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Old Apr 29, 2011, 12:28 AM
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Sterling S.E.5a electric conversion

After a thoroughly enjoyable and successful electric conversion of the Sterling 36" Aeronca C-3 for funbuild 4 I decided to give another Sterling kit a try. Sterling was bought by Estes at some point and reissued a few of their kits in the 90's. One of them was the S.E.5a, number A-17 from the old "A" line of rubber powered or control line kits that Sterling produced in the 60's and 70's. I picked the Estes version because it was cheaper and I felt less guilty about cutting in to it. The box says 24" wingspan but the original was 22" and the plans confirm it still is. The plans have obviously been redrawn but still look well laid out, complete and straightforward. I'm glad the parts outlines are on the plans since this is still a die-cut kit and I may have to make a few. The wood looks alright compared to old Sterling kits but the crunch is still there.
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Old Apr 29, 2011, 01:48 AM
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I've already decided to laminate the tail outlines to save weight and I figure the less wood I use out of the box the better. When I started removing and sanding the die-cut ribs I realized it would be less work to make them from scratch. Step one is to make some parts from copied portions of the plan. One nice thing about small models is you can reproduce parts of the plan you need with a home printer/scanner.
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Old Apr 29, 2011, 05:39 AM
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Nice, another Sterling conversion!

I do the same thing, scan the plans in sections and tape together if necessary. Also copy the patterns and cut new parts out of decent wood. This way I preserve the kit to build or sell someday.
Signing on
Glenn
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Old Apr 29, 2011, 01:59 PM
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Thanks Glenn
With the C-3 I ended up cutting all the wood but still used the plastic pieces and decals so the kit really became unusable. Who would want to use Sterling wood in the first place, right? I'm already cutting all the wing pieces since there aren't that many but may still use the fuse formers that came with it, we'll see. I have a number of vintage Sterling kits that I would never build due to their collect-ability but I'm always on the lookout for incomplete or beat up ones to break in to.
Mike
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Old Apr 30, 2011, 01:29 AM
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I used two 1/16" x 3/32" wide balsa strips for laminating and built the tail feathers 3/32" thick instead of 1/16" as originally called for on the plans to give me extra sanding material, after sanding they'll be a little thicker than 1/16" for some added strength. The rudder came out pretty flimsy so I remade it using 3 plys instead. I have a hard time removing the strips from the foam shapes after the glue has dried so I wrapped the foam with a thin strip of blue tape beforehand this time and it worked great. I've heard some don't like building over waxed paper because glue still sticks to it but I like to leave flat parts stuck down until after I block sand.
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Old Apr 30, 2011, 09:45 AM
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"I've heard some don't like building over waxed paper because glue still sticks to it"

Wax paper just ain't what it used to be. Used to be that the only sticking with wax paper, was caused by glue getting down to the base paper through the pin holes. The last time I used it, almost every glue I used stuck to the surface, of the paper.

Les
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Old Apr 30, 2011, 10:59 AM
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I don't think anything is like it used to be Les, they try to cut costs on material and the quality of the end product goes down. I almost exclusively use wood glue to build and, while it does stick to the waxed paper, releases fairly easy. I lift the part with the waxed paper attached about a quarter inch off the bench then gently push the paper down off the part through openings in the structure. One of the nice things about building over metal is you can use wood glue right on top of it and pop parts off with a razor blade. Apply a little car wax and CA releases too, this is also a good way of temporarily attaching jigs to power saw/drill press tables.
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Old Apr 30, 2011, 11:34 AM
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Try parchment paper, nothing sticks to that stuff.
Sanding while the part is still stuck down flat is a good idea. It's getting the bits of paper off the bottom side that's the problem for me.

Glenn
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Old Apr 30, 2011, 12:18 PM
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Quote:
Originally Posted by glewis View Post
Try parchment paper, nothing sticks to that stuff.
+1 on the parchment paper.

After Glenn mentioned it in another thread I went and bought some at the grocery store.

Wow! Great stuff.

Best thing I've ever come across for this.

