Jump to content

Update for 1970s Sterling Schweizer 1-34


Recommended Posts

I've been working on a replica of the Sterling Schweizer 1-34 kit from the 70's.  I built one their 1-26s from the same era.  It wasn't easy to build with all of the stringers and curved sheeting.  And I don't recall it flying very well.  This was back in the 70's when these kits were "new".  I got interested in the 1-34 and found the Outerzone plans online.  After some study I decided it wouldn't be too hard to build if I made a bunch of modifications based on building sailplane models for many years.  

 

It's kind of a standoff scale approach.  All shapes and outlines are the same as the Sterling kit (mostly, there are a few variations).  I also wanted to build it light, so, most design decisions are in the direction of reducing the weight as much as possible.

Link to comment
Share on other sites

So some of the major changes I made are here:

 

All curved fuselage parts are made from styrofoam glued to balsa.  Once shaped, the styrofoam is filled with light weight filler ( Ace hardware light weight filler is the best), then coated with Flecto-Varathane.  The varathane sands easily and if you want to put in a little time, you can get a molded like look.  Paint over the varathane as desired.  I may fiberglass the bottom nose area depending on how it holds up on the slope.  BTY, I use old time, hard, styrofoam.  There are some other products on the market that are advertised as Smooth foam, but its too soft.  

 

Tail surfaces are simply made from 1/4 balsa sheet with lightening holes.  

 

Wing is a simple 2 piece design, mounted to the fuse with wing rods, and aileron servos in the wing.  Wing construction is styrofoam, with carbon tape type spars and full 1/32 balsa sheeting.  Im using a wing rod from a Volantix Phoenix.  Its very light.  Its an aluminum tube with a carbon tube inside.  I crashed the Phoenix a while back (pretty violent impact) and the rod was undamaged, so i thought I'll use this.  BTY, the Phoenix is still flying. I've made other wings that were sheeted styrofoam, but there, the sheeting was a 1/32 balsa/fiberglass laminate. They also had internal spruce spars and plywood sheer webs.  Super strong and probably overbuilt.  So I've modified the recipe for these 1-34 wings.  

 

That's about it.

 

I'll start adding a photo build blog soon.

 

 

Edited by Slope445
Link to comment
Share on other sites

So I tested how well the styrofoam/filler/varathane/paint construction and finishing approach would work. I’ve used the varathane finishing method before but it was many years ago so some testing seemed like a good idea. Here’s what you can get. I can be as smooth as you want it and I think it’s about as dent resistant as balsa. It’s nothing like plastic or fiberglass for toughness but it’s a compromise. It’s very light weight.  I still may fiberglass over nose areas that can get damaged during slope landings. 

BF23E226-2A12-405C-BC60-E7F33FD39A48.jpeg

Link to comment
Share on other sites

 

The Outerzone plans do not show outlines of the formers.  Not sure why that is. So I had to make my own outlines.  A study of the plans shows there are flat fuselage sides from which you can measure the height of the formers both above and below the flat sides.  Once you have those measurements you can sketch the formers.  I just assumed the fuselage was an oval cross section above and below the flat sides and the finished fuselage came out looking fine.  Note that former 1 appears to be a circle on view you can see on the plans so that is what I used there.  Also note that I did not have a 1:1 full size plan.  I was going to print a small copy and scale it up using my printer/copier, but the printer hard failed on me so, in desperation, I figured out the scale factor, zoomed up the Outerzone plans to the proper image size on my Ipad, and traced what I needed.  A little tricky but it worked.

 

Here are the former patterns I used.  I took these shots from directly overhead so someone else could still print and use them.  Note that notches were cut in for the flat fuse sides after cutting these out.

F83D0B6E-9CF8-45B8-BEF4-D22808061FEF.jpeg

6D2B171C-E53F-483B-8B8F-026362E09BEF.jpeg

Link to comment
Share on other sites

Here are the first steps in assembling the fuselage. The nose area structure is 1/8 in plywood, epoxied of course. The keel piece is copied off the plans and is 2 pieces of ply. There’s a splice under F3 with a reinforcing piece added. 

0C54EE01-99EC-41C9-ACEC-27840B154159.jpeg

18D46758-A116-4EA5-B190-6F155122E202.jpeg

Link to comment
Share on other sites

Fuselage sides are added next. The sides are cut from patterns traced off of the Outerzone plans. I used 3/32 bass wood for the front portion and 3/32 balsa for the rear section. Due to the length of this fuse, there’s a splice under the wing. I thought about moving the splice but I left it where the plans had it. I did reinforce the splice with a 1/16 ply strip. 

 

 

 

After the sides are epoxied, the rest of the formers can be added. 

