RickWoodall

RickWoodall

Well Known Member
Anyone know of any issues, accidents caused by trim tab flutter with any rv's? The reason I ask is that my inspector seemed to have an issue with it, and kept bringing up the fact that NO homebuilts should have trim tabs. He made it sound like there have been lots of failures. Never heard of such a thing.

Also..i have manual trim and there is about a 1/4 inch of slop in the cable. Vans say that is normal build on and that with a mechanical cable with ball and socket at each end there is no way to make it 100% tight, all is fine. Again, it seemed a sticking point with the inspector. He passed it, but...just let me know he doesnt like the design, slop or fact there is even a trim tab. This is beyond me, just wondered if those with more experience have any info on issues, failures etc. I have never heard of a single event with rvs in regards to trim issues. SEE ATTACHED VIDEO OF ISSUE.

http://www.youtube.com/watch?v=tCcQAwdmcV4
 
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Yeah, I see RV's crashing all the time because of the trim tab.:rolleyes: Personally I think there would probably be more accidence if they didn't have trim tabs. But then again, I'm no expert.
 
It sounds to me like you got an old fashioned inspector who has a completely closed mind and is unaware that aviation has progressed since the Wright's first beach flyer. We all run in to those types innovation now and again - they can't point you to any data, but sure have lots of opinions!

As long as he signed the plane off, you're done with him. RV's are a well proven design - put your mind at ease.

Paul
 
I had a run-a-way down electric elevator trim last weekend. I can say that if the RV-4 didn't have trim I would never get in it. I think I still have arm pump from holding the stick back. With both hands.
 
Safety Trim

Curious what caused your runaway trim. Is it something internal to the trim motor that causes this.

I have not flown but I have the Safety Trim module, it simplified the wiring (no relays) and it has the added features of the ability to reverse the runaway trim to get it where you want it then cut power to the servo. Also you get slower trim motor at higher speeds. Oh and it has a 3 second cut out feature, it will not let a motor run for more that that time. I think it would be an easy retro fit. Oh I don't work for them just think they make a nice product

Sid Lambert said:
I had a run-a-way down electric elevator trim last weekend. I can say that if the RV-4 didn't have trim I would never get in it. I think I still have arm pump from holding the stick back. With both hands.
Click to expand...
 
The 13 year old, 900 hour Ray Allen switch went bad. I managed to get it back to a basically neutral position before I attempted to land. The new switch from them is deeper but seems to be better built. (I had to disassemble & rewire one for use with flaps)

All that run-a-way trim protection stuff seems cool but I don't think I'll retrofit my -4. I would say that you need to fly the airplane during phase 1 with the trim at the stops for up and down. See if you can maintain alt at around 80 MPH.
 
My plane with electric trim will get readily identifiable (most likely colored), pullable circuit breakers within sight and reach of the pilot.
 
Airframe Buzz

I'll share an experience with my RV-3 that may or may not be related to the trim tab. Cruising in smooth air at 9500ft, WOT turning about 2600rpm I throttled back slightly and pointed the nose down a bit to start a descent for fuel. Shortly afterward I felt a short, distinct, high-frequency ?buzz? through the airframe. Only lasted a second or less, but sure got my attention. Eased the nose up and throttled back, then finished the descent at considerably lower airspeed. On the ground, no obvious signs of damage, so I refueled and finished the trip.

A data dump from the 496 shows a max ground speed of 220mph at the "buzz" point (two consecutive points with a 15-sec sample rate). VNE is 210mph TAS, and I had an estimated tailwind of 20-25mph. Could be that I exceeded the envelope in that 15-sec interval. (Note: the plane was flutter-tested in smooth air at 10,000ft up to 230mph IAS when built back in 1982).

nv5xr8.jpg


I have a retrofit electric elevator trim with the servo mounted on the deck below the vertical stabilizer. While checking the airframe I noticed about 3/32" play in the elevator trim tab, measured at the outboard trailing edge. Also noticed some flexing of the deck that contributed to the play. On prior flights in smooth air I had experienced at random times an uncommanded nose-up bump in trim. Speculating that the flex was contributing to the trim bump, and that the trim tab play may have contributed to the "buzz", I stiffened the servo mount with some angle. Now the tab play is about 1/32".

