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Building a Scratch Built Cub

stknrddr

Registered User
Greenville (north east), Wi. U.S.A.
I'd like to share my process building my scratch built Cub with this group, as I have mentioned in a recent previous post in "New Member Introductions".

Myself and a building partner friend of mine are each building scratch built Cubs together. My intentions are to share my progress, learn from the group, have good discussion, all while I work toward a completion.

John
 

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Builder's Update: I thought I'd share a fixture I made to align the torque tube masts which I built (thanks Christian Sturm showing how to make the mast on his web site). I used a piece of 1-1/4" thick material, shaped it as shown, and drilled 2 holes at the appropriate distance apart to position the masts. I fixtured the parts up, clamped in place, then my building partner did the welding.
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Having seen no more of your project than what you've posted, I have no doubt that, if you stay with it, you will build a "high-craftmanship" airplane. Apparently you've built airplanes before.
 
Lunch Time Aviation presents a builder's update: It's lunch time, so I thought I'd take a little time to provide my project update. Continuing with the Torque Tube assemblies, I have attached photos of the torque tube bearing mounts. I typically draw any flat steel parts on paper, then glue (spray adhesive) the paper template to the sheet, than cut out the part. Here I used a portable hydraulic punch I borrowed from work. I got lucky that the large hole I needed to punch was the same diameter as one of the punch and die sets we had. Electricians use these punches to punch holes in electrical panels. After punching, and cutting the part out using a cut off wheel or a sheet metal shear if applicable, we bent up the flanges, and assembled. In order to cut out the curved lines to fit to the bearing tube, I drilled a series of small holes just outside the line, then wiggled the scrap part away from the good part, followed by using the bench top grinder to smooth out the steel to the shape of the curved line. We fixture up the parts welded. My project partner has been doing the welding while I typically fabricate many of the parts and the fixtures. It works out well for us. We're building two cubs, so our combined interests works out well for both of us.
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Lunch Time Aviation presents a builder's update - My building partner (Charlie) and I (John) now have the majority of the tail feathers, fuselages on landing gear and much of the torque tubes made. All scratch built. Today, I want to share progress of my front seat. We decided to build non-adjustable front seats. I modeled my front seat, seen in the photos, to the same dimensions as a PA-18 seat, when the seat is in the most rearward position. I will not have any brake pedals for the rear passenger, so the rear legs on the front seat can be straight up and down, and land on existing cross members. I designed and made the fixtures, and that's Charlie welding the seat parts up in the photo. My intention is to lighten up the seat a little, and sacrifice passenger brake pedals for weight savings. I hope to install toe brakes for the pilot only similar in design to those I use on the Rans Courier I fly, and like just fine.
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I'd encourage you to do the Atlee style folding seat mod on your front seat. Also add about 7-10 degrees of recline to the seat. You will be glad you did! Nobody sits at 90* angle! The seat bracket templates are on my web site.
 
Thanks for the thought Bugs, I've seen that seat, and I'll take a look at the drawing. The seat back is actually leaning back a few degrees, and I struggled a little on leaning it back as far as I did, as I tend to lean forward when I drive and fly... I mocked up a wooden seat and placed it in the fuselage prior to welding this one up. To my surprise, the seat was really easy to fabricate, after a fixture was created, so any changes will not be a heart ache.
Thanks all for your support from all the folks. I appreciate it, and it helps. I have a list of questions to run past folks when the right he time is right.
john
 
In addition to what bugs said consider egress from the rear seat. Without a folding seat back and the seat located further aft rear seat entry is restricted.
 
Everybody has different needs. I have a couple thousand hrs in the back seat of J3s, Pa11 and my Ex 18 all with solid front seat backs and don't see it as a problem. Stay flexible.

Glenn
 
Not everybody you give rides to is as flexible and cool as you.

Thank you, But the 275lb farmer thought it was cool being back there also, he didn't fit in the front so we switched. Never had a folding front seat but probably like it if I had one. Just thinking the rigid one is better protection when things come to a sudden stop?

Glenn
 
Posting some photos of my landing gear fabrication:
Landing Gear 3.jpg
Landing Gear 1.jpg
Landing Gear 4.jpg
Landing Gear 2.jpg
Landing Gear 5.jpg
I hope these photos may help a person down the road, and I appreciate the positive feed back and suggestions I received from this group. Thanks, john
 

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John,

Really Nice looking craftsmanship, it was nice talking to you at the EAA Ski Plane Fly in, good luck with your build, im sure many will be looking on with interest as you proceed to the outcome, I'm looking forward to seeing the end result!

