Storm & High winds, Part II
There are a number of places on this planet where, if you would park your aircraft, you need to take extra measures to make sure the aircraft survives the weather or high winds. Airports close to the sea or large bodies of water, and for example in New Zealand when north-westerlies are blowing or locations where tornadoes are common, are known for these dangers. In fact, small aircraft parked outside during high winds or storm will need some form of protection against the elements.
Any aircraft parked outside should be secured after all operations for the day are finished, and if necessary between operations. This will make sure that your aircraft is safe against unpredicted local weather. High winds can cause for thousands of dollars of damage to aircraft, sometimes even beyond repair. These claims ultimately result in higher premiums for the owner and we should do everything to avoid this.
Securing the Aircraft
When selecting a suitable tie down site make sure to allow for enough wingtip clearance and check to see if aircraft close by (or any other object for that matter) are secured properly. It would be a shame, after having your aircraft tied down properly, to find it the next day with another aircraft parked on top of it...sort of.
The aircraft should be parked and tied down as nearly into the wind as possible. Make sure to check the weather forecast to see the prevailing winds if you must leave the aircraft parked outside for a longer period of time. Do check on it from time to time. Sometimes it can be handy to dig holes in front of the wheel and park the aircraft in it. This blocks the wheels and in case of a taildragger it lowers the wing and angle of attack for the incoming wind.
These are used to lock the flight controls and prevent them from banging against the internal stops and thus damaging the system. If there is no internal control lock then use an external one. Sometimes it pays to always use external control locks as the internal type locks at the steering column (Cessna) combined with play in the system makes the control surfaces move in the wind. This could cause damage. Any large enough external locks relieve the system from any stress by the wind.
Tail draggers should lock the elevator up when parked with their tail down and nose in the wind. All others lock the elevator in neutral. Set parking brake and chock the mail wheels.
Doors, windows and other openings like hatches must be closed and locked. Engine cooling openings, like intakes and exhaust, oil coolers should be covered to prevent the entry of debris. Do not forget to cover the pitot tube.
Topping off the fuel tanks increases the weight of the aircraft, this adds mass and stability during gusty winds. Make sure the fuel tank caps seal properly, to prevent the ingress of water during heavy rain. Adding sandbags inside of the aircraft could help as well.
Tying down the aircraft
Knots are used to tie the rope to the aircraft and ground anchor, they could be the weakest link. Ideal, the knot must not slip or loosen whilst easy to undo. If a knot fails it does so through vibration and movement when there is too little load on it or break when load is applied and finally a knot can pull out when a load is applied.
Tie down knots
The strength of a knot is by design, some are stronger than others. Security of a knot is determined by the way the end of the rope is finished or locked in the knot. Secure knots as necessary and not as secure as possible. The US FAA has published AC 20-35C tie down Sense, with tips on aircraft tie downs. Read FAA AC-20-35 part one and FAA AC-20-35 part two.
Use the proper tie down rings to attach the ropes to the aircraft, never tie down an aircraft at the struts as they will collapse during heavy gusts. Aircraft parked near the sea have a increase risk at corrosion, check the tie down rings during regular maintenance for proper fit and remove any corrosion. When gusty winds are predicted it helps to tie down the nose wheel too at its tie down ring.
The ropes should extend from the tie down ring to a position one meter forward and two meters outboard to the under wing attach point. The middle of the tail tie down rope should be attached under the tail section with a knot and each end of the rope at an angle of about 45° to the ground anchors. This keeps the tail fixed in one position so it will not move about. While tying down the tail, make sure the nose wheel doesn't lift off the ground.
Do not over tighten the ropes but keep some tension without too much slack. This will not over stress the tie down rings and structure of the aircraft.
As aircraft are meant to generate lift while the wind is blowing over the wings, this principle is undesirable in bad weather conditions with the aircraft parked on the ground. The use of spoilers on top of the wings can help to spoil the unwanted generation of lift. These spoilers should be used when anticipated wind speeds exceed the liftoff speed of the aircraft and attached span wise at 25% chord. You can make them yourself from a piece of 2 x 4 with a rubber strip at the bottom to prevent damage to the wings.