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Building Tips and technical articles. => Building techniques => Topic started by: aba183210 on July 01, 2016, 12:29:29 AM
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Good evening.
I have built and flown several large RC sailplanes in the past-Olympic 650, Olympic II, Paragon. They have wing joiners made of hardwood or plywood that join the panels.
I am presently building my first large CL plane: a Sig Banshee. I note that the plans don't call for the joiners I have seen in RC planes. So, how do I join the wing spars and halves together? Thanks.
Thanks.
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the joiners on R/C are called dihedral braces, and they are paramount due to the rolling maneuvers that surely would brake them in half
in control line, we don´t have the rolling motion, so pretty much we rely on the center sheeting to brace both wing sides
if your kit have nothing called on plans, you´re fine
i just improve all of my spars joining doing them with 45 degrees like the picture
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Actually a roll is probably more gentle on a sailplane than a loop. What isn't gentle is a winch tow (have you watched your sailplane wings on a winch tow?) or landing fast on one wingtip (we won't use the word "crash" -- oh no!).
I do make scarf joints or use other reinforcement on my spar joints, but that's probably just a leftover from building RC planes.
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Actually a roll is probably more gentle on a sailplane than a loop. What isn't gentle is a winch tow (have you watched your sailplane wings on a winch tow?) or landing fast on one wingtip (we won't use the word "crash" -- oh no!).
I do make scarf joints or use other reinforcement on my spar joints, but that's probably just a leftover from building RC planes.
i do agree, loop will be more stressfull!
and i uploaded the wrong picture lol!
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...and i uploaded the wrong picture lol!
Dang Fred, I squinted at it for a while and decided it must be the cleanest joint I ever saw Lol.
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Same here, thought my eye sight was gone. I my self make my spar splices out in the out board wing. The angle is what I do at the moment. Then to reinforce a piece of scrap is glued over the joint as it is between a couple of ribs.
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Thanks for the info and pics. I started my model aviation career with wooden 2m sailplanes in 2000. No motor-I learned to read thermal lift and I frequently specked out. When you are able to take a 3 meter unpowered plane so high that it looks like a speck, you become addicted for life. These composite monster sailplanes (about 3.6 m wingspan) can weigh as much as a control line Strega.
It was in 2002 or so when I moved to a composite plane: a 2m Organic.
Now I own a Smile F3K discus launch sailplane. All carbon, 600 dollars used but mint. Flies like a charm and weighs about 9 ounces but has the wingspan of a Strega CL stunter.
Yes, I have seen hi tech RC sailplanes (Xplorers, Addictiions, and the like) on winch launches. The wings tend to curve a bit upward even with all that carbon and Kevlar, and the carbon reinforced wing joiners. A woody sailplane built stock needs either a high start or an extremely gentle winch launch or it will die. I have also seen woodies on hard launches but these have things like D-tube sheeting, built up trailing edges, and very beefed up joiners. In the club I used to belong where I learned to fly RC Soaring, there was a 2M woody that could be winch launched pedal to the metal all the way and be zoomed at the end of the launch. It had the construction techniques I just described.
This is why I expressed my concern regarding joining the two halves in a control line powered plane. As you can see, my experience with powered flight is recent.
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Just look at a bunch of plans and you'll see that there is what looks like a vastly inadequate amount of reenforcement at the wing join -- and yet, control line stunters do not routinely clap their wingtips together in competition.
I wouldn't go less than what you see -- but you hardly need to beef it up like a sailplane.
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Good evening.
I have built and flown several large RC sailplanes in the past-Olympic 650, Olympic II, Paragon. They have wing joiners made of hardwood or plywood that join the panels.
I am presently building my first large CL plane: a Sig Banshee. I note that the plans don't call for the joiners I have seen in RC planes. So, how do I join the wing spars and halves together? Thanks.
