The Wings – Page 3

 

 

Right wing is now up to the same point as left wing. Since right wing is already in the shop I will continue on with it. Ready for step 13.

 

I modified my wing rib jig to accept rib number 2. I assembled the rib just as I have the other ribs, except that I left off the trailing edge web. Once it dried, I trimmed off the top cap strip flush with the rear edge of the main web. I then glued 1/8” strips to the trailing edge web section. Bowers says use 1/8” x 1/8” here. I used 1/8” x 3/16” for two reasons: first, the 3/16” was available and second, attaching it to the 1/8” web made the top cap of the rear web match the ½” cap of the main section which is necessary in order to glue up the rib laying flat in my jig. Back in the jig, I glued on the trailing edge web. I then cut the nose rib back the 1 ½” for the tip bow mounting. I permanently attached rib 2 to the spars and added tri-stock corner blocking. I then cut back nose rib 2F the 1 ½” and mounted it permanently. I now added glue/nail blocks to both sides of 2F and the trailing edge web (outboard side only) of rib 2 for attach points for the tip bow. My blocks are 3/8” x 5/8” cut to appropriate lengths.

 

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Calling on the help and experience of a couple of buddies, we began to position the first lamination of the tip bow on the right wing. We leveled the wing to make sure we didn’t induce any wash-in or wash-out of the wing in setting the tip bow. We clamped in rib #1 to hold the spars rigid. After trying several different positions and making very minor sanding adjustments to the attach points, we came to a consensus and glued the first laminate using T88. We used small blocks of wood to hold pressure against the glue points. I will let this first laminate dry before moving on. Doing all twelve laminates at once is more than I want to attempt at this point.

 

    

 

The tip bow is one of the items that I would suspect is a bit different on every Fly Baby you see. While I want my tip bows to look good and proportioned, I am much more concerned that they are consistent between wings. My tip bow will end up being a little more rounded than the tip bow shown in the plans, which is more of an elliptical tip.

 

Because of the limited pot life of T88, I decided to use Titebond II to glue the laminates of the tip bow. I brushed the glue on in large quantities with a brush, doing a small section at a time and clamping as I went. Each laminate was held in place by about 115 clamps. I eventually was able to glue on a laminate in about 30 minutes. I added the leading edge stiffener prior to the last 5 boards. The plans call for 12 laminates to total 1 ½ inches of thickness. It only took 11 laminates for me to exceed the 1 ½ inches, partly because of slightly thicker stock and partly because of glue seam thickness.

 

I added gussets to the spar/bow intersections just for peace of mind.

 

    

 

Rib #1 is a “build in place” rib since you can no longer slide the rib onto the spars. I started this process by cutting and sanding the #1 nose rib and the #1 trailing edge to fit between the spar and the bow. With the nose rib and the trailing edge sections sanded to the right dimensions, I once again modified my rib jig to the size of the #1 rib. I assembled the rib in the jig but did not glue the bottom cap strip to the assembly. Once the assembly was dried I was able to slide it down into place over the spars. I then glued the bottom cap strip to the rest of the rib, in place. I glued on nose rib 1F and added corner blocks to #1 rib.

 

I sanded the glue squeeze out off the top and bottom of the tip bow to have a smooth surface for gluing scabs onto the bow. Scabs were put on the top and bottom of the bow. I had ordered my laminates 11 ft. long so I was able to use the extra off the ends as my scab material.

 

Next was to determine a “sand to” line around the bow. I started by transferring the top and bottom points of the spars and the ribs to the outside laminate by use of a plumb bob with the wings level. From here, you can center your line all the way around to give you something on the face to sand to. I had envisioned a level line all the way around the bow. What I wound up with was a line that moves slightly upward from the leading edge to the front spar, somewhat level between the spars and dropping to the trailing edges. After studying the plans, this made perfect sense based on the dimensions given so I guess it’s right. Time will tell. I also used lines on the back side of the laminates marked with the top and bottom of the bow according to points listed by plans.

 

I used many different methods to eliminate unwanted wood from the bow – sanding drum on a drill motor, rasp, hand plane – I found that a mini-plane and a belt sander with 40 grit paper seemed to work the best. There is a lot of wood that gets cut away here. On the next bow I might even consider turning a reciprocating saw sideways and cutting away some of the material.

 

To shape the leading edge of the bow I used the “negative” image of the nose ribs cut out of stiff poster board as a template. This worked fairly well. I decided to retain a small amount of the “D” shape of the leading edge around between the spars. I did this by simply dropping my reference line below the center line to sand to. The bow changes to a more symmetrical shape aft of the rear spar to lead to the aileron section. The bow turned out very nice. (Thanks to my Pitts builder friends for help with finishing touches.) Because of the camera angle, the picture below at right makes the bow look a bit pointed. It is not. It has a nice rounded appearance. One note item: the plans say that you should leave the bow 1/8 inch above and below ribs 1 and 2. I could only reason to leave it this way on the aft section of rib 2 for the plywood cover between it and 2A. Thus, my bow is flush with the leading edges and flush with the trailing edge of rib 1. Hope this doesn’t come back to haunt me.

 

 

 

While taking breaks from sanding I have done some small jobs such as gluing in the 4130 tubing used as bushings in the wing wire blocks, fabricating the 2A “sister rib,” and sanding the bottom of ribs 7 and 2 down to the webs.

 

I finally finished the left tip bow. The key here is consistency between the two bows. The calipers, rulers and eyeballs got a good workout making sure the left was as similar to the right as possible. I have included some pictures here of the wings “belly-to-belly” to compare tip bows.

 

      

 

 

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