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0. 12:25 AM - Just A Few More Days To Make Your List Contribution... (Matt Dralle)
1. 02:17 PM - Re: Re: Kitfox 2 (Noel Loveys)
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| Subject: | Just A Few More Days To Make Your List Contribution... |
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The only way I know of checking whether an engine is loading properly is by the
tachometer. I only mention this because when I first got my plane I had the
devil of a time getting off the water. It turned out the Westach instrument was
reading way high. In fact it was reading about 30% - 35% high across the board.
I found out about it one day when on takeoff the tach wound up the rich
side of 8K a bit of an impossibility while dragging the plane too. I got a
TinyTach and on the next take off I found I was actually getting only around 4500
rpm on takeoff ... At the same time the Westach was reading 6700RPM.
Noel
-----Original Message-----
From: owner-kitfox-list-server@matronics.com [mailto:owner-kitfox-list-server@matronics.com] On Behalf Of mikeperkins
Sent: November 24, 2011 11:34 PM
Subject: Kitfox-List: Re: Kitfox 2
The wisest counsel that could be offered is to suggest that before you start tweaking your prop pitch, watch the EAA webinar Is Your Two Stroke Engine About to Fail?. The link for it is: http://www.eaavideo.org/video.aspx?v=626943072001
The webinar explains just how easy it is to overload the engine with incorrect
pitching and how unreliable an engine immediately becomes when it is overloaded.
It is also possible to underload an engine, also with detrimental effects.
Before changing anything in the engine or prop, its important to know just what
your EGTs are in all phases of flight slow cruise, fast cruise, descent, cruise-climb,
and Vx climb. An accurate EGT is your best friend when it comes to
knowing how reliable your engine will be, as is an accurate tach.
I have a Kitfox Model I that I finished in 1994. Its 532 with B gearbox and a three-blade
66" GSC prop has run for 375 hours with minimal maintenance. Pistons,
cylinders, and rings are currently all nominal. I replaced the rings at 100
hours because they were stuck tight, probably from using synthetic oil which
I no longer use.
Full-throttle static RPM in 60-degree temps varies from 5800 to 6100 (one variable
in static RPM readings is the windspeed towards the prop). Full-throttle climb
at Vx is between 6500 and 6700. For cruise, I set the RPM at 5800 - 6000,
which gives me about 72 MPH TAS. My airframe has the optional lift-strut fairings,
but that is all.
I know that I could coarsen-up the prop pitch, but Im also aware that the engine
would soon become overloaded. Ive set the combination of the carb needles and
the prop pitch to make the EGTs read about 1100 in cruise, 900s at full-power
in climb.
It is important to have two things before repitching your prop: an accurate tach
and an accurate dual EGT.
The EGT probes need to be located at the correct distance from the piston skirts,
which I believe is 4. If you are unsure about the accuracy of the EGT in any
way, Id strongly advise getting a new one you have to be able to trust it
absolutely.
Tachometer calibration is also important. Some EAA chapters and A/P mechanics have
remote-reading tachometers (based on a photocell that remotely senses the
frequency of the blade-passings), and borrowing one can help you discover if your
tach is reading correctly.
Im stressing the value of accurate EGT and tach because Im aware of how often they
are inaccurate and also how their inaccuracy can cause an owner to make his
engine less reliable rather than more reliable.
Watch the webinar - it's very valuable.
Mike Perkins
EAA TC/FA
Read this topic online here:
http://forums.matronics.com/viewtopic.php?p=359142#359142
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