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 Goldberg "Gas Bird" Construction Project Session #13

By Tommy Gray
AMA 17063

In the last session, I mounted the Stab assembly to the fuselage, and filled in the pushrod guide pieces. Here you can see the one for the elevator pushrod.  I used Du-Bro clear plastic pushrod tubes for all the pushrods.  I also used .047 music wire for the pushrods themselves.  The .047 wire will flex to the curvature of the tube nicely and will also give a solid feel to the controls.  The plastic type pushrods, will expand and contract with temperature and cause a trim change.  I have never had to re-trim my planes due to temperature when using the solid wire pushrods.  You can also see in this photo, that I have started covering the stab with the Polyspan covering.

Next, I added a piece of 1/8" lite plywood to the rear fuselage bay to mount the elevator and rudder servos on.  I doubled the area adjacent to the servo to give a thickness of 1/4" where the mounting screws will go by gluing a piece of 1/8' ply cut to 3/8" wide and long enough to reach from side to side to the bottom of the mounting plate.  NOTE: I first glued a couple of 3/16" square sticks to the fuselage sides to give something for the plywood to mount to. 

You can also see the 1/8" square pieces at the sides of the open bays, which I added to give the 1/8" balsa hatch covers something to rest on to keep them flush with the outside of the fuselage. I will add some cross pieces of lite ply at the front and rear of each bay, to give the hatches something to bolt down to.

In the picture below, you can see that I added a scrap of 1/8" balsa so that the pushrod tubes would have something to attach to beside the servos.  I first sanded the outer surface of the tubes so that the thick CA glue would have something to stick to.  The tubes are slick and if you don't roughen then up the glue will not stick.  I also sanded the other ends where they terminate in the filler pieces I added to the rear of the fuselage longerons.

Where the tubes exited the fuselage, I trimmed them flush with the filler piece after I glued then on both the outer and inner sides.  I then sanded them with a sanding block so that they were flush and smooth with the outside of the filler piece.

Below you can see that I have finished covering the bottom of the stab.  I used the trim iron to get a good fold where the Polyspan bends over the edge.  Without the heat of the iron, it is very difficult if not impossible to get a good edge.  I have more details about covering with the Polyspan in my Phantom Fury build also on this website.

In the next picture you can see that I have covered the top and the rudder, and temporarily fitted the elevator hinges to see how things are working out.  I have not glued the CA hinges in yet, but as you can see they are starting to come together

Another view of the stab with the elevators fitted.

I completed the tail feathers and have started covering the wing by covering the bottom side.  Now normally, I would use a single piece to cover the bottom, but since I had numerous smaller pieces of Polyspan left from one roll, and none were large enough to reach all the way from tip to tip, I opted to cover the bottom in 3 pieces.  Here I have started with the tip.  I applied some dope to the outline of the structure and using my finger, I worked the covering down to the undercambered bottom of the ribs.  I kept gently rubbing periodically until the covering was securely stuck to the ribs.  Otherwise, it would have pulled loose when it was doped into place.

I repeated the process for the spars to assure that the covering was securely attached to all the wood.

Next, I doped the sides of the rib at the dihedral joint and folded the covering over onto the rib, using a little heat from the covering iron to make sure that it was securely attached.  I wait until the dope has dried enough that the iron will not stick to it before touching the covering with the iron.  I DO NOT shrink the covering in the bays until I have everything attached to the wood and trimmed and folded with the iron, over the edges.  Here you can see me rubbing the dope into the covering so that it will stay down. Once it is down and the dope has dried a little I take the iron and put it down tightly.

Next, I took the Monokote iron, and creased the covering so that it will give a clean edge. After the dope has dried, and I have trimmed off the excess, I go back and iron the edge completely down.

Same thing for the other edge

Here you can see that I have completed the covering of the bottom, and the dope is starting to dry.  The darker spots are where the dope is still wet. You can see however that the covering has stuck nicely to the curvature of the bottom of the ribs.

Well, we are two weeks away from the 2009 champs so I am in high gear finishing up the plane.  I will have more later in the week. wish me luck in getting it finished and trimmed before we have to leave to drive out to the Champs.

More to Come....Tommy!

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