• Version
• 115 Downloads
• 32.77 MB File Size
• 1 File Count
• March 9, 2016 Create Date
• March 9, 2016 Last Updated

Assessment of Lift Augmentation Devices

The purpose of this lecture is to describe in fairly general terms the stalling of conventional aerofoils and the
effects of mechanical high-lift devices thereon. The factors affecting maximum lift coefficient are discussed in the
context of estimation methods. Drag is also discussed.

Various empirical correlations of maximum lift coefficient of aerofoils have been made in the past. The classic
works of this nature centred on the era 1936 to 1946, a time when the calculation of potential flow pressure distribu-
tions was not generally possible for “the average aerodynamicist”. At the end of this period the potential flow
pressure distributions were however available for the NACA aerofoils, tests of which formed the main part of the
empirical data. Nevertheless the most successful correlations were in terms of simple geometric parameters rather
than in terms of pressure distributions. Some of the most significant of these empirical analyses are those of
References 1 and 2.

Dating from about 10 years later, Reference 3 by Gault gives a classification of the three main classes of stalling
behaviour which, for conventional aerofoils, has not been improved upon. The omission of any mention of Mach
number, even though all the data is probably for Mach number less than about 0.18, is a feature which may be
regretted.

These correlations were based almost entirely on data measured on the NACA digit, 5 digit and 6 series aerofoils,
these aerofoils providing then the only large body of high Reynolds number data. Whilst computerised pressure dis-
tribution methods, both “forward” and “inverse” have now enabled design aerodynamicists to depart from these
families of aerofoils, there has been no corresponding expansion in published high Reynolds number data. The coming
of computerised boundary-layer calculations might be expected to improve the situation by releasing us from this
straight jacket of geometric correlations: however, though attempts had undoubtedly been made I am unable to
report any improved method of estimation based thereon.