Feature 3 | Helo/AircrAft HAndling
Through-life effects on flight deck assessed
frazer-nash consultancy has also recently undertaken an analysis of the through-life effects of aircraft landing vertically
on the new QE class carriers. The work has produced useful data on the likely transfer of heat through the flight deck and a
further assessment of effects of distortion and fatigue on the working life of the ship. the study has helped to demonstrate
that the deck will not be damaged by vertical landing operations.
As the development of the royal navy’s new Qe class aircraft carriers continues, frazer-nash has been continuing to
provide advice to the consortium responsible for the design and build of the two ships, the Aircraft carrier Alliance (AcA),
on a design for the new carriers’ hull structure. As part of an overall assessment of the ship’s structure and potential risks
associated with the operation of f-35 Joint Strike fighter (JSf) on the carriers, the team evaluated the effect of the high
thermal load which is likely to be produced by the aircraft when landing.
In particular, this identified a potential risk to the structure as a result of heat being emitted directly towards the flight
deck during a vertical landing sequence. the concern was to ensure that the thermal load produced by the aircraft did
not influence the structural performance of the steel flight deck, leading to distortion of the deck, bulkhead and stiffeners,
or causing problems for equipment located below the deck.
to assess the risk, frazer-nash developed three computational models to model the jet plume beneath the JSf and
calculate the likely conduction of heat throughout the aircraft carrier structure, before assessing the possibility of distortion
occurring in the flight deck and the consequent likelihood of cracks occurring in the structure.
The consultancy used computational fluid dynamics (CFD) to create an ‘aero-thermal’ model of the F-35’s jet plume
during vertical landing. By creating a 2-D view ‘slicing’ through the jet plume, the model shows not only the heat of the jet
plume, but also the velocity contours of airflow as it reaches the deck.
Significantly, the model is transient, showing the entire vertical landing sequence from initial hover to touch-down.
the team was therefore able to evaluate the temperature and velocity of the jet plume at various stages of descent and
examine the transfer of heat to the flight deck throughout the manoeuvre.
the cfd work then provided data on the heat directed at the deck, which could be applied to an fe analysis of the
deck’s structure. to do this, frazer-nash created an fe model of a cross-section of the ship, showing the full width including
the forward island ‘footprint’ and uptakes/downtakes for the ship’s funnels/stacks. Using the known thermal properties of
the structural steels, the FE analysis showed the structure as a ‘mesh’ of elements, each of which had specific heat diffusion
properties.
To test the likely heat transfer between these elements, the team considered a specific scenario involving F-35 aircraft
landing in short sequence a total of eight times, either over the bulkhead or away from the bulkhead position. the team
made assumptions about likely ambient air temperature and solar radiation, and assumed that the deck would have no
thermal protective coating or wind flow across the deck.
Using the above scenario, the FE work was used to predict stresses and strains on the structure through a flight deck
distortion analysis which revealed that any temporary distortion will be insignificantly low. Using the stress ranges
calculated above, the team then determined that the fatigue life of the deck will be greater than the proposed service life
of the carrier.
The work of the team has firstly produced useful data on the flow regime of the jet plume of the F-35 JSF. The subsequent
calculations for deck surface temperature, distortion and fatigue have then proved the suitability of the structure for
operational use and verified that the deck plating and stiffening in place is adequate to enable a service life of 30 years.
Importantly, it will also enable the ACA to create requirements for future inspection of the flight deck for degradation and
crack initiation. the information on likely temperature increases below the deck will also be used to address risks to any
equipment located in the compartments immediately beneath the flight deck, an important consideration as the ship’s
development continues towards completion.
that the installation weld is between be easily inspected and cleaned. The the tie-down point. It was recommended
similar metals, with any welding of team also identified an opportunity to that the weld between this material and
dissimilar metals incorporated into the remove the requirement for through-life the holding ‘pot’ be protected using a
assembled part. servicing. In order to therefore meet a Thermally Sprayed Aluminium (TSA)
Given the lesson learned regarding 30-year life requirement, options were coating. The team also increased the
moving parts on the Invincible class, considered for reducing wear. diameter of the crossbar to provide a
the team’s analysis of maintenance The first was the selection of a stainless greater wear allowance.
requirements stipulated no moving steel known as ‘Super Duplex’ in the Finally, after making the above
parts plus an open design that could construction of the main cruciform of design decisions, the team was finally
22 Warship Technology March 2010
WT_Mar-2010_p20-22-23.indd 22 23/02/2010 15:55:39
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