TAILPLANES AND FINS AS ENDPLATES (see Fig. 6.7, p.74)

Tip endplates can be useful to increase the effective aspect ratio of a tailplane or Tin, with possibly good effects on stability and control response. A tailplane or canard forewing fitted with end fins will have a steeper lift curve slope and become more powerful. The end fins can serve as fins for the whole model so their drag will be hardly any greater than that of a simple central fin of equal, or slightly less, area. However, the twin fins will have four tips and their aspect ratio will be very low reducing their effectiveness, and this, with their structural vulnerability, makes their use of doubtful value. They may cause more trouble than they are worth in practice. However, the tailplane itself may act as an end plate to a fin. if it is mounted on top of the fin, in ‘T configuration, or if the fin is mounted entirely above it. This restrains the vortex at one end of the fin and increases its effective aspect ratio. The T tail arrangement also carries the tailplane out of any possible airflow disturbance caused by the wing-root-to-fuselage junction. Both fin and tailplane may then be slightly reduced in area, which helps to compensate for the increase in structural weight caused by the necessity to stiffen the fin to carry extra loads. A high mounted tailplane is also less likely to blanket the fin during the towline launches or spinning. It is more vulnerable in ground loops and heavy landings but less easily damaged in normal landings because higher off the ground than a low tailplane.

Fins mounted ahead of or behind the tailplane are often preferred for their structural simplicity.