Tubular boom from sheet?

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Riggerrob

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Monocoque fuselages were given up for a reason. Unless you go with ultra rigid composites, you need a pretty thick and heavy tube to do what a semi-monocoque structure will do.
Correct!
The vast majority of modern airplanes are semi-monocoque. They started as simple monococques, then added stiffeners around doors and windows, then bulkheads, etc.
At minimum, monocoque need to be thick-walled with foam or honey-comb separating the inner and outer skins.
 

ultralajt

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Bowlus Baby Albatross Vintage Sailplane has a rolled aluminum sheet tail boom, with a vertical seam riveted on the top of it.
 

Bigshu

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Rolled skin tapered tube around bulkheads is how the Hummell designs finish out the tail area. once you get to the cockpit, you're using multiple skins, but the first couple of tail sections are bulkhead at the back, stiffener along the longitudinal rivet joint, the circumferential rivet joint to attach to next section forward. Light, and apparently sturdy enough for ultralight up through an 800 # TOW.
 

rv7charlie

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How did monocoque get into the discussion? Even the BD spar tube is reinforced by the surrounding rib structure.

BTW, that's the 1st I've heard about the BD4 spars being rolled stock. All I ever heard about when I owned one shortly after the turn of the century was the seamless tubing. Back then, several guys on the BD forum were trying to find a way to get a new run of tubes made (stock size tube in the original BD4 was non industry-standard size). The spar-root interface was a near-interference fit. I'd think it would be pretty tricky to make that work with a stepped surface circumference and fasteners.

Charlie
 

Bill-Higdon

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Going on memory here but As I remember it the prototype had rolled sheet metal spars, but the production kits all had extruded spars.
The Piper PA-8 Sky Cycle rear fuselage aft of the Corsair drop tank was a basically a rolled sheet metal tube.
 

BBerson

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A rolled high strength alloy tube might have superior properties compared with extruded. Or a custom extrusion with thicker caps might be ideal. The kits were probably round "drawn", which is not the same as "extruded".
 

KAF

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Apr 20, 2014
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Missouri
I could be wrong, but it seems like I've seen pictures of Rotorway tailboom construction which appeared to be a flat sheet pulled into a tube with a bunch of ratchet straps and riveted.
 
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