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Airframe and Powerplant

Ropes, Knots, and Spoilers

Tie the airplane out of harm's way Mike Moll flew small airplanes — Piper Super Cubs, de Havilland Beavers, and Cessna 185s — in Alaska from the minute he turned 16 years old until he died in the early 1990s. His father, who also made a living flying in Alaska, taught Moll how to take care of himself and his airplane.

Tie the airplane out of harm's way

Mike Moll flew small airplanes — Piper Super Cubs, de Havilland Beavers, and Cessna 185s — in Alaska from the minute he turned 16 years old until he died in the early 1990s. His father, who also made a living flying in Alaska, taught Moll how to take care of himself and his airplane. You see, Alaska pilots have to know how to safeguard their airplanes — or find the money to pay big recovery and repair bills. Not to mention find a way back home. When the weather trapped Moll, he followed the five-point plan. First, he tried to fly out of harm's way. When he couldn't do that, he looked for a windbreak such as a grove of trees or a hill to lessen the wind's force. Moll was taught that each windbreak must be evaluated for potential hazards. It's better to face the winds without a windbreak than to have the airplane damaged by a wind-blown branch or by a tree blown over on the airplane. Next he pointed the airplane into the wind. Then he secured the control surfaces; and finally, he tied the airplane to secure anchors with good, strong rope, and, in extreme cases, reduced the wings' angle of attack or attached lift spoilers to the wings. The good news for all airplane owners is that it's not that hard to put these five airplane-saving rules into your bag of airplane-care tricks.

Run away

In the movie Monty Python and the Holy Grail, knights and commoners observed yelling, "Run away, run away," when a fight was imminent were admonished to use the more knightly term retreat. Call it what you like, the best course of action when the forecast turns really ugly is to fly the airplane out of harm's way. This is not always possible because many airplane owners have other more important tasks to perform when a big storm is bearing down.

Being able to retreat is one advantage of a flying club or shared ownership — there's more than one pilot available to fly the retreat. Another option is to add a qualified fellow pilot or local flight instructor to your insurance policy so he or she will be able to move your flying flivver to a safer airport.

If retreating is impossible, the next choice is to move the airplane into a hangar until the storm passes. If that can't be done, find a windbreak such as a sturdy building to park behind. If that isn't possible, consider parking a truck or heavy car in front of the airplane — it'll help break the force of the winds and provide an extra tiedown point.

Secure the control surfaces

In my first real cool job in aviation one summer I loaded my tools into my 1961 GMC Carryall and drove from Renton, Washington, to Redmond, Oregon, to maintain two Douglas DC-3 smokejumper airplanes. The DC-3 co-pilots I worked with always counted off seven items before closing the doors and trudging up the sloping floor to their seats before engine start. Two items were the main landing gear down-lock pins — the other five were external gust locks. These gust locks slid into the spaces between the aileron inboard edges and the wing, between the tail cone and both elevator inboard edges and between the bottom edge of the rudder and the top of the tail cone to prevent the control surfaces from banging to and fro on the ground. The gust locks were held in position by bungee cords.

Rule number one is that all control surfaces must be secured after every flight. This is the first place many owners fall down. Some light airplanes, such as Cessna and Rockwell Commander single-engine airplanes, are equipped with rudimentary gust locks that consist of a small pin that, when slid down through a sturdy collar on the pilot's instrument panel, engages a hole in the shaft of the pilot's yoke. This prevents both the ailerons and elevators from moving.

Many small airplanes are not equipped with any provision for locking control surfaces except for pulling the control wheel — or control stick — aft and looping the pilot or co-pilot seat belt around or through it to secure it in position. Again, this is better than nothing, but both the locking-pin and the seat-belt methods put quite a bit of stress on the control system cables, turn barrels, and hardware of each control actuating system, especially if the airplane can't be pointed into the wind.

There's much less potential for damage to flight-control-system components when the control surfaces are secured with exterior control locks. Any Internet search for "airplane control locks" provides a variety of control-lock solutions that use inexpensive materials such as PVC pipe, padded wooden battens, or commercially available products such as the Pad-Lok, which is sold by various suppliers.

Knots and ropes

Just because there's a chain or rope at the tiedown spot where you park your airplane doesn't mean it's strong enough to secure your airplane in a big storm. According to FAA Advisory Circular 20-35C, "Tiedown Sense," the minimum recommended tiedown rope is one that resists a pull of approximately 3,000 pounds for single-engine airplanes, and no less than 4,000 pounds for a typical light twin-engine airplane. A Civil Air Patrol bulletin recommends both ultraviolet-resistant nylon and Dacron tiedown ropes, with Dacron being the first choice because of its ability to withstand chafing. Three-eighth-inch nylon is rated at 3,400 pounds. Three-eighth-inch twist Dacron is rated at 3,120 pounds; one-half-inch braided Dacron is rated at 3,800 pounds.

