TAILWHEEL LINKS

LAA Inspector Trevor Reed says set up that break-out tailwheel correctly…

The majority of taildraggers use tailwheels that are linked to the rudder, always moving with it, but automatically disengaging to allow full castering on the ground. Setting the tension in the spring linkage is critical for successful operation and there is often an inclination to set the linkage too tight, believing that taking out any slack will make it easier to steer on the ground. Such belief is erroneous – too tight a setting can induce serious problems such as the tailwheel being reluctant to unlock, which can overload the rudder bearings, leading to premature failure of the bearings and pins. If the system is very slack, it can give vague steering with the possibility of tailwheel shimmy.

So, what we have to achieve is a setting that gives full movement of the tailwheel in normal operation, but which allows breakout of the internal locking mechanism when full castering is needed but is not so slack that shimmy is likely. However, it can be tricky to get it right and I am indebted to Mike Mold who has kindly sent me a link to a YouTube posting (https://youtu.be/QtokU8mIDQk) which gives the clearest procedure that I have encountered to date. It comes from the US, but our ‘country cousins’ do things like this so well! However, please don’t copy this chap’s jacking methods, you should never work on an unsupported aircraft; balancing the tail on top of a trolley jack is not acceptable!

The method shown for setting the springs is very straightforward. Raise the back of the fuselage on a trestle, so that the tailwheel is clear of the ground and disconnect the links and springs from the arms on the tailwheel. Move the tailwheel gently one way, say to port, until you feel the resistance of the unlocking detent. Then, making sure that the tailwheel stays put, move the rudder in the same direction until it is fully deflected. Now, with your third hand, connect up the starboard spring so that it is just snug.

The length of the tailwheel steering chains should be adjusted to get the desired tension by either removing or adding chain links and the screwable shackles should be secured by either split pins or locking wire.

OK, that’s one side done. Repeat the process with the other side and the work is almost complete – you need to check a couple of things. Make sure that rudder travel, stop to stop, isn’t impaired by the spring set-up and that the tailwheel arm can’t approach an over-centre situation at full travel, i.e., it cannot go so far around that it will not return to straight ahead as the rudder is moved back to centre.

And don’t forget to carry out a taxi test, with weight on the tail spring the geometry may change slightly, so make sure that the steering breaks only at full rudder deflection, just as it did when setting it up.

Finally, make your logbook entries, including duplicate checks, as you have disturbed a primary control, and get your Inspector to approve your work.

Above The correct setting of the tailwheel break-out spring tension is critical for good ground handling; too tight and it will strain the rudder hinges, too loose and steering can be vague and may cause shimmy. The use of asymmetric ‘Maule’ style springs also helps. Duplicate checks

Technical Leaflet TL2.05, explains all you need to know, as a pilot/owner, about carrying out one of the two independent checks necessary after a control has been disturbed. The rules are quite clear and unambiguous, if an engine or flying control has been disturbed, the checks are mandatory, and both should be carried out by LAA Inspectors. However, if only one Inspector is available, it is acceptable for the second check to be carried out by the owner/pilot or a licensed aircraft engineer. So, what should you do if called upon to carry out a duplicate check? Firstly, you must remember that

Reference

AIRCRAFT DUPLICATE INSPECTION RECORD LAA/IC-DUP Issue 4

Sheet No of

A/C Type

Item No Control/System Registration

Detail of Work Carried Out Serial No

First Inspection by Inspector* (Signature/Insp No/Date)

Second Inspection** (Signature/Authority/Date)

Duplicate Inspections are required whenever engine or flying controls and their systems are disturbed or at the completion of an aircraft build project. The control/system should be inspected for correct assembly and locking and for full range and freedom of movement in the correct sense. Some aircraft have ‘Vital Points’ (such as wing attachment bolts) and whilst not required to have a Duplicate Inspection it may be considered wise to carry out such inspections on Vital Points. The signatory requirements for a duplicate inspection are: *The first part of the duplicate inspection must be certified by an LAA inspector. **The second part of the duplicate inspection may be certified by a second inspector or by a licensed pilot who is a current member of the LAA. When doing so, the pilot must include their full pilot’s licence number with their signature and date as the authority. Alternatively, the second part may be signed for by a licensed engineer, or acceptable equivalent (see SPARS for details). Where two LAA inspectors are signatories, no seniority is implied by the first or second inspection, but convention is that the inspector overseeing the work as a whole will sign the first. The PMR statement must also be signed by the LAA inspector. Duplicate Inspections may be recorded in the aircraft’s log books. Note: All worksheets should be attached or referenced in the logbooks of the aircraft to which they refer and are considered to be part of the aircraft’s legal maintenance record.

such a check is not a trivial matter, it is not just a cursory look, a signature and ‘let’s go flying’. You are being asked to confirm the integrity of the control system that you are checking, including correct assembly and locking, range of movement, free movement and, most essential, sense of movement. Do not assume that, just because the first check has been completed, all is correct. Make sure that you get a clear brief from your Inspector and ask for guidance if you are uncertain.

I recently had to complete the inspection for an engine installation after an engine rebuild. I was the only Inspector on site and had to brief one of the pilots in the group to carry out the duplicate check on the engine controls. As checks go, this was not a particularly difficult set with only the throttle, mixture and hot air controls to be checked. However, apart from checking the wire locking Above When you have to carry out a duplicate inspection, use the appropriate LAA Form, LAA/ IC-DUP, for your records. It can be downloaded from the LAA website. or split pinning, each control had to be operated from the P1 and P2 positions to ensure that, when it got to the engine, each worked in the correct sense and gave the full range of movement to the engine control. An important part of this was to confirm that the outer part of the cable did not move when the control was operated. It was not until I started to brief the pilot, that I realised that what may seem routine to an Inspector, was outside the pilot’s norm and guidance was necessary.

When it comes to recording the checks, there is an excellent form (LAA/IC-DUP) available on the LAA website. While it is not compulsory, this form makes the paperwork easy. It also contains a useful guide to the procedure as a whole.

This article first appeared in the Devon Strut newsletter. My thanks to the Strut and Trevor Reed for permission to use it. Ed. ■