Are dual spark plugs still needed?

Discussion in 'Firewall Forward / Props / Fuel system' started by Hot Wings, Aug 22, 2019.

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How necessare is dual ignition or dual spark plugs.

  1. 100% required. We all know that magnetos fail.

    3 vote(s)
    10.3%
  2. They are a very good idea because they help the engine be more effecient.

    10 vote(s)
    34.5%
  3. Dual ignition is required but not dual plugs. A back up ignition system is just as good.

    5 vote(s)
    17.2%
  4. Dual plugs are no longer needed with distributed COP style ignition systems.

    8 vote(s)
    27.6%
  5. Dual plugs are still needed with COP systems unless there is no single point failure mode.

    3 vote(s)
    10.3%
  6. Dual plugs lets me use both a magneto and an electronic ignition.

    7 vote(s)
    24.1%
Multiple votes are allowed.
  1. Aug 22, 2019 #1

    Hot Wings

    Hot Wings

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    There is a short old 2009 thread about dual ignitions but we can't tack a poll onto an existing thread so:

    I'd like to get some feed back about just how many think dual ignition is needed for aircraft use and why. Back when the 2009 thread was alive things like Coil On Plug or smart coils weren't very common. Maybe opinions have changed?
    My personal interest at the moment is with regard to a clean sheet head for the VW conversions, but lets not limit the responses or discussion to one specific engine?
     
  2. Aug 22, 2019 #2

    pictsidhe

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    I believe a big reason for dual plugs was lead fouling? With 100LL and mogas, that is now far less common.
    I would have given a yes and no answer. There are other systems that fall outside your options.

    Why not cast your heads with two bosses, and drill however many the customer wants?
     
  3. Aug 22, 2019 #3

    Wanttaja

    Wanttaja

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    Dual spark plugs, maybe not. Dual IGNITIONS, yes. Even the electronic ignition systems fail. I've got 38 accidents related to electronic ignitions/controllers in my 20-year database. What's also important for the electronic ignitions is to ensure the two systems have independent power sources.

    Ron Wanttaja
     
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  4. Aug 22, 2019 #4

    wsimpso1

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    In what type of engine? Traditional airplane engines? Automotive conversions?

    With what type of ignition? Magneto? Electronic with distributor? Electronic with waste spark? COP?

    The opinions will depend on which of the eight cases from the two questions above the writer is working from...
     
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  5. Aug 22, 2019 #5

    Dana

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    I have had three magneto failures. One complete, if I didn't have a second mag it would have resulted in a forced landing. One on the ground, single ignition, had to push the plane back to the hangar. One partial, also single mag, ran rough but got back home.
     
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  6. Aug 22, 2019 #6

    Pops

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    Never had a mag failure or problem. Did put new spark plugs in the Cherokee 140 and one quit firing about about 2 hrs.
     
  7. Aug 22, 2019 #7

    Hot Wings

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    The above is kind of what I'm interested in getting a feel for what the average HBA type thinks is the current best/cheapest option. Since most aircraft engines already come with dual I'm thinking this would apply more to conversions, be they automotive/marine/or motorcycle.

    I'd kind of like a general discussion rather than specific to my current doodling. But:

    On the VW due to the way they designed the cam (cheap/need to keep it up high for ground clearance) the pushrod tubes limit the options. Most of the current VW dual plug heads are asymmetrically positioned, Revemaster being an exception.

    By moving a few things around there is enough room to put a couple of 10mm thread plugs in a symmetrical position that is also good for flame propagation. There is actually enough room for a standard 14mm plug, but not enough room for the socket to get them out. :(

    Being a clean sheet casting, that is not bound by the constraints of a VW engine compartment, I've got a few options. ;)
    I'm not sure there is room for COP and still keep the cowling tight.......unless there are some really short ones that I haven't seen yet?
    Ordered one for a Nissan 200SX to measure.
     
  8. Aug 22, 2019 #8

    Vigilant1

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    Sorry, a little off topic.
    More fin area. Consider added heat sink pieces could clip on to your new heads. Slather some heat transfer paste on to the existing head fin tips, clip in the new pieces the friction fit onto all the fins at once, tighten down a few screws into pre-tapped holes to keep everything in place. Instant "fat fins". Probably not needed on the intake side of each cylinder.
     
  9. Aug 22, 2019 #9

    Pops

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    Picture of the single port head that I will be using. Drilled for 10mm lower spark plugs. There is room for a socket to install and remove between the pushrod tubes. See the flashing in the air passages that I need to clean out.
     

