An indirect method of determining aerodynamic Angles: an angle of attack and an angle of sideslip

Аuthors

Maksimov A. K.

Research institute of aircraft equipment, 18, Tupolev St., Zhukovsky, Moscow Region, 140182, Russia

e-mail: akm_point@mail.ru

Abstract

An indirect calculation procedure for an angle of attack and an angle of sideslip of any aircraft is considered with using flight parameters measured by aircraft systems. A lift coefficient is calculated from flight dynamics equations which include such parameters as dynamic head, weight and wing area, and normal g-load. Analytical expressions are obtained for the lift coefficient and attack angle relation with an approximation technique using the plots of this relation which are constructed as a result of aircraft model wind-tunnel tests. In addition, the dynamic head is calculated for each dynamic pressure value determined in flight with a pitot tube using the known dynamic head dependence of dynamic pressure. It is shown that an angle of sideslip can be indirectly determined from a side force equation. Probable calculation errors for an angle of attack and an angle of sideslip are considered. These errors are estimated with taking into account the measurement errors for the parameters which are involved into the angle calculation formula. A possibility to estimate the systematic and random components of the measurement error is considered. With a great number of measurements, the random error follows the normal law. With a small number of measurements, the confidence probability and the confidence interval are estimated by using the Student’s distribution.

Calculations are performed to estimate the indirect determination error for a lift coefficient for a typical flight of such airplanes as Yak-52 and M101T «Gzhel». The airplane wind-tunnel tests yield the indirect determination errors for an angle of attack. The accuracy estimation results meet the known measurement accuracy requirements stated in certain publications. Calculations are performed to estimate the indirect determination error for an angle of sideslip for a typical flight for a M101T airplane. The resulted estimates satisfy the accuracy requirements known from publications.

Keywords:

angle of attack, angle of sideslip, measurement, accuracy estimation, measurement error, mean square deviation, random error, normal law of distribution, indirect measurement estimation equations

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