FREQUENCY DOMAIN METHODS FOR CONTROL RESPONSE ASSESSMENT

When the handling qualities research that formed the background to the LHX programme and led to ADS-33E [5.2] was conducted the traditional methods of quantifying control response were found deficient. It became clear that the frequency response of the helicopter was of greater importance, for certain flying tasks, than its response in the time domain. Indeed it was found that pilots flying rotorcraft with vastly different step response characteristics (natural frequency and relative damping) but identical frequency response characteristics would give similar handling quality rating for tasks that required frequent small control inputs. More precisely Hoh [5.5]

Table 5.2 Large amplitude response requirements.

Attitude command

Rate response types

response types

Achievable angular rates (deg/s)

Achievable angle (deg)

Level 1

Levels 2 & 3

Level 1

Levels 2 & 3

Agility category MTE

Pitch Roll

Yaw

Pitch

Roll

Yaw

Pitch Roll

Pitch

Roll

Limited agility Hover Landing Slope landing

+ 6 +21

+ 9.5

+3

+ 15

+5

+ 15 +15

+ 7

+ 10

Moderate agility Hovering turn Pirouette

+ 20

Vertical manoeuvre Depart/abort Lateral reposition

+ 13 +50

+ 22

+6

+ 21

+9.5

-30 +60

+ 13

+ 30

Aggressive agility Vertical remask Acceleration-deceleration

+ 20

Sidestep

Target acquisition and tracking Turn to target

+ 30 +50

+ 60

+ 13

+ 50

+ 22

+ 30 + 60

-30

+ 30

found, when conducting simulated deck-landing tasks, that pilot opinion remained unchanged for configurations with relative damping between 0.5 and 1.3. Later analysis showed that the common factor in all the configurations tested was the similarity in bandwidth or the range of input frequencies useable by the pilot.

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