It is an open question. Some aviators who have made very careful observations of birds in flight deny that the tails have anything to do with their direction. The theory is advanced by some scientists that the birds used their heads to change their course, operating them as a forward rudder, much as do some types of aeroplanes. They argue that since a rudder is much more effective when placed forward the smaller surface presented by the flat heads and necks of birds has more effect than a comparatively large tail. What is the relation of the wing surface to the weight and horse-power of the biplane as compared with the monoplane? The Wright biplane carries a trifle more than two pounds of weight for each square foot of lifting surface. The Bleriot monoplane carries about five pounds weight to every square foot of lifting surface. On the other hand the Wright machine carries about forty pounds per horse-power, whereas the Bleriot will only carry about twenty-seven pounds. These figures do not work out for all biplanes or monoplanes but they indicate broadly the relation between the two general types of aeroplanes. What would be the effect of bending down the outer ends of the wings of an aeroplane as the wings of some birds droop? The experiment is well worth trying. It would seem that this angle would give increased stability, although if the model were knocked off its course it might increase the resistance considerably. An elaborate test of this form has been made by an aeronaut named Weiss in England, who believes he has gained automatic stability in this way. Mr. Weiss has built and flown a number of aeroplanes, varying in size from one weighing five pounds to one which carried a weight of 140 pounds, and the tests are reported to have been very satisfactory. What is meant by the phugoid path of a model aeroplane? The line described by the machine in flight. Every aeroplane left to itself flies in a series of waves swaying more or less up and down from the horizontal. In a aeroplane under the control of an aviator this is largely overcome by manipulating the rudders controlling the vertical motion. Every model aeroplane or soaring machine has a phugoid path peculiar to itself which is affected by the power of its motor, the form of the wings, its ability to right itself, etc. It is obvious of course that if the path of your model aeroplane is irregular the machine must travel more slowly and its distance qualities are therefore reduced. Is a variable wing surface an advantage and can it be applied to model aeroplanes?