All,
Operating 'oversquare' in the piston a/c
world is normally interpreted
as MAP (in inches of water) being larger than
engine rpm divided by 100.
Ex: 28" MAP & 2200-2400 rpm during
takeoff and climb is oversquare, and
would be a normal occurrence with a fixed
pitch Lycoming operating from
an airport near sealevel. And virtually all
turbocharged a/c engines are
*always* operating oversquare to some degree.
So the hazard of
'oversquare', in and of itself, is largely an
'old hangar tale'. What
Lynn said is the limiting factor in piston
engines, just like the rotary.
Not sure how you'd apply the metric to a
rotary anyway, since its higher
rpm would mean it is almost never in the
'oversquare' area.
Charlie
> Thanks Bobby.
> We are just NA, but the idea of a turbo
and 250hp is appealing and would make the Glasair hum
along at altitude!
>
> Steve I
>
>>
>> Hi Steve,
>> Are you running a turbo? I didn't
see it listed when you asked about oversquare, so I
thought you were running NA.
>>
>> Sent from BlueMail
>> Steve,
>>
>> I used 6800-7000 rpm, 36-38” MP with
F/A in the 12’s for takeoff. Around pattern altitude I
would reduce to 6000 rpm and 30-32” MP with F/A a little
richer than best power in the 13’s. I monitored EGT’s
during all phases of flight and would make mixture changes
as needed to keep EGT around 1600 or less during high
power operations. I used a vernier cable to control the
super charger bypass and could dial in the desired MP. For
the turbo I was planning a 4# waste gate with an air
control valve to apply more pressure to the top of spring
at higher altitudes or lower rpm. Still using the same
target numbers as with the super charger. But no turbo for
the S21 project. I guess I need to sell it at some point.
>>
>> So I only used boost for takeoff and
for normalization most of the time. I liked operating 28-
30” with the prop between 1700-2000 rpm. Rich or lean to
keep the EGT under 1600F and intake temps under 140F.
>>
>> Bobby
>>
>> Sent from my iPad
>>
>>>
>>> Thanks Bobby.
>>> What boost are you running?
>>>
>>> And I meant to ask, my friend is
asking what power setting we consider the engine to be OK
with for continual operation?
>>>
>>> Steve Izett
>>>
>>>>
>>>> My preferred cruise economy
settings 30” MP, 4800-5200 rpm. F/A 15:8 lean. Or 30-34”
MP, 5200-5400 rpm F/A 14:0 or whatever was need to keep
EGT below 1600F and intake air temp below 140F.
>>>>
>>>> Bobby
>>>>
>>>> Sent: Friday, July 17, 2020
7:10 PM
>>>> To: Rotary motors in
aircraft
>>>> Subject: [FlyRotary] over
square and detonation of a rotary for my pilot friend
>>>>
>>>> Hi people.
>>>>
>>>> My test pilot friend and I
are continuing our journey of extending the phase#1
envelope and now experimenting with engine settings.
>>>> With a flight adjustable
prop he is asking questions about 'over square' and
detonation.
>>>> Can anyone give me an answer
for him?
>>>>
>>>> Thanks
>>>>
>>>> Steve Izett
>>>> Glasaie Super IIRG Renesis 4
port RD1C variable pitch prop.
>>>>
>>>>
>>>>
>>>>
>>>>
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