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Elevator Control Slop & Vibration

twcroy

Active Member
I wasn't sure where to post this question. I noticed a couple of days ago the back/forward (elevator up/down) control has about a 1/2 inch dead space / slip in it where it clunks a little in the fuselage at each end of the slack / gap in the control motion. It seems to be a little more than what I remember earlier, but my A&P looked at the control connection behind the baggage compartment and said it's ok and is due to tolerances. Before this happened, I had the rudder stabilizer fairing off and after a 40 minute flight I noticed a screw missing and a couple others half way out. I obviously didn't tighten them tight enough with the electric screw driver. I don't know if this would have caused this? I also had the plane tied down (vs. hangared) two weeks while awaiting weather and repairs prior to flying from DC to MI with the controls secured against gusts - don't know if this could have caused it. Probably nothing to be concerned about, just curious if others had this occur.

Lastly, I had some propeller leading edge plastic guards installed in May since the last field I was based at in DC had "dirty" taxiways. Does this require the prop to be dynamically re-balanced? I think there is more vibration now since the install of the guards, lowered idle RPM, and possibly evidenced by a subsequent loose connection at the GRT AHRS computer next to the firewall.

Sorry for the long post, but I appreciate any thoughts. I retired from the military now and am back in MI, so I'm happy to be "home" again and hopefully have more time to fly and interact on the list.

Blue Skies,
Tim
 
You need to find a friend that knows RVs. No way would I fly an RV with 1/2" of slop in the elevator. If I feel a 'top top' in the elevator I find the problem before flight. An A&P isn't an indication of intelligence or mechanical ability. I think the -9 has 4 places the elevator could be loose not counting the actual elevator mounting bolts.

Please find someone knowledge about RVs before you fly.

It never hurts to have a prop dynamically balanced after you've changed something about it.
 
I would have an A&P (preferably another one) or a local RV builder look at this portion of the control system under the forward portion of the seat.

Vans use a different bearing of an internal sleeve at the cross bearing attached to the stick and that may have been assemble incorrectly sometime in the past.

fba569ab0bdc64471dbaf59565e2244714478_DSC_0988.JPG


Pic shamelessly stolen from Mike Hoovers builders log...
 
Thanks Sid and Gil. I'll be out of town until 30 July, but it will be my priority to check this when I get back. I'm based at 35D now, and I met the A&P there yesterday. I'll check with him unless there are other RV'ers with this experience near Allegan, MI. I need to check for EAA Chapters also. It sure will be nice to have more time for this.

Much appreciated,
Tim
 
Tim,

Test the amount of "dead space" (I'm assuming you're measuring the 1/2" at the end of the stick) when moving both control sticks. Is it the same, or does one stick have more or less "dead space"?
 
Hopefully, 1/2" is an overstatement, but definitely have someone hold the elevator and find what is contributing to this slack.

One thing to check easily, is the long pivot bolt at the base of the stick (the one in Gil's picture above) . I am not flying and had to replace the stick due to that hole being out-of-round. From memory, I guess maybe 1/4" movement at the top of the stick. I replaced the stick, and custom machined a new bushing and now it is snug.

Any slop seems too much to me.
 
ask a builder.....+1

....... my A&P looked at the control connection behind the baggage compartment and said it's ok and is due to tolerances.
...what is he referring to? as others said, there are about 6 mechanical connections, and 3? pivot points that should have 'tolerances' that are more like a thousandth of an inch...so that adds up to 9 thou....not half an inch.

rod ends, bellcranks, hinges, etc should be individually stressed in each direction, and verified as installed correctly, safetied, and sound (obviously..not cracked, bent etc.)
at the grip, my perceived play is about 1/16" total, without putting a mic on it. The stick is likely the biggest, low-tolerance connection, so that's a good starting point.

you are smart to ask the question, let's see if we can find the answer!
 
Look at this photo-------there are 3 separate locations that can have slop in each pushrod. And, that goes for each end of the push rod.

