Spirit 2M ARF wing joiner.

[jrgospod]

Spirit 2M ARF wing joiner.

I have a Spirit 2M ARF glider that I folded the wings on during a winch launch. No other damage just the joiner. I know I can add a new plywood joiner, glue the wings together and glass it over. What I would like to do is make/buy a new joiner and keep the two piece wing. Any suggestions on what to use and how to make it, or where to buy it?

Thanks.
John

[Ollie]

If you want to make a new wing joiner out of wood, you can almost double the strength compared to birch plywood. If you make it out of solid birch or maple. This will almost double the strength because about twice as much grain crossection will be in the load bearing direction. With plywood the cross grain plies are about nine times weaker than with the grain.

The best wood for the joiner is ramin. It has a compression strength about 16% greater than birch. Do a Google search for ramin. Ramin is available and inexpensive in dowel form. A large diameter dowel can be milled to the desired thickness of flat stock and the joiner cut from that. Ash or honey locust also make strong joiners. A solid joiner made form any of these three woods will be more than twice as strong a joiner as birch plywood. BTW ramin has straighter, finer grain than ash or locust and machines easier.

[Soar_dude]

I would go with a aluminum joiner. That seems to be the biggest headaches with the GP Spirits(The wing joiner that is). On my stretched wing Spirit 100 I went with a aluminum wing joiner "Oh yeah I streched to a 120 inch". With a aluminum joiner it will bend before it breaks but the rest of the wing will be toast before that happens.

Soar Dude

[jrgospod]

Thanks Ollie and Soar_dude

I would do an aluminum or carbon or wood if I could get it pre-made. But alas know one has pointed me to one. If the joiner is stronger than the wing then is a moot point which it is made of. My spirit is so light weight that I could use some ballast anyway. I have maple and if the wings will rip apart before the joiner breaks then maple it is (aluminum is harder to come by and shape). The launch that broke the original joiner was not any harder than others I have done, but fatigue must have been building in the aluminum joiner caps. One question. Should I coat the new maple joiner with CA to resist nicks etc?

Thanks again for you input.

John

[Ollie]

The main reason to paint or CA the wood joiner is to prevent swelling due to moisture absorbtion or shrinking due to drying out. Epoxy makes a very good vapor barrier. Wood is not nearly as brittle as carbon fiber so minor (less than 1/32") nicks will have little practical effect.

[jrgospod]

Thanks again Ollie!

John

[jrgospod]

Ollie,

In the way of an update, I made a solid maple joiner and broke it the first time out. That may sound bad but it was good. I was just about done flying when I made a bad final turn (tip stall) and nosed it in. The joiner broke and the wing was fine. I am making several more joiners now just to have on hand. Something had to give and I'm glad it was the Joiner. I think the joiner will be fine for winch use but give me the safty I need when I crash.


John

[aeajr]

I need to ask a dumb question.

I have been flying my Spirit 2 Meter since July. I launch off a very strong hi-start. A NE Sailplanes Standard with 1/2" rubber and 3/32 wall. I pull it back to the point that I can barely hold it, givei it a push and up she goes to 450+ foot launches.

Before I put the wing on I tape the two halfs together with clear packing tape. I am not seeing any evidence of wing flex, nor do my coaches who keep telling me that I am over pulling the hi-start for this plane.

I only have 3 winch launches of my own, though others have winch launched for me. They tap the pedal.

Is my use of tape to join the wings, along with the joiner, an unusual step? Do you spirit flyers who have two piec wings do this as well?

[jrgospod]

Hi aeajr,

I’m not sure how common it is to use tape on a spirit wing but I see several people in our glider club using it on other wings and tails. I do not use it yet. I plan to use it for my next outing. I am going to place a two inch wide strip of clear packing tape base on the wings and then cut it where they join. That will give me a base to protect the covering. Then I will use one inch medical tape to hold the wings when I fly. The intent is to have the medical tape remove without damaging the covering or the clear packing tape. I have seen that recommended. Good luck.

