SLOW or SPORT MODE for best Power/Distance efficiency?

[Skymax]

Assuming Mavic Platty Pro, perfectly still air, 75deg temp, 60% Humidity and Sea Level Alt.
If I want to fly a set distance is it more power-economical to fly in Sport Mode to the destination as you are moving much faster or is slower "Normal GPS Mode" going to use less battery power to travel the same distance even though it takes longer?

 

[Tinmania]

I read in a thread somewhere, that of course I can’t find now, that 30 mph is the sweet spot between speed and battery power.

You can go up to about 30 mph in P mode if obstacle avoidance is off.



Mike

 

[Divebomber]

Well, all other considerations aside, the most basic formula for wind resistance (drag coefficient) ignoring air density and a few other variables is that for every unit of measure increased, drag increase by the square of the the velocity increase. That’s a very complicated way to say the faster you go, the drag increases exponentially. Going really fast in sport mode is the least efficient way to get good range. You’ll go much farther at a moderate speed. An analogy is to think of how much fuel your car uses on the highway at a moderate speed v. Heel to the steel.

 

[Tinmania]

Well, all other considerations aside, the most basic formula for wind resistance (drag coefficient) ignoring air density and a few other variables is that for every unit of measure increased, drag increase by the square of the the velocity increase. That’s a very complicated way to say the faster you go, the drag increases exponentially. Going really fast in sport mode is the least efficient way to get good range. You’ll go much farther at a moderate speed. An analogy is to think of how much fuel your car uses on the highway at a moderate speed v. Heel to the steel.

But doesn’t the forward motion of the rotors through the air provide a measure of lift, similar to a wing on a FW aircraft? That is the reason DJI seems to give when explaining why hovering can use more battery than actually flying.



Mike

 

[Divebomber]

But doesn’t the forward motion of the rotors through the air provide a measure of lift, similar to a wing on a FW aircraft? That is the reason DJI seems to give when explaining why hovering can use more battery than actually flying.



Mike

Yep. You’re right, Mike, in a quadcopter or anything that can hover, the circle described by the rotating blades, is actually considered a sort of virtual wingwh n calculating lift. However, just like the shapes of wings on aircraft, there is a point in flight dynamics (forward velocity) where increasing the speed reaches a point of diminishing returns. Where fighter jets with swept wings can go faster than a Cessna with almost straight wings, the Cessna, up to a given speed, is a lot more fuel efficient per unit of lift. The Cessna, and for that matter the fighter, will reach a point where it’s sucking fuel, mostly just to overcome drag. Your question was which is better, fast or slow. A quad copter, flight dynamics wise, is a lot more like a Cessna. Above a moderate speed, it’s going to use a lot more juice per unit of distance. Give it a try. Pick s convenient measured point. Fly the drone as fast as it can go to the point and back until the battery dies. Then try it again at a more casual speed.

 

[Mavflyer]

I've been wanting to test this out myself and see what results I get. I think I might just do it tomorrow, weather permitting. What do you guys think would be the best way to do It? Fly out from the homepoint many times in P-mode(about 20mph), S-mode(about 40mph), and P-mode with OA off(about 30mph), until I hit 60% battery and record the distance?

It has always seemed to me that the difference in P and S mode, as far as efficiency, has been pretty close. I could be totally wrong, but it seems that way.

 

[Tinmania]

Yep. You’re right, Mike, in a quadcopter or anything that can hover, the circle described by the rotating blades, is actually considered a sort of virtual wingwh n calculating lift. However, just like the shapes of wings on aircraft, there is a point in flight dynamics (forward velocity) where increasing the speed reaches a point of diminishing returns. Where fighter jets with swept wings can go faster than a Cessna with almost straight wings, the Cessna, up to a given speed, is a lot more fuel efficient per unit of lift. The Cessna, and for that matter the fighter, will reach a point where it’s sucking fuel, mostly just to overcome drag. Your question was which is better, fast or slow. A quad copter, flight dynamics wise, is a lot more like a Cessna. Above a moderate speed, it’s going to use a lot more juice per unit of distance. Give it a try. Pick s convenient measured point. Fly the drone as fast as it can go to the point and back until the battery dies. Then try it again at a more casual speed.

Thanks. Makes sense. I’m not the OP but thought I read something about 30 mph being optimal. I thought it was calculated though and not actually tested.

Testing something like this—I think—would take multiple runs in nearly the exact same conditions (not that that ever stopped many a YouTube video). Maybe one day when the conditions are right I will compare. It’s hard here with near-constant wind fluctuation.



