Remi Guerner wrote:
> Hi Rowland and all,
>
> In my opinion, EGT indication on any Rotax engine is useless. EGT
> indication is extremely sensitive to the position of the probe inside
> the exhaust stack. This is one of the reasons why, on any piston
> engine, the EGT indication in itself cannot be used to determine
> whether a cylinder is running too lean or too rich. The highest EGT
> cylinder is not necessarily the leanest. The only way to determine the
> mixture condition is to pull the mixture control progressively and
> monitor the EGT on all cylinders. The leanest cylinder is the one
> which will reach peak EGT first. Of course you cannot do that on a
> Rotax as there is no mixture control. The only thing EGT can do on a
> Rotax, in case of a big engine problem, is to help diagnose which
> cylinder is the culprit.
> Additional comments:
> With the Europa XS cowling, the EGT probes on cylinders 1 and 2 are
> cooled by direct ram air from the round intakes and this has proved to
> affect their indication.
> The Rotax Flydat has 4 EGT channels but shows EGT on two cylinders at
> a time and switches automatically back and forth. That makes EGT very
> uneasy to read. Any other engine monitor on the market is certainly
> better.
> My plane was fitted with a 914 with Flydat and 4 EGTs when I bought
> it. When I replaced the engine with the 912S five years ago, I kept
> the Flydat but did not install EGT probes and it works for me.
> Regards
>
> Remi Guerner
> F-PGKL
>
Remi
We had a Classic with a Grand Rapids EIS and 4 EGTs. I soon noticed that
EGT varies in an unusual way with throttle setting. The mixture is
affected by throttle position because of the effect of momentum on the
fuel droplets, which tend to go to the front cylinders at WOT and the
rear at part throttle.
One thing is apparent, the very high EGTs the Rotax has in normal
operation. This means the exhaust system is under considerable thermal
stress.
I tend to the feeling that EGT is worth having for diagnostic reasons
but difficult to understand on the Rotax.
Graham
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