You build it in one piece, for the most part. You don't need to beef it up inordinately because the airplane is lighter, and the wing is much thicker than a sailplane. The sheeting is in one piece across the center, so you also spread the load much better than a point load like the joiners on glider wings.
BTW, since it came up - we actually have had a rash of wing failures of stunt planes, that started, not coincidentally, about the same time we got decent engines. Good engines like the 40VF, etc enabled much tighter cornering, which greatly increased the stress on the wings. It actually started with the ST60, and was pretty famous in New Jersey in the "Alligator Sticker Era" of Stunt News, because of incorrect finishing techniques used at the time. If you build the entire airplane, then tissue it afterwards, you had better beef up the center section of the wing because the tissue ending at the fuse sides creates a stress riser right at the point of highest load. Ringmasters with good engines have been notorious for flying apart when powered with Veco 19s, 15FPs, etc, because they can actually corner pretty well compared to a Fox, and the wing structural design is almost the worst you can envision
Brett
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I don't know if you have access to a decent hobby shop or even a craft store that sells balsa, but you can use 48" length 1/4" spars, with no joint at the center. Or, you can use 36 inch lengths and make a splice nearer the outboard tip on one spar and the inboard tip on the other spar. You can "sister" a piece of 1/4 square alongside the kit spars if they join at the center of wing. Same for the leading edge, find a 48 inch piece and substitute it for the stock pieces. Don't use butt joints, which have about zero strength, use a kerf joint splice wherever the spars join. The Banshee is a relatively small and light model so the loads will not be extreme no matter how you build it. BTW there are modifications to the Banshee that are discussed on this forum and make it fly much better. Do a search for "Banshee."
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I always do as Mike suggests and stagger the joints off-center so no two butt joints line up. Assuming the kit spars and LE & TE sticks are long enough to allow staggering. Of course, proper glue joints are usually stronger than the surrounding wood, but it makes me feel better. And I use epoxy rather than wood glue for those pieces. I like to use wood glue for the rest of the wing components aside from the BC mount.
Rusty
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Well, for a guy that doesn't like building wings, I'm designing two right now for the Ag Cat 164 A I'm scratch building.
Dihedral on both wings and four spars. I'm thinking about the joining issue.
Charles
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'thought these photos would be more of interest than it turned out. Failing any outside input, I think the spar grafting will hold.
When I build balsa spars from shorter lengths of stock, I diagonal the joint and use CyA, because it is much stronger than balsa and disperses/wicks into the balsa, spreading and tapering off the stiffness. So the extension of the joint and the dispersion of the glue make the joint very strong without concentrating the stress critically. I usually put the joint as far out on the half-span as possible.
'think this will work?...
Rebuilding a SkyRay that I demolished 12 years ago required reattaching spars and leading edge near the root. One spar was badly warped; so I grafted the broken end, which made a good fit with lots of surface area, to a new spar with a scarf joint. All were done with epoxy, since I wanted some gap filling for the l.e.and didn't expect penetration advantage from CA cement on the spruce spars. The scarf joints seem very strong. The leading edge had to be butt jointed, but I made 1/16" plywood laminates for the two flat sides and rely on the sheeting and rib to help unload that joint. I'll probably reinforce the l.e. with glass, but the silkspan should strengthen it. The last pictures must illustrate what's left, as I temporarily fit some ribs, because I forgot to take pictures of the jigged leading edge. The lamination technique is shown on a piece of 1/2" square stock that I was thinking of using as a replacement leading edge. If these repairs don't hold up, the loss is not so great. I can't re-paper the wing through the fuselage and should have left some silkspan on near it.
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Ya gotta love it when a modeler takes a plane and brings it back to life.
Nice work Serge. H^^
Charles
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Ya gotta love it when a modeler takes a plane and brings it back to life.
