We are finding it a bit difficult to set the mixture using
Tracy's computer on the dyno. In an aircraft at low altitude there is
a much simpler set of situations where intake manifold pressure
is strictly a function of throttle opening. On a dyno
the load can be varied over a wide range. Tracy's in the air method
of setting the map works quite well but it is less well suited
to a dyno situation.
Never the less we got one useful data point where the throttle
was 3/4 open at 5250 and intake air temp of 84 degrees F.
The HP was 148. BSFC was .53 and EGTs were 1402 and 1477.
EGTs were down about 100 F from peak 1532 and 1580
The air:fuel mixture was about 15:1
Unfortunately the mixture knob was set to full rich at that point.
We were using the default mixture settings.
Frankly I am not entirely sure what we are going to do next.
Paul Lamar
Aren't you going to start bumping up the injector map settings? It
makes sense that the default settings are too lean for a PP right?
I think many of us are waiting eagerly for results. Keep up the good
work Paul.
Hans
Well Dave Lemon is getting a bit apprehensive. He has not been paid
yet. This engine is easily capable of destroying itself if it is not
properly loaded at high RPM. Mixture could go very lean at 12,000 RPM
or higher. He is rightly concerned. Most of his dyno experience has
been with carbs that usually provide a near usable mixture setting
throughout the power band. Also carbs tend to have a moderate throat
size to provide a good fuel signal at the low end. This tends to limit
HP and RPM at the top end compared of course to say; a p-port with a slide
throttle. In an airplane the load is always there. The prop runs
into a load brick wall around 2700 RPM which of course limits the
engine RPM to 2.85 times that or 7700 RPM.
I am debating with myself if we should move the engine to a prop
dyno which is more suitable for setting the mixture using Tracy's
programming methods.
Paul Lamar
Can't he program the dyno to have a load curve with respect to rpm that
mimics a prop load curve?
Bill Schertz
KIS Cruiser # 4045
I don't think this dyno is that sophisticated. I am not sure
as I have not read the dyno manual. I'll ask. There is a big
hand crank on the left that sets the load.
Paul Lamar
Hi Paul
Looks like you are working with some sort of water brake absorber compared
to a more versatile and expensive eddy current absorber. Forgive me for
asking but is your purpose to test this way in hopes to get some quick data?
In the last a few months you have convinced me to test with a C/S prop and
of course that means a buying the redrive first. I understand that suddenly
increases testing costs but I have to buy a redrive any way. I haven't
found an electrically adjustable prop (or club) that can handle the load yet
though.
Perhaps someone could lend you these items for a few weeks.
Cheers
Doug in Japan.
There is a cheaper way Doug. I am building on as we speak.
I know you can handle this.
Build an engine simulator. At $500 a day for dyno time
you need to tune your engine much faster and much better.
I'll get back to you on the voltage and pulse width you use
to simulate the crank angle sensor. I am sure you have plenty
of oscillators lying around doing nothing.
Connect a dual channel oscilloscope to the primary
injectors and watch the pulse width to change the mixture
settings with RPM and simulated manifold pressure changes
using an auto parts store vacuum pump. Gather a bit of
preliminary data with the real engine to put you in the
ball park.
Do the same thing for the secondary injectors.
When the engine is running leave the scope connected
to the secondary injectors as an indication of computer failure
or sudden change in pulse width. Sync the scope to
the crank angle sensor. Not to say the computer is anywhere
near likely to fail but it is just one more thing to monitor.
This is very similar to the engine simulator Tracy uses.
I am building one as we speak.
Paul Lamar
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