Why inceased power consumption upwind?

[Dronedevices]

It would be interesting to look at your footage with the angle indicator. I doubt you'd be seeing a 2-3° difference but that would have an impact on power already.

The very best would be to download the aircraft DAT logs that will show the exact attitude.

The whole thing is logical when you consider that the stick input is a ground speed command, and the tilt angle is a max tilt angle. With headwind it will need to use the max tilt angle to achieve the desired groundspeed, while with no wind it's tilting less than the set maximum.

There is a 2° margin of measurement error which may explain some of the power difference. I first tried using the downloaded DAT logs in CsvView (since DJI Assistant 2 won't display data), but the pitch and power data was erratic and unusable. The tilt angle is still nearly the same 35° within 2° margin of error for upwind and no wind, with full forward in sport mode.

 

[vkm083185]

I totally agree with you and others, but in this case it doesn't explain my observations; why (looking at the power meter) it takes more power with the same tilt angle physically measured with inclinometer (full forward on the stick) to head up wind at a slower rate relative to ground, then with no wind? I can't find an explanation, especially if you're using the moving slab of air mass concept, upwind it should require the same power (because of same tilt angle or air speed) but drift back as you mention with the wind, reducing the speed over ground (GPS) by the amount of the wind speed. Does, any one else have the same observations of different RPM/power upwind vs with no wind (full forward stick in sport mode)? Which doesn't go with the physics.

Maybe this is what you are asking about...

Yes, the air may LOOSELY be referred to as a "slab", but in reality, it's not. There are three aerodynamically prescient variables that aren't addressed in the "slab of air" concept.

1> Variable Density Dynamic

Air is NOT the same across the spectrum of encounter. A "slab" of air has MANY HUNDREDS of variables within a very few inches, let alone several hundred feet. Now...let's take that same air and add dynamic motion. Your increased variable rate just went up by a factor of an exponential per .1 knot of windspeed. ALL of these play into the effect on each of your 4 props...

2> COMPOUND SURFACE RESISTANCE

When air encounters compound curvature on any surface, it moves across it differently in relation to the above variable density dynamic. The higher the wind velocity, the greater number of permutations are active on each prop at any one instance of time (this was widely studied in NASA's Aerospace Technology Center (aero...section).

3> PROPULSION ENERGY DRAIN...

...is in direct proportion to VARIABLE resistance over a measure of time. There are myriad studies about this across several theorems dealing with aerodynamics in relation to flying....

To summarize, the air that your props encounter when in a headwind is not the same as the air that your props encounter in dead, low, tail, or cross wind instances, even when using the same tilt/power/etc input for each. Add the mass (true, it's small, but still it is mass) of the drone itself, and you can even see greater power consumption variation in different wind instances.

Well, you can tear into that, but that's my take on it, and I studied aero with some really great guys down South...

Have fun...and drone on...
Kevin

 

[sar104]

There is a 2° margin of measurement error which may explain some of the power difference. I first tried using the downloaded DAT logs in CsvView (since DJI Assistant 2 won't display data), but the pitch and power data was erratic and unusable. The tilt angle is still nearly the same 35° within 2° margin of error for upwind and no wind, with full forward in sport mode.

How exactly are you measuring power - you mentioned radar? The DAT data are almost certainly not unusable - they just need filtering and smoothing. The DAT pitch/roll data will be far more accurate than any effort to extract pitch from video. Also, how are you ascertaining that the upwind data are obtained flying directly into the wind? If it isn't then you need to account for roll as well.

Power goes approximately with thrust to the power of 3/2, and thrust varies inversely with cosθ, so power is somewhat sensitive to angle at these kinds of tilts. A back of the envelope approach suggests that a 2° change around 35° should result in around a 5% change in power.

 

[BudWalker]

There is a 2° margin of measurement error which may explain some of the power difference. I first tried using the downloaded DAT logs in CsvView (since DJI Assistant 2 won't display data), but the pitch and power data was erratic and unusable. The tilt angle is still nearly the same 35° within 2° margin of error for upwind and no wind, with full forward in sport mode.

I suspect you weren't taking advantage of the MotorPower calcs available in CsvView/DatCon. E.g. Motor:Watts:Avg:All is smoothed power signal for the motors. To include the MotorPower calcs go to the menu bar and select DatCon Fields -> MotorPower. The pitch signal shouldn't be too noisy. Here is an example of some data I took when trying to figure out the wind calcs that are done on the Mavic (and other platforms) and then recorded in the .DAT. There are 4 cycles, each with 1) a leg flying away from the HP with full elevator, 2) some rotating to gauge the wind speed, and 3) a leg returning to the HP using RTH. Here is one of those cycles. Outbound has a ground speed of 9 m/s, pitch -9.3 and motorWatts 81. The teal background represents the RTH where ground speed has increased to 10, pitch to -13.5, and motorWatts to 86.



That's best looking cycle and is the 2nd out of the 4 cycles. The first 2 cycles are the same path out and back, while the last 2 cycles were a path ortogonal to the first 2.