Was this a trim tab flutter issue? Don't know, and I'm not inclined to go back to the envelope edge to test it. In the succeeding 15hrs of x/c flight in smooth air the "bump" hasn't returned. I don't normally cruise at WOT, but on that day I was trading fuel for time so I could land in the daylight. Be cautious at the upper end of the speed envelope ? these RVs pick up speed quickly when pointed downhill. And my understanding is that flutter is a function of TAS, not IAS.
 
No issue.

To be clear I dont believe there is any issue, just with the inspector bringing it up, made me think a bit and wondered if there is a second chapter to the story I need to know??
I do know a local rv9a that tried to take off one time with trim set at limit and he really had to fight it to get airborn and it was a scare. He could not believe the impact that little panel has. Anyway, the comments about trim on homebuilts was aimed at the weakness of the linkages etc I believe. He commented that if the trim had springs on it, kind of like the manual aileron trim on rv's (springs in both directions) it would be ok, but he wasnt impressed with the engineering as is. Anyway, no issue just figured if there was something to this that I have missed over 4 years of reading the forums daily, I would like to know.
 
jcaplins said:
What makes a homebuilt trim tab so different than a certified trim tab?
Click to expand...
The type certificated aircraft has to be free from flutter following any single failure in the trim tab control system - i.e. if the tab linkage fails so the tab is free floating (see FAR 23.629 f). I doubt many amateur-built aircraft builders do flutter testing with the tab disconnected.
 
RV-3 Trim Tab

With an eyeball guess, I would assume that the RV-3 trim tab would be less prone to flutter than the tab on the RV-4 and later versions, simply because the chord of the -3 tab is significantly shorter, and the span of the tab is also very much shorter, which should result in greater stiffness.

Although I'm not aware of any destructive flutter accidents in the RV-3, I would still be more concerned with the reduction of elevator flutter margins as a result of the -3's lack of mass balancing.
 
trim tab

what would happen if the trim tab became free floating during flight due to broken cable, linkage, ect would the trim tab stay centered with the elevator? could you fly the plane with the stick and power?
 
trim tab failure

I was flying a Beech Baron when the control rod to the elevator trim tab broke. We were just leaving the pattern at about 120 kts. Took two of us to hold the yoke. Looking aft, it looked like the hs tips were flexing up and down about 45 degrees. The whole aircraft was shaking violently.
 
Heart Flutter

To the thread starter, I would listen to the inspector. I had a severe elevator flutter in a homebuilt type similar to an RV6 but not a Vans design. A trim cable sheath had slid just enough to allow a touch of slop in the cable. I started a gentle pull up at about 165 IAS (well below the often seen VNE) and all **** broke loose with a buzz(actually the trim tab) along with a arm wrenching, but lower frequency pitch oscillation of the entire elevator. I pulled power to idle and headed more or less 45 degrees upward to bleed off speed. There was only enough time to think I might not survive this. 2-3 seconds and it stopped and I was about 1000 feet higher. A close inspection on the ground found the problem. Trim tabs, trim cables, end yokes and cotter pins now get my full attention on preflight. I am not an inspector, just a very lucky pilot. A few years later a purchased an F1 Rocket from a builder that was a retired US navy pilot and former navy mechanic. The only trim surface he built into the AC was the elevator. I think VAN has an excellent design, but I have zero desire to test the controllability of this, or any other AC with a free pivoting trim tab.
 
F1R said:
To the thread starter, I would listen to the inspector.

snipped

I think VAN has an excellent design, but I have zero desire to test the controllability of this, or any other AC with a free pivoting trim tab.
Click to expand...

How many of Van's aircraft have been flying for how many years?

Obviously the inspector is not too familiar with the history of Van's designs.

With thousands of Van's designs flying for all of these years..........are we just really a "test" pilot of this design, at this stage of the game?

