Runaway Flaps and Trim - Page 2

TomVal · #11 05-31-2014, 08:06 AM

My RV8 had inaccessible fuses for circuit protection, therefore, I installed aileron and elevator trim cutout switches. If I had accessible CB's, I would not have installed the switches. (JMHO)

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Walt · #12 05-31-2014, 08:18 AM

Quote:

Originally Posted by DanH

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.

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.

Lan Vinh Do · #13 05-31-2014, 08:30 AM

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.

g zero · #14 05-31-2014, 01:54 PM

Thanks for the replies , gonna keep it simple no extra switches .

That was why I went with a fuse block over breakers , simple .

SteinAir · #15 05-31-2014, 09:04 PM

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

flightlogic · #16 05-31-2014, 09:32 PM

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 · #17 06-01-2014, 06:32 AM

Quote:

Originally Posted by SteinAir

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

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.

GeneL · #18 06-01-2014, 06:50 AM

How about TURN THE MASTER OFF? It's the big red one, you won't have to search for it!

KRviator · #19 06-01-2014, 07:24 AM

And immediately lose your radios, transponder, TCAS, lighting, GPS and perhaps your EFIS?

KISS? Not really.

Low Pass · #20 06-01-2014, 08:19 AM

Quote:

Originally Posted by KRviator

And immediately lose your radios, transponder, TCAS, lighting, GPS and perhaps your EFIS?

KISS? Not really.

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.