Kitfox Aircraft Stick and Rudder Stein Air Grove Aircraft TCW Technologies Dynon Avionics AeroLED MGL Avionics Leading Edge Airfoils Desser EarthX Batteries Garmin G3X Touch
Results 1 to 9 of 9

Thread: 912 throttle cable connection

  1. #1
    Senior Member
    Join Date
    Apr 2010
    Location
    Bryan, Texas
    Posts
    558

    Default 912 throttle cable connection

    I am second guessing my throttle connection and wanted to see how others have done theirs. I have the dual throttle friction control. I ran the cables to the drilled pin looking thing that goes through the throttle lever on the carbs. A set screw then pinches the cable to keep it in place. Is there something else to this? It seems that if this set screw let loose, the engine goes to full RPM and this could be a real problem. I did locate a post about the bell crank type throttle problem but I think this is a different set up. Is there a secondary set screw type lock that I could add or what about bending the cable back around and safety wiring it to itself so even if the set screw comes loose, there is basically a loop holding onto this pin. I hope this makes sense. I fast glanced the manual and didn't see anything on this. Thanks.

  2. #2
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,562

    Default Re: 912 throttle cable connection

    Jerry, the "screw" uses an elastic nut so if properly tightened should never come loose. The full throttle "safety" springs were removed from my carbs so that is not a possibility on my 912S. Don't like the idea of them , never have. Going to full throttle in the air might not be so problematic but on the ground not so good. Visions of chopped up multi-million dollar business jets fill my mind.


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  3. #3
    Senior Member
    Join Date
    Apr 2010
    Location
    Bryan, Texas
    Posts
    558

    Default Re: 912 throttle cable connection

    I guess I am not seeing the elastic nut? I am going back together with what I got with the unfinished kit that was already put together once. What I have looks like a pin that the cable goes through. The end of the pin is drilled and threaded. There is a set screw that contacts the cable as it runs though the hole in the pin. I wonder now if I have the correct setup? I also did find some bushings that fit the throttle lever but they don't fit the pin so I am not sure if they came form this project or one of the three other project parts that got mixed in when I bought it. I'll try and get pics tonight. I too wonder about the full throttle thing. I have to really make a concious effort to hold the throttle when running the engine and make sure that the friction nut is holding good when I let go or else it was really speed up.

  4. #4
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: 912 throttle cable connection

    Hi Jerry,

    I pondered the same question you are entertaining.

    Our installation uses the vernier throttle cable, the connector does have the nylon insert (elastic) stop nut; and, we have retained the throttle springs. But there has been a modification to our aircraft from plan I will explain.

    I considered two issues with this.

    1) The use of a nylon insert (elastic) nut under the cowl where engine heat is a factor is counter to generally accepted repair practices (AC43.XX) where the standard is to use a metal crimp nut, not a nylon insert (elastic) nut under the cowl - save the elastic ones for places not subject to heat and not subject to torque. Having said that - there are a lot of aircraft out there with this basic configuration - and I have not heard that this is a common failure.

    2) There is no redundancy to retain the throttler cable if the single clamp fails. Again, there are a lot of aircraft out there with this basic configuration - and I have not heard that this is a common failure.

    So, what did to do? Once the basic installation was set - I made sure there was some additional cable core sticking out past the single clamp; then, fabricated a small collar with a pointed set screw to serve as a redundant retainer - a person needs to leave a small distance between the original clamp and secondary clamp to prevent binding as the throttle arm swings - an 1/8 of an inch will do it with a small diameter secondary collar/clamp.

    If I recall - this has been referred to as a retaining "bug" by some - Also - I have some vague recollection that someone posted that a person could get a ready made "bug" from a hobby R/C store.

    I think the question boils down to what is a relatively better or worse situation in failure mode - engine to idle, engine to full throttle or somewhere in between. For the Rotax with two carbs - the possibility of an entirely syncronous failure on both sides at once is right up there with santa clause delivering THE winning lottery ticket to one of us. My estimate of a real life failure would be to lose the throttle control on one carb but not the other - That begs the question that it might be worthwhile to consider an emergency procedure to deal with the possibility. With the throttle spring in place - a person would have 4 choices to work with - a) predictable full power - b) between full and half power by regulating the connected carb and putting up with the vibration; c)killing one mag to reduce power on both sides d) killing the ignition and gliding to a landing with the possibility of restart along the way if needed.

    Also - throttle linkage can be a preflight checklist item.

    Sincerely,

    Dave S
    KF7 Trigear

  5. #5
    rcsfca's Avatar
    Join Date
    May 2009
    Location
    Lafayette, CA
    Posts
    31

    Default Re: 912 throttle cable connection

    Please take the time to click through to the post (below) I wrote in May of 2009 after my cable-style throttle came apart on me while on the ground. The carb springs were in place and put the plane at full throttle. As Desert Fox mentioned, this kind of situation is bad news when it happens on the ground, and it definitely was bad news.

    Runaway plane - serious mishap - throttle cable


    Rich C.
    Model IV - 1200 / 912

  6. #6
    Senior Member Dave S's Avatar
    Join Date
    Oct 2008
    Location
    St Paul, MN
    Posts
    1,833

    Default Re: 912 throttle cable connection

    Rich,

    My apologies if I did not consider the bell crank design - my comments were only considering the dual cable design - I can see that the bell crank design is a whole different deal which can affect both sides silmultaneously.
    It sounds like the redundant safety on the bell crank design is absolutely essential and the springs present a bigger risk if there is a failure.

    Sincerely,

    Dave S

  7. #7
    Senior Member
    Join Date
    Apr 2010
    Location
    Bryan, Texas
    Posts
    558

    Default Re: 912 throttle cable connection

    Bing carb throttle 1.jpg

    Bing carb throttle 2.jpg

    Here are some pics I took. I like the suggestion of the "bug" in addition to the main "pin" or threaded "barrel" as I have also find it called that. I believe I will use some thread locker on the set screw and also put a 90 degree bent in the cable after the "bug". I think two redundants should do the trick. Thanks for the comments and suggestions.

  8. #8
    Administrator DesertFox4's Avatar
    Join Date
    Aug 2008
    Location
    Arizona
    Posts
    3,562

    Default Re: 912 throttle cable connection

    Jerrytex, your set up looks slightly different from mine. I'll try to get a photo next time out to the hangar. Might be a few days as rain/snow is moving into the Phoenix area for a few days. Snow??


    DesertFox4
    Admin.
    7 Super Sport
    912 ULS Tri-gear


  9. #9
    Senior Member SkySteve's Avatar
    Join Date
    Jun 2008
    Location
    Huntsville, UT
    Posts
    1,054

    Red face Re: 912 throttle cable connection

    Desert Fox 4, DO NOT say the "snow" word as I am sitting at PHX right now waiting for Salt Lake City to plow the s--w off the runway so I can go home. Waiting, waiting. Oh, sorry. Got a little off subject there.
    Steve Wilson
    Huntsville, UT
    Kitfox 85DD
    912A / 3 Blade Taper Tip Warp Drive
    Convertible Nosewheel & Tailwheel
    SkySteve's SPOT Page
    SkySteve's You Tube Videos

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •