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Jack Capen PA-18 wing

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Old 09-07-2012, 12:29 AM
  #1
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Default Jack Capen PA-18 wing

I am getting ready to start my 1/4 scale Jack Capen PA-18. I am going to do the wing first and so far I can't make up my mine on doing the build up wing that is 90% ply and bass wood or do a foam wing that would be a lot less work, see after 60 years of building planes what old age can do to you. Any pro's or con's on what way to go.

Ken
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Old 09-07-2012, 05:57 PM
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Default RE: Jack Capen PA-18 wing

How about using "stressed skin" construction (skipping the Plywood and Basswood)using built up Balsa ribs and sheathing, use a bit of carbon fiber veil and lacquer to harden and smooth the balsa sheathing?
With your years of building I bet you could get a real light wing that way, and it would probably be stronger than either the original or foam core version.
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Old 09-08-2012, 02:39 AM
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Default RE: Jack Capen PA-18 wing


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ORIGINAL: iron eagel

How about using "stressed skin" construction (skipping the Plywood and Basswood)using built up Balsa ribs and sheathing, use a bit of carbon fiber veil and lacquer to harden and smooth the balsa sheathing?
With your years of building I bet you could get a real light wing that way, and it would probably be stronger than either the original or foam core version.
That sounds like a good plan, I like it and thats what I am going to do. Thanks
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Old 09-08-2012, 07:59 AM
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Default RE: Jack Capen PA-18 wing

Glad you like it, it sounded like a good choice for what you were doing.
I use this for inspiration for building this way.
This is a photo of a original Jenny rib at a friends house in Taunton at one of the oldest continually operational airfields in New England.
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Old 09-11-2012, 04:55 PM
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Default RE: Jack Capen PA-18 wing

Started to get my wood list together today.This plane is loaded with hard wood, I can see why it weight 21#s. Going to see if I can't take a few lbs off. I needed 2 sheets of 24x24 birch ply for the front sides of the plane, come to find out no one sells 24x24 just 12x24, so I went looking and found one place that had it and every other kind of wood you would ever need but no balse.
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Old 09-12-2012, 09:21 AM
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Default RE: Jack Capen PA-18 wing

You may want to look at using the truss side construction like the Sig 1/4 scale cub. I have a 1/6 scale Bellanca Airbus/Cruiser with a 11' wingspan and it's built with the truss style construction and is powered by a Zenoa 38, the only Plywood used was for the firewall. The nose was reinforced using balsa ply made up of 3 layers of 3/23 balsa laminated together as far back as the lower wing only. Well there was other plywood used for gussets on the frame, but the entire construction of the plane was pretty much done with balsa. It came in at about 19 Lbs but it's a big plane to start with and the semi Bi-Plane type of configuration adds a lot of weight to the build.
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Old 09-12-2012, 12:37 PM
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Default RE: Jack Capen PA-18 wing

Thanks for the tip Iron Eagle. The only reason I needed 24x24 ply was because of the size of the template, after it is cut out there is not a lot of ply left from the 24x24 sheet.
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Old 09-12-2012, 03:11 PM
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Default RE: Jack Capen PA-18 wing

You can order that size stock from Aircraft Spruce if you need to have it.
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Old 09-13-2012, 03:18 PM
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Default RE: Jack Capen PA-18 wing

I looked there first but at $60 for 2 24x24 sheets I had to pass them up. Got it at another supply house for $18,grade AA birch.
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Old 09-13-2012, 03:22 PM
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Default RE: Jack Capen PA-18 wing

Wow, that's quite a difference in price, Glad you found some at a far more reasonable price.
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Old 09-22-2012, 12:53 PM
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Default RE: Jack Capen PA-18 wing

I need a little help with the wing print. Between the ribs they have a little line at the leading edge called a fake rib. I no not what they are talking about. I also have the print for the 40 size same thing on that print.
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Old 09-22-2012, 12:57 PM
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Default RE: Jack Capen PA-18 wing

Is that the short ribs that go from the leading edge back only as far as the spars between the full length ribs?
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Old 09-22-2012, 02:53 PM
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Default RE: Jack Capen PA-18 wing

Yes that is what it is, but could find no detail about it on the print.Thats a lot of ribs. I guess they did that because they covered to the spar with 1/32 ply. I may leave them out because I am using 3/32 balse. Thanks for your help.
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Old 09-22-2012, 03:16 PM
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Default RE: Jack Capen PA-18 wing

