Controls catching on something

[Rusty]

Hello,  I was gifted a built, full body stunt plane.  The plane has a nice finish and is worth flying.  I don't think it was ever flown.   The issue is that about neutral in the controls there is something catching and causing them to stick.

I have cut a hole where the leadouts leave the bell crank.  It has one of those carbon bellcranks that comes with the leadouts attached.  I found that they were rubbing on the ribs and causing friction, but not the catching issue.  I cut holes under the elevator and looked at the control horn. I took the clevis off and centered the flaps and elevator better, but that did not fix the catching.   I then cut a hole in the fuselage to look at the flap control horn.  It was okay, but the push rod was rubbing the cockpit floor when full control was applied.  I used a rat tail file and cleaned that up.   None of this has solved the catching and sticking of the controls.   

What do I do next, or do I abandon the plane?  I would have to cut the whole bottom or top of the fuselage to get to the bellcrank which has sheeting over it.   

Any ideas?

Rusty

[Paul Van Dort]

Hi Rusty, you have a lot of experience, so giving hints from the other side of the pond is probably not very helpfull. What is the difference between"catching" and "rubbing"? I had an issue with Stiletto where the elevator pushrod was rubbing a former, only when there was centrifugal force. Statically it was super smooth.. This jeopardized every flight. Could it be overtight ball links? Seems the control system is pretty advanced with the carbon crank... I would try to solve the mystery. let alone for you night sleep :-)

[Tom Luciano]

Dubro hinges have flashing right at neutral that cause a click or slight lock. Might be what you're experiencing, that's not as visible as a rub or linkage catch.

Good luck,
Tom

[Dan Berry]

You need a stethoscope. 
Listening to it should help you isolate where the problem is.

[Rusty]

Thanks guys.   Those are some very helpful suggestions.   

Now that you mention it, in building planes before CA hinges (RC planes) they used the two piece pin hinges and they could get stuck and even click.   I'm not sure this is it, but will check into it more. I have a box of those hinges and while building my Vector, I had to sort through them to find ones that didn't have the flashing.   Over half did.  I don't know how, exactly, you would remove the flashing.  I guess by sanding.  I won't worry about that until I need those hinges.

The controls do actually stick and it takes some force to go through this part of the movement arc. 

I don't have a stethoscope.  When I was a mechanic I used a long screwdriver and put on end on where I thought a noise was coming from and the other end against my ear.  It amplified the noise and you could usually find where it was coming from. 

I will work on it more and report back.

Thanks

[Ken Culbertson]

I am guessing that you do not have removable surfaces.  If it is a minor "rubbing" and not something that requires additional force to overcome it may loosen up after a few flights.  If you anchor the plane and slowly work the controls from full up to full down do you feel it when it passes neutral?  A sticking ball link will pass this test but not if you start at neutral. I stopped using the DuBro type hinge for just what Tom posted.  No matter how hard I tried I still had some binding.  Before I stopped using them completely I would sand them slightly to increase the gap between the sides and use a smaller full span pull wire.  I am fighting this right now on a new ship that is fortunately unfinished.  My bind is at near full deflection.  Down is fall down smooth up I can feel some resistance near 30 degrees.  I only mention this because with removable surfaces it was easy to spot that it was my inboard flap that needed to be beaten into submission.  My first surgery would be to remove the flaps and elevators first.  If the controls free up you can fix that.

Another thing that can cause what you are describing is a slightly bent or misaligned flap horn.  You mentioned that the BC came with the leads attached.  Are the bolts holding the leadouts perhaps slightly over tightened so there is a small bind in one of them?  If that is the case, it will probably safely loosen up with some flights.

Are the wing leadout cutouts clearing the leadouts?  They are at their widest point at neutral.  If it is barely rubbing that will saw itself clear when you fly it.  Anything more could be bad.  Especially if you move them dramatically later.  You won't like the fix for that.  Can you weasel a camera snake into the leadout guide?

Enough brainstorming.  I am putting my money on a ball link or a flap rubbing at the fuselage but those have already been covered.

Ken 

[Dave_Trible]

Dubro hinges have flashing right at neutral that cause a click or slight lock. Might be what you're experiencing, that's not as visible as a rub or linkage catch.

Good luck,
Tom

I've experienced that on more recent batches of hinges from Dubro.   Might indicate too much mold pressure in the injection process or their molds in rough shape.   In any case I check for it now and sand it off before installing.    The similar hinges I have gotten from China through Ebay haven't had this issue.  It was sure frustrating trying to find the cause of the 'catch' before I knew.

Dave

[bob whitney]

Snap-On makes an automotive stethoscope with a long rod that u can probe into it with

[Jim Svitko]

Do you know how the leadouts are attached to the bellcrank?  One popular method is to loop the cable thru some brass tubing, and that tubing is passed thru the bell crank and bent to a teardrop shape.  The cables are then wrapped just like the lines.

Although that methods works most of the time, I never trusted it.  I have seen instances where that loop of tubing, thru the bellcrank, is not all that free.  I have see it rotate up or down a bit and thus gets bound up. 

