Giant scale R/C aircraft have been around for some time now and have displayed some very impressive undertakings by various people. We initially started in giant scale with aircraft types that were simple to construct and easy to fly. After a few years and many of these tame models later, more and more modelers have gotten the urge to build something from the W.W.II warbird era.

At first we started with the liaison or reconnaissance type aircraft. This satisfied a few of us for a short time but our appetites were really hungry for some of the big iron stuff. As the first few giant scale W.W.II fighters appeared we found they flew fairly well if they were built light enough. They sure looked great in the air, but something always seemed to look out of place. The out of place culprit was the landing gear. It was always hanging out in the breeze. Somehow it just didn't look right to see a P-51 Mustang or a F-4U Corsair doing strafing runs with the landing gear hanging out. It didn't take long for a few industrious individuals to come to our rescue. Retractable landing gear for giant scale models started to appear on the market: some good, some not so good. Fortunately for us warbird lovers, the good guys are still around and have been joined by a few more good quality units. Now that we had retracts our warbirds started to look much better. But something was still amiss. When a fighter flew overhead we noticed that the gear was up, and boy did it look great, but there was always a hole left in the wing showing an exposed wheel! Most fighters had sequencing inner landing gear doors to cover these holes, but for the modeler to duplicate these mechanisms became one of our most feared nightmares.

One solution many used was to leave them off. Others built warbird types that did not have these doors. There are a variety of aircraft like this but the most popular seem to be the AT-6 Texan, SNJ, Harvard series. Retracts in this ship were simple: no inner doors required and the tailwheel; didn't retract at all. Great! However, some of us weren't happy with "trainer" type warbirds. We still wanted the real stuff: the gunfighters. To satisfy our desire many different methods have been tried with varying degrees of success.

What I'd like to present to you in this article is one method I've employed on three of my P-47 Thunderbolts. But before I begin it must be understood that certain liberties and "deviations from scale" have been taken in order to provide a very basic and simple method of accomplishing the task required which is to create the illusion of operation similar to the full size ship.

I generally make all my landing gear doors out of fiberglass cloth with K8 B finishing resin and mold them right on the sheeted wing. I install my retract mounts in the wing prior to sheeting it. This prevents you from having to chop up a competed wing. Once this is done and the wing is sheeted use a felt tip pen to layout the landing gear strut cover and inner door right on the sheeted wing.

Over this layout place some clear wax paper and tape it down around the edges. Use a piece large enough to overlap your layout by approximately 2 inches all around. On top of the wax paper lay-up 2 layers of 2 ounce fiberglass cloth and resin. You should be able to see your layout through the fiberglass and wax paper. Let the fiberglass cure in this location to insure that you have landing gear doors that will match the wing's airfoil shape perfectly. After curing, sand this area smooth and apply another coat of resin. Let this cure and lightly sand again. Now trace your layout onto the fiberglass. Note that the inner door and the strut cover will be one piece at this time. Mark where the separation line will be. Remove the masking tape holding the wax paper to the wing and lift this lay-up off the wing. Peel away the wax paper from the back of the fiberglass. At this point it is time to trim around the outside of the lay-up. I usually trim leaving 1/8 inch excess material around the entire shape. After completion you'll see that this lets all the covers and doors lay on the wing surface rather than fit into the wheel well. I prefer this method to fitting doors to the inside of the well for various reasons, but the best one is that it allows for misalignment due to bent struts etc., without binding the strut cover in the well. Remember we're looking for a practical solution to generate the illusion of being like the full size version.

At this point it's time to cut out the wheel well opening on the previously drawn layout lines. The landing gear can be temporarily installed and the fiberglass lay-up placed over the opening to check for any gear strut-to-cover interference's. Trace the outline of the fiberglass cover onto the wing. This outline will be your reference lines from now on. Cut the inner door away from the strut cover now and sand each edge to provide a smooth surface. Remove only enough material to allow 3/32" to 1/8" gap between the two when you lay them back on the outline.

Mount the strut cover to the landing gear strut. Various methods can be used and they all have their good points. I prefer to use machine mounting blocks from aluminum that slip over the strut and are held in place by a pinch bolt. The inner doors are now mounted and hinged. I use small brass cabinet hinges that are found in your local hardware store. I use these because they are cheap yet sturdy and will take a lot of abuse. And believe me, inner doors take a beating! The hinge pin area must be opened up on one side of each hinge to allow for a free, almost sloppy, operation. When mounting the hinges (use two per door) keep the two hinges lined up with one another. Sometimes the hinge line must be below the wing surface in order to provide a straight "line of sight" hinge line. This is very important because you are trying to hinge a curved door that conforms to the airfoil shape of the wing. Sometimes this requires the hinges to be bent into weird shapes. This is another good reason for using brass hinges.

Next a trip wire is bent and mounted to the door. Use 1/16" diameter piano wire. Don't use anything smaller or softer. It just won't last. When mounting the wire to the door check for any interference areas and adjust as needed. As you close the door on the wing note where the trip wire is located. Cut a notch in the wing and the rib you have the hinges mounted to. This notch should be large enough to provide clearance for an over-center spring.

On the inside of the wing skin and on the inboard side of the rib install a retainer plate for the spring. Use 15 minute epoxy and after it has cured you can install the spring. The spring should want to pull the door in either direction once the door goes past 45'. Adjust as needed to accomplish this. You'll notice that when in the open position the spring will fold the door back onto the wing. To regulate the amount the door opens use a piece of monofilament fishing line attached to the trip wire approximately 1 - 1 1/2 inches from the door. The other end of the monofilament is attached to the small eye hook that is mounted in the inboard rib close to the top sheeting. Adjust the length of the monofilament to restrict the door to approximately 90' opening.

With the retracts mounted operate the system manually. Watch for binding of the wheel to trip wire and door interference areas. It may take some "tweaking" of the trip wire and the monofilament to make things work properly. If you've tweaked everything just right you'll notice that the over-center spring will keep the inner door open the gear is down and pull the inner door closed when the gear goes up.

I hope between my explanation and the accompanying pictures you'll be able to achieve a somewhat realistic operation of an often omitted feature. The tailwheel doors present different problems and hopefully I'll be able to address them at a later date.

Inner Door in open position showing trip wire and monofilament. Stiffener on door helps maintain airfoil shape.

Monofilament attached to the trip wire with the opposite end attached to a small eye hook. The notch for the over-center spring can also be seen along with the hinges secured to the inner wheel well rib.

Over-center spring protrudes below wing surface with gear door open. Also shown are the two hinges bent to provide a straight hinge line

Wheel just beginning to contact trip wire. Also note bend of front hinge.

This view shows how the strut cover and inner door lie on the outside surface of the wing. The exposed "line of sight" hinge line along with the notch to clear the over-center spring are also evident. Note 1/8" gap between strut cover and inner door.

Strut cover attached to landing gear strut by two aluminum pinch blocks. Wheel diameter is 6.0 inches for size comparison.