Should the projected area of a V-tail be the same as a conventional tail?

From : Don Stackhouse

I see that old wives tale about sizing a v-tail using the projected area of a conventional tail has reared its ugly head again.

All other things being equal, for equivalent control authority a conventional, T, or V tail should all have the same TOTAL area. This is because of the need to be able to use full rudder and full elevator at the same time. If you make a V tail with the same PROJECTED area as your supposedly equivalent conventional tail, you will be able to make the same elevator force, or the same rudder force, but not both at the same time. For certain maneuvers (such as recovery from a spin), this difference can be very significant.

This rule refers to control authority, i.e.: how much correcting force the tail can make about the pitch and yaw axes. The calculation for equivalent stability is a little more complex, because the apparent change in angle of attack to a given disturbance for the V and conventional tails are not the same. The effective area of a V tail for pitch stability is equal to the total area times the cosine squared of the tail's dihedral angle. If you make the total area the same as the original conventional tail you will be in the ballpark.

Some have reported that their models seemed to be more maneuverable using the projected area method for making their substitute V tails. This makes perfect sense; in general, when you reduce stability (in this case because the "projected area" tail is smaller than the original tail) you generally increase maneuverability. The model has less damping about the pitch and yaw axes, so it takes less to disturb its flight path in those directions. Nothing wrong with any of this, just recognize that you have just re-engineered the basic design of your model by reducing the area of the tail, in addition to the change in tail configuration. Depending on how much surplus tail the model had to begin with, the results may or may not be satisfactory.

Don Stackhouse @ DJ Aerotech