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

• I chose a PILOT Model Number 1068BC, which is a driving-fog lamp combination, that uses H-3 halogen bulbs. These are readily obtainable from auto parts stores, and draw 55 watts each. I felt that this gave me the flexibility of having either 55 or 110 watts by turning on one or both of the bulbs in the plane. Others have used a "Blazer" light in the wing-tips, etc. My main concern was redundancy and ease of bulb replacement.

  This is the same bulb/light combination that Dave Tate used, and a picture was included on Bob Reed’s web site of Dave’s installation.

Landing Light Location

• I chose wing leading edge over the cowling because of the experiences that we have had with the flying club airplanes (Piper’s and Cessna). Those with the leading edge light go through bulbs at a much lower rate than those with lights in the cowl. I attribute this to less vibration, and possibly less heat.

  I positioned the opening 3 inches inboard from the outer wingtip joggle. I felt that this "looked right" in terms of it’s location relative to the wingtip strobes and running lights. This location is arbitrary.

Other Considerations/thoughts

• 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.

Mounting instructions:

• 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 reasonable.
  
  

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 ya’s" 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

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Time, Minutes