Most battery efficient speed to cover a distance

[cpper]

Nice discussion, thanks guys
A factor which would speak for a better efficiency at higher speeds is the basic fact that when flying faster, the drone communicates with the remote controller for a shorter period of time. Not sure how much battery the communication consumes, comparing to the actual flying, though.

 

[sharkface]

fly it like you stole it !! ... no ! don't take that advice. I ride scooter a lot . the air starts building up pressure at over 16-18 mph ( things start to get windy). that would be my best guess. but I still fly it like I stole it .

 

[SteveKB]

Just like to give my thoughts on this thread as an aeronatical engineer (retired): an aircraft has to be in balance to maintain a certain altitude and speed that means that thrust( forward vector )must equal drag to maintain that speed, more thrust = acceleration and also incidentally more drag which actually needs more power than the actual accelleration should require as a doubling of speed actually give a quadrupling of drag ..... there are formulas to calculate the numbers but as a drone forward speed is also a function of the angle of the drone relative to the air met moving forward that angle also is a function of drag ---- so the least drag possible would require the least power consumption above normal consumption to stay in the air. Think I'll stop now 'cos this sounds like ranting. P.S. the formula is something like Drag = 1/2 xPxV**2 where p is the area which would create drag, v is the aircraft velocity (which is squared), hmmm should I post this or not ?

 

[cpper]

 

[Grazuncle]

Just like to give my thoughts on this thread as an aeronatical engineer (retired): an aircraft has to be in balance to maintain a certain altitude and speed that means that thrust( forward vector )must equal drag to maintain that speed, more thrust = acceleration and also incidentally more drag which actually needs more power than the actual accelleration should require as a doubling of speed actually give a quadrupling of drag ..... there are formulas to calculate the numbers but as a drone forward speed is also a function of the angle of the drone relative to the air met moving forward that angle also is a function of drag ---- so the least drag possible would require the least power consumption above normal consumption to stay in the air. Think I'll stop now 'cos this sounds like ranting. P.S. the formula is something like Drag = 1/2 xPxV**2 where p is the area which would create drag, v is the aircraft velocity (which is squared), hmmm should I post this or not ?

That's would correlate with the atmosphere resistance figures I posted in the dept of transport regarding electric cars and why they use a lot more energy relatively with higher speeds.
Thanks for posting your information @SteveKB

 

[SteveKB]

That's would correlate with the atmosphere resistance figures I posted in the dept of transport regarding electric cars and why they use a lot more energy relatively with higher speeds.
Thanks for posting your information @SteveKB

Glad you understood my post .... had to read it twice myself

 

[iowa_jim]

From a vector analysis standpoint, the force to maintain the drone in level flight remains constant while the forward force vector will be related to the forward speed and drag. This shows that the range for a slow forward speed condition is limited by the energy expended to remain at altitude, while the range for high speed flight condition is limited by arodynamic drag associated with the increase of velocity. The peak flight time would occur when the forward force is equal to the downward force. The peak flight distance will be close to this value.

So i havent actually answered the question. At the slow speeds we are talking about, i estimate that max speed would produce the max distance.

 

[Drbobk]

From a vector analysis standpoint, the force to maintain the drone in level flight remains constant while the forward force vector will be related to the forward speed and drag. This shows that the range for a slow forward speed condition is limited by the energy expended to remain at altitude, while the range for high speed flight condition is limited by arodynamic drag associated with the increase of velocity. The peak flight time would occur when the forward force is equal to the downward force. The peak flight distance will be close to this value.

So i havent actually answered the question. At the slow speeds we are talking about, i estimate that max speed would produce the max distance.

I agree with this conclusion, but maybe not the logic, and I’d phrase it differently. Think of the problem this way:

At zero forward speed, all of the battery life is used up holding the drone up in the air. At a fairly slow speed, much more energy is used holding up the bird rather than propelling it forward, so that by the time the battery is used up, very little distance has been covered. So the problem is really how do I maximize the percentage of battery power used for forward propulsion rather than simply generating lift. Since the amount used for lift would seem to change very little with speed, using as much battery as possible for speed is the answer. In other words, max speed is the approximate solution to max distance. Where I might differ with Iowa_Jim is that I have no idea if this means that we are using equal amounts of battery to stay up and to go forward. (Consider a drone which has barely enough motor power to hover much less move forward. It will achieve max distance at max forward speed, but only a small fraction of the battery power would go to speed.)

All this ignores the increasing effect of drag due to the speed, but I think that in the regime of 0 to 40 mph, the wind resistance probably isn’t a big factor. If the drone could do 80mph, that would create 4 times the wind resistance felt at 40, or 16 times the effect at 20mph, and might affect this conclusion.

On the other hand, anyone who rides a bike can attest to the increasing effort needed to go faster into the wind. You notice it immediately when you try to maintain speed into a wind gust, and we’re not talking about doing 40 either. I sometimes ride a Street Strider, a standup elliptical bike. There’s a huge difference in a wind compared to riding a regular bike due to the increased cross section that you’re showing to the wind because of the standing position. I mentioned this cross section effect in an earlier post, and assume it will affect the leaning drone also, but probably not significantly.

