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George,
You need to solve for the area of the circular segment opened by the slide throttle. The formula is A=1/2[rl-c(r-h)]
A=area, r-radius, l=lenght on the perimeter, c=chord, h=chord height
Since lenght on the perimeter can be tough to determine, there is an alternate formula. There is a slight error (less than .1%)
A=4h^2/3 times sq root of c^2/4h^2+0.392
area equals four times h squared divided by three times the square root of c squared divided by 4 times h squared plus 0.392
(pg 75 mahninery's handbook 21st ed.)
That will give you the cordal area of 1/2 of the opening obviously. You can figure the cross-sectional area of the needle to remove. You can do openings at various throttle openings and then graph of extrapolate the points between. Good luck!
Bill Jepson
-----Original Message-----
From: George Lendich <lendich@optusnet.com.au>
To: Rotary motors in aircraft <flyrotary@lancaironline.net>
Sent: Sat, 22 Sep 2007 4:55 pm
Subject: [FlyRotary] Re: Area of a circle
Al,
I am using a slide throttle and initially thought I would just do trial and error, but figured if I could just get a handle on variables it would help with the initial taper grind on the needle. I guess I could just go linier and see how that goes. I could use an O2 sensor to check fuel/air ratio, then regrind a new needle.
George (down under)
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