If the leading edge of the wing is sheathed with the 1/32 plywood they just stiffened it over the span between the ribs, using the heavier sheathing they probably won't do much other than add weight.
I am curious about the spacing between the full length ribs, how far apart are they? As long as your sheathing is not going to sag over the bay I wouldn't worry too much. If you feel that it's close to borderline you can tighten up on the spacing of the full length ribs and add one or two, and still forget the short ones.
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Old 09-23-2012, 02:36 AM
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Default RE: Jack Capen PA-18 wing

The spacing for the ribs is 4.5 to 5 inch's. I looked at the spacing on some of my other big wings and the spacing is about 3.5 to 4 inch's. I think I will use the short ribs per the plan.
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Old 09-23-2012, 06:52 AM
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Default RE: Jack Capen PA-18 wing

Ken,

I'm not familiar with the Jack Capen plan set...Where can you get it and how scale is it?

Thanks,

Gordon
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Old 09-23-2012, 08:13 AM
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Default RE: Jack Capen PA-18 wing

4.5 to 5 inches is a fairly large distance, now I can see why they used pony ribs to stiffen the sheathing on the leading edge...
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Old 09-23-2012, 11:00 AM
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Default RE: Jack Capen PA-18 wing


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ORIGINAL: gordon_mcln

Ken,

I'm not familiar with the Jack Capen plan set...Where can you get it and how scale is it?

Thanks,

Gordon
http://www.scalercmodels.com/rcplans.html#6

Try this, as being true to scale this I don't know.

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Old 09-24-2012, 12:18 PM
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Default RE: Jack Capen PA-18 wing

If I were the one doing a large scale model of this sort I think I'd want to find out what the rib spacing is on the real aircraft and then build my model with the same number of ribs as full size with the spacing scaled to match. To me that suggests that 4 to 5 inch spacing uses less than the scale number of ribs as it is quite extreme. In looking up the Capen design it's apparently 1/4 scale. That suggests that the full size rib spacing would have been 16 to 20 inches. In my experience that seems like a lot for a fabric covered wing. So a little checking and maybe modifiying the number of ribs would be worth considering.


106 inches of wing area will carry quite a bit of weight. But I tend to suspect that if you can lower the final weight to more like 16 to 17 lbs that it would fly at a more scale like speed.
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Old 09-24-2012, 12:50 PM
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Default RE: Jack Capen PA-18 wing

Thanks for that info, I am going to check that out. I am sure it will help. I am cutting a lot of the weight out I hope.
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Old 09-24-2012, 12:51 PM
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Default RE: Jack Capen PA-18 wing

I found this drawing of a full scale it says 16 ribs.
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Old 09-25-2012, 02:51 AM
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Default RE: Jack Capen PA-18 wing

Thanks for posting the wing print. I know they say thewing span is 106", how they got that I don't know. On my print the wing is 51.5" x 2- 103" add the fuselage and we have about 108". Back to the wing on my print, it has 13 ribs, if I make it 16 ribs I get the wing spacing to 3.25 but would have to add 1 more rib because the first 2ribs only have a 1" space at the root end.
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Old 09-25-2012, 07:26 AM
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Default RE: Jack Capen PA-18 wing

I like the 3.25 spacing that sounds a lot more workable...
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Old 09-25-2012, 08:31 AM
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Default RE: Jack Capen PA-18 wing

I like the 3.25 too, so that will be the plan. Just waiting for the wood to show up now.
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Old 09-25-2012, 09:21 AM
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Default RE: Jack Capen PA-18 wing

I thought those pictures might hep you you notice the different spar were they attach the struts? As far as the wingspan, it's interesting how much what you actual get as opposed to what the specifications say. Where you building a more modernized version of the cub you can pretty much claim some license on the build like skipping the cloth covering.
To this day I can not understand why the haven't developed a updated full scale version using composites. These planes are workhorses and there is a need for that type of plane today in a lot of areas still, awesome float plane.

I think that rib spacing ought to work well with the sheathing and the carbon fiber to make a light stiff wing.
Have you considered balsa and carbon fiber for your shear webbing for the spars?
Are you going to build your version with or without flaps, I know they came both ways in the later versions?

Any chance of you posting some pictures of your build from time to time?
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