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Using S Pot for idle control

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Using S Pot for idle control

Old 03-29-2020, 06:41 PM
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Fireflite82
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Default Using S Pot for idle control

What's happenin' everyone!? I was curious to find out if anyone here on the gasser/nitro world was using an S Pot on any FrSky Tx's for Idle control? Or better yet what is everyone using for idle control using their setups?
Old 03-29-2020, 08:16 PM
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jester_s1
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Are you looking to do a high idle to make sure your engine stays running when doing aerobatics and then be able to lower it enough to land? Honestly, I've never needed to do that on a properly set up and tuned engine. But if you really do, a switch is a better choice. Set up a high idle and low idle and go fly it.
Old 03-29-2020, 08:23 PM
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Fireflite82
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What type of fuel?

I ask because I am new to wet fuels, on my gasser there was an idle screw on the carb. That was easy to navigate, more recently I bought a couple of nitro planes. I've heard of people just using trim to adjust idle.

Can you describe your set up?
Old 03-29-2020, 08:37 PM
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tedsander
 
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Sounds like you are just substituting S1 or S2 for the Throttle trim. Why not just use the trim lever? They even include a handy "Idle trim only" checkbox, so the trim only changes the low end of the stick, and doesn't change the high end.

On my gasser, I have 3 global variables defined, each controlled by a switch. Depending on the choice, it adds to the low end of the throttle - one as a very fast idle, used for initial starting, one a medium low throttle (needed when the engine isn't at full operating temp), and then the lowest possible idle, after it has come up to temp in flight and for landings. And then I have the normal trim, if for an odd reason it needs a bit of fine tuning. On glow, I just use the trim lever, set so at the lowest the engine will barely keep running. Adjust the trim as needed after startup for low dependable idle, which varies a bit due to conditions of the day. Then I have a switch set as "kill" that closes the carb completely.

Later edit: I got fancy above, because with the radio, one can. For the most basic - adjust linkages/radio so that at full down engine trim, the carb is completely closed. This allows you to kill the engine. Move the trim up to open the carb a little bit, for starting and then adjusting for a nice low, dependable, idle speed. Of course, adjust the high end, with the stick fully up, to completely open the carb. This is where the "idle trim only" checkbox is a great addition - moving your trim lever doesn't do anything to the high side, it only adjusts the speed on the low end.

Last edited by tedsander; 03-30-2020 at 07:38 AM.
Old 03-29-2020, 08:51 PM
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tedsander
 
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Just to be clear for both gas and nitro - the trim controls adjust the speed of the idle (just like the sticks, but not as large of a range). The screw on the carb controls the fuel/air mixture, which once set properly, rarely needs adjusting again. Set the carb screw to get the most dependable performance possible - doesn't cough, sputter, or kill when accelerating and will maintain an idle until you run out of fuel. Use the trim to adjust how fast the engine runs at idle.
Old 04-05-2020, 08:31 AM
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Fireflite82
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Originally Posted by tedsander View Post
Sounds like you are just substituting S1 or S2 for the Throttle trim. Why not just use the trim lever? They even include a handy "Idle trim only" checkbox, so the trim only changes the low end of the stick, and doesn't change the high end.

On my gasser, I have 3 global variables defined, each controlled by a switch. Depending on the choice, it adds to the low end of the throttle - one as a very fast idle, used for initial starting, one a medium low throttle (needed when the engine isn't at full operating temp), and then the lowest possible idle, after it has come up to temp in flight and for landings. And then I have the normal trim, if for an odd reason it needs a bit of fine tuning. On glow, I just use the trim lever, set so at the lowest the engine will barely keep running. Adjust the trim as needed after startup for low dependable idle, which varies a bit due to conditions of the day. Then I have a switch set as "kill" that closes the carb completely.

Later edit: I got fancy above, because with the radio, one can. For the most basic - adjust linkages/radio so that at full down engine trim, the carb is completely closed. This allows you to kill the engine. Move the trim up to open the carb a little bit, for starting and then adjusting for a nice low, dependable, idle speed. Of course, adjust the high end, with the stick fully up, to completely open the carb. This is where the "idle trim only" checkbox is a great addition - moving your trim lever doesn't do anything to the high side, it only adjusts the speed on the low end.

I'm finding out there are 30k ways to spin this lol! I'm going to give your method a shot! Thanks for you input!
Old 04-05-2020, 08:36 AM
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Fireflite82
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Originally Posted by tedsander View Post
Just to be clear for both gas and nitro - the trim controls adjust the speed of the idle (just like the sticks, but not as large of a range). The screw on the carb controls the fuel/air mixture, which once set properly, rarely needs adjusting again. Set the carb screw to get the most dependable performance possible - doesn't cough, sputter, or kill when accelerating and will maintain an idle until you run out of fuel. Use the trim to adjust how fast the engine runs at idle.

Understood, but the screw that I was referring to was the idle adjustment screw on a Wahlbro Carburetor, It allows you to essentially do what we are talking about but doing it by physically tightening or loosening the screw to adjust the level of idle, not to be confused with the High/Low needles in carb. Me not wanting to drill a hole in my cowl for idle adjustment, due to ambient conditions, I omitted the idler screw and now will program that adjustment into my radio. Thank you for your response!!
Old 04-05-2020, 03:35 PM
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tedsander
 
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Originally Posted by Fireflite82 View Post
Understood, but the screw that I was referring to was the idle adjustment screw on a Wahlbro Carburetor, It allows you to essentially do what we are talking about but doing it by physically tightening or loosening the screw to adjust the level of idle, not to be confused with the High/Low needles in carb. Me not wanting to drill a hole in my cowl for idle adjustment, due to ambient conditions, I omitted the idler screw and now will program that adjustment into my radio. Thank you for your response!!
Yeah, I think most of us throw away that screw!
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