Just Noticeable Differences for Variations in Quasi-Steady Stall Buffet Model Parameters

Abstract

To gain more insight into human sensitivity to variations in simulated stall buffets, Just Noticeable Difference (JND) thresholds were estimated using a passive human-in-the-loop flight simulator experiment. Using an in-house developed flow separation-based stall and buffet model of the Cessna Citation II, JND thresholds were determined for the model's buffet characteristic frequency parameter omega0 and the buffet onset threshold parameter Xthres for the vertical stall buffet only. With a subjective yes/no 1-up/1-down staircase procedure that uses repeated pairwise comparisons of quasi-steady symmetric stall simulations (where one is a stall with the baseline buffet model and the other one has an offset buffet parameter), upper and lower JND thresholds were measured from 21 pilots. The experiment results show that the pilots noticed the differences in simulated buffet dynamics at comparably similar percentage-wise offsets for Xthres and omega0 with respect to the baseline parameter values. The maximum observed JND thresholds did not exceed 30-35% across all experiment conditions, indicating that pilots are fairly sensitive to even small offsets in the key stall buffet model parameters. Moreover, the estimated JND thresholds for omega0 are in agreement with the +/-2 Hz tolerance currently used in stall buffet simulation qualification standards. However, for Xthres, the results show that human pilots already notice differences in stall buffet onset characteristics well before the maximum allowed tolerance (+/- 2.0 deg angle of attack) is reached, which suggests that stricter tolerances on simulated buffet onsets for quasi-steady symmetric stalls may help to further enhance stall training in simulators.