Anyone have access to a wind tunnel, or wind tunnel results for our size drones?

 

[sar104]

I agree with this conclusion, but maybe not the logic, and I’d phrase it differently. Think of the problem this way:

At zero forward speed, all of the battery life is used up holding the drone up in the air. At a fairly slow speed, much more energy is used holding up the bird rather than propelling it forward, so that by the time the battery is used up, very little distance has been covered. So the problem is really how do I maximize the percentage of battery power used for forward propulsion rather than simply generating lift. Since the amount used for lift would seem to change very little with speed, using as much battery as possible for speed is the answer. In other words, max speed is the approximate solution to max distance. Where I might differ with Iowa_Jim is that I have no idea if this means that we are using equal amounts of battery to stay up and to go forward. (Consider a drone which has barely enough motor power to hover much less move forward. It will achieve max distance at max forward speed, but only a small fraction of the battery power would go to speed.)

All this ignores the increasing effect of drag due to the speed, but I think that in the regime of 0 to 40 mph, the wind resistance probably isn’t a big factor. If the drone could do 80mph, that would create 4 times the wind resistance felt at 40, or 16 times the effect at 20mph, and might affect this conclusion.

On the other hand, anyone who rides a bike can attest to the increasing effort needed to go faster into the wind. You notice it immediately when you try to maintain speed into a wind gust, and we’re not talking about doing 40 either. I sometimes ride a Street Strider, a standup elliptical bike. There’s a huge difference in a wind compared to riding a regular bike due to the increased cross section that you’re showing to the wind because of the standing position. I mentioned this cross section effect in an earlier post, and assume it will affect the leaning drone also, but probably not significantly.

Anyone have access to a wind tunnel, or wind tunnel results for our size drones?

You note that the power to produce lift is approximately constant, that power to overcome drag dominates in calculation of range, and the drag increases with the square of the airspeed, but then you argue that at the airspeeds in question, drag is not a factor. That's obviously not correct since, if it were, airspeed would not be drag-limited. Or to recast your observation - if the drone could do 40 mph (which of course it can) then that would create 4 times the drag at 20 mph, or 16 times the drag at 10 mph.

I linked to an old post with a mathematical treatment and parameter study of the problem in post #33, so I'm a bit baffled by the continued rather random speculation in this thread.

 

[Rich QR]

That's true. My point was, it uses x Watts to hover, and you're going nowhere. So effectively x Watts is "wasted power" in regards to moving forwards.

Moving will use x+y Watts, with the y component being the proportion contributing to actually moving forwards. The faster you move, the greater y becomes.

Except that, at slow speeds, y is negative, and it becomes more negative until you reach the speed where minimum power is required to maintain altitude. The minimum power required to remain aloft does not happen in a hover, but at a certain speed. If we believe DJI's figures as quoted by spudster in post #7 of this thread, max endurance happens at 4.7m/s for the MM2. I believe all rotorcraft require less power to move forward at a slow speed than to hover - the rotors are more efficient in clean air.

That doesn't tell me what speed allows one to cover the max distance for a given amount of battery charge, though.

 

[arq_gg]

I have a question, why does my mini 2 battery not charging, I have tried everything and I’m using the original charger but for some reason when I charge it, the only the thing that happens is the 2 lights in the middle stay solid except the left and right lights are off

 

[iowa_jim]

I agree with this conclusion, but maybe not the logic, and I’d phrase it differently. Think of the problem this way:

At zero forward speed, all of the battery life is used up holding the drone up in the air. At a fairly slow speed, much more energy is used holding up the bird rather than propelling it forward, so that by the time the battery is used up, very little distance has been covered. So the problem is really how do I maximize the percentage of battery power used for forward propulsion rather than simply generating lift. Since the amount used for lift would seem to change very little with speed, using as much battery as possible for speed is the answer. In other words, max speed is the approximate solution to max distance. Where I might differ with Iowa_Jim is that I have no idea if this means that we are using equal amounts of battery to stay up and to go forward. (Consider a drone which has barely enough motor power to hover much less move forward. It will achieve max distance at max forward speed, but only a small fraction of the battery power would go to speed.)

All this ignores the increasing effect of drag due to the speed, but I think that in the regime of 0 to 40 mph, the wind resistance probably isn’t a big factor. If the drone could do 80mph, that would create 4 times the wind resistance felt at 40, or 16 times the effect at 20mph, and might affect this conclusion.

On the other hand, anyone who rides a bike can attest to the increasing effort needed to go faster into the wind. You notice it immediately when you try to maintain speed into a wind gust, and we’re not talking about doing 40 either. I sometimes ride a Street Strider, a standup elliptical bike. There’s a huge difference in a wind compared to riding a regular bike due to the increased cross section that you’re showing to the wind because of the standing position. I mentioned this cross section effect in an earlier post, and assume it will affect the leaning drone also, but probably not significantly.

Anyone have access to a wind tunnel, or wind tunnel results for our size drones?

