what is a capstrip?

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11 years 5 months

Posts: 1

can anyone explain to me what the cap strip is in a wing of an aeroplane? is it the member that gives the rib its aerofoil shape??
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Member for

11 years 11 months

Posts: 2,101

can anyone explain to me what the cap strip is in a wing of an aeroplane? is it the member that gives the rib its aerofoil shape??
No, the ribs will have their shape from manufacture. The Cap Strip is the old method, and still used by Boeing (Which is NOT a negative) of producing the Main Wing Spars. This method has a flat plate for the vertical Web of the spar, to which they bolt/bond L shape cap strips to. The Final assembly cross section is an open C shape, the C faces into the wing-box. The Skins (Or covers as they are now getting called) are bolted to the cap strips (And the Ribs/stringers too). Some Cap strips can be a slanted T shape, with the long bit attached to the web, the top bit can take the skins and the Forward top bit is a landing/register for the D nose leading edge, or the traling edge panels. With the advent of NC machining of metal, the spars became machined from solid (Vickers Viscount was the 1st BTW) complete with pockets, rib posts, caps and whatever else was previously assembled onto a web. Cap strips are now generally confined to light a/c, especially home builds. Boing use this method because it's a damn sight cheaper to produce than hogging a Spar out of a plate of al alloy. Some of these plates can get 10 inches thick (Eg where the U/c pintles are attached to a rear spar or the lump is hanging off the Front spar), and a very expensive forging is made, to prevent massive material wastage. I don't know if B787 Carbon Spars are made of a Web & Cap Strips, or they have formed them round a mould of some sort to form the C shape. HTH.