Obviously the clecos are temporary, and will be replaced with rivets----------but the machined end bell can still be loose in the push rod tube. Also, the threaded fitting can be loose in the machined fitting-----and, although not shown in this photo, a jam nut in essential. Finally, the inner swivel ball can get loose in its housing---the "banjo" fitting.

Then there is the possibility of either a worn bolt, or even an undersized one being used. By the way, the bolt should NOT be free to rotate inside the ball.

dsc06230.jpg
 
Also borrow a copy of the -9 plans from a local builder.

Make sure the correct hardware is used at all of the 'swivel' points in the elevator system and that some previous well meaning A&P hasn't replaced the locking nuts used in most locations with castle nuts and cotter pins...:(
 
You can buy the plans on CD from Vans. It's inexpensive.

Personally, I'd never use an electric drill or electric screwdriver on a light airplane. I much prefer to feel the removal or installation using a hand screwdriver. Then there's no doubt that the screws are tightened appropriately.

Regarding the tape on the prop, yes, dynamic balancing is the way to go, for sure. It will make a real difference.

Having the plane tied down outside with the controls locked should be fine. If there was weather strong enough to cause damage, would the FBO have told you? If so, that's okay.

Dave
 
Control Slack

The only slack mine has is the play between the control stick base and the brass pivot bushing- hasn't changed in 200 hrs of flying.
 
Thanks all. This is very helpful information. I will do hand tightening from now on. I probably over-tightened the fairing after finding it loose before making my first flight over the mountains Thursday from DC to MI. I'll loosen them after I get back in town 30 July and re-tighten appropriately, as well as check the control connection points as discussed (very helpful), and re-balance the prop.

Thank you for everything, God bless,
Tim
 
Tim, in addition to the slop in the various components of the control stick/pushrod system, there is one more place I can think of that slop may occur---------and that is the actual hinge on the elevator (or rudder).

The hinges are the same style of rod end used in the pushrod, and also require a jam nut as shown in the photo below. A loose jam nut can cause cracking in the spar where the rod end mounts---------which this particular photo is showing quite well. Here is the thread. http://www.vansairforce.com/community/showthread.php?t=104551

P1130051.jpg


You might want to spend some time reviewing any applicable threads in the "ongoing maintenance" forum too. http://www.vansairforce.com/community/forumdisplay.php?s=&daysprune=&f=76

Lastly, factory service bulletins--------make sure the plane is up on them also. http://www.vansaircraft.com/public/service.htm
 
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If you really have a half inch of rattle in the stick you'd better at least identify the source before you fly. You may have a bolt falling out. Half hour with a screwdriver. Follow it from stick to elevator.
 
and that some previous well meaning A&P hasn't replaced the locking nuts used in most locations with castle nuts and cotter pins...:(

It has been recommended to me to change all the flight system critical bolts to castlated nuts and cotter keys (throttle, mixture, prop, elev, ailerons, rudder etc). What is wrong with the castlated one?

Bevan
 
Nothing wrong with using castilated nuts and cotter pins if they have been properly torqued.

I think what Gil is getting at is that many times well meaning people think that if you use castilated nuts, they don't have to be torqued.

Castilated nuts are primarily designed for use where the nut cannot be torqued, such as on "forks" like rudder cables or other places where the bolt is subject to rotation. If the bolt is holding bearing, such as on pushrod ends, they must be properly torqued, regardless of what kind of nut is used.
 
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Bevan, use the nuts in the plans and torque them correctly. Have you traced the elevator control end to end yet?
 
Nothing wrong with using castilated nuts and cotter pins if they have been properly torqued.

I think what Gil is getting at is that many times well meaning people think that if you use castilated nuts, they don't have to be torqued.

Castilated nuts are primarily designed for use where the nut cannot be torqued, such as on "forks" like rudder cables or other places where the bolt is subject to rotation. If the bolt is holding bearing, such as on pushrod ends, they must be properly torqued, regardless of what kind of nut is used.