Nice work Serge. H^^
Charles
No kidding, that one was a mess. I have a 1/2A I call the Refried Bean that folded a wing and has been a hangar decoration for 3 years. You might have provided me with the inspiration to get her back in the air. It was a fast fun one with a bladder fed Norvel .061. I made it from the remains of the Li'l Jumpin Bean I built to learn to fly loops with.
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I like it. H^^
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Yeah. That one deserves a revival for sure! Nice work.
Edit: Thanks Charles! Ribs are attached now and it's time to refit some t.e. sheeting.
SK
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Now I'm hooked. I just watched a video of the Refried Bean, it's too good to collect cobwebs. I'll look this thread over for spar rejoining ideas and get her back in action.
I promise I'll stop hijacking aba183210's thread after this.
It's on 45' in this video. Also sagging lean. I was playing it safe with a 6x3 Master Airscrew and breaking the Norvel in too. I later went to a 5.25x3 and promptly folded the wing in a not so lazy 8. MA is my favorite 1/2A prop for long lines.
This is also before I began flying bigger planes and learning PA(I didn't know such a sport existed in 2012):
https://youtu.be/RobymeDXZkc
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I count on the bell-crank mounting system to act as a joiner between wing halves.
But failing that I think the formula with splicing is that the length of the splice should be at least 3X as long as the square side of it, so if you have a 6mm square spar then the length of the cut should be at least 18mm.
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i Think that according to FAR 43 ( if I recall correctly) which is the manual for repair of full scale aircraft, my recollection says that like CHris says, its a 3 to 1 ratio,, although I seem to recall that the angular amount mentioned was in the range of 20 degrees, I cant find my manual right now or I would look it up
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i Think that according to FAR 43 ( if I recall correctly) which is the manual for repair of full scale aircraft, my recollection says that like CHris says, its a 3 to 1 ratio,, although I seem to recall that the angular amount mentioned was in the range of 20 degrees, I cant find my manual right now or I would look it up
mYbad, its AC43
http://www.faa.gov/documentlibrary/media/advisory_circular/ac43.13-1b.pdf
if you go to page 79 you can see the aproved method for a structural repair of a spar
SPLICING OF SPARS. Unless otherwise specified by
the manufacturer, a spar may be spliced at any point
except under the wing attachment fittings, landing
gear fittings, engine mount fittings, or lift and
interplane strut fittings. These fittings may not
overlap any part of the splice. A spar splice repair
should not be made adjacent to a previous splice or
adjacent to a reinforcing plate. Spacing between two
splices or between a splice and a reinforcing plate
should be no less than three times the length of the
longer splice.
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5:1 slope Mark, page 81.
(I am amazed that you sourced that so quickly!)
P.S. actually page 87 give a minimum ratio of 10:1 plus cover strips. (That does seem like an overkill though.)
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(http://4.bp.blogspot.com/-jZVaw78PWLc/TmR0kXSWsTI/AAAAAAAAAgo/ORnGP3ssyD0/s1600/Tindal-Chipmonk.jpg)
10 G is 10 G afterall . Sit the wingtips on blocks and sit 550 Oz on the fuse of a 55 oz aeroplane ! VD~ S?P
(https://encrypted-tbn0.gstatic.com/images?q=tbn:ANd9GcRuVlXAcyvWHnH6N2fSY0xzw7Kvf7r_VDhi3p9hDIN058dF1FHg)
S?P
Theyre all called George . So This is a 60 G load test . :! LL~
(https://s-media-cache-ak0.pinimg.com/736x/d8/19/20/d8192044297665f0d73c79a6c56b70c3.jpg)
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5:1 slope Mark, page 81.
(I am amazed that you sourced that so quickly!)
P.S. actually page 87 give a minimum ratio of 10:1 plus cover strips. (That does seem like an overkill though.)
Google is yoru friend,, I had time to find it, but not time to do a thorough search within the document,,
thanks for narrowing it down, I now have saved it to my computer for my reference,, just in case i need to do some riveting or something on my new stunt ship I have it close by ;D