Trim and A/P problems related?

[Robert C.]

Hi Gang,

Am puzzling something through and hope you might have some ideas.

Last year i had a few flights where the trim was sticky. Quick tug on the trim wheel would loosen it and after that the electric trim would handle i againt. Had my AP look at it during the annual but he didn't see anything wrong and couldn't replicate it on the ground.

On subsequent flights I had a few more incidents like that.

Then while shooting approaches with my CFI in December I had what felt like a "runaway trim" event.  I did some test flying afterwards and concluded that the Alt Capture mode and the Vertical Speed mode on the STEC are no longer working as advertised. I go through the altitude....the trim starts working to get the nose down/up....and works till full trim deflection without STEC then capturing the correct vs or alt hold.

I'm wondering if the sticky trim has burned out the autopilot servos or something like that.

So I'm dropping off my Ovation at an avionics shop (VIP Avionics at KHFD) on Tuesday to have them take a look at it and see what they can find. Am also thinking of calling my AP and asking him what else he can do (relubing the jackscrew?). The 100hr/annual list specifies inspection of the empennage trim system but doesn't say anything about opening it up and looking for hardened grease so that may not have been done at the annual.

Any thoughts on what questions to ask the avionics shop and my AP?

Thanks in advance.

Robert 

 

[Piloto]

On my my 1982 M20J the tail jackscrew cover still looks good but I cannot remove it for lubrication without tearing it apart. I poke a 1/8" hole on it to allow the WD-40 straw through it for lubrication. It work out pretty good. I do not want to remove the cover because it prevent dirt from getting into the jackscrew that could cause it to jam. I had a similar A/P problem as yours and found out that the yoke shaft on occasions bind to the panel guide. I lubricated the shaft with WD-40 and problem solved. 

José

Edited April 3, 2016 by Piloto

[N201MKTurbo]

If you trim it full up, the little aluminum block on the indicator screw will jam against the supporting frame. You some times need to give it a little push to get it loose. I think I saw a service bulletin about this.

[Marauder]

What is the VS indicator light doing on the STEC when this is happening? If the VS light is blinking, it may mean there is something wrong with the pitch control (VS doesn't match the required or set rate of descent or climb).

Also are you using autotrim?

Sent from my iPad using Tapatalk

[Robert C.]

Hi Marauder,

 

As I recall the vs light is steady. Yes, autotrim is installed and has worked fine (until recently at any rate).

Thanks everyone for your thoughts. I'll share all tehse with my mechanic and the avionics shop.

Robert

[Robert C.]

Update: VIP Avionics determined that the brushes in the pitch servo had worn and that the dust from the wear was causing it to glitch and the alt hold and vs to be inop. They see no relationship to the sticky trim so that is a separate issue. Am glad to hear the trim isn't causing the A/P problem

Robert

[Danb]

Robert that makes sense mine did the same thing at about 200 hours, we have the same setup, in the next yr I started having more problems with the trim and pitch, I went through 2-3 circuit boards and had all the servos replaced before 400!hours, in the past 3 years the stec system has been flawless. An engineer at Beechcraft avionics seems to think there was a batch of bad servos around the time my plane came from kerrville, who knows, he stated there were quite a few failures similar to mine , maybe yours to ?

[Robert C.]

Dan,

Thanks for sharing that experience and glad to hear that you had a trouble free 3 years. I have been very pleased with the 55X and I look forward to having it fully working again.

Robert

[Danb]

Robert I agree I think there awesome autopilots, now if we can somehow get affordable WAAS, just dreaming. STEC pretty much screwed me on the whole deal, the last two boards didn't need replacing and they would not repair the last board unless I replaced the servos, they had me in a bind but in the end it all worked out. I went through hell for about a year I was scared to fly hard Ifr due to the problems that occurred.

[Marauder]

Robert I agree I think there awesome autopilots, now if we can somehow get affordable WAAS, just dreaming. STEC pretty much screwed me on the whole deal, the last two boards didn't need replacing and they would not repair the last board unless I replaced the servos, they had me in a bind but in the end it all worked out. I went through hell for about a year I was scared to fly hard Ifr due to the problems that occurred.

I guess you better not watch my YouTube videos of my lowly F model flying WAAS enabled LPV approaches.

