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Building Tips and technical articles. => Building techniques => Topic started by: Bootlegger on December 10, 2011, 07:15:05 AM
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Putting together another kit that calls for the M/M's to be 1/4" from top of fuse.
What method do you use to get this measurement as close as possible to correct?
In other words, what would you suggest to get this right??
Thanks, Gil
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1/4 X 1/4 balsa or 1/4 sheet across the engine mount. H^^
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M/M's ???
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M/M's ???
Melts in your mouth, but not in your hands?
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Putting together another kit that calls for the M/M's to be 1/4" from top of fuse.
What method do you use to get this measurement as close as possible to correct?
I would do as Mr. Holiday suggests and use a shim to the top of the fuse side if I wanted to get the 1/4" measurement as dead nuts on as possible. A stick that's sold as 1/4" isn't always exact, but it should be more than close enough.
If I had a piece of aluminum or brass the right size I'd use that, because yellow glue doesn't stick to it and when I'm not in a hurry that's what I use for joining hardwood and balsa.
In other words, what would you suggest to get this right??
Ah. That's an entirely different question. "Right" to me puts a lot more weight on getting the wing, motor, and tail all lined up at 0-0-0 (or whatever the design calls out) than it does to put the tip of the spinner at some measurement down from the top of the flat part of the fuse side. I'd double check both fuse sides to make sure that their tops really were straight, then I'd correct as necessary to make it so. Then I'd measure 1/4" down from the fuse top at the very front and very back of the piece (assuming that it's dead straight all the way). I'd mark it with a very fine, soft pencil, and I'd use a straight edge long enough to span the two marks, laid across the top of the piece (with appropriate shims, or with both pieces on my building board laid top-to-top). Then I'd glue in the motor mounts by butting them up against the straight edge (again, this is assuming yellow glue and an aluminum straight edge. If you're using epoxy, make sure there's waxed paper between straight edge and motor mount, or make sure your straight edge is polished and waxed).
When I was done and the glue was drying, I'd sit back and appreciate the fine job I did, and reflect wryly the fact (assuming the motor mount is wood) that over-tightening the screws fore and aft by just a hair is going to put a lot more up- or down-thrust into the engine than any inaccuracy in my super-detailed motor mount installation.
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Putting together another kit that calls for the M/M's to be 1/4" from top of fuse.
What method do you use to get this measurement as close as possible to correct?
In other words, what would you suggest to get this right??
Thanks, Gil
Hi Gil,
Since I always to use 1/8th alum. mount pads, I alter the firewalls where the MM go through and use ink lines to assemble the MM crutch system to the fuselage sides. I generally have the fuselage sides and other formers built n my fuselage jig so mounting the crutch just needs to be aligned and clamped with wood worker clamps.
Big Bear
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Putting together another kit that calls for the M/M's to be 1/4" from top of fuse.
What method do you use to get this measurement as close as possible to correct?
In other words, what would you suggest to get this right??
I build the engine crutch as one piece and then glue on the fuse sides, but a good old fashioned sacrificial spacer of 1/4" square balsa works pretty well. Build the crutch, tack the 1/4" on the top in the front and back of the mount, then lay it flat on the table, and glue the fuse sides to that. If you are inclined to put in downthrust, put a second shim under the front spacer.
If you must, the same thing will work when gluing the mounts the fuse sides, as long as you are very careful to keep the fuse sides square to the mounts when you do it. And, truth be told, with any current 40-60 stunt motor, you aren't going to have any problems with engine runs if the mounts aren't in perfect alignment. Maybe with a Fox or McCoy, but not a PA61. The engine will pull it straight. Maybe you will get stress cracks later but it won't screw up the engine run
Brett
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H^^ Thank's guy's sure do appreciate all the help... #^