Fighters Without Vertical Tails

The designers of the B-2 stealth bomber proved that the stability and control requirements for a subsonic-level bomber can be met without vertical tails. What is not clear is whether the more severe fighter stability and control requirements can be met without vertical tails.

All designs in a USAF Wright Laboratory multirole fighter study have either small ver­tical tails or none at all (Figure 22.4) (Oliveri, 1994). The preferred replacement for normal vertical tails is thrust vectoring and split ailerons. These controls were used successfully on the NASA/Boeing X-36 Fighter Agility Research Aircraft. A 28-percent-scale remotely piloted model was flown in 1997, reaching an angle of attack of 40 degrees.

A thrust vectoring scheme used to replace fighter vertical tails must have a high – bandwidth actuator responding to sideslip signals for directional stability as well as other stability-augmentation system signals and commands from the pilot. Unless split ailerons are used, for safety reasons it would seem necessary for a thrust vectoring sideslip loop to provide directional stability even at idle thrust. Alternately, engine thrust could be di­verted left and right when idle thrust is needed and modulated for directional stability and control.

All in all, stability and control engineers should come well prepared at design meetings where stealth is the topic.