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Thread: Trim with the Garmin G3x

  1. #21
    Senior Member PapuaPilot's Avatar
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by Shadowrider View Post
    Ah makes sense now what your doing. As for trim indicator yeah it’s not really needed. With the 915 I will give you the gouge. All the way nose up for landing, and almost all the way nose down for takeoff. Its not like a turbine aircraft, if it’s trimmed wrong it’s not going to kill you.
    I really like having the trim indicator. Initially I had the cable & coiled spring mechanical indicator, then I put a RayAllen linear rheostat on the horizontal stab that shows on the G3X screen. With that said it has been inop a couple times and I found I could count to 7 to retrim from full nose up after landing and it would be perfect for takeoff.

    While I agree it's not going to kill you I would highly suggest practicing some full power go arounds at altitude with the trim in the full nose up/landing position. This might be a bigger issue for planes without the trim assist spring. There is a big pitch change that happens when power is applied that takes a fair amount of force on the stick to counter.

    I just wrapped up my condition inspection yesterday where installed the trim assist spring kit and the TCW Safety Trim Booster. I hope I have time to do the post inspection flight today before traveling on business tomorrow.
    Phil Nelson
    A&P-IA, Maintenance Instructor
    KF 5 Outback, Cont. IO-240
    Flying since 2016

  2. #22
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    Smile Re: Trim with the Garmin G3x

    The trim indicator is nice and I like as many gadgets on the g3x as possible. I setup my trim indicator with a green takeoff section and trim direction to match the corporate aircraft that I fly. I prefer No trim assist because I prefer heavier controls also to help with transfer from the corporate aircraft I fly. Yes it takes a lot of input when you are trimmed full nose up for landing and you do a go around, and also removing flaps, but the aircraft would not be safe if it was not possible to do go around safely as every landing has a possibility of a go around. I have done too many to count as it’s IMO something you should do when landing in the backcountry in a new off-airport spot. I know you are not arguing against this and I agree with you, you want to practice a go around so you know what you can expect. There are some aircraft that if you where to attempt a takeoff with the trim in the wrong position you literally will not be able to takeoff, ie wreck and possibly die.

    I know an operator that attempted to take off in a falcon 900 with the recommend trim position and was not able to rotate. They did a high speed abort past V1 and departed the end of the runway into a burm and the aircraft was destroyed and they suffered injuries. Well, the manufacturer discovered recommend trim settings in the manual where incorrect and the operator was awarded a new aircraft. Point is, some aircraft will not fly with trim in the wrong position, but not the kitfox. I think if I didn’t have an indicator I would just trim full nose down for takeoff and turn around and glance at the stab and verify. I like the trim indicator but if you don’t install one it’s not that big of deal IMO.

    The safety trim is nice and I also like the feature on the G3x that you can slow down the trim with speed. Makes smooth trimming at "high speed" :]!
    Last edited by Shadowrider; 04-19-2022 at 08:19 AM.
    Dustin Dickerson

    Building 7ss STI x 2
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  3. #23
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    Default Re: Trim with the Garmin G3x

    I just started doing my wiring diagrams this past weekend. I've always had it in my mind that I was going to use the Safety Trim unit because I want to control stab trim through the rocker switch on my center console and the hat switches on the sticks. From reading on this forum I understand that the rocker switch has a hard life because of the current going through it, and I'm quite sure the hat switches would be happier working through relays.

    And this will sound funny but I wanted a Ray Allen LED trim position indicator because the hole is already cut on my center console for an indicator there. A few months ago a guy popped up on the EAA forum with a Ray Allen trim indicator and the Ray Allen rocker switch for cheap, so I bought them. I have the ability to put a trim indicator on my MGL displays too (and I may do that just for laughs). The web site for the Safety Trim has a diagram for the hat switch/RA rocker switch combo so I incorporated that into my design.

    trim.jpg
    Per the instructions I also incorporated a stab trim cutout switch, which I need for sure now that I went away from Klixon type breakers to an hidden fuse block. My kit came with the stab trim position sensor (it's basically a rheostat, right?) to go with my LED indicator. I'm going to bench test that setup to make sure the pieces play nicely together.

    One of those things I hadn't thought of is that the trim position portion of the system doesn't share a single wire with the stab trim motor, switches, etc. I mean it makes sense, I just hadn't put any neurons to work over it until now.

    Interesting thoughts on not using the trim assist kit. It's one of those things that is easy to retrofit. I have not yet put the airspeed switch in the diagram which gives you the two speed trim motion. Still considering it.
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  4. #24
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    Default Re: Trim with the Garmin G3x

    Alex, I gotta ask......what are the diodes for? The drawing was hard to read on my computer so I can't see how they are connected to the Safety Trim and I can't see how your panel switch is wired. I am assuming it's like the switch in the Safety Trim instructions.

    Gary
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  5. #25
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by Geek View Post
    Alex, I gotta ask......what are the diodes for? The drawing was hard to read on my computer so I can't see how they are connected to the Safety Trim and I can't see how your panel switch is wired. I am assuming it's like the switch in the Safety Trim instructions.

    Gary
    Yeah that image didn't work out very well. I'll figure out a better way to share it so it can be viewed clearly.

