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Ignition noise in Jabiru engine.

 
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nuckollsr(at)cox.net
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PostPosted: Thu Jan 18, 2007 8:31 am    Post subject: Ignition noise in Jabiru engine. Reply with quote

At 10:07 AM 1/18/2007 -0500, you wrote:

Quote:

<dleonar1(at)maine.rr.com>

RE: the noisy ignition Jabiru.
http://www.aircraftspruce.com/catalog/eppages/magnetofilter.php
My Viking / Continental/ Bendix mags was noisy unitil I installed these
capacitors in the P leads. Then it stopped. I really don't know enough
about it to explain the mechanics of this, but it definitely took the noise
out of the audio. I assume the Jabiru mags have a p- lead somewhere, is
there any kind of filter on it?

The way to confirm whether or not the p-leads are
contributing to the noise is to simply disconnect them
at the mags and run the engine. A wire that is NOT connected
cannot conduct or radiate noise.

If the noise goes away, then try wiring the mags as shown
in Figure Z-26 and Z-27. Note that shields for p-lead are
grounded to the ENGINE end only while the same shields
PROVIDE GROUND for the ignition switch.

If the noise comes back in spite of this treatment of shields,
then a p-lead filter is in order.
Quote:
I'm sure one of the geniuses ( my boss used to call us F*****g geniuses), on
this list can find you a $.97 Cap that will do the job, I'm ashamed to say I
paid $35.00 each for thes for my certified bird.

P-leads are connected across the magneto's timing
points which already has a high quality capacitor
tied across it. An on-purpose filter for the purpose
of attenuating noises conducted out of the mags on
p-leads would be a combination of inductance and some
SMALLER value of capacitance than what already exists
inside the mag. It's more than a $.97 capacitor.
Quote:
Are the Ignition wires shielded style? I was told by an avionics guy ( King
factory type years ago) that a small amount of extra resistance in an old
plug wire , or a bad shield will make it noisy as well.

Loss of shielding on a plug wire demonstrated to benefit
by shielding is a potential threat against electromagnetic
order. However, "resistances" in plug wires is another
matter. It was discovered over 70 years ago that much
radiated ignition noise from plug wires was a function of
the wire's efficiency as an antenna. Solid copper conductors
were much better radiators when circuit losses were low
a radio frequencies.

Predecessors to the modern EMC facility like the one
shown here . . .

http://www.aeroelectric.com/Pictures/Misc/Screen_Room_circa_1935.jpg

. . . were used to explore the effectiveness of various
noise mitigation techniques. It was discovered back then
that adding resistance in moderate amounts had little
effect on spark performance but a lot of effect in
killing the plug wire's efficiency as a radiator of
energy. Autolite, AC and others offered "resistor plugs"
with devices built into the assembly for the purpose of
reducing noise. Later, resistance wire replaced the
resistance plug . . . better to have the losses distributed
over the length of the wire as opposed to concentrated at
one end.

Bob . . .


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icubob(at)newnorth.net
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PostPosted: Thu Jan 18, 2007 7:32 pm    Post subject: Ignition noise in Jabiru engine. Reply with quote

bob,
let me talk thru this and see if i have it right as i have questions about
this. wires that ground the jab coils at the ignition switch are shielded.
this shielding is grounded at the engine end of the shielding . this
shielding is used at the ignition switch to ground the switch. the shield is
attached at the switch where you would attach a wire to ground the switch.
this shielding is providing the same ground to the switch as if the switch
had been attached to a negative ''forest of tabs''. have i got all this
right? thanks for yourhelp, bob noffs
---


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DonC



Joined: 18 Jan 2007
Posts: 1
Location: Western Aust

PostPosted: Thu Jan 18, 2007 10:30 pm    Post subject: Re: Ignition noise in Jabiru engine. Reply with quote

This is my first post here - I just had to add to the comments about Jab ignition interference. I have a factory built J230 and since new I have experienced interference when receiving anything but strong signals - no problem with transmissions , only reception.
I changed to resistor plugs and they made a slight difference. one thing I cannot understand is when receiving a weak station and I turn the right mag off the noise all but disappears and the signal doubles in strength!!
Turning off left mag makes no difference. I have swapped coils from side to side , checked dizzy caps and rotors , fitted new ht leads ,all to no avail. As a last resort I am considering sheilding upper and lower cowls with adhesive aluminium foil and electricly bonding them to the firewall. Any suggestions please?


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jetboy



Joined: 22 Jul 2006
Posts: 233

PostPosted: Sat Jan 20, 2007 1:32 am    Post subject: Re: Ignition noise in Jabiru engine. Reply with quote

You might like to check the thread at Yahoo

http://groups.yahoo.com/group/jabiruengines/message/16777

we have been testing inductive suppression HT leads and I have posted the radiated noise plots from the various types of HT leads in the files section.

Ralph


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N81JG(at)aol.com
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PostPosted: Sat Jan 20, 2007 10:35 am    Post subject: Ignition noise in Jabiru engine. Reply with quote

I have had an ignition noise problem in my VariEze composite (very susceptible since no metal frame to shield RF noise) plane since installing a CD ignition form Lightspeed Engineering in place of one of the mags. I tried the aluminum foil over the coil to plug leads grounded to the hex at the plugs with no effect. After consultation with Klaus Savier at Lightspeed I removed the foil and tightened the plug and coil clips and cleaned the contact surfaces. That made a big improvement with my radio reception coming through with only slight background plug firing noise. I am waiting for Klaus to ship a set of plug leads with better wire and clips that should be even better. Seems that any slight loose connection creates RF interference when the very high voltage (40,000 volts plus) jumps the connection. I will make sure the connections are tight and use a thin coat of dielectric grease (available at auto parts stores as a Permatex product) on the connections. Hope this will solve the problem. Be sure and check all your high voltage connections.

Good luck. I will report back if my changes work.

John Greaves
Redding, CA
VariEze N81JG
[quote][b]


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N81JG(at)aol.com
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PostPosted: Sat Jan 20, 2007 10:54 am    Post subject: Ignition noise in Jabiru engine. Reply with quote

Hi all,

I forgot to mention that my VariEze has an O235 Lycoming with the CD ignition and one mag. Didn't mean to confuse with the Jabiru, but ignition noise is similar source from HT plug or coil leads.

John Greaves
[quote][b]


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paul.r.kuntz(at)gmail.com
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PostPosted: Sat Jan 20, 2007 11:53 am    Post subject: Ignition noise in Jabiru engine. Reply with quote

Regarding dielectric grease -- the dielectric adjective denotes the fact that the grease does NOT conduct electricity. Its use for electric connections is to lubricate (which helps ensure that screw connections and sliding connections mate completely and achieve the full metal-to-metal contact desired), then after being displaced by the connecting process the grease keeps oxygen away and helps prevent corrosion that can eventually break down the connection. The dielectric (non-conducting) property also prevents the grease from forming a conductive pathway to adjacent circuits.

This isn't to say you shouldn't use it, particularly if Klaus recommends it. I'm not an expert on high-voltage applications, and Klaus has a lot of practical experience. Just trying to clarify and improve the underlying knowledge base.

Regards,
Paul Kuntz
Cozy MKIV and
Pipistrel Sinus 912 motorglider
http://www.pipistrelbuilders.com/
[quote] ---


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