Tom
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Old May 01, 2011, 01:41 AM
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Parchment paper, I'll have to get some. After a couple evenings making shapes I got down to assembling some wing panels. As I mentioned before I decided to cut all the wing parts from scratch rather than use the stuff from the kit. I replaced the 1/16" square balsa spars with basswood and used lightweight balsa for everything else except the trailing edge and stringers where I used some harder stuff. I start by gluing the trailing edge, tip outline and ribs together then induce washout with a shim before gluing the rest. Notice the 1/16" shims at the leading edge, this is to align it with the front of the ribs which taper up on the bottom a little bit before meeting the leading edge
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Old May 01, 2011, 02:19 AM
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I'm going to keep things simple and light so only three channels on this one. Since it will be rudder only I matched the dihedral on the plans, they provide a template on the plans that I used to make a jig. I have also provided a shot of the rib outline to show the curve at the bottom leading edge. This is the first three channel kit I have built where the wing isn't flat all the way across the bottom and have no idea how this will change it's flight characteristics.
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Old May 01, 2011, 09:16 AM
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You're moving right along on tis one. Nice job so far.

I like your magnetic hold downs. A buddy gave me a stack of magnets but I don't have any sheet steel for the surface. Where did you get yours?

The Clark Y airfoil you posted is perfect.
After converting a lot of rubber free flight models I have come to the conclusion that the Clark Y is the best airfoil for the way I like to fly my models.
Good lift at a reasonably scale speed, not too draggy and minimum speed/pitch coupling.
A completely flat bottom airfoil has a very narrow speed range. Try to push it through the air faster and it will pitch the nose up. Chasing the pitch trim is very annoying and while fine for rubber free flight I don't use them on my conversions anymore.

Looking at the wing pic, did you shim the leading edge strip up off the surface to match up with the top of the ribs? Kinda looks like the strip is too low but it could be just the pic.

Dihedral, I used the free flight dihedral on my Sterling SPAD conversion.
The rudder is very effective and it turns well. I will do a nice snap roll too with only rudder. Last weekend I snapped to inverted, flew a half circle then pulled out in a half outside loop. Did it again but that time used rudder to roll into inverted, flew a half circle then rudder rolled back to upright.
Not scale, but kind of cool for a rudder only model. Only downside is the SPAD looks kinda goofy with a thick wing and dihedral.
Here's a pic of my SPAD for inspiration, hope you don't mind.

Glenn
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Old May 01, 2011, 01:21 PM
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Glenn

I got my steel sheet from a metal duct fabrication shop. You want something thick enough not to bend but thin enough to sit flat against the bench, I think mine is 10 gauge. Cold rolled steel from a metal welding shop is no good since it will never be truly flat and won't conform to the bench like sheet steel.

In post #11 nothing has been glued yet so your right, the leading edge is too low. In post #10 everything is being glued and you can see the shims there. I should have posted them in reverse order I guess.

Thanks for your input regarding airfoil and dihedral, it sounds like I should have a decent flyer when I'm done as long as I don't screw anything up. Your Spad looks great, that is an excellent in flight photo! How much is your AUW on it?

Mike
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Old May 01, 2011, 02:04 PM
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Wonder if one of the home improvement stores would have some sheet metal.

Looks like I was looking at the wrong pic. I see what you mean, the finished wing panel looks good.

SPAD weighs 13.4oz RTF with a 2 cell 800 battery installed.
Had to add 2oz of lead to the nose to get the cg close.

Pic was taken by Jay Smith with his whizzbang Nikon SLR camera that has about a bazillion pixels and a lens the size of a beer can.
Glenn
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Old May 01, 2011, 02:08 PM
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I got dihedral and washout so now I need to decide on incidence. The plans show what looks to be about 3 degrees of positive incidence in both wings while the stab is at zero. I'm assuming the wings are mounted like this to eliminate down thrust at the prop which I like but I don't know if I should keep them equal. I think most non-aerobatic bipe models have positive incidence in their bottom wing only so the leading edges are closer together than the trailing edges but I don't have a lot of experience in this area. Any input or experiences on this subject would be appreciated
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