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#31
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Why no plywood monocoque homebuilts?
Orval Fairbairn wrote:
In article .com, " wrote: Morgans wrote: "Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote The hard part would be to come up with a reasonable replacement for the spars in the wings. To avoid the big expensive spruce planks, one might have to consider an engineered product like Laminated Veneer Lumber (LVL)... Have you ever used those? They are HEAVY, with a capital "H". SNIP -- Jim in NC Jenny Craig strikes again :-) I am still very intriqued by filament winding. Spars would probably be most obvious use of this technology. Take a look at the pictures on this page to get an idea why. http://www.boatdesign.net/forums/sho...11160b889f2560 2fba&t=1774&page=2 Doesn't that kindof suggest the ability to make a whole spar, wing, fueselage or control surface in one shot? I am presuming scaled composites uses something similar but bigger. I've seen pictures of the system NASA uses for booster casings, they stand about 20 ft. tall if I remember correctly. I will be checking the local yellow pages to see if there are any mast-makers where I live. I'd like to take a closing look at a system like this. -Matt Actually, filament winding would be a poor choice for spars, as the filaments should run primarily parallel to the spar and be concentrated at the top and bottom. You do need some in the webs, to handle shear loads, but an "I" section is the most efficient. A tubular spar for a wing is also a poor choice, as it concentrates a lot of its tensile strength at its center, where it doesn't get much loading. Couldn't that be controlled by adjusting the weave? Perhaps weave in three angles instead of two, with the third being parallel to the length axis? The form could be semi-rectangular as well, which would give you your ability to concentrate fibers on the top and bottom. Obviously you can't escape some wastage, but "perfect" is the enemy of "good enough". A mast is a different story, as it is expected to take similar bending loads in all directions; a spar does not. Are you quite familiar with filament winding? I've got a lot of questions if you've got the time. -Thanks -Matt |
#32
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Why no plywood monocoque homebuilts?
In article .com,
" wrote: Orval Fairbairn wrote: In article .com, " wrote: Morgans wrote: "Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote The hard part would be to come up with a reasonable replacement for the spars in the wings. To avoid the big expensive spruce planks, one might have to consider an engineered product like Laminated Veneer Lumber (LVL)... Have you ever used those? They are HEAVY, with a capital "H". SNIP -- Jim in NC Jenny Craig strikes again :-) I am still very intriqued by filament winding. Spars would probably be most obvious use of this technology. Take a look at the pictures on this page to get an idea why. http://www.boatdesign.net/forums/sho...ec4011160b889f 2560 2fba&t=1774&page=2 Doesn't that kindof suggest the ability to make a whole spar, wing, fueselage or control surface in one shot? I am presuming scaled composites uses something similar but bigger. I've seen pictures of the system NASA uses for booster casings, they stand about 20 ft. tall if I remember correctly. I will be checking the local yellow pages to see if there are any mast-makers where I live. I'd like to take a closing look at a system like this. -Matt Actually, filament winding would be a poor choice for spars, as the filaments should run primarily parallel to the spar and be concentrated at the top and bottom. You do need some in the webs, to handle shear loads, but an "I" section is the most efficient. A tubular spar for a wing is also a poor choice, as it concentrates a lot of its tensile strength at its center, where it doesn't get much loading. Couldn't that be controlled by adjusting the weave? Perhaps weave in three angles instead of two, with the third being parallel to the length axis? The form could be semi-rectangular as well, which would give you your ability to concentrate fibers on the top and bottom. Obviously you can't escape some wastage, but "perfect" is the enemy of "good enough". Filament winding wraps the material (carbon, Kevlar, glass, etc.) around the item, whereas you want the filaments in the spar caps to run longitudinally, because that is the direction of tensile and compressive stresses. Filaments wrapped around the spar will carry shear stresses, but are of little help in taking up bending loads, which comprise the major stresses in a spar. A mast is a different story, as it is expected to take similar bending loads in all directions; a spar does not. Are you quite familiar with filament winding? I've got a lot of questions if you've got the time. I haven't done any filament winding, but I am familiar with filament-wound rocket motor cases. |
#33
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Why no plywood monocoque homebuilts?
