I am getting ready to put on my ultracote to the wing of my Chrysalis 2 Electric. What is the best sequence of putting the covering on?

My plan is to start on the bottom of the wing and attach the transparent red to the main spar ...then down and around the trailing edge ..then up and over the leading edge .. and then attach it on the main spar under the wing. Then I will put my cub yellow trim on top of the transparent red. The solid cub yellow trim will be the full length of the wing which will be from the leading edge down to the bottom of the main spar on top of the wing. Will this long wide cub yellow strip add to much weight to the wing. I feel like I need to cover the entire wing with he transparent red to give it strength.

The other option I thought about was to cover everything with transparent red except the strip of yellow and then just attach the yellow to the open space but I feel the leading edge does not give me enough wood to attach the yellow stripe to.

From : Don Stackhouse

Excellent questions, and fortunately I have some good answers for them.

First of all, avoid putting covering on top of covering unless it's a very narrow strip, say about 1/2" wide or less. It's very difficult to keep from getting trapped air bubbles, especially over the open areas between ribs. It also adds weight, and the strength from having an extra layer of covering really isn't necessary.

Also, it is possible to wrap the covering around a straight edge (such as the trailing edge), but it's extremely difficult without getting some major wrinkles. It's generally not worth the trouble.

Wrapping it around a curved edge like the leading edge, and still having it smooth enough to continue covering on the other side, is essentially impossible.

There is enough wrap around the leading edge for enough overlap between the upper and lower covering pieces for an adequate bond, as well as for an adequate bond between the film and the wood. I know some of the covering instructions recommend more, but in my experience, 1/8" to 1/4" of overlap between the pieces, assuming the edge is ironed down firmly and with enough temperature to properly activate the adhesive (Ultracoat and Oracover need a little more heat than other coverings in this regard) is generally enough to get the job done. Practice on some scrap wood first, and then try peeling it loose, to make sure you have the right temperature settings and technique.

Step 17 of the wing instructions shows the covering pattern. It's basically just one piece for the top and one piece for the bottom on each wing panel. If you want to do a 2-color scheme, splicing at the main spar is generally the easiest place. Cover the rear portion of the panel first, then the front part, so the outside of the overlap seam between the front and back pieces faces aft. That makes it more difficult for air, raindrops, grass, rocks, corn stubble, etc. to get hold of the edge and start to peel it up.

General rules of covering: put opaque colors on top of transparent ones, try to have all seams facing aft, try to put darker colors over top of lighter colors.

In your case, I'd cover the upper aft part of the wing with transparent red, iron it down to the main spar, and wrap it around onto the underside of the trailing edge about 1/8". Iron it down to the entire upper surface of the trailing edge stock, this will help prevent the covering tension from pulling up the trailing edge stock when you shrink the covering. To get the covering firmly bonded to a wide surface like that, first tack then edge in the middle, then at the ends, then at the 1/4 ad 3/4 points along the panel span, then the whole edge, and finally run the iron slowly along that entire balsa surface with one hand while you follow right behind the iron with a folded up soft rag in your other hand. The adhesive in the covering will still be hot and sticky enough to bond when the rag pushes the covering down against the surface of the wood.

Shrink most of the slack out of that aft-upper patch of covering, keeping the iron over the open areas, not over the edges that are bonded to the wood, or you could make it come loose and cause wrinkles. Do not shrink the covering all the way to "drum-tight", wait till the underside is covered to do that.

Next cover the forward part of the upper surface, overlapping at the main spar, and wrapping around the leading edge dowel to around the 6:00 position on the underside of the dowel. Once again, shrink out the worst of the slack in the covering (so you can verify that any remaining wrinkles will indeed go away when you finally shrink it up to full tension), trim off the excess edge material, and iron the edges down firmly.

Cover the underside the same way, aft portion first, then the forward part. Iron the covering around the leading edge dowel up to about the 8:00 position, then trim off the leading edge covering at about the 9:00 position (a strip of masking tape along the leading edge to help guide the knife can help here), peel the tape off and iron the remaining edge down firmly. I know that probably doesn't look like much overlap, but it will be sufficient.

Make sure the covering is firmly bonded to the entire surface of the balsa at the trailing edge on both top and bottom, then shrink the lower surface up tight all over. Now, block the wing down to your work table with shims for the correct washout as shown in step 20, then shrink the upper surface tight. Take it off the table and check for any wrinkles on the underside. Re-shrink the lower surface if necessary, then block it back down on the table with the correct shims and re-shrink the upper surface. By now the covering should be tight and smooth on both top and bottom, and the wing should have the correct washout. If not, do the re-shrinking process again.

One nice thing about an open-structure wing of this type, unlike a sheeted D-tube structure, is that you can build it all warped and shaped like a pretzel, and still block it down and straighten it out by re-shrinking the covering. Unfortunately, that also means it can get warped again with abuse (leaving it in a hot car, etc.) or weather. It's far more forgiving than a sheeted structure, but does require occasional inspection, which is a good habit to instill in beginners anyway. If this was a model intended only for experienced builders and flyers, we might have designed it differently, but for beginners the open-structure arrangement is much more appropriate.

The final step, make sure the covering is bonded firmly all around the edges of the spoiler openings, then cut them out and iron the cut edges down firmly, prior to installing the spoiler panels. It is possible to use strips of covering for the spoiler hinges, but for beginners in particular it may be easier to use a tape hinge, such as 3-M Nexcare "Blenderm" (if you can find it, you might try on the web from Gabe Baltian at www.airdyn.com), or 3M-600 vinyl tape (good-quality "scotch" tape, available at most office supply stores). These will also work for rudder and elevator hinges.

Everything here makes sense to me but I'm having trouble knowing where 6:00 is on the leading edge for the top upper panel and 8:00 & 9:00 is for the the bottom piece that attaches to the leading edge. Is 6:00 at the bottom center of the dowel?

Looking at a cross-section of the wing with the leading edge to the left and the trailing edge to the right, the 6:00 position on the dowel is at the bottom center, and 9:00 is at the left center, where a horizontal line through the center of the dowel would intersect the leading edge.

Don Stackhouse
DJ Aerotech