Strength of Golf Shaft spars

[shaneyee]

I can get a supply of graphite golf shafts. I use them for booms for my 3m gliders. Since I have so many though, I thought of using them for wing spars for a hotliner. I know how to calculate the load capability of a rectangular spar ( thanks to Ollie ) but I am unsure of the strength of these tapered round sections.

I have PING 350 regular shafts and they are typically 37"-42" long, about 2oz each, 5/8" at the thicker end and the wall thickness is 0.04mm ( 1mm ). If I use them on a 72" wingspan hotliner say, 500sg in, what kind of wing lift load could it take? The Aegea 2m spar is designed for 150lbs wing lift load at 50m/s so thats the sort of figures I am hoping for.

Thanks

Shane

[BMatthews]

They will be plenty strong but the key is how flexible they are. If they let the sheeting and other stuff flex to the point that it can buckle then it's no good. However if you've had good results with them as booms then it's probably good.

[vintage1]

Its probably easier to test one to destruction than to calcualate it.

Clamp teh fat end ina vice and hang weights off it.

I bet it flexes too far rather than breaks though.


Best to make up an I beam oit of CF strips I'd say.

[shaneyee]

They feel very stiff and the TLAR principle says that they are good enough. Was hoping to get some numbers though and learning how to is very satisfying.

I have made 2 planes with I beam spars ( an Allegro E lite and a Bubble Dancer ) and I agree that they are the best solution. BUT....you can't beat the price on the golf shafts - they're free! I have a friend in the golfing business and he gets them for me by the dozen.

Shane

[vintage1]

Well!

Try clamping one end in a bench and seeing how much weight you can hang on the end.

At a guess, provided is about ten times model weight with acceptable deflection, you have some main spars!

[banktoturn]

I can get a supply of graphite golf shafts. I use them for booms for my 3m gliders. Since I have so many though, I thought of using them for wing spars for a hotliner. I know how to calculate the load capability of a rectangular spar ( thanks to Ollie ) but I am unsure of the strength of these tapered round sections.

I have PING 350 regular shafts and they are typically 37"-42" long, about 2oz each, 5/8" at the thicker end and the wall thickness is 0.04mm ( 1mm ). If I use them on a 72" wingspan hotliner say, 500sg in, what kind of wing lift load could it take? The Aegea 2m spar is designed for 150lbs wing lift load at 50m/s so thats the sort of figures I am hoping for.

Thanks

Shane

Shane,

The graphite shafts are really strong in tension, and pretty strong in compression, if you prevent buckling. I would assume that they would be too flexible to be stand-alone spars. If you fabricate a spar with graphite shafts at the top and bottom, joined by shear webbing, I think you would find it to be immensely strong. Their shape is not ideal for this, but if you can get good glue joints with the webbing, they should work fine.

banktoturn

[shaneyee]

Shane,

The graphite shafts are really strong in tension, and pretty strong in compression, if you prevent buckling. I would assume that they would be too flexible to be stand-alone spars. If you fabricate a spar with graphite shafts at the top and bottom, joined by shear webbing, I think you would find it to be immensely strong. Their shape is not ideal for this, but if you can get good glue joints with the webbing, they should work fine.

banktoturn

I cant do the shear web outside the shaft as the wing is only 3/4" thick at the root and the shaft is 5/8" thick but I can try to push some blue foam or vertical grain balsa into the shaft...that will stiffen it a bit I'm sure. Thanks.

Shane

[vintage1]

I think it will make almost no difference at all actually.

[Sparky Paul]

You also should test the shaft for torsion. How stiff it is can affect a vee-tail in an amusing manner... :)

[John O'Sullivan]

I have used carbon golf shafts as tail booms in gliders and in my Eyespy photo planes. They are very good, but the distribution of fibres is not optimum for lightness. The length of my rods is 42 to 47 inches and runs from an OD of just over 0.6" to 0.37". The layup of carbon appears to be of constant carbon amount throughout the length, (CG is about 1/2 way along the rod) This results in a thicker wall at the rear end than at the front (about twice the wall thickness). This layup is probably optimum for the designed flex for golf, but leaves much to be desired for our purposes. This does not make a big drawback in my photoplanes as the extra weight is not a concern. However for a lightweight boom some sanding of the rear portion of the boom (set up in a lathe or in a hand drill would work), would help. Likewise the use as wing spars would benefit from lightening of the thin end.
I am not a great fan of using tubes as wing spars as most of the weight is concentrated in the central part of the diameter, where the properties of carbon have the least contribution to strength of the spar. I prefer to use flat strips of carbon, bonded firmly to the top and bottom of a decent balsa or basswood spar.

Remember the potentially dangerous properties of sanded carbon when doing any sanding (sand wet and dispose of dust properly)
John O'Sullivan

[shaneyee]

Thanks all.

I suspected that the wall thickness was greater at the end but I thought it was just local reinforcement where the club head joined the shaft. I didnt think it was because of the use of a constant amount of carbon in the layup. That would make it easier to produce.... and give it more strength and whip at the small end at the expense of stiffness. I might cut them down in length to minimise the change in diameter...

Shane