Airbus Helicopters

The industry of UAVs (Unmanned Aerial Vehicles) has experienced a significant development
over the last decades. These types of platforms have been implemented in a wide range of
applications such as surveillance, photography, and weather monitoring, both for military and
civil purposes. Among other benefits, their implementation eliminates the risks associated
with having a pilot and potentially reduces the operational costs.
Within the wide spectrum of UAV categories, rotary wing unmanned aerial vehicles
(RUAVs) constitute a popular solution to perform a wide variety of tasks. Their hovering
capability makes them suitable for surveillance and rescue missions, whereas their vertical
take-off and landing (VTOL) capacity allows them to operate from deteriorated landing areas.
These characteristics make RUAVs capable of completing tasks inconceivable for fixed wing
UAVs. Among these, the operation from small ships has drawn the attention of industry and
academia.
t is defined as helicopter shipboard operations to the set of techniques and tasks that
allow a rotary wing vehicle to be launched and recovered from a ship . Nowadays, these types
of missions need to be performed with a pilot on board, because a fully autonomous system
does not exist. The highly demanding environment encountered by pilots when operating
near a frigate has encouraged engineers to develop tools to facilitate the mission success
(such as the LPD [
8
]) and to design autopilot systems that eliminate the necessity of an
human operator. The later has only been demonstrated by Northrop Grumann's Fire Scout
helicopter under benign sea and wind conditions. However, automated landing under high
sea state levels remains an unsolved problem, as it involves the inclusion of the following
factors which limit the operation of the helicopter:
2
Introduction
1.
Stochastic airwake:
The turbulent flow developed behind the frigate bulk generates
large spatial and temporal gust velocity gradients which increase the pilot's workload
and might push the helicopter outside its operational envelope. Predicting the loads
induced by the airwake in the helicopter represents a highly complex problem itself, as
these will depend on the helicopter and ship specifications, their relative position and
their relative motion. Therefore, practical implementation of airwake for simulation and
control design purposes requires multiple simplifications which will add a significant
competent of uncertainty to the problem.
2.
Ship motion:
The high amplitude stochastic nature of ship motion in high seas is
amplified at the flight deck, due to the design tendency of placing this at the stern of
the frigate. Accurate real-time predictions are subjected to high levels of uncertainty
and are only available in short windows (5-10 seconds)
3.
Control design:
Helicopter control under these gusty conditions represents a difficult
problem for designers, as tuning controllers requires some knowledge on the distur-
bances encountered. However, as stated before, the estimation of these disturbances
depends on a high amount of variables which are dependent on the helicopter/ship
combination and the Wing Over the Deck(WOD) conditions.
To summarize, the implicit uncertainties in ship motion prediction, airwake characteristics
and helicopter response are the inherent problems to this subject which explain why the
automated landing problem remains unsolved.