F. E. Potts owned an air taxi service and flew small airplanes in the Alaska bush for 22 years before writing Guide to Bush Flying: Concepts and Techniques for the Pro. This book is a must have for real airplane enthusiasts. Potts says the only rope he uses is high-quality one-half-inch twisted three-strand mountain-climbing nylon rope. He replaces it anytime it chafes or every two years.

Got the rope? Good. Now for the knots. The advisory circular mentions two knots — the bowline and the square (or reef) knot. Learn to tie the bowline — it's a wonderful knot that can be used for many things. I've never seen anyone with any experience use a reef knot to secure an airplane. Potts likes the bowline to secure his rope to the anchor in the ground and then uses what he calls a "hurricane knot" to secure the rope after running it through the aircraft tiedown ring. Actually Potts wrapped the rope twice around the uppermost end of the wing strut after threading it through the tiedown ring. In his opinion (and mine) Super Cub tiedown rings are too flimsy looking to trust and they should be used only to ensure that the rope does not slide down the strut.

Potts' hurricane knot is tied by taking all the slack out of the rope and applying a slight tension before wrapping the free end of the rope twice around the length of rope between the airplane and the anchor and pulling the second wrap tight so it jams. This wrapping and jamming is repeated twice and then the end is secured down the tiedown rope with a half hitch.

Reducing the wings' angle of attack or installing spoilers

Moll once told me that one storm was so severe that he had to dig holes for the main landing-gear tires of his Super Cub. He reduced the wings' angle of attack by rolling the wheels into the holes. After the storm passed he dug out ramps and taxied the airplane up out of the holes before taking off for home. As all pilots know, lessening the angle of attack reduces the amount of lift generated by the wing. It's a good trick if you're out in the middle of the bush somewhere, but it won't work at a paved airport.

A modern paved-airport equivalent is spoiler boards, which are pieces of lumber (2 inches by 2 inches or 2 inches by 4 inches) that are secured to the top of each wing to spoil lift generated by airflow over the wing surface. The boards are padded with carpet or foam (glue it on to prevent metal fasteners from scratching the wing) and are secured in position slightly aft of the leading edge on the top wing surface. Drill a series of holes through the boards and run a length of nylon cord through each hole. Knots need to be tied on each side of the board to prevent the spoiler boards from sliding aft on the wing, and then the cords are secured to hold the boards in position. Examples of spoiler boards are shown in the advisory circular mentioned previously.

On the ramp

Always take the time to survey the tiedown methods and equipment used to secure other airplanes near the spot you've selected to tie down your airplane. Move away from poorly secured airplanes before tying down. Typical tiedowns on public airports consist of either a pair of parallel steel cables or three ground-level tiedown rings.

The cables — which are more often seen on the ramps of airports located in mild weather zones — are strung approximately 15 feet apart. Each cable is secured at each end and at 30-foot intervals along its length. Airports situated in wild weather zones almost always are equipped with the three ground-level tiedown rings. The chains and ropes provided for aircraft in tiedown areas should be closely inspected for security and condition before use.

It's better to carry and use ropes that you know can withstand the required loads than it is to count on locally supplied gear.

The cables are spaced to provide secure anchors for both the tail and wing tiedown rings. If supplied chains are used, the airplane should be positioned directly over the cables and the chains should be adjusted as tightly as possible so the airplane is permitted to move only as the tiedown cable moves between its anchor points.

When using ropes it's better to position the airplane between two rows of cables so the ropes extend outward from the wing and tail tiedown rings at an angle. Ideally, airplanes should be secured with six ropes — two from each of the wing tiedown rings and two from the tail tie-down ring. For instance, each wing tiedown ring should have ropes radiating out forward and aft from the ring.

The wing tiedown ropes also should radiate out from the aircraft centerline. Two ropes from the tail tiedown ring also should extend aft and outboard from the aircraft centerline. If correctly tied down, the airplane will appear to be captured in the center of a spider web of six ropes.

Tiedown anchors

Potts created secure tiedowns by wrapping steel chain around engine blocks and burying the blocks. There are five or six commercially available portable tiedown anchor systems on the market. These can be located by typing "aircraft tiedowns" into any Internet search window.

According to testing by Aviation Consumer in 2001, none of the portable anchor systems provided the security specified in the advisory circular, but one commercially available kit, and the one that Aviation Consumer rated highest, is the FlyTies kit. New systems have been introduced since the 2001 tests — many type club forums and message boards have suggestions on which kits work best.

If a really big storm whips across your airport and you haven't retreated to safety or at least tried to move your airplane into a local hangar, the only thing that's going to protect your airplane from storm damage is how well you have prepared.

E-mail the author at [email protected].

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