Mike

 

[Skymax]

Yes I am aware of the more speed more drag curve as i own an Fi156c and it's max economical speed is 63-65 Knots but the Storch is a draggy STOL Aeroplane.
So I thought maybe the curve was flatter as the MP has little Form Drag and does get Translational Lift as mentioned above that allows the power setting to be lower than hover.
I believe the advertised top speed is 65Kmh which is not so fast..
Well I have a 7 Kilometre long uninhabited beach nearby so it looks like I will be doing some tests as i don't think this question has been answered yet as aircraft with fixed wings may not be directly comparible to rotorcraft.

 

[AnzacJack]

im pretty sure i read somewhere that 35k/h was the sweet spot. i have set my rth for this. But as you know, this is airspeed not ground speed so will depend on wind.
I do have a wind tunnel at work so may be able to test this out. Ill give it to some students as a project

 

[anom3]

Without doing any sort of extensive testing, I find I get best results when using P-Mode with obstacle detection turned off.

Gives me about 13.5-14.0m/s which is about 50km/h.

At this speed I am able to get about 18 minutes of full throttle flight time (with plenty of juice to land) and can cover over 15km.

While I know this is quite a bit off from the advertised 27mins, but were talking about 18 minutes of constant movement at a fair speed. Good enough for me from one battery.

 

[BossBob]

Another reason why the battery life is shorter in hover than while moving is that hovering for any length of time sets up a downward column of air within which more power will be required to maintain altitude. While moving, the rotors push down on new still air. Of course, if at really low altitude, ground effect occurs reducing the amount of power required to maintain altitude even more.

 

[joejaxvic123]

This is an interesting topic. I'd like to see a couple of guys get together with their mavics and run the same routes at different speeds to get some more definite answers.

 

[Skymax]

im pretty sure i read somewhere that 35k/h was the sweet spot. i have set my rth for this. But as you know, this is airspeed not ground speed so will depend on wind.
I do have a wind tunnel at work so may be able to test this out. Ill give it to some students as a project

Ta, I didn't know the RTH airspeed was selectable.
At first my question was simply about which of the Two modes was more efficient for distance covered with stick held fully forward.
Probably because I wasnt sure if accurate speed could be held with you're thumb on the stick but I suppose the day will come when future models allow you to dial in you're airspeed and that could save you're bird one day.

 

[Skymax]

Without doing any sort of extensive testing, I find I get best results when using P-Mode with obstacle detection turned off.

Gives me about 13.5-14.0m/s which is about 50km/h.

At this speed I am able to get about 18 minutes of full throttle flight time (with plenty of juice to land) and can cover over 15km.

While I know this is quite a bit off from the advertised 27mins, but were talking about 18 minutes of constant movement at a fair speed. Good enough for me from one battery.

Interesting, I didnt know turning obstacle avoidance off affected the speed in P Mode.

 

[Tinmania]

Interesting, I didnt know turning obstacle avoidance off affected the speed in P Mode.

Yep it gains about 50% in speed from P Mode with OA on.

The Mavic Air turns off OA on its own in P Mode, if it needs to in wind. This is why there early reports that the “Air performs better in wind than Mavic Pro!” In fact the Mavic Pro, with obstacle avoidance off, performs exactly the same—but of course you have to turn it off manually (which is okay with me as if rather know for sure if it is on or off). Of course a quick flip to Sports mode is even faster.


Mike

 

[kakao]

Probably because I wasnt sure if accurate speed could be held with you're thumb on the stick ....

This opens another question, as to how to make the speed constant, the speed we agree its most power-economical?!

/

 

[Skymax]

Yep it gains about 50% in speed from P Mode with OA on.

The Mavic Air turns off OA on its own in P Mode, if it needs to in wind. This is why there early reports that the “Air performs better in wind than Mavic Pro!” In fact the Mavic Pro, with obstacle avoidance off, performs exactly the same—but of course you have to turn it off manually (which is okay with me as if rather know for sure if it is on or off). Of course a quick flip to Sports mode is even faster.


Mike

Thanks, umm, when you say, "it gains about 50% in speed from P Mode with OA on." you meant to type "with P Mode Off" didnt you?

 

[Tinmania]

Thanks, umm, when you say, "it gains about 50% in speed from P Mode with OA on." you meant to type "with P Mode Off" didnt you?

While I certainly didn’t word that good, that’s not what I meant. I’ll rephrase: In P mode with OA off the Mavic gains 50% in top speed compared to P mode with OA on (from 20 to 30 mph).



Mike

 

[Skymax]

While I certainly didn’t word that good, that’s not what I meant. I’ll rephrase: In P mode with OA off the Mavic gains 50% in top speed compared to P mode with OA on (from 20 to 30 mph).



Mike

Thanks, i could not understand why it was flying below the slow speed of others I have seen on YT. I clocked 85Kmh down my beach with a strong tailwind once now it would have gone faster if I knew that. You dont need CO in most circumstances.