(October 1957), Research Paper 2795, p. 253.) showed an 

 error range of +0.5 m/sec at 1405 m/sec to -0.1 m/sec at 

 1505 m/sec when the manufacturer's equation, C = 0.5 F, 

 was used. However, if the equation for this particular 

 instrument is changed to C = 0.499565 F + 0.025 (t - 20°C) + 

 1.15 m/sec, the error based on the same test results is 

 within a range of ±0.1 m/sec. 



A calibration equation which includes a term to 

 compensate for effects of temperature change on the sound- 

 path length of the instrument is used. The equation is 

 of the form C = a + b (t - t ) + dF where (a), (b) and (d) 

 are constants and (t - t ) is the difference between in- 

 strument temperature (t) and the temperature (t ) at which 

 the manufacturer has established zero temperature correction." 



(6) This temperature coefficient is due to the use of stainless steel 

 as a base for the acoustical path. Why the temperature coefficient 

 of the ACF instrument should be half this value is not clear. The 



expansion of the stainless steel base should result in a T. C. of 



—6 

 velocity of: a = 18 x 10 x 1500 =0.027 m/s deg. 



(7) Made by Lockheed Electronics Company Avionics and Industrial Products 

 Division, 6201 East Randolph Street, Los Angeles 22, California, 

 Tel: 213-722-6810. 



(8) With temperature of velocimeter known to 5°C. 



(9) As this velocimeter does not fold the acoustic path, the full com- 

 ponent of flow in the direction of the acoustic path adds to or sub- 

 tracts from the sound velocity. 



(10) Transducers protected by 0.002" steel diaphragm. 



(11) Made by Dyna Empire, Inc., 1075 Stewart Avenue, Garden City, New York, 

 Tel: 516-741-2700. 



31 



artbur ZD.Uittlc.Hnr. 



