RCU Forums - Elevator CA Hinge Problem

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Elevator CA Hinge Problem

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? 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? I would think the outside would shear off first if this is the problem.
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.
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?
Any inputs would help. Thanks

RE: Elevator CA Hinge Problem

Hmm... the inboard two on mine failed as well... unfortunately I flew the plane into the ground, so I can't really tell if I had the same recurrent problem you do.

RE: Elevator CA Hinge Problem

Quote:

ORIGINAL: fstevenj

1. What size hinge points should I use?

Either the 3/16 or the 1/8" will work, but I would use the 1/8"

Quote:

2. Obviously I have a Manufacturing Problem, What could it be? The hinges didn't bind, the gap was not sealed, I didn't notice any flutter, but not sure I could recognize it.

Manufacturing problem? Doubtful. It sounds more like an installation problem.

Quote:

3. How can I fix this design problem? Are the hinge points more robust?

While the elevator is still attached, draw 3 lines (each side) on the bottom of the stab and elevators. Then remove the elevators and use the lines as a guide for drilling the holes for the new hinge points. Make sure that the holes are centered top to bottom and directly on the drawn lines. If the holes are slightly off, you can make them larger and fill in the excess with epoxy.

Quote:

4. I did notice that at full elevator motion I have a little torque in the stabilizer could there be a slight alignment problem? I would think the outside would shear off first if this is the problem.

There COULD be an alignment problem, but there's no telling where it would break without seeing it first hand.

Quote:

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.

Doubtful with an LT-40 unless it's WAY overpowered.

Quote:

7. The design has a fairly long distance from the last support to the horn, potential issue?

Possibly, Put your hinges about 3/4" in from each end, and one in the middle.

RE: Elevator CA Hinge Problem

Quote:

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.

RE: Elevator CA Hinge Problem

Quote:

ORIGINAL: fstevenj

Any inputs would help. Thanks

All of my elevator CA hinges on my LT-40 failed also. It started in the middle and then the outside ones failed. A cheaper fix is to use either 20lb fishing line or dental floss. I drill 1/16" holes on both sides of the CA hinges and criss-cross the line (up one side, down through the gap, then up on the other side...repeat to next 2 holes) and CA each hole as I pull the line through. With this method, you only have to fix the hinge that failed instead of removing all of them to fix the middle ones.

RE: Elevator CA Hinge Problem

By manufacturing problem, I meant build/installation problem. One thing pointed out to me by some aeronatical buddies is that maybe the stabilizer needs to be stiffer. They said if the stabilizer is not as stiff as the elevator and when loaded it is flexing more than the elevator hence causing the hinge to fail.
One question on the hinge points is that since it is a stick build up stabilizer the hinge point is longer than the the stick is wide so some of it won't be glued in. Is that a problem?
I was going to install the hinge point at the very end since there is wood there. Is that a problem? MINN you said put it in 3/4".
Another question is how many hinge point do you recommend I install. The are a total of 4 CA hinges holding the elevator on, but was going to install 6 hinge points. What do you think?
Last comment, Campy you say that the wood will tear before the CA hinge, well this is not what happened. Twice I have had the CA hinges tear at the gap an no structural damage has occured to the wood that they are in.
Thanks again for your help

RE: Elevator CA Hinge Problem

While I don't have a lot of experence with building, I will tell you that if your control is not stiff, then your surface will flutter and this will wear out your hinge. Make sure that the rod connection both sides is stiff and that the control cannot flex. If it is one complete control surface, make sure the control is stiff and will not flex.