Sounds like a bit of air leaking into the headers proving enough oxygen to light unburned fuel in the headers or muffler. Look for combustion products leaking from any joints. Lowest pressure is closer to the flange right on the engine.

 

Lynn E. Hanover 

 

I am not talking about a closed throttle descent.  I am talking about a full
throttle descent.  When I started to descend, I just set the autopilot for a
500ft/min descent and let er go.  Prop and throttle were left alone.  The
mixture was already at the mid-point because I can't tell where I am since
the mixture graph is not working at present.

I am also getting this hiccup at idle.  I have always had that, so I thought
it was normal.  It is not as strong at idle as it is at cruise.  But still a
quick BUHT! From time to time...

Bill B

-----Original Message-----
From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Ernest Christley
Sent: Sunday, April 29, 2012 5:05 PM
To: Rotary motors in aircraft
Subject: [FlyRotary] Re: Hiccup

You can cut the fuel on descent, just like in a car, and still get the lube
from mixed oil by cutting the ignition a few cycles ahead of the fuel cut.



Tracy <rwstracy@gmail.com> wrote:

>The only thing I can think of that would match that symptom is an
intermittent open in one of the crank sensor connections.
>
>If it happened only at high throttle, that would match the symptom I had
way back when I had a failure of the welds that fixed the sun gear to the
input shaft.  I assume your drive is either a later model after I went to
the pinned input shaft or it has been retrofitted with a pin.   In this
case, The symptom FEELS exactly like an engine miss or backfire but is
really a momentary slipping of the input shaft before it temporarily
friction welds itself back to the sun gear.  This happens at high power
setting, not at low throttle in a descent though so I don't think that's
what's happening here unless you have two unrelated problems.
>
>An engine miss during descent can be caused by the engine running at a very
low MP (due to windmilling prop) where there is not enough combustion
chamber pressure to give reliable combustion.   Cars avoid this (in a
downhill coasting situation) by cutting the fuel injection completely.  I
chose not to do this on the EC2/3 because we depend on a little fuel-oil
injection to lubricate the apex seals.  What many builders perceive as a
MISS is often an occasional FIRE when there happens to be enough fuel and MP
to combust.
>
>This is only general info so don't take it as the gospel on what your
engine is doing.  I'm a long way from your engine and going on very little
info. 
>
>Tracy
>
>Sent from my iPad
>
>On Apr 28, 2012, at 6:34 AM, "Bill Bradburry" <bbradburry@bellsouth.net>
wrote:
>
>> The hiccup is like a backfire.  It really shakes the engine.  You can
feel it thru the airframe.  But it is quick, like it was a single event.
BUP! Then it is smooth again for a minute or two.  Much closer together if
you are in a powered decent.
>> 
>> Bill
>> 
>> From: Rotary motors in aircraft [mailto:flyrotary@lancaironline.net] On
Behalf Of Tracy
>> Sent: Friday, April 27, 2012 5:36 PM
>> To: Rotary motors in aircraft
>> Subject: [FlyRotary] Re: Hiccup
>> 
>> Don't know about the hiccup but you can easily calibrate the airspeed.
Go to calibration screen for TAS, adjust the sensor offset parameter to one
less than the current ADC reading.  Do this at zero airspeed of course.
>>
>> Tracy
>> Sent from my iPad
>>
>> On Apr 27, 2012, at 2:58 PM, "Bill Bradburry" <bbradburry@bellsouth.net>
wrote:
>>
>>> I am experiencing an occasional hiccup while in cruise and more often
during a decent under power.  I am pretty certain that I saw a comment on
this previously from Tracy but I have not been able to find it.  Can someone
set me straight on what to do about this?
>>> 
>>> My mixture graph is not working and I will be sending the EM-2 to Tracy
as soon as he returns from Colorado.  I also show a true airpspeed of 22 mph
in the hangar and it seems to be about that much or a little more in error
in cruise.  I don't think I can calibrate this item?
>>> 
>>> Bill B
>>

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