MODEL AEROPLANE NOTES.

Dominion, Volume 30, Issue 154, 27 March 1937, Page II (Supplement)

MODEL AEROPLANE NOTES.

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AILERON

The Aerodynamics of Models. Many large volumes have been written on aerodynamics, volumes filled with statics, dynamics, calculus, and other mysteries. But there is no need to worry about mathematics to get a knowledge of aerodynamics'. This fearsome word only means “the reason why an aeroplane dies, and the reasons for the different positions it takes up while in all stages of a flight.’’ Every model-builder picks up some ideas about this, and the study of aerodynamics is only a matter of collecting the ideas and expressing them properly. A few of the things we know about the flight of a model are given below. Look at the first drawing. It shows a model aeroplane flying in level and steady flight. (The large arrow, un-uamed shows, in each drawing, the exact direction of flight.) The arrow, T, in front, shows the thrust, or the pull of the propeller, drawing the plane along. The arrow. D, represents the total “drag’’ of the model (wings, fuselage, tailplane, wheels) pulling it back. Now in steady flight. T anil D must: always 1. equal. Why? Because if they were not, the model would speed up or slow down. In the same way. L represents the lift of the wings (which are at a small angle of incidence. shown by “a”) and M the weight of the whole model. This weight is always shown as acting at the balancing point, or centre of gravity (C.G.), of the model. It pulls downward, of course. When a model is correctly balanced, the lift of the wings acts immediately above the centre of gravity, as shown here. When you slide the wing of a model along to get balance, yon are making use of this principle. Now in steady flight L and M must always be equal, because if they’ were not, the. model would climb

or dive (depending on which was the greater). Tims we have the four arrows, representing the four "forces” which act on a model in flight. This is the first principle of aerodynamics and i.s very important.

The second drawing shows the wing only, the same forces acting on it. The dotted lines indicate the air-flow over the wing, as a matter of interest. The chief points to be noted when a wing section is being chosen are the life, L. and the drag. D, at any’ given angle of incidence. A comparison is made of these, and the proportion of lift to drag noted. The higher this figure is. the better is, the wing section. The final result, i.e., direction. of both lift and drag acting on the wing is shown by the arrow L. I). Drawing 3 shows why a model comes back to level flight after having its nose accidentally raised. As shown, the wing has a large angle of incidence,, "a,’’ but the elevator is now lifting, being at an angle of incidence “n.” This raises the tail and brings the model level once mor”. Drawing 4 is similar, but shows how, when a model is diving, (he negative angle of incidence, "n." of the elevator causes it io pull down and bling the model level once more.

The last drawing. 5. shows how a dihedral angle helps to make a model steady in flight. The air spills out from under the raised wing and causes it to lose lift. In addition, the weight of the model causes the fuselage to swing down as low as possible, as shown by the curved arrow. These combine Io bring the model back to the normal flight position. All this is only a beginning. But it should be clear now that aerodynamics is not. as complicated as its sounds. And it is very interesting to know just what goes on during the flight of a model aeroplane.