[Danb]

i wish my lowly bravo could

[Steve Dietrich]

On 4/3/2016 at 3:32 PM, N201MKTurbo said:

If you trim it full up, the little aluminum block on the indicator screw will jam against the supporting frame. You some times need to give it a little push to get it loose. I think I saw a service bulletin about this.

ERASED MY REPLY AS I MISREAD AS TRIM JAMMED  RATHER THAN INDICATOR

Edited April 20, 2016 by Steve Dietrich
CORRECTION

[Robert C.]

Steve, thanks for the tip. I'll start looking for that. This aircraft seems to have been well maintained and neither the pre-buy and the 2 annuals since then turned up any ADs that weren't complied with but you never know.

[jlunseth]

Sometimes its simple.  In my aircraft the carpet is cut out under the trim wheel, making a little well.  There is very little clearance between the bottom of the trim wheel and the hard floor.  It does not take much in that well to get under the trim wheel and jam it or bog it down.  Any piece of FOD will do, or food chunks.  I periodically check to make sure that area is clean.

[Steve Dietrich]

On 4/15/2016 at 7:23 AM, Robert C. said:

Steve, thanks for the tip. I'll start looking for that. This aircraft seems to have been well maintained and neither the pre-buy and the 2 annuals since then turned up any ADs that weren't complied with but you never know.

 

Edited April 20, 2016 by Steve Dietrich

[StevenL757]

On 4/13/2016 at 9:00 AM, Danb said:

i wish my lowly bravo could

That's roughly equal to "my lowly Acclaim".

Oxymoron of the century.  :-)

[Txbyker]

This morning I was climbing out with my G-1000/STEC pressed the HDG button like I always do when ATC tells me to fly a certain direction and the nose pitched up to 1600 fpm and was trying to go higher.  I was doing nothing with the ALT or VS.  I flipped off the Trim and Autopilot and the trim was keeping the plane hanging on the prop.  I forced the trim wheel down manually until the plane stopped trying to climb like a rocket.

After this the yoke trim no longer works.  With autopilot engaged in HDG or GPS, the ALT would hold and every time the plane tried to correct to hold ALT I would get the four loud beeps like when you disengage the autopilot with the red button on the yoke.  Landing the long body with the trim wheel is pretty tricky but I got it down.  Luckily I was taking it in to the shop for some other work so now add this to the punch list.

Any ideas why the trim would run away like that and why the yoke trim wouldn't work now?  

Russ

 

[Cruiser]

check the autopilot computer is firmly seated in the tray. Known problem with S-tec 55x

[Robert C.]

Russ,

in my case it turned out that the brushes in the pitch servo were pretty worn and dust from the wear was causing the the pitch related modes (VS and Alt Capture/Hold) to fail.

don't recall the repair cost as it was taken care off at the same time as the IFR cert.

I' certainly ask your avionics shop to take a look at that.

Robert

[jetdriven]

On April 3, 2016 at 6:00 PM, Piloto said:

On my my 1982 M20J the tail jackscrew cover still looks good but I cannot remove it for lubrication without tearing it apart. I poke a 1/8" hole on it to allow the WD-40 straw through it for lubrication. It work out pretty good. I do not want to remove the cover because it prevent dirt from getting into the jackscrew that could cause it to jam. I had a similar A/P problem as yours and found out that the yoke shaft on occasions bind to the panel guide. I lubricated the shaft with WD-40 and problem solved. 

José

I just want point out that this is horrible advice, and before Jose gets someone killed, remind everyone that only aeroshell 7 or 5 grease, it its equivalent is allowed on the stabilizer jack screw.  The reasons for this are because that grease prevents galling and prevents freezing in cold temperatures and it doesn't dry out and limit trim travel as it gets older. WD-40 is nowhere listed in the service manual FOR ANYHING ON THE AIRCRAFT, nor is is suitable of a lubricant to protect expensive aircraft parts from damage.  Certainly for a flight control such as a jack screw.  If you want to know what happens when you use the wrong lubricant, and the bereaved family members from the Alaaka crash a few years ago. Changed lubricants.  Galling. Eventually stripped the jack nut out. Follow the service manual here. 

