Chapter 21 - Section 8

Top Skin


I decided to perform the pressure test (Section 9) before glassing the top skin because if I get a leak, it would be much easier to fix. In fact, it would be much easier to detect a leak.


Returning from Section 9...No leak!


Closing The Seams

With the pressure test behind me, the first task was to close all the seams from the outside - that includes the top seams inside the luggage cutouts and the outboard seams of R57. The work was pretty straight forward, except it was difficult to get to, especially the seam joining the top skin and the fuselage. I have to do the floxing and glass using a mirror. 



I did not pay close enough attention to the Plans and made a flox corner and glassed the bottom skin to the side of fuselage with 2 layers of BID (as shown in picture in blue). I have not glass in the top skin lip yet but I drawn it for illustration purposes only.













Here a picture of my cutout and the lip...


Recognizing the deviation from plan and that it may be structural, I think I should make the necessary correction with the 2 options below: 


Option1: (per Plan)

Trim the lip off (together with the flox corner, ouch!) such that the baggage cutout is flush with the bottom skin. Then re-glass the bottom skin with 2 ply BID strip. Starting from 1" into the bottom skin, wrap over the cutout edges and 1" down the inside of the fuselage.


Option 2:

Leave the existing flox corners and 2 plies BID as is, but add an additional 2 Plies BID layer over the the existing plies and wrap over the lip, then down the side of the fuselage. (as shown by the red lines). I do not know if Option 2 actually add more strength to the joint or weaker than the Plans version. I certainly wanted to stay with the stronger version. 


I got a confirmation from Marc Zietlin that - structurally, I am fine the way it is and that I can leave it alone if I want. What a relief. Now I can move forward and complete all the seams...


Pre-Sand Top Skin

I prep-sand the top skin foam using a straight edge and 36" sanding board. I recalled a comment that 'its easier to sand foam now than micro later'. Here's a picture of my top skin after I smoothed out the top skin.  










Pre-Cut UNI with Top Skin Templates

In order to cut the UNI layers for the top skin, I modified the bottom skin paper template for the top skin. This time, I marked clearly (on the template) the orientation of the glass fibers. These paper templates allows me to pre-cut all the necessary UNI for the top skin AHEAD of time and it made the lay-up effort much easier. I did not have to struggle (as much) when lining up the glass layers onto the strakes.



[Hindsight] The paper templates were a great help, but its easy to get confused with the glass orientation.






Glassing The Top Skin

I applied thick micro in all the seams and gaps on the foam surfaces. Susann and Cassandra decided to help me with the top skin. We decided to stand the plane up in its Space Shuttle pose to help with the glassing effort. The most difficult part was to get the UNI to lay down squarely as Plan. The extra two pairs of hands sure helps! After the 4 layers of UNI were epoxied in place, we applied a peel ply and let cure.


It turned out nice...











The next day, Susann and I glassed the top skin to the left. Good results as well.  











Strake End Covers (Not in Plans)

Some builders mounted their magnetometer in the cavity between R57 and the strake end ribs, such that they are less affected by electrical interference. Since I am planning to do the same, this cavity needs to be protected from the elements. I decided to add a cover (door) to the end of the strakes.


All I did was to trace out the opening of the strake end ribs, layup 6 layers of UNI with different orientations. The reason I used UNI is because I happen to have 6 scrap pieces of glass large enough for the covers. 6 layers of glass provides the necessary stiffness. In addition, it is thick enough for countersink screws. I used 3 stainless screws and nut plates to hold the covers in place.