John

[Fred_L]

I have built a standard Spirit 2m from the kit. This is my first model aircraft. The wing joiner in the kit is a single blade of what looks to be about 1.5mm or 1/16" aluminium sandwiched on both sides by plywood. I think the ply is just to build up the thickness so the joiner fits the wing boxes without too much play. I don't think the strength of the ply would come near the strength of the aluminium, but the ply probably adds a little strength. I wrapped the wing boxes, inside and outside, in fibreglass since that was all I could easily get my hands on.

This weekend in our 2M competition I achieved a burst wing box when attempting to do a very strong zoom from a reflex hand tow launch. I put in quite a bit of up elevator during the climb and there was heaps of tension in the line when I commenced the zoom. Plane accelerated down like crazy and when I attempted to pull up and pop off the line it was obviously all too much for one wing box as the wing box burst and the joiner smashed right through the top spruce spar. That wing detached completely and the rest of the plane spiralled in from about 400'. The wing joiner looks to be unscathed, with no bending, so I will reuse it.

So my experience is that the standard single blade aluminium wing joiner was stronger than the wrapped wing box.

Fred

[Ollie]

A strong zoom launch isn't safe on any kit design that I know of which uses only spruce or bass wood spar caps. A possible exception is the Gemini with a 15% thick airoil for great spar depth. A stronger wood like ramin for the upper spar cap on the inner panels will increase wing bending strength by about 80%. The best precured unidirectional spar caps are about 49 times stronger in compression than spruce for the same spar cap crossection. Unless sparcaps are prevented from buckling by generous sized vertical grain balsa shear webs, they can't develop their compression strength potential.

[jrgospod]

Fred_L

The bottom line is that the spirit 2M is not a full strength launch ship. It is an entry level floater and unless you do extraordinary things in the build to make the wing bullet proof, you are going to blow it up on a hard launch. If one wants a full pedal, full zoom launch ship you have to buy one designed for it, or redesign the wing. The Spirit is not designed for that purpose.

John

[Fred_L]

Yes, I was aware that the Spirit was only an entry level glider. I was flying in competition on a dull overcast morning and the maxim of 'he who launches highest wins' was in force. So the need for a higher launch. Anyway I found where the limits are for this aircraft. I always understood that aircraft don't last in pristine condition for ever as things just go wrong.

The aircraft is really neat, and flies beautifully. Couldn't be happier really. It is my first R/C aircraft of any type and on my second flight (another club member launched it) I managed to score a couple of thermals and had an extended 12+ minute flight.. Got a few similar flights by catching thermals on that day. So I was ecstatic.

I'll fix this one and make a couple of changes while I am at it, like drilling a hole in the nose to move the lead balancing weight further forward. I will wrap the wing boxes in carbon tow this time round too. I had already built a new stabiliser that was held on by two screws rather than glued on as originally built. The removable stabiliser aids in transportation as the fuse is just so much less bulky and this hopefully will reduce hangar rash. A new fin has an upright rudder hinge line to let me get at the stabiliser mounting screws.

Anyway, I am still on the learning curve and having a ton of fun.

Fred

[jrgospod]

Fred,

My spirit is an ARF and I have never had the covering off so this may not apply. The one thing I have been told to do is to epoxy carbon fiber spar cape on the wings (Bottom and top, but I believe that the bottom is more important.) to give them that extra strength on the launch. If you rap the boxes and CF spar cap the wings you will have a really zoom ready ship. Good luck!

John


P.S. you will also need a stronger joiner.

[Ollie]

Fiberous materials like wood and carbon fiber in epoxy are stronger in tension than in compression. If the top and bottom spar caps are of the same crossectional area, the top spar cap will fail before the bottom spar cap. That is why the top of the spar is what needs reinforcing most. Until the compression strength of the top spar cap exceeds the tension strength of the bottom spar cap any thing you do to strengthen the bottom spar cap is wasted. This analysis applies to wings with airfoils that have appreciable mean line camber like the Spirit wings because they can generate more maximum lift upright than inverted for a given air speed. It also assumes that the shear webs are adequate for shear loads and to resist buckling in the top spar cap.

[jrgospod]

Thanks Ollie,

I guess I had that bottom side up.

[sierra-gold]

Ollie,

Therefore, that's the reason I recently read somewhere to put two strips of carbon tape on the top spar and one on the bottom? (Assuming equal thickness of the tape)

Thanks,

Sierra Gold
AMA 12351