Is this experience with or without the Skydrive carb.heater? Which may help
to answer Carl's original question.
Don't forget that the heater works by warming the carb body so that ice
does not form on it (or is shed easily once it has formed?); the heater
does not significantly heat the air. This would not help much with keeping
the butterfly warm (and thus to prevent impact ice that had formed in the
venturi upstream accumulating on it). Its not clear which of these two
aspects your temperature sensor is monitoring (i.e. carb body or
airstream).
Does anyone know what the water flow rate is across the Skydrive heater (or
the pressure differential betwixt the two water tappings on the system)?
Duncan McF
On Tuesday, October 29, 2002 1:22 PM, Nigel Charles
[SMTP:72016.3721@compuserve.com] wrote:
> Message text written by McFadyean
> >Nigel Charles (?) also mentioned carb. temperatures he had measured.
> I would argue that the close proximity of the rear cylinder exhaust he
ader
> pipes (on the Classic, not the XS) provide a considerable amount of
> radiated heat to the body of the carb.<
>
> Whilst the aluminium used in the construction of the carbs is a good
> conductor of heat or cold I believe there is likely to be quite a
> temperature gradient across the carb. Many of us have fitted tray type
> heatshields below the carb to protect the float chamber against the heat
> of the exhaust manifold. Even so the ambient cowl temperature tends to
warm
> the carb anyway. In contrast temperatures within the carb in the vicinity
> of the throttle butterfly often go below zero during colder weather. My
> sensor protrudes into the carb at just this point so is a reasonable
> indicator as to the temperature at the point where ice might form. Like
> most other Rotax operators I have not experienced icing but I monitor the
> engine more closely once I get a warning that the carb temp is below
zero.
>
> As an aside it is possible to cause carb icing using carb heat. Carb
icing
> is most likely to form in the temperature band zero down to -5degC. If
> during cold weather operation, with a carb temp at say -10degC, carb heat
> is used it will bring the carb temp up to the danger zone. With this in
> mind, if carb heat is to be used, it is important that it can always lift
> the carb temp above zero. I think the large source of heat provided by
the
> coolant in the Skydrive unit should be able to achieve this but this is a
> relevant point for aircooled engines. In case anyone thinks they are not
> likely to operate with carb temps down to -10degC the drop in pressure
and
> loss of heat through fuel vapourisation reduces the carb temp well below
> the OAT(in early October I saw the carb temp read -5degC with an OAT of
> +5degC).
>
> Nigel Charles
>
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