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#11
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Why no plywood monocoque homebuilts?
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#12
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Why no plywood monocoque homebuilts?
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#14
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Why no plywood monocoque homebuilts?
Yes, you are correct. Thanks.
Bud Orval Fairbairn wrote: In article .com, wrote: wrote: Semi-Monocoque is the term, not "complimentary." Whatever. My professor in graduate school (a Stanford Ph.D.) called it complimentary, since the stringers and longerons compliment the skin in that, as I said, they provide strength in a direction that the skin does not have, which is out of plane stiffness. Since a true Mono (meaning a single) coque (shell) structure has only a shell for structure (an egg is a perfect example), any deviation from this is often called semi-monocoque, even when the skin carries no load, which is an incorrect way of describing such a structure. You mean "complementary," meaning "completes the function," not "complimentary," as in "offerimg compliments." |
#15
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Why no plywood monocoque homebuilts?
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#16
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Why no plywood monocoque homebuilts?
I refer the original poster to Low Power Laminar A/C Design by P.
Strojnik... A series of three books... Fascinating reading... The EAA should have them at the book store... But, to answer the question, the biggest impediment to the home builder for making a monocoque fuselage in wood is the need for a plug to cold mold or laminate the wood onto... If the fuse is symmetrical, a half plug will work and join the two halves later... The favored material is cement for making the plug, mostly for cost reasons I suspect - it certainly would hamper portability... The Mosquito was done this way, as was (I believe) much of the Spruce Goose... Much of the Cirrus airplanes are plug molded as semi-monocoque structures, but I don't think they use cement plugs denny |
#17
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Why no plywood monocoque homebuilts?
"Denny" wrote in message oups.com... I refer the original poster to Low Power Laminar A/C Design by P. Strojnik... A series of three books... Fascinating reading... The EAA should have them at the book store... So, I take it that the cold molding and/or laminating process is extensibly covered in these books? I might be interested in a read, if that is the case. I'm a carpenter/cabinet maker, but I have to admit to being clueless about the cold molding process. -- Jim in NC |
#18
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Why no plywood monocoque homebuilts?
Saying that something is the primary structural member doesn't mean it
is the only structural member. Aircraft structures typically have several members sharing the load, hence the term "complementary structure", as they complement each other in carrying the load. The forward belly skin on my Cessna is .040 in thick, and 44 in wide. This is approximately 1.75 sq. in. The forward side skins are .032 by 24 in tall and has approximately .75 sq. in of area. The structural channels you mention don't have anywhere near this much area, and are themselves mounted to the forward skins. They are major structural members and carry significant load, but the skin is still the primary load carrier. The load paths and stress distribution of aluminum skin versus fabric covered aircraft are very different. This is why fabric covered wings require internal diagonal wire bracing, and aluminum skinned wings do not. Fuselages behave in the same manner. Bud wrote: wrote: Your average CessBeeMooPip is semi-monocoque in the aft fuselage. The fuselage skin from the firewall back is the primary structural member everywhere except at the wing spar attachments, and the landing gear on Cessnas. The forward fuselage on the Cessna has heavy structural members. There are hat-section channels to which the engine mount is attached, and these run back to the doorposts, which are the primary lifting members in the fuselage, since the wing's front spars, the spar carrythrough and the strut attachments are all part of that big bulkhead. The skin contributes much less in the way of tensile strength in that area, and it's not a true semi-monocoque. There are sturdy ribs under the floor and fuselage top, another bulkhead at the rear doorpost/aft spar attach and carrythrough, and more frame members behind that, especially around the windows, until we get to the aft passenger compartment bulkhead. Past that point it's mostly skin. The framework around the doorframes is fairly heavy to keep them square; even at that, we find some distortion when we jack the R182 to swing the gear. If those doors aren't set right, they end up taking flex loads from the airframe and the hinges eventually break. Dan |
#19
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Why no plywood monocoque homebuilts?
Earlier, Denny wrote:
...Much of the Cirrus airplanes are plug molded as semi-monocoque structures, but I don't think they use cement plugs... I'm pretty sure that the Cirrus airplanes are female molded, which seems to be the standard in modern composite aircraft construction. I don't know of any modern male-molded composite aircraft. The only composite male-molded production aircraft I can think of offhand is Gerhard Waibel's ASW12 sailplane, and that was just for the fuselage. Thanks, Bob K. http://www.hpaircraft.com/hp-24 |
#20
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Why no plywood monocoque homebuilts?
Denny wrote: I refer the original poster to Low Power Laminar A/C Design by P. Strojnik... A series of three books... Fascinating reading... The EAA should have them at the book store... Thanks! I'll take a look. But, to answer the question, the biggest impediment to the home builder for making a monocoque fuselage in wood is the need for a plug to cold mold or laminate the wood onto... If the fuse is symmetrical, a half plug will work and join the two halves later... The favored material is cement for making the plug, mostly for cost reasons I suspect - it certainly would hamper portability... The Mosquito was done this way, as was (I believe) much of the Spruce Goose... Much of the Cirrus airplanes are plug molded as semi-monocoque structures, but I don't think they use cement plugs denny I saw a concrete mold like that in a picture of lockheed factory taken when the vega was being produced. I've been very interested in sorting out what manufacturing techniques would be most appropriate for mass production of light aircraft given modern tooling. Robotic welding is of high enough quality to handle steel tubing these days. Obviously filiment wound composits present very high levels of automation as well, but a much higher material cost. Aluminum obviously has a reasonably high material cost, good workability, but the size and flexibility of the sheets would concern me somewhat. I'd be inclined to guess aluminum requires more skill in jigging than the alternatives. I wonder whether filiment winding could be used with non-standard materials. Could you filiment wind a fuselage with say... twine? Sounds bizarre, but if it is encased in epoxy it might have a hope of achieving a certain level of strength. If course most of the cost is probably in the epoxy and not in the filiment. Suprisingly I keep coming back to wood as material for mass production since the whole of the structure could be made of one material. There are obvious logistic benefits there, and I think most wood techniques could be practically achieved robotically. If you designed an aircraft to leverage modern production lines, what would it be made of? Thanks! Matt |
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