I agree that our positions are very close to one another. In my hypothesis I did not explain this but the underlying assumption is that as the forward speed increases the drag increases exponentially and that this indicates that fast speeds will reduce the overall range because of the energy lost due to the increased inefficiencies of higher speed travel. The resulting greatest efficiency is then created when the forward energy expenditure is equal to the upward energy expenditure. I then hypothesize that since the speeds we are talking about are relatively small, that the drone will be at a maximum range at its maximum speed, but this is yet to be proven.

 

[spudster]

What effect does the attack angle have at different speeds and how does this effect efficiency compared to extra energy consumed by the higher speeds? Just a quick look and estimate I would say that the frontal area at least doubles under full throttle.

 

[Tomk_]

Attack angle between a rotorcraft and airplane is completely different. Attack angle is relative to the "wing". On a rotorcraft, that is the prop.

Increased drag is relative to the speed of the prop... much more than the airspeed of the craft. Induced drag increases as rpm increases, regardless if you are using that power to climb or move forward.

 

[iowa_jim]

I agree that our positions are very close to one another. In my hypothesis I did not explain this but the underlying assumption is that as the forward speed increases the drag increases exponentially and that this indicates that fast speeds will reduce the overall range because of the energy lost due to the increased inefficiencies of higher speed travel. The resulting greatest efficiency is then created when the forward energy expenditure is equal to the upward energy expenditure. I then hypothesize that since the speeds we are talking about are relatively small, that the drone will be at a maximum range at its maximum speed, but this is yet to be proven.

I am using two different references for relative speed in this discussion, and I think people are following along, but to be clear, the drag associated with high-speed travel is most pronounced at speeds in excess of what our mavics are traveling at. As such, the max speed for the mavic mini 2 in my case is not going to create a punitive reduction in range vs the competing energy drain from hovering. If the mavics were to travel past 100 mph, we would see a need to reduce speed in order to maximize the unit's range. But with a max speed of nominally 35 mph, I predict that we can go full throttle, e.g. maximum speed, to obtain the best range.

 

[Alan Mac]

Most experienced drone flyers seem to suggest the most efficient way to get a drone back against a headwind is flat out in sport mode.
Begs the question: at what strength (weakness) of headwind does this cease to be the best option?

 

[iowa_jim]

Most experienced drone flyers seem to suggest the most efficient way to get a drone back against a headwind is flat out in sport mode.
Begs the question: at what strength (weakness) of headwind does this cease to be the best option?

According to my line of thought offered previously in this thread, the airspeed reduces the range at speeds beyond what the drone is capable of, so the faster the better within the speed range offered by the mini 2. This seems to align with your anecdotal information regarding range. Of course, your anecdotal information is better than my theory, but they seem to be in alignment. In short, the drone's range is the worst at hover and at extreme speed, but there's a point in-between where the true maximum range is obtained, and that point of diminishing returns is beyond what the drone is capable of, or so I propose.

 

[Grazuncle]

Most experienced drone flyers seem to suggest the most efficient way to get a drone back against a headwind is flat out in sport mode.
Begs the question: at what strength (weakness) of headwind does this cease to be the best option?

Depends on the strength of the headwind rather than the mode needed. A light headwind may not require a change of mode. However a really strong headwind could render a drone stationary even at max in sport mode.

 

[spudster]

Attack angle between a rotorcraft and airplane is completely different. Attack angle is relative to the "wing". On a rotorcraft, that is the prop.

So you are saying that the higher angle and frontal area that a drone has at the higher speeds has no effect on range?

IMHO, no one knows that answer (other then maybe DJI) to the OPs question as there have been no studies done that I can find. So people are just making stuff up to bolster their believes. So, until a place can be found with no wind and be able to fly at a several consent speed and direction runs until a battery runs out (or use a wind tunnel) then no one will know.

What we do know is that there is a finite amount of power available so the distance you want to travel has to come into play. If your end point 1500' away then the faster way to get there and back is the fastest speed. If it is 3 miles away you most likely won't make it back before before the battery runs out where with a slower more efficient speed you might.

 

[iowa_jim]

So you are saying that the higher angle and frontal area that a drone has at the higher speeds has no effect on range?

IMHO, no one knows that answer (other then maybe DJI) to the OPs question as there have been no studies done that I can find. So people are just making stuff up to bolster their believes. So, until a place can be found with no wind and be able to fly at a several consent speed and direction runs until a battery runs out (or use a wind tunnel) then no one will know.

What we do know is that there is a finite amount of power available so the distance you want to travel has to come into play. If your end point 1500' away then the faster way to get there and back is the fastest speed. If it is 3 miles away you most likely won't make it back before before the battery runs out where with a slower more efficient speed you might.

Tomk suggested that the frontal area effect was subordinate to the other effects, rather than to suggest that there was no effect. I don't suspect that any of us are making things up to support our agenda, but why not test these theories out?

I propose we get our MM2s up in the air to 200' AGL, then run them for 2000' at max normal mode speed, and then again at max sport mode speed. We then repeat the following day with a fully charged but cold battery and drone, but this time running at sport mode first. We will need to record the travel time and actual travel distance, We need to know the starting and ending battery level, and the elevation msl wouldn't hurt either. Send me the data and I'll sort it out.