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Thread: Key Ignition vs. Toggle Switches

  1. #11
    Senior Member jiott's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    I am still wondering about the Kitfox supplied ignition switch in their catalog as a asked a little ways back in this thread. It doesn't give any specs. I keep hoping John McBean will reply about it. Also wondering what Kitfox uses in their SLSA?

    Jim

  2. #12
    Senior Member av8rps's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    I have two friends with Just Aircraft 912s powered Highlanders that had rough running engines that NOTHING fixed. Finally Brian from Leading Edge told one of them to get rid of that ACS switch, and like magic, the problem was cured. So my other friend did the same to his Highlander, and saw the same result.

    Ironically, I purchased a Highlander last year that has a little over 200 hours on it, and it runs much rougher than does the 912ul in my Kitfox. I initially blew it off as probably being caused by my 2 blade sensenich prop, but after trying a Warp on it I got the same roughness. I haven't replaced the ACS switch yet with toggle switches, but will be doing so as my next step. Both of my buddies are insistent that is the thing to do since it did so much for their 912's.

    Oh, and both of them use the ACS switch for operating the starter. They've just eliminated the mag leads from the R and L positions and replaced them with high quality toggle switches.

    I can understand where an electrical engineer might not agree with the voltage statement discussed earlier in this thread. I could be wrong, but I think the problem with the ACS switch is a poor quality contact causing intermittent contact for the mags, essentially causing an erratic on-off-on-off situation for the mags (and therefore rough running engines too). I wouldn't think that would be any too good for these rather sensitve (and did I mention EXPENSIVE) 912 electronic ignition boxes.

    So John and Larry, I think you are both right
    Last edited by av8rps; 04-17-2012 at 05:27 PM.

  3. #13
    Senior Member jdmcbean's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    OK.. I tried staying out of this one.

    We (Kitfox) and I personally have years and decades of OPERATIONAL use of the key switch. Any switch can and has failed, be it a toggle switch or a key switch. The wiring and or connector that is used is most likely the issue.

    Our S-LSA aircraft use this same switch without issue and one of them is operating in a training environment with over 1400 hours in the last 2 years. Along with 1000's of other aircraft including ours personally.
    I recently changed our aircraft to using toggles and a push button start because I like that setup not for any other reason.

    Specifically, regardless of the style of switch the Rotax "mag" is simply going to ground. If it grounds it's off.. if it doesn't it's hot. The switch specs required according to Rotax are Min 250V .5A which the ACS switch meets.

    While I personally consider LEAF and Lockwood professionals and I'm sure they have seen switch failures. I would challenge them or anyone regarding this issue. While anything can happen, it is unlikely that a switched "mag" wire to ground is going to cause a module failure.

    I suspect that some may have had switch failures.. while others may have had a wire or connector issue (more likely).

    On that note: We are looking at other alternatives... the ACS keyswitch is simply expensive.
    Last edited by jdmcbean; 04-17-2012 at 07:34 PM.
    John McBean
    www.kitfoxaircraft.com
    208.337.5111

    "The Sky is not the Limit... It's a Playground"

  4. #14
    Senior Member Slyfox's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    good response John. I have the same thing. throw switches for the mag. there is no way I would do differently. allows me to turn the engine over with mags off. Good for many things, like getting oil pressure after oil change, making sure there is good oil pressure before the start, getting a good choke before first start. I have a key switch for starting and that switch is from 95. If that goes out I will do the push button. I have that setup on the RV and love it.

  5. #15
    Senior Member jiott's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    Could someone post a simple wiring sketch for the setup with toggle for mags and keyswitch for starting. This is probably a dumb question, but I am not very confident in electrical issues and need to start learning real soon since my panel build is coming up.

    Jim

  6. #16
    Senior Member Dorsal's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    Whether you use the key for starting with switches for the mags or use the key for the mags and a push button for starting I do like having a key (that can be removed) somewhere in the system. As others have said I also like being able to turn the engine over with the mags off so I can use the Slyfox starting method among other things.
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  7. #17
    Senior Member cap01's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    I don't have a picture handy but the rotax installation manual has all the diagrahams you'll need also specs for wire and switches . Only the wire sizes are in mm not awg .
    chuck
    kitfox IV 1050
    912ul warpdrive
    flying B , yelm, wa

  8. #18
    Senior Member jtpitkin06's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    The discussion of the ACS switch with other engineers put me in contact with an owner of a homebuilt (not a Kitfox) with a Rotax 912. He had experienced an ignition switch failure and replaced it with toggles. Did he still have the bad ACS switch?

