Roll Angle-Sideslip Mode Ratio

The ratio is computed at the Dutch roll (DR) frequency. This modal characteristic helps in deciding the damping factor (damping ratio and frequency product). It signifies the relative roll oscillations with respect to the sideslip excursions. The latter aspect is of high significance in turn coordination.

10.4.2.2 LD Modes

Various LD modes are evaluated. These are discussed here.

Roll mode: The requirements are specified in Table 10.5. A good correlation is found between roll mode time constant and pilot rating.

Spiral stability: The time to double the roll angle should not be less than the specified values (see Table 10.6) following a disturbance of up to 20° in roll angle. This would reduce the workload of the pilot.

TABLE 10.5

Handling Qualities Specified Values for Max Roll Time Constant

Category of Flight Phase

Class of the Aircraft

Level 1

Level 2

Level 3

A

I, IV

1.0

1.4

II, III

1.4

3.0

B

All

1.4

3.0

10

C

I, II-C, IV

1.0

1.4

II-L, III

1.4

3.0

Source: Shaik, I. and Chetty, S. HQPACK User’s Guide, Vols. 1, 2. PC based SW package in MATLAB ver 5.2 for the prediction of handling qualities and pilot induced oscillation tendencies of aircaft. NAL Project document, PD-FC-9810, December 1998.

Coupled bank-spiral oscillations: The aircraft should not have a coupled bank – spiral mode for flight phase of Category A. It should not have coupled bank-spiral oscillation for Category C. For Categories B and C, the roll-spiral damping coeffi­cient Zrs vrs should not be greater than the specified values. The idea is that the roll control effectiveness should not be sacrificed. Also, the combined time delay due to various components in the aircraft-control loop should be limited so that the pilot’s tracking is not degraded (Table 10.6).

Dynamic LD response parameters: The minimum required values are specified in Table 10.7. The damping limits the DR oscillations.

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