Keep in mind this is the same person who recommends a relief tube on the belly, and claims it and salt water cannot corrode aluminum. 

keep in mind this is the same person who advocates tying a pencil to a string and hanging it from the sun visor clip to use in case of an attitude indicator failure.  If you don't have string, set a bottle of water on the glare shield and keep the water " exactly level" . Great advice, maybe he will save a life.....

You can unscrew the jack screw cover from the tail and push it forward, then lubricate the screw with the PROPER lubricant. Seeing as how the screw and nut cost over 1200$, and seizure or stripping the jack screw unit out can KILL you, I think it's good advice.  

[Piloto]

1 hour ago, jetdriven said:

I just want point out that this is horrible advice, and before Jose gets someone killed, remind everyone that only aeroshell 7 or 5 grease, it its equivalent is allowed on the stabilizer jack screw.  The reasons for this are because that grease prevents galling and prevents freezing in cold temperatures and it doesn't dry out and limit trim travel as it gets older. WD-40 is nowhere listed in the service manual FOR ANYHING ON THE AIRCRAFT, nor is is suitable of a lubricant to protect expensive aircraft parts from damage.  Certainly for a flight control such as a jack screw.  If you want to know what happens when you use the wrong lubricant, and the bereaved family members from the Alaaka crash a few years ago. Changed lubricants.  Galling. Eventually stripped the jack nut out. Follow the service manual here. 

Keep in mind this is the same person who recommends a relief tube on the belly, and claims it and salt water cannot corrode aluminum. 

keep in mind this is the same person who advocates tying a pencil to a string and hanging it from the sun visor clip to use in case of an attitude indicator failure.  If you don't have string, set a bottle of water on the glare shield and keep the water " exactly level" . Great advice, maybe he will save a life.....

You can unscrew the jack screw cover from the tail and push it forward, then lubricate the screw with the PROPER lubricant. Seeing as how the screw and nut cost over 1200$, and seizure or stripping the jack screw unit out can KILL you, I think it's good advice.  

Byron I think you misunderstood my statement, it is not an advice but my own experiences with my plane. You are free to use whatever lubricant pleases you. When you mature you will find that not everything has to be by the book, there are other options.

José

[jetdriven]

Sorry, Jose.  I know that you do to have to adhere to the book exactly, but you had better have a compelling reason why, if you choose not to. I'm not sure "sprays easily" qualifies. 

I would like to know how many Jackscrews you have taken apart, reassembled and regreased. Lets start from there.

wd40 is NOT a lubricant. Especially not a high pressure lubricant.  I can't believe I have to say this. It does not belong on an aircraft. If you choose to maintain your aircraft like a lawn mower then at least list the tail number so nobody makes the mistake of buying it. 

Edited August 6, 2016 by jetdriven

[Piloto]

1 hour ago, jetdriven said:

Sorry, Jose.  I know that you do to have to adhere to the book exactly, but you had better have a compelling reason why, if you choose not to. I'm not sure "sprays easily" qualifies. 

I would like to know how many Jackscrews you have taken apart, reassembled and regreased. Lets start from there.

wd40 is NOT a lubricant. Especially not a high pressure lubricant.  I can't believe I have to say this. It does not belong on an aircraft. If you choose to maintain your aircraft like a lawn mower then at least list the tail number so nobody makes the mistake of buying it. 

My early experience (40+ years ago) with WD-40 was trying to remove rusty bolts on Caterpillar engines onboard cargo ships. Spray WD-40 and the bolt (screw) comes out smoothly. Not a secret, is well know in the marine industry. Since a jackscrew is a form of screw or bolt I would assume it works in the same way in my plane. So far it has worked very well. Boat owners buy WD-40 by the case. It is a low cost no mess rust inhibitor lubricant that works pretty well. Try it.

José

[Txbyker]

Does anyone know why there is no circuit breaker on the panel of G-1000 aircraft for the autopilot and elevator trim?  You have a rocker switch for the A/P and trim but no circuit breaker.  Are the rocker switches really the breakers and they are put there to make them obvious?  My plane is still in the shop and the servo is on the way to overhaul.  My trim runs away and this last time with the switches off and the trim still pitching straight up and me hanging on the prop I had to crank hard on the trim wheel and am sure I probably broke something in doing so.

Russ

[Robert C.]

I wondered the same thing after that happened to me last year; unfortunately I never found an answer. I can only speculate that with the trim on/off switch they decided a CB wasn't necessary.

Robert