Folding Struts 102

I know several of you have built the old style of folding struts for your cubs, due to the number of emails I have received.  During the build of my L-4 I did a little reworking on my struts.  I guess you could say I went a little more scale with them.  The old style is still great, but let’s take a look at the new way.  This process can only be done to a cub that is still being framed up.

What you will need extra that is not in the kit

4 rods with 4-40 threads on one end 30 inches long made by Dubro #145
4 4-40 solder on threaded ends by Dubro #336
4 4-40 threaded rod end cleaves by Dubro#302
12 2-56 bolts with nylon insert lock nuts 1/2 inch long by Dubro
4 2-56 bolts with blind nuts 1 inch long by Dubro
4 4-40 bolts with blind nuts 1 inch long by Dubro
4 4-40 bolts with nylon insert lock nuts 1/2 inch long by Dubro
4 3-32 E/Z adjust Aileron Horn by Dubro
1/2 foot of small silicon fuel line by Dubro
Some small scrap blocks of aluminum to make the upper strut ends.
2 1/2 x 1, 1/2 by 1/16 thick aluminum strips
2 3/4 stream line aluminum tube by K&S
2 5/8 stream line aluminum tubs by K&S
3/16 x 3/32 C channel by Special Shapes or 3/16 x 1/32 flat aluminum strips
4-40 tap and drill bit

Prep work on fuselage

The easiest way to attach the struts to the bottom of the fuselage is just to bolt the strut to the ply plate on the bottom of the fuselage per plans and be done.   Just drill the 4 holes for the 4/40 bolts and install the blind nuts.  For a more scale look, recess a pocket into the fuselage for the struts to slide into.  Sorry guys I did not get any photos of this section but refer to my cad drawing.
fus plate
IMG_0027

Take the strut mount tabs that are supplied with the kit cut to shape per drawing.  Next mark the outline on the landing gear block and using a rotary tool carve the area out.  It’s best to use a router base to get a true flat section.  This area should be cut 1/8 deep.  Next cut your covers from 1/16 ply and using the above method cut the space for the covers to fit.  When finished insert the strut fitting in to slot and drill the holes thru the assembly.  Take the 4/4/0 threaded couplers and place them on the tab to mark the location for the holes. They should fit side by side with very little gap between them. Drill the holes and reinsert the couplers and install screws.

 Wing attachment points.

 

100_1344

Now with the strut attachment to the fuselage side done, set the plane up and install the wings.   Block the wings up so you have the correct dihedral in the wings. Locate on the wing where the struts attache.  This is located on the front and back spar.  Now with a straight edge project a line as if the strut was to continue through the wing to the top of the wing.  This will give you a correct angle in the wing to mount the attachment point for the struts.

On my L-4 I went with the C Channel.  This gives it a more scale look then the flat stock.  Sorry I can not provide exact measurement for the parts as they will differ according to what manufacture of Cub you have.  As you can see from the photo I glued a strip of hard wood on top of the spar and then finished filling the gap with balsa.  Before you ask about the brass tube…… That is part of the scale aileron hinge setup.  Check out my plans in the store for scale ailerons.  Mark the locations for your bolts.  With the C channels back to back with each other drill two sets of hole through them that will accommodate the 4-40 bolts on each end.  Place the C channels on the lines you projected through the wing.  You will need 4 sections of C Channel per wing.  I use a 4-40 bolt with a nut on the other side and a few drops of CA to lock the nut on.  Do not over tighten as it will crush the wood and flair the strut end.  Next I glued some scraps of hardwood to the spars to keep the channels from moving up and down.  Finish it up by using balsa same thickness as your cap strips and dress out the attachment area.  If I had it to do over, I would probably extend the C Channel through the rib to a hard block on the other side of the rib and use two 4-40 bolts per spar.  I have over 100 flights on this setup without any issues.  Complete this for all four strut attachment points on the wing.

Now time to make our strut ends for the wing side of the strut.  This step has a lot of geometry in it to get everything to fit.  You can still use the 4-40 ball links as in the Struts 101, but for a more scale look read on.  Feel free to use hard balsa to make your patterns and then transfer them to the aluminum blocks.  My recommendations on make the parts. Shape the block so it will slide into the end of the strut.  You will need to make one for the front and one for the back.   Cut the strut tubing just long enough to go between the fuselage and the wing mounting points.  Now install your block you just made with 1/2 inch of the block in the strut and 1/2 inch of the block sticking out of the strut.  With the strut held in place sketch lines onto the block and trim away the scrap.  Yes I know it’s hard to get an idea of what I’m doing, buts it’s just as hard trying to tell you how to do it.
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I guess the best thing to do is say this is what it will look like when you are done.  Sorry the photo is not sharp.  This attachment is rough cut and ready for final sanding and smoothing.  Remember you will need one for the front and on for the back.  When you are happy with your blocks, now transfer them to the aluminum blocks.  For the end that fits into the strut tubing, you will need to drill and tap it for your 4-40 rod plus drill the hole for your 4-40 bolt to attache it to the wing.

