Vertical Tail Size for Models
MODELERS know that the vertical tail is a necessary item for conventional full-scale airplanes and models, but they are often not aware of the effects of its size. This can be unfortunate, because its size can make or break the good flying ability of any airplane or model. There are two kinds of effects. Too small a tail will cause Dutch roll troubles for any airplane and also controllability troubles for piloted types. Too large a tail will cause either a slower recovery from lateral upsets by gusty air or, worse, no recovery. This means a spiral dive for models with little or no dihedral (Free Flight Scale models) and the inability to climb very steeply and achieve good duration for the high-powered Gas or Rubber Duration model. To understand this better, one must know the difference between trim and stability, since they are completely different things.
Vertical Tail Size for Models
PART ONE of this two-part article discussed the combined influence of vertical tail size and total effective dihedral on your model's stability in flight-and, for piloted airplanes, the influence of vertical tail size on in-flight controllability. This month's conclusion explains how to adjust vertical tail size to correct problems that show up in flight, discusses how to achieve a reasonable vertical tail area during the design stage, and explains turning trim, wing dihedral, and effective dihedral. A summary and appendices are included at the end of the article.
Wing and Tail Dihedral for Models
THE PURPOSE OF wing dihedral is to return the model to its proper (trimmed) attitude after is has been upset laterally (banked) by a disturbance such as gusty air or an improper launch. The model may be trimmed for either wings-level or a wings-banked flight, but when it is upset laterally, one wingtip will drop and the model will begin to sideslip downward in that direction. The sideslipping airflow then generates a slightly larger lift on the lower wing and a slightly smaller lift on the higher wing, which rolls the model back to its proper attitude (wings level or wings-banked).
Tails for Models
So-called V-tails have been used on full-scale airplanes such as the Beechcraft Bonanza and the Davis DA-2A, and modelers have used them occasionally on FF duration models and RC models. To the author's knowledge, however, there have been no design procedures published for the modeler's purpose. The purpose of this article is to provide the reader with a procedure for sizing V-tails for FF and RC. A V-tail is shown in Fig. 1. It consists of two panels having a dihedral angle, A, and a total panel area, S. S is the area if both halves of the V-tail were laid flat. A narrow center section can be provided for easy mounting on the fuselage.
