Schweizer 1-26E ~ 1/2.5-scale Kit by Peter Goldsmith (Build thread by JimD)

[JimD]

Several more things have to be done before the top wing skin is added. The excess 1/32" plywood needs to be trimmed off and we started with the trailing edge. Measure back about a strong 1/8" behind each rib and use a long straight edge to draw a straight reference line. Using a nice sharp blade, cut along this line (need about 4-5 passes to cut through) and remove the excess.





We just had to test the sheeting joint...made a nice tight bend and it acted like one continuous piece. I'm impressed!!



We used a rotary saw blade on our Dremel tool to cut the root tip sheeting away and then sanded the raw edge flush with rib W1.

[JimD]

Next, we cut out the skin over the aileron servo mount. A rough cut was made from the inside of the wing skin (to locate the opening) and then the servo tray/cover was used to draw the outline for the opening. Again, the Dremel tool was used to trim the 1/32" sheeting back to the reference.line drawn.



Parts were test fit for accuracy.



The servo cover/mount is recessed by the thickness of the 1/32" wing sheeting. A 1/32" plywood piece is supplied to bring this cover/mount up flush. Laminate the parts together and now you have a nice flush assembly. Binder clips make great tools for this kind of job.

[JimD]

The bottom of the wing is flat from just in front of the spar all the way to the trailing edge. Up to this point, the sheeting has not been attached to the forward section of the ribs. The wing was weighted down (to keep it flat on the building surface) and various sizes of sticks were used to shim up the sheeting against the ribs,



Aluminum angle was use to shim up the very front of the sheeting against the ribs.




Here is a look at the orientation of our spar scarf joints. Wing tip is to the right and root is to the left.



Once the glue has dried, the 3/8" square balsa leading edge can be added. We used a scrap piece of thick plywood stick to keep the tip rib straight while gluing the tip rib to the sheeting and as a stop for the leading edge. Again, binder clips make great tools for holding parts together.



Speed Bond glue was painted onto the sheeting and leading edge balsa and allowed to dry. Flipping the wing over, the forward sheeting was dampened with water and a hot iron used to bond the sheeting to the leading edge.

[BryanB]

I noticed you didn't trim the bottom sheet leading edge until after gluing up and adding leading edge stock.

[JimD]

Bryan, that is correct. Thought it made bending the sheeting over the leading edge easier. Sort of like having excess covering hanging over your structure that enables a better grip holding onto the covering while sealing down edges.

[JimD]

Using the Dremel with the rotary wood cutting blade, the aileron section of training edge sheeting was cut out and edges sanded flush. Using scrap pieces of balsa, 45 degree angle braces were fabricated and attached to the wing tip. A cardboard template was made for the wingtip bottom panel.



Using scrap 1/32" wing skin, the template was used to make two wing tip panels. Once glued in place, this panel was sanded level with the top of the wing.



Then the underside was sanded smooth.





Looking at the top edge of the balsa training edge in the aileron cutout, we decided to add a little extra "meat" using 3/16' square stick. Finally, internal wiring was added using the wiring nice holes provided in the ribs. We like to make our own extensions and our standard procedure is to use twisted white/red/black for the aileron servo and twisted yellow/red/black for the spoiler servo (flap on airplanes). Okay, I know your serious sailplane guys have multiple servos in each wing...so this would not work for you. Remember, I am a tow pilot at heart so humor me!







Okay, I think we are ready to cover it all up with the top sheeting now.

[BryanB]

Have you mentioned hinging plan for ailerons? I guess I missed that.

[BryanB]

Excellent work by the way!

[Stew2]

Jim,

Excellent work as usual. Do you find a #11 X-acto blade a bit flexible when trimming the 1/32 ply? I have and moved over to using the small box knife/snap blade knives for trimming it. The much more rigid blade gives me a cleaner and truer cut. Looking forward to the maiden in March!!

Scot

[JimD]

Bryan, thanks for following 🙂 The hinge plan is to use a covering hinge on the top of the aileron. Will produce a sealed hinge and clean profile. This is a technique that Peter also uses on the Swallow on both ailerons and elevators.

