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Yes, I've always enjoyed using math to try to get a
model for what the real world is doing. But, as I always say our Math
models are a dumbed-down representation of the real world,
so don't be surprised if you find differences between the two
(:>).
Have fun, George.
Ed
----- Original Message -----
Sent: Sunday, September 23, 2007 2:47
AM
Subject: [FlyRotary] Re: Area of a
circle
Ed,
I intend adding a notch to the square slide for a
couple of reasons, but I don't know if either reason is valid, but I can
just treat it as an add-on.
The graph seems to validate what I had done
manually today - it's all very interesting isn't it!?
George (down under)
Ah, well, George, if you are using a slide
throttle, then forget the spreadsheet I sent you - that was assuming a
rotating plate. In that case it will depend on the shape of your slide,
if a straight plate then the area is fairly easy to find. I
am assuming a throttle with a flat straight edge sliding plate across the
throttle area.
Since there is no revolving throttle plate, the angle
in the spreadsheet is actually the angel between the center of the circle
area to the points where the sliding plate enters the throat.
So when the plate is fully across the opening or
closed - this angle is zero, the angle is 180 deg when the plate is
half way open and 360 degree when it is fully open.
That's about all I can along these lines. If the
end of the sliding plate is anything other than straight (no "V" notches,
etc) then this is not going to be accurate.
Ed
----- Original Message -----
Sent: Saturday, September 22, 2007
8:06 PM
Subject: [FlyRotary] Re: Area of a
circle
Thanks Ed,
I'm looking at it - again!
Mind you I'm wanting to use a slide throttle,
so the butterfly thickness and rod are not a factor in my non-venturi,
straight through 44 mm dia carb design.
George
----- Original Message -----
Sent: Sunday, September 23, 2007
2:25 AM
Subject: [FlyRotary] Re: Area of a
circle
I agree with Al, George.
However, if you wish to enjoy the thrill of
calculating that area (which is not a trivial task), here is a document
that has all the information (formulas) you need.
Now if you are willing to
assume that the throttle plate thickness and its rod are not a
factor (maybe not a bad real-world assumption just to get
the area of the opening - but different story regarding its effect on
air flow which is why Al's suggestion is a good one), I have attached a
spreadsheet with this simplification of the math.
Ed
----- Original Message -----
Sent: Saturday, September 22,
2007 12:06 PM
Subject: [FlyRotary] Re: Area of
a circle
George;
Determining
the area of the opening of a circular butterfly with position is
certainly complex enough; but the flow is likely not directly
proportional because of the complexities of the flow characteristics
and pressure changes. I would think measuring it is really the
only way. Do you have access to a flow bench?
Sorry;
probably not very helpful,
Al
G
-----Original
Message-----
From:
Rotary motors in aircraft [mailto:flyrotary@lancaironline.net]
On Behalf Of George
Lendich
Sent: Friday,
September 21, 2007 9:21 PM
To: Rotary motors in
aircraft
Subject:
[FlyRotary] Area of a circle
I am trying
to work out the area of carb inlet as it is opened
incrementally.
This involves
the overlapped portion of two circles, as well as, a circle cut into
slices ( straight cuts).
This should
give me an indication of the linier or otherwise, volume of air as it
sweeps through the carb.
This then
should indicate the shape of the grind of the needle in
maintaining continuity of the mixture ratio of fuel to
air.
Any helpers
with this one!?
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