"Morgans" wrote in message
... "Capt. Geoffrey Thorpe" The Sea Hawk at wow way d0t com wrote The hard part would be to come up with a reasonable replacement for the spars in the wings. To avoid the big expensive spruce planks, one might have to consider an engineered product like Laminated Veneer Lumber (LVL)... Have you ever used those? They are HEAVY, with a capital "H". More fitting would be something like an engineered product such as "silent floor" joists, which is best described as a wood "I" beam. A cheaper wood, like fur could be used, because the wider flange top and bottom of the "I" is the only part that is real wood, and there is not that much volume of wood to incur very much weight penalty. Holes can be put in the plywood web to help lighten it, with very minimal strength loss. Of course, this is a practice very similar to what is currently being used in some homebuilt designs, today. g A box spar is one of the best uses of strength to weight for spars, not using a solid plank. The amount of real wood, top to bottom and spanwise varies, so there is no extra wood where it is not needed, thus giving maximum strength to weight. Also, you do not have to use expensive Sitka Spruce, and if you do, you can cut up smaller (cheaper-no waste) pieces, and splice them, and laminate them, to get all of the grain going in the right direction. I was thinking of a routed spar to save some of the weight, but you are absolutely correct - a box spar would be the way to go in order to avoid the big expensive spruce plank. -- Geoff The Sea Hawk at Wow Way d0t Com remove spaces and make the obvious substitutions to reply by mail When immigration is outlawed, only outlaws will immigrate. |
#34
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Why no plywood monocoque homebuilts?
Orval Fairbairn wrote: Actually, filament winding would be a poor choice for spars, as the filaments should run primarily parallel to the spar and be concentrated at the top and bottom. You do need some in the webs, to handle shear loads, but an "I" section is the most efficient. A tubular spar for a wing is also a poor choice, as it concentrates a lot of its tensile strength at its center, where it doesn't get much loading. A mast is a different story, as it is expected to take similar bending loads in all directions; a spar does not. The spar in my Jodel is a one-piece box spar and is the only spar in the wing. It takes the lifting and landing loads, the drag loads, and the torsion loads. The washout is built into it. It's about 7" deep and 12" wide at the center. It has four lumber members, one in each corner of the box, and the top two are larger than the bottom two, since wood is stronger in tension than it is in compression. Plywood diaphragms maintain the box shape and the whole thing is closed with plywood skins with the outer plies at 45° angles to take advantage of the maximum directional strength of the wood. The lumber members are heaviest at the center and lightest at the tips. The dihedral is in the outer panels, and the lumber members are spliced at those points. Shrike had suggested building wooden airplanes with semi-skilled labor; I don't think I'd want such a spar as this to be built by someone who wasn't either thoroughly trained and apprenticed or who would be eventually flying it. It's a most elegant piece of engineering and is the most complex and time-consuming part of the whole airplane. One foolish mistake in jigging or gluing could just about trash the whole thing. Dan |
#35
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Why no plywood monocoque homebuilts?
wrote I don't think I'd want such a spar as this to be built by someone who wasn't either thoroughly trained and apprenticed or who would be eventually flying it. It's a most elegant piece of engineering and is the most complex and time-consuming part of the whole airplane. One foolish mistake in jigging or gluing could just about trash the whole thing. It is possible to use mass production techniques to this whole process. Picture cutting enough individual parts for 50 spars, with each part being reproduced in exact precision. By careful setup, (by one exacting craftsman) you would produce parts at least as good as you could do, just making one. Instead of jigging for one spar, a permanent steel jig could be set made that would make the spar almost impossible to put together incorrectly. Semi-skilled labor would be all that is needed to assemble the spar and glue it, if they are taught and all of the parts fit right. I live in the furniture belt, here in NC, and they do some pretty complicated assemblies; much more so than a spar. Granted, the spar being wrong is a lot more critical than some poorly assembled furniture. Quality control would be important, but possible. It would be advisable to test to destruction, a few at random, to verify correct assembly. -- Jim in NC |
#37
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Why no plywood monocoque homebuilts?
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