Week ending Friday, May 23, 2008

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
half.

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 
                                                                       into place.

That is a wrap for the week!

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Week ending Friday May 16th, 2008

We continued to make steady progress this week. Saturday, we hotwire cut the port elevator. 

                
                 Chuck is positioning the elevator template in preparation for
                 cutting out the port side elevator.


After cutting out the elevators, we cut the leading edges off of both elevators.

            
             Chuck and I are using a hotwire tool to cut off the leading edge
             of an elevator.



             
              Chuck rounding the edge with coarse sandpaper. This will
              allow the fiberglass to make better contact as it folds around
              the corner.


We marked the areas on each elevator where the hinge brackets will go. we also cut steel counter-weight rods and potted the weights and wooden spacers on the two elevator leading edges. The wood areas will be removed so that the hinge brackets can be riveted into place later on. 

            
             This is a view of the two elevator leading edges. The dark
             areas are the steel rods used as counter-weights. The light
             areas are wood dowels used as spacers. The dowels will be
             cut out at a later step.



            
             This picture shows the same leading edges after the counter-
             weights have been bonded with micro.



On Wednesday, I made 6 backing plates While Chuck cut out the areas on the elevators where they would be placed.

     
Inboard backing plate.         Middle backing plate.            Outboard backing plate.


Chuck made a channel on each elevator leading edge for the torque tube. He also cut out an area for the trim tab servo access panel.

   
This is a view of the leading edge                    The square area is where the trim tab
showing the trough that Chuck cut out.           servo will be located. Chuck cut out this
The elevators will be rotated by the                 area and Darryl will make a backup plate
torque tube that will be located in this             that will be embedded next week.
area.


Thursday morning we attached two wooden shelves to the side of the table to hold the two elevators (2008)05_17P19,30). We then mounted all the brackets with dry micro. We also fiberglassed the two torque tube channels (2008_05_17P12). Later in the morning we drove up to Napa to visit Zeke Smith and to talk about the upcoming workshops at Marysville’s GoldenWest fly-in.  When we got back in the afternoon, the morning’s epoxy had pretty well hardened. Chuck razor trimmed the two tunnel’s fiberglass.

  
The two elevators are mounted to the side of the worktable using 5-minute epoxy.
Note that the backup plates are in position. We have placed short pieces of duct-
tape below them so that excess resin will not stick to the foam surface.



Friday morning, Darryl went to the Hayward airport to watch the Hayward Air Rally start. Here is a picture of fellow EAA’er Bruce Cruikshank’s RV9-A. It is a beauty.

         
          Bruce Cruikshank’s RV9-A, preflight inspection before the Hayward Air Rally. 
          He is a member of Experimental Aircraft Association’s Livermore Chapter 663,
          to which we also belong. He finished this plane late last year.


Later in the morning Darryl drilled out the backing plate tubes so that they could be filled with flox on Saturday. Chuck received the LED tail light from SteinAir. We will be mounting it on the top rear edge of the rudder.

  
Off ……………………………………..and……………..On!

Week ending Friday May 9, 2008

On Saturday I inspected the Rudder counterweight arm’s top surface. It looked great. I did a rough trim with the Fein Multitool and then put the entire rudder under black polyethylene and set out under the sun. This is a technique that we use to heat-cure parts in order to make sure that the resin cures completely. 


                      
                       This is the Fein Multitool. The blade vibrates back and forth. It
                       produces very little dust and cuts fiberglass like it was butter!

Monday, I sanded the top edge and the vertical sides of the counter-weight arm (CW arm). With a good resin cure, It was easy to sand and shape the surfaces.

Tuesday, I prepared the bottom of the CW arm for glassing. Like the top surface, I cut a trough out of the foam along the perimeter and then filled it with fairly dry flox (resin and cotton fibers). I then applied two layers of bi-directional (BID) glass cloth to complete the bottom skin.

Underside of counterweight arm showing foam removed around
inside edge. This trench will be filled with flox and then two layers
of bidirectional fiberglass cloth applied.


Rudder positioned and ready to layup the counterweight arm’s
bottom surface.

The next morning I took a look at the CW arm. After doing a rough trim with the Fein tool, I test fitted the elevator on the fin… Looks great!

Here is the rudder with finished counterweight arm mounted onto the
vertical fin.

I spent the rest of the week working on the pitot/static assembly and the vertical fin cap. I used flox to attach the pitot/static assembly to the inside of the cap.

 
This is a view of the pitot/static tube assembly and      I have applied flox to the area between the two tubes.
 how it fits into the vertical fin cap.                             This will glue the pitot/static assembly to the inside of 
                                                                              the cap.


                                    
                                     The pitot/static tubes are now floxed in place. I put the cap 
                                     onto the top of the vertical fin and am holding the tubes in 
                                     place with red duct tape.


I put the cap on the fin to and used tape to make sure that the tubes were pointing straight ahead and aligned with the airplane centerline. I almost waited too long to remove the part after letting it cure for about 8 hours. I was finally able to get the cap off with a great deal of effort. Luckily, the cap wasn’t damaged, and the pitot/static tubes remained solidly in position.

Chuck came over today (Friday) and I greeted him with a vertical tail with the following: A rudder with counterweight mounted, the pitot/static tubes on the cap and last but not least our strobe flashing on top! It is starting to look like a real airplane.

We got to work making the templates for hot-wire cutting our new elevators. We took a break and went to the Metal Supermarket (its real name) and bought 1/2″ diameter rod for the elevator leading edge counterweights and some other miscellaneous aluminum. We ended the day by hot-wire cutting the starboard elevator. Below you can see how an elevator emerges from a solid block of foam.


