standard corrections

[Bruce Bowling]

It is often desirable, when comparing test data taken on differnet
days, to convert measured readings to a known "standard".  There
are two commonly-used corrections - the "standard", and the 
SAE J1349, which differ only in whrer they define standard temp.

The correction, applied to obtained torque values with noted
temperature, baraometer, and humidity, is the following:

Standard correction STD:

CF = (29.92 "Hg)/(TBaro - VP) * sqrt((459.7 + CAT)/519.7)
with:
Tbaro = Test Barometric pressure in inches of mercury
VP = Vapor Pressure
CAT = "Carburetor" Air Temperature in degrees F  (engine inlet)

For SAE J1349:

CF = (29.92 "Hg)/(TBaro - VP) * sqrt((459.7 + CAT)/536.7)
with:
Tbaro = Test Barometric pressure in inches of mercury
VP = Vapor Pressure
CAT = "Carburetor" Air Temperature in degrees F  (engine inlet)


Using one of the CF values, the corrected torque is:

Tcorr = (Tmeas + Ft)*CF - Ft
with:
Tcorr = Corrected Torque
Tmeas = Measured Torque
Ft = Friction Torque (see below)

Friction torque (measured) table:

Piston Speed    Factor
----------------------
0               0.088
500             0.105
1000            0.120
1500            0.145
2000            0.170
2500            0.203
3000            0.233
3500            0.265
4000            0.308
4500            0.368
5000            0.433
5500            0.503
6000            0.573
6500            0.650
7000            0.725

With Piston Speed = (RPM *Stroke)/6
RPM revs/min
Stroke = engine stroke (inches)

So Friction Torque is:
Ft = Factor(Piston Speed) * CID

with CID = Cubic Inch Displacement

I have a subroutine (in "C") which computes all of the
above which I wrote.  It determines vapor pressure from humidity,
and has altitude correction.  I can post it if there is interest.



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               Bruce A. Bowling
  Staff Scientist - Instrumentation and Controls
 The Continuous Electron Beam Accelerator Facility
    12000 Jefferson Ave - Newport News, VA 23602
                 (804) 249-7240
               bowling at cebaf.gov
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