L.Adamson --- RV6A with elevator & aileron trim tabs. Would like one on the rudder too!
 
I agree on checking the trim tabs for security prior to flight. I am the one who found the busted cable holder for the RV-10 trim cable which led to the service bulletin. I did find it on the preflight. :)
Many years ago (in the 80's to be exact) I had a good friend who died along with another friend in his RV-4. For all practical purposes it looked like the classic stall/spin while turning base to final. Both guys were fairly large, and anyone who has flown the RV-4 with a large person in the back knows how light the pitch feel can get. However, what I noticed in the newspaper picture was that the trim tab was almost 80 degrees down! NO way should it be like that the way the aircraft was loaded. I couldn't wait to go see it in person. I finally did a day later, and sure enough the trim tab was completely disconnected. We will never know whether this was the cause, or was just contributory (most accidents have a chain of events), but it has always bothered me. That's why I religiously check the trim tabs.
No, I don't think it became disconnected as a result of the crash. It was actually assembled wrong. It was a manual trim cable and it was connected to the trim tab via a bolt and a castellated nut, with the cable going through one of the holes in the nut, where you would normally put a cotter key. So, clearly there wasn't the ability to get the cable tight. My friend was an aeronautical engineer, so to this day there is no explanation for this.
Vic
 
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Rick, you mentioned "about a 1/4 inch of slop in the cable". Just curious; is that measured at the cable end or at the trailing edge of the surface?

Either way, linkage slop means the tab is free floating within the limits of the slop. Are you sure this much freeplay is normal when cable trim is installed in an RV9?

Personally I would not accept a 1/4" of freeplay in a trim tab on my new airplane, as freeplay always gets larger with age and wear.

More than one classic homebuilt has been revised because of flutter-related elevator trim tab issues. The Skybolt biplane is a good example. The original had a push-pull cable with a lock button, and like most push-pulls the internal clearance resulted in tab freeplay. The revised design changed both the tab arrangement and the control system (to tensioned cables).
 
slop

With the plane buttoned up for first flight, all linkages inspected and approved...you can take the trailing edge of the trim tab and it has definite slop. I will try and take a video of it as it is a concern.

Here is the exact working from Gus at Vans...when I asked about the slop. This is a direct quote.

"It's normal. You can't get a 180" long cable with no play in it, and the small amount of movement in the cable/horn usually comes out to about 1/4" at the TE of the tab"

It just doesnt seem right to me and my inspector brought it up too. Soooo, not expecting my plane to fall apart but..would like to make this better. Will post a video in the next 24 to show it and see if others have a solution for me. Thanks all.
 
Dont freak out

Gus is exactly right.

I've built two RV's now with manual elevator trims, and looked at lots of others. That's the way the cable assembly comes out. But it doesn't flap around in flight at all. The aerodynamic loading on the tail moves the tab to one side of the deadband or the other and effectively removes the slop. This ends up producing a very precise trim system that is preferred by some of us.

This is one of the niceties of the manual trim. At cruise speeds in an RV, VERY small trim changes are needed. The manual trim can be adjusted easily for this by turning the knob a few degrees. The electric trims just can't compete with this, or a complex system of speed controllers is needed to attempt too.

Then at slow speeds, multiple turns of the trim knob can be made very quickly for large trim changes.
 
trim tabs

Not RV's BUT: I know of three cases where an elevator trim tab disconnect caused problems. First, an early Cessna Conquest was lost due to trim tab actuator disconnect. This resulted in the dual trim tab actuator found on all subsequent Conquests. On a Pitts derived homebuilt(standard Pitts S1 trim) and an EAA Biplane trim tab dicsonnects caused the stick to be yanked out of the pilots hand. I don't care if there are a million RV's flying with no issues, this IS A POTENTIAL PROBLEM. It is a generic problem that can affect any airplane , even the 100 m/h EAA Biplane. The tolerance for trim tab play on some production airplanes is plus or minus 1/16" at the trim trailing edge. On Piper Navahos I have felt a buzz in the yoke at high speeds when the trim actuator wear was at or near limits. I would not personally use a push pull cable for trim actuator.
 
not a push pull problem

Tab disconnect IS bad. But the push pull cable and its deadband isn't the problem.

