Development of augmented control laws for a tiltrotor in low and high speed flight modes

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Vigan, L.
Riccardi, F.
Leonello, D.
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Tiltrotors present unique features with respect to both conventional helicopters and fixed wing aircrafts. The use of traditional cockpit flight controls, particularly if complemented by standard albeit Fly-By-Wire stabilisation and command augmentation systems, may cause a high piloting workload as the pilot is required to manage the thrust vectoring and the flight path control manually. This paper presents a novel control strategy for a future Tiltrotor which aims at reducing the piloting effort, and it is enabled by the combined use of state-of-art active stick technology and highly augmented control laws. The paper focuses on the control functions investigated so far, namely Translational Rate Command for hover and low speed (helicopter configuration), and flight path control for high speed (airplane mode) operation. Both control strategies embed peculiar characteristics that differentiate them from the corresponding standard fixed-wing and rotary-wing application counterparts. The paper presents numerical results of the proposed control algorithms obtained through a fully non-linear Tiltrotor simulation model developed by Leonardo Helicopter Division.