Why tiny helicopters are so hard to fly


Tiny remote control helicopters have become all the rage in the last few years as lightweight motors and materials have plummeted in price. But if you’ve ever played with one, you’ll know how hard they are to control.

That’s not the result of poor construction. Small helicopters are harder to control than big ones because of the laws of physics: moments of inertia drop in proportion to the fifth power of vehicle size. This gives small helicopters quicker response times, making them more agile. But the real killer is that the main rotor tip speed in a small helicopter is the about the same as it is for a large helicopter. So the ratio of the rotor moments to the moments of inertia can become huge and unmanageable.

That’s when you need to develop a model of helicopter dynamics so you can design remote control systems or an autonomous flight control system that can manage this agility, say Hardian Reza Dharmayanda and pals at Konkuk University in Seoul, South Korea.

And that’s what they’ve done in this paper: built and tested a control system for a Yamaha R-50 helicopter, which uses a two-bladed main rotor with a Bell-Hiller stabilizer bar. The next step, they say, is to make the helicopter fully autonomous using their model.

These guys may be re-inventing the wheel but it’s interesting to see how they’re doing it.

Ref: arxiv.org/abs/0804.4757: Analysis of Stability, Response and LQR Controller Design of a Small-Scale Helicopter Dynamics

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