CONFIGURATION LAYOUT

The design of various parts of the WIG will be look into in this section. As most of these parts are coupled with other disciplines, the discussion will focus on how they are

integrate with the knowledge of aerodynamics. Reference will have to be made for more details for the design of the respective parts.

4.3.1. PROPULSION SYSTEM INTEGRATION

With the majority of the airframe components determined, the next item will be the propulsion system to drive the craft on air.

The propulsion system integration is done with Mr. Toh Boon Whye who is in charge of the propulsion system in this project. To determine how much thrust is needed to propel the craft forward will then depend on the drag force acting on the craft. In cruise condition, the thrust produce must be equal to the drag of the craft at that cruising speed.

Hence the selection of the propulsion system will depend on the cruising speed of the craft. At this stage, a better weight estimate of the craft will now be available since most of the design work is done.

Table 4.2: Second Estimation of mass breakdown of components

Components Mass / kg % total Mass

Propulsion ( Prop, motor + speed controller )

0.350 21.5

Structural (fuselage, wings) 1.100 67.5

Electronics (servos, receiver, wires ) 0.180 11

Total Mass 1.630 100

Base on the second estimate of the weight of the craft, the required cruising speed is obtained from the Lift:

1 L

Where CL is obtain from Fig. 4.6, S is the projected area of the craft on the ground plane, and ρ∞ is density of air.

From the thrust analyses conducted by Mr. Toh Boon Whye, the thrust characteristic of the different propellers is plotted in Fig. 4.11 with the drag force predicted by CFD.

The intersection of between the thrust characteristic and the drag curve represents the cruising speed of the craft. Hence of the four types of propellers available, only the two 7 inch diameter propeller are found match the thrust requirement for the craft. The four blades 7 inch diameter is selected finally as it produces slightly more thrust than its two blades counterpart.

0.00

Fig. 4.13. Thrust Characteristic for different propellers.

4.3.2. POSITION OF CENTER OF GRAVITY

Similar to an aircraft, the c.g position of the WIG plays an important role in achieving longitudinal stability. The analyses for stability of the craft are done with Mr. Quah Yong Seng, Jonathan who is in charge of the flight control system design. To achieve longitudinal stability calls for the following two conditions to be met ^[12]:

0

C^mα< and - (4.4)

0

Cm⁰> - (4.5)

Mathematically, equation 4.4 and 4.5 means the WIG moment characteristic curve must intercept at the positive y-axis and has a negative gradient.

Fig. 4.14 shows the moment characteristic curves of the craft taken at different c.g position. It shows that a wing alone design is normally not stable especially if the airfoil used is positively cambered as regardless which position the c.g is placed, it will never meet the above two requirements. Typically, a convenient position for the c.g. is chosen to be near or at the aerodynamic center which in this case at 33% of the chord. This is done in particular to enable the horizontal stabilizer to be easily design to suit conditions 4.4 and 4.5 and will be discussed in further details in the next section.

c

Cm Vs AOA

-0.4 -0.3 -0.2 -0.1 0 0.1 0.2

-3 -2 -1 0 1 2 3 4 5

AOA

Cm

0c 0.333c 0.5c

Fig. 4.14. Moment characteristic curves with different c.g position.

4.3.3. HORIZONTAL STABILIZER

The horizontal stabilizer is used to provide longitudinal trim and stability of the craft. For an aircraft, it can be either mounted behind the main wing which is the conventional way or in front of the main wing and is known as the canard. Here, the conventional design will be chosen and therefore the horizontal stabilizer will be mounted at the tail of the craft.

In addition to longitudinal stability, a WIG requires height stability. In order to achieve height stability, the horizontal stabilizer is normally mounted high out of ground effect.

More detailed analyses of longitudinal and height stability is carried out by Mr. Quah Yong Seng, Jonathan. Since the horizontal stabilizer is like a secondary pair of wings mounted on the tail and is mounted out of ground effect, hence the horizontal stabilizer will be taken as a wing in the absence of ground effect.

-0.06

Fig. 4.15. Pitching Moment Characteristic of WIG.

The total moment acting on the WIG is the sum of the moment contribution about the c.g from the wing-fuselage combination and the tail. When expressed in dimensionless form, the moment equation taken with respect from the c.g is given as:

Cmwf + Cmt = Cmwft - (4.6)

The blue curve represents the desired condition for stability. The moment characteristic of the wing-fuselage combination is obtained from Fig. 4.15 with the thrust taken into account. The tail moment characteristic curves can be obtain from equation 4.6 and is presented as the red curve.

To design the tail, the slope and the intercept of the tail moment characteristic curves can be written as

where VH is the tail volume ratio which is proportional to the tail area, ε0 is downwash angle at zero angle of attack, iw is the wing angle of incidence and in this case 3 degrees, and finally it is the tail angle of incidence.

The size of the tail will therefore be determined by the slope of the curve. will therefore determine the angle of incident of the tail, i

m0 t

C

t. From calculation, the tail size

requires will have a span of 0.4 meters with a chord of 0.2 meters mounted at an incident angle of 0.65 degrees.

Detailed working of obtaining the tail size and its angle if incident can be found in the Appendix F.

4.3.5. RESULTING LAYOUT

All aspect of chapter four is to achieve the final layout of the craft beginning with the weight estimation, determining the wing size, fuselage design, propulsion system integration and finally the control system. From this point onwards, fabrications are done base on the final layout drawings shown in Fig. 4.16. The final weight of the craft with all individual components integrated is given in Appendix E.

Plan View

Side View Front View

Fig. 4.16. Resulting Layout of WIG