making the blade's root soft.

So, taking into account these modifications, at the end you obtain an RC helicopter just like the one in the picture I posted :)

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  • $\begingroup$ Does this question, and associated answers, suggest that the stability dynamics of the helicopter in your picture are considerably different than the one in the question? aviation.stackexchange.com/questions/64969/… $\endgroup$ Dec 26, 2022 at 13:29
  • $\begingroup$ @quietflyer: for sure not, the same stabilising bar might be needed, but the general idea isn't something new and should be feasible. $\endgroup$
    – sophit
    Dec 26, 2022 at 13:36
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    $\begingroup$ I’d recommend being more specific in your answer. The design you show is feasible because of the unique characteristics of counter-rotation, which is absent in the concept. As I mentioned in another comment, the counter-rotating blades don’t just simplify the design by eliminating a tail-rotor gearbox; They simplify the design by countering asymmetric lift. Without counter-rotation, you have two problems to solve, not just torque. $\endgroup$
    – Max R
    Dec 26, 2022 at 17:22
  • $\begingroup$ @MaxR: you're right, I actually wanted to expand that part of my answer but it's always a bit difficult to understand when it gets too long, technical and boring... Maybe I'll link some other answers dealing with those topics. $\endgroup$
    – sophit
    Dec 26, 2022 at 19:08
  • $\begingroup$ @sophit just to be clear. The design the question poses is not feasible. It possesses no roll stability, an no means to counteract. I am sure that you are aware, that this is due to the fixed propeller. The design which you link has fly bars and flexible linking of the blades which is part of its stability concept. The proposed design lacks these features. I propose that you modify your answer accordingly. Because your first statement is wrong. The proposed design is not feasible. $\endgroup$
    – U_flow
    Dec 26, 2022 at 21:00

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