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Agree, Brian, something is amiss (no pun
intended).
One question I have - is your prop 88(Dia) x 74 (pitch) or
more likely 74 (dia) x 88 (pitch)? - conventionally the diameter is mentioned
first.
CHECK THIS
One thing you may want to check. While it doesn't
have any bearing on your rough running it may on your static rpm.
Two folks I know have had Catto props made for the rotary - in both cases
the chord of the prop was way too much and over loaded the engine and surpressed
rpm and power.
Measure your cord across the broadest point
in the blade. The Props which cause folks problems measure around
8" - whereas my 74 x 88 Performance Prop chord measured 5 1/2". Sam
Hodges, Rv-7A with Renesis, had worked months trying to get his static
rpm above 5000 including making several intakes. When we put my
prop on his engine, it immediately got 6000 + static rpm - it
was the prop all along. So measure that chord.
The reason for the emphasis on the prop, is that with that
set up and a prop the size of mine - you should be turning 6000 rpm static (at
least). All of this referenced to sea level air density.
Another aspect, what type of air/fuel ratio indications
are you getting while the engine is stumbling? Is 18" Hg near your staging
point?
- there is the possibility that something is happening
after you stage - for example if your primary injectors were OK, then the engine
would run smoothly - until the engine went to all four injectors - then if is
there was a problem with one of you secondary injectors you could get rough
running.
Then as you suggest, it could be an ignition
problem. As you know several folks have had ignition
misfiring problems using the Renesis type pulley timing mechanism - particularly
at the higher rpm -apparently alignment is very critical - I can not
recall if you are using the CAS or the Pulley type.
TRY THIS
It is either your fuel or your ignition - try to eliminate
one or the other - using an oscilloscope can help in that type of trouble
shooting, but if you don’t have access or experience in using one - well, need I
say more. I would try to determine if it is fuel related first - because I
think that could be the easiest to work with.
Here is what you can try - if you turn
off power to your secondary injectors, then when you go through the staging
point only the primary injectors will be firing. Two 450 cc/min or larger
primary injectors can easily get an engine up to 6000 rpm (provided you are not
over propped). So if you engine runs smoothly all the way up past 5300 rpm
on primary injectors alone, then I would strongly suspect something in the
secondary circuitry (injectors, intermittent connection, etc). So
take the secondary injectors out of play by turning off their power. While
I have had no problem staying airborne on two injectors, I don't suggest you try
flying with two - just do this test on the ground.
IF running on just the primary you get to 5300 rpm and the
engine starts to miss or run rough, then I think we can eliminate the secondary
injector circuit as the problem and perhaps concentrate on the
ignition.
That's all I can think of to suggest at the
moment
Good luck Brian
Ed
Sent: Tuesday, June 21, 2011 12:19 AM
Subject: [FlyRotary] This has got to stop
I'm going to ground my airplane until I get to the bottom of this. I can
tune it on the ground and it will run just fine all the way from idle to full
throttle. I get about 5300 rpm at full throttle at 29 in hg. MP. I have 12 hours
in the air so far but can't get past this issue. Other than this, the plane is
an absolute joy.
When I get off the ground, when I go through around 5400 RPM, I start
to get stumbling and engine roughness. At this RPM I am about 18 inches MP. Just
below this point, I am making about 50% power and the engine will run smoothly.
I went to another airport and had a lot of roughness on takeoff, but I am
used to it and so continued on my way to my home airport. When I got back I
found out that someone at the other airport wanted to report me to FSDO because
he thought my engine was going to blow up, but he didn't get my tail number.
So, I thought I had it sorted out before I flew today, but it's back to the
drawing board. I've tried both leaning and enriching the mixture at all throttle
settings, but to no avail. At and above 5400 rpm I start getting all sorts of
roughness so I think that it has to be an ignition issue. My injector wiring is
separated from my coil wiring, but could I be getting inductance between the
different coil wiring?
I have a 93 13 BREW normally aspirated, 2.85 RWS redrive, EM2, EC2, 88x 74
CAtto Prop. This is getting to be really frustrating. It's got to be something
simple that I'm overlooking. I don't know anyone with an ocilliscope, and have
never used one.
Brian Trubee
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