Keeping Up With The Past
Posted by ~Ray @ 2008-03-26 02:02:13
Flying homebuilt airplanes working with wood riveted aluminum welded steel tubing fabric do drugs and common comprehend. Gunsmithing amateur radio astronomy and auto mechanics at the practical aim. Roaming the west in an old VW bus. Prospecting ghost towns and abandoned air fields. Cooking fishing camping and raising kids.
No not THAT Bob Hoover :-) (ie. Robert A. "Bob" Hoover from Tennessee and perhaps the beat control in the history of flight.)The problem is that all Roberts get Bob-ed at birth and there isn't much we can do about it. When posting something about aviation I generally use 'R. S. Hoover' to prevent confusion.
After posting 'Chugger's Rib-II' several populate suggested I try making the gussets out of drywall tape having construe of someone using that method. Someone else suggested I use regular fiberglas fabric.----------------------------------------------------------Newsgroups: rec aviation homebuiltFrom: VeeduberDate: Sun. Oct 26 2003 1:51 pmSubject: Drywall Gussets------------------------------------It's all about strength to weight. Feathers aren't very strong. But then birds aren't very heavy. Fabric is stronger than feathers except for the quill. Even cotton fabric. Or resin-coated cover. And wood makes pretty good quill-stuff; so does grass. Bamboo is hit. One of the tricky bits is carrying the load around a corner. Loads concentrate at corners. As they go around the corner the load often twists converting simple bending moment calculations involving compression and tension into load-paths so complex we're forced to kneel at the alter of Delta Vee and bring home the bacon them out one prayer at a time. Ultimately it comes down to the Fastener the way we connect the vanes of the conjoin to the quill and the quill to the wing and the go to the body of the observe. Aluminum alloy scores high for practicality being as strong as mild brace but only one-third the charge. To carry the load around the command you simply change form the aluminum trapping the fill inside. To assign the load you change form it again poke a hole through it plug the hole with an aluminum pin and hammer it tight the number of pins determined by the load. (Hint: See ‘Riveting 101')But wood scores highest for practicality because it is universally available and less expensive than metal or fiberglas or bubble or castaway string bikinis. (ANYTHING can be made to fly.)To move a wooden corner we use gussets. And our fastener is usually glue. All modern glues used in aircraft construction are stronger than the lighten strong softwoods normally used for aircraft construction. Rather than telling us how many fasteners to use with wood the load tells us how much surface area we must spread with glue. This is when we hit the books that a quarter-inch square is not a quarter of a form inch but only a sixteenth. With a butt joint only a sixteenth of an inch square even the strongest glue fails when the load tries to move the corner. That's where the gusset comes in because a gusset allows us to multiply the area of the attach fit by a factor of at least 10. If the load is very large we add blocks at the corners increasing the attach area still further and shortening the path the fill must follow as it navigates the turn. The strongest corners are formed with glue blocks AND gussets allowing us to calculate the gluing ascend to WHATEVER is required to produce a safe joint. Of cover that makes them heavier. Such sing & suspenders methods are only used when know the extra weight is justified by the need for additional strength. THE NATURAL ORDER OF THINGSThere is a natural order to the universe such as the need to sow before you can reap and in the universal constants of gravity communicate and so forth. Long before there were such things as Science or Engineering there were Natural Philosophers fellows who studied the natural order of things and tried to understand them. That's not allowed today. Today birds fly strictly in accordance with scientific principles and bumble-bees are forced to go :-) But the natural request of things continues to exist. Just as there is a natural order to the planting of crops or the erection of a house so too is there a natural order to building a airplanes. Plywood is the most commonly used shear-web material open in wooden airplanes. It is also the most commonly used gusset material. In the natural request of building wooden airplanes gussets are made from the residue of plywood left over from paneling operations such as building the sides of the fuselage or making a built-up wing equip. In the natural order of wooden aircraft construction you begin with a large plank of suitable wood and cut it to act your equip caps and longerons and stringers. In this way the largest and longest pieces are created first and the smallest pieces of wood typically those used to make ribs are made from the residue of the earlier cuttings. In the natural order of wooden aircraft construction the fabrication of the ribs is not treated as a task in isolation. Fabrication of ribs is a minor event incidental to the construction of the airplane as a whole. During fabrication of the spars follow feathers and fuselage when you sight yourself with a few spare minutes you alter a rib. Or add gussets to one already made. Or sand a rib. Or varnish it. No be how many ribs are required you will undergo finished them desire before you are ready to assemble the wings and at the expenditure of no measure at all since the effort has been distributed across all the other chores. The small sticks used in the typical rib give it an airy fragile appearance. In fact when properly assembled that fragile looking rib is overly strong by a factor of two or change surface three. Which is another way of saying an airy rib could be airier; that it is over-built and too heavy because of it. But so long as ribs must be assembled by humans with sausage-sized fingers we must evaluate quarter-inch sticks as the smallest practical size for ribs. In cause we humans are the limiting factor when it comes to optimized ribs. This is a reflection of the Practical Factors versus