Preparing to square the edges.

Formica template of the elevator attached to end of foam block using nails.

This is the elevator after we have used a hot wire. We used the Formica
template to guide us. The template has been removed.

The starboard elevator foam core.

Week ending Friday May 2, 2008

Several weeks back, Chuck and I  realized that our elevators were not going to function properly. The problem was that the horizontal stabilizer’s aft spar did not have a deep enough channel to allow the elevators to rotate down before their leading edges contacted the spar. The picture below shows an elevator mounted to the stabilizer. The area labeled “Leading edge of elevator” will bump into the area labeled “Stabilizer aft spar” when the elevator rotates downward.



There were two solutions to this problem; both of them painful. One route was to make a new horizontal stabilizer and the other was to make two new elevators. After some soul searching, we decided that the least time consuming approach was to re-make the elevators. On the bright side, last week we had just finished fitting the rudder to the vertical fin, and we were very happy with the pin and rod-end bearing method of mounting a control surface to the airplane. Chuck decided to look into using a similar approach in mounting the new elevators.

Chuck stayed home this week and worked on the new elevator design. Using his cad program, SolidWorks, he quickly worked out the new design. In order to make sure that the new way of mounting the elevators would be strong enough, Chuck analyzed the stresses by using a finite element analysis (FEA) program on the new concept.

This image shows an output from Chuck’s analysis. The red areas are regions of highest stress.
Don’t worry, the stresses are very low (ask Chuck for the details!).


He also brainstormed on a new joystick design which we ultimately decided to reject. Next he updated the current joystick design to match our mockup dimensions.

Tuesday, Darryl worked on trimming the rudder counterweight arm to fit snugly against the rudder spar web. A pocket was cut out at the top forward surface for the lead weight. After the shaping was complete, the rudder was mounted onto the vertical fin. The counterweight arm was glued into place using epoxy resin containing microspheres (“micro”), its position was maintained by a wood shim between the arm and the vertical fin cutout.
 
This picture shows the counterweight arm as it gets epoxyed into
place.


Wednesday, the lead weight was potted into place with dry micro (epoxy mix with lots of microspheres).

 
Lead weight set in place.                                         Side view with lead weight potted into place
                                                                                 with micro. 

Thursday, the rudder was removed from the vertical fin and positioned against the worktable so that the counterweight arm was pointing up. The rudder was secured with Bondo. The foam under the lead
counterweight was sanded to shape. I was now ready to apply the side skin.

Rudder is secured against our work table. The counter-weight
arm can be seen sticking up from the rudder top end (nearest).

The sides of the cw arm were skinned with two layers of BID (bidirectional fiberglass cloth) and an outer layer of UNI (unidirectional fiberglass tape).
  
Spreading micro on cw arm side.  First layer of BID glass covering.  All three layers covering side of arm.

Friday Darryl trimmed the fiberglass top and bottom edges and removed foam on the top side in preparation of making a strong flox corner edge for the top glass layers.

Top view looking down on counter-weight arm. Note that we 
used two different types of foam: the rudder is made up of blue
Styrofoam while we used pink high density PVC foam for the
counter-weight arm.

Week ending Friday April 25, 2008

This week we attached the hinge brackets to the Rudder. We spent a lot of time test-fitting the hinge brackets to the rudder to make sure that the pins slide smoothly into the three rod-end bearings mounted on the vertical fin. We used duct tape a first to get a general idea of the positions of each bracket.
    
Duct tape holding middle rudder bracket in place.         Duct tape holding bottom belarm in place


Once they were in the correct position, we used dabs of Bondo(TM )to fix them in place.  
Bondo holding top bracket onto rudder.                                Bondo holding bottom belarm onto rudder.


We made sure that the hinge pins were all lined up and that the rudder would move side to side easily. We found that the middle bracket needed to be shimmed an additional 0.044″ with a fiberglass spacer (4 plys). With all the brackets tested and bondo’d into position, we drilled all the holes with a 1/8″ drill bit. 
 
First drill a couple of holes then use clecos to hold bracket.   Once clecoed in place drill rest of holes.


After the holes were all drilled, we popped the brackets off and removed the remaining bondo from the aluminum brackets and fiberglass skin. The aluminum was wiped with acetone to remove oil and ink, and then sanded to remove the oxide.The fiberglass skin where the bracket was to be mounted was lightly sanded to roughen the surface and then wiped with 70% alcohol. We applied resin followed by dry micro slurry to each bracket and fiberglass and pressed into place. We used a couple of “clecos” on each bracket to securely position and then pop-riveted into them permanently into place.

The other thing that we began this week was the rudder counterweight arm. Last week we ordered high density PVC foam slabs from Aircraft Spruce. Luckily the order arrived in time so that Chuck could cut out the two pieces for the arm. Friday, Darryl glued the two pieces together with dry micro slurry.

 
Two pieces of high-density pvc foam cut for counterweight arm.  First paint epoxy resin on the two surfaces.

  
Next “dry micro” squeegeed onto the two surfaces.                   The two foam pieces are put together and weights placed on top.


Chuck and I made new measurements of our mockup and confirmed and refined the positions of the joystick, rudder pedals/brakes and flap handle.

Darryl trimmed the lead counterweight.


Rudder lead counter weight was cast earlier. Now Darryl put it in a vice
and trimmed it with a hacksaw.