.
Relocate the obstructions
.
Relocate the helideck.
If none of these are successful, then a more detailed assessment is required, and an aerodynamic specialist should be consulted.
To minimise the effects for other wind directions, then obstructions should be located as far away as possible from the helideck. In the case of the exhaust stacks, these should be sufficiently high to ensure that the plumes are above the helicopter approach path. To achieve this, it is recommended that the exhaust outlets be no less than 20-30 m above the helideck.
NORTH
SOUTH
157.5 degrees
NORTH
Unacceptable obstruction location
SOUTH
Acceptable obstruction
NORTH
location
EAST
157.5 degrees
Figure 10.16 - Third most favourable helideck location is at the east corner. About half the prevailing wind directions will carry turbulent wakes towards the helideck. The location permits clear into-wind approaches to be flown but many prevailing wind directions will have an obstructed overshoot path.
10.9.6 Estimating Helideck Downtime Due to Wind
The installation flow studies outlined in Section 10.9.2.2 are likely to identify combinations of wind speed and direction which result in flow conditions over the helideck that do not comply with the guidance requirements (0.9m/s downdraft, 2oC temperature rise etc.). Ultimately the wind speed and direction conditions that lead to these will need to be communicated to the helicopter operator (see Section 10.10).
However, in these circumstances it is important to estimate the likely severity of the flight limitations. It may be that they will be sufficiently limiting to operations that the cost to the field operator will be too high (this cost being experienced in terms of flights that cannot operate when required, and payloads that are less than maximum). This operating penalty may be avoidable if design changes are made to the helideck, its location or to other installation topside features (e.g. turbine exhausts). These changes may involve additional capital costs that need to be assessed against the operating penalty.
A rational decision can be made about such design changes if a quantitative estimate of the helideck downtime is made and presented to the platform operator.
A wind speed and direction frequency table (see example in Figure 10.18) can be used to make the estimate of downtime.
On the frequency table highlight all combinations of wind speed and direction that flow studies have indicated will not fulfil the guidance requirements. Adding up all the highlighted values will give the estimate of the total percentage of the time that the helideck will be unavailable for flight operations or where payload limitations may be imposed.
Beaufort Number Wind direction (from)
中国航空网 www.aero.cn
航空翻译 www.aviation.cn
本文链接地址：离岸直升机起落甲板设计指南 OFFSHORE HELIDECK DESIGN GUIDELINES 2(26)
