Tubular Spars

[mr_wood]

Hi,

I am thinking about building a 2m electric light-weight glider. I have taken a look at the E-Allegro Lite and Winddancer and it seems the WindDancer used tubular spars - I like this idea as its easy to construct. Anyone have any experience with tubular spars and what the pros and cons are ?

Thanks
Tim

[Ollie]

Tubular spars have a poorer strength and stiffness to weight ratio than the carbon-balsa-carbon, kevlar wrapped spars of the Allegro ELite. The main advantage of tubular spars is that building with them is much less labor intensive.

[dephela]

A few years ago Model Aviation had an article and plans for a tube spar sailplane. I think it used a 1/2 diameter item. Tube spars work, I'm completing an F1H plane right now with one, I've seen 2M+ span F1A planes fly with them also. It's just important to make the diameter as large as possible. Yes, the construction is easy!

[mr_wood]

Thanks for the replies,

what sort of diameters are suitable ? I have 8mm tubes - will they be ok in a 2m plane for the center section ? How big are the ones in the WindDancer ?

[Tony D.]

Since the skin of a tubular spar wing is very critical to the strength of the wing, if you damage or have a partial delam on this type of wing/spar system you have decreased the overall strength of the wing significantly and are more likely to suffer wing failure even if you repair the damage.

Although the balsa carbon capped spar is more work initially it will have greater survivability and longevity over the long haul and after damage such as a delam because the spar is doing the load handling on the wing, not the skin.

The carbon capped spar is more robust, stronger and more effiecient.



T.D.