Rick
 
Thanks Rick. And for those who have not seen Rick's build (finished last August), here's a photo of it when he flew in to the EAA Ski Plane Fly In last month. Really nice.
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As I am preparing to mount the tail surfaces (we scratch built) to the fuselage, I thought I'd share how I made a tube bending fixture to bend the leading edge spar of the stabilizers.
We first tried to bend the tube around a flat surface, and the tube kinked. I then researched, and found a tube bending fixture from the Tony Bingelis book series that EAA sells.
Here's the fixture I made and the bending procedure:
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The fixture has different bend radius's on it to create different bend angles in the tube.
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I used a 1-1/4" thick piece of counter top material, and routered the edge all around.
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The routered edge closely matches the tube diameter that we need to bend.
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A steel "wrap around hold down clamp" is needed to retain the tube firmly against the fixture. Here, a person can decide which part of the fixture to bend the tube on.
I inserted a spring to guarantee the tube doesn't kink again. This worked so well, I never tried bending the leading edge stabilizer spar without the spring in place.
The spring is about 9" long or so.
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Slide in the tube and start bending (downward pressure). It's a good idea to draw a line (lengthwise) along the top of the tube, to use as a reference,
in the event a person needs to remove the tube from the fixture, test fit it, then stick it back into the fixture to bend it a little more.
Remove the spring when finished.
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Fit the tube into the stabilizer fixture.
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All the sheet metal ribs were fabricated by cutting the steel on a shear, then bending the steel to the required shape using a sheet metal break.
Then back into the fixture for final fit up and welding.
Similar procedures were used to fabricate the remaining tail surfaces, however the bending fixture was not needed when bending the smaller diameter tubes.
I hope this helps a person work through this part of the build.
john
 

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Lunch Time Aviation presents - Fuselage Construction.

I should include some documentation of the fuselage construction for folks. We started by drawing the layout of the sides of the fuselage directly onto our flat work bench.
We used a hand held conduit bender to bend the longerons to shape, then pieced the tubes in place. Everything was hand fitted. We used a bench top grinder to notch the tubes.

1  Cut and Fit Tubes.JPG
We're building 2 planes, so by the time we got to the fourth assembly, we blasted through it very quickly.

3 Use plumb bobs.JPG
With matched sets of "sides", we drew a center line on the table and set the sides in place.
Plum bobs, framing squares, wood blocking, and diagonal cross wires with turn buckles provided the needed method to square up the fuselage to add the cross members.

5 Check your set up often.JPG
Keep an eye on the plum bobs and adjust the fixtures to keep things correct.

8 Fixturing up the tail post.JPG
I built this boxed fixture to maintain the correct longeron angles and to set the tail post in place for fitting and welding.
The boxed fixtures are screwed to the work bench to ensure things stay in place.

9 I like building fixtures - tail post tacked in place.JPG
Here's the Tail Post Fixture removed after tack welding. This worked very well.

10 Our basemant work shop.JPG
Looks pretty good so far.

6 Fuselage progress.JPG
The fuselage.

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Then we moved the fuselages to another shop where my build partner, Charlie TIG welded things up.

END.
 

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Rudder Fabrication - If a person wants to build a rudder and does not have a rudder to copy the shape of,
here's a pretty simple way to draw a smooth curve to make the rudder look correct.

rudder print coordinates.png
Refer to the Rudder print to get the coordinate's of the rudders' curve and required dimensions (if you want it to match to the plans).

Rudder Layout 3.jpg
Layout the coordinates and other required dimensions onto your work surface.

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Rip of long continuous piece of wood banding from a length of soft lumber (pine?).
Attach some blocks to the work surface to locate the rudder post and used to clamp the banding in place.
Lay the banding on edge, making sure the banding intersects the required coordinates.
Clamp the banding to the wood blocks at these coordinates or other locations in order to get the banding to intersect at the correct coordinate locations.
The nature of the wood banding creates a nice smooth curve as it intersects the coordinate points.
Only light clamping pressure is needed on the banding to maintain the smooth curve. Too much clamping will distort the curve.
Trace the shape of the curve onto the work surface, then remove the banding.

Rudder Assembly.JPG
Bend and fit the rudder tubing to match the profile drawn on the work surface.

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Sheet metal ribs can be fabricated using a sheet metal shear and break to form the ribs.

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Weld it up. Then on to the Vertical Stabilizer. It may be wise to use the rudder as a guide to ensure you end up
with a nice transition at the leading edges of the vertical stabilizer and rudder.

finished rudder.jpg

I'm sure there are other good ways to form a rudder, and I hope this helps a person if they elect to scratch build.

john
 

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Very very nice John. I hope you're keeping all those jigs for your next build. I particularly liked the camming circle in the vice to get your curves right for the stabs leading edges. I did mine with a tube roller and that worked well too. Love to see these scratch built cubs..... Looks like you're making good time too. :up:up
 
I'd like to share work completed on various scratch built ribs. I made the three samples shown in the photo, and I like each sample for different reasons.

