.
The flow around large items of superstructure, notably cranes, drilling derricks and exhaust stacks. Like the platform itself, these are bluff
bodies, and it is the turbulent wake flows behind these bodies that are important
.
Hot gas flows emanating from exhaust outlets and flare systems.
The current design criteria are based ultimately on achieving two objectives:
.
The vertical mean wind speed above the helideck at main rotor height shall not exceed ± 0.9m/s for a wind speed of 25 m/s; this equates to a wind vector slope of 2°
.
The maximum temperature rise, averaged over a 3 second time interval, in the vicinity of the flight path and over the landing area, shall not exceed 2oC.
These criteria are defined in CAP 437 [Ref: 40] and are taken to be the limiting conditions for safe helicopter operation. If they are exceeded under any conditions then the helicopter operator is to be advised, and in most circumstances an appropriate flight limitation should be entered into the HLL [Ref: 69].
It should be noted that, at present, there is no criterion for the severity of turbulence that can occur in the helicopter flight path. However, research is currently in progress to derive one and later versions of these guidelines are expected to contain such a criterion.
NOTE: The issue arises of how high above the landing area these criteria should be applied. CAP 437 [Ref: 40] says ‘…at a height above helideck level which takes into consideration the airspace required above the helideck to accommodate helicopter landing and take - off decision points.’ The recommendation in [Ref: 41] is more specific, saying ‘… up to a height above the helideck corresponding to 30 feet plus wheels - to - rotor height plus one rotor diameter’.
10.4.3 Plan Location of the Helideck
A key driver of the helideck location is the need to provide a generous sector clear of physical obstructions for the approaching / departing helicopter, and also sufficient vertical clearance for the helicopter to lose altitude in the event of a single engine failure. This requirement is for a minimum 210o obstacle free sector, with a falling 5:1 gradient below the landing area over at least 180o of this arc (see Section 6.4).
From an aerodynamic point of view the helideck should be as far away from the disturbed wind flow around the platform as possible. This objective, and the 210o obstacle-free sector, are most readily achieved by locating the helideck on a corner of the platform with as large an overhang as possible. In combination with an appropriate elevation and air gap (see Section 10.4.4), the overhang will encourage disturbed airflow to pass under the deck leaving a relatively horizontal and clean flow over the top.
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(7)
