About the propeller influence on aircraft stability derivatives

Abstract

Propellers can significantly effect aircraft flying characteristics and stability. Depending on the aircraft configuration this influence of propeller on aircraft stability derivatives can be more emphasized, as for example with single pusher propeller. Methods still used in prediction of propeller stability derivatives are based on blade element theory with the axial component of induced velocity determined from the classical propeller momentum theory. This could lead to uncorrect prediction of induced flow near the propeller and its wake. In presented paper propeller model and prediction of its influence on the aircraft stability derivatives is based on the propeller vortex theory. The numerical model is using discrete vortices to form vortex sheet that is leaving each propeller blade. This model is suitable for implementation in component build–up method used in prediction of propeller driven aircraft stability derivatives and it can be applicable for different aircraft configurations.

Aerodynamic characteristics of propeller in non‐axial flow

“…Propeller model (1,2) was analyzed on the example of two-bladed propeller for the cases of flow with three different angles of attack α = −6 • , 0 • , 6 • [3]. Results of presented model for normal force coefficient and yawing moment coefficient are given in Fig.…”

“…Lifting line model is applied for the propeller blade model [2]. Each blade is described with n discrete horseshoe or Π vortices consisting of bound vortex (v) and trailing vortices (parts sf 1 and sf 2 on the blade and s1 and s2 free in the wake).…”

“…Induced velocity at the vortex filament from (2), defining the vortex filament position in the wake, depend on the Π vortex circulation Γ k defined in the propeller blade model (1). Since the solution of the propeller blade model (1) is needed to solve propeller wake model (2) and vice versa, these two models have to be analyzed simultaneously. First step is to determine the circulation distribution along the blade from propeller blade model (1) with the assumption of Goldstain's helicoidal propeller wake.…”

“…First step is to determine the circulation distribution along the blade from propeller blade model (1) with the assumption of Goldstain's helicoidal propeller wake. After that wake geometry can be determined from (2) and using that result blade circulation can be recalculated from (1). The loop between (1) and (2) is enhanced with pseudo-implicit predictor corrector scheme for integration of (2) and results convergence is checked with L 2 norm.…”

“…In case when free stream velocity is under the angle of attack or the side slip angle, or their combination, with regard to propeller axis of rotation, velocity on the blade section is dependent on its angular position ϕ so blade circulation varies with ϕ. Since velocity at the blade section is determined separately for each blade and with respect to ϕ, it is possible to analyze propeller in non-axial flow with propeller model (1,2). Furthermore, for non-axial flow propeller wake geometry is also changed and the angle of trailing vortices at the trailing edge of the blade is different from the case of axial flow.…”