- Category: Quickie Plans
- Published: Wednesday, 29 October 2008 01:00
- Written by Dan Yager
- Hits: 4693
Cutting the UNI Spar Caps
The spar caps used in the main wing and the canard are strips of UNI cloth that you will cut from the roll provided in the kit.
Begin by unrolling the roll on a long, flat surface. The example to be used here will be a spar cap that is 8” wide by 50” long. You would measure a 8-1/4” wide piece (to allow for frazzling of the edges) by 5O” long, with the fiber orientation running along the 50” edge.
The technique is one of finding the one strand that is at the edge of the 8-1/4” width, cutting it, and then pulling that whole strand the length of the spar cap to remove it. You will now see a clearly visible gap in the UNI cloth where that one strand used to be. Now, using an exacto knife or razor blade, cut all of the cross fibers along that gap, thus severing the spar cap from the rest of the roll.
Carefully mark the cap with a centerline(in this case at the 25” point) and roll it up to keep dirt out of the fibers.
When you next unroll it, you will probably find that the edges are frazzled. As long as you don’t reduce the width below the original callout(in this case 8”) you may pull off strands that are frazzled. Be carefull to only pull loose one strand at a time or else the whole spar cap will start coming apart
In order to improve the rigidity of a part, you will occasionally be asked to perform a glass-to-glass layup, sometimes abreviated as GTG.
The example shown here is a glass-to-glass layup on a bulkhead. Begin by glassing one side of the bulkhead as usual. Next, having turned the bulkhead over after curing to prepare the other side for glassing, you will remove foam with a smooth transition so that your next layup will butt up against the previous glass layup.
The amount of “overlap" necessary varies with the loads. On bulkheads, use a minimum of 3/8”; on the trailing edges of ailerons and elevators use 1/4” minimum, and on the trailing edges of the wing, use 3/8” minimum.
Quite often during the construction of your Quickie, you will be asked to use glass tapes to join to pieces together.
A glass tape is a strip of BID cut at 45 deg which is used to lap up onto both surfaces that are being joined. For proper strength, the tape should be at least 2” wide.
Before bonding phenolic to any surface, be sure to sand the phenolic dull(i.e. to remove the shiny surface) immediately prior to doing the layup. This avoids getting grease from your hands, etc. in the layup, whch might cause poor adhesion and subsequent failure of the layup.