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Multi-part wings - strengthening query for 2M Sailplane (SIG Riser Replicant)

Hello Everybody,

My name is Martin, and and I am based in Auckland, New Zealand.
I am self-confessed 'slope trash' in that I fly gliders almost exclusively (the exclusion being a HK Spitfire Mk. 24), and slope gliders in exclusion to almost everything else.

In Auckland we are very lucky in that a big chain of arts and crafts stores known as Geoff's (or John's, depending on who owns them) Emporium sell Adams Dollar Tree Foam Board at $5 per sheet. While not US$1, its still not going to break the bank purchase wise. The sheets are available white and other colours too.

I am getting to grips with building out of foamboard, and have been enjoying the Versa Wing as an incredibly manoeuvrable slope soarer.

For a forthcoming project, I have found my old plans of the SIG Riser 2M sailplane. I am of course scheming to buy balsa, ply etc to build a new one off plans, unless I decide to buy a Spirit 2M kit, or perhaps the Gentle Lady kit at the local hobby store. Nevertheless, some cursory work with the plan overlaying with foamboard allowed me to see that the fuse is very nearly 30" long, and the wing panels are 20" wide.....

So, requesting your expertise, I'd like feedback on the following questions - please feel free to give me all your thoughts and experience.

Project - A Foamboard SIG Riser - Lets call it the FT SIG Riser Replicant (or something)

Concept :
User FB to build the thing - total cost = 3.5 FB sheets.
Electronic : 2 x 9g, but there will be room inside for 2 x full sized ones, a 4 x AA NiCd/NiMH 1100-2400mAh.
Control : 2 FT-style control horns, on Rudder & Elevator; I am using 2 x Dubro 1/2A horns, as at $3 thats pretty good. Control runs will be as the FT Simple Soarer, with 1mm piano wire, z-bend at the servo, and with Dubro E-Z Links / Control Stoppers at the horn side. A generous 2cm of wire beyond the easy link to allow good adjustment.

The wing panels will be 4 x 20" segments, with Armin Wing construction, as this give a full aerofoil. The rest of the bird will be FT-style swappable. The Nose cone will be removable, with the option for putting in a FT-swappable power pod (which I do not believe in, but anyway).

Construction :
FT Style / Armin-Wing Style, with tape covering. Upper surfaces while, lower surfaces alternating red/blue tape. Nose doublers of 3mm Correx/Corflute/Twinwall, for strength. Ditto fuse underside, external to foam - makes the bird tougher. I am also considering a totally corflute fuse as well, research already begun. This would give tough light fuse, big smooth light wing.

The Armin Wing lends itself to multi-part construction, but so does the FT wing as per the simple soarer. I also really love the undercambered wing of the Flyboys Ridge Runner.

So : Can any of these wings be built multi-part with confidence in terms of good strength ?

Notes : This is a light-wind slope glider design, an emulation of the original SIG Riser. It will not be engaged in High-G flying - if anything, its a relaxed glider for flying on calmish days, and for catching thermals. It could be high started, using the FT-hook and/or a glider tow release. Its going to be a pure glider, as that is what I like.

Given all of these, looking forward to hearing from everyone - I treasure your thoughts.

Martin - Auckland Slope Trash.


Junior Member
Are you planning for a wing that can be taken apart? If not, I would think that the techniques that Ed at Experimental Airlines uses should be directly applicable to your build. The use of lightweight arrow shafts seems to work well for flat wing sections. Dihedral joints can be made with light ply doublers. Gluing the wing joint and then reinforcing with a wrap of tape should get the job done.

A wing that can be disassembled will offer more challenge...

Hello Dwight,

Thanks for your feedback, its hugely appreciated.

A 2M wing will fit handily in the boot of my Toyota Celica with the rear seats folded, so multi-part wings are not a huge concern. However, I will immediately do research into that. From what I can see, the excellent Experimental Airlines Armin Wing has capacity for a spar - which means that I can build a dihedral piece from some spare aircraft ply I have available, using the dihedral angle from the original Riser plan.

I'll do some investigation into arrow shafts too - as NerdNic is working on a remarkable $10 (or NZ$30) discus launch glider model, which needs one as the tail boom. I'd be building one as a sloper of course :)

Thanks too for the data re the wing joint strength - Peter Sripol (Foamandtape) demonstrated the robustness of the FT construction method with the new mini-Corsair + rockets (huge fun watching that!) recently on the site.

My thoughts were to use the construction method, and re-inforce the joints with fibreglass strapping tape, as I have a lot of that available for re-skinning my EPP slope gliders.

I will be getting cracking, and starting a new post with plans for the Riser Replicant.

Wishing you a happy Christmas,

Martin in Auckland
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Thanks for ideas - enormous help :)

Hello Ram, thanks for the link, its hugely appreciated.

To help understand where I am going, and to see what people think, here are two quick and dirty sketches of what I am building this Christmas holiday :


This is the Riser Replicant - I am thinking of calling it the Nexus 6 (I was watching Blade Runner last night)

Then there is the full-house ship, with wings & tail a replication of the Jaro Muller Ellipse 2V:


Currently doing some design work fettling in AutoCAD 3D at the moment.

Martin in Auckland
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WWI Flying Ace
For what it's worth, I built a 2 meter-ish sailplane in FT style, and it worked very well. It was very much like the Sig Riser, which I had one of when I was younger. I built the wing in one piece. The center section was flat and 30 inches wide with a 9 inch chord. The outboard panels were 20 inches wide and the chord tapered from 9 inches to 6 inches at the tip. I used 1/2 inch square dowel as a spar, and cut it down the middle, making it a 1/2 x 1/4 inch spar to save weight. I used light ply as dihedral braces, glued to the spar to strengthen the joint. I made the wing all at once, starting with the bottom, adding the spars and dihedral braces, then folding the top panels over and gluing them down to the spar and the trailing edge. The wing was 70 inches long and I used it with an FT style fuselage that I also designed, similar to the Riser. I designed it with a removable power pod so I could go powered or unpowered. It honestly was one of the best flying planes I ever had. The wing was extremely strong, holding up to aerobatics that I never should have attempted with it. I never had an issue with it. I had that glider for several years and it held up amazingly. What finally did it in, was taking it to FliteFest 2015. It never made it out of the van, but the humidity from all the rain delaminated the paper from the foam and it literally fell apart.
I will rebuild it again one of these days.