Out on hover power
This is about a production helicopter whose case of 'Hover OGE power being outside limits' found line pilots struggling. The hover power measurement for this twin engined helicopter is in terms of torque, which was out by 4-5% on each engine (A total of 10% of MORE power was required to hover than the stated performance).
The established deficiency in performance in NIL wind conditions was corresponding to a weight of approximately 300 kg at sea level, which for 5.5 ton Dhruv helicopter is significant.
Following were checked and found correct:-
1. Power Assurance requirements for ascertaining correct power output from each engine.
2. Empty weight of the helicopter through re-weighing.
3. Torque calibration.
4. Fuel and OAT gauge calibration.
Just that it doesn't go unsaid, this was a unique case in itself.
Having finished with the above checks without any worthwhile results, wouldn't it be prudent to check back the rigging angles of main rotor blades, which may be out of limits and thereby spoiling the L/D ratio of the rotor disc as a whole.
I opine that the additional drag as a result of the 'spoiled' L/D ratio due to the incorrect rigging angles may be resulting in higher torque values to provide the same rotor thrust, and therefore the helicopter is hovering at the given all up mass with higher torque values.
This opinion is also in light of the this helicopter undergone MGB change immediately before the problem surfaced. Though, the only factor which kept me wondering was whether a marginal variation outside the OEM stated rigging angles would result in a Hover OGE power variation corresponding to 300kgs?
Requesting for subject opinion and any suggestion to resolve the issue. Thanks