landing gear unfolded landing gear folded

I want to design a rotational lock mechanism for the landing gear of an aircraft. It's function is to make sure the landing gear stays folded when the aircraft is on air and the landing gear's position is not changed due to external forces.

An electric motor will be used.

When the aircraft is landing, the lock will be deactivated and landing gear unfold. For that purpose, I will use this rotational lock mechanism to keep it locked in folded or unfolded position.

rotational lock mechanism

But the problem here is that this is able to rotate only clockwise, which means, once it gets locked the landing gear can't unfold.

To overcome this issue, I want to use a reverse planet gear mechanism, similar to those in automatic transmissions.

reverse planet

I will add a clutch pack to this reverse planet and it will be like an optional path in power transmission route.

When I want to fold the landing gear, the clutch pack of the reverse planet stays deactivated and landing gear shaft rotates in the same direction as the lock wheel does.

When I want to unfold the landing gear, the clutch pack of the reverse planet applies and landing gear shaft rotates in the opposite direction as the lock wheel does.

By using these two mechanisms together, I will make sure the lock wheel always rotates clockwise no matter what direction the landing gear shaft rotates.

I want to know if you guys have a better idea or if there are generally accepted engineering designs to prevent rotational movement. Nothing here is a solid design constraint. I am just brainstorming here. You can suggest a different mechanism for rotational lock.

  • 3
    $\begingroup$ More parts bad. Less parts good. What moves the gear? $\endgroup$
    – Transistor
    Feb 4, 2022 at 22:28
  • $\begingroup$ Electric motor will be used. I know this is too complex and that's why I started this topic. $\endgroup$
    – Kaan
    Feb 4, 2022 at 22:42
  • $\begingroup$ An electrically released spring brake would be simple but you'd need to look at the potential failure modes. I've seen plenty of gear-up landings on YouTube. I've only a passing interest in aviation but I always liked the idea of a backup hand-pump on a hydraulic system. $\endgroup$
    – Transistor
    Feb 4, 2022 at 22:57
  • 1
    $\begingroup$ I'd say if you want the job, research how it's done on actual planes. See if you can find a maintenance manual for something from the 1950's or 1960's. Pulling an idea out of my butt, I'd think bidirectional electric motor via H-bridge, one shaft, two cams. One cam raises/lowers, and rotates more after raising but does nothing; other cam locks while the first cam is doing nothing. $\endgroup$
    – Pete W
    Feb 5, 2022 at 0:20
  • 1
    $\begingroup$ more parts, some fail. look into simple linkage mechanisms to grant mechanical advantages. personally i like how a toggle clamp moves a pivot to zero out a lever arm. $\endgroup$
    – Abel
    Feb 5, 2022 at 17:39

1 Answer 1


Input drive is an electric motor. Output is a slowly and rarely moving landing gear. High reliability is needed. High protection from vibration and shock is needed.

I would suggest a worm drive near the motor - it is low efficiency, high wear, but it is not like the landing gear will retract 50 times a second. It provides one-way energy transfer, it locks by itself. Even against vibration, that could unlock the delicate fence mechanism. It is also cheap and lightweight and gives large gear ratio that is needed for higher force.

For landing gear movement I would suggest rack and pinion. Gear would be much heavier, as it would need to tolerate much higher moment, as leverage is worse. During the landing forces are extreme, and if something can survive it, I think it would be a pinion. Other than hudraulic, thats much more complex. Pinion can bend in extreme case, and still perform its function, where other mechanisms would break or disconnect from the shaft. It also provides large force advantage, that is desirable.

This combination also has much fewer parts, and every part can be made bigger as a result, and chance of problems would be lower.

Better option would probably be a piston, that is much more tolerant to shock. Or a tether that can stretch to absorb the shock. But both would likely requite complete redo of the rest of the plane.

  • $\begingroup$ Thanks for the comment. What I posted here was my first idea and then I changed it completely. I designed a mechanism similar to a ratchet wrench, but on a bigger scale, which is able to do bi-directional locking. Your comment inspired me but unfortunately, it was too late to make a change on the design because I was running out of time. I had to send what I got to the company ASAP. But still thanks. $\endgroup$
    – Kaan
    Feb 10, 2022 at 14:04

Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.