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Throttle springs with less tension.

in General Tech Discussion 13 years ago
This is from a guy who understands that this issue is one of personal preference, however I would really like an option to have less strong springs on the carburetors. It seems to me it could be possible to have weaker springs that would still have sufficient tension to achieve the safety factor of having the carbs go to full throttle in case of a cable break. I fly a Van's RV-12 with the 912ULS, and I am aware of other owners with the same issue.

It would be nice if Rotax offerred an alternative spring of less tension, but lacking that, has anyone located a source for good quality springs of the correct length, tension, and hook configuration?

  • Re: Throttle springs with less tension.

    by » 13 years ago

    Hi John,

    Why do you feel these springs are too much? Do they seem to over come your throttle setup? They need to make these springs to overcome any cable or throttle linkage problems and to work with all throttle configurations. Your throttle setup shouldn't have any issues with these springs if setup properly and with the correct throttle friction. I happen to have a Flight Design Ct and our throttle has nothing to hold it in the proper place other than a friction setting so our throttle is free to move. The springs work fine and the throttle is nice an easy to move and if adjusted properly doesn't move.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
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  • Re: Throttle springs with less tension.

    by » 13 years ago

    The throttle cables on the RV-12 are quite short and have little friction. My throttle creeps forward unless I crank the friction so tight the throttle can't be moved at all. I think springs with about half the tension would still have the desired safety effect, and provide a much more controllable throttle.
      
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  • Re: Throttle springs with less tension.

    by » 13 years ago

    I have a similar problem on my Eurostar where the throttle friction has to be set incredibly tight to prevent the throttle from creeping. I remember reading an accident report where an owner crashed his new plane when it did not respond to sudden full power on a go-around. It transpired that he had changed the throttle springs to weaker ones and they had not managed to pull the throttles open when needed :-(

    I have been very reluctant to touch these springs and in fact in the UK to do so would count as a modification and would require approval.

    Bear in mind that if you have a non-solid inner to your throttle cable then if anything goes wrong with either of your springs then you have BIG trouble.
      
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  • Re: Throttle springs with less tension.

    by » 13 years ago

    The correct way to handle the throttle/spring issue is leave the springs alone as there is nothing wrong with them. Fix the throttle problem. You may need to install a new throttle, but replacing the springs is subverting the real issue.

    Roger Lee
    LSRM-A & Rotax Instructor & Rotax IRC
    Tucson, AZ Ryan Airfield (KRYN)
    520-349-7056 Cell

      
    Report

  • Re: Throttle springs with less tension.

    by » 13 years ago

    Kevin,

    Yeah, I have read that report also, and that is why I am reluctant to make my own "mod". Not sure what you mean by "non-solid inner." The cable supplied with the kit is a double cable coming out of the control knob. The inner cable on each side is a stranded wire, and it seems very substantial. Having flown certificated airplanes for years, I am having a hard time trying to adjust to the throttle being pulled out of my hand, and not being able to lock it down so it doesn't creep with a reasonable amount of force.

    Roger,

    I'm afraid if I was to order a new cable from Van's, it wouldn't make a difference. I think it is a design issue, not a defect or wear issue.

    I understand the fail-safe intention of the design, but why do those springs have to be that strong? It seems logical that a weaker spring would work just as well if the cable broke, but would allow a finer/smoother adjustment of the throttle, and would not overpower the throttle friction control.

    Apparently I am in the minority on this issue, since I only hear a few others complaining about it! So, ultimately, I will probably just have to stop whining and hold on to the throttle knob harder.

    John
      
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