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-   -   Skyview or VP-X for flap and trim control (https://vansairforce.net/community/showthread.php?t=126439)

penguin 06-16-2015 03:22 PM

Quote:

Originally Posted by vlittle (Post 990569)
Hi Pete, I'd like to respectfully disagree with your value assessment of autotrim.
I developed an autotrim controller that works with the SkyView systems as a separate stand alone box. If the EFIS fails, it works as a standard trim controller with speed scheduling determined by flap position. It also has fail safe/recovery mode. This agrees with your premise.

However, I think your assessment of the servo motor authority over the RV speed range is incorrect. Before Autotrim, I was getting constant demands for manual trim intervention from the Dynon Autopilot in my Harmon Rocket. With my autotrim controller, I can change throttle settings and let the autotrim take over. I can even engage the autopilot with large trim offsets so that the servos slip and my autotrim controller will converge to neutral.

This means that I can use smaller, lighter servo motors and I have a lot fewer distractions in the cockpit.

My SOP is take-off, level off at 2000 feet (about 30 seconds later in an HRII), slap on the autopilot and let the trim take care of itself while I tidy up the cockpit.

I would never go back to manually controlled trim with an autopilot. An autopilot without autotrim is so last century.

Hi Vern - I did say in RVs ... clearly more use in an Rocket with its greater stick forces. Still not on my wish list!

For Dynon, I won't be using a breaker to switch off anything I might want to disable in flight, I think that is poor advice.

Pete

dynonsupport 06-16-2015 06:53 PM

Pete,
You are welcome to use a switch as well, but you are going against general airplane implementation. You only ever need to pull this in the case where the software or hardware fails and causes your trim to move uncommanded. This is basically the exact reason pull-able breakers exist, for the very rare cases that you need to disconnect something in flight that is never done normally and you need to turn just it off. We absolutely don't think you should be turning off the trim controller on a normal flight, so a panel switch for it is overkill and in fact adds complexity to the system which is almost always a bad idea.

Unless you are going with all very old radios, transponders, etc in your plane, the request to turn them off from the front panel is a request to software, not a hardware switch (if they even have a power switch, which many certified boxes don't). So if you distrust software, you very much need a way to switch each box off individually. Again, in most planes this is done by having breakers for emergency situations. If you think having certified software is the solution, then you haven't paid much attention to the huge stack of AD's on certified devices. As was once told to me by someone with tons of certified software experience - "I'd much rather fly in a plane with 1,000 hours of real world experience and no certification than a plane with level A certification on the first flight".

If you consider trim runaway a critical condition, we highly suggest you have a way to disconnect your mechanical trim switches as well. A mechanical switch can break and fail and leave your trim moving just as easily as software can fail. Ironically, this is something the software protects against in a software based trim controller.

All that being said, Dynon doesn't think you need a breaker or switch for the trim controller in an RV. You can fly an RV with trim at the extreme, the chance of failure is very low, and a simple electrical system made up of automotive fuses has a lot of nice benefits. The great thing about experimental planes is you can actually choose for yourself.

--Ian Jordan
Dynon Avionics


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