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Thread: Dual STI build log

  1. #241
    Senior Member rv9ralph's Avatar
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    Default Re: Dual STI build log

    I've also been reading about the recommended orientation of the master relay but am confused by the terminology used to describe it. The attached picture is the relay I'm using.
    For my own clarity, is it recommended to be mounted as shown in the picture, with the crimped on end pointing down?
    After seeing your picture of your firewall, with the contactor over the battery, and seeing this post. I think your contactor may be mounted inverted.

    Ralph

  2. #242
    Senior Member efwd's Avatar
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    Default Re: Dual STI build log

    Im fairly certain that it does not matter what side is up. I can't find my reference but I believe it even states that they are frequently mounted this way in aerobatic planes that are capable of pulling enough G forces to overcome the magnet.
    Eddie Forward
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  3. #243
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    Default Re: Dual STI build log

    I assume you are using a 'Star Ground' system and, for what it's worth (and only from book-read 'expertise' at that), I think your 'forest of tabs' copper plate should be isolated from the airframe and not connected to it (as it appears to be).

    As I understand it, the airframe should should be grounded to the battery only through the firewall pass-through bolt. I don't claim to understand it all but I think by having your copper plate in contact with the firewall you're opening up a pathway for stray wigglies to go to ground through that plate instead of a single point (the pass-through bolt) and then onto the battery -ve.

    Based on the reading I've done and, specifically the article below, I've 'designed' my ground system to look like the attachment. Yes, it is a blatant copy of the article's recommendation. I'll still use the same 'forrest of tabs' as you but instead of the bolt going through the copper plate and the firewall, I will have a wire from the isolated plate to the bolt which passes through, and is attached to, the firewall.

    Will that make any difference? I genuinely don't know but I just thought I would point out that someone who seems to know what they're about says we should isolate the ground bus from the airframe/firewall.

    The article:

    http://www.kitplanes.com/issues/31_7/builder_spotlight/positively_negative_21028-1.html


    My diagram may appear below, depending on whether I've managed to sort out these attachment things or not
    Attached Images Attached Images

  4. #244
    Senior Member Av8r_Sed's Avatar
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    Default Re: Dual STI build log

    Hey Dustin,
    I’m loving your build, it’s manificent. Everything you’ve laid out looks really well thought out.

    Minor detail, but based on another post yesterday, the relay (starter?) is recommended to be mounted with the crimped cap down. Looks like you can flip it with no issue.
    -- Paul S
    Model III SN910
    582 IVO Med

  5. #245
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    Default Re: Dual STI build log

    I had it mounted the other-way, but I was reviewing some photos of Nikks plane that I had. I noticed he had his mounted upside down. Trying to figure out why, then I looked at the wire routed and it made sense why it was upside down because the routing of the wire is more direct routing. Didn't think it matter on which way it was mounted??


    PaulSS I am defiantly not a electrical guy....did not seem that it mattered if it was grounded to the firewall or not? I figured the electricity would pass through the pass of least resistance which I figured is the pass-through? Scott turned me onto this passthrough, I will have to ask him if it matters as he has used these? (He is an electrical guy!)

    Dustin Dickerson

    Building 7ss STI x 2
    Oratex
    29" shock monster
    EP912STI 155hp
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    N33TF......FLYING!
    N53TF......FLYING!

  6. #246
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    Default Re: Dual STI build log

    To be honest I initially thought to set mine up exactly as you have. My thinking was why would they design a product which pretty obviously attaches to the firewall by the big bolt that goes through the copper plate. The only reason I mention isolating the plate is because of what I read in the article. Particularly:

    Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.

    As I say, I'm not an electrical expert and I'm 99% sure your set up would be absolutely snagless. I'm only passing on something I read


  7. #247
    Senior Member jrevens's Avatar
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    Default Re: Dual STI build log

    Quote Originally Posted by PaulSS View Post
    I assume you are using a 'Star Ground' system and, for what it's worth (and only from book-read 'expertise' at that), I think your 'forest of tabs' copper plate should be isolated from the airframe and not connected to it (as it appears to be).

    As I understand it, the airframe should should be grounded to the battery only through the firewall pass-through bolt. I don't claim to understand it all but I think by having your copper plate in contact with the firewall you're opening up a pathway for stray wigglies to go to ground through that plate instead of a single point (the pass-through bolt) and then onto the battery -ve.
    There is nothing wrong with using that “forest of tabs” just as is, directly mounted on the firewall. That is the way that Bob Nuckolls designed it to be installed. Literally hundreds, if not thousands, of homebuilts have used these (from B&C) in this way with no problems. Obviously, all connections should be clean & tight, and ideally sealed from air & moisture, just like all of the electrical connections.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  8. #248
    Senior Member jiott's Avatar
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    Default Re: Dual STI build log

    My ground cluster is mounted directly to the airframe with no problems. I believe that's what those two tabs are for that are welded to the upper angled tube behind the panel-I used them to mount a ground strip.
    Jim Ott
    Portland, OR
    Kitfox SS7 flying
    Rotax 912ULS

  9. #249
    Senior Member jrevens's Avatar
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    Default Re: Dual STI build log

    Quote Originally Posted by PaulSS View Post
    To be honest I initially thought to set mine up exactly as you have. My thinking was why would they design a product which pretty obviously attaches to the firewall by the big bolt that goes through the copper plate. The only reason I mention isolating the plate is because of what I read in the article. Particularly:

    Avionics Ground Bus—All other aircraft systems should be grounded through the avionics ground bus. This can be a "field of tabs" bus or simply a copper strip to accept ground wires from each of the systems. The avionics ground bus should not be grounded directly to the airframe. It should be locally isolated from the airframe with appropriate mounting. An 8 ga. wire should connect the avionics bus to the firewall pass-through bolt to complete the ground path.

    Just to clarify my response to this... the above quote is referencing the Avionics buss. It is recommended & common practice to run a wire from that main bolt on the forest of tabs directly to another ground point(s) on the instrument panel, for instance for the avionics, and not rely on airframe ground alone. I think that the forest of tabs would probably be more useful mounted so that the tabs are on the back side of the firewall, although some mount 2 "forests", both front & back so that you also have some easily accessed ground points in the engine compartment. There is no reason that I know of to isolate the forest of tabs with an insulator, and then connect it to the firewall/airframe with a wire (which is grounded to the firewall). "All other aircraft systems should be grounded through the avionics ground bus(sic)" is definitely incorrect, I believe. This is based on what I believe I've read by Bob Nuckolls, but as always I could be wrong, and I hope someone will correct me if so. It would be interesting to run this by Bob to get his take... I may do that.
    John Evens
    Arvada, CO
    Kitfox SS7 N27JE
    EAA Lifetime
    Chap. 43 honorary Lifetime

  10. #250
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    Default Re: Dual STI build log

    Hi John,

    The 'danger' of my quote is that it is taken slightly out of context. It is well worth reading the article in Kitplane that I posted a link to, in order to see what the author was saying in its entirety.

    The use of the 'avionics bus' term was to distinguish it between any other bus i.e. one that may have high current draw on it and should be a separate bus. I attach a picture from the article to (hopefully) better explain what I am blathering on about

    I would, of course, be extremely interested to know what Bob has to say.
    Attached Images Attached Images

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