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  #1  
Old 05-06-2022, 11:30 AM
olyolson's Avatar
olyolson olyolson is offline
 
Join Date: Dec 2009
Location: St Louis, MO
Posts: 1,220
Default Go Around button

I have a GTN 650, an AFS 5500 touchscreen EFIS and a Dynon autopilot control panel.

The current method of activating a missed approach has too many button pushes. I have to execute the Go Around on the GTN 650 for lateral tracking guidance to the MAP but ALSO engaging a vertical mode with the autopilot.

Is there a way to have ONE BUTTON to execute a Go Around then just add power like Garmin does? The Dynon HDX Manual talks about it but not a lot of specifics on how to install it or wire it.
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  #2  
Old 05-07-2022, 08:37 AM
rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
Posts: 1,005
Default Diode Isolation Circuit

Yes there is. The best option is a double pole - single throw momentary button which allows you to have both the GTN and AP receive a discrete signal simultaneously. I haven't installed Dynon products, but I'm assuming they also use a discrete active low ground signal for this.

The G3X installation manual, which is a free download, has this depicted for their installations on their interconnect drawings as the recommended method.

I have my TO/GA button on my stick, which makes installing the DPST button a little harder with confined space and the fact it came with SPST buttons already installed. So, I use another option, which is to make a diode isolation circuit. Sounds fancy, but it's essentially just two diodes wired to a common point. One is wired to the GTN, and then the other to the AP discrete point (keep in mind that the cathode end goes to ground. That's the end of the diode that generally has a stripe {the mnemonic I use is that cats lay on the ground} ).

The combined output of the diodes goes to your single momentary button, a single pole, single throw type, and then to good signal ground, preferably the same electrical point as your devices are grounded to (or your aircraft ground block, if you built it that way). I recommend two N4001 diodes, which are inexpensive and widely available (amazon, digikey, mouser, etc...)

This circuit keeps both devices electrically isolated from each other, but allows you to use a single button to activate both.
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Last edited by rongawer : 05-10-2022 at 10:16 AM.
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  #3  
Old 05-07-2022, 11:17 AM
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olyolson olyolson is offline
 
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Default Go around button

Thanks Ron, thatís exactly the information I needed
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  #4  
Old 05-07-2022, 10:04 PM
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N402RH N402RH is offline
 
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Default

Have you tried wiring a button to a GTN650 input and configuring it as Remote Go Around?

As soon as the GTN Activates a missed approach the AF-5000 autopilot will climb to the altitude bug. When I am on an approach in the RV-10 as soon as the autopilot vertical mode switches to VNAV I set the altitude bug to the missed altitude. When I use the GTN650xi in the RV-10 I need to press the Activate Missed Approach button so that the autopilot will fly the missed approach guidance from the GTN.

When I am using the Avidyne IFD550 it will automatically sequence to flying the missed approach at the MAP without any button presses.

Rob Hickman
N402RH RV-10
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  #5  
Old 05-08-2022, 08:50 AM
rongawer rongawer is offline
 
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Location: Brentwood, CA
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Default

Quote:
Originally Posted by N402RH View Post
Have you tried wiring a button to a GTN650 input and configuring it as Remote Go Around?

As soon as the GTN Activates a missed approach the AF-5000 autopilot will climb to the altitude bug. When I am on an approach in the RV-10 as soon as the autopilot vertical mode switches to VNAV I set the altitude bug to the missed altitude. When I use the GTN650xi in the RV-10 I need to press the Activate Missed Approach button so that the autopilot will fly the missed approach guidance from the GTN

When I am using the Avidyne IFD550 it will automatically sequence to flying the missed approach at the MAP without any button presses.

Rob Hickman
N402RH RV-10
While that does work for sequencing, having the function of Go Around allows you to immediately activate the mode and have the AP pitch for go around, generally at Vy, which can be done at any time while flying, such as if you want to cancel an approach or even if you have no approach selected in the GTN, or commonly after you've flown past the MAP and encounter "is that a deer on the runway?"...

