What's new
Van's Air Force

Don't miss anything! Register now for full access to the definitive RV support community.

trim/autopilot failures

jhearnsberger

jhearnsberger

Active Member
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.
 
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 :eek:

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.
 
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.
 
AP disconnect on the stick top and both AP and trim power on switch-breakers accessible from both seats.
 
RV10inOz said:
Any decent autopilot will have a reliable disconnect.
Click to expand...

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
 
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
 
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
 
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.
 
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
 
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)?
 
RV-10 trim forces

The trim forces are significant and increase with speed. Go to my RV-10.com and read Tim's write up on the trim forces and the Safety trim system and the installation process. It should answer all your questions.

Don Orrick
N410JA
 
midwest rv-10 said:
The trim forces are significant and increase with speed. Go to my RV-10.com and read Tim's write up on the trim forces and the Safety trim system and the installation process. It should answer all your questions.

Don Orrick
N410JA
Click to expand...

Don hit it right on. The trim force produced by a trim tab (or tabs) is directly proportional to the aircraft speed. If the stick force because of a trim failure feels too high for your comfort, pull back on the throttle and reduce speed. A trim force that feels very heavy at 180 kts may seem like very little at 100 kts.
 
Vic

I see your point.....however the failure of a solid state bit of gear is far less than the little button failing.

For the few hundred dollars its a no brainer.

Sure you can pull a breaker, but if the trim starts running away you will be busy keeping control of the plane let alone reaching for the breaker etc.

The safety trim controller only allows 3 seconds woth of trim travel at any one application of the button. Even if you realise the button has stuck and trim is running away, it will only go so far and you have time to use the reversing function, then you can continue using the REV function to trim forward and reverse until you get on the ground and can fix the problem.

Best value device I can think of for trim control.

DB:cool:
 
If you have a nose up runaway and you increase speed, then you are plain dumb! As you reduce speed, the aircraft will come more in trim.

If you have a nose down runaway at high speed, then you have a problem when reducing for landing. I am not fully aware of the certification requirements for light aircraft, but I would have thought that it would be mandatory that the aircraft would remain controllable even if it required a bit of grunting. In any case, keep the speed up till required for landing and test controllability at altitude. Then if necessary, increase landing speeds.
 
"The trim forces are significant and increase with speed. " Of course. That's still not a quantitative answer. I guess what I'd like to know is... Can an out of trim 10 be flown by someone with normal arm strength? As far as being too busy to pull a breaker, I don't buy it. You're just pushing or pulling & It's not hideen behind your back like John Denver' fuel selector. BTW, remember that an anti-trimmed surface has more authority than a trimmed surface. I read Tim's writeup, still doesn't really answer the question, he just says its "scary" or something.
 
aerhed said:
"The trim forces are significant and increase with speed. " Of course. That's still not a quantitative answer. I guess what I'd like to know is... Can an out of trim 10 be flown by someone with normal arm strength?
Click to expand...

I think it is difficult to answer with the answer you want.

The forces that need to be countered are dependent on airspeed and how far out of trim the pitch trim is. The ease in producing the countering force is dependent on the strength of the person holding the stick. So it is not whether it can or can't.... it depends on a number of factors. Can it be controled at full deflection up to VNE. Probably not and probably no airplane can, so to answer your question it would require more specific information.
The control system is designed for a maximum amount of force that a person would likely be capable of inducing at the stick so the limiting factor will be the pilots strength.
I am pretty sure the RV-10 was tested to be controllable at both extremes of trim deflection but obviously that is at a much reduced airspeed for the reason I mentioned previously. I have not ever done any testing on a 10 my self (I have on other models) so I can not give specifics.

Sounds like a good thing for a 10 owner to add to their phase one test program. This could be done very safely if started at low airspeeds and slowly worked up to more and more trim tab deflection and speed.

Personally, this is one flight qualities item that I wouldn't take anyone else's word for.

Practice it in your airplane. This practice coupled with a practiced procedure for quickly disabling the electric pitch trim if need (having this should be a given) should keep RV-10 pilots out of trouble.
 
Last edited:
"Sounds like a good thing for a 10 owner to add to their phase one test program. This could be done very safely if started at low airspeeds and slowly worked up to more and more trim tab deflection and speed."
That's a dandy idea. I can always mod the trim later however I feel appropriate, based on real testing. Not that big a deal to do really. Thanks.
 
An RV10 taking off with a lot of nose uptrim is a very nasty beast......yes you can fly it, but it takes two hands on the stick and you have to ease off the power :eek:
 
Vertical Power VP-200 has some nice trim safety features built in, as well. Similar to Safety Trim.
 
I happen to be phase 1 flight testing my RV-10, so I tried some trim scenarios this evening. I don't have the wheel fairings on, so it might be slightly different when complete. What I learned:

1) If trim runs away nose up, let the speed bleed off, and it becomes manageable at about 110 kts with power to hold altitude. Let speed drop further and lower the flaps, and you can fly hands off around 75 knots. A slow trip home, but the landing should be uneventful.

2) If trim runs away nose down ... here I got surprised. I started at 110 kts, and the stick required 1 very strong hand. I increased power to increase speed, figuring it would trim out. Instead, stick forces increased beyond my ability to hold, and the plane started into a dive. Fortunately I was at altitude and able to trim the plane out ... definitely would have been interesting if I was unable to trim the plane out. I then repeated the experiment, but slowed the plane down from 110 kts. In this case, the stick forces got marginally lighter, and I could hold with my hands (strong force still required at 80 kts). Flaps also surprisingly didn't seem to make a difference at 80 kts, so I would put them down for the landing. This would clearly be a much more difficult landing than nose up trim, but it could be accomplished.

So bottom line for me, if I have runaway trim in either direction, slow the plane down below 100 kts, and fly to the nearest airport for a
flaps down landing.

Aaron
 
Thanks Aaron, makes me wonder when you'd need that kind of down trim. In other words; why is it rigged in there to be gin with, aft load? Anyway I hope to find out soon.
 
You must log in or register to reply here.
Back
Top