Scot, maybe I am not using as much pressure on the #11 blade. Typically make about 4-5 passes to cut through. Thanks for the suggestion of the utility knife, I will try that technique when we do the other wing. Guess my mind thinks X-acto knife for models and utility knife for heavy construction.

[Asher Carmichael]

Thanks for sharing this build, Jim. Great craftsmanship, information and insight as usual.

[Stew2]

DeWalt makes a nice small snap off blade knife with a 9mm wide blade, a little under 3/8"(.353) that I find very helpful in the shop. Check it out the next time you are at Home Depot or Lowes. It is not the big clunky 25mm wide one nor any where as big as a sheet rock knife either. The project that turned me onto it, was the 1/32 cap strips and sheeting on the Ton Elliott Petrel. I needed a knife that I could pierce through the plywood because I was making rectangular cutouts. For trim cuts where you can start off the sheet and bring the knife in the edge of the sheet to start the cut an X-acto will work fine. Here is an Amazon link to the knife.

https://www.amazon.com/DEWALT-DWHT10037-Single-Blade-Snap-Off/dp/B0051QI5X2

[Tom]

Bryan, thanks for following 🙂 The hinge plan is to use a covering hinge on the top of the aileron. Will produce a sealed hinge and clean profile. This is a technique that Peter also uses on the Swallow on both ailerons and elevators.

Jim......covering hinges are all well and fine for small airframes but a 40% airplane needs a proper hinge! I find over time the covering hinge will begin to fail and you will end up using tape to cover the failure. My EPP 3 meter Ka6 has them and they are failing......Plastic hinges work well as an “under layment” to a covering hinge......they will keep the hinge line in “line” so to speak and will help at the control horn location where the first signs of failure will appear.

[JimD]

I am reporting what Peter has suggested for his design. Ultimately, the builder must decided how they wish to do this.

[JimD]

Two sheets of 24" x 48" x 1/32" Plywood were joined per the method used on the bottom sheeting. A 12" x 2" piece of scrap 1/32" plywood was added to the trailing edge at the root. With the outside of the top wing skin facing up, the wing was placed on top of the skin and positioned. The trailing edge was marked so that the top and bottom would match.



The ribs at each end of the spoiler box were marked and distance from trailing edge to edge of spoiler box was noted.



The dimensions of the spoiler box are roughly 16-1/2" x 1-3/4"





After removing the wing from the top skin, the spoiler box cutout was marked off and cut out (we made this slightly undersize).

[JimD]

The trailing edge was cut to its exact alignment and 3" of the excess length was cot off at the tip end. The leading edge was cut slightly over size. The spoiler box and the trailing edge was used to align the sheeting before gluing in place. Speed Bond glue was painted on all of the ribs, spar, leading and trailing edges, and around the spoiler box.







Once alignment was verified, the hot iron technique was used to seal the top skin to the underlying framework.



Now the excess sheeting needs to be trimmed away and all sides sanded to proper contour.

[JimD]

Stab/Elevator

With the wings completed, we move on to construction of the stab and elevator.

The "spine" of both the stab and elevator are the parts that also make the hinge line.




These spines are made of 1/8" x 1/2" spruce and 1/4" x 1/2" spruce or basswood. Hinge points have balsa "donuts" for added gluing surface. The position of these donuts was transferred for the plan to the spruce and once the spine assemblies were glued together, the donut holes were used as a drill guide to make the hinge point holes through the hardwood. We drilled these hole through using a drill press to keep them as straight as possible.



This recess gives the ribs a slot to tab into. (Note S3)



At the center line of both the stab and the elevator, there are ribs that get laminated together and then glued to the spine as a sub-assembly.

Center elevator rib assembly is made of 5 parts. The middle balsa rib is a spacer and the forward space forms the slot for the G10 elevator horn.






The center stab rib assembly is made of 4 pieces of 1/8" plywood.



The leading edge of the elevator is made of 3/8" diameter wooden dowel rod. The S1 center rib assembly and the S2 ribs get sandwiched between a top and bottom layer of 1/8" lite ply (part S6). Note the S2 ribs in the picture above come to a narrow point. In order to make a good joint between S2 and the dowel leading edge, drill a hole in the dowel for the point of rib S2 to fit into.

