Van's Air Force
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Runaway Flaps and Trim
- Thread starter g zero
- Start date
Mike S
Senior Curmudgeon
If you do put in a switch, most likely a DPDT Off/on/momentary will allow you to reverse a runaway trim/flap, as well as shut off the runaway.
Like shown here.
http://popular.ebay.com/business-industrial-d-j/dpdt-toggle/momentary-dpdt-toggle-switch.htm
Like shown here.
http://popular.ebay.com/business-industrial-d-j/dpdt-toggle/momentary-dpdt-toggle-switch.htm
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Lan Vinh Do
Well Known Member
On off reverse
I did the same thing in my rv-10. I was afraid of a runaway trim on the elevator as i am sure i can't fight it.
I add a on /off/ reverse for the same reason as Mike and i add a switch gard over it to be sure that it's on the good position normally
I didn't do anything with the aileon or flap
I did the same thing in my rv-10. I was afraid of a runaway trim on the elevator as i am sure i can't fight it.
I add a on /off/ reverse for the same reason as Mike and i add a switch gard over it to be sure that it's on the good position normally
I didn't do anything with the aileon or flap
MauiLvrs
Well Known Member
We used a fuse panel for almost everything.
The trim and AP are two of the items that we have a pull type breaker for.
Have never needed it ... but just incase .... it is there.
vlittle
Well Known Member
Most runaway trims are caused by failed (stuck) relays or trim switches.
Here's a variable speed dual trim controller that is 100% electronic (no relays) detects and indicates stuck trim switch faults and allows an external secondary switch to correct the fault.
Having said that, someway of cutting off power to your flaps and trim system is good advice. I prefer a pullable breaker because you eliminate one more potential fault source (the toggle switch), its terminals and wires.
In general, a back-up system should be more reliable than the system it's protecting, otherwise it's part of the problem, not the solution.
Here's a variable speed dual trim controller that is 100% electronic (no relays) detects and indicates stuck trim switch faults and allows an external secondary switch to correct the fault.
Having said that, someway of cutting off power to your flaps and trim system is good advice. I prefer a pullable breaker because you eliminate one more potential fault source (the toggle switch), its terminals and wires.
In general, a back-up system should be more reliable than the system it's protecting, otherwise it's part of the problem, not the solution.
I've heard of flap troubles (mostly failed to operate as in a failed motor, but if they are powered by a fuse, you may have blown it due to inrush current which can be solved by a simple re-set of a breaker. I have fuse blocks and breakers. A separate fuse/breaker for each circuit. Some things you may want control over when flying or for ground maintenance:
Auto pilot, maybe just the circuit that powers the servos.
Starter control, for ground safety (people sitting in the cockpit) especially if you have a stick mounted start switch.
Flaps, for runaway control and inrush trip
trim, for runaway control as mentioned
aux power outlets, cause plugging things in and out sometimes cause funny things to happen.
fuel pump,
strobes (because inrush current make trip a fuse)
Landing lights (because inrush current make trip a fuse)
P-mags (if you have them) because they are NOT to be powered from a fuse.
There are probably more. I have 12 positions designated for resettable breakers. I think I have used 9 so far. Everything else has it's own fuse, and there are lots of them.
Bevan
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Pull able breaker on pitch trim servo can be priceless. As in, keep you from dying.
Excellent questions. I notice a strong tendency toward two builder diseases.
(1) Generalized Anxiety Disorder: Worrying about a backup for a system with a very low failure rate and a benign failure mode.
(2) Optionitis: Adding toys with a low value/complexity ratio, but high time and money cost.
Think about it. RV trim systems are typically quick. If it runs away, do you really think you'll (a) register the problem, (b) diagnose it, and (c) find the switch or breaker before it is way out of trim? Maybe a better approach would be to stop worrying, and just go fly it with the trim at the stops during Phase One.
Now think about flaps. The same human factors apply...register, diagnose, and action are unlikely to take place fast enough to make a difference. The common failure mode is motor failure; not runaway. If it does run away, so what? The airplane was within the flap envelope, or the pilot would not have been fooling with the flap system. Up is never a problem. If you were putting them down, you were going to land anyway, and an RV with flaps down will climb just fine for a go-around.
KIS is always best. Things not installed weigh nothing, cost nothing, and never cause a problem.
Trim loads are airspeed dependent. Runaway trim will give much higher loads and maybe uncontrollable at cruise speed but manageable at approach speed. Unfortunately the trim is used often in cruise to fine tune trim but also used more aggressively during landing as flaps and airspeed are adjusted. Which trim usage is more likely to cause a runaway? Unknown.
I have trim breaker pull switch right in front of stick so easy to find/reach just in case but do not think it will matter due to a) b) and c) in Dan's response above.
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Walt
Well Known Member
Agree 100% with Dan, failure rates on both systems are practically non existent (most failures are due to poor workmanship) and do not warrant fail-safe back-up systems IMO.
From where I stand you'd be much better off spending your time, money and energy on FWF systems where most of the problems actually exist.
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Lan Vinh Do
Well Known Member
Runaway
I had a runaway aimeron trim in my rv-7 because of a short and could 't care less. Easy.
The elevetaor trim on the 10 can be quite a suprise if the passenger hit the switch. I made the choice to put the on off reverse switch so i can reverse it if there is a short and put it to off when in neutral position. Cost only few dollars for the switch. I feel safer. Low rate of failure but cheap fix , really low time mod. My point of view for the rv-10. A rv-8... Don't know if i would do the mod.
I had a runaway aimeron trim in my rv-7 because of a short and could 't care less. Easy.
The elevetaor trim on the 10 can be quite a suprise if the passenger hit the switch. I made the choice to put the on off reverse switch so i can reverse it if there is a short and put it to off when in neutral position. Cost only few dollars for the switch. I feel safer. Low rate of failure but cheap fix , really low time mod. My point of view for the rv-10. A rv-8... Don't know if i would do the mod.
On top of the excellent points made by Dan and Walt, realize that some of the modern autopliots do this for you anyway, as can Vertical Power. Remember, if you design the whole airplane and all of it's systems for the "1th percentile", it'll never fly. The entirety of a flying contraption is an exercise in compromise and risk management to begin with!
Cheers,
Stein
Cheers,
Stein
Walt is correct. But, in the same space as a Vans breaker, you can put a pull able one Cheap way to shut down the motor. Stick force is VERY high at cruise speed with out of trim condition.
TomVal
Well Known Member
The GRT autopilot system will give you a color coded display (green or red) on the EFIS showing the degree in units that you are out of trim and the direction you must trim in order to correct the imbalance. The "units" are a measurement of the amount of torque the pitch servo is holding to maintain a given flight command. Basically, when the display is "blank", you are in trim. Nice feature.
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Really, it is and it sounds good to me. Not unlike smelling smoke or suspecting a serious electrical system problem. Need to control the plane then neutralize the problem quickly.
14 years this week, and never a runaway trim condition.
Mike S
Senior Curmudgeon
Celebration time
Yes, thanks Mike!!! Having an RV in the hangar is life transforming, and I've been lucky to have it.