    I pirated that section of the diagram from the Safety Trim instructions, which fortunately covers my desire to have the hat switches and rocker switch enabled. It calls for the specific Ray Allen rocker switch I have in my possession and says something about it being internally shorted. That and "don't pee on a horse fence" are about all I know when it comes to electricity.
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  6. #26
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by alexM View Post
    ......I pirated that section of the diagram from the Safety Trim instructions, which fortunately covers my desire to have the hat switches and rocker switch enabled. It calls for the specific Ray Allen rocker switch I have in my possession and says something about it being internally shorted. That and "don't pee on a horse fence" are about all I know when it comes to electricity.
    If you have the time, is there a link to that diagram you could post? My instructions don't have any of that in it and shows the rocker switch as wired like the Kitfox instructions (which is why I was asking about the diodes). Peeing on the horse fence is indeed one of those important life lessons that thankfully I did learn early on working on my uncle's farm. When I went to nerd school they left that lesson out of the curriculum - which may go a long way to explaining some things.

    Thanks

    Gary
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  7. #27
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    Default Re: Trim with the Garmin G3x

    Gary,
    Here's the link
    https://www.tcwtech.com/wp-content/u...t-Switches.pdf

    In case that link doesn't work, on the TCW web site if you click on the documentation tab, look in the Safety Trim section, the second from the bottom is the link for the above document.
    Kitfox 5 (under construction)
    Commercial SE/ME, CFII

  8. #28
    Senior Member Eric Page's Avatar
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by alexM View Post
    ...Safety Trim instructions, which fortunately covers my desire to have the hat switches and rocker switch enabled. It calls for the specific Ray Allen rocker switch I have in my possession and says something about it being internally shorted.
    That's the only explanation that makes any sense WRT the diodes. If the "up" and "down" contacts of the RS2 switch are shorted internally when the rocker is centered, then pins 5 and 6 on the Safety-Trim would be shorted together. The diodes prevent that. Pin 5 can't push current through the left diode to pin 6 and pin 6 can't push current through the right diode to pin 5, but the switch can pull either of those pins to ground through their respective diode.
    Eric Page
    Building: Kitfox 5 Safari | Rotax 912iS | Dynon HDX
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  9. #29
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    Default Re: Trim with the Garmin G3x

    Quote Originally Posted by alexM View Post
    Gary,
    Here's the link
    https://www.tcwtech.com/wp-content/u...t-Switches.pdf

    In case that link doesn't work, on the TCW web site if you click on the documentation tab, look in the Safety Trim section, the second from the bottom is the link for the above document.
    Nope that worked. I see where my corn-fusion was - It is hooking up to a Safety Trim Controller and not the Safety Trim Booster that I am using. Different animal. What has to happen with the booster is that the Up/Down commands to the booster need to swap polarities depending on which way you want the motor to go. I couldn't see how that worked with the hook up you had. I didn't look closely at the controller but if I read the description right (albeit quickly) it takes care of the swap internally for up to an 10A draw from the motor. Still not sure about the diodes but hey, you're right - it's in the instructions that are written by the guys a lot smarter about this than me.

    Thanks for the clarification.

    Gary

    Just read Eric's post and that makes sense cause there would be 12V from the controller floating out there waiting for a ground command. - Thanks Eric.
    Last edited by Geek; 04-20-2022 at 11:45 AM.
    Gary (Geek) Phenning
    Leavenworth (Not the Prison), WA
    Kitfox STi in Building Stage

  10. #30
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    Default Re: Trim with the Garmin G3x

    I have been following this thread with great interest. I have a few thoughts and questions

    1) I am using GRT avionics and VPX. I plan to control the trim motor through HAT switches on the stick that are connected to the VPX. The KF option trim position sensor (really just a voltage divider) will feed the VPX and get sent to the EFIS through the serial bus.

    2) I measured the actual current draw of the KITFOX trim motor and found it to be about 1.5-2.0 amps (under load). I am unclear why KF calls for a 7A breaker, but so be it. The issue arises when trying to control the KF pitch motor with the VPX, which has only a 1A output.

    4) Apparently, some have used the TCW booster to increase the current to that required by the KF trim motor. There has also been discussion about the virtue of variable speed trim, depending on the speed of the aircraft. Sounds really keen.

    5) I am not an engineer, but believe that there is a simple and inexpensive way to get the required current to the KF trim, and that is through the use of a MOSFET. MOSFETS are voltage devices and will conduct when voltage is applied to the gate. Depending on the MOSFET chosen, you can supply very high currents with a small voltage (from the VPX) applied.

    6) So far so good, since MOSFETS are only a few dollars, way cheaper than the booster. You would need one MOSFET for trim up, and one for trim down.

    7) I spoke with a tech guy at VPX today who told me that the way the VPX regulates the speed of the trim motor is by varying the voltage sent to the trim motor. That confounds things, because if you do use a MOSFET, it will turn on hard with voltage applied to the gate and completely conduct above some minimum input voltage. That effectively does away with the speed dependent function

    8) I do not know how the BOOSTER works, but I am guessing that it uses a circuit similar to the design I have in mind. If that is true, the booster will not control the trim motor speed at varying air speeds.

    So after all that, here are my questions:

    A) Has anyone tried a MOSFET control of the trim motor?

    B) For those of you who are using the booster, are you sure that the speed of the trim motor is really dependent on airspeed? If so, how have you determined that?

    I appreciate your thoughts

    Fred
    7SS, 915is
    In the process of covering and playing with avionics

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