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Building Tips and technical articles. => Building techniques => Topic started by: John Watson on September 28, 2019, 02:51:14 PM
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Anyone used fishing line for hinges. I saw that somewhere I think an RC site...……………
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If you are talking about figure 8 hinges, you could use just about anything that is tough. The new spider wires stuff would be great. monofilimaet would make for stiff movement I would think. The old fashioned way was to use dacron 1/2A flying line, carpet thread, or dental floss. Dental floss was the original composite material!
Type at you later,
Dan McEntee
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But if you do use Spiderwire, keep in mind it is really thin stuff, and wicks CA.
I tried it on a few test pieces and was afraid it would cut through the balsa. That, and it really wanted to wick the CA, so keep it far from the edges or the hinge line stiffens up! I probably drilled the holes too big. If I tried again, I'd just stab the wood with a heavy T-pin rather than the puny drill bit I used.
I prefer a slightly heavier cotton/polyester thread just to keep it from cutting the wood. A drop of CA at each hole is all it takes to keep the thread from moving like a saw. Jump over to CEF...the remnants of the Scientific P-40 shows how tough a good, sewn hinge can be. I tore the tail off that bird, but the elevator stayed on the stabilizer. The BHM Mosquito also held up to a pretty rough "landing."
Come to think of it, this has been a banner 12 months...I wrecked my two favorite planes! Yeesh.
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I am a huge fan of "sewn" hinges. Not the old school "Frankenstein" sutures that some guys just can't get over. I'm talking about a figure 8 wrap like Porsche_Jim suggests. The 30 lb test Spectra works great on anything up to a 40-sized rat--and probably bigger, but I've never tried anything bigger. The solution to cut-through is to use a thin spruce spar or edging on the hinge line of both the fixed and moving surfaces. Then you can pull the wraps as tight as you like. Using spectra without the reinforcement will likely damage the surfaces as Jim notes.
You don't need any more sewn hinges than you would pinned plastic hinges. Space them out just the same.
I like to use either 3 or 4 wraps laid side by side in one pair of holes. Drill a hole about 0.040" or so. Do the inside hinges first and work outward. Put the knot on the bottom. With a little finesse, you can push the knot into one of the holes and make a smoother job. Tie a square knot and soak with CyA. Then clip with your sidecutters. CyA does not make the hinges stiff. These, done right, will allow the surface to flop down from gravity.
One oddity of the geometry of a sewn hinge is that you don't actually need to shape the edges of the surfaces. No rounding, no wedge shapes. The instantaneous hinge line shifts up and down with the surface motion, keeping the OML flush to each other. Also note that if you can make your surface edges truly straight, then the hingeline gap is just the thickness of the Spectra. In the case of the 30 lb test, that is only 0.011".
The Spectra is far superior in this application to anything else you can name: dental floss, 1/2A Dacron, carpet thread, monofilament line, Kevlar line, etc. The only reason to use any of these is that they are sitting on your bench and you can't work up the energy or collect the coin to go get the Spectra....
The Divot
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Mr. Dave,
I'm a Frankenstein-hinge guy. But what you suggest has me re-thinking my hinge lines.
Are you suggesting that the drilled line of holes goes on the seam, or glue line between the balsa and spruce? That would make sense since the Spectra would be pulling against the spruce, and not into the balsa.
Then the stresses on the Spectra get spread out along the entire hinge line by the laminated edges. If that is the case, then it means I can actually make a few, smaller hinges along the hinge line, instead of one longer run per side of the tail. They will appear to be less visible.
Since I build smaller models, I'm thinking about trying this with bamboo skewers instead of spruce. They are already pretty close to the thickness of my surfaces.
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Mr. Dave,
... Are you suggesting that the drilled line of holes goes on the seam, or glue line between the balsa and spruce? ...
I can't speak for Dave, but that's what I do -- or if I have some really hard balsa (12lb or more) I'll use that.
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Personally, I just use a large needle. No need to drill a hole when you can just push a needle through the balsa.
And now that someone said "Bamboo skewer", I think I'll try that great idea! y1
Jerry
PS: On my RC ship......... (No pretty points anyway!)
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After the holes have been poked through, the balsa can be toughened up with glue of several kinds. Rubbing glue intop the hunge material and the balsa surface after installing can help out also.
Type at you later,
Dan McEntee
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Porsche_Jim,
Yes, I think you are visualizing what I am trying to describe. I tried to find a close-up photo to show you...but no luck. (I could text you a photo if you'd like; just leave a number in the private message place.)
I guess I should have clarified what I mean by Frankenhinges. This is the kind that spaces a bunch of single wraps all the way down the hinge line. You used to see them in the photos of the 1950's and 1960's on sport planes, rat racers, etc. I think they are overkill and buh-tugly. That said, they work fine, I'm sure. If you combine them with the thick, hairy Kevlar line that sounds so techie to some, then you have a monster turbulator that probably makes your control surfaces, well, turbulent. I'm sure that has appeal to some of the aero guys....
Instead, as you have deduced from my less-than-the-best description, if you glued a spruce, bamboo, or other harder material along both edges of a balsa stab and the elevator where they normally meet, and you drill holes directly opposite each other thru the glue-line, then you can pull the Spectra wraps fully tight. I actually use a small pair of needlenose pliers to cinch it up and avoid cutting my fingers. Along a small 1/2A elevator, I put in two hinges per side. Even on a .40-powered Quickie Rat I only use three "hinges" per side--just like I'd do with Klett plastic hinges. That means you only drill 4 or maybe 6 pairs of holes to do an entire split elevator. The holes don't need to be big. Just enough to thread three passes of .011" diameter line thru.
You don't need much of a spar. I've even used the thin basswood strips from the hobby shop. If you are worried about weight, just use a little softer balsa for the surfaces themselves--now that you have a spar to help carry the bending loads.
I'm not the paint and finish guy around here, but I have seen these sewn hinges relieved into the wood surfaces and then filled and painted over. They practically disappear.
There's lots of ways to do things and people develop methods that suit their tastes and skills. I'm just explaining a way--and the materials that go with it--that appeals to me.
The Divot
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I used 1/2a Dacron flying line for A, B, B Proto and C (.65 then) (total of about 9 or 10) speed models, a FoxBerg/NW Sport Racer and a .40 Rat. I just drilled 3/32" holes about 1/4" from the hingeline on stabilizer and elevator. Hinge stations spread along the hingeline about like our modern pinned nylon hinges. About a half dozen 8's of the Dacron line and fill both the holes with Ambroid or Duco. A little wiggling freed them up pretty nicely.
Last step was to trim off the excess after the glue dried. The trimmed off place would be on both top & bottom of the elevator, just to be consistent. For F1A gliders, I did something very similar for the rudder hinges, but used smaller holes and finer thread of some sort...maybe nylon, maybe dacron, I don't remember. Hardening the wood around the holes with thin CA (before doing the hinges) might be worth doing, but I don't recall ever doing that, and I never had a failure on any of them. The whole reason, of course, was to make them repairable on the field... LL~ Steve