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TIE-DOWN FOR SAFETY



In the aftermath of unusually strong winds wreaking havoc on metropolitan areas, television weather reporters like to show downed trees and power lines, bare roofs where shingles used to be, and kid’s tricycles lying crippled in neighbourhood streets. They also like to show inverted aeroplanes lying on the ground at local airports, with their undercarriages pointing awkwardly towards the sky. Can owners do a better job anchoring their aeroplanes to the ground? Walk along the flight line at any local flying club, and you’ll always spot the ones looking to be wrestled from their dormancy should winds unleash a destructive fury. A flight isn’t finished until the aircraft is properly and securely picketed. Here’s a few things to think about when bolting the aeroplane down.

A tricycle-gear aircraft tied down with its elevators in the “up” position – as may occur when tying a control stick back using the seat harnesses of the cockpit – may allow strong on-coming winds to push down on the tail. A consequence of the wind’s power acting downward on the tail is an angle of attack being induced on the main wings. The lifting force that’s generated by the wind as it slips underneath the exposed leading edge of the wings, in turn, puts greater strain on the tie-down ropes and their respective fastening points. Gust-induced wagging of the tail can hammer the aircraft from side-to-side too, causing twisting and stretching of the ropes even more, pushing them to their limits of tensile strength.

Merge the above scenario with an aircraft parked with one aileron “down” and the other “up”, and an exacerbation of matters could readily lead to the aircraft dancing away from its moorings. Simply put: a fixed aircraft with its tail being pushed down and around, and one wing being pushed up, is a prescription for it to end up on its back. On tricycle-geared configurations – especially if facing into the predominant direction from which the wind blows – elevators should not be left in the “up” position, nor should ailerons be “up” or “down”, as it invites weather storm post-mortem news broadcasts that make aircraft owners shutter.

For greatest prudence, use external control locks to hold control surfaces – ailerons, flaps, elevators and rudder – in their neutral positions. Clamps – be they from the manufacturer, a pilot supply shop, or improvised in the basement of one’s home – can slip between the fissures separating flaps and ailerons to keep the latter properly in place. Locks of some sort or another – be they pedal-mounted or external – can ensure the rudder remains immobile too. A locking pin through the control yoke where it extends from the instrument panel is a popular means to freeze the position of elevators.

A caveat should be appended to the use of internal locking devices. Gusts and forceful winds can exert pressure on the various control surfaces, moving them within any slack that may be present from the imperfect fit of the internal locks. Over time, such forces can stretch control wires that, in worst case scenarios, lose their factory-set tension in later life and hasten their risk of control surface flutter.

A stool, or carpenter’s bench, under the tail is a simple, (though not necessarily elegant), solution to keep a tail from moving down if, with seatbelts holding a control stick aft, elevators are positioned “up”. In snowy winter months, an aircraft sitting idle awaiting the song of Spring, sits best with snow on its wings: the extra weight helps secure it if winds blow stronger than normal, while snow also acts as a “spoiler”, killing the generation of lift.

Chocks placed snugly in front of, and behind, the wheels will help keep your aircraft in the same place as you parked it. Tie-down ropes should be made of a high grade nylon, and should only be limited in diameter by the size of the airframe attachments to which they are clasped, tied, or through which they loop. Weighted anchor points buried in the ground are best for latching the rope to the ground; stakes, pegs or corkscrews are adequate, but if the ground becomes saturated with rain, these can easily be pulled out.

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