Further to my earlier posting. Thanks to all those who responded. I found
Bob's earth block last night but unfortunately I don't have time to wait for
one from the States. It is exactly what I want and I think I'll have to make
one. Unless someone knows of a UK source for some similar item.
For all those who kindly took the time what I have done re earths is this:
Wire from the battery to a 5mm brass bolt on the fire wall ( my fire wall is
carbon fibre ) then all heavy loads back to this ( ie Gyro, Trim motor, Flap
motor ) Light loads to a buzz bar earth ( If I can find or make one ) on the
panel to a heavy lead back to the fire wall bolt. If I get any noise on the
radio or intercom then I'll move them back to the fire wall as well.
The earth point is only a few inches from the regulator and I have just one
22000 mF capacitor for the time being. I'll try adding the second if I get
any noise coming down the line.
regards
Jerry
Flying Hi - Wish I was
jerry@flyinghi.demon.co.uk
http://www.avnet.co.uk/touchdown
-----Original Message-----
From: Dave Simpson <Dave_Simpson@londonweb.net>
<europa@avnet.co.uk>
Date: 10 January 1999 19:23
Subject: Re: Electric earthing
>Jerry,
>
>Although I haven't done my electrical work yet, I have a plan. For what
>it's worth:
>
>Simple electrical earths, ie. those which serve only as the return (-ve)
>line for electrical consumers, could be attached to a ground strip, bus bar
>or single (big( terminal) more or
>less anywhere - the bulhead is a convenient place. However the proper
>grounding
>of electrical screens to attenuate Radio Frequency Interference (RFI) is
>another matter.
>
>The inductance of even a few feet of thin wire presents high impedances to
>very high frequencies; that is to say long wires cannot effectively work as
>screen grounding lines if they are very long. So if you want to, say,
>screen HT leads, or other ignition lines which carry high frequency (HF)
>components and/or high voltages, (and it's always best to try to screen
>noise at source rather than at the receiving end) you must ground each
>screen as near to one of its ends as possible. Classic, lay theory, says
>you should not ground a screen at both of its ends for fear of generating a
>ground loop. ie. a circulating current passing through the screen which
>itself induces unwanted RFI on to the signal lines it contains. However,
>almost as often as not, you can achieve best results by doing just that -
>terminating screens at both ends. This tends to be the case where the lead
>is long. Eliminating electrical noise is a bit of a black art.
>
>I admit that on composite aircraft with no metal airframe, to which we can
>connect screens locally, all this is a bit academic. But we can achieve
>good quiet radio and intercom installations with a little care. Virtually
>all the electrical noise comes from the engine, some radiated from spark
>plug and ignition system leads and some from the Rotax rectifier/regulator
>(which generates its own HF and RFI) - this latter can be both radiated and
>transmitted along the lines. Make your -ve terminal as near to the
>regulator/rectifier as possible and connect there two capacitors: a large
>electrolytic, say 2,200mfd and a second non-electrolytic in parallel, value
>say 0.1mfd.
>
>Certainly on the Rotax (and Robin) 2 strokes the ignition switch lines
>carry noisy signals and act as transmitting antennas. I'm not sure if this
>is the case with the 912 but if so, then it would be wise to screen these
>lines too; particularly since they run behind the firewall into the panel.
>(I've just remembered that there is a Rotax bulletin on this demanding that
>they be screened; this after someone flew over a microwave transmitter in a
>Katana and the engine missed once due to interference with the electronic
>ignition system).
>
>I'm currently operating a Pelican (Canadian kit plane) with a 912, and
>there is some radio interference. I would like to try grounding one side
>of the alternator output which is currently floating, and carry this ground
>through to the engine, dc -ve and screens' earth point. Has anyone out
>there tried this?
>
>I've seen some stuff from Bob Nuckolls (Aeroelectric Connection) which is
>sound; you may like to ask his advice.
>
>Dave Simpson
>
>
>----------
>> From: Jerry <jerry@flyinghi.demon.co.uk>
>> Subject: Electric earthing
>> Date: 10 January 1999 14:02
>>
>> I am interested to know what people have done with their earth wires? I
>have
>> so many it would be difficult to put them all on one bolt on the fire
>wall
>> plus if I have to take one off I could have to take them all off. Has any
>> body used fast-on crimps and some sort of earthing strip?
>>
>> I wait in anticipation.
>>
>> Jerry
>>
>>
>> Flying Hi - Wish I was
>> jerry@flyinghi.demon.co.uk
>>
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