Gyrocopter Rudder Control & Design

Sycamore gyrocopter rudder controlSycamore gyrocopter rudder control

There have been way too many accidents involving loss of gyrocopter rudder control. This is inexcusable and I cringe every time I read of another one with someone’s pride and joy wrecked. There is no reason in the world that a loss of rudder control should result in an accident, (barring loss of the rudder itself).

Firstly let me say that I am not having a go at anyone here but rather trying to offer some help that may save someone else’s gyro from the same fate, or better still, save some one from injury.

Good gyrocopter rudder directionality

Good gyrocopter rudder control & directionality

Poor design in the gyrocopter rudder control system is probably the biggest culprit, and it can be from the pedals, through the cables and guides to the hinges and rudder itself. Common faults include too much rudder movement, stiff hinges in rudder or pedals, poorly routed and/or binding cables, incorrect cable angles on pedals or rudder horns and incorrectly mounted springs.

First and foremost the rudder should be designed so that it will center itself under ail conditions of normal flight, with the cables free. This is better done aerodynamically but it can be done by mechanical means.

Aerodynamically, an effective conventional fin and rudder will center every time with no problems. A fully flying rudder can be made to self center by using an anti-servo tab, but it needs to be more effective than that found on most tall tails because a tall tail by nature usually has a larger area because of its proximity to the C of M.

As such it needs to overcome the powerful effect the wind has on the larger rudder and the exposed side of the H/S. An H/S that is attached directly to any rudder can suffer from this problem but it can be overcome with sound design engineering. A conventional fin and rudder will also need sufficient fin area to direct the airflow straight over the rudder resulting in insufficient gyrocopter rudder control.

At this point I would suggest that it is always a good idea to have either light springs hooked to the rudder pedals just strong enough to take the slack from the cables, or pedals interconnected with a bell crank or a cable around a pulley, to minimize the possibility of slack cables fowling bolts or other parts of the airframe.

Mechanically, centering a rudder is a much more demanding process to get right. Hooking extension springs on to the pedals or horns will not fix the problem because they simply cancel each other out, leaving a neutral feeling with no improvement in self centering. Springs, if used, should be strong enough to overcome any tendency of the rudder to move off center in flight, and to return the rudder if it is off center.

This could provide considerable pedal pressure in some cases. The springs must be relaxed so that neither is in tension in the center position, and either one or the other will come into play when the rudder is moved off center.

The easiest way to do this is to connect the springs with a short piece of cable, and close the loops on the spring so that they cannot disconnect when they are in the slack position.

Another way is to relax mount the springs on a rod and fix the rudder sliding link in the center to give the same result. Of course the springs have to be the correct rate so that they do not set up a harmonic flapping of the rudder. It is becoming obvious why it is generally easier (and more technically correct) to control the rudder aerodynamically.

The integrity of a rudder can be tested quite readily by any experienced pilot. Like all in-flight testing, it must be done in small increments, starting with simply relaxing the feet off the pedals and noting any untoward behavior. Small sample rudder movements should be made to check auto returning characteristics, leading up to full deflection and release.

The rudder should always return to center, and be such that you could fly any journey with your feet off the pedals. As such, the rudder will gently “float” the gusts giving a more directionally stable and comfortable flight. Ultimately the gyrocopter rudder control tests should be carried out under all conditions likely to be encountered, including engine out. All Gyros should have full rudder control at all times.

VISIT: ASRA (Australian Sport Rotorcraft Association)

Stable gyrocopter design

Stable gyrocopter design

Gyrocopter Rudder Control
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Gyrocopter Rudder Control
There have been way too many accidents involving loss of gyrocopter rudder control. This is inexcusable and I cringe every time I read of another one with someone's pride and joy wrecked.
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