Mailing List flyrotary@lancaironline.net Message #65239
From: Stephen Izett stephen.izett@gmail.com <flyrotary@lancaironline.net>
Subject: Re: [FlyRotary] Re: EC2 Mixture Pot Failure Modes
Date: Wed, 18 Sep 2019 06:48:07 +0800
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
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:
>
> 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
>
> Hi there guys.
>
> 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.
>
> 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
>
> --
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