Racefan132

i broke many spars with my great planes spirit. Should i make one out of aluminum? Or some other king of wood? I usualy make them out of plywood of uluminum.

RRW_SOAR

If you're talking about the wing joiner, in my case I'd use plywood, or aluminum sandwiched between plywood. Plywood is very resistant to shear forces.

Racefan132

i did use plywood. I made over 20 alredy in less than a month.

RRW_SOAR

Do you tape the wings? When the wings are joined some electric tape would add strength to the join. In my case I used the stock joiner and then glue the halves. Never had a problem and I have hi-started it very hard.

Take care.

Racefan132

how much tape should i use?

RRW_SOAR

One layer, on both sides, upper and lower.

Racefan132

ok great thanks for the help

aeajr

My Feedback: (2)

I would not expect electric tape to add a lot of strength. I tape mine together with 2" clear packing tape It is almost as strong as glassing them together.

jschuring

Race....
the absolute lightest and best way to strenghthen built up sailplane wing spars is to adhere carbon fiber tape to the bottom of the bottom spar member with epoxy. since when under launch and flight loads, the bottom spar is under huge tension and the top spar is being compressed, it does little good to put carbon fiber any where on the top spar....additionally,
making sure that the shear webs fit well, and are securely glued to both the spars and each rib is extremely important. these bits of balsa form an I-beam of the spars and contribute immensly to the overall bending strength of the wing.....

RRW_SOAR

How do you avoid tear off Monokote when you take off the tape?

Slope Flyer UK

The trick I use, is to put a layer of electrical insulating tape around the wing root. Iron the covering down first, before applying it.........then use another strip on insulating tape to hold the wings on to the fuz.

ejett

My Feedback: (4)

What event is causing you to break the joiners? I just don't understand what is happening. You are just hand launching this plane? If you are pulling down on it when you throw it you might be putting enough stress on it to break it. Otherwise, what's happening is a mystery to me.

Do you have two piece wings? I assembled mine with the standard joiner as a one piece wing. It has never broken and I destroyed the original fuselage and one wing tip in a "radio off" high start launch. The wing center and joiner survived just fine.

If you have built it as a two piece, I have a design that you can use that would probably be stronger than the stock setup.

EJ
Athens, LA

Racefan132

well after some more handlaunches and broken pieces i taped the wings together with packing tape and made the spare smaller and taped arround that. now it hasnt broken yet. Now I have my friend run with a string with a ring hooked on the loop on the plane and it goes up about 150 ft.

Bad_Daddy

I can agree with the rest of what you said, but this part is exactly wrong. In bending, the failure mode of ANY material is for the collapse of the side in compression, first. It takes a high-speed camera system to catch the action, but that is always the result. That's why (in aerospace engineering) we always verify the strength of a material with a compression test. It might take 100+ tons of tension to break a piece of material, but it will only take 1/10 of that to fail it in compression, and 10 ton presses are a LOT cheaper (and safer) than 100 ton models.
Put the carbon fiber strips on the top of the top spar - a strip on the bottom of the bottom spar is nearly useless baggage.

As another note, the grain of the vertical shear webs should be vertical, to transfer loads from one spar to the other. If the grain is horizontal, they will shear in half under relatively little load.