Comments on "Navy Variable-Stability Studies of Longitudinal Handling Qualities"

Abstract

EFERENCE 1 by J. A. Eney contains a misapplication of criteria which leads to erroneous conclusions. Mr. Eney incorrectly states that his Refs. 5 and 6 both have envelopes that are normalized about a steady-state value that is not defined. We found that it was not feasible to specify a single criterion encompassing both the transient and steady-state responses of the longitudinal control system. We therefore specify a criterion for the transient response and a separate criterion for the steady-state response. The envelopes to which Mr. Eney refers are envelopes for transient responses normalized to their own steady-state value. All responses therefore reach a steady-state value of 1.0. By rescaling his curves in Fig. 10, Mr. Eney will find that most of the 2.5 rated responses fall within the envelope. The conclusions reached by Mr. Eney about the inadequacy of the criteria of Refs. 5 and 6 are therefore highly distorted. The steady-state response is governed by stick force per g in the current military specification. As Mr. Eney pointed out, stick force per g is of little consequence in visual landing approach. This is because vertical acceleration is not predominant due to the pilot during landing approach. We found that stick force per C* provides a steady-state criterion that includes landing approach. The steady state FS/C* criterion described below has somewhat arbitrary limits, but it does show how steady-state criterion can be applied separate from the transient criterion. A forward velocity of 1500 fps was selected to set the Fs/n2 limits between 3.32 lb/gr and 8.85 Ib/gr. The corresponding Fs/C* limits were then found to be 2.62 Ib/g and 7.0 Ib/g and were assumed independent of forward velocity. The variation in Fs/nz limits was then computed as a function of forward velocity corresponding to the constant FS/C* limits. A plot of these limits is shown in Fig. 1. Also included on this plot are values of F8/n, and FS/C* for a typical supersonic fighter.