 

790CE163-9692-4EBD-ACF7-63F910419B2B.jpeg

Link to comment
Share on other sites

I added a  1/16 shear web in the nose area to stiffen it and provide a surface to glue the foam to. 

 

 

Then add styrofoam and start shaping. The foam sands down quickly. 

8A719353-4F9A-43EB-8F2D-EF0EBC7AF36F.jpeg

8AAE1044-566E-49CE-8ABA-19EBA2F7CA80.jpeg

Edited by Slope445
Add photos
Link to comment
Share on other sites

A41F0708-2789-4A8A-A52D-27D63B2381FC.thumb.jpeg.1e33152a47ac4a400e01a3d441e93bba.jpegThe plans do not show the profile of the nose cone. So, I sketched out a profile I thought looked about right. I think it’s actually longer than the one that came with tho original 70s kit but it’s ok.

 

i made some hard balsa forms, glued them to F1 and filled in the 4 quadrants with softer balsa. 

3E1CFF74-3364-43C6-AD1D-F898382DE1FC.jpeg

99FC87F7-4731-42E2-9A49-8D887F0DCB24.jpeg

Link to comment
Share on other sites

Here you can begin to see the overall look of the fuse “bones”. I put in a 1/16 balsa web piece across and between the formers to stiffen the rear fuse. I alternated between the top and bottom to save weight. I also added a spruce stringer since I wanted more strength right at that narrow point in front of the fin. The fin and stab are also cut out and placed in position just to get a look at them.  No lightening holes yet. 358D728E-8BE6-43C0-8584-D4077BD751F2.thumb.jpeg.9252d67b907b8682e9bccf29a2736b52.jpeg

D2FC3490-B857-4ED9-9164-8310C284E0CC.jpeg

Link to comment
Share on other sites

These photos show the stab mounting block and the vertical fin mounting block. The blocks are both 1/4 inch bass wood, epoxied in place. The stabilizer is bolted on using nylon bolts. I made it removable in case it needs shimmed later. It also seemed very small so I can replace it with a larger stabF7D95C48-3122-4739-9B98-FC747A4B70CD.thumb.jpeg.fe38ad368665e99a28ad601368c7f359.jpeg if necessary. Before permanently installing the fin, a small faring is made (see photo)  A small balsa form fits around the fin. Foam is added and the fairing is tack glued in place for final sanding without the fin getting in the way. After the fin is installed, the faring is installed. 

D33801A4-383B-4F27-8B3A-321D1DC706C4.jpeg

Link to comment
Share on other sites

 

 

11774FC7-00FA-4F8A-B327-2F0C0318506B.thumb.jpeg.5b3e34e524e7bc0b807914667bfafcfa.jpegExcept for more foam on the bottom bays, the fuselage basic structure and tail components are complete. 

 

I tried to make the internal rudder linkage work but struck out. There was way too much slop so I routed it externally. I think a ball link would have worked but too late now. The internal linkage for the elevator worked out fine. 

 

 

 

 

3436FD3C-FA2E-435F-BCEE-103CCD8914A7.jpeg

 

 

43F2FA32-C60C-4E31-87D0-F4D2A6EE9594.jpeg

D5AC5D07-9318-4E28-B49A-267C81658FA0.jpeg

Edited by Slope445
Link to comment
Share on other sites

Still looking for minimal weight, I used the tiny Hitec servos for rudder and elevator. I made adaptors so they’d fit in an old plastic servo tray with a switch mount area. The tray can be removed for access to the forward battery compartment. 

8BC735DF-1ECC-4633-955C-6DD388954A58.jpeg

 

After the canopy fell out a few times I decided I’d better make a latch. I put it together using a few pieces of brass tubing, a spring, a C clip and a nail. The latch can be removed so the servo tray can be removed. The brass pin catches a hole in a piece of basswood added to the center of the canopy. I have to admit, grabbing that nailhead can be tough. I may have to come up with a retrofit!

83DCD8B7-75BD-4AE5-8182-36A9BE30ADD9.jpeg

F326812A-8FBE-4249-BF72-193A6BAD3CDE.jpeg

42980EC0-C121-4EAF-9F0D-30C395BB3EE0.jpeg

Edited by Slope445
Link to comment
Share on other sites

Before starting into the wing design and construction, it’s worth noting that including the fuselage, tail surfaces, servos and battery and excluding the wing, wing rods and wing mount, we’re weighing in at about 16 ozs.

 

I like it!

Link to comment
Share on other sites

Wings

 

The wing construction I’ve chosen for the Schweitzer is styrofoam with carbon spar strips, 1/32 balsa sheeting and plywood root and sub rib.  The TE is balsa as well as the LE. Wing mounting tube is brass. Adhesives used are spray on contact cement, wood glue, epoxy and water activated Gorilla glue.  

