Density Altitude

[Peterpilot7]

Just wondering if anyone has noticed an increase in drone noise the higher you go in density altitude (DA)? It seems like my Mini 3 pro is a lot louder at 8000DA compared to 2000DA, wonder if it has anything to with having to spin the rotors faster to compensate for a higher DA.

 

[akdrone]

literally more air...more sound...no sound in a vacuum...

 

[Cymru]

Thinner air == less lift == higher RPMs needed to produce the same lift == more noise.

(yes theres some attenuation caused by the lower density air but not enough to swamp the above physics).

 

[Galopin]

Two different opinions from akdrone and Cymru, but I would go for Cymru. Cheers!

 

[BigAl07]

literally more air...more sound...no sound in a vacuum...

That's kind of proving the opposite of what the OP is seeing (aka hearing).

As you go UP in Density Altitude (and Altitude in general) you actually have fewer air molecules. This is why the aircraft has to work harder for the same amount of lift to be generated than it does down lower.

Keep in mind that Density Altitude isn't an actual height but a numerical representation of how the air "acts/feels" when environmental factors are calculated into the equation. For instance, a local runway has an actual altitude of 4,000' MSL. But it's a very HOT and HUMID day so the the Density Altitude could be more like 7,500'MSL. This tells you that your aircraft will operate as if you were flying at 7,5000' instead of the actual 4,000' you're at which allows you to make more informed Aeronautical Decisions.

So as your UAS is flying in hair with a higher DA is is absolutely having to make adjustments to motor speed etc to compensate as compared to flying in a lower DA.

 

[akdrone]

That's kind of proving the opposite of what the OP is seeing (aka hearing).

As you go UP in Density Altitude (and Altitude in general) you actually have fewer air molecules. This is why the aircraft has to work harder for the same amount of lift to be generated than it does down lower.

Keep in mind that Density Altitude isn't an actual height but a numerical representation of how the air "acts/feels" when environmental factors are calculated into the equation. For instance, a local runway has an actual altitude of 4,000' MSL. But it's a very HOT and HUMID day so the the Density Altitude could be more like 7,500'MSL. This tells you that your aircraft will operate as if you were flying at 7,5000' instead of the actual 4,000' you're at which allows you to make more informed Aeronautical Decisions.

So as your UAS is flying in hair with a higher DA is is absolutely having to make adjustments to motor speed etc to compensate as compared to flying in a lower DA.

not proving...just conjecture on my part

 

[hiflyer201]

ust wondering if anyone has noticed an increase in drone noise the higher you go in density altitude (DA)? It seems like my Mini 3 pro is a lot louder at 8000DA compared to 2000DA, wonder if it has anything to with having to spin the rotors faster to compensate for a higher DA.

These drones have an interesting speed control so that they will not go faster than their published speed no matter the tailwind...just like my electric scooter going downhill or uphill. So, I would guess they control power at altitude in the same manner. I regularly fly at an DA of 5000 ft., and I don't notice the difference a sea level but I'm guessing thats my poor ear and that you're correct about the higher revs.

 

[Cymru]

These drones have an interesting speed control so that they will not go faster than their published speed no matter the tailwind...just like my electric scooter going downhill or uphill. So, I would guess they control power at altitude in the same manner. I regularly fly at an DA of 5000 ft., and I don't notice the difference a sea level but I'm guessing thats my poor ear and that you're correct about the higher revs.

Not exactly. They're GPS and pitch restricted, whatever is sooner.

With a strong tailwind speed is going to be limited by GPS max speed. Into a strong headwind speed is likely limited by the maximum permitted pitch angle for that flight mode.

If you switch to ATTI mode that GPS limitation disappears and you can get much faster with a decent wind.