FLYING QUALITIES OF PILOTED AIRCRAFT - CAFE Foundation

MIL–STD–1797AAPPENDIX ARecoveryRapidityRecovery controlsDemandsAbility to recognizeAbility to perform necessary control actionAFWAL–TR–80–3141, ASD–TR–72–48, AFFDL–TR–78–171, and AFWAL–TR–81–3108 give moreguidance on design criteria for departure resistance. Critical factors include Cn β dyn (static directionalstability modified by product–of–inertia effects), a Lateral Control Divergence Parameter (yawing momentdue to roll control as a function of static directional and lateral stability), aerodynamic cross–axis couplingderivatives while sideslipping, and asymmetric nose–vortex shedding at zero sideslip.VERIFICATION LESSONS LEARNEDIt has not been uncommon to find that small configuration or mass changes, or even the addition of flight–testequipment (nose boom, spin chute), can change the post–stall behavior. While earlier models of the F–5 werequite benign at high angle of attack, increased stabilizer control authority in later models made loss of controlsomewhat easier. Some small changes to the contour of the wing–root leading–edge extension had apronounced effect, as did altering the nose shape.While spin–tunnel, rotary–balance and drop–model tests have been reasonably successful in predicting spinmodes, there has not been quite as good success in predicting the aircraft’s ability to get into some modessuch as a flat spin.See discussions on the deep stall characteristics of the F–16 (“Lessons Learned,” 4.8.4.2.3) concerning theaugmentation system effects on departure and modifications used for recovery.The departure rating scale shown on figure 257 was used in an experiment conducted by NADC(NADC–85091–60) to investigate candidate departure criteria. This experiment was performed on theDynamic Flight Simulator (DFS) and found inconsistencies in the pilot ratings especially with regard to“Departure Warning.” It was concluded that a departure/no–departure cutoff would be beneficial as well as abetter definition to the pilots of what is meant by a “clear” departure warning. In addition, more descriptorsbetween the 1–5 ratings would make the scale more useable. These descriptors, however, should preservethe linearity of the scale. Another conclusion of that experiment was that it would be worthwhile to consider amore Cooper–Harper–like scale for departure in order to “lock” the pilot into a departure rating moreconsistently.634