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06-09-2010, 09:22 PM
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Join Date: Mar 2010
Location: Springhill, LA (KSPH)
Posts: 81
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trim/autopilot failures
What are some scenarios that could take place causing the trim and/or autopilot to fail or go haywire? Also, what backups could be put in place to counteract the failures? I had an airline pilot friend look at my kit tonight and he suggested getting manual trim.
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Cessna 150/150
N22190
(KSPH) Springhill, LA
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06-09-2010, 11:30 PM
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Join Date: May 2008
Location: Brisbane Qld. Aust.
Posts: 2,271
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Any decent autopilot will have a reliable disconnect.
As for trim, run away trim has been a big killer....well it has killed a few times..you get what I mean.
If you have an RV10 the elevator forces are huge if out of trim. Imagine if the little buttons on your trim failed closed
You can get a device called Safety-Trim....and in my opinion it is a MANDATORY Install.
http://www.tcwtech.com/Safety-Trim-Page.htm
Cheap insurance for you, your family and your plane.
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06-10-2010, 06:33 AM
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Join Date: Jan 2009
Location: Salt Lake City, Utah
Posts: 554
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Some jet aircraft have pulling the trim CB on the emer checklist as a memory item. It is good to know right where it is.
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A&P RV-10 Flying 1000+ hours
SuperSTOL Flying 170 hours
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06-10-2010, 11:40 AM
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Join Date: Feb 2007
Location: Mpumalanga, South Africa
Posts: 1,065
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AP disconnect on the stick top and both AP and trim power on switch-breakers accessible from both seats.
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Paul
Mercy Air, White River FAWV
RV-10 ZU-IIZ - "Zeus"
Building Bearhawk Bravo - RV-18 not available
2019 Donation Made
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06-10-2010, 11:43 AM
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Join Date: Mar 2007
Location: Woodinville, WA
Posts: 533
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Quote:
Originally Posted by RV10inOz
Any decent autopilot will have a reliable disconnect.
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In my opinion, the only sufficiently reliable disconnect is a switch that disconnects power to the servos. I'm using a pullable breaker for this purpose.
Also, another vote for the safety trim system, though that should also have a power disconnect.
-Rob
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Rob Kochman
RV-10, Flying as of March 2011 ( blog)
Paine Field (KPAE)
EAA Chapter 1440
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06-10-2010, 12:03 PM
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Super Moderator
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Join Date: May 2005
Location: Locust Grove, GA
Posts: 2,626
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I don't know if I totally agree with the safety trim being a MANDATORY install, as it, too, is an electronic device that can fail. I do believe in a pitch trim power disconnect switch either right in front of the pilot, or in a clearly marked place in the cockpit that can be easily reached IMMEDIATELY in the case of a trim run away.
And, as mentioned, trim runaway checklists are a mandatory memorization item on some airliners, such as the Bombardier 600's.
Vic
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 Vic Syracuse
Built RV-4, RV-6, 2-RV-10's, RV-7A, RV-8, Prescott Pusher, Kitfox Model II, Kitfox Speedster, Kitfox 7 Super Sport, Just Superstol, DAR, A&P/IA, EAA Tech Counselor/Flight Advisor, CFII-ASMEL/ASES
Kitplanes "Unairworthy" monthly feature
EAA Sport Aviation "Checkpoints" column
EAA Homebuilt Council Chair/member EAA BOD
Author "Pre-Buy Guide for Amateur-Built Aircraft"
www.Baselegaviation.com
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06-10-2010, 01:33 PM
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Join Date: Feb 2005
Location: Minneapolis
Posts: 2,473
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Also keep in mine that with all A/P servos that I'm aware of (TruTrak, Dynon, Trio, etc..), they can all be overpowered by the pilot, even at full torque. I'd be much more nervous about trim than I'd be with the autopilot. Since our experimental autopilots are driving the flight controls themselves (not servo or anti-servo tabs) at relatively low power/torque setting, it's very easy to usually just overpower them. Remember, don't make things any more complicated than necessary to make them safe. Sometimes the belt+suspenders+another belt+more suspenders can make things actually less reliable.
Cheers,
Stein
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06-10-2010, 02:48 PM
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Join Date: Feb 2008
Location: Largo, FL
Posts: 1,029
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My big concern
is that a runaway trim condition cannot be "reset". You can pull the breaker to ensure the runaway does not go any further, but in the -10, I am not sure you could fly the plane to a safe landing. Would be nice to have both manual and electric trim, like most certificated light aircraft.
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06-10-2010, 03:32 PM
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Join Date: Oct 2008
Location: Pleasant Prairie,Wisconsin
Posts: 67
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runaway trim
That's part of the design of the safety trim system, you can stop the trim and reverse the polarity of the motor to reverse it to achieve a neutral or at least controllable trim setting. I have it on my RV-10 and love it. one more feature is the dual trim speeds: slow trim speed when you are fast and fast trim speed when you are slow. This also works on the aileron trim as well. If you have concerns regarding runaway trim I would seriously look at this system.
Don Orrick
N410JA
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06-10-2010, 04:52 PM
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Join Date: Dec 2008
Location: Big Sandy, WY
Posts: 2,567
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Okay guys with 10's. I'll be done soon, but still have time to pick a trim option (barely). Question: How big is the stick force for an out of trim 10 really? WIll it bend the sticks or fail something? Or just really annoying. Can anyone compare it to a spam can model (207 or something)?
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