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Date: Fri, 09 Oct 2009 16:25:45 -0400
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Subject: Re: [LML] Re: LOP MP setting for TSIO-550E
From: "John Schroeder" <jschroeder@perigee.net>
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I took the Advanced Pilot Seminar in Ada, OK. Didn't pay much attention to
the turbo stuff because I have an IO-550N. However, the LOP procedure they
teach is to always run Wide Open Throttle (WOT) on all engines. One varies
speed they get by setting higher or lower cruise RPM (raises or lowers the
mass airflow, respectively). Mixture then controls HP (speed) by using
more or less of the mass airflow. On turbos, one has to pay particular
attention to the TIT. I would see if John Deakin can shed some light on
the TIT aspect.

I am not sure the 14.7 you use is correct. The factors they use are
derived from a calculation using BSFC.
For LOP, the factor is (quoted from the APS paper on the subject):

14.9 for 8.5-to-1 compression ratios (most normally aspirated and
turbonormalized engines)
13.7 for 7.5-to-1 compression ratios (most factory turbocharged engines)

Another way to look at it is (Quoted from several of their slides):

ROP = excess fuel. Therefore power is controlled by mass airflow (MP and
RPM)
LOP = excess air. Therefore power is controlled, and ONLY controlled, by
fuel flow (MIXTURE)

Hope this helps the discussion.

John Schroeder

On Fri, 09 Oct 2009 10:08:43 -0400, paul miller <paul@tbm700.com> wrote:

> I think the flaw in that argument is the GPH per HP for a specific
> regime (ROP versus LOP) as your specific fuel consumption will change
> depending on that setting.  Your HP should be directly proportional to
> RPM and MP at any mixture. I think I'm correct in that last statement
> regardless of whether the engine is ROP or LOP.  When I ran the
> TSIO-520NB with GAMI the procedure would be to bump up the MP to keep
> the desired HP (65%, 70% or whatever you choose).   You have to bring
> the MP back up as the fuel flow drops off.    So, I would pick your
> desired power setting for LOP ops (say 65% for talking purposes) and
> get the MP and RPM for that power setting.   When you go LOP work
> towards bringing the MP back up to maintain your target power.  That
> is what I recall for the GAMIs so I would be interested if that might
> be what was being taught more recently.  As I said in an earlier
> posting, the only problem with high altitude turbo ops LOP was the
> need to bump up the MP to keep the wastegate from bootstrapping.
> Others may need higher MP for pressurization but I never experienced
> that in the twin.  Hope that all makes sense.
>
> Paul Miller
> Calgary (Legacy)
> On 2009-10-08, at 6:13 PM, Isaac Heizer wrote:
>
>> My ES-P has a TSIO-550E with GAMI injectors, and i've recently been
>> through advancedpilot's web LOP course.  But I'm still unclear on at
>> least one point.
>>
>> My TSIO-550E will happily run at 17.5 GPH at a MP of any of 30, 31,
>> 32 (among others).  All cylinders remain below 380, and TIT is
>> reasonable.
>>
>> My understanding is multiplying 14.7 x GPH yields HP, in this case
>> 73.5% power
>>
>> Is it 73% power no matter how I set the MP, so long as temperatures
>> remain in control?  If that's true, why would I select one MP over
>> another (realizing I can't run wide open throttle)?
>