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  #1  
Old 05-07-2014, 09:14 AM
N208ET N208ET is offline
 
Join Date: May 2007
Location: St. Helens OR
Posts: 433
Default Takeoff Roll Got My Attention

I had a, hummm, interesting situation yesterday. I flew to a local airport, landed, was out of the plane for about 15 minutes doing my thing. I get back in and fire up, taxi out to the runway, all is good. Do a quick runup, roll out on the runway and start the takeoff roll. My plane has always wanted to roll left when I put in full power on the takeoff roll, so I have gotten into the habit of compensating with right aileron, a lot at first and slowly decreasing defection as speed builds up. This is where things get a little hairy. I go to put in right aileron, and the stick won't move. Mind you the power is still in and I'm in the early stages of the takeoff roll. I pull the power out and as I roll down the runway start playing with the stick, elevator travel is fine, it just won't move left or right. I taxi off the runway and keep playing with it the entire way. The stick will move about 1/2 to 1 inch left and right, that's it. I shut down the plane and the problem immediately goes away, the stick moves freely. I have a dual axis dynon autopilot with the servo out in the wing. I have checked the entire control system and I can't see anything that would have caused this situation. When I engage the autopilot test function on the ground, the stick is still able to move 1/2 to 1 inch. Is it possible that the servo caused this? I have had to replace a shear screw on this servo in the past and had no idea that it had sheared until I went to use it one day. I don't think this has anything to do with the situation at hand, but ya never know.

One things for sure, this will freak ya out!

Randy
8A
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  #2  
Old 05-07-2014, 09:27 AM
flightlogic's Avatar
flightlogic flightlogic is offline
 
Join Date: Nov 2013
Location: Prescott, AZ
Posts: 1,674
Default

Before the takeoff, were the controls clear? It sounds like the servo might be involved... but?
Foreign object tossed up into an aileron from the ground? Just wondering.
Good thing you shut it down right away. Surprises like that can spike the heart rate for sure.
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  #3  
Old 05-07-2014, 09:29 AM
krw5927 krw5927 is offline
 
Join Date: Aug 2010
Location: Wichita, KS
Posts: 1,987
Default

Definitely something you need to fully investigate before further flight. Are any bellcranks able to go over-center or anywhere close to over-center?

My first thought was maybe the roll servo was engaged and you had to overcome its force causing it to slip before it would move. On a recent flight I had the AP engaged and, not realizing that I had it engaged, I tried moving the stick. It sure gets your attention when something resists your control inputs!

Good luck with your inspections and please let us know what you find.
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Last edited by krw5927 : 05-07-2014 at 09:34 AM.
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  #4  
Old 05-07-2014, 09:30 AM
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pierre smith pierre smith is offline
 
Join Date: Jan 2005
Location: Louisville, Ga
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Default

Randy, it sounds to me like the autopilot was engaged on the ground, before your takeoff roll. Once you shut everything off, the autopilot had no power, so the stick was free to move.

Just another pre-take off item to check.

Best,
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  #5  
Old 05-07-2014, 09:49 AM
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BCP Boys BCP Boys is offline
 
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Location: Kennesaw, Ga
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Default

Definitely sounds like the autopilot is engaging some how. Do you have a separate fuse for your autopilot? If so, pull it and re-test. I bet the problem goes away.
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  #6  
Old 05-07-2014, 10:00 AM
ao.frog ao.frog is offline
 
Join Date: Sep 2006
Location: Manstad, Norway
Posts: 866
Default Before t/o?

As mentioned above: it would be really interesting to hear how the controls where during the "before takeoff check"?

For example: did they feel normal or binding during the check?
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  #7  
Old 05-07-2014, 10:07 AM
Mike S's Avatar
Mike S Mike S is offline
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Location: Dayton Airpark, NV A34
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Default

Quote:
Originally Posted by N208ET View Post
I get back in and fire up, taxi out to the runway, all is good.
Did you notice if the stick was free during taxi???

Quote:
Originally Posted by N208ET View Post
I go to put in right aileron, and the stick won't move. Mind you the power is still in and I'm in the early stages of the takeoff roll.
Quote:
Originally Posted by N208ET View Post
I shut down the plane and the problem immediately goes away, the stick moves freely.
Did the problem go away after shutting down the engine, or engine and electrical system??
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VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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  #8  
Old 05-07-2014, 10:09 AM
sailvi767 sailvi767 is offline
 
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Location: Charlotte NC
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I agree with the above. How were the controls on the pre takeoff check. I think the control check before takeoff is the most critical check we can do.

George
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  #9  
Old 05-07-2014, 10:34 AM
N208ET N208ET is offline
 
Join Date: May 2007
Location: St. Helens OR
Posts: 433
Default Good question

And I tried to remember that myself. I am in the habit of rolling the stick around before takeoff but to be honost, I'm not sure that I did that. My preflight was a little less than ideal since it was the second flight of the day, and I had only been on the ground 15 minutes. No excuse I know, but a fact none the less.

When I shut the engine down, I shut everything off. I wish I would have turned off my servo power switch, that would have gave me an immediate answer. But before I did shut down, the stick wouldn't move but that little bit right and left. After shutdown, free motion. I checked and double checked the entire control system, looked closely at the ailerons for any sign that something got lodged and came up with nothing, everything looks good. So I went out and ran up with the servo power off, everythings perfect. The plane has over 400 hrs on it, the servo system around 100. I am going back out today for another inspection and play with the servo some more. Testing the servo on the ground produced normal results. But I keep asking myself, I definitely didn't engage the servo, and the autopilot isn't suppose to function below a certain airspeed, 100 mph is what I have the lower limit set at. Is it possible for the servo to even do this? I'm heading to the airport now and will report back any findings.

Randy
8A
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  #10  
Old 05-07-2014, 11:07 AM
Mike S's Avatar
Mike S Mike S is offline
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Default

Quote:
Originally Posted by N208ET View Post
I am in the habit of rolling the stick around before takeoff but to be honost, I'm not sure that I did that.

So I went out and ran up with the servo power off, everythings perfect.---------- Testing the servo on the ground produced normal results.

Is it possible for the servo to even do this?
I suspect the AP is going to end up being the culprit here, but the real questions are going to be why and how did it happen.

If you did in fact check control freedom prior to your application of take off power, as per your stated norm, then it would appear that the high power application is what caused the AP to engage.

High power equals high vibration levels.

I would then suspect a wiring issue-------bad switch, loose connection, chaffing wire etc.

This is a pretty loose logic chain, but it is in line with what you have mentioned so far.

Good luck with your investigations today.
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VAF 909

Rv-10, N210LM.

Flying as of 12/4/2010

Phase 1 done, 2/4/2011

Sold after 240+ wonderful hours of flight.

"Flying the airplane is more important than radioing your plight to a person on the ground incapable of understanding or doing anything about it."
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