If you want no deadband, then install the electric trim. It should have NO deadband since the servo is in the elevator and uses a pushrod about 6 inches long, which is okay, but the trim system will not work as well as the manual.

(I fully expect to be flamed here by a large number of people that haven't flown the manual system, or for that matter, the electric, but "know" that its inferior) :D:p

While some airplanes may need the trim tab deadband to be really small, that does not imply that the larger deadband on the RV is inherently bad or a problem.
 
Wow

Interesting thread.
And all this time I've been worried about my nosegear leg :eek:

I knew other airplanes have had issues with trim tabs, but was never worried about mine. Thanks.

Mine is electric and I think it works great. I'll be looking at it closer from now on. Makes me wonder about the plastic parts for sure.

Mark
 
push pull cable and end specs

I also find that one of the few things on my walk-around that nags at me is the trim tab and plastic clevis. I ensure the wire hinge pin is safetied, and when I jiggle the trailing edge, ( less than 1/4") and check that the locknut on the clevis pin is in place, the slop always bothers me.
Then, I think that I should replace the 'model airplane' plastic clevis with an aircraft aluminum one....which I would hope would be less prone to wear, and the increase in slop that would accompany this.
...or does this mean replacing the entire cable?

Due to the airframe having only 130 hours, I always defer to 'the next annual'.

How & when should this be dealt with?
 
flyboy1963 said:
I also find that one of the few things on my walk-around that nags at me is the trim tab and plastic clevis. I ensure the wire hinge pin is safetied, and when I jiggle the trailing edge, ( less than 1/4") and check that the locknut on the clevis pin is in place, the slop always bothers me.
Then, I think that I should replace the 'model airplane' plastic clevis with an aircraft aluminum one....which I would hope would be less prone to wear, and the increase in slop that would accompany this.
...or does this mean replacing the entire cable?

Due to the airframe having only 130 hours, I always defer to 'the next annual'.

How & when should this be dealt with?
Click to expand...
If you have about 1/4" or so on the electric trim, then I would take a closer look at it and possibly see where the movement is coming from. I inspected mine yesterday and the movement is less then 1/16" I would say, I can hardly move it.
 
flyboy1963 said:
I also find that one of the few things on my walk-around that nags at me is the trim tab and plastic clevis. I ensure the wire hinge pin is safetied, and when I jiggle the trailing edge, ( less than 1/4") and check that the locknut on the clevis pin is in place, the slop always bothers me.
Then, I think that I should replace the 'model airplane' plastic clevis with an aircraft aluminum one....which I would hope would be less prone to wear, and the increase in slop that would accompany this.
...or does this mean replacing the entire cable?

Due to the airframe having only 130 hours, I always defer to 'the next annual'.

How & when should this be dealt with?
Click to expand...

I found this on the vans web site it looks to be a Steel Clevis
Part Number = F-453A
 
Video

I have received a lot of feedback on this so here is a video showing the issue.

http://www.youtube.com/watch?v=tCcQAwdmcV4


Vans says its ok, inspector wasnt happy, certified aircraft mechanic wasnt happy and both indicated it is safe, but...should be better. Open to ideas. I certainly do not expect the tail to fall off, dont get me wrong. BUT, this just nags at me. Comments welcome.
 
Checked my electric trim today, and it's about 1/16" on the trailing edge of the tab. It's all in the clevis & pin, with no slop from the servo.

L.Adamson --- RV6A
 
From a guy who has experienced, and lived through in-flight wing flutter, I'm very comfortable with my 18 year old RV manual trim.
 
