Throttle return spring poll - RCCanada - Canada Radio Controlled Hobby Forum
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View Poll Results: Throttle return spring leave or disconnect
Leave 17 37.78%
Disconnect 28 62.22%
Voters: 45. You may not vote on this poll

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Old 04-08-2011, 07:50 AM   #1
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Throttle return spring poll

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I've posted this in the main forum hoping for the maximum number of opinions. Hopefully it doesn't get moved. For those of you flying gas engines I'd like to hear opinions on removing or not removing the throttle return spring. I've read about this a bit here and on another forum and I'm still undecided. What does everyone think?
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Old 04-08-2011, 07:57 AM   #2
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Re: Throttle return spring poll

In all my years of flying in RC, I have yet to have a throttle servo pack it in.

For the days when I was running gas engines, the butterfly valve was so smooth that it put zero load on the throttle servo. So why bother with a spring? Besides, wont the spring put a strain on the servo, forcing the servo to "fight" the spring load and perhaps cause it to fail prematurely?

I say "No spring"
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Old 04-08-2011, 08:27 AM   #3
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Re: Throttle return spring poll

The throttle arm spring serves 2 functions:

1) To return the throttle to idle or kill the engine if the linkage breaks or fails.

2) To minimize the butterfly shaft from vibrating back and forth inside the carb body.

Item #2 is much more important than item #1. If you completely remove the spring, your carb will eventually develop leaks around the area where the butterfly shaft meets the carb body. This is something that you can not fix and you generally have to replace the carb.

Also, you may find that your throttle may bounce or jump because without the spring, the butterfly can float a bit.

The trick is not to remove the spring, but to disconnect it from the throttle arm. You can either clip the very last piece of the spring that is touching the throttle arm, or use a small pair of needle nose pliers to bend the spring away from the arm. Once the spring is disconnected - you will find that the throttle moves without resistance, and that the butterfly shaft has very little room to move back and forth in the carb body.

It is best to disconnect the spring, because the spring can load the throttle servo and cause binding.

If you are concerned about killing the engine in an emergency, use an alternative method such as a Opto Kill switch or a servo on the choke that will give you the ability to kill the engine remotely.

Hope this helps,

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Old 04-08-2011, 08:45 AM   #4
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Re: Throttle return spring poll

Thanks for the information so far. I guess I should have put the third option: disconnect without removing the spring. I've read a lot about that too. I have an electronic kill switch for it so I guess I can get away without the spring as third fail safe. I think I read somewhere about someone who was passionate that the spring be left as a mechanical fail safe. It's not something glow engines have though and we fly them safely.
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Old 04-08-2011, 08:57 AM   #5
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Re: Throttle return spring poll

I agree with Jeff.

Leave the spring in, but disconnect it.


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Old 04-08-2011, 08:59 AM   #6
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Re: Throttle return spring poll

The throttle spring constantly fighting the servo will prematurely drain the battery and possibly cause the throttle servo to overheat and fail. that would mean "bye, bye" airplane. The throttle shaft wear would take several hundred hours and carb's are cheap aircraft are not.

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Old 04-08-2011, 10:05 AM   #7
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Re: Throttle return spring poll

I find the springs have to much tension in them to begin with, so I just unclip it and unwind it 3/4 of a turn and clip back on... The spring is still connected but has allot less tension (it will still go back to idle if the linkage breaks but it won't "SNAP" back)...
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Old 04-08-2011, 10:10 AM   #8
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Re: Throttle return spring poll

use silicone hair elastic. cheap, last a while. i lost my t linkage once and without the spring it would have been bad.
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Old 04-08-2011, 02:06 PM   #9
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Thumbs up Re: Throttle return spring poll

I say unclip the spring and leave it on. make sure it can not bind, bend the clip a little if you need to..I concur with Jeffs points.

As for failsafe, run an opto kill or my current preference an IBEC. And theory on
radio fail safe...only good if you loose signal and there is nothing wrong with your throttle servo ! I had a throttle servo fail OPEN, I used my IBEC to kill the ignition and landed. No spring could have forced the carb closed the servo totally locked up. I was using a JR821, I know of others doing the same without an issue...never again for me ! Now my choice is a HS7985MG or HS985MG...not for torque but decent centering, speed and robust gear train at 6v. If and when the metal gears wear I will worry about it then.
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Old 04-08-2011, 02:37 PM   #10
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Re: Throttle return spring poll

I just unhook the little spring and leave it there, behind the throttle arm (so worrys about butterfly vibrating) and I use a TX operated Optical Kill Switch for safety (but have never needed it).

as for using the return spring for a fail safe, what do you use on a glow engine?

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