The rib in the bottom of the photo represents a "one-piece-sheet metal rib". The rib blank was sandwiched between two wood shapes,
then the flanges hammered using a plastic mallet. I then used fluting pliers to shrink the flanges where needed. The lightening holes
would be punched and flared using a "Mittner Punch". I only have access to a 4" diameter Mittner punch, so the lightening holes would be a little small.
Stiffening beads can be added using a bead tool, however the bead on the rib was made by hand. The rib material is 0.020" 6061T6 aluminum.
11.04 ounce (3/4 rib) before holes are punched.


2421.jpg
The rib in the center of the photo is a "three-piece-stamped rib". Here, I made forms (nose, center, long tip, short tip) to router out the rib blanks, then form the
rib using a hydraulic press (hydroforming) using similar dies. I made all the forms and dies by hand. The rib shown requires the ribs to attach on the web of the spar,
however, the ribs can be attached to the top and bottom flanges of the spars, with similar forms and dies. The rib material is 0.020" 6061T6 aluminum. 11.62 ounce (full rib).

The trussed rib at the top of the photo is made of Carlson cap strips, and 0.020" 6061T6 aluminum. I have since made another using 0.016" aluminum (I like it). I included stiffening beads,
and later I added lightening holes all over. 12.32 ounce (full rib). Very, very strong rib. I've seen similar rib come in lighter than this one. I also bent up a piece of 6063T52 aluminum angle,
1/16" thick, 1/2" x 1/2", and like it as well. I like the trussed rib a lot simply due to being able to use very simple tools to make it. A person can almost make these in their living room.
I made two forms for the trussed rib, one form to pre-bend the cap strip, and a second form to maintain final shape during assembly.

My build partner Charlie was able to buy some beat up stock Piper ribs, and one of the FULL ribs I weighed came in under 7 ounces! I checked my scale calibration,
and feel confident that that is a good weigh. The Piper cap strip is so light and flimsy, that I feel any of the ribs I made are "over built".

More to come as I learn.

john
 

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Project Update - Upper Cabin Structure in Process

We're back to building after a break for EAA Airventure and New Holstein. Had a great time at both, and enjoyed meeting some folks.

The Throttle Brackets were fabricated and tack welded in place. I used a straight pine board
to align and plumb the brackets.
1.jpg

I then fixture up the Upper Cabin Structure Roof using an assembly of wood, wire and turnbuckles.
The X-Roof weldment sets on a sheet of medium density fiber board (MDF) with wood cleats holding it squarely on the board.
A second sheet of MFD sets on the upper longerons, with pine boards clamped in place to position the roof per the plans.
I'm using the stock roof angle, so the front edge of the roof is 24-3/4" above the upper longeron ,
and rear edge of the roof is 22-1/4" above the upper longerons. Angle of incidence can still be adjusted using wing attachment fittings if desired.
The entire assembly is held taught using diagonal brace wires, with turnbuckles to adjust the tension, and to square up the structure.
Plumb bobs, levels and tape measures are used all around to check alignment.
The cabin cabanes were then cut, fit, and tack welded in place.

3.jpg 10.jpg

Before final welding, we thought we'd better make sure we can get the fuselage out of the basement work shop.
That's Charlie up there, relieved to know that we are good to go.

5.jpg

Thank you, john
 

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A Builders' Update - Fabricating and installing motor mount spools, and the diagonal tubes under the wind shield.
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A sheet of flat plywood was used to ensure the motor mount spools all lie on the same plane.
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A flat sheet of medium density fiber board was used to create the fixture required to lay up the diagonal tubes.
Tube lines and intersection lines were drawn to locate the tubes.
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With tubes in place, the tips can be cut off to create a butt joint weld at the intersections of the tubes.
Tack weld the tubes while the fixture is in place.
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Remove the fixture, and finish weld. I still need to add the short tube running from the intersection
of the tubes down to the fuselage cross braces tubes for additional stiffening.

Recent Fly Out Photos - My wife, Mollee and I flew to near by Wausau, Wisconsin to see the leaves.
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The good people at the FBO offered us to take the bicycles to town for lunch.
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So we did.

Thank you all for your good comments regarding our two projects.
John
 

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Speaking of bicycles.....getting a folding ebike (Montague) in the back of a Cub without a folding front seat back seems to be about impossible. At least it appeared that way to me at JC this year, when I was checking out the XCub while Jim Richmond took my bike for a spin. My thought at the time was IF that front seat folded forward like the RANS does, at least the seat back, it would have fit. As you have an S-7 I'll be curious to see if your scratch Cub build has anything from that design, like a larger door for one. I've shamelessly stole many Cub mods and ideas for my own S-7!

Nice build, great explanations of what and how your doing things, educational but entertaining also.
 
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