Down Your Airplane
When the gusts are large, and the wind
direction is just right, airplanes by nature will try to lift off.
Each year numerous airplanes are damaged by windstorms due to
negligence and improper tiedowns, according to the FAA. Due to the
large number of airplanes in attendance, tiedowns are required at EAA
Airplanes should be tied down with
equipment capable of withstanding sufficient tensile forces. The FAA
recommends tiedown anchors for single-engine aircraft should each
resist 3,000 pounds or 4,000 pounds for multi-engine aircraft. The
weight alone of a multi-engine aircraft will not protect it from
Several types of anchors are available
for tiedowns. EAA does not recommend the "doggie ring" style
that can quickly fail. The triangle-shaped top portion straightens
under heavy loads and the anchor can easily be pulled from the ground.
Screw-type tiedowns are also not recommended. Both the auger and
spiral style loosen the surrounding dirt as they go into the ground,
weakening their anchorage. Cable anchors (straight stakes with one
helix at the end), however, make good tiedowns because of their
The best anchors are multi-pin anchors
that consist of several stakes entering the ground at different
illustration 1). These anchors can easily be constructed as shown
in the August
1993 issue of EAA’s Vintage Airplane magazine.
Effective tiedown anchors can also be
made from ½-inch diameter steel rods with a minimum length of 18
inches. The stakes should angled away from the airplane and be driven
all the way into the ground at an angle of at least 30 degrees. All
anchors should be placed outwards from the aircraft, not directly
underneath the wing (see
Effective tiedowns also depend on the
quality of the rope. The best ropes are UV-resistant braided nylon or
dacron. Manila ropes are not recommended because they shrink when wet,
are subject to mildew and rot, and have considerably less strength.
All ropes should be regularly checked for damage due to chafing.
Planes should be tied down only at the
tiedown rings. Tying rope to a strut can cause damage and may bend the
strut. The tension of the tiedown ropes should allow for one inch of
movement. Too much slack allows the aircraft to jerk against the ropes
and can cause structural damage. The jerking motion can also pull out
or damage the tiedowns. Tight tiedowns impose inverted flight stresses
that many aircraft are not designed to withstand.
A tiedown rope, however, holds no
better than its knot. Antislip knots, such as a bowline or a square
knot are recommended (see
illustration 3). For maximum strength, tie ropes through the loop
of the anchor and around the stake.
Along with tiedowns, it is a good idea
to fully secure your plane whenever it is unattended. Secure all doors
and windows to avoid interior damage. Engine openings (intake and
exhaust), and pitot-static tubes can be covered to prevent damage and
debris from entering.
Locking or restraining flight control
surfaces can prevent damaging movement. For airplanes not equipped
with integral gust locks, external padded battens (control surface
locks) can be positioned or the control stick and rudder pedals inside
the cockpit secured.
While it is important an airplane is
properly tied down, it may still be in danger if its neighboring
planes are not secure. Sharing tiedown information with other pilots
will protect their airplane, as well as your own.
For more information see the FAA
Advisory Circular #20-35C titled "Tiedown