Hi all

[GaryBridge1]

Hi to everyone, I've been building and flying R/C fixed wing and helicopters for around 8 years. I have a 2.4M Heron foamie glider which I fly regularly and am just about to commence my first glider build. A 3 Metre - Schempp-Hirth Standard Cirrus - Balsa - Short Kit supplied by Sarik Hobbies UK. Whilst I'm a fairly experienced builder, having completed a 72" Mosquito and a 79" Super Chipmunk; this being my first glider build; the plan is not too clear on the method for joining the detachable wings. I'd appreciate any pointers ref wing joins please? Gary

[Peter Balcombe]

Surprised that there is nothing at all shown on the plan, especially in the root rib area -assuming this is a built-up wing construction.
There is usually something identifying joiners and how the required wing dihedral is to be arranged.
Unless this is a fairly modern design, I would have thought that a flat steel strip (probably 12 x 2mm) in the mating brass box would be the norm - as used on most of the Mike Trew 1/5 scale (3m span) designs. That’s also what is used on the Pat Teakle 1/5 scale Dart.
Normally the main joiner would be at/between the main spars, with a 10SWG or similar piano wire rear incidence pin, again sliding into a mating brass tube.

[Peter Balcombe]

I see that the Sarik Cirrus kit is of the Mike Trew plan, so have just looked up my Mike Trew 1/5 scale Fauvette plan (118”).
This shows a Graupner wing strip case (brass box for 12x2mm steel strip joiner strip) set into the wing between the spars on both the wing plan and the fuselage root rib on side view. There is also a span-wise wing section of the root area showing how the box is mounted between the spar at the 2 degree dihedral angle.
There should be similar info on your Cirrus plan.

There is also a 10SWG brass tube fitted between ribs 1 & 2 about 60% of the way back between main spars and TE. Note that the rear incidence tubes need to be set into the wing at the same dihedral angle as the main joiners, then a straight joiner strip & rear incidence rod can be used in the fuselage.

[GaryBridge1]

Hi Peter, Many thanks for your responses, yes on the Mike Trew plan it does show the Graupner wing strip and the 2 degree dihedral. I have never heard of this before, so was wondering if I could adapt some other method, perhaps by use of carbon tubes slotting in, or am I going down a wrong avenue?

[Peter Balcombe]

Gary,
You could use a carbon rod main joiner sliding into a suitable tube, fitted in a similar way to the steel strip/brass box.
I would think that you would need to use at least an 8mm diameter carbon rod, so your tube will be 10mm dia. or so.
Overall, it should be slightly smaller & lighter than the steel option. Either way, it’s a good idea to infill the space between joiner & main spars with hardwood/epoxy to get a solid connection from joiner through to the spars.
You could also use carbon for the rear incidence rod.

The steel rod/brass box is available from Gliders Distribution (comes in 1m lengths). Stock Ref. GLB12
£16 for 1m of strip + brass box.

Another point to note with Mike Trew designs is that they will usually show fuselage mounted aileron/brake servos, connecting via bowden cables. These days, it is possible to modify the arrangement to put suitable servos in the wing, even if they have to go at the root end.

[GaryBridge1]

Peter, Excellent info. I have used the carbon tubes method on my 72" Mosquito as wing joiners, but thank you for pointing out that Gliders Dist sell the steel rod/brass box. That makes more sense now to see the actual item. On the plan there is no mention of steel strip, so I couldn't understand how the wing attached. Got it now though and yes I am going to use the thin wing servo's for ailerons. Do you make the air brakes as per plan or buy ready to fit, that I've seen at RC World circa £60 ?

[Peter Balcombe]

Gary,
Not sure what airbrakes are needed for the Cirrus, but probably equivalent to the mechanical Multiplex ones. Topmodelcz do the mechanical equivalents in a range of sizes and provide a good service.
Gliders Distribution also do airbrakes (see under glider accessories), but appear to only have a single servoless type listed at present.
A 250mm top acting set should be fine for a 3m glider.
(My Fauvette had scale top & bottom brakes so had to be made from scratch).

[GaryBridge1]

Hi Peter, Just looked at Top Model CZ and ordered some spoilers for €30 along with a tow hook for the nose; ideal and a great price, as long as the postage isn't too expensive? Spruce spars and additional balsa arriving tomorrow; so I'LL be cracking on with the build. Many thanks for your help.

[Peter Balcombe]

I look forward to seeing progress on the bench.