Frightening Trim Flutter Test

I have watched this thread with great interest and can't stand it anymore. I have to tell my story. The FAA Inspector that signed off my RV-4 in 1991 was concerned ablout the amount of play in the elevator trim tab. He concluded that there was nothing I could do to tighten it up, so he signed it off, but asked me to test it for flutter when I get comfortable with the plane. He said to take it up and dive it to 10% above the red line in 5 mph incerments. About 10 hours into the test flight period, I decided it was time. I took it up to 8,500 ft and pushed over into a dive, throttling back just enough to keep the RPM under 2,700. I pushed it over to 205, then 210, and 215 indicated. I wanted to dive it to 225, but as I pushed over some more it wouldn't go past 215. I pushed harder and got very steep with a lot of wind noise, but I couldn't get more than 215. Then all of a sudden the needle seemed to come unstuck and jumped somewhere over 250. The heart rate went off the scale at this point. I closed the throttle and released the forward pressure instantly and held my breath. The nose came up pretty quick and the RV slowed down without any problem. I have no idea what my true airspeed was, but I feel very sure you guys don't have to worry about trim tab flutter. Thinking back, I believe the inspector should have realized that there were a lot of RVs flying around with the same trim system with no problems and he shouldn't have asked me to test it for flutter.
 
A year ago I was instructing in a composite LSA when the trim tab linkage broke. The trim tab flopped from stop to stop, even when I slowed to 40 kts. Was able to get it on the ground before the elevator separated completely (it was hanging on by one attach point).

Way different plane than my RV, but the trim tab looks exactly the same. Every time I preflight the RV I look at the tab and wish is was not installed. In that sense I agree with the inspector.
 
Testing for flutter is up to the individual.
Having experienced flutter in my Moni Motorglider that partially "un-skinned" the right wing and tore ribs loose from the rear spar, I did test my -6 up to 226 mph IAS.
I found absolutely no indication of flutter.
 
All the Cessna singles that I used to instruct in had a small amount of play in the trim tabs as I recall. Never had a problem with flutter even in the 150 aerobat in diving maneuvers at high airspeeds.
 
Just a bit of data here, draw your own conclusions: there are a large number (hundreds) of Rockets flying with RV tails on them. Many have modified trim tabs on them, some considerably larger than stock tabs.

It's safe to say that virtually all of the Rockets are flown out to speeds that few RVs can reach.

There may be Rockets with RV tails out there that have fluttered. I've never heard of one.

My Rocket has a mostly stock RV-4 tail and it's been out to 250+ many times and past redline (275mph) more then once or twice.

Does this prove anything? No, but it does make me feel pretty good that the system works well as long as nothing breaks.

YMMV
 
elevator trim wiggle

I've read every elevator 'trim tab' wiggle thread in the search section. Guys, my FSDO inspector is adament that the 1/4" of wiggle is unacceptable. I placed a small rubber washer on the nipple that drops into the recess (at the control knob), hoping that it may take up some slack. This had no material impact on the wiggle. I have the cable attached to an adel clamp on the flat tail panel (where the cable exits the aft fuselage and goes into the horiz stab). I was thinking tht I could severely tighten this adel clamp and put some pressure on the cable, thus placing some friction on the inside push-pull cable. At this point, I'm not looking to bash the inspector, but rather find a solution to minimize the wiggle. Somewhere in the past, Smokey posted a thread stating that he set some adel clamps, etc., and ended up with nearly no wiggle. That's what I'm looking for.

Desperate Jim
RV-7A
Piper Memorial Airport, Pa
 
I tried Smokey's method, Jim, but no dice. Mattered not a bit. I have an email from Van's saying it is normal, impossible to get out, and a non-issue. You might try getting the same from Van's and give a copy to your inspector. Good luck.
 
Jim, the majority of the play in the trim tab is the result of clearance between the cable and the cable housing.
If you stretched out the control cable in a straight line with no bends or curves, there would be just about zero play.
As installed in side by side RV's, the cable makes about a 150 degree reversal in direction at the knob end. This causes the clearance between the cable and the housing to become a longitudinal play in the cable that can bee seen at the trim tab. Play at the trim tab was not nearly as evident in the original RV-3 and 4 installations because the cable was installed in a straight line (no curved section for the cable to move around in).

