"bryan.wilkinson" wrote:

---------- Forwarded message ----------
Date: Thu, 18 May 2000 14:45:29 -0400
From: William S. Stewart <bill@helixsys.com>
To: Europa List <europa@avnet.co.uk>
Subject: Europa_Mail: 914 High Cyclinder Head Temp

I have been experiencing high CHT readings on my Rotax 914 since I started
flying my Europa (XS Monowheel).  The Europa people and Rotax seem to think
it is an instrumentation problem, but I am not so sure, so I thought I
would solicit the opinions/advice of you out there.

At cruise with an OAT of 27C (82F) at about a 65% power setting (about 27"
and 4800rpm) I consistently read about 130C (266F) for CHT. I have checked
this several different ways:

1.  I am measuring CHT with a Rocky Mountian Instrument engine monitor,
which requires a J thermocouple input for CHT.  My initial installation
used a J thermocouple designed to mount under the spark plug.  This gave
very high readings - up to 140C.

2.  The Rotax rep at Sun N Fun said this was improper, and said I must use
the well in the cylinder head provided for CHT.  So I purchased a J
thermocouple probe designed especially for the 912/914 and installed it.
It read somewhat less, but still settles out at 130C at cruise as described
above.

3.  I have checked the readings using an infrared thermometer supposedly
accurate to 2C and it agrees completely with the  CHT from the RMI, at
least at the temperatures I can check (It is impossible to get the
temperature up to 130C on the ground with the cowling off).

4.  I reinstalled the original Rotax CHT sensor, which has a resistance
inversely proportional to temperature.  At the flight conditions described
above, I measure 23 ohms with two different digital ohmmeters, which
corresponds approximately to 130C per the graph in the Rotax installation
manual.

        As a result of all the above, I am now convinced that my CHT is running
130C at low power, compared to what I understand is normal for higher power
of 100C - 105C (212F -221F).  Although this is not over the absolute limit
defined by Rotax of 135C, it leaves no margin for higher power operation or
climbing.

        I have received a plethora of advice on how to correct this.  I have
flushed my radiator and it seems to be free and unblocked.  If the problem
is the water pump I have not figured out a way of determining this other
than disassembly, which requires removing the engine from the aircraft.  I
have increased the  air outlet at the lower rear of the duct to provide for
more air flow over the cylinders.  Although the air flow over the number 3
cylinder seems to be greatly impeded due to the engine mounting bracket and
the air plenum from the turbocharger, I see no way of correcting this.

        Note that even though my CHT is consistently high, the oil temperature
remains normal or below normal.

        Any advice/suiggestions would be greatly appreciated.

Bill Stewart, N6LB (A098)

We are not the only ones with cooling problems.

Paul Lamar

The Aircraft Rotary Engine Newsletter.              Powered by Linux.

http://home.earthlink.net/~rotaryeng/            http://www.linux.org