There are so many places where there can be a clash of components to cause the problem you are having.  Why it was not discovered during building is a question I have.  I never button up anything until I am absolutely certain the controls are totally free.

[Motorman]

Just cut into it and start dissconnecting stuff. Good luck. If it's not some obvious interferance you might find it's a misalignment of the flap or elevator connecting wire and the hinge line, a wing warp or maybe one hinges is too far in or out. Any of those will make it click over center.

MM

[Rusty]

Just cut into it and start dissconnecting stuff. Good luck. If it's not some obvious interferance you might find it's a misalignment of the flap or elevator connecting wire and the hinge line, a wing warp or maybe one hinges is too far in or out. Any of those will make it click over center.

MM

Clicking is not the issue, it is catching / snagging / binding in about neutral position.  When I get time I am going to cut the top of the fuselage off from where the bellcrank is, back to the flap control horn and then cut the wing sheeting off so I can see what is going on.   I may ruin it, but it no good this way, anyway. 

[Ken Culbertson]

Is it a floating bellcrank mounted to a spar doubler or an I Beam?  Those are both vulnerable to centering blockages of some sort.  Maybe a smaller set of holes to disconnect the flap pushrod from the flaps would tell you which half was the problem.  Good Luck!  It has been my experience over the last 60 or so years that planes that have undergone life threatening surgery are very grateful and perform well for you after recovery. 

Ken

[Dennis Toth]

Rusty,
Before doing major surgery you might want to try to isolate where the problem is. Since you already have holes cut I would disconnect the pushrod from the flap horn to the elevator and see if the catching stops then you would know it's either something on the pushrod (like a glob of glue) hitting a former or the horn connection. If that is not it, disconnect the flap horn from the bellcrank and check.

Best,   DennisT

[Rusty]

Rusty,
Before doing major surgery you might want to try to isolate where the problem is. Since you already have holes cut I would disconnect the pushrod from the flap horn to the elevator and see if the catching stops then you would know it's either something on the pushrod (like a glob of glue) hitting a former or the horn connection. If that is not it, disconnect the flap horn from the bellcrank and check.

Best,   DennisT

Thanks Dennis.  I hope all is well in your new home.

I did part of what you are recommending.  I did disconnect the clevis from the elevator to check how it worked.  The elevator moves free.  I adjusted it because the flaps and elevator were not synched well.   I cut a hole by the flap horn, but could not disconnect it   I saw the bellcrank pushrod was hitting the cockpit floor.  I filed that down. 

I have been messing with this, off and on, for a few months.  I'm burned out.  Itls CHAIN SAW time!   

[Ken Culbertson]

I thought of one more place to get an "Ah Sh**" at center.  The aft bellcrank arm's leadout or it's connecting bolt is hitting the flap pushrod.

Ken

[Dave Hull]

You can get a pretty decent borescope attachment for a smartphone. Gives you a pretty good look prior to wholesale surgery. Best to have a strategy of isolation; keep dividing the problem in half if you can. Sounds like you did that by ruling out the entire elevator setup. You might learn something if you changed orientation. One thought there is to attach one of your old, heavy handles directly to the leadouts and put that wingtip straight down. Now try wiggling the elevator. Then try wiggling the flaps. I have rebuilt and/or repaired quite a few OPPs (other people's planes) and find that control installation does not always get the attention it deserves. And, simply put, a lot of commercially available bellcranks have waaaay too much wobble. You can fix that, but most people don't. And it can lead to slop and glitches. One test that is just as important as feeling how smooth the controls are is an end-to-end slop test. Grab the leadouts with one hand right at the wingtip and put tension on them and don't let them move. Now wiggle the elevator. Then wiggle the flaps. Is there a lot? Does it go clunk-clunk? A lot at the elevator but not much at the flaps? A lot at both? With even a small access hole to see the flap horn you can reach in with large forceps and grab the flap pushrod. Wiggle it with the leadouts locked. Springy? Clucnk-clunk? All diagnostics to help isolate. Oddly, I have had to cut into some really nicely finished planes that on the outside looked great. But the controls were, um, slightly worse than poor. You just can't tell without testing, and even then, they can feel fine right up until some poorly executed construction locks up or saws thru something.

Don't trash it! If you get frustrated come back to it later. Good luck!

PS--I almost chuckled when you talked about the file using inside the plane. I made a special file quite a few years ago that is really useful. It is a coarse rat tail file that I heated and put a 30 degreeish bend about in the middle. Amazing for accomplishing stuff that seemed too hard to get to....

Dave

[Tim Wescott]

If the hinges are catching you can clean up the flashing with a fresh #11 blade and a steady hand.  This is way easier if the hinges aren't pinned, but if you're desperate you can do it any time (ask me how I know).

[Steve Helmick]

A piece of aluminum tubing (3/8" > 3/4" dia. x 12" > 36" long) works pretty well as a stethoscope.

I'd suggest any future builds include removeable flaps & elevators. Removing the pins from those DuBro hinges (via danger disc & Dremel) solves the problem with the hinges...makes it easy to see and remove the mold flashing.  Steve