It may look bad to someone who is unfamiliar, but in thousands of flying RV's it has proven to be trouble free. Years ago, when a GVT analysis was completed on the original RV-8A prototype (manual trim with a reversal in the direction of the cable), the test technicians had some seriously raised eyebrows during their initial inspection of the airplane when they saw the amount of play in the elevator trim tab. At the completion of the testing they were surprised that the test data showed that the airplane was more than satisfactory for the design VNE.

Unfortunately you are stuck satisfying your inspector at this point (unless you want to jump through the hoops of having a denial and then reapplying with someone else).

One thing a few builders have done (It is not necessary but it makes some people <inspectors included> feel better), is to install a biasing spring between the trim tab and the elevator. The spring will keep the tab always pulled to one side of the play range. It is important to use a spring strong enough that air loads will not be likely to ever move it against the spring pressure or you could actually be inducing a flutter potential that wasn't there to start with. I have seen springs attached directly to the elevator and trim tab, and I have seen springs installed over the push/pull rod of the control cable so that the compression of the spring was acting between the horn on the trim tab and the anchor point of the end of the cable.

Hopefully this might be of some help, but as I already mentioned, use caution caution in choosing a spring if you go this route. Make the force too light and you could induce a problem, make it too heavy and over time it could cause damage to the trim tab.
 
Using FAA AC 43.13 for limits:

"If the tab span does not exceed 35 percent of the span of the supporting control surface, the total free play at the tab trailing edge should not exceed 2 percent of the tab chord."

For an RV with approximately (from memory) a 5" tab, that would give you 0.100" free play. An 1/8 is .125"
 
Walt said:
Using FAA AC 43.13 for limits:

"If the tab span does not exceed 35 percent of the span of the supporting control surface, the total free play at the tab trailing edge should not exceed 2 percent of the tab chord."

For an RV with approximately (from memory) a 5" tab, that would give you 0.100" free play. An 1/8 is .125"
Click to expand...

I am not sure what the relevance of this is here...
43.13 is a guidance to mechanics for maint. and repairs.
True, it is also good reference regarding standard practices, but there is also many allowances for deviation. Example... The standard down, aft out orientation direction for installation of fasteners, "Unless specified otherwise by the aircraft manufacturer"

As already mentioned, the manual trim system on RV's has been substantially proven by GVT (ground vibration testing) and flight testing within a rather large fleet of flying RV's. It has well proven it self to operate without problems if installed as currently designed. If you (or someone that can require you too) decides you don't like it the way it is, you are of course free to change it (after all, RV's are experimental aircraft). But as already mentioned, I suggest you use caution in doing so. Adding a spring or anything else to the system will change its natural resonant frequency. You could actually induce a problem by modifying the current design.
 
trim tab flutter

Well my be I am just dumb, but I do not see how the trim tab free play will have an affect on flutter. In flight, the trim tab free play is taken up by the loading. Unless the elevator is in trail and the trim tab is in trail, I do not see a method for flutter to start. Now if the trim tab linkage is weak or not rigid, and a small force change will affect the position, then even loaded I could see trim tab flutter creeping in. But nobody has talked about how rigid or sloppy it is, so I suspect the trim tab system is quite rigid when loaded. JMHO. Your mileage my vary.
 
Experience from my A&P IA days.

jdiehl said:
I've read every elevator 'trim tab' wiggle thread in the search section. Guys, my FSDO inspector is adament that the 1/4" of wiggle is unacceptable. I placed a small rubber washer on the nipple that drops into the recess (at the control knob), hoping that it may take up some slack. This had no material impact on the wiggle. I have the cable attached to an adel clamp on the flat tail panel (where the cable exits the aft fuselage and goes into the horiz stab). I was thinking tht I could severely tighten this adel clamp and put some pressure on the cable, thus placing some friction on the inside push-pull cable. At this point, I'm not looking to bash the inspector, but rather find a solution to minimize the wiggle. Somewhere in the past, Smokey posted a thread stating that he set some adel clamps, etc., and ended up with nearly no wiggle. That's what I'm looking for.

