This week we made great progress on our (second generation) elevators. As I mentioned before, we made the first set of elevators back in October, but discovered that not only were they very difficult to mount onto the horizontal stabilizer, but there was a problem with the leading edges bumping into the stabilizer when the elevators were deflected downward. We either had to build a new horizontal stabilizer, or redesign and make two new elevators. We chose to re-make the elevators. Although the new design is a bit more complex, it is easier to attach to the stabilizer and should function better than the first design.
This past Saturday, I filled the holes in the 6 aluminum backing plates with flox (epoxy resin with cotton fibers). The flox ensures that the backing plates are very firmly anchored to the foam and fiberglass skins of the elevators.
Backing plate with flox. The flox fills the holes in the plates and
helps anchor them to the foam.
It was not until Tuesday that I got back to work on the elevators. By then the flox was as hard a a rock. It took me a day’s work to grind off the excess using a wire wheel on a dremmel tool. It was very time consuming but the results were worth it.
Chuck came over on Wednesday. I cut out the servo cover and cover backup plates out of aluminum sheet. I then drilled the screw holes in both parts to match. Next I positioned 8 nutplates under each hole on the backup plate and drilled holes for the rivets. Finally, I riveted each nutplate into place. I added beeswax to the nutplate holes and embedded the backup plate into the starboard elevator.
In the meantime Chuck cut out two foam pieces for mounting the tail light on the rudder (we made the rudder several weeks ago).
Two foam pieces will form the fairing for the tail light that will be
mounted on the rudder. I will go into more detail in a few weeks.
On Thursday we finished cleaning up the backup plates and then cut out the fiberglass for the top skins of the elevators. Next we vacuum the part to remove any dust .
Before we wet out the glass cloth, we painted resin onto the foam surface. Next we added micro and worked it well into the foam surface using a squeegee tool.
Chuck spreading a slurry of micro (glass microspheres and resin)
onto the surface of the foam. This ensures that the fiberglass
bonds really well to the foam.
Next we applied epoxy resin to the fiberglass cloth. We used the “prepreg sandwich technique” to wet out the cloth. This is a technique where we draw the exact final shape of the fiberglass on the bottom of a piece of polyethylene sheet. We then place a slightly oversized piece of fiberglass cloth on top of the polyethylene and fold the rest of the plastic over the fabric forming a “sandwich”. The next step is to wet the fiberglass sandwich with epoxy resin. We do this by folding back the top sheet and then pouriing the resin on top of the fiberglass cloth. After re-folding the plastic back onto the cloth, we use squeegee tools to work the resin into the fiberglass. After the glass is throughly impregnated with the resin, we cut out the fiberglass sandwich along the lines drawn on the bottom sheet. We peel off one layer of the plastic, and apply the fiberglass and attached polyethylene backing layer to the elevator. Having a backing layer of polyethylene film makes it much easier to handle and position the epoxy empregnated fiberglass cloth. See the drawing below:
Here are two fiberglass sandwiches ready to for resin. The long
piece in the foreground will cover the entire length of an elevator.
The shorter piece in the background will cover only the inboard
Next, we use the squeegee tool to press the glass tight against the foam. Once we have the glass positioned well, we can remove the plastic film. We spent 15 minutes with a paintbrush to get all the airbubbles worked out between the fiberglass and foam. We applied fiberglass to both elevator’s upper skins.
Chuck cut out a thin piece of plywood to make a mounting plate for the servo. We painted one side with epoxy resin and embedded 4 screws to act as posts for the servo.
The servo is upsidedown on the bottom. Next is a layer of poly-
ethylene to protect the servo. Finally, a thin piece of plywood is
mounted to the servo using 4 screws. The wood is coated with
resin and flox (cotton fibers and resin) are covering the screwheads.
Friday, Darryl trimmed off the excess glass off the two elevators. He also filled the trailing edge trough with micro. The micro makes the trailing edge stiffer and stronger.
Micro slurry is applied to the trailing edge. Trailing edge after micro has be smoothed
That is a wrap for the week!