Aerial-aquatic robots: adaptive & multi-part designs (I) - 8 Flashcards
What is the motivation for using structural adaptation approaches in UAAV design?
The motivation for using structural adaptation approaches in UAAV design is to improve the performance and versatility of these vehicles. Structural adaptation allows UAAVs to better handle the different physical properties of air and water, thus enhancing their ability to transition between aerial and aquatic environments.
Why is folding back the wings helpful for UAAVs with lifting surfaces?
Folding back the wings is helpful for UAAVs with lifting surfaces because it reduces both lift and drag. This can be used to initiate a dive and reduces impact forces, making the transition from air to water smoother and less damaging to the vehicle and requires minimal control.
What is meant by plunge-diving? What are the main risks associated with this type of manoeuvre and why is it nonetheless attractive for UAAVs?
Plunge-diving refers to a steep dive that results in the UAAV plunging into the water at high speed. The main risks associated with this type of maneuver are the potential for structural damage due to the high impact velocity and safety concerns related to high-speed dives from high altitudes. Despite these risks, plunge-diving is attractive for UAAVs because it allows them to reach depth passively, saving power and requiring minimal control if the robot is well-designed
How does folding back the wings help a UAAV to initiate a passive dive?
Lower lift, lower drag. Folding back the wings helps a UAAV to move the center of pressure backward, which, combined with a decrease in lift, initiates a passive stable dive. Also, an increase in the static margin is achieved with the award shift in the CP.
What factors influence the underwater depth that can be reached by a passively diving UAAV?
The underwater depth that can be reached by a passively diving UAAV is influenced by the altitude and velocity at the start of the dive as well as the increase in size.
Why is buoyancy a design challenge for fixed-wing UAAVs?
Buoyancy is a design challenge for fixed-wing UAAVs because it affects the UAAV’s ability to submerge and resurface. Too much buoyancy can prevent the UAAV from diving, while too little can make resurfacing difficult. Additionally, in the air a profiled wing is desirable for aerodynamic performance, but a profiled wing generates buoyancy which affects depth control negatively.
What are the main force terms involved in fixed-wing UAAV operation in air and water? Which forces are influenced by wing folding?
The main force terms involved in fixed-wing UAAV operation in air and water are propulsion, lift, drag, and gravity in air and water. For water, we have added mass and buoyancy. Wing folding influences both lift and drag, reducing these forces and making the transition between air and water smoother
How do the lift and drag change underwater, compared to the aerial case?
Underwater, the lift and drag change due to the different fluid properties of water compared to air. The wings are folded back, so there is significantly less area for lift. The tailplane is still effective and generates large forces because of the far higher fluid density. Folding back the wings reduces drag significantly, and skin friction dominates.
What time-varying effects occur during air-water transition and what forces do they influence?
During the air-water transition, time-varying effects influence the hydrodynamics (Area variation), mass (geometry variation), and buoyancy (volume variation) of the UAAV.
How are water impact angle and velocity influenced by velocity and altitude at the start of a passive dive into the water?
The water impact angle and velocity are influenced by the velocity and altitude at the start of a passive dive into water. The UAAV tends towards terminal velocity and a steady dive angle, but it needs time (sufficient altitude) to reach these conditions. Increasing initial velocity reduces the overshoot, leading to shallower impact angles
What characterises a “successful” water entry?
A “successful” water entry is characterised by the UAAV reaching the water at a velocity and angle that allow it to penetrate the surface and reach the desired depth without causing damage. This is achieved by ensuring that the UAAV is well-designed and that the momentum from the high-speed dive gets the robot into the water
