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Thread: Cruise stop

  1. #1
    dplunkt's Avatar
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    Default Cruise stop

    My tri-pacer owners hand book says

    "A cruise stop in incorporated in the throttle mechanism of each Tri-Pacer. This stop is set to 75% of power at low altitudes under normal circumstances."

    It also says that the power is controlled by small spacers in the throttle friction lock and can be added or removed to adjust the power setting. How do I check, remove, or add these spacers if they are still there?

    Dan

  2. #2

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    (uhh, engine off) Pull your throttle all the way out ("idle"). Unscrew the friction nut and slide it back towards the knob end. You will see (IF you have an original Piper throttle cable assembly!) a shallow "ring" machined into the shaft. The friction lock should also contain inside it's bore what looks like a small, slit ferrule (like the ones used for standard plumbing compression fittings -only, steel- slanted on BOTH sides). This is your throttle stop. The "shims" are thin steel collars that you add or subtract as required, and are not either beveled on their edges, nor are they "split". If you wish to add or subtract these shims, you loosen the jam-nut that secures the throttle knob, and unscrew both from the shaft. This is also the only way you can see inside the friction nut to get a look at the ferrule. Remove as much parts-wise as you need (or, add). If you need to snake the ferrule out of the friction nut, you can make a ninety degree "pick" out of a short hunk of welding rod. Reassemble. Do a ground check. Once you figure out what exactly 75% power actually IS per your engine operator's manual graph, you pretty much don't need the throttle stop anymore anyway. The "cruise throttle stop" (once it is set and/or confirmed to be correct) only saves you about 30 seconds after you get stabilized anyway; What ta heck else do you have to do anyway, once you get to cruise altitude? Another "editorial comment" might be that MOST tachs don't read exactly correct...you should buy, beg, borrow (or "liberate") a strobe-type prop tach before you start out doing ANYTHING, so you aren't setting yourself up for changing something that isn't being indicated correctly anyway!

    The throttle "stop" doesn't really "stop" anything. There is a SLIGHT "detent" when the ferrule tries to cross over the "ring" cut into the shaft and unless your throttle works as smooth as silk (and most don't) you may not notice it anyway. 'Sides, it is VERY critical to the friction adjustment... set too loose, it doesn't seem to be noticeable. Too tight, and it doesn't seem to be noticeable. For my taste, it is too much rigmarole trying to get the throttle set up this way. On my own airplanes (when the groove in the throttle shaft is present) I just remove the "stop" stuff, then set my throttle up so that I can plant my fingernail in the shaft groove and when that "marker" touches the friction lock, there ya are...same setting. I do this by relocating the throttle clamp (for "rough" adjustments) and then tweak in the attach "bug" (fork) that is on the very end of the throttle cable with the 32 threads per inch, infinitely adjustable method. You should always be able to move the throttle if and when you need to, no matter how much you have the friction nut snugged. So it all gets down to having to look at your tach every now and again, anyway. So, what's the point?

    This was some kind of Advertising Department ploy perpetrated by the Sales Department based on their belief that the buying public might think it was something special. It has little actual real-world use. If you ever get yours working the way it should, you'll probably decide that it wasn't worth it... Where you might find the shims, or a new "ferrule", I cannot say. I got laughed out of a Piper Dealership (as much -or more- my own doing, as it was theirs) several decades ago when I asked if they still had a line on these parts. The "cruise throttle stop" was really pretty much a "Huh!?" right from the beginning. Something of a "non-event". I suppose that some people might swear by it as being the coolest thing since knobs on drawers. I pretty much set the throttle at the rpm I want, and then I check it regularly (for rpm drop) anyway. I'd rather get TWO Univair UN-throttle-stopped throttle cable assemblies than ONE with a cruise throttle stop, for the same amount of money. To me, that silky smooth operation is better, anyway (than an abused, never lubricated, kinked outer housing, and/or whacked like a pretzel slider when somebody that couldn't pat their head and rub their tummy always shoved DOWN and TO ONE SIDE every time he slammed it in instead of schliding it reverently in to the firewall). That's "just me".

  3. #3
    dplunkt's Avatar
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    Hi John, thanks for the explaination. I pretty much just want to get rid of it if the parts are there. I don't see any advantage, and some disadvantages, with the limitation. so now I know what to look for.

    Dan

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    Flyjeep's Avatar
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    Default Cruise stop and friction lock?

    I read in the poh about a cruise stop and was just wondering what it is and if my plane has it. Also the friction lock doesn't seem to be doing anything, but again it's all new to me so maybe I'm doing it wrong..
    Last edited by Flyjeep; 12-06-2018 at 10:29 AM.

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    tnowak's Avatar
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    Default Re: Throttle stop and friction lock?

    Usually the throttle stop is on the carb itself and adjustable (two small screws). They set the range of throttle movement with the idle setting being most important.
    With the throttle pulled all the way back you don't want 1000 RPM idle!
    Regarding the friction lock - most likely the throttle cable friction thingy (O ring?) has worn away. I have the same problem on a Luscombe I fly - no usuable friction...
    TonyN

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    Administrator Steve Pierce's Avatar
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    Default Re: Throttle stop and friction lock?

    Turning the serrated knob around the throttle knob at the panel should lock the throttle. If it doesn't work you might unscrew it all the way and have a look.

  7. #7
    Zac Weidner's Avatar
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    Default Re: Throttle stop and friction lock?

    The "throttle stop" you read about is likely the "cruise detent" or whatever you might call it. there's a little groove in the throttle shaft right where the friction lock is, and you can just barely feel it if you know where to look. Mine is set at around 2150, a nice low cruise setting for putting around and looking at things (crops, in my case). It can be adjusted a bit by adding or removing washers somewhere around where the throttle passes through the panel. I can't remember exactly where they are at the moment, but I think you have to unscrew the friction lock completely and remove the knob and check nut to adjust.

  8. #8
    Flyjeep's Avatar
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    Default Re: Throttle stop and friction lock?

    Quote Originally Posted by Steve Pierce View Post
    Turning the serrated knob around the throttle knob at the panel should lock the throttle. If it doesn't work you might unscrew it all the way and have a look.
    That's what I thought just wanted to make sure. I never flew with thIs kind of set up, I was trained in archers that have the lever.

  9. #9
    Flyjeep's Avatar
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    Default Re: Throttle stop and friction lock?

    Quote Originally Posted by Zac Weidner View Post
    The "throttle stop" you read about is likely the "cruise detent" or whatever you might call it. there's a little groove in the throttle shaft right where the friction lock is, and you can just barely feel it if you know where to look. Mine is set at around 2150, a nice low cruise setting for putting around and looking at things (crops, in my case). It can be adjusted a bit by adding or removing washers somewhere around where the throttle passes through the panel. I can't remember exactly where they are at the moment, but I think you have to unscrew the friction lock completely and remove the knob and check nut to adjust.
    OK now I know what to look for.

  10. #10
    Flyjeep's Avatar
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    Default Re: Throttle stop and friction lock?

    Quote Originally Posted by tnowak View Post
    Usually the throttle stop is on the carb itself and adjustable (two small screws). They set the range of throttle movement with the idle setting being most important.
    With the throttle pulled all the way back you don't want 1000 RPM idle!
    Regarding the friction lock - most likely the throttle cable friction thingy (O ring?) has worn away. I have the same problem on a Luscombe I fly - no usuable friction...
    TonyN
    Sorry I meant cruise stop. But thank you. I'll changed the post to cruise stop.
    Last edited by Flyjeep; 12-06-2018 at 10:30 AM.

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