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  10. Aug 22, 2019 #10

    N804RV

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    I have a single Slick 4316 magneto on my Sonerai. For the last 180+ hours, I have flown it without a miss. All the spark plug show a nice healthy engine. This last annual inspection, I found some unusual wear on the phenolic spacer that goes between the magneto and the drive hub on the engine. It probably would have continued to run just fine, without any symptoms for hours to come. But, if it failed, it would be an instantaneous and total engine failure. This is why I do 25 hour inspections and very comprehensive annuals.

    I think, if you're just flying mostly local hops and are meticulous with your maintenance, you can get by with a single ignition. If you're doing long cross countries, carry passengers, or want something you can hop in and go, dual ignition is definitely a must!
     
  11. Aug 22, 2019 #11

    Hot Wings

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    That was the initial reason to consider a new casting. But mission creep has taken over :rolleyes::cool:
    The top center head stud nut washers are still in the same place and it uses VW Tp1 valves and guides but the rest is.....unique o_O
    They are probably going to be little more than Vaporware unless I trip over a bucket of time and money......or???
     
  12. Aug 23, 2019 #12

    rv6ejguy

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    Use a reliable, crank triggered EI and single plugs. No moving parts to wear out or fail. No maintenance, no failures in 430 hours on mine. I prefer coils mounted away from heat.

    I have some customers with over 2000 flight hours, EIs have never been touched.
     
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  13. Aug 23, 2019 #13

    pictsidhe

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    I had a car that had space for a 14mm plug and only a 10mm socket. yep, 10mm headed 14mm plugs.

    I had some BMW COP units that had a detachable extension. the actual COP was pretty short. Come up with a short extension and you'd have a fairly compact unit.

    [​IMG]
     
    Last edited: Aug 23, 2019
  14. Aug 23, 2019 #14

    TFF

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    It depends on size of engine and type of ignition. VW small piston area. Easy to get the flame front to all corners. A big Lycoming or bigger with 5-6-7” diameter piston, lots of real estate there. You can tell with mag drop checks. More timing the drop gets smaller. You can tell the performance loss though. You just have to decide on the compromises you like.
     
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  15. Aug 23, 2019 #15

    narfi

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    I have changed plenty of failed mags on aircraft engines, I have never had to change both at the same time due to failure.

    The whole point of redundancy isn't for parts that are working, but for when parts fail.

    So ask yourself, "If the part fails, can I still fly home?"
    If the answer is yes, then redundancy is less important, if the answer is no, then it seems pretty critical to me.
     
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  16. Aug 23, 2019 #16

    Daleandee

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    As others have noted, for a lot of various reasons ... it depends. My Corvair is dual ignition with single plugs. Both ignitions are in the modified distributor. One is EI the other is points. Each has a separate coil mounted away from the heat on the firewall. I have used iridium plugs the last couple of years but used to run stock AC and even ran Autolite plugs for a few months. I have never had a plug failure.

    Part of my comfort level is that I have six cylinders and losing a cylinder isn't quite the nightmare it would be on four cylinders. I haven't run this particular test on my plane that William explains here, but it is reported that the plane will not only maintain level flight on five cylinders but will also climb (I did test V-speeds during phase one). Here is some interesting reading from William Wynne about this:

    https://flycorvair.net/2016/12/22/c...knowing-roc5-rate-of-climb-on-five-cylinders/

    I use a mix of 100LL & mogas (90 oct E-Free) to help keep lead out of the engine. The iridium plugs looked great at condition inspection but for forty bucks a set I just replace them.

    Dale
    N319WF
     
    Last edited: Aug 23, 2019
  17. Aug 23, 2019 #17

    bmcj

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    Two build on what Ron and Narfi said, dual ignition YES, but aside from flame front propagation, you can get by with a single plug. If you lose a plug, you will still have three running cylinders that can help get you to a safe landing.
     
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  18. Aug 23, 2019 #18

    blane.c

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    I think for multi-engine designs a modern type single ignition is adequate as the additional engine(s) are your backup.
     
  19. Aug 23, 2019 #19

    Pops

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    You could have longer or shorter time to decide where you are going to crash.
     
  20. Aug 23, 2019 #20

    blane.c

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    I've had a lot of engine out time, in fact I used to tell my boss he had the only 3 1/2 engine airplanes in the world … 4 engines on the way out 3 engines on the way back averages 3 1/2.

    The thing is to make sure there is a sufficient amount of power on remaining engine(s) if you lose one then no problemo' of course if you go for marginal extra power maybe redundant ignition remains a good idea.
     
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