cap strips - so what are they all about ?

[mr_wood]

cap strips - so what are they all about ?

I have seen models that boast carbon d-box and carbon cap strips - but I fail to see where this adds strength.

Spar = bending loads on the wing
d-box - torsional loads
cap strips - hmm - a marketing ploy ???

Can someone explain,

Thanks
Tim

[MrClean]

Carbon doesn't stretch much at all, so if you have a cap strip on top and bottom of your box, it won't deform (ie bend). You can make a hefty wood box that won't bend, or you can make a wee little box with carbon cap strips that won't bend the same.

[nuevo]

The most weight efficient way to build a strong spar is to put all the strength at the very top & bottom of the spar box. Hence the carbon cap strips. Usually, vertical grain balsa connects the two cap strips.

[SoCalGliderFlyr]

Cap strips were a means of reinforcing the rib and their surface assisted in covering contact. Covering was once silk or tissue and butrate (dope). You needed a surface to adhear to. This is still important where there is some undercamber of the wing. I just use 3/32" balsa for ribs rather than the more common 1/16".

On large scale ships the ribs are built up rather than solid. This is where the cap strip will reinforce the airfoil shape.

[schrederman]

Rib cap strips reinforce the rib by making an I-Beam of it. This is necessary in some designs to create the necessary torsional rigidity to prevent flutter, and to make the aft protion of the ribs strong enough to carry the air loads. In the Houston Hawk design, I opted for 3/32 ribs on 2" centers. Coupled with a d-box that extends beyond the thickest point of the wing. the torsional strength is pretty awesome without the bother of cap strips. They are great hwere they are needed. The carbon caped ribs do add a great deal of strength to some of these ships, like the AVA and Topaz.

Jack Womack