Hovering in the wings
1
We didn’t directly smooth the Npers at any flight regimes in the Lynx I was involved with , we “controlled” their levels through regular vibration surveys and maintenance actions some of which I listed in my posting. One other significant check that I omitted were the main rotor flying control actuator linkages .
We would always attempt to get the ride quality best at cruise conditions 120~140kts but that effort was directed solely at 1R through blade tracking { pitch link and tab only we had no balance adjustables as all blades delivered from the blade facility were deemed “compatible” <img src="wink.gif" border="0"> }
We did not have absorbers in any shape of form fitted then as they carried a weight penalty which any naval aviator would rather trade fuel for!
( I believe later marks with some equipment fits may have a F/A absorber fitted now) .
The Army had rotorhead mounted spring absorbers to make life easier for the TOW sighting system (I think), as Nick said they are only effective for a narrow tuneable band of Nr, their effectiveness on the Lynx was limited as the engine control system was then hydro-mechanical governors with a static droop range of 107 to 102.5% Nr and their power on Nr was quite lively within that range so the absorber was only working effectively in stable regimes of flight when the crew had selected the Nr for which the absorber had been tuned. A Fadec equipped machine would probably control the Nr significantly better and thereby keep it in step with the Absorbers tuned frequency band.
2
On the metal bladed Lynx (I can only speak from experience on these) once clear of the transition in forward flight the Lateral and vertical Nper rev figures rose almost linearly with increasing airspeed the F/A levels rose almost exponentially however. The characteristics may well be different with the composite bladed machines with the cropped stabilisers and elastomeric Engine Gimbal bearings.
The worst steady regime of flight that I remember for vibration was doing Para-drop type max rate climbs at about 60kt but I think that was the (original shape) stabiliser taking a beating and as I never had any kit fitted for those flights could not say for sure whether it was Nper 1R or some cocktail in and around those frequencies.
Wunper {8 <img src="smile.gif" border="0">
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