Choosing the UAV model (characteristics)

Defining the power and propulsion subsystems

Let's first choose an aircraft configuration. In this our first Solar UAV, we are going to use Sky-Sailor [1] as the basic prototype.

Therefore, we need to set its specific wingspan (3.240m) and aspect ratio (12.9) in Noth's MATLAB code.

Electric power.

For defining the electric power subsystem, we are going to follow this procedure:

1. We need to determine the day duration and maximum intensity for the month of July.

2 Adjust the MATLAB Code for the wingspan and aspect ratio of the plane.

3. Execute MATLAB Code and get all data of the only solution in the table, for "a" equal to 1.00.

4. Now, check that the Electric design (Excel calculations meet the required mass, area, power and energy). Adjust them if required.

4. Select an MPPT device for Lithium batteries from this list https://genasun.eu/collections/genasun-lithium-mppts check its MATLAB parameter k_mppt = Weight/Power.

A good comparison of the different lithium batteries can be found in https://batteryuniversity.com/article/bu-205-types-of-lithium-ion

5. Iterate the whole process and check the results again.

Propulsion.

Once the electrical system design is OK, we proceed to design propulsion.

1. Open the Ecalc Ecalc online application (ask keys to your professor) and the Set Up Finder section to set up the main plane characteristics. 

2. You can approximate our batteries voltage using a set of three NiCd batteries for each of our Lithium batteries.

3. We are going to use three gear ratios 9:1, 5:1, and 1:1. With two standard propellers for each group. Around 22 x 11 inches (this would require a folder propeller and an Electronic Speed Controller ESC with brake). And a second smaller propeller for studying the possibility of changing motor location (as the Mini-Phantom) and using wheels for doing a softer landing. The latter can be 10 x 7 inches or smaller up to 8 inches in diameter.

4. Once you select the pair propeller - motor, continue to the PropCal (propeller calculation) section to calculate the propeller performance, check if the plane is able to fly and the performance of the motor.

5. Finally click on "performaceCalc" button to check the plain performance, the required power for cruise and the available thrust (therefore the maneuverability of the aircraft).

6. Now, go back to the MATLAB code and check that the propulsion system meet the initial requirements. Otherwise, adjust them and iterate the whole process.

7. Now you should check if the required cruise electric power  (minimum Power for Level Flight) matches the electronic design calculated electric average power. If so, your design should be able theoretically to perform an endless flight. Otherwise, we would need to iterate the process. We can look for other propulsion variants or we can repeat the process with a=1.05 (over dimensioning the power system and checking the results). 

8. It is also very important to check the available power (dynamic Propeller Power) as it defines the maneuverability of the aircraft (load factor).

To summarize, we need at least six different results for the propulsion system:Std - mean standard propellers. One place to look for standard propellers is APC Propellers Electric Motors

Now, the only part of the electrical subsystem pending is the servomotor that actuates on control surfaces, but this is upcoming on the next post.