That's correct, but I was also getting at the fact that some folks look at the self locking nuts in our control systems and think (very incorrectly) that the bolts are the actual hinge points and that rotation could loosen the self-locking nuts. They replace the bolt/nut combination with castle nuts and leave the nut slightly loose so the bolt can rotate.

This just lets the bolt and the hole in the steel bell crank wear. :(
 
Not trying to hijack the post, but here's my situation. After returning from OSH and a short flight Saturday I have started to notice a stiff stick and yesterday I decided to investigate. Mike in your post you state that the pushrod should not rotate on the bolt. Where my pushrod connects to the elevator horn, I have some rotation. That is the only problem I have found so far, and all the jamnuts are tight. I will look at it closer today. Thanks for your help.

Jim Fogarty
RV-9A flying 65 hours
 
Yes, the bolt through the spherical bearing needs to be tight so the rotation is all in the bearing. I don't know your situation, but when I built my pushrods, I didn't let the primer inside the tubes dry long enough. (Overnite isn't long enough) Any way I put the rod end in too soon and the out gassing of the primer messed up the internal lub and some of them froze and the controls were very stiff. I got them to loosen up, but I didn't trust them any more and replaced them all. My 2 cents. Bob
 
...what is he referring to? as others said, there are about 6 mechanical connections, and 3? pivot points that should have 'tolerances' that are more like a thousandth of an inch...so that adds up to 9 thou....not half an inch.!

If he is talking about half an inch at the stick, then that is amplified by the length of the stick. It could well be that a very small amount of slop due to wear could translate into something very large at the end of the stick. It also could be that something is improperly assembled or is broken. You just don't know until you isolate it. It could be the stick assembly, the bellcrank behind the backage compartment or the elevator torque tubes or hinges. It is not that difficult to nail it down. It could also be a buildup if it is an older airplane. The most important thing is to find out what it is - then you can decide if it is a safety issue or not. It might be nothing important or it might be waiting to kill you. Seriously.
 
All,

Sorry for the delay in getting back to the plane, I've been re-habbing a house to move into now that I'm back from DC, among other requirements. I've been running the plane up every 2-3 weeks to 180F oil temp to keep the engine lubed. I checked the elevator control system and noted about a 1/4" slop at the top of both control sticks, about 1/16" (guesstimate) between the outer sleeve / weldment at the base of each stick and the encompassing bracket - a castle nut and washer are used at the end of the bolt - I can check tomorrow whether the bolt rotates here which I guess will indicate whether the castle nut was torqued properly? I think there was minimal movement if any around the bolts' diameters there. There is minimal movement to none at the bell crank's upper rod connection behind the baggage compartment and it does contribute to a clunk after the control stick slop's clunk sound - this is the area / bell crank the A&P in DC told me was "in tolerance". I didn't note any slop in the elevator bell crank connections at the center-line aft, and didn't check the push rod bearings for each elevator side for a possible crack - I don't think I have an inspection plate to see the area. So next I want to check if the bolts rotate and anything else you think I might want to check. A question I have pertains to the picture of the base of the control stick. I don't know if the roughly 1/16" slop between the outer sleeves (in which the bushings sit) and brackets are ok? Thinking back now it could have been that way for a while and I just noticed it due to the clunking sound it made when I moved the control sticks quickly back and forth, which I think causes the sound to resonate through the pushrod and is amplified in the fuse behind the baggage compartment.

-- I tired to include a picture of my control stick base, but I was unsuccessful. Hopefully you can understand what I'm saying.

Thanks again,
Tim
 
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All,

I wanted to close this out so you know what I found out and did. My priority has been repairing a home to move into since returning to MI - close to done! I checked the connections in the elevator control system based on your and Van's technical recommendations (thank you) and understand all are in tolerance for slippage - minimal to no slop - about a quarter inch slop at top of stick. I'll monitor the control system over time for wear.

I flew it yesterday for the first time since returning to MI - sure was nice to get back in the air.

Thanks for your help,
Tim
 
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