 

The styrofoam is typical hard styrofoam found in a arts and crafts store. It comes in blocks that are 2 in. X 28 in. X 12 in. For this model That’s enough for one wing panel. 

 

Since my hot hot wire cutter only has an 18in wire length, I had to cut 3 pieces to make a wing core. Here I’ve cut the raw trapezoidal blocks and laid them out by the fuse to get a feel for how the model looks and make sure my “scaling” and tracing the wing outline from my IPad doesn’t have some gross error.  I’m pretty sure it’s OK. 

 

 

 

29D9B425-F4BA-4C4B-B0E2-5382C4D957F5.jpeg

 

 

 

EFB0FA43-C43E-4F95-9EA6-B61A18B16CA4.jpeg

Edited by Slope445
Link to comment
Share on other sites

ACD0AB91-BEA1-405F-A37E-69BDBEB1A957.thumb.jpeg.6cccae764e12b6c47a8573d9c859393c.jpegWing cores are hot wired using a standard method. I make a two piece template. Cut the top, remove the top template, then cut the bottom surface. I use a homemade version of a Feather Cut hot wire cutter. 

 

Since I wanted a balsa TE I cut off a 1 inch strip of the TE foam after epoxying the core sections together.   There’s also about 2 degrees of washout cut in. 

8541FEA5-5352-4D3A-9CCC-9C6D4704199B.jpeg

 

 

500D91E9-F4A7-4584-9600-B6D333950364.jpeg

Edited by Slope445
Link to comment
Share on other sites

Since the Phoenix wing rod I plan on using is straight, I built in some dihedral into the wing tube mount.  The tube is angled slightly downward  within the wing. This gives about 3 degrees of dihedral.

 

To install the wing tube, the core is cut about 8 in from the root. The a sub rib is installed at that location. I also designed in some reinforcing sub spars at that location. After the tube and ribs are epoxied in, the tip portion of the core is epoxied back on. 

 

The photos should be self explanatory. 

 

 

AA6C9CD4-9FB8-4119-BA67-BF62C81F1094.thumb.jpeg.0a1d94fd5f2f7d7eeebcfa5e45b40d3e.jpeg

 

 

6B80B1A1-1A7E-420B-A6F5-03CEDC55996D.jpeg

 

 

2E1283F1-D772-40DC-BE9A-B712462ECC23.jpeg

Edited by Slope445
Link to comment
Share on other sites

The next step is to add the carbon strips. These are about 5/8 in. wide by about 0.010 and run the entire length of the core.  I did not try to embed them. They are so thin the plan is to simply sand out any trace of them appearing on the sheeting.

 

I set the raw cores on the fuse to get a sense of the “look” again. The wings are like wet noodles at this stage.

 

The carbon is glued on using the Gorilla glue. Epoxy would be fine but I hate mixing that much epoxy. 
 

After the carbon is glued on I can hold the core level by the wing tip. Very stiff. 

 

C7420A6D-7768-4828-92ED-AEE92A56924C.jpeg
 

 

 

AB8E42C4-9362-4B63-87D7-1DD14E4E003F.jpeg

Edited by Slope445
Link to comment
Share on other sites

Yes. I tested it by gluing the carbon to a scrap of styrofoam and pulling in the long direction of the tape until it failed. The foam failed leaving pieces of foam stuck to the carbon strip. I used the type of Gorilla glue shown here. I also roughed up the carbon before gluing. 

94403085-55E3-4954-AD5C-F6650A36894A.jpeg

Link to comment
Share on other sites

For the balsa trailing edge I glued a

piece of 1/8 X 1 in. balsa to the edge of a piece of 1/32 balsa sheet. This assembly was then glued to the bottom TE of the core using spray contact cement. Before applying any top surface sheeting, the 1/8 balsa was sanded down and feathered in to the contour of the core. The top sheeting was then applied over the top so the original 1/8 balsa, now a triangular cross section, is sandwiched between the top and bottom sheeting. 

 

Since I was using the contact cement, and you can’t easily reposition anything after it sticks, i made and installed some temporary alignment dowels. This allows the core to slide down over the dowels to get perfect alignment the first time. The small brass tubes/ply bases are only tack glued and popped off afterward. Then the dowels are cut off. The balsa TE assembly is set on the bottom core bed when ready to do the bonding and the wing core is installed from the top and weighted down. 

CF19D70A-868A-4D34-939F-3EC47D30AA47.jpeg

Edited by Slope445
Link to comment
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

 Share

×
×
  • Create New...