From: "Stephen Izett stephen.izett@gmail.com" <flyrotary@lancaironline.net>
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Subject: Re: [FlyRotary] Re: EC2 Mixture Pot Failure Modes
Date: Wed, 18 Sep 2019 06:48:07 +0800
References: <list-12965949@logan.com>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
In-Reply-To: <list-12965949@logan.com>
Message-Id: <D62C20CA-5C8D-4ED9-AD2B-3BEA425BE05D@gmail.com>

Thanks Jeff
I think Tracy having selected a quality pot mitigates against failure, =
but all single point of failure components introduce risk.
I thought my test pilots question was a  good one for us to consider.
One of the contractions he flys is a twin jet CriCri whose throttle is a =
Bournes Pot.

Cheers

Steve Izett


> On 17 Sep 2019, at 10:15 pm, Jeff Whaley jwhaley@datacast.com =
<flyrotary@lancaironline.net> wrote:
>=20
> Steve, this what-if scenario of the mixture pot failing is not =
something ever discussed before.  What I can say based on experience =
with the EC2 is that IF the pot failed at full-lean and then Cold Start =
was selected that the outcome would likely be acceptable; on the other =
hand, IF the pot failed at full-rich the outcome would not be good.
> How can a potentiometer fail ?  Given that it is a resistor the most =
likely scenario is exposure to excessive current and again from =
experience, the resistor value can end up anywhere from an open circuit =
to a dead short.  Another possibility is the wiper mechanism can fail, =
leaving you without adjustment and stuck at whatever the last setting =
was  - if you're lucky it should be near the middle and all will be =
okay.
> Jeff=20
>=20
> Hi there guys.
>=20
> A friend of mine who is testing our Glasair has asked after the =
failure modes and consequences of the mixture pot on the EC2/3 =
controller.
> I'm figuring it would go full rich or full lean. Either being a real =
problem for keeping the engine running effectively.
> Not sure what a faulure of the pot to full lean and then selecting =
Coldstart would yield as far as mixture, I imagine far too rich.
>=20
> I take it Tracy used quality pots to mitigate this risk factor.
> Has anyone discussed this before?
> I'd like to be able to give my friend an answer.
>=20
> Cheers
>=20
> Steve Izett
>=20
> --
> Homepage:  http://www.flyrotary.com/
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