How to Increase the Hovering Time for Drones – Part II

How to Increase the Hovering Time for Drones – Part II

How to Increase the Hovering Time for Drones – Part II

A technology with growing aspects

By improving drone’s manufacturing process,

  • We can use a diesel-based motor instead of a battery-based drone.
  • We can decrease the drones weight and increase the fuel capacity instead.
  • We can increase the flight time by approximately four times more than a battery-based drone.

In the previous article, we discussed a new criterion called ∂.

The goal for considering such criteria was restricted to two reasons;

  • First to have a criterion for promotion of drones’ power
  • The second reason, after professional evaluations, regarding the classification of fuels, people with lower expertise will be capable of expressing their innovations.

In this series of articles, we are intended to make a connection between professional assessments and the innovations by less professional individuals. In other words, we are determined to link between professionalism to people with less creativity.

This phenomenon was experienced before, for instance, Edison, was not a man of thermodynamics or the professor of statics, but using the information gathered by specialists with higher expertise, he was able to present the greatest gift to the human community. On the other hand, Goodyear was not a classical chemist, but with his serious diligence and using theories of other chemists, he did a masterpiece that created an evolution in the scientific community.

Therefore, I would like you to have the same approach to the context of these articles and try to present innovative designs using the ideas in these articles.

Let’s go back to our discussion:
In the previous article, we comprehended that it is possible to determine a criterion for the functionality of the fuels. Likewise, we talked about the coefficient of η. Now let’s resume our discussion from there.

If you refer to HHV for Butane and Gasoil, a simple comparison tells us that if we could reduce the tank weight, it is obvious that with this amount of fuel the drone would hover in sky 1.2 times more than Gasoil, and 3 times more than the battery.

It is possible to solve the tank problem by using metals with a higher yield stress.
For instance, considering ASTM A316 as the tank material, containing a liquefied Butane at 30°C, the tensile stress on the wall would be equal to 3.75 x 107 which is bearable by a 2 mm thickness of an 80 mm diameter Cylinder.

Which is much less than the yield strength of the ASTM A316

Here are the hoop stress calculations:

In fact, most cylinders containing butane gas are manufactured with a wall thickness of 1/20 of the external diameter of the cylinder and therefore, they are considered as thin wall vessels in theoretical calculations.

Thus, the amount of stress on the wall layer of the tanks are calculated based on the following formula:

Furthermore, if the maximum environmental temperature is taken as 30°C the saturated pressure of the butane gas would be equal to 0.284 MPa, which indicates that we must take P equal to this amount.
Meanwhile, if we take the amount of σmax equal to 276 MPa, then it will be obvious that by increasing or decreasing di we can obtain the minimum thickness possible for the tank. It implies that we have a very light tank, capable of carrying liquid butane.

However, tripling the energy or making it 1.2 times more is not the final step, as seen in the previous article; the coefficient of efficiency determines the amount of energy converted into useful work.

In thermodynamic cycles, the greatest efficiency belongs to the turbines. Now, assume that we are making a mini turbine in accordance with the Brayton Cycle. This is something absolutely feasible, a project at the level of a simple university assignment without any professional complexities.

Such a turbine can surely turn the blades and with an efficiency of 50% can provide an energy equivalent to 1.5 times more than the Diesel cycle.

You can see that, up to this point, with an equal weight of fuel, we could obtain approximately four times more energy, with respect to the battery. So, our drone will hover in the sky for a longer time.

You can read my description of the Brayton Cycle in the next article.

One Comment

  1. Jan Davel
    June 29, 2017 Reply

    Mosay, good article. Just one comment. The stated efficiency of a micro turbine may be an overestimate. a Small turbine efficiency may even be less than a small 4 stroke petrol or diesel engine. Thank you Jan Davel

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