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Thread: Experimental cat pilots

  1. #11
    Stephen's Avatar
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    Default Re: Experimental cat pilots

    Quote Originally Posted by EddieFoy View Post
    Seen that before. The kicker is that you have to leave one conventional mag.
    I've had Electroair for a couple of years. It starts easy and runs smooth. My static rpm is up 50 plus. I see little value in dual electronic, my rpm drop when switching off my mechanical mag is usually around 20 rpm compared to 70 plus drop when switching off the Electroair. Electroair does the majority of the work.

    I saw no change in fuel flow rates. Leaned at 2450, in the winter I can get 8 GPH or lower. I don't do as well in warm weather. The rare trip to 10k my rates are higher because the throttle is open more.
    "You can only tie the record for flying low."

  2. #12
    EddieFoy's Avatar
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    Default Re: Experimental cat pilots

    Quote Originally Posted by Gilbert Pierce View Post
    Not really. Some Continental engines, C145 and O300 for example, stagger the mag timing of the top and bottom plugs by several degrees.
    Yes but a modern electronic ignition only needs one plug.

  3. #13
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    Default Re: Experimental cat pilots

    Quote Originally Posted by EddieFoy View Post
    I understand that, but in a perfect world, all plugs would fire at the same time.
    Let me rephrase this. A modern electronic ignition only needs one plug per cylinder. May fire multiple times per cycle though.

  4. #14
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    Default Re: Experimental cat pilots

    Lets just say you only need one plug but you will probably never see "one plug" on a certified electronic aircraft ignition system.

    It has everything to do with the regulations and nothing to do with performance. The FAA certification branch defines ignition controlling software as Class 1 and Class 2. Class 1 is FADEC, full authority digital engine control, which needs its redundancy to be in multiple channels of software and multiple power sources. Class 2 software is Limited authority, a stand alone system with its built in redundancy being a mechanical backup. Class 1 so far has proven to be to cost prohibitive as a modification to general aviation, and systems like TCM powerlink have not gained acceptance due to the minimal real world performance gains.

    Class 2 software systems like Electroair and LASAR are certified with a mechanical backup. Dual channels for the Electroair and a defaulting system in the LASAR. In theory the electronic portion can fire up to 45 degrees before top dead center. In truth it never does, most of the time it only advances about 2 degrees based on the timing map and the manifold pressure. Meanwhile the fixed backup portion is still firing and sparking away, kind of like the "waste spark system" in old Harley Davidson's.

    The real truth is on a magneto both plugs never fire the same. Its called "cam spread". One side of the cam is higher due to manufacturing tolerances and build up tolerances which causes the timing to spread 2 to 4 degrees from the magneto cam while at speed. In other words, you spend all that time timing the mag to 25 degrees BTDC # 1, have you ever rotated it to 25 degrees BTDC #2 and seen what the timing is after you set number 1? Wanna wager that it could fall in around as early as 23 or as late as 27 degrees. Cam spread is normal and acceptable in magnetos, but its the only redeeming benefit of the electronic ignition. It is what makes the engine so smooth, no magneto induced engine roughness due to cam spread.
    Last edited by Vagabondblues; 08-20-2016 at 08:36 PM.

  5. #15

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    Default Re: Experimental cat pilots

    Quote Originally Posted by Vagabondblues View Post
    It has everything to do with the regulations and nothing to do with performance.
    It does have a significant impact on performance. Two plugs gives you two separate flame fronts that spread out from each plug. That results in a shorter time to get all of the mixture burned. Shorter burn time gives an increase in performance (power and economy). The ideal engine would have an instantaneous burn of the entire mixture at TDC. In the real world you can't get that; the flame front takes time to consume the mixture. Hence the need to set ignition timing before TDC.

    A second benefit from the short burn time is reduced potential for detonation. By consuming the mixture faster there is less time for unburned mixture to spontaneously ignite. Dual spark plugs allows the engine manufacturer to use a higher compression ratio or more ignition timing without getting too close to the detonation limit.

    All of this is independent of what you use to generate the spark.

    Tim

  6. #16
    EddieFoy's Avatar
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    Default Re: Experimental cat pilots

    The new 3rd Gen Hemi uses two plugs per cylinder. Wonder if they fire simultaneously?

    Just getting rid of breaker points, cams, and distributors, would be a huge step..
    Last edited by EddieFoy; 08-21-2016 at 07:25 AM.

  7. #17
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    Default Re: Experimental cat pilots

    §33.37 Ignition system.

    Each spark ignition engine must have a dual ignition system with at least two spark plugs for each cylinder and two separate electric circuits with separate sources of electrical energy, or have an ignition system of equivalent in-flight reliability.



  8. #18

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    Default Re: Experimental cat pilots

    Quote Originally Posted by Vagabondblues View Post
    §33.37 Ignition system.

    Each spark ignition engine must have a dual ignition system with at least two spark plugs for each cylinder and two separate electric circuits with separate sources of electrical energy, or have an ignition system of equivalent in-flight reliability.
    Is this in response to my post?

    Tim

  9. #19
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    Default Re: Experimental cat pilots

    Quote Originally Posted by bluejeepdad View Post
    Is this in response to my post?

    Tim

    No. I was just posting to support my post in response to the post in context with modern electronic ignition needing only one plug.

  10. #20

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    Default Re: Experimental cat pilots

    OK, thanks.

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