Typically in RC plane power requirements ranges from few tens of watt to hundreds of watts. And if we talk about solar energy it is having very low power density (power/area) typically 150 watts/m2 max., that to reduce and varies as per season, time, weather and solar panel orientation. So while making a solar plane challenge is to make flying possible using very low power (so lightweight airplane).
But this is not a first timer plane due to two reasons:
1. As discussed this plane need to be extremely low weight with sufficient strength (such that solar cells do not damage due to flying loads) that requires some experience.
2. Flying plane with low power is also difficult and any crash can result in a broken solar panel.
Still, this project is worth giving a try. As in results, you will have an RC plane that can fly the whole day (hopefully) without charging.
You can also refer the attached video for similar details.
Step 1: Background
Previously I tried to make an RC plane that purely fly using solar energy with battery to power its control surface this plane was able to fly if weather conditions are good. This plane was having the peak power output of 24 watts in ideal condition.
For more details please refer the link:
This plane will be having hybrid power. The solar panel will continuously charge the battery as well as gives the power to plane. At the time of peak load requirement (take off) battery also provide power along with solar cell. We will also try to keep its weight below 150g.
Step 2: Required Material
- Sunpower c60 solar cell: 5nos ( recommended to buy few extra)
- Coreless motor with prop such that thrust to Power ratio 0.2
- minimum Reciever brick with inbuilt servo and ESC: I have used receiver brick from wltoys.
- Carbon rod: Dia:1mm, Dia:4mm
- 5mm Dapron sheet,
- Battery with built-in protection circuit 500mah 1s (get protection circuit separately is it is not present)
- Soldering iron
- Hot glue gun
- Ca glue
- Transparent tape
- Paper cutter
- Hackshaw blade
Step 3: Making Wing and Tail Section
After gathering required part plane making can be started by making the wing. As it is the mon part of our plane and all another part will be assembled over the wing. This plane is having the wingspan of 78cm. To make a wing below is the procedure that I follow. However, you can also use a hot wire cut or other procedures.
- Depend on the thickness of your dapron sheet available to cut rectangle pieces and stick them together such that airfoil can be shaped out of it.
- After stick, these sections together with glue (i have used standard SH fevicol) we need to sand out useless material and make it nice smooth. The curvature of the upper surface of airfoil needs to be lower such that solar cell needs to bend minimum while sticking. Otherwise, there is a good chance of cell cracking.
- Make a cut to the mid of the wing apply hot glue and put carbon rod. This will make the wing stiffer.
Similar way glue the carbon rod for the tail section. And make rudder and elevator using 5mm dapron sheet. Rudder and elevator dimensions are directly taken from tiny trainer by flight test. To make all these part refer the drawing available at the link.
Step 4: Preparing and Assembling Solar Cells:
To power our motor we meed 3.7 volts, and battery highest voltage is 4.2 volt. So we need to provide a continuous supply of 5 volts. The cell we are using (SunPower c60) gives the voltage of 0.5V with 6A peak supply. However, for the size, we are aiming 10 cells cannot be accommodated. So we will cut these cells into half and use it. In this case, each cell gives the voltage of 0.5 V but current will be halved at 3A. We will connect 10 of these half cells in series which will give 5 volt supply and 3amp peak current.
For cutting these cells refer to this video. As these cells are very brittle cutting it is difficult. Once you cut them a copper wire can be soldered to each of these such that all of the there cells are in series. You need to be careful of the polarity of half cell as sometimes it gets confusing. Than solar panel can be stuck to the wing. I have used hot glue for so. Use a good amount of hot glue such that there is not any gape in between wind and solar cell.
Now to protect the solar cell I have covered it with transparent tape. This is actually a bad idea to do so, but to protect it from dust and other contamination it is necessary. You can also use other better techniques for encapsulation. Now open circuit voltage and short circuit current need to be measured.
Once everything is ok you are good to move to the next steps. And of voltage shown is lower than 5.5-6 v than you might have made mistake in soldering -the mistake is soldering correct polarity to make a series.
Plan can be downloaded from: http://diy-india.org/wp-content/uploads/2019/02/Us...
Step 5: Nose Section and Control Surfaces
Size and shape of nose section are very much dependent on the size of the battery, motor and receiver brick you are going to use. carbon fiber rod is used to give it strength and receiver brick is assembled over it.
As I am using single motor it is assembled at the nose of the plane. But if you wanted to use 2 motors it can be assembled under or over the wing.
This plane has 3 channel control. so we only have the rudder, elevator control along with motor control. Here thin carbon fiber rod (of 1mm dia) is used for motion transfer. here receiver brick is placed in front of wing to maintain CG.
Step 6: Electrical System
As explained earlier, this plane has hybrid power. Battery and solar panel connected in series. This comes with the problem. we are getting an open circuit voltage of 6 volts and the battery having the highest voltage of 4.2. so the battery can be easily failed due to overcharging which is bad.
I am going to use a battery that is having inbuilt battery power management circuit (kind of...). this circuit does not let is overcharge or even protect it from deep discharge. Typically all LiPo used on toy quadcopter or airplane comes with this type of inbuilt circuit. however, any Hobby grade battery does not have such a circuit. so you need to take care while selecting the battery and if the battery does not has such a circuit it can be purchased separately and used with the plane.
While in operation high current needs are taken care off by the battery while the continuous supply of 1-2.5 Amp is provided by solar cell which can be directly consumed by plane or can be stored in battery depending on throttle setting.
Step 7: Testing:
Here I have carried out two tests on the plane to check overall performance of solar charging.
1. Continuous run till battery run out:
The throttle was set to 100% and the voltage across the battery is monitored until battery empties. In the attached video, you can check out where I placed a plane with 100% battery with 100% throttle and the battery lasted for around 22 mins. this was 10 AM of time and as it was winter solar angle was around 50 degree (maximum). so this performance will be further improved in other days of the season as this was the time for minimum solar energy available. And while flying plane does not require 100% of throttle every time. So to know the exact contribution of battery and solar cell I conducted the next test.
2. Monitoring current from Battery and Solar cell:
One Amp meter is connected to the solar cell to monitor current input and voltage from the solar cell while another Ammeter is used to measure the current consumption of airplane. I have captured around 3 min video of it at full throttle. At full throttle, it takes around 1.3-1.5 amp of current out of which 1.2 amp is provided by the solar cell.
There is a single video which starts with test 2 and then with test 1.
Step 8: Flying
So the plane is ready to fly. but it needs some final touch to make it happen. CG of the plane need to be adjusted to a typical 25% of the wing as a starting point and can be tuned by doing some glide trials.
As this plane is having very low thrust it will gain height slowly and as this plane is having very low wing loading it is a bit difficult to fly in windy days.
You must need to be very careful while flying to do not let it crash. as it can damage the solar cells of the plane. and it is very difficult to repair it. Video of flying can be seen in the previously attached video.
This plane needs to be further improved for better payload capacity and some surplus power to run other stuff (like FPV cam).
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