cranfield0014

<DOC>
<DOCNO>
14
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<TITLE>
piston theory - a new aerodynamic tool for the aeroelastician
.
</TITLE>
<AUTHOR>
ashley,h. and zartarian,g.
</AUTHOR>
<BIBLIO>
j. ae. scs. 23, 1956, 1109.
</BIBLIO>
<TEXT>
  representative applications are described which illustrate the
extent to which simplifications in the solutions of high-speed unsteady
aeroelastic problems can be achieved through the use of
certain aerodynamic techniques known collectively as /piston
theory ./  based on a physical model originally proposed by
hayes and lighthill, piston theory for airfoils and finite wings
has been systematically developed by landahl, utilizing expansions
in powers of the thickness ratio and the inverse of the
flight mach number m .  when contributions of orders and
are negligible, the theory predicts a point-function relationship
between the local pressure on the surface of a wing and the
normal component of fluid velocity produced by the wing's
motion .  the computation of generalized forces in aeroelastic
equations, such as the flutter determinant, is then always reduced
to elementary integrations of the assumed modes of motion .
  essentially closed-form solutions are given for the bendingtorsion
and control-surface flutter properties of typical section airfoils
at high mach numbers .  these agree well with results of
more exact theories wherever comparisons can be fairly made .
moreover, they demonstrate the increasingly important influence
of thickness and profile shape as m grows larger, a discovery that
would be almost impossible using other available aerodynamic
tools .  the complexity of more practical flutter analyses-e.g., on
three-dimensional wings and panels-is shown to be substantially
reduced by piston theory .  an iterative procedure is outlined, by
which improved flutter eigenvalues can be found through the
successive introduction of higher-order terms in and  .
  other applications to unsteady supersonic problems are reviewed,
including gust response and rapid maneuvers of elastic
aircraft .  steady-state aeroelastic calculations are also discussed,
but for them piston theory amounts only to a slight modification
of ackeret's formulas .
  suggestions are made regarding future research based on the
new aerodynamic method, with particular emphasis on areas where
computational labor can be reduced with a minimum loss of precision
.  it is pointed out that a mach number zone exists where
thermal effects are appreciable but nonlinear viscous interactions
may be neglected, and that in this zone piston theory is the logical
way of estimating air loads when analyzing aerodynamic-thermoelastic
interaction problems .
</TEXT>
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