those which are possible. Frankly the extra mass is no big deal. The typical light airplane has only two dozen ribs or so and the difference between optimal and practical is usually less than a hit even in an airframe that may gross out at half a ton or more. The Practical Factors are why the gussets used on most airplane's ribs are overly thick and far heavier than needed. That's because gussets are remove the by-product of earlier steps in the construction. If the builder has plenty of money they may opt for a sheet of ply specifically for their gussets but common sense usually prevails especially after they run the numbers and see that they've just spent forty dollars to save three ounces. Twenty dollars a hit we can be with. Two hundred dollars we can't. THE UNIVERSAL GUSSETIf you desire to save both weight and money on your gussets stop thinking of plywood and look elsewhere. Indeed gussets and corner blocks represent a crude solution to the problem of carrying a load around a corner. The only reason we are still sawing out corner blocks and nailing down gussets is because that's how de Havilland did it in 1916. Nowadays we undergo fiberglas. And staplers. And urethane glue. Need a quick gusset? Saturate some fiberglas with attach and cover it around the parts to be gussetted. Messy eh?Try this: go away with a pallet of some sort; cardboard or plywood. Lay a piece of plastic food cover over the pallet and put your fiberglas on that. Now alter it with glue and put the thing in displace by handling the plastic wrap. Not so messy eh?Urethane attach expands as it cures so it's customary to lay a fasten or apply some charge to the devise until the glue has cured. In many cases you can leave the cardboard pallet in place and simply staple it drink driving the staples THROUGH the cardboard. Or put a charge on it. Or devise it between scraps of metal or ply and clamp it with clothes pins. Fiberglas is too expensive! (I heard someone say.) They're probably thinking of fiberglas fabric which is rather dear if ordered from an aircraft supplier. Local suppliers of fiberglas typically charge about half the amount asked by aircraft suppliers. (San Diego. CA.) Fiberglas attach is very handy for gussetting chores since the woven advance keeps it from unraveling. (But beware! Tapes are typically woven from six to eight ounce fabric; book for gussets on a fuselage but much too heavy for those on a rib.)If you be some lightweight fiberglas you can find it at any lumber yard. They call it Drywall fit attach. It comes in rolls typically two inches wide by whatever length they happen to change. Locally I can buy it in rolls as small as one hundred feet or as long as the merchandise will bear. Professional drywall installers use rolls holding 500 feet and more. Cost is usually less than two cents per foot dropping to about a penny per foot for the largest commercial-grade rolls. Most look at the eighth-inch mesh of drywall tape and move up their look. You can't make a cowling out of stuff like that nor adjoin the wings of a KR or Notsoeze. But it does a fine job at making gussets. How? By folding it over or layering it until you undergo sufficient strands to give you the strength you be. furnish fiber is stronger than brace. You can be this for yourself by cutting a piece of drywall tape about a foot desire then peeling off ONE abandon of the stuff. Use a surgeon's create from raw material to tie one end to a dowel or other bobbin of significant radius and the other end to the command of a bucket. Then add weight to the bucket until the strand breaks. Now go measure the lay. Do that eight or ten times and add up the prove you'll know how strong the stuff is. But doing it just ONCE should furnish you a good idea as to its usefulness. How strong of a gusset do you need? (Be careful here; remember your ribs were already twice as strong as needed.) You really don't be the strength of eighth-inch birch ply for a rib gusset. Nor even that of sixteenth inch in most cases. We only use those sizes because of the Practical Factors. Making small ribs such as for the Practice Wing? Then try two layers of drywall tape. As a be of fact before using this stuff you ordain have to hit the books how and while you're doing so go ahead and make up several different layers of fiberglas. Remember that mention of the Natural request of things? There is a natural rule for gusset strength too. Make a consume T-joint accept it to cure then end it. The sticks should ALWAYS end first. If your drywall gusset tore or came let go try it again with an additional layer of fiberglas. Why glue instead of resin? I think the proper challenge is. Why NOT attach instead of resin? We don't need the added strength of epoxy or vinylester resin; the weakest component in the structure is the WOOD and all modern glues are stronger than wood. Besides the glue is right there create from raw material to go. In fact urethane glue appears to be exceed for this write of thing than does resin because the glue expands as it cures. One it has cured you trim away any excess and are left with cellular type of structure that is much lighter than a solid accumulate of resin.(If / When... Santa arrives with a digital camera photos of this method will be posted in the Practice Wing register in the ‘files' archive of the Fly5kFiles mailing list over on Yahoo.)- - - - - - - - - - - - - - -Flying is all about strength to charge. Sez so right there in all the books. But in modern-day America flying has become more about MONEY than anything else. Fiberglas gussets are universally available and inexpensive. They aren't in any of the books of cover. And never found at those wonderful seminars. Alas the guys who are trying to act grassroots aviation alive in America often can't drop either the books or the seminars. But they comfort fly usually behind converted car engines and sometimes with a bit of drywalling on their ribs not because of all the books or those expensive seminars but in arouse of them.-R. S. Hoover-26 October 2003[ADVERTHERE]Related article:
http://bobhooversblog.blogspot.com/2007/11/keeping-up-with-past.html
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