So at this point you should have everything made to attach the strut to the wing end, and have the fuselage attachment in place also.

 

 

Build the struts.

I highly recommend doing one side at a time. Take the Dubro#302 cleaves and use the 4-40 tap to clean out the threads.  Screw about 3/4 the way in the solder on threaded ends (Dubro #336) into each cleaves.  Now attach them to the fuselage attachment point.  Taking the 4-40 rods, screw them about 3/4 way into the strut attachment blocks you made above.  Next mount the blocks to the wings with a 4-40 bolt.  If you did everything correct…..(I hope you did) the 4-40 rods will match up with the cleaves on the fuselage.  You will need to trim the 4-40 rods so they will fit into the solder on ends.  With this done for all 4 of them, take it all apart leaving the 4-40 rods in the blocks you made.  Unscrew the solder on threaded ends from the cleaves.  Solder the ends onto the rods.  Cut several section of fuel tubing (about 1/4 inch long) and insert them on the rods about every 6 inches. This keeps them from vibrating as bad in the stream line tubs.  . Take the K&S streamline tubing and cut to length, large one up front and small in back. For the fuselage end of the strut I recommend two options.

  1. Using hard balsa, make the lower end of the struts to shape and insert them into the strut and glass them.
  2. Using the strut its self cut and form down to make the shape you need. Remember you have to have a hold in the end for the solder on threaded connecter to poke through.

Now re install the rod into the strut with and reattach the cleaves to the end.  Attach the wing end first, swing the strut up to the fuselage attachment point and adjust the cleaves as needed.  Complete this for all four struts.  Now all that is left is to make the jury struts.

Jury Strut.

The bends and length of the parts below will need to be made custom four your plane.  The wing mount side is a little work, and yes it’s another one of those hard to tell you how to do it.  I used some hard balsa 3/8 thick and some scraps of 1/16 balsa.  Take a look at the sketch and photos to get an idea of what we are making.   Basically we are making a pocket for a section of 3/8 by 1/16 brass stock to slide into at a 45 deg angle. Then a 2-56 screw goes through the box to secure the attachment.  You will need 4 of them when you make them.  My approach is this.

 

Take the K&S sheet and cut 4 strips 1/4 inch wide about two inches long. Next step will take some guesswork; you may want to use card stock to make a template. What is required is to make a band the will go around the strut the will hold the aileron horn. You will need one for the front and one for the back. After band is made you will nee to drill holes for the 2-56 bolts. Now assemble band on to struts with the aileron horn in place and snug the bolt. The horn should rotate freely on the bolt. Take s section of 3/16 OD tubing and measure off for the cross strut smash ends and mark the hole locations. For the front jury strut flatten the end of the tube and bend forward, and for the back one you will need to bend the tube back drill holes and mount to wing. Bring the front and back jury struts in and trim to length. Now flatten the end of the tube and mark holes for attachment to the struts. Now insert a screw from the plane side through the aileron horn, cross strut and the upper strut. Install a nylon lock nut and tighten. Now repeat for other side.

Disassemble the jury struts for painting. Remember to keep each side separate from the other. Main struts can be paints as they are, just mask the end off the attaches to the fuselage side. After all is painted reassemble Jury struts. Before attaching the bracket on the strut for the Jury strut wrap a small section of black ribbon around the strut and assemble. Attach struts to the plane.

To remove the wing, I remove the two 4/40 bolts from the bottom of the fus. that hold the alumni strip to the plane. Unfasten you wing and pull straight out. Remove the 4/40 bolts that attach the jury struts to the wing, fold jury strut toward the fus and fold the whole assembly down. Insert a towel between the strut and wing to protect the finish.

Look at photo page below for help. If you have any questions, email them to me. CubMan

TIP
As with take 1 on the struts it is recommended to usa a small sheet of plywood in place where the Jury struts attach when folded down. This is attached to the wing with the same holes and screws that the jury struts do. It keeps the nuts of the jury strut from digging into the covering when they are folded flat.

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