Sunday, 17 February 2013

Helicopter rotor with cyclic control

In 2012, LEGO released the 9396 Helicopter model. While this is a good set, with realistic looking helicopter blades, the blade operation is still far from realistic.

The model includes collective pitch adjustment for the rotor blades. The word collective in this case refers to the fact that the pitch of all the blades change at the same time, collectively. This is all well, however, not really anything new, since this feature was also included in the 852 Helicopter model from 1977!

The key to the success of the helicopter is the cyclic rotor pitch adjustment, usually operated through the pilot's stick. This involves having a swashplate below the rotor, to which there are rods connected to the rotor blades. The rods control the pitch of the blades. As the swashplate is tilted, the pitch of the rotor blades change cyclically through the rotation. This animated GIF explains how the a tilted swash plate affects the cyclic blade pitch:

Animation made by Richard Wheeler (Zephyris) for use in Wikipedia, and uploaded using the GNU Free Documentation License

In the animation, the disc below the rotor is the swashplate.

Using the cyclic pitch control, the lift vector of the rotor can be adjusted. With the cyclic centred, swashplate level, the lift vector points straight upwards. When the swashplate is tilted, the lift vector can be set to point in different directions, e.g., forwards, for normal travel. Or it can point to one side, to allow the helicopter to move sideways, and so on.

This can, of course, be recreated using Technic Lego. As the swashplate, I used a 56 teeth turntable:

In the picture above, the helicopter rotor assembly is fairly similar to that of the original 9396 model. However, I used a 1x15 technic beam as the rotor axle, for rigidity. Using a normal axle is probably a lot simpler.

The top grey part of the turntable is connected to the axle using the grey 1x4 liftarms, to make sure the top part of the turntable is aligned with, and rotates like the rotor axle.  The lower black part of the turntable can be tilted using the three black rods (one sideways, and two lengthwise). The black part of the turntable does not rotate when the helicopter rotor rotates.

Here is a video that demonstrates how the blades operate:

Additional images of the rotor assembly:

As a side note, the 8856 Whirlwind rescue from 1991 had a more usable swashplate assembly. However, the model used this specialized part only to tilt the rotor, not for genuine cyclic rotor control. The 8412 Nighthawk from 1995 also had the same part, and again, only used it for rotor tilting, which is not realistic at all.

1 comment:

  1. Do you think that you could possibly post a tutorial or some sort of clearer image of the rotor assembly slightly disasembled as it is quite difficult to see the very inside of the mechanism