[NSRCA-discussion] First day out with OS 140RX (somewhat long)

[David Flynt]

Today was one of those beautiful California days, in between the rain, and I
have the week off, so I finally got my ZNline Supreme in the air for several
trim flights.  Also, I switched from the Webra 160 with M/C to the OS 140RX.
Below are my initial impression of OS, along with comparison to YS 140DZ:

I was particularly careful while breaking in the OS.  I wanted to ensure no
problems, and the engine was ready for fly time.  I broke in on the bench
with one gallon of fuel.  I saw 7800 rpm with a 16.5x12w prop mounted in the
plane today, fairly rich.  I'm hoping I have it set way too rich, and that
it will gain more power as I get more fuel through it.  My setup is a Karl
Mueller header at 9 3/8 inches from from exhaust flange to the entrance of
the pipe, and an ES 2C140M80 muffler.  Cool Power 15%.  The Mueller header
has a sharper rise over the OS or Hatori header, and I needed that to clear
my firewall.  Total length due to the sharper rise is near the same as the
stock OS header.  What a nice header BTW.  It has the right thrust built in
so it is straight down the middle of the pipe tunnel.  It came with a short
extension so that there is stress relief on the header to prevent it from
breaking.

Big two strokes are new to me.  Before this engine, I was running a YS
140DZ, and before that, YS 120 - 140.  Here are my initial observations and
comparison between the 140DZ and 140RX:

Ease of use:  Probably a toss up.  The OS is very user friendly, and is
simple, and runs on sport fuel.  It is not as easy as the YS in that you
need to tune header length and select optimal prop and muffler/pipe, however
for the OS you can stand on somebody else's shoulders, and that is what I
did for the most part.  I don't know if I am done tuning it however.  Both
engines are pretty much hands off once broken in and set (at least what I
hear for the OS).  I flew 300 times with the DZ, and never touched the
settings after break in.

Ease of start:  Hands down, OS.  This engine starts with ease.  The DZ, once
you learn it, will start easy so long as you have a strong starter and
strong glow source.  But it can lock up on you if you allow it to flood.

Idle:  Definately the OS.  I had a good idle after one gallon, and I still
have not touched the low end from factory setting.  The YS will idle ok for
a while once warmed up, but it won't idle forever.  It does not really
matter so long as you do not let it idle for long periods.

Reliability:  No way to know since I don't have time on the OS, but one
strike against it today.  It flamed out at the bottom of the reverse
avalanche.  I just made it back, heart pounding all the way.  This is
probably an anomaly, and I only have 1 1/2 gallons through it (I should not
have been practicing the reverse av with such little time on the engine, but
oh well).  Idle speed was 2000 on the ground.  On the first flight however,
I overshot the runway twice, and I had to go around.  So, it stayed lit when
it counted.  The DZ never flamed out during flight.  I speculate that the DZ
is more reliable, but I am splitting hairs.

Quietness in the air:  OS is quieter, like a whisper compared to the DZ.  DZ
has a lower pitched noise.

Vibration:  OS is much less vibration and very smooth at idle through full
thottle.  There is an area about 1/4 throttle where it shakes a little, but
not bad compared to the DZ.  The 160DZ I hear is a lot smooother than the
140DZ, which would be nice.

Torque:  Hands down, the DZ.  The DZ has a smooth, linear throttle curve and
usable torque at any throttle setting.  This is what is so great about the
DZ.  The OS is fairly limp and useless until you get past 1/3 throttle.  At
half throttle it comes alive, and at 5/8 throttle to full throttle, there is
little difference in output.  I think this is one of the major differences
between two cycle and four.

Power:  The OS does ok, but the DZ is far more powerful.  Maybe I need more
time on the OS before a fair comparison.  I have a gut feeling however, from
running this and watching other OS owners over the years, that the DZ
dominates in power.

Weight:  OS with ES muffler is probably 3-4 ounces lighter than a DZ with
similar muffler.  But I think the DZ might be equivalent weight with a
Hatori short pipe.  Not sure.

Fuel requirements:  DZ runs best on one type and brand of fuel:  Cool power
30% heli.  This is expensive stuff, and is my major gripe with the DZ.  The
OS ran outstanding with 15% sport fuel.  For economy, you cannot beat this.

Smoke trail:  DZ has a thick smoke trail with CP 30%.  This OS had fair
amount of smoke, but I expect it to decrease as I lean in.  None of OS' that
I see at contests have a heavy smoke trail.

Overall preference:  This is a little tough because the DZ performs better
for pattern, but the OS is probably good enough.  Greg Frohreich flies very
well with his OS, and until I can fly better, I wonder if I need a better
engine.  Still, the DZ is a pleasure to run, with exception of the expensive
fuel.  I choose the DZ as my preference, but I like the OS for the positive
characteristics I mentioned.


David