    Yes! was the answer.

    Great! Let’s have a look inside to see what happened.

    The first picture is of the switch as removed. It is an ACS products A-510-2 manufactured on Jan 31, 2001. It has off-right-left-both-start positions.

    Upon opening the switch we found a burned contact. But the evidence shows the contact was burned from arcing in the start circuit, not from the ignition grounding circuit.

    The next two photos show the burned contact on the rotor and the switch plate.

    Seeing the location of the burn in the start circuit I suspected emf surge may be the culprit. I asked, “Do you have a diode across the starter solenoid?”

    “A what?” was the reply.

    A diode across the start solenoid prevents a surge of current from the starter solenoid (relay) from racing backwards through your electrical system. A diode is like a check valve. When the starter switch is activated the electrical energy goes through the coil inside the solenoid creating a magnetic field. The magnetic field closes the high current contacts for the start motor. When you release the start switch the magnetic field in the solenoid collapses and stored electrical energy races backwards toward the switch. (If this sounds familiar, it is how an automotive ignition coil works.)
    A diode allows the stored energy to bleed off harmlessly instead of frying your starter switch.

    Without the diode the reverse current enters the start switch and jumps across a gap to the ground terminal creating an arc and burning the points. This is the same surge that loves to fry your radios on engine starting. Your instructor did teach you to have the radios off when starting, right?

    So how does this affect the ignition?

    The design of the ACS switch uses 3 sliding contacts for multiple functions.

    In the start position one slider connects the battery to the starter relay. That same slider is used for grounding the right mag when left mag is selected and it grounds the right mag differently when off is selected.

    Due to the construction, the burned contact cannot cause an inadvertent grounding of the mags to off, but it can cause a failure to shut the ignition off leaving the right ignition hot. This type of failure would show no mag drop when selecting left mag during a test. It is also possible the engine would still shut off normally because the slider uses different contact points when off is selected. It is important to remember the switch does not turn the ignition on. It can only turn it off by grounding.

    There are several possibilities for those wishing to improve on the system.
    First is to ensure you have a diode across the start relay. Be sure to hook it up with “reverse bias” Positive to negative and negative to positive. Put the end with the stripe on the positive terminal. A Radio Shack diode 1N4001 with a 1 Watt rating works well.

    If you have a diode installed and everything works fine, you may wish do nothing and fly with the standard mag switch happily ever after; or,

    You may chose to replace the ignition/starter switch to a keyed switch without the start function and use a separate starter button. This option allows engine cranking without the ignition; or,

    You may retrofit to separate toggle switches for ignition and use a keyed automotive/marine type switch for just the starter. This option also allows engine cranking without the ignition while you still have a key; or,

    Eliminate any key switch in the system and just go with toggles for ignition and spring switches or pushbutton for start.

    Something for everyone.

    This post is a bit long, so… whether you want to flame me or send kudos, (I don’t care which,) please don’t quote the entire message. Trim the post and just quote the part that makes you bubbly happy or boiling mad.

    Regards,
    John Pitkin
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  9. #19
    Senior Member Dorsal's Avatar
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    Default Re: Key Ignition vs. Toggle Switches

    Makes sense to me
    Dorsal ~~^~~
    Series 7 - Tri-Gear
    912 ULS Warp Drive

  10. #20

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    Default Re: Key Ignition vs. Toggle Switches

    Good stuff, John. I built my RV-4 with toggles and a pushbutton (and a diode), figuring that a motivated thief could easily get past the key switch anyway. It occurs to me now that the propellor of an unattended plane with only a pushbutton poses a potentially lethal risk should some bonehead reach in and start pushing buttons. I know it's unlikely, but if some idiot accidentally chops his friend to bits with my prop I know exactly who'll get sued . I think this build will have a keyed switch somewhere in the system.

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