ORIGINAL: fstevenj
Have a SIG LT-40 that has sheered off the inboard CA hinges two times now. Not sure why this is happening. I guess I'm going to replace them with hinge points by Robart since I don't have much wood left. I have many questions:
1. What size hinge points should I use?
2. Obviously I have a Manufacturing Problem, What could it be?
>I do not believe it is a design/manufacturing problem. This
>plane has been around for a long time and I am certain that
>if this were a common problem, not only would others have
>commented on it, but it would have been noted and corrected.
The hinges didn't bind, the gap was not sealed, I didn't notice any flutter, but not sure I could recognize it.
3. How can I fix this design problem? Are the hinge points more robust?
4. I did notice that at full elevator motion I have a little torque in the stabilizer could there be a slight alignment problem?
>It sounds like you MAY have a warp in the fixed or moveable part
>of the elevator. This will cause little if any binding at low movement
>but will cause some binding as you go to full movement. Other
>possibilities for the "torque" include wood that is cracked under the
>covering (try moving the offending part), the horizontal stab (elevator)
>is not completely glued and/or the fuselage in that area may have
>a crack under the covering.
I would think the outside would shear off first if this is the problem.
>Have you ever tried to tear a CA hinge ? I doubt you can do it.
>If they are CAed in place PROPERLY, the wood will tear BEFORE the
>CA hinge does. The best way to install a CA hinge is to drill a
>small hole in the center of the slot FIRST. Then when you apply
>the THIN CA it will wick into the hinge and wood (2 or 3 drops per
>side).
5. Also is there a potential for overspeeding the aircraft such as powering though a loop instead of letting off power at the top of the loop? I'm just a beginner and not doing too much to the airframe.
>There is always a potential for overspeeding a plane. Personally I
>wouldn't be overly concerned about it.
6. Not much slop in the control surface from what I can tell, so don't think that is a problem.
7. The design has a fairly long distance from the last support to the horn, potential issue?
>While it MAY be a POTENTIAL issue, I wouldn't worry about it. This
>plane is a trainer, and won't be flown at high speeds or doing precision
>aerobatics where it would be noticeable.
Any inputs would help. Thanks
The wood in the area of the hinges is now hardened/sealed with CA. What this means is that CA (or any glue) will not soak into the wood in that area. You will need to use an area that has not had CA applied to it (relocate the hinge location). You MAY need to cut out and replace the wood if you can not relocate the hinges.
CA hinges are VERY strong IF INSTALLED PROPERLY. I have a Gee Bee Y with an OS 1.60 in it that uses CA hinges and I have never had any problems. I also have CA hinges on other planes that I fly at speeds in excess of 120 mph and have had no problems.
If you want to change hinges, I would use nylon "pin" hinges. They have a brass pin connecting the two halves together and are installed using epoxy and possibly also toothpick "pins" through the wood AND the hinge. DuBro (among others) make them.
I would suggest relocating the hinges and, after checking for a warp, install new CA hinges.