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Message-ID: <4B0C524B.4080605@gmail.com>
Date: Tue, 24 Nov 2009 16:38:19 -0500
From: Steve Brooks <cozy4pilot@gmail.com>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: No start
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Jeff,
In my case, which is a pusher, my aft battery sits just inside the 
firewall on top of the wing spar. I have #10 wires that connect from the 
batery terminals to feed the power and fround buss for the fuel puels, 
coils, fuel injectors, EC-2, etc. I have two 1/0 AWG cables that also 
connect to the battery terminals. The positive runs back tot he starter, 
and is about 6 feet long. The negative did run to one of the tapped 
holes for the A/C compressor on the front engine housing. The ground is 
about 4 ft long currently. I am going to remove that cable and run the 
ground from the battery to one of the starter mounting bolts, which will 
also make it about 6 ft long.

I also find it hard to believe that given all of the bolts in the 
mounting plate, and the torsion bolts through the engine, that it 
wouldn't be a really good conductor, but I would apparently be mistaken. 
I am not exactly clear on how it interferrs with the CAS signal, but it 
does. My ground was mounted just below the CAS about 8 inches, so 
perhaps that has something to do with it. It works fine there though for 
several years, before I started having difficulty starting the engine.


Regards,
Steve Brooks
Cozy MKIV
Turbo rotary

Jeff Whaley wrote:
>
> Good point on the anodizing Tracy; also a .005” layer of silicone 
> isn’t conductive either, even with bare aluminum – conduction is made 
> through the bolts and not the entire mating surface of the plate. The 
> math checks out too. I’m still curious about their specific setups 
> though; I can see how a stack of aluminum/iron/aluminum, etc with a 
> layer of hylomar in between each stack might not be the best conductor 
> – the sub-mount plate has to help.
>
> In my setup the battery is behind the cabin for weight and balance 
> considerations. Ground is made to a steel tube frame with about 1 foot 
> of #1 welding cable; Positive runs through Master relay under the 
> floor to firewall with about 6 feet of same #1 welding cable, then 
> another 2.5 feet to starter. The engine ground is via stainless braid 
> from front iron to engine mount hardware at the firewall/airframe. So 
> if the starter current path is from post to post on the battery, then 
> in my case it has to be close to 16 feet! I’ve never had any starting 
> problems, but it would be interesting to see if an extra ground strap 
> from starter bracket back to the airframe makes the starter spin 
> faster or engine fire sooner … will test that and post results.
>
> Jeff
>
> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] 
> *On Behalf Of *Tracy Crook
> *Sent:* Tuesday, November 24, 2009 9:43 AM
> *To:* Rotary motors in aircraft
> *Subject:* [FlyRotary] Re: No start
>
> I doubt anodizing is a factor. Keep in mind that the starter we use is 
> a light duty one but its rating is 1.2 KW. With a typical cranking 
> voltage of 10 volts, that's 120 amps. With that kind of current, the 
> only logical routing of the ground cable is as directly to the load as 
> possible.
>
> Do the math. At that current level, it only takes about .008 ohms to 
> drop your working voltage a full 1 volt. That's 10% of your cranking 
> power lost. Rotaries are especially sensitive to cranking speed 
> because they lose more compression than piston engines at low speed. 
> Low compression makes starting more difficult. Losses in this circuit 
> must be minimized for many reasons. Also note that the ground 
> connection point that many have said they are using goes very near the 
> crank sensor and its wiring. This proximity makes inductive coupling 
> into the CAS circuit more likely.
>
> Add all these factors up and it is not surprising that many builders 
> have starting problems.
>
> Tracy
>
> On Tue, Nov 24, 2009 at 8:52 AM, Jeff Whaley <jwhaley@datacast.com 
> <mailto:jwhaley@datacast.com>> wrote:
>
> I’m curious about the engine mount style you guys are using with this 
> voltage drop situation.
>
> I can’t imagine this problem occurring with the bed-mount/aluminum 
> plate between the oil pan and engine block configuration.
>
> Surely a 3/8” or ½” plate of aluminum and 20 bolts will conduct from 
> housing to housing? - unless maybe it was anodized?
>
> Jeff
>
> *From:* Rotary motors in aircraft [mailto:flyrotary@lancaironline.net 
> <mailto:flyrotary@lancaironline.net>] *On Behalf Of *Mark Steitle
> *Sent:* Monday, November 23, 2009 4:41 PM
> *To:* Rotary motors in aircraft
> *Subject:* [FlyRotary] Re: No start
>
> Steve,
>
> Glad you got things figured out (we were running out of suggestions). 
> Sure gives one a good feeling after battling a problem for so long. 
> BTW, I have two grounds on my engine. One is to the front cover, one 
> to the front side housing. I'll check into moving one up to the starter.
>
> Mark
>
> On Mon, Nov 23, 2009 at 3:33 PM, Steve Brooks <cozy4pilot@gmail.com 
> <mailto:cozy4pilot@gmail.com>> wrote:
>
> Al & Mark,
> I would say that many people may have their ground to the engine 
> block. Mine has been that way since I built the plane, and worked fine 
> for three or four years before I started having an issue.
>
> I had to order a couple of new crimp connectors, so that I can make a 
> longer ground cable. Hopefully they will arrive before Thanksgiving, 
> so that I can get it all hooked up over the long weekend.
>
> Steve Brooks
>
>
> Al Gietzen wrote:
>
>
> Steve,
>
> I read your other post on what you discovered regarding your bad 
> ground. I wonder how many of us have our engine grounds tied to a bolt 
> near the front cover or end housing? (Mine does...)
>
> Mark S.
>
> Mine does as well – bolts to the front cover. I have never had a 
> starting issue, but I have followed this discussion with interest 
> because a couple of years ago I did a starting spark check and found 
> the sparks considerably weaker than the mode 8 (or whatever) check. I 
> just assumed it was due to the voltage drawdown when the starter was 
> running. Now it’s worth another look.
>
> I recall giving it some thought when doing the wiring (My EC/EM 
> manuals apparently predated Tracy recommended wiring diagram). I 
> concluded that the various things bolted to the engine, like the 
> manifolds, would provide good conduction paths regardless of the 
> sealing between layers – and the 20B has a couple more layers. Both my 
> intake and exhaust flanges are continuous and connect all the layers, 
> and there are other things making the connection to the front cover, 
> so this would be less of an issue compared to an installation having 
> separate flanges to each housing.
>
> Anyway, Steve; I’m glad you found the problem. And thanks; it’s a help 
> to the rotary community, and again proves the value of a list such as 
> this.
>
> Al G
>
>
>
> --
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