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Frequency-domain methods are used to identify the open-loop dynamics of the XV-15 tilt-rotor aircrafl from flight tests. Piloting and data analysis techniques are presented to determine frequency response plots and equivalent transfer funclion models. The open-loop pitch and roll dynamics for the hover flight condition exhibit unstable low-frequency oscillations, whereas the dynamics in the remaining degrees of freedom are lighlly damped and generally decoupled. Comparisons of XV-15 flight-test and simulator data are more favorable for high-frequency inpuls (o>1.0 rad/sec) lhsn low-frequency inpuls. Time-domain comparisons of the extracted lransfer funclions with step response flight data are very favorable, even for large amplitude motions. The results presented in this peper demonstrate the utility of the frequency-domain techniques for dynamics identification and simulator fidelilv studies. Notation6. , 6, , 6, az =vertical acceleration, uositive downward, g's f =discrete frequency, an =transfer function {P, rr ~, V )~G u~Y )~G , v~) =input, output, and cross-spectral functions Wp.% Lan =aileron roll sensitivi l / deg-aileron T~,~~, T~, T + L Mae =elevator pitch senslnvlry, ueg/ sec2/dea-elevator =aileron surface deflection (deg), elevator surface deflection (deg), and rudder surface deflection (deg), respectively =pitch and roll mode damping ratios, respectively =pitch and roll mode natural frequencies, respectively =heave, pitch, roll, and yaw transfer function time delays, sec -P. 4. r =roll rate, pitch rate, and yaw rate, respectively, deg/sec

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The determination of sensation thresholds has applications ranging from uses in the medical community such as neural pathway mapping and for the diagnosis of diabetic neuropathy, to potential uses in determining safety standards. This study sought to determine the sensation threshold, and the distribution of sensation probabilities, for pulse trains ranging from two 10 ms pulses to nine 10 ms pulses from 2.01 μm laser light incident on a human forearm and chest. Threshold was defined as the energy density that would elicit sensation 50% of the time (ED 50 ). A method of levels approach was used in conjunction with a monovariate binary response model to determine the ED 50 . We determined the ED 50 and also a distribution of threshold probabilities. Threshold was found to be largely dependant on total energy deposited for smaller pulse trains, and thus independent of the number of pulses. Total energy becomes less important as the number of pulses increases however, and a decrease in threshold was measured for a nine pulse train as compared to one through four pulse trains. Thus we have demonstrated that this method is a useful and easy way for determining sensation thresholds from a 2.01 μm laser for possible clinical use. We have also demonstrated that lower power lasers when pulsed can elicit sensation at comparable levels to higher power single pulse lasers.

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