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Top Flite B-25J Mitchell Project

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Page 10

       The next step in my build was to finish the outboard wing panels. I decided to add landing lights to the panels for added scale appeal so I purchased a set of Ram RC LED landing lights (Cat #RAM123). The set consists of two white light LED lamps that produce a lot of light for a small package.

       The LED lights are powered by a 9 volt battery that is controlled by a voltage regulator and microswitch. The voltage regulator feeds just enough voltage to the LEDs to keep them burning bright even when the 9 volt drains down a bit. It’s a simple and effective system to use on RC aircraft.

       I studied a few pictures of full size B-25s to get a location on where the landing lights should be installed in the outer wing panels. The measurement I came up with was about 180 mm out from the root of the outboard wing panel as seen below.

       The next step was to drill a hole in the leading edge to accommodate the landing light. I used a 7/32” drill bit and carefully drilled the leading edge at about the apex of the LE as seen below:

       The covering was then cut off the LE to reveal the bare balsa wood. The cutout patch was made 25 mm wide by 20 mm tall.

       I used a hobby knife and a Dremel bit to hollow out the dummy reflector cone in the LE. Be sure not to remove too much wood from the LE or you may weaken the wing at this point. The outer diameter of the reflector cone should be about 10 mm and taper down to the 7/32” hole.

       To help strengthen the wing at the landing light hole some thin CA glue was brushed into the wood. This will regain any loss in strength lost by drilling the hole in the LE. Notice the blue painters tape used to protect the covering from the glue.

       After sanding the glue treated wood a little I applied some of the Testors black paint I was using earlier to the wood.

       The next step was to paint the dummy reflector on the landing light hole. For this I used a Pactra “Indy Silver” (Cat #BC62) model paint. I use this paint for all of the silver accents on the B-25 including the dummy radial engines and the nose gunner pivot. There are too many uses to list for this color on RC aircraft projects!!!

       The cones were painted a little bigger than they actually are to give a larger appearance as seen below.

       To install the actual LED lights I used upholstery thread fished through the back of the LED power posts as seen below. This will keep the led from falling into the wing and allow me to control the position of the lamp in the hole.

       At this point I already have the LED wires installed into the wing and they are protruding through the root of the wing. It was fairly easy to fish the wire in using the servo hatch and a bit of solid copper wire used as a fishing device. The next step was to glue the LEDs in place using 5 minute epoxy. Of course you could use whatever glue you like but I like epoxy as you have time to adjust the lights before they are set in place.
       I applied the epoxy to the hole and the back of the LED carefully. I avoided getting the epoxy on the reflector of the front of the LED itself. If you do you can clean it up with isopropyl alcohol on a paper towel.

       Because these LEDs have a built in reflector they should be aimed in the right direction before the glue sets. I darkened the room and turned in the LEDs to see where they were pointing. Once I was happy with the direction they were set at I let the glue cure and cut off the thread “handles”. The LED wires themselves proved to be the best method of aiming the LEDs in the wing. I did this by pulling or pushing the wires into and out of the wing root gently.

       To help steady the LEDs while the epoxy was curing I taped the wires to the root of the wing as seen below.

       To add the final touch to the landing lights I decided to make lamp windscreens out of K&S .015 thick clear plastic sheeting (Cat #1304).

       I cut out a strip of the clear sheeting at about 34 mm wide. It cuts easily with a hobby knife and a straight edge.

       To help form the windscreen to the LE shape I used a screwdriver shaft and “rolled” the sheeting over it using my fingers until the shape was made. Notice the blue tape used on the screwdriver to help reduce scratching the plastic surface. Once formed the windscreens were trimmed to fit the LE cutouts (just about 4 mm overhang around the cutouts).

       The next step was to drill out the #0 x 1/4” screw holes in the sheeting with a 1.15 mm drill bit. I spaced them evenly, three on each side.

       The last step was to screw down the windscreens to the wing.

       I could now see how they would look at night on the wings!!!

       These very bright lights will add a scale accent to the warbird and even be seen during the daytime!!!

       I could now move on to installing the outboard wing servos. I chose to use Hitec HS-5625MG digital servos for my ailerons mostly for their durability. My B-25 will more than likely weigh over 20 pounds so in turn the servos need to be able to move a lot of weight around. In reality a good 40 ounce servo will work on the ailerons but in truth I just like to overkill sometimes :0)

       I really like the metal servo arms that come stock with the Hitec digitals. They cannot shatter and when hooked to a metal gear servo they are nearly indestructible.

       Just like the inboard flaps I installed a set of HS-5245MG digital servos in the outboard flaps. Whenever I install servos I always set the servo centers and control rod geometry using a “bench” radio system. This way the servos are ready to be programmed into the “flight” radio without doing any (or very little) mechanical adjustment later. I set up the ailerons to throw about 3/4” inch up and down and the flaps to about 45 degrees.

       Once again I made a set of Dubro 4-40 rods for the linkages.

       Because the wings will now have a group of servo and lighting wires routed through them I decided to make wire loom anchors to be glued into the ends of the wings. These anchors will keep the wires from yanking at the servos in the wings when being attached and disconnected.

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