ESDU Engineer
Issue 16
PROPELLER SLIPSTREAM EFFECTS
ESDU 06012 The influence of propeller slipstream on aircraft rolling moment due to sideslip
Multi-engined propeller driven aircraft are known to suffer from a reduction in lateral stability due to sideslip (the “dihedral effect”), particularly at a combination of high power and large flap angle. An example which arises during certification is the baulked-landing case.
The origins of this effect are discussed in ESDU 06012, which shows it to be dominated by the propeller slipstream passing over the wing. A method of estimating its magnitude in the linear range is presented. Non-linearities due to flap end effects are illustrated and further general limitations are discussed. A worked example is provided.
The method has been derived using data from conventional twin-engined, single-fin configurations. It proved possible to ignore certain parameters in the development of the method. These include the effect of wing taper, the presence of engine nacelles, the proximity of the fuselage and the possibility of the slipstream impinging on the tail unit. Because a satisfactory correlation has been obtained with the simplified method it is concluded that these effects are of minor importance for such configurations.
In principle the method is equally applicable to four-engined layouts, provided care is taken if the outboard slipstream is close to the outboard flap end, because in this situation non-linearities may well be encountered. The method is accurate to within about 0.003 on rolling moment coefficient increment.
PROPELLER SLIPSTREAM EFFECTS
ESDU 06013 Propeller slipstream modelling for incidences and sideslip ESDU 06013 relates the forces acting on a propeller to the characteristics of the far (fully-developed) wake, both for the axial case and a propeller at incidence or sideslip. Compatibility is shown between blade element theory (propeller forces), actuator theory (momentum balance) and the wake model (vorticity). Comparisons of the slipstream deflection in the far wake are made with the predictions of Ribner’s early work. Expressions for the development of the slipstream at intermediate stations are related to the conditions in the far wake. The results are illustrated graphically.
Current work
Listed below are some examples of work currently being undertaken by our Engineers
MMDH ESDU 00932 Supplement 46, consisting of 44 new and updated Data Sheets, is being issued.
MECHANISMSD well-Rise-Fall-Dwell cam lawsSpring dynamics DYNAMICSFlutter of aircraft
STRESS AND STRENGTHShafts with intereference-fit collars