Wing Chapter Supplement
Installation of a Landing Light in Wing Leading Edge
By Bill Schertz, KIS Cruiser #4045
The prototype KIS Cruiser did not have landing lights, therefore the installation
is left to the individual builder. In order to provide some input for future
builders, I am documenting in a "how to" description the method I used for
a landing light in the wing leading edge. This modification is not in
the standard KIS Manual. The information described below is strictly
for the discretion of the individual builder.
I will attempt to explain some of the design considerations that entered
into my choice of method of construction.
Landing Light Choice
Landing Light Location
I had purchased the acrylic lense covers (leading edge shaped) from John
Petrie, in South Africa. They are nicely formed, but I feel that they would
not be too hard to replicate if I need replacements.
I was concerned with the mounting of the lights. They have a threaded bracket
on the ends of the light, and if possible I wanted to use that. I also wanted
to be able to adjust the aim of the lights a couple of years down the road
when I complete the airplane. I was also concerned with heat build up in
the leading edge on the composite structure, therefore I wanted to design
a mounting system that promoted cooling of the lights.
1. After you decide the position, cut a rectangular opening in the leading
edge of the wing. I started 3 inches from the wing-tip joggle, and made the
opening 7.5" long. After looking at the lights, which are 1.75" high, I decided
that the horizontal cuts would be made just at the point where the tapered
foam meets the leading edge skin. This would give me ~1" of bid layup on
the tapered foam, and seemed to "look" right. This is shown in Figure 1 below.
FIG. 1 Opening in leading edge for Landing Light
Since the lights have their "bases" protruding from the rear of the fixture,
I cut a rectanular slot (6" x 1.5") in the front spar. This was sized to
just fit the width of the fixture, and was 1" longer than the light fixture.
I then cut 3 aluminum plates from 0.050" aluminum sheet that I had. The large
piece is 10" x 3.25" with a 6" x 1.5" hole centered in it as shown below.
The two smaller pieces are ~2.5" tall x 3" wide, and are bent to a right
angle to form mounting ears for the lights as shown in the sketch below.
Then cut the edges off of the tongue so that the bracket can slide down into
the slot when it is attached to the light. (See Figure 3 for the view of
the mounting ears attached to the light.)
Figure 3 Landing light components shown
Drill a ***1/4" hole for the mounting bolt in the L-shaped bracket, then
position the assembly, with the aluminum backing plate in place, into the
leading edge opening. While everything is in place, drill for the 8-32 screws
that will be used secure the light. The L-shaped bracket is wider than the
slot in the large aluminum backing sheet, so it overlaps the excessive length
of the slot, and covers it nicely.
Remove the assembly and use a 3/8" drill to enlarge the holes for the rubber
grommets in the back aluminum plate. These are there to space the Al plate
out from the front spar, and allow cooling air to circulate. The mounting
nuts were standard fiber-retaining nuts, (visible in Figure 1) which are
bonded into the holes with micro-flox. There is not sufficient room to get
a rivet squeezer into place to place the rivited nuts. The net result is
an assembly that has the light suspended on the two aluminum ears, which
are separated from the aluminum backing plate by the grommets, which is separated
from the composite spar by the other side of the grommets. This provides
a longer path for any heat to be conducted from the lights to the composite,
and should limit the temperature that the composite material sees to something
Fabricating the Flange
John Petrie (from South Africa) mentioned the use of "calibrated wax" to
set the depth of the flanges equal to the thickness of the plexiglass cover.
This technique works quite well, although there are a couple of "gotch
yas" available. Calibrated wax is a product that comes as a sheet of
wax (1/16", 1/8", etc.) with adhesive on one side. It is available from McMaster
Carr in Chicago via mail order. [I bought the 1/16" sheet, and used two layers
to get the 1/8" needed for the plexiglass. That way, excess material can
be used for other applications where 1/16" would be the required thickness.]
Cut 1" wide strips of the wax. Using the rolling "pizza cutter" works well.
Cut some 3" wide strips of thin flexible aluminum (flashing material from
the hardware store works okay)
Tape the aluminum around the opening with a uniform 1" overhang. See Photo
Peel the protective paper off of the wax strips, and carefully apply a layer
to the inside of the aluminum, where the aluminum overhangs the fiberglass
opening. Repeat if using 1/16" wax and 1/8" Plexiglass.
Make up 2" wide, 3-ply bid prewet strips, and apply them over the wax and
onto the surrounding fiberglass of the wing structure. This is done by reaching
through the opening.
Figure 4. Aluminum flashing taped around opening
Potential gotcha -- When laying the fiberlass in place, I found (after
it had cured) that the weight of the fiberglass/wax combo, pressing on the
Aluminum on the bottom side of the curve, caused the aluminum material to
"sag" away from the desired position. This caused the step that is the desired
result to be a little shallow. I will have to fix this later. I suggest extra
checking and something to hold the assembly tight is in order.
Figure 6 Clamps of Al-angle held long straight edges in place nicely, but
the "sag" was on the curved surface lower edge.
After curing, remove the aluminum and the wax, clean up the surfaces, and
trim the overhang to your desired value. I used 3/4" as a final value, but
may cut it down to as low as 1/2" on the ends.
Figure 7 Showing the flange and light in place
Affix nutplates to the flange to hold the lense in place. Three on the top
and bottom flange seem adequate.
Figure 8 Illuminated!
Temperature Rise Concerns
Because of the confined nature of the light, and the fact that it dumps 55
watts of electric power into the space, I was concerned that the temperature
might rise to an unacceptable level when in use. To get a handle on this,
I did some experiments. I purchased an "indoor-outdoor" digital thermometer,
and put the outdoor probe between the back Aluminum plate, and the fiberglass
spar. Then I sealed up the lense, and turned on the taxi light bulb (they
are both 55 watt bulbs). I monitored temperature with time, and the results
are shown below.
After 30 minutes, the temperature rise was slowing, and I then put a small
fan 28" from the leading edge, simulating a gentle breeze across the wing.
You can see the effect on temperature. I feel that in actual use, with a
plane moving at ~100miles per hour, that temperature will not be a problem