Chapter 9 - Section 2

Preparing the Strut for Installation


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Sanding Down the Strut

I bought my strut from Feather Lite and it was delivered within 30 days. The quality looked so good compared to my work, I didn't want to touch it with any sandpaper. However, the plan says - dull the surfaces with 36 grit sandpaper... oh well .


I didn't use any power tools for the task because over-sanding it can be a costly affair. Though I relied on elbow grease, it only took me a couple of hours and half of sheet of sand paper. I did not sand down to remove all those little nicks and trenches. I think that will take too much glass off, besides, I can probably fill them with flox before the first layer of glass.    





Trimming the Main Gear

I followed the plan method except I was not sure how to get the 'mid-chord' location along the inside surface of the strut. If I draw a line joining the mid-point at the center of the arch to the mid point at the end of the strut, it will look awkward. I decided to pull out my laser and put a horizontal line along the inside arc to guide my filament tape. I hope I am right. If you look real close, you can see the edge of my tape sits right along the laser line. My filament tape turned out to be 96" which means I need to remove 1" excess or .5" from each leg.






I cut out a couple pieces of wood block with a 8o angle as a guide for trimming the end of the strut. At first I clamped the blocks onto the strut to guide my saw with little success. The blocks tend to shift around and the saw blade kept snagging the blocks and so on... I finally took the blocks off and used my FEIN tool instead. First, I made a deep scribe line along the pencil marks on both sides of the strut. These scribe lines guided my final cut with the hack saw. I used a new blade with 18 teeth. Since the strut has been pre-cut, I only needed one hack saw blade for both ends.






Once completed, I sanded down the tips with a hand sander, checked them against the wood blocks and made sure the 8o angles were achieved. Looks pretty good!









As a final check, I used a cross laser to make sure that both legs are close in length from center. The picture looked green because the laser did not show up well under normal light, so I have to turn the light off before taking the picture. I think I got it pretty close as well...








Removing the Bulge

The next step is to find the spot that is 5.75" wide and trim it down by 1/8". With the strut laying on the table as is, I slid a square along its side. I found the high spot easy enough, and drew a level line 1/8" below the highest point. The vertical line shows the highest spot and everything above the horizontal line is to be removed.








I used 36 grit paper and removed the bulge. Since the next step requires a 4 ply UND over this trailing edge, I made sure I rounded off the edges as well. This is the 'after' shot showing the contour after sanding.









Applying 4 Ply UND Onto Main Gear

I did not use a protractor to measure out the 30o for cutting the UND because a little bit off from my small protractor could mean a lot at the other end. I just used a bit of trigonometry and calculated the lengths of the UND required. Since the width of the UND roll is 38", if you mark the base to 65.82" and every 24" apart, you'll get a 30o - 12" strip EVERY time. Just make sure the UND is laying straight against the edge of the cutting table. In addition, I used the masking tape method to keep the strips in tact before cutting. I cut 9 strips instead of 13 as called out in the plans. I figure each strip has a 'usable' length of 55" and half of the strut is 47.5", I only need 8 strips with 1 for spare. I ended up screwing up 1 strip and used the remaining 8 to finish the task - good planning, I'll say .  


I supported the strut with three 2" screws on top of wood blocks for glassing. I knew I was in trouble once I laid down the first layer - there was just not enough room for me to see or get to the underside for any serious glass work. But it was too late to move the strut around and I knew I was going to have some sanding work to do afterwards.








The first layer was the toughest because I was trying to get the UND to wrap perfectly at the underside - with no success. Eventually, I decided to trim the UND off at the bottom edge and just do the best I could.   


The other layers were not as bad once I got the hang of it. None-the-less, the whole task took me a good 6 hours. The temperature dropped below 70o through the night and my layup took 2 days before it cured.






As expected, the glass at the top side of the strut turned out well, but the bottom edge did not. I have uneven glass coverage and glass spikes all along the bottom edge. Not good - I thought... Fortunately, there will be 4 more layers of UND to be wrapped around this forward edge. All I need to do is to smooth out the UND and blend them back to the basic strut.







With a lot of patience and sanding, I was able to clean up the forward edges. I used a full range of 36 grit to 150 grit sanding papers for the task. Actually, via this task, I learned to use the 36 grit paper better and be comfortable with it. See... something good can come out of a not so good situation !          







Here's the strut with the first 4 ply of UND applied...--> 






Trailing Edge Support

The O.D. of the brake lines supplied by Matco is 1/4" in diameter. I took me a bit of treasure hunting to find soda straws with I.D. larger than 1/4". Wendy's and Taco Bell's are too small - I eventually found them at In-And-Out Burgers. In addition, the soda straws have two opposing red stripes on it such that I can line up the bottom strip along the ridge of the strut and build up the trailing edge support along the top strip.


I did not follow the plans exactly when securing the straws onto the strut. I used scotch tape and hot glue gun instead of the 5 min epoxy. First, I drew a line along the crest of the trailing edge (of the strut) and lined up the red stripe (of the straw) along the line. Then I used scotch tape to secure the soda straws in place. This way, I can move them around and re-tape until the straws take the bend along the lines as intended. Now my hands are free to do the final securing with the hot glue gun. This way, I do not have to rush to get the straws in place before the 5 min epoxy cures. Once the hot glue is cured (normally within seconds), I remove the scotch tape and am ready for the micro.


Don't forget to seal the seams of the straws with scotch tape, I did... Unfortunately, I found out after I built up the 2-ply trailing edge support. I had to push hard with my brake line to break off the micro that seeped inside  the straws through the joints. Got me sweating a little....   


Instead of using the aluminum tape, I followed Rick Maddy's foam wall approach. I took a 3/4" piece of foam and laid it on top of the straws. I traced out the profile of the strut (instead of the straw) on the foam. I trimmed along the line with the band saw and sanded smooth. Then, I wrapped the foam edge with packing tape and weighted it down prior to glassing.


I filled the gap between the soda straws and the strut with micro and smoothed out the transition surface for the glass. I then glassed and peel plied. Rick's method works well and was not difficult to achieve a reasonably good result.   





Here's a picture of the completed trailing edge strut support viewed from the back side and ready for the next micro and 4-ply UND.  









Applying 2nd 4 Ply onto Main Gear

I repeated the above UND cutting process for the 2nd set of 4 ply (above) except, I cut it a bit wider (13.5") to accommodate the trailing edge support. I cut a total of 8 strips of UND because that's what I used the last time. I did a couple things differently though:


1) I raised the blocks another 4" totaling ~8" above the table surface such that I can reach the bottom edge of the strut during the glass work;





2) I wet out the UND on a thin packing plastic sheet before laying them down onto the strut. This approach was faster because I can wet out the UND much quicker when it is flat on the bench and I can move the glass around much easier for lining up its fibers to the 35o of the strut.


I tried to be real careful with the UND wrapping around the strut at the bottom - they just won't stay put. I ended up sanding them down as I did with the first. After a bit of sanding, it turned out fine.




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