This question can raise a few eyebrows in the drone Industry, but with aerial spraying there are many factors which determine application speed. The fact is drone spray systems are generating larger volume outputs than ever, which allows for a faster travelling speed as the spray system is able to keep up.
Going from an XAG P30, (maxed out at 2 metres per second) to The DJI T40 (averages 7 metres per second) has a significant effect on the duration of a job. This is where faster is definately better, as the T40 is a much younger machine with higher pump output.
Besides the Spray volume output and speed in which a spray drone can travel, there are a few important factors to consider. The winds speed and direction has a major effect of how fast the drone will travel, as it is important to keep spray droplets directly beneath the propellors.
Propellor wash (Prop wash) generated by the drones propellors downward force, helps push the droplets down into the plants canopy, allowing for greater coverage and saturation. If a head wind is too strong the droplets will trail too far behind and hover in the air, causing the prop wash to not have any effect. Slowing down the travel speed will help reduce the trailing effect.
The same thing can happen on a still day with the drones travel speed being too quick! where there is not enough time for the prop wash to distribute droplets effectively. This can cause an anomaly called an “Inversion” where the droplets are left hovering on a layer of air and get carried away which ever direction the wind is flowing.
With a strong tail wind if travelling too slow, the droplets can actually trail infront of the drone! Although this is more favourable than trailing behind it’s still important to keep an eye on how the droplets are falling.
When spraying complex hilly terrain with obstacles and steep embankments, it is good practice to slow the travelling speed down. This gives the drones obstacle avoidance and Terrain sensors time to read the sites features, giving the drones Flight controller time to react accordingly. Flying too fast can result in the drone not being able to climb a steep slope quick enough or potentially crashing into something!
Broad-acre applications allow for drone operators to take advantage of a spray drone’s speed, as there is considerably less risk compared to complex hilly jobs, but there is still the matter of wind effects on spray droplets.
Spray drones are constantly evolving in terms of spray output and application speed, which provide limited advantages. Things like wind, complex terrain and obstacles will always be challenging to aerial Spray drones and application speed and just because the drone can go faster, doesn’t necessarely mean it’s a good idea.
