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Building Tips and technical articles. => Building techniques => Topic started by: Allan Perret on February 03, 2010, 05:18:20 PM
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Realized after the fact that I used finishing resin instead of regulare epoxy when I put the front end of fuse together. I built the motor crutch assembly using slow cure epoxy, and used finishing resin to laminate the ply doublers to the two fuse balsa sides; both intentional. Not intentional was when I put those 3 components into the fuse jig, I used the finishing resin by mistake for the joint between each of fuse sides and the motor crutch. I had good fits, wetted both surfaces where everything mated, and got good glue squeeze out at all the joints. The joints in question were either ply to ply or ply to maple.. Question is will the finishing resin be strong enough for that portion of the nose construction ?? Plane is a 60 size SV design using PA65.
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I'd say no problem.
While some epoxies may be stronger than others, all are very strong. It could be argued that your joints are stronger BECAUSE of the lower viscosity an superior pentrating ability of the slower curing resin. The real key is as you noted, good joints, good wheeting and good squeeze-out.
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plus the PA65 is very smooth running verses a ST60 pounding at it
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Thanks guys for the reply. I did notice that there seemed to be better penetration. That should have been a clue to me that something was different, but no..
I did not want to start over because I did some other experimenting with this fuse construction, result being that I already have about 20 hours into it. Years ago in one of his videos I saw Bob Hunt mold / curve the two fuse sides into the spinner ring. I always wanted to try this as it eliminates the need to carve through the ply doubles as you taper the front to the spinner. So building the jig to mold the curves into the fuse sides, I probably have double the amount of time it normally takes to get to this point in the construction. Bob used a foam buck, but I dont have foam cutting equipment and made mine from a MDF lamination.
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Hmmm if I read that right it sounds like your fuse will be stronger than normal because you are curving and not carving away plywood? That is way cool!
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Hmmm if I read that right it sounds like your fuse will be stronger than normal because you are curving and not carving away plywood? That is way cool!
Yes I am hoping to get a little increase in nose stiffness from laminating the ply doublers into the curve shape.
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That looks great and I beleive your glue up is okay also.
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Hi Allan,
A great big thumbs up on both choices! The resin will be fine, and the curved fuse sides is a winner! I got a set of foam bucks from Bob years ago to do this and have never looked back. ;)
(it just takes a bit longer to carve/sand down those motor mounts, etc. LL~ )
Big Bear
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Full speed a head! Not a real fan of the plastic tank though. Good luck!
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Full speed a head! Not a real fan of the plastic tank though. Good luck!
Seems like a lot of people are doing OK with the plastic tanks, so I decided to give it a try. I had to increase the width of the fuse to
2-3/8" (inside) to accommodate the Sullivan R-8 tank, power will be PA65 on pipe. If I have issues with it I can always go back to a metal tank because there is lots of space in there.
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our club has seen two things with the plastic tanks: The stopper shrinks across time, Check it each spring or after sitting for a while and we have had two split at the seam with age. (They were the real soft tanks that would sqeeze in tight places) They are cheap enough so after a two or three years, replace it. I see this in the RC planes after a few years also, they start to drip so it;s not worth the health of a good plane over fuel dripping inside the fuse. Keep us posted....looks great!
Terry
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One issue with using finishing resin is that so much can penetrate that the joint ends up starved for glue and is weak.
WEST recommends painting the surfaces with pure resin, then putting on a layer of resin mixed with a thickener to hold glue in the joint. And the proper thickener adds strength itself.
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I doubt you have a problem. With all that surfact area, the joints I'm sure are sound and durable.
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As to the plastic tanks, I've used nothing but since 1990 with only one problem. That was caused by jarring the plane on a bad road and the clunk bounced forward and stuck there. What a surprise when I turned under in the reverse wingover! Had to happen at the nats, too. The plane wasn't hurt as I got it to the grass down over the hill.
I use the Sullivan flex series for all my PA's, both the 65, the 75, and the 61's I used to have. The one in my first crosswinds is now 7 years old and still fine. Yes, you need to do preventive maintainence every winter, but that goes for ANY tank. I'll never go back to metal.
Blessings,
Will