runaway trim

[1bigdog]

Originally Posted by N941WR

Search AO Frog's posts. I seem to remember he designed a dual trim system by putting an electric motor that can turn the manual trim knob.

Bill

I've looked for lots of possible variations of. Frog and trim but nothing like what you suggest. I can guess how it work. You stick a reversing axial motor on the cable and the knob on the other side and it would rotate the knob instead. Of using a servo.

If you or someone knows a link because I can't seem to find it and would prefer to see something. That works before I experiment.

I'll keep looking otherwise.

Thanks

[DaleB]

I had thought about designing some kind of a safety override for the trim. However, it occurred to me that any electronic safety mechanism would have at least as many failure modes as the trim system, possibly more. Don't get me wrong, I love electronics and have been making my living in that sphere for a few decades now. I've just seen enough stuff fail to know that no matter how nice and how clever it is, it can fail in ways you never expected.

I like the idea of electric trim and flaps. Both will have a way to quickly cut power by the time I'm flying.

[1bigdog]

Originally Posted by DaleB

I had thought about designing some kind of a safety override for the trim. However, it occurred to me that any electronic safety mechanism would have at least as many failure modes as the trim system, possibly more. Don't get me wrong, I love electronics and have been making my living in that sphere for a few decades now. I've just seen enough stuff fail to know that no matter how nice and how clever it is, it can fail in ways you never expected.

I like the idea of electric trim and flaps. Both will have a way to quickly cut power by the time I'm flying.

Hey Dale

I don't mind that things fail as long as they fail safe so when I started researching trim servos I was caught off guard by how they fail. I like the idea of placing a motor in the middle to slowly turn the cable. If it fails, who cares. You can still turn the knob. In this scenario you can still use a speed controller or a reverser or cut off power but your not stuck at a dangerous position. I like this.

I'm looking forward to seeing how Frog did it but I definitely have an idea now of how to do this.

Thanks.

Michael B

[1bigdog]

Originally Posted by 1bigdog

Hey Dale

I don't mind that things fail as long as they fail safe so when I started researching trim servos I was caught off guard by how they fail. I like the idea of placing a motor in the middle to slowly turn the cable. If it fails, who cares. You can still turn the knob. In this scenario you can still use a speed controller or a reverser or cut off power but your not stuck at a dangerous position. I like this.

I'm looking forward to seeing how Frog did it but I definitely have an idea now of how to do this.

Thanks.

Michael B

Hilarious. I have what I need in the next room. Its the vernier cable motor drive for my telescope. It even includes a quick disconnect mechanism from the cog on the cable. It has a reversible controller with 2 speeds.

Manual it is.

Cheers

[Toobuilder]

I think this is one of those areas where people are worried that just because there is the possibility of failure, then we need to fix it. We really need to focus on the probability, then determine the severity. If the probability and severity are low, press on with current design practices.

[ao.frog]

It can't be me mentioned in the post above.
I have wired the power-wires for the trim and and flap motor through a separate switch.
In case of a run-away, I simply turn off the switch.

To have the trim system as simple as possible, I have installed only one trim switch per system: one switch and one indicator for aileron trim, and ditto for the elevator trim.
In other words: I only installed the trim parts which came from Vans.

Having flown with this setup since 2008, I have not yet missed to have the trim on the stick. The panel mounted switches works fine for me.

The power cutoff switch in question is the second one from the right in this pic, is red and it's labeled "TR/FL CUT-O"

[Bevan]

I beleive the manual trim was heavier.

Bevan

[N941WR]

Originally Posted by 1bigdog

Bill

... I can guess how it work. You stick a reversing axial motor on the cable and the knob on the other side and it would rotate the knob instead. Of using a servo.

If you or someone knows a link because I can't seem to find it and would prefer to see something. That works before I experiment.

I'll keep looking otherwise.

Thanks

Yes, that is what I recall seeing but it doesn't sound like it was Capt. Frog who made that mod. Keep searching, it is in the archives.

Originally Posted by Bevan

I beleive the manual trim was heavier.

Bevan

Yes it is; however, it is very simple to install and doesn't require electricity, breakers, switches, relays, etc. and is very effective. About the only drawback is that it fills one hole through the spars and as i have made changes over the years, it has been challenging running wires aft.

[MarkW]

Originally Posted by DaleB

I had thought about designing some kind of a safety override for the trim. However, it occurred to me that any electronic safety mechanism would have at least as many failure modes as the trim system, possibly more. Don't get me wrong, I love electronics and have been making my living in that sphere for a few decades now. I've just seen enough stuff fail to know that no matter how nice and how clever it is, it can fail in ways you never expected.

I like the idea of electric trim and flaps. Both will have a way to quickly cut power by the time I'm flying.

+1 Dale

Toobuilder I think this is one of those areas where people are worried that just because there is the possibility of failure, then we need to fix it. We really need to focus on the probability, then determine the severity. If the probability and severity are low, press on with current design practices.

+1 Michael

[vlittle]

Originally Posted by dynonsupport

The trim controller in the Dynon system will time out a single stuck switch and still allow you to use the opposite direction switch to return the trim to neutral after a failure, or still use the buttons on the other stick.

Here's the problem...
1. As I recall, using a timeout to limit trim operation is patented by TCW.
2. Trim timeout is an unnatural operation that interferes with the desired operation when operating normally. For example, dialing in a lot of trim pre-takeoff or when extending or retracting the flaps requires multiple trim 'blips'. For example, In a go around in a 300 hp Rocket, both hands are very busy and blipping the trim is an unwelcome, possibly unsafe procedure while trying to keep the nose below a 45 degree deck angle with forward stick, retracting the flaps and managing the stuff that makes noise.

The trim switch failure recovery method in the MakerPlane device always recognizes a failed trim switch without interfering with the normal operation of the trim system. It also allows the faulted pole on the trim switch to be bypassed witout the complexity of additional hardware by re-using an existing mode/programming pushbutton. Finally, it indicates a fault with a lamp or EFIS system contact input.

I will admit that a simple trim timeout may be 'good enough' for lower performance aircraft, but how does Dynon stickhandle around the TCW patent on this?