High AR EPP wing twist and sparing systems

[Cody WIlson]

I am working on a few designs- idea's really. They involve largish (1.5-3M span) high AR wings, and I want a spar system that will prevent wing twisting and flexing under aerobatic loads. I was thinking of setting it up like a typical "A" frame found in many combat wings, but at a much shallower angles. Maybe even using a 1/8" or larger carbon rod on the LE and a flat carbon rod on the TE with a simple arrow shaft spar or larger on the CG.

Another wing that I have in mind would have multiple LE tapers to make the planform more like a typical molded sailplane. So my spars would all have to fall within the wing itself, which rules out the rods on the LE. I want to keep the weight down as much as possible and still have a stiff wing. I might also use strapping in an X pattern to help out with torsional loads.

Any thought's?

Cody

[Antonsoarer]

Cody, you should consider sheeting the wing. I have tested some old EPP wing off-cuts and I just sheet covered a set of large Ailerons 32"x5". The ailerons are very light, have no spars but are stiffer than any EPP wing I have made to date. I only used 3m77 and 3/32 balsa with 1/32 birch ply ends and LE. I am now trying out EPP wings with carbon & wood spars and ply sheeting glued on using PU, need to use my wing press with the PU approach. If the sparred wing doesn’t flex much span wise there is little danger of the sheet failing, all twist disappears.

You may ask what’s the point? Why not just use EPS?

Sheeted EPP is much tougher than sheeted EPS.

Tony.

[Andy W]

Glass will also work, if you have a way to bag it.
..a

[peterangus]

Cody

To maximise bending stiffness and torsional stiffness, all the structural materal should be in the skins. The skins should form a closed tube, enclosing as much cross-section area as possible.

Rods at the LE and TE will contribute little.

[grybeard]

Cody

To maximise bending stiffness and torsional stiffness, all the structural materal should be in the skins. The skins should form a closed tube, enclosing as much cross-section area as possible.

Rods at the LE and TE will contribute little.
I have been reading the threads in an attempt to catch up on modern model technology. After about five years of retirement I am back to modelling after 30+ years, I built stick and silk.
I do however disagree slightly with your contention that all the structural material should be in the skin. In a I beam you will find a shear web. The skins must be kept apart and unable to slide over one another.
Flatten a dandelion stalk and see how much stiffness is lost. Many plant structures are stiff by using a tough skin with a soft matrix to hold the skin surfaces apart.
As an aside from structures, if you fly as badly as I, a bit of strength at leading and trailing edges doesn't come amiss. I must admit I feel terribly out of my depth concerning models and model builders of today. My current interests are a Black Magic and a Flyihg Quaker.

[Antonsoarer]

I have been reading the threads in an attempt to catch up on modern model technology. After about five years of retirement I am back to modelling after 30+ years, I built stick and silk.
I do however disagree slightly with your contention that all the structural material should be in the skin. In a I beam you will find a shear web. The skins must be kept apart and unable to slide over one another.
Flatten a dandelion stalk and see how much stiffness is lost. Many plant structures are stiff by using a tough skin with a soft matrix to hold the skin surfaces apart.
As an aside from structures, if you fly as badly as I, a bit of strength at leading and trailing edges doesn't come amiss. I must admit I feel terribly out of my depth concerning models and model builders of today. My current interests are a Black Magic and a Flyihg Quaker.

Doesn't matter how good the spars are, torsional stiffness (Cody's primary concern) will not be addressed until you apply a good skin.