2.2.4. Empennage

According to Raymer [18], the empennage should typically be considered to be conventional. Nevertheless, unconventional tail configurations may have advantages in special use

cases. The criteria related to structural connections, dimensions, mass and flow interactions must be considered when deciding on the type of empennage [18].

Depending on the chosen propulsion concept, the yawing moment must be considered when designing the vertical tail plane (VTP). If the propulsion concept is not different from the reference aircraft, the empennage is dimensioned with a volume coefficient similar to the one of the reference aircraft. Since the configuration includes wingtip propellers, the volume coefficient of the VTP has to be increased to provide a sufficient yawing moment during wingtip engine failure. The increase is calibrated using the reference aircraft. First, the volume coefficient of the reference aircraft is determined. The ratio between the yawing moment created by the engine in the one engine inoperative (OEI) case and the volume coefficient of the VTP of the reference aircraft is calculated. This ratio is used to increase the conventionally calculated volume coefficient to account for the unconventional architecture.