Desperate Jim
RV-7A
Piper Memorial Airport, Pa
Click to expand...

The Extruded hinges have less play than the rolled hinges. Additional note, the material of rolled aluminum hinges are also not as strong. Stainless rolled hinges are much stronger than the rolled hinges but I do not know how much. Be careful putting stainless directly on aluminum due to the potential of dis-similar metal corrosion, the aluminum will suffer.
 
rvbuilder2002 said:
I am not sure what the relevance of this is here...
43.13 is a guidance to mechanics for maint. and repairs.
True, it is also good reference regarding standard practices, but there is also many allowances for deviation. Example... The standard down, aft out orientation direction for installation of fasteners, "Unless specified otherwise by the aircraft manufacturer"
Click to expand...

My point was that this is likely what the FAA inspector is using as his guide, if you can't show that the Van's Design has some other limit then you may end up butting heads with him. Perhaps Van's would be willing to provide some spec so you could satisfy him.

AC 43-13 is the "FAA accepted" standard when no other specification is provided.
 
Another personal experience supporting the design

When I built our RV-6A and I completed the manual pitch trim installation I observed the play in the system and I called the company. I was told that is normal and it is not a flutter problem so I proceeded to completion and flight with this reservation in the back of my mind. When I flew it, all of that reservation went away. The trim is so smooth and effective it feels like an extension of my finger tips. I race the plane at low and sometimes up to the no supplemental oxygen required limit altitudes (in the east bound AirVenture Cup race) as fast as the airplane will go with occasional turbulence and there has been no hint of a problem of any kind. I have been flying the plane for 8 years.

Bob Axsom
 
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This might have already been covered but my opinion is

The free play results from the cable slack in the 180 degree bend near the vernier knob end. Lay the trim cable straight - no free play.

If the trim tab is to flutter it has to move about 80% of the trim cable core as well. I think this provides all the damping required to prevent any flutter, further the force coming from the tab is pretty light.

It is difficult to say if the aerodynamic pressure biases the slack, I have never felt any abrupt change in trim that would be expected if you adjust through this slack point.

Not changing my manual trim.... it just works!
 
MAnual trim cable in my RV9

I also notice some extra movement in my manual trim cable at the trim tab. Investigating , I found that it was inherent with the vernier cable and found nothing loose at either end. I did install a compression spring on the cable at the tab and found that eliminated some of the motion. Just keeps the slack pushed to the extend direction. Anyone else noticed excess movement in the vernier cable trim?
 
I had a "pilot" passenger pull me aside yesterday on a flight on my day job telling me that our "aileron was fluttering in flight". I took a look at it and sure enough both ailerons had about 1/4-1/2" of movement at the trailing edge. This airplane is quite a bit faster than an RV. I checked several other planes of the same make and model and they all had the same travel. I am no engineer but for the life of me can not imagine how a properly rigged control surface, with a bit of slack in the system could ever create flutter. Seems to me that you would need to have opposing forces to make it flutter. Such as a dual trim tab out of rig. One rigged up and the other down.
 
Manual Elevator Trim Tab

On my last thread (#38) I was wrestling with how to satisfy the FAA Inspector that didn't like the 1/4" of wiggle in the elevator trim tab. Well, yesterday, he returned and I got the pink slip!
I used the advice of many from this forum along with some of my own ideas and did the following:
- Removed the cable at the cockpit trim knob, set the nipple of a grease gun at the point where the inner cable exits the trim cable, wrapped it all in gorilla tape and proceeded to pump viscous bearing grease into the annular space around the inner cable. I pumped 'till the grease started to slip out around the tape. I'm rather certain that I was able to squeeze the grease well into the cable.
- Reinstall cable to control knob fitting
-Installed an Adel Clamp around the cable immediately before it enters the horiz stab.

Result: Less than 1/8" of maximum wiggle--- and the wiggle does not feel loose. I'm happy as is the FAA.

J. Diehl
RV-7A
 
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