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Helicopter Decks

In document Indian Coast Guard Ships (Page 112-117)

Figure : Stresses of Panel for buckling assessment Boundary conditions

Buckling load cases are to be applied suitably to the buckling panel under evaluation, depending on the stress distribution and geometry. In general simply supported boundary conditions of all edges will be applied.

7.4.4 Deflection of primary girders

The maximum relative deflection of primary girders is not to exceed the following criteria:





δ =


δmax: Maximum relative deflection [mm]

li : Span of primary girder [mm]

Section 8

are to be complied with. Consideration is to be given to airflow over the landing area & surrounding structures. These rules assume that the helicopters are fitted with oil/gas dampers and pneumatic type under carriages, arrangements other than these, will be specially considered.

8.1.2 Definitions OLEO load is defined as the load, which will cause the damper and tyre combination to reach the end of their travel. The All-Up-Weight (AUW) is the maximum weight that will be encountered for the specific application under consideration. It includes the maximum total weight of helicopter, personnel, fuel and payload.

8.1.3 Documentation Plans showing the proposed scantlings and arrangements of the structure are to be submitted for approval. The type, size, the OLEO load and AUW weight of each of the helicopters to be used are also to be indicated. Details of arrangements for securing the helicopter to the deck are to be submitted for approval. A landing guide should be provided as part of the ships’ documentation. This is to contain all the relevant information of the helicopters on which the helicopter deck design has been based, identification of landing, parking and maneuvering areas, tie down arrangements, weights and a summary of the design calculations.

8.1.4 Flight deck arrangements The landing area is to be sufficiently large to allow for the landing and maneuvering of the helicopter, and is to be approached by a clear landing and take-off sector complying with the applicable regulations. Normally, for maximum flexibility in helicopter operations, the landing area is to be taken as a square, with each side not less than 1.25 times the rotor diameter. Where the operation of helicopters is restricted to known helicopter types, the areas of deck structure to be assessed for the landing condition are to be taken as squares, with each side not less than two times the maximum wheel strut spacing. The squares are to be centered on all the normal landing points, at all specified landing orientations, for all helicopters. The takeoff and landing area are generally to be free of projections above the level of the deck. Projections above 25 mm may only be permitted where allowed by the helicopter undercarriage design standard. Projections outside the landing and takeoff areas are to be kept to a minimum such that they do not hinder helicopter maneuvering operations. The structure is to be designed to accommodate the largest helicopter type which it is intended to use. It is advised that an allowance be made for future growth of the helicopter weight such that future operations are not restricted to lower sea states. Suitable arrangements are to be made to minimize the risk of personnel or machinery sliding off the landing area. A non-slip surface and anchoring devices, and in the case of independent platforms, safety nets, are to be provided. The following lighting arrangements are to be provided for the helicopter landing area as per the requirements of the Indian Coast Guard Authority.

a) Safe landing area perimeter indicting lights;

b) Flood lights / LED arrays for illumination of landing area;

c) Obstacle marking lights.

8.1.5 Fire safety The requirements in respect of fire protection of helicopter landing, maneuvering and parking areas and in way of the helicopter facilities, are to comply with the requirements given in Chapter 9 Section 7.

8.2 Design Loads

8.2.1 Helicopter deck loading The load cases to be applied to all parts of the structure are defined in Table

Table Tyre Force Loading Tyre Force to be considered

Structural element >> For Plating For Stiffening

Load Case Fpl


Fstiffr kN Helicopter Landing Cases

Crash Landing 1.2 * f1 * Woleo 1.6 * f1 * Woleo

Normal Landing 0.6 *1.2 * f1 *Woleo 0.6 * 1.6 * f1 * Woleo

Operation on decks

Manoeuvring 1.6 * f2 * Wty 1.6 Wty

Parking ( stowed condition ) (1 + 0.6 av/g) * f2 * Wty (1 + 0.6 av/g) * f2 * Wty

Table (Contd.) Where,

f1 = 1.15 for landing decks over magazines, manned spaces, e.g. deckhouses, bridges, control rooms, etc.

= 1.0 elsewhere

f2 = 1.10 for exposed decks

= 1.0 for internal decks not directly exposed to weather

Wty = static load, on the tyre print, in kN; with the centre of gravity in a position that causes the highest load. In the absence of specific helicopter manufacturers’ information on the static distribution of load, Wty may be taken as Wauw divided equally between the two main undercarriages ignoring the nose or tail wheel. For helicopters with twin main rotors Wty is to be taken as Wauw distributed between all main undercarriages in accordance with the static load distribution.

Woleo = Oleo Ultimate Load, kN (and not collapse load, which refers to complete failure) of undercarriage

Wauw = the maximum all up weight of the helicopter, in kN, as defined in av = vertical acceleration [m/s2], See Chapter 3, Cl 2.1.3

8.3 Scantlings

8.3.1 Helicopter deck scantling The scantlings of helicopter deck structures are to meet the requirements given in Section 3.2 below for helicopter landing cases and those given in Section 8.3.3 below for cases related to helicopter operation on decks using respective loads as given in Table

8.3.2 Scantlings for helicopter landing loads Deck Plating

The net thickness ’


net’ of deck plating subjected to landing loads as defined in Sec 8.2, is not to be less than :

2 pl_landing

net 1 a

c b s p

t f [mm]



C σ



The deck panel dimensions a,b,s,l [mm], fa , C2 and m are as given for plating in, Section 9.3.1 and



= Fpl_landing 103 / ( a.b ) [N/mm2]

Fpl_landing = Tyre force for plating & the landing case under consideration, as per Table [kN]

C1 = 1.8 for crash landing case, and = 2.1 for normal landing case Deck Stiffeners

The scantlings of stiffeners subjected to Crash/Normal Landing are also to meet the following requirements:

- The net section modulus is not to be less than:

3 stiffr_landing a

c ab p

Z m σ

= l

 [cm3]




= Fstiffr_landing 103 / ( a.b ) [N/mm2]

Fstiffr_landing = Tyre force for stiffener & the landing case under consideration, as per Table [kN]

C3 and m are as given for stiffeners in Section 9.3.2


a =


Y for for crash landing case, and

= as given in Table for normal landing case

Suitable lugs are to be fitted in way of crossing of deck stiffeners and the primary girders to provide weld connection on either side of the stiffener . The total area of the weld connection as well as the area of the stiffener web, each is not to be less than:

3 2

2 w

5R(m 2m 2)

A [ cm ]


− +




[N/mm ]


3 σ


τ =

R = Fstiffr_landing for the crash landing case m = a/

l Deck primary girders

The scantlings of girders will be specially considered based on the most severe location of the tyre print. The resulting stresses, based on net scantlings, are not to exceed allowable stress,


a, is not to exceed 0.9


Y for crash landing case, and


a as given in Table for normal landing case.

The deflection of the girder due to landing loads is not to be greater than (1/325)th of the span of the girder.

8.3.3 Scantlings for loads related to helicopter manoeuvring and stowage on decks The scantlings of deck plating, stiffeners and primary girders in respect of loads related to helicopter operations on decks are to be determined in accordance with Sec 9- Vehicle Decks.

However, the tyre print pressure as per Sec 9 is to obtained by using the Fplating in lieu of “W”.


Fplating = Tyre Force as per Table in Manoeuvring or Stowed condition whichever is greater :

Section 9

In document Indian Coast Guard Ships (Page 112-117)