I happened to be reading the EC3 operating manual –
doesn’t everyone do this for pleasure reading{:>)? When I came across
something that may explain something that Joe and I observed (and may have
played a role in the hard to start problem we initially encountered (after the
CAS wiring problem was fixed)
Joe has the later version of the EC2 where the lower rpm
operating of the fuel MAP (or more correctly the MCT - Map Correction Table),
where the common assumption/understanding is that the operating point below 2300 rpm is based solely on rpm.
Turn’s out that assumption is not quite correct per this extract from
the EC3 manual.
EC3 Mixture Correction
Table addressing
is illustrated on the following page. Note that below 2300 rpm and 13” manifold pressure (absolute), the MCT address is a function
of rpm as opposed to manifold pressure. If you have an EM2 engine monitor to
display the data, you can use a copy of this chart to record your table data
after the engine is tuned
Not that there are two conditions that must be met before
the EC3/EC2 uses only rpm to determine the lower operating point. The engine
rpm must be below 2300 AND the manifold pressure must be below 13” Hg.
So that implies that if you are operating at 2000 rpm, but your manifold
pressure is at 13.5 or 14 or higher then the EC2 is using the manifold pressure
to determine the operating point and not the rpm.
So lets say you are trying to start your engine – rpm <
2300 but manifold pressure > 13. Therefore the MCT pointer may be pointing
to the bin corresponding to a manifold pressure that is close to ambient (29.92”
Hg). That is also the point for WOT throttle (Lots of fuel). So its safe to
say that on the first turn of the prop that is where your Ec3/2 is at. The
instance the engine fires, the manifold pressure immediately begins to drop –
how fast it drops will depend in part on what throttle setting you have. If
you throttle is closed, the manifold pressure will almost immediately drop to
low values (presumably below 13” hg) and all is well. If however, your
throttle is set at ¼ or more open, then the manifold pressure is not as likely
to drop below 13” hg. If this is the case, then the operating point is
going to be based on manifold pressure which may be considerably above 13”
Hg. That point in turn may be overly rich for idle conditions and your engine
fails to sustain operation do to excess fuel and floods.
Tracy, of course,
may have algorithms to deal with this, but based solely on the comments in the
manual – looks like this could happen. Particularly in the early stages,
before you get the MCT tuned.
Thought I would pass this on – my older EC2 only uses
manifold pressure across the entire range.
Ed
Ed Anderson
Rv-6A N494BW Rotary Powered
Matthews, NC
eanderson@carolina.rr.com
http://www.andersonee.com
http://www.dmack.net/mazda/index.html
http://www.flyrotary.com/
http://members.cox.net/rogersda/rotary/configs.htm#N494BW
http://www.rotaryaviation.com/Rotorhead%20Truth.htm