The paper presents the results of the calculation of forces acting on the flaps of the Su-22 aircraft during take-off and landing. Four different analytic and experimental calculation methods were used to increase the reliability of the obtained results. The results will be the basis for performance of fatigue testing of the flaps which are structural components of the aircraft wings. The tests will be performed as part of a wider research program aimed at the extension of the Su-22 aircraft service life.