Chapter 25 - Section 3

Filling and Sanding - Wings

Balancing Elevators and Ailerons


Sanding the fuselage bottom and strake bottoms was a learning experience. I have yet to find the perfect sanding tool to ease my cramps.  As the old saying goes, nothing beats experience. So...


Fill...Sand...Fill...Sand...Fill...Sand Continues...

This page is for documenting the filling and sanding of the wings and winglets.


After most of the fuselage and strake bottoms were filled and sanded, I turned to the wings and winglets. I removed the rudders for a cleaner edge management. It was difficult to reach the top of the winglet for sanding. I decided to lower the wings to floor level - that was well worth the effort. It still took me 2 days to fill and sand the left winglet and rudder.   
A picture of the right winglet, another 2 days of fill and sand. You can barely see the 9 layers of BID on the winglet.


After sanding, I hung the rudders back on and made sure they fit ok and move freely as before. At this stage, I am getting a much better feel with sanding. I started using my Porter & Cable palm sander longer. Besides removing the rough spots (cured micro), I used it to do my initial smoothing on the hills and valleys (micro) before going to the long boards. I like the palm sender better than the Dual Action sander because my palm sander has almost no vibration allowing much better control over the Dual Action sander.
So far, I was not able to do a good job in making large batches of micro and spreading them out quickly. With smaller batches, I was able to take time to spread them and minimize air bubbles that tend to cause pin holes. Since the glass work was quite smooth to begin with, I found that I do not have to put on too thick of a layer of micro. Note that I did not fill and sand the level board area. It is because I forgot to write down the wing level degrees (for washer adjustment). I have to come back later to fill and sand these areas (when I fill and sand the top surfaces). There were quite a few bumps on this wing surface & I had to chase a few low spots along the spar cap. I had to re-visit one particular spot 3 times before I was satisfied with the surface.
Prep sand the right wing with ailerons removed. Took me a while to remember how the control rods were mounted...

Again, I left the level board areas alone for now, though I remember my right wing lined up to the fuselage perfectly (0o). I have less bumps on the right wing and the sanding went much easier than the left wing. Though you cannot see it in this picture, the 9 ply lay-up can be seen just below the micro surface. 

The ailerons were not difficult to fill and sand because they were relatively small and flat. Again, I used both the palm sander and the DA sander a bit more before going for the long board (36 grit), then the long flat sanding T bar. It took me a bit under 30 minutes to sand down each face of the aileron.

Both ailerons completed.


I have to build a couple taller saw horses for sanding the bottom of the wings (to accommodate the winglets). I decided to clamp the tall saw horses to my work table and stand/sit on it for the sanding effort. It worked out well for me.  
Wayne Hicks was visiting while I was getting ready for the underside of the left wing. Wayne recommended to pre-fill first because it will minimize low spots that I have to chase down and re-fill (2-3 times). I followed his advice and did a pre-fill and sand. After the intermediate step, I did a complete final fill and sand. It turned out to be my best surface so far. I have no low spots except a few pin holes and mouse bites. Thanks Wayne for the advice!  
With the results I got from the left wing, I decided to pre-fill the right as well. Here's my right wing bottom after final fill and sanding. Note the final fill is not very thick. It is because my wing surface has been pre-filled and relatively smooth at the final fill stage. It minimizes excessive micro and reduces subsequent sanding effort. It was 92o and the loose micro loves to find its resting spot on sweaty areas...

[Hindsight] As I gained more practice with this filling and sanding effort, I developed somewhat of a routine that works for me. I mixed up a couple squirts of raw epoxy first and applied a VERY thin layer (with a credit card) onto the prep-sanded surface. Though many builders feel it is unnecessary, I find it helps to keep the micro layer from curling up on me. However, if I mix the micro a bit wetter, I do not need the epoxy layer. As I mentioned earlier, I have difficulty in keeping a large batch of micro from hardening up on me (i.e. no more than 4 squirts of resin & hardener). I add about 11-12 oz of micro with 4 squirts of epoxy. This micro mixture is quite dry, but it spreads well on the epoxy layer. I found the dryer micro allows the sand paper to grab onto it better - thus effective sanding. I did the same for both pre-fill and final fill.

I also have difficulty in catching the right (cheese grating) moment per Wayne Hick's suggestion. Therefore, a majority of the time I just wait till the micro cures before sanding. Wayne recommended 209 slower hardener - I will certainly try it after I use up the current can of 206. Once cured, I started with my (Porter & Cable) palm sander, to get rid of all the high/rough micro peaks. It took me about 10 minutes for the entire wing bottom. Then I switched over to a DA sander to level out the excessive high spots. This took longer, maybe about 20 - 25 minutes. Then I switched over to my 36 grit long board until the underlying features started to show. Now, that takes a long time. Then I switched over to my favorite 22" aluminum T-bar from Aircraft Spruce (01-25007) for under $8. Its light and it will give you a straight edge and a nice level surface. I used 80 grit Dura-Gold roll sanding paper with the T-bar. I stay with the T-bar until I am done, as shown in the above pictures. Be sure to use the 45 degree sanding pattern - you won't regret it!

With most of the underside of my Cozy filled and sanded, my engine finally arrived! I decided to take a break from sanding and tackle the mounting of the engine...back to Chapter 23. But wait, don't forget to clean out all the dust in the shop... - its everywhere.

Locking the Cozy in Place for Sanding

Once the wings are sanded, I mounted them back onto the strake to make sure nice leveling and such. Besides, I have to remove the level boards and perform my final touch up and sanding. I was surprised that the Cozy would not stand still while I sand the surface of the wings. Just a chock behind the wheel did not work for me. I ended up making a simple yet effective tire blocks for the occasion.


Here's the wheel lock for the main gears. The weight of the plane holds the wheel locks in place - works great!






Here's the wheel lock for the nose gear. The 2 triangle blocks keep the plane from wobbling around!











Two More Times...

I was not expecting multiple times of prime, sand, fill cycles to prepare the surface for paint. For me, it took 3 cycles until I was happy with the surface. I don't think I am too picky, but lack of good sanding skill. Here's a couple of pictures of my wings after the 3rd prime. 




Initial Balance Checks (Elevators and Ailerons)

Balancing our elevators and ailerons is key in controlling flutter. A final balance on these components should be performed AFTER they are painted because the primer and paint adds weight to them. I decided to check them out at this time because my parts are all filled and primed and its good to know where I stand. I will need to do a final balance after they are painted. You can find a lot of discussions on this topic in the Cozy forum. I followed the directions as suggested in the archives with the following results:


Aileron right:    Weight 6 lb 0.4oz. Requires 1 oz of weight at the balancing rod to level bottom surface;

Aileron left:       Weight 6 lb 1 oz. Requires 3.2 oz of weight at the balancing rod to level bottom surface;

Elevator right:   Weight 3 lb 11.2 oz. Leading edge pointing downwards when hanging from hinge pin with safety wire;

Elevator left:     Weight 3 lb. 11 oz. Leading edge pointing downwards when hanging from hinge pin with safety wire;

Rudder right:    Weight 2 lb 7.4 oz;

Rudder left:       Weight 2 lb 7.2 oz.   


Per Plan, the max balancing weight one can add to the ailerons is 4.8oz.



Things to Do:

 Add balance weight to ailerons