**3.2 Concrete models analysis**

Four concrete models with varied wing parameters listed in table 6 were choosen for some further investigation. We carried out this new series of experiments in the hope of providing the effects of wings, rudders and propeller on the /*L D* and *l* α ′ at different glide angle of attack when the velocity is 0.5m/s and the angle of attack on the rang of 0°~20°.The model one has the highest glide efficiency and glide stability in the table6; The models 2~4 were proposed in order to evaluate the affects of location, aspect ratio and chord of wings on the analysis index as shown in the table 6. The Figure 8 gives the pressure distribution chart of model 3. The calculation results of different models are shown as Fig. 9~ Fig. 12.


Table 6. The parameter of the concrete model

The location of the wings has little influence on the *L*/*D*, which means it has little influence on the glide efficiency illustrated in Figure 9, but it has dramatic effects on the glide stability which can be seen in the Figure 10. From the figure 9 and 10, it can be seen that the *L*/*D* decreased and the *l* α ′ increased obviously when the aspect ratio and chord reduced, but the effects is more dramatically to decrease the chord of the wings for the *L*/*D*. It has the biggest lift to drag ratio when the angle of attack at 6 degree shown in Figure 9, that is means the maximum glide efficiency can be gain when the angle of attack at 6 degree.

Fig. 8. The pressure distribution chart of model 3

46 Autonomous Underwater Vehicles

It is well known that the chord and aspect ratio of the wings should be increased, and the backswept decreased for the higher glide efficiency when PETREL is operated in the gilde mode. Simutaneously, the backswept of the wings should be increased and the wings should be moved backward father behind the center of the vehicle for the higher stability. It indicates that the effects from the increment of the backswept of the wings are inversed in increasing the glide efficiency and the stability. The backswept of the wings should be

chord (mm) aspect ratio backswept location (mm)

Four concrete models with varied wing parameters listed in table 6 were choosen for some further investigation. We carried out this new series of experiments in the hope of providing

attack when the velocity is 0.5m/s and the angle of attack on the rang of 0°~20°.The model one has the highest glide efficiency and glide stability in the table6; The models 2~4 were proposed in order to evaluate the affects of location, aspect ratio and chord of wings on the analysis index as shown in the table 6. The Figure 8 gives the pressure distribution chart of

models chord(mm) aspect ratio backswept(°) location(mm) 1 200 10 40 0 2 200 10 40 100 3 200 8 40 0 4 150 10 40 0

The location of the wings has little influence on the *L*/*D*, which means it has little influence on the glide efficiency illustrated in Figure 9, but it has dramatic effects on the glide stability which can be seen in the Figure 10. From the figure 9 and 10, it can be seen that the *L*/*D*

effects is more dramatically to decrease the chord of the wings for the *L*/*D*. It has the biggest lift to drag ratio when the angle of attack at 6 degree shown in Figure 9, that is means the

maximum glide efficiency can be gain when the angle of attack at 6 degree.

′ increased obviously when the aspect ratio and chord reduced, but the

model 3. The calculation results of different models are shown as Fig. 9~ Fig. 12.

α

′ at different glide angle of

determined in terms of other capability indexes of the underwater vehicle.

the effects of wings, rudders and propeller on the /*L D* and *l*

Fig. 7. *l* α

′ Tendency chart

**3.2 Concrete models analysis** 

Table 6. The parameter of the concrete model

α

decreased and the *l*

Fig. 9. The relationship between *L*/*D* and angle of attack

Fig. 10. The relationship between *l* α′ and angle of attack

Hydrodynamic Characteristics of the Main Parts of a Hybrid-Driven Underwater Glider PETREL 49

The orthogonal experiment shows that glide efficiency is most significantly influenced by the chord length while stability of the vehicle is most remarkably affected by the sweep angle. Further numerical calculations based on four specific models with the attack angle in the range of 0°-20° indicate that location of the wings mainly affects glide stability but has little

When the vehicle glides at about 6° attack angle it has the maximum ratio of lift to drag. The range of the hybrid glider with the same configuration as PETREL will be decrease

The rudders parameters include root chord, half span, aerofoil and backswept, which are shown in Figure 13. As defined in the [23], the chord is denoted by*C* , the distance from the leading edge to trailing edge in a given two-dimensional section. The chord is measured in parallel with the section at the root of the rudder. In general, the chord can vary along the span, in which case the geometric mean chord,*C* , is used in computations unless noted[21].

> 2 *C C t r <sup>C</sup>* <sup>+</sup> <sup>=</sup>

foil section

thickness

Root Chord *C*r

(10)

leading edge

**3.3 Results and discussion** 

influence on glide efficiency.

**4.1 Rudder parameters** 

Fig. 13. Rudders parameters

Fig. 14. Foil section and hydrodynamic force

Rudder post

10%~35% compared with the legacy gliders.

**4. Rudder hydrodynamic design [22]** 

The *C* is defined based on Figure 14 as

Tip chord *C*<sup>t</sup>

trailing edge

semi-span *b*/2

Fig. 11. The drag ratio of rudders and propeller

Fig. 12. The lift-drag polar curve of four concrete models

The drag of the hybrid glider will be increased because of the drag generated by the rudders and propeller compared with the legacy gliders in the glide mode. The range in the glide mode will be decreased because of the drag of these parts . The ratio of drag on the propeller and rudders to whole drag is illustrated in Fig. 11, where we find that the ratio changed as the angle of attack increases, and the values is within the range of 10%~35%. Compared with the legacy gliders, the range of the vehicles with the same configuration as PETREL will be decrease 10%~35%. The Lift to Drag polar curves of the four concrete models are shown as figure 12. The model 3 and model 4 have the bigger lift than the model 1 and model 2 when the drag coefficients from the figure 3-9 is less than 0.5, but the lift of model 1 and model 2 increases greatly when drag coefficients gets bigger than 0.5. Due to the drag of the vehicle need overcome by the variable buoyancy *B* in the end and there is equation (9), so the net buoyancy supplied by the buoyancy driven system and glide angle should be taken into consideration.

$$B\sin\theta = D\tag{9}$$

Here *B* is the net buoyancy, θis the glide angle, *D* is the drag of the glider.
