From: "Jeff Whaley jwhaley@datacast.com" <flyrotary@lancaironline.net>
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To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Subject: RE: [FlyRotary] RE: EC2 Mixture Pot Failure Modes
Thread-Topic: [FlyRotary] RE: EC2 Mixture Pot Failure Modes
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Date: Tue, 17 Sep 2019 14:15:00 +0000
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Steve, this what-if scenario of the mixture pot failing is not something ev=
er discussed before.  What I can say based on experience with the EC2 is th=
at 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 a=
t 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 r=
esistor value can end up anywhere from an open circuit to a dead short.  An=
other possibility is the wiper mechanism can fail, leaving you without adju=
stment and stuck at whatever the last setting was  - if you're lucky it sho=
uld be near the middle and all will be okay.
Jeff=20

Hi there guys.

A friend of mine who is testing our Glasair has asked after the failure mod=
es 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 proble=
m for keeping the engine running effectively.
Not sure what a faulure of the pot to full lean and then selecting Coldstar=
t would yield as far as mixture, I imagine far too rich.

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.

Cheers

Steve Izett