AND the engine is NOT running.
However, once you run it WOT and get a good reading at sealevel you can very accurately tell your max MAP available....
E.g. Robinson helos run a airfilter permanently without ram-air, so there is always a pressure drop once the engine runs. On most specific aircraft I have flown for a while ( to get used to any one of them...) I could tell at take off whether it was possible to get in and out at some destination, just by looking at the MAP.
e.g. If I needed 25" MAP at sealevel (where the base was...) to get into a hover I knew I can get out with the same weight at 2000', as the engine could pull around 27.5" at sealevel.
On a hot day I might need all 27" to get off, so 2000' would not work. I always could pull MAP, how much power I got depends on the OAT.
Same for high altitude destinations - If I needed 25" to get off a t sealevel and the client wanted to go to a 5000' destination it was a no-go right there:
29.92 -5 = 24.92 - about 2' loss in the filter is no more than 23' at the most (praying for cooler temps). I need 25" to hover, so: no joy... :(
However a MAP indicator and the engine stopped is a good "power available" indicator....
TJ
On 6/4/07, wrjjrs@aol.com <wrjjrs@aol.com> wrote:
Absolutely Correct Bill. If the sensor is calibrated properly.
Bill Jepson
-----Original Message-----
From: Bill Schertz <wschertz@comcast.net>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Mon, 4 Jun 2007 3:54 pm
Subject: [FlyRotary] Re: EC-2/EM-2 manifold pressure
I understand that, but what I was asking:
My field elevation is 700 feet. I set the altimeter needle to 700 feet,
the Kohlsman window reads (whatever it is that day), and that is the
manifold pressure that the EC-2 should be reading - isn't it?
Bill Schertz
KIS Cruiser #4045
----- Original Message -----
From: Thomas Jakits
To: Rotary motors in aircraft
Sent: Monday, June 04, 2007 10:22 AM
Subject: [FlyRotary] Re: EC-2/EM-2 manifold pressure
Well Bill,
if the Kolsman window is where you set your altimeter setting (mb or
inches mercury) you will never see field elevation (pressure) unless
you are at sealevel.
E.g. if you have 29.92" at sealevel (and in the window) you still have
29.92 in the window (you set it there!) when you get to 6500'. Your
actual ambient pressure is around
23.42".... (which you should be
reading on your manifold pressure gauge - engine stopped...
Unless, I got it wrong the last 15 years and 9500 hours - ohhh my...!!
TJ
On 6/4/07, Bill Schertz <
wschertz@comcast.net> wrote:
Al, thanks for the clarification on what sensor the EM2 is reading.
When I set an 'old fashioned' altimeter to field elevation, the engine
is not running, isn't the Kolsman window reading the local pressure --
ie the 'manifold' pressure?
Bill Schertz
KIS Cruiser #4045
----- Original Message -----
From: Al Gietzen
To: Rotary motors in aircraft
Sent: Sunday, June 03, 2007 11:55 AM
Subject: [FlyRotary] Re: EC-2/EM-2 manifold pressure
Ed,
When I have my EM-2 on, EC-2 off, the Manifold pressure reads the
barometric pressure (29.7 today).
When I then turn on the EC-2, the manifold pressure increases to 32.9.
This seems peculiar, have you noticed anything like this?
Bill Schertz
KIS Cruiser #4045
When the EC2 is off, it is using the reading from the sensor in the
EM2. When it is on, it is reading the sensor in the EC2. I have also
found considerable disagreement on these sensors. I also found that I
had to change the calibration on the MAP pressure channel on the EM2 to
get the correct reading (with EC2 on, we don't care what the sensor in
the EM2 is reading). I have no idea why the calibration should be
different on different units that use the sam e sensor; but there it
is. You can get a vacuum gage (actually a pressure gage, so you have
to subtract from atmospheric) at a reasonable price from McMaster-Carr,
or I could loan you mine.
Also, it should not necessarily read the barometric pressure; you have
to adjust for altitude. Barometric is equivalent sea level (or
something like that).
Al
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