A technology with great prospects
By improving the drone’s technology;
- We can build drones capable of hovering in the sky for days.
- In the near future, drones are able to achieve heavy and dangerous assignments.
- Soon, drones will be able to carry a wounded person from the deepest forests.
- Drones will be able to perform welding projects on oil platforms in offshore constructions.
Nowadays, drones are facilitating and simplifying many affairs in various aspects of our life that were unimaginable before. These aspects include protection of echo system, missions for rescuing forests or risky environments, military affairs, multimedia presentations, filming and carriage of recording devices and even delivery of purchased goods to the customer’s house.
What are the common points in designing a drone for miscellaneous uses
The goal is different in all above-mentioned aspects but let’s consider the most important common points. For instance, during its mission, a drone is hovering for a specified time for data delivery. It is important to note that it has a specified duration of time, and usually the functionality of a drone is evaluated by its capability and quality of data transfer. Moreover, the duration of time for the continuous work of a drone is considerable.
The most important factor in designing a drone
In this article, we are aimed at focusing on this factor, i.e. the parameter of time.
Based on the first law of thermodynamics, hovering and remaining in the air (hovering time) certainly needs a force equivalent to the gravity force and this means the energy consumption. Perhaps, in particular circumstances, it would be possible to increase the time duration by using Helium capsules or special bags, but this increment in time is surely concurrent with the decrement of operative power. Here, we are focused particularly on energy consumption and its relationship with the parameter of time.
Definitely, other parameters, such as the shape geometry, the aerodynamics, the number of blades, spokes and … have their own influence, but at this stage, we are intended to take them for granted.
Optimization of the drone efficiency based on laws of thermodynamics
In thermodynamics, there are parameters called η1 and η2 where η1 is related to the system efficiency regarding the first law of thermodynamics in thermodynamic cycles, and η2 is related to the system efficiency regarding the second law of thermodynamics.
Here, you can find an inclusive definition of Energy conversion efficiency.
For more examples, read here: Efficiency of Energy Conversion Devices
At this point, I’d like to define a new parameter ∂1 and ∂2 where ∂1 is defined as follows:
Es is the amount of energy source in kJ
Wf Is the weight of energy source IN KG
Regarding the fuel as a source of energy, we have something similar to which is called (HHV) but maybe, such a unit is not found for the other sorts of energy. There is no similar unit to define the relationship between the amount of energy and weight.
As the variations of gare negligible inside the flight zone of the drones, we can ignore ∆g.
Different energy sources are kept in different vessels, for example, gasses are kept in capsules, liquid fuels in specific vessels and the electrical energy inside batteries. Therefore, it is better to enter the second parameter, Ɵ2, as well.
Cs is the amount of energy of the source container
Ws is the weight of a vessel containing the source of energy
Obviously, for the batteries, it is possible to assume = zero, and subsequently to calculate the entire weight. Therefore,
To simplify the subject, we can ignore η2 which has a negligible effect on cycles used in the drones, and thus, the expression “∂η” implies the number that is equivalent to the drone efficiency.
Here, let’s expand the expression as follows:
At this point, by preparation of a list including all energy sources, it would be possible to have a reasonable evaluation of the system, which will help us optimize the functionality and efficiency of the drone.
Table of Energy Sources
|Type of the Energy Source||
|Li-ion Battery||2.8×104 j/kg||
|5||Solar Battery||1.7×105 j/kg||
Referring to this table, we are able to determine the amount of energy saved inside a gram of gas oil, and to specify how many Li-ion Batteries are required to have the same amount of energy.
Here, knowing the amount of energy saved by each source of energy, the way is open for the next stage of drone design. This issue is very extensible, similar to the EXERGY ANALYSIS in thermodynamics.
In the final stage, considering each one of the best options, it is necessary to find the best thermodynamic cycle for using the relevant source of energy and this is how you can increase the hovering time for drones.
This approach to the subject of drone design classifies this part of the industry in a way to consider it as a new scientific major of study (preferably as a branch of robotics.)