[JimD]

The 1/2" balsa parts E6 and S7 fit into the 1/2" slot in the spines. The 3/8" wooden dowel that makes the leading edge is added to complete the outline of the stab. Use scrap pieces to shim S7 and the dowel. !/8" thick shim under S7 and 1/16" shim under the dowel. This keeps all of the pieces centered.



The trailing edge is made of carbon fiber rod. We used a 1" piece of plumbing solder inserted into the joint between the two pieces of carbon rod to reinforce the butt joint and to keep the two sides aligned while gluing.



1/8" shims were added under the 1/2" balsa E6 parts and a round file was used to make a rounded slot in the back surface of E6 for the carbon rod to nest in. CA glue was used to attach the carbon rod to these balsa and plywood parts.



The ribs were sanded to match the angle of insertion into the spines.



A round file was used to angle the ribs as they attach to the leading and trailing edges.





Once all of the ribs are in place, the top 1/8" plate is added to the top of the center stab area. It works best if the stab and elevator are built over the plans. 1/4" spaces were usded to keep alignment between the stab and elevator.





Once all of the glue joints were secure, the parts were removed for the building board and the 1/4" thick balsa leading edge was added to the elevator. This will get sanded to a V to allow movement of the elevator. The trailing edge of the stab remains flat with square corners top and bottom.



We glued the elevator trailing edge to the elevator spine and then clamped the stab and elevator together to maintain a nice straight assembly.



The hinge point holes were drilled through the balsa after the glue cured.

[68mustang]

Excellent build Jim. With all the little extra tips this will be an great manual.

[JimD]

Thanks! That is our hope.

[JimD]

Fuselage

Final sanding of wings, stab/elevator, etc. will be done when we have weather so I can go outside. Way better than making a bunch of dust in the shop.

Step one is to locate all of the fuselage parts. Spend a little time and punch out all of the parts now so they will be ready to use as the build progresses.







Start by gluing the side pieces together. Note that the position for the formers is scribed onto the sides so as to make a left and right side.



Basically, these side panels get outlined with 1/4" x 3/8" spruce. You will need to make a number of angled cuts and scarf joints in this process.



We used weights (bricks and metal) and binder clips to hold things together.





The exception to this outlining process is under the stab area. You can use the formers F12 & F13 to set the proper spacing of the spruce sticks.

[BryanB]

Ack! I could never wait to sand those tail feathers and fare those round parts with the square parts. That would drive me nuts..

[Tango Juliet]

Heck, I wish I could sand outside. But with the kind of humidity we have on the Gulf Coast it would turn into "wet sanding" and that doesn't work so well with balsa wood!

[JimD]

Progress and a couple of tips & tricks

I keep a box of small scrap pieces and often find just what I need for making small parts or doing repairs.



While making the scarf joints to complete the fuselage sides, I got a little too aggressive with sanding a joint and came up slightly short. Wasn't a critical place but it still bothered me to leave it...what to do??? Over to my scrap box and found some 1/64" plywood that was about a 1/4" wide strip. Cut a two lengths and glued them into the gap.



Sanded a bit and perfect!


All of the spruce stringer added and held in place with weights and binder clips.



Also, I save the tapered pieces that were cut away for the scarf joints. Make great shims to hold things in place while glue dries...and a servo box makes a great storage container!



I typically use flux brushes to "paint" on epoxy, but I don't like the flex in the standard bristles. Cut them off at an angle and they work much better.



Decided that the F26 plywood doubler that fits around the wing tube area should be glued on with epoxy. We mixed up a batch and painted it on and then added weights on to keeps things nice and flat and glue joint tight. Make sure that the holes all line up (Peter's laser cutting is very accurate, but the location of the spruce stringer can vary slightly). I had to sand the bottom side of F26 slightly to get the best alignment.

[Tango Juliet]

To help maintain the alignment of the F26 Doubler, I would have used the wing tube or other similarly sized dowel to ensure nothing shifts while I'm adding weights/clamps, then remove it before the epoxy sets. Just a suggestion from my own experience.

[JimD]

Yes, I used the wing tube to align and that is why I sanded slightly. The spruce stringer keeps F26 from moving that direction. An ink line was drawn around the part onto the fuselage side as a further reference.