1. Technical The Vigilant Tailwheel © Crown copyright 2014. No part of this presentation may be reproduced without the permission of the issuing authority. The views expressed in this presentation do not necessarily reflect the views or policy of the MOD. CGS Ground School

2. Basic operation On the outside of the aircraft the Vigilant tailwheel is quite a simply structure consisting of a tail fork and a tailwheel. Inside the aircraft however is a more complex system that provides tailwheel steering. This presentation concentrates on the internal system. The Vigilant tailwheel provides steering proportional to rudder movement up to 30° deflection either side of centre. When deflected beyond 45° it will ‘break out’ and act as a caster. When this break out occurs the directional control of the aircraft is due to the rudder (aerodynamic forces) and the mainwheel brakes (independent operation).

3. Parts of the tailwheel assembly Viewed from above Control rod from rudder pedals Pivot flange (attached through the fuselage base to the tail fork) Front lever Rear lever Lever connecting springs Engaging spring Rudder connection

4. Operation up to 30° If the left rudder pedal is pressed the control rod will move rearward. This turns the rear lever clockwise. Through the spring connection this clockwise motion is translated to the front lever. The front lever is directly connected to the tailwheel and moves it in the appropriate direction to start a left turn. The rudder connection moves forward which deflects the rudder to the left.

5. Operation beyond 30° If the tailwheel angle exceeds 30° the springs linking the two levers will contract and expand accordingly. To understand what happens next we need to view the front lever (cross-section), the pivot flange and the engaging spring from behind. As the angle increases beyond 45°, the engaging spring is compressed to allow the front lever to move up. This exposes two small lugs on the underside of the front lever that normally sit in recesses (detents) on the pivot flange. With the two lugs exposed the tailwheel is free to rotate. When this happens the lever connecting springs regain their original shape and reset the front lever to the same angle as the rear lever. The tailwheel is prevented from locking back in to place 180° out because the detents and the lugs are slightly offset. Thus meaning that it will only re- engage when the wheel is pointing inline with the front lever. When it does re-engage it does so with a noticeable ‘clunk’.

6. Unserviceabilities Easy breakout If the lugs or the detents are worn the retaining spring will not require as much vertical compression to allow the lugs to disengage and therefore allow the tailwheel to “breakout” much easier. Likewise if the retaining spring is weakened, it will tend to disengage much easier. Difficult breakout If the connecting springs are worn or too slack they will allow too much tailwheel movement before breakout is achieved. Likewise, if the retaining spring is too stiff or corroded it will be very difficult to achieve breakout.

7. THE END Any Questions?