spite of existing damping actions. The effects of various damping 

 terms are discussed and three special cases for which the determination of 

 the critical flutter speed and frequency are of interest are treated. These 

 CEises occur for (l) damping which arises only from terms in the lift 

 force and associated moment, damping due to friction in the surrounding 

 flmd being excluded; (2) a foil rigidly mounted on a beam; and (3) a low- 

 frequency approximation, in which shear effects in the beam may be ignored. 

 For the latter case, it is shown that any low- frequency harmonic vibration 

 of the foil that can occur with the beam attached can also occur without 

 the beam and at the same frequency and stream speed provided certain simple 

 changes specified in the text are made in the foil. In subsection G.G, a 

 simple form of similitude is described. The parameters of the foil-beam 

 system are assumed to be changed in certain ratios with resiilting changes 

 in the frequency of vibration and in the critical flutter speed. The 

 necessary restrictions on the ratios are specified in detail. The 

 relations derived here may be of interest in designing a model to represent 

 a much larger system. 



T. In Section T, two simple cases of flutter are treated in order to 

 reduce the mathematical complexity to a point where int\ntive ideas of 

 the flutter process are relatively easy to arrive at. The cases discussed 

 are for (l) a foil attached elastically to an immobile base; and (2) a 

 foil elastically mounted with damping on a free rigid body. 



For these cases various concepts , relatively simple equations , and 

 criteria for flutter are presented; and methods are described for 

 determining the critical flutter speed and frequency from these equations. 



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