View Full Version : Hunting and Fishtailing
Montyd890
4th Jan 2010, 13:12
Hi hopefully someone can help me please.
Im trying to find out what the definitions for engine "Hunting" and helicopter "fishtailing" are please.
Thanks Mike
Hi Monty,
Forgive my terminology but...
If "Fishtailing" is to do with the inherrant stability of helicopter flight, then I know this as either:
Dynamic Instability, (where a disturbance will increase in oscillations if not otherwise corrected) or
Neutral Stability, (where a disturbance remains at the disturbed level of oscillation unless otherwise corrected) or
Dynamic Stability (where a disturbance will naturally reduce oscillations to a neutral level).
Engine "Hunting" happens when a change in power (Collective) setting requires a change in engine settings (to adjust engine revs to suit).
This normally results in a temporary engine "Droop" and a follow-up compensatory "Underswing" to automatically correct the engine settings for the required power.
When the Underswing is too coarse this can result in an overcompensation of fuel which can be followed by an undercompensation of fuel, that can then be repeated, going under and over the required setting, resulting in a hunting for the required fuel setting and a "pulsing" of the engine as it seeks the elusive 'middle'.
Hope this is simple enough, and not type specific.
N1 Vibes
5th Jan 2010, 04:42
Hunting - exactly as described by Rigga - can be the same sort of mode on fixed wing turbine engine controls. One of the more well known phenomena in the Civil aviation community is the RB211-22B 'pod-nod'. Caused by a very small seal in the fuel pump pulsing and leaking additional fuel to the burners.
Brgd's
N1 Vibes
nodrama
10th Jan 2010, 12:16
"fishtailing"....
an oscillation of the tail, caused by changes in Nr and resultant torque effect that isn't compensated for by yaw control. Or caused by a faulty yaw auto-pilot/ SAS actuator. Or caused by the pilot #*@king about.
Of course. In a twin, if you have a hunting engine then this MAY cause the a/c to fishtail.
Is this what they're after??