An additional function, at least with Garmin and I would imagine other manufacturers, is that the operation provides for Take Off setup as well establishing pitch on the AP/FD prior to take off.
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Last edited by rongawer : 05-08-2022 at 09:02 AM.
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  #6  
Old 05-08-2022, 09:33 AM
Strikhedonia Strikhedonia is offline
 
Join Date: Jan 2020
Location: Steamboat Springs, CO
Posts: 126
Default

I asked Garmin about doing this and was told it was not acceptable. Unfortunately I was not able to locate the email/exchange. Might be good to get G3X Expert to pipe in.

Quote:
Originally Posted by rongawer View Post
Yes there is. The best option is a double pole - single throw momentary button which allows you to have both the GTN and AP receive a discrete signal simultaneously. I haven't installed Dynon products, but I'm assuming they also use a discrete active low ground signal for this.

The G3X installation manual, which is a free download, has this depicted for their installations on their interconnect drawings as the recommended method.

I have my TO/GA button on my stick, which makes installing the DPST button a little harder with confined space and the fact it came with SPST buttons already installed. So, I use another option, which is to make a diode isolation circuit. Sounds fancy, but it's essentially just two diodes wired to a common point. One is wired to the GTN, and then the other to the AP discrete point (keep in mind that the cathode end goes to ground. That's the end of the diode that generally has a stripe {the mnemonic I use is that cats lay on the ground} ).

The combined output of the diodes goes to your single momentary button, a single pole, single throw type, and then to good signal ground, preferably the same electrical point as your devices are grounded to (or your aircraft ground block, if you built it that way). I recommend two N4001 diodes, which are inexpensive and widely available (amazon, digikey, mouser, etc...)

This circuit keeps both devices electrically isolated from each other, but allows you to use a single button to activate both.
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  #7  
Old 05-08-2022, 10:27 PM
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Bill.Peyton Bill.Peyton is offline
 
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Default

Oly, a wire from pin 11 of the discrete connector on the GTN to a push button switch will accomplish what you want
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  #8  
Old 05-09-2022, 10:39 AM
rongawer rongawer is offline
 
Join Date: Dec 2007
Location: Brentwood, CA
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Default

Quote:
Originally Posted by Strikhedonia View Post
I asked Garmin about doing this and was told it was not acceptable. Unfortunately I was not able to locate the email/exchange. Might be good to get G3X Expert to pipe in.
It may not be "acceptable", as in the approved method that I provided earlier, however it is definitely a good solution. You might be surprised to find that diode isolation circuits are used in quantity inside the Garmin boxes, as well as just about every electronic device made. Guess how the dual power supplies for the GDU's work? Diode isolation circuits as a method of power auctioneering.

Quote:
Originally Posted by Bill.Peyton View Post
Oly, a wire from pin 11 of the discrete connector on the GTN to a push button switch will accomplish what you want
While this will work, it wires both discrete values together without diodes, and is likely the unacceptable method Garmin disapproved of due to the potential difference between the ground reference of the two units.
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Last edited by rongawer : 05-09-2022 at 10:43 AM.
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  #9  
Old 05-09-2022, 12:48 PM
g3xpert's Avatar
g3xpert g3xpert is offline
 
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Location: Olathe, KS
Posts: 3,323
Default TO/GA Switch Wiring

The intent of the dual pole switch is to isolate the discrete input on the GTN from the discrete input on the GEA 24. If one of the units is powered off, it can inadvertently pull the input on the other low, the dual pole switch prevents this from happening. Other isolation methods such as diodes would be acceptable.

Thanks,

Justin
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  #10  
Old 05-09-2022, 01:14 PM
Longez's Avatar
Longez Longez is offline
 
Join Date: May 2009
Location: KS
Posts: 483
Post TO/GA Button Diode Isolation Examples

Here are some example wiring diagrams using diode isolation between 2 discrete inputs and a simple SPST TO/GA button.

Click image for larger version

Name:	TO_GA Button Diode Examples.png
Views:	194
Size:	88.6 KB
ID:	25650

Steve

Last edited by Longez : 05-09-2022 at 01:24 PM.
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