Note, that the ground speed under RTH is always 10 m/s but the pitch and motorWatts varies to meet that requirement.

This data/experiment isn't quite what's needed to answer @Dronedevices 's question. But, it could be a good start.

 

[BudWalker]

Maybe this is what you are asking about...

Yes, the air may LOOSELY be referred to as a "slab", but in reality, it's not. There are three aerodynamically prescient variables that aren't addressed in the "slab of air" concept.

1> Variable Density Dynamic

Air is NOT the same across the spectrum of encounter. A "slab" of air has MANY HUNDREDS of variables within a very few inches, let alone several hundred feet. Now...let's take that same air and add dynamic motion. Your increased variable rate just went up by a factor of an exponential per .1 knot of windspeed. ALL of these play into the effect on each of your 4 props...

2> COMPOUND SURFACE RESISTANCE

When air encounters compound curvature on any surface, it moves across it differently in relation to the above variable density dynamic. The higher the wind velocity, the greater number of permutations are active on each prop at any one instance of time (this was widely studied in NASA's Aerospace Technology Center (aero...section).

3> PROPULSION ENERGY DRAIN...

...is in direct proportion to VARIABLE resistance over a measure of time. There are myriad studies about this across several theorems dealing with aerodynamics in relation to flying....

To summarize, the air that your props encounter when in a headwind is not the same as the air that your props encounter in dead, low, tail, or cross wind instances, even when using the same tilt/power/etc input for each. Add the mass (true, it's small, but still it is mass) of the drone itself, and you can even see greater power consumption variation in different wind instances.

Well, you can tear into that, but that's my take on it, and I studied aero with some really great guys down South...

Have fun...and drone on...
Kevin

Still trying to figure what all this means. I'm currently stuck on "variable rate just went up by a factor of an exponential per...".

Anyway, would it be fair to say that this is an explanation of why drag is so complicated? If so, how is it material to the OP's question?

 

[Doug Lare]

Generally, an aircraft flying into the wind, experiences greater lift, than flying across or with the wind. Mavic rotors are wings, but their RPM's are so fast, compared to wind velocity, I'm wondering if the lift advantage pretty much dissipates, so that your increase in power can be explained as the additional power required to pull the weight of the Mavic into the blowing wind, essentially, I guess I'm saying there is zero advantage from flying into the wind, and like any vehicle going up hill, or in this case into the wind, more power is required. Sort of like a projectile at a low velocity in a particular wind drifts way farther than a high velocity projectile in the same wind.

 

[sar104]

Generally, an aircraft flying into the wind, experiences greater lift, than flying across or with the wind. Mavic rotors are wings, but their RPM's are so fast, compared to wind velocity, I'm wondering if the lift advantage pretty much dissipates, so that your increase in power can be explained as the additional power required to pull the weight of the Mavic into the blowing wind, essentially, I guess I'm saying there is zero advantage from flying into the wind, and like any vehicle going up hill, or in this case into the wind, more power is required. Sort of like a projectile at a low velocity in a particular wind drifts way farther than a high velocity projectile in the same wind.

That wasn't the point of the OP's observation, which was that if one considers the frame of reference of the air (always provided that the state variables of density and temperature are held approximately constant in time and space), any given pitch angle should require the same power, independent of whether or not the air has a bulk horizontal velocity relative to the ground.

 

[Dronedevices]

Maybe this is what you are asking about...

Yes, the air may LOOSELY be referred to as a "slab", but in reality, it's not. There are three aerodynamically prescient variables that aren't addressed in the "slab of air" concept.

1> Variable Density Dynamic

Air is NOT the same across the spectrum of encounter. A "slab" of air has MANY HUNDREDS of variables within a very few inches, let alone several hundred feet. Now...let's take that same air and add dynamic motion. Your increased variable rate just went up by a factor of an exponential per .1 knot of windspeed. ALL of these play into the effect on each of your 4 props...

2> COMPOUND SURFACE RESISTANCE

When air encounters compound curvature on any surface, it moves across it differently in relation to the above variable density dynamic. The higher the wind velocity, the greater number of permutations are active on each prop at any one instance of time (this was widely studied in NASA's Aerospace Technology Center (aero...section).

3> PROPULSION ENERGY DRAIN...

...is in direct proportion to VARIABLE resistance over a measure of time. There are myriad studies about this across several theorems dealing with aerodynamics in relation to flying....

To summarize, the air that your props encounter when in a headwind is not the same as the air that your props encounter in dead, low, tail, or cross wind instances, even when using the same tilt/power/etc input for each. Add the mass (true, it's small, but still it is mass) of the drone itself, and you can even see greater power consumption variation in different wind instances.

Well, you can tear into that, but that's my take on it, and I studied aero with some really great guys down South...

Have fun...and drone on...
Kevin

Good

How exactly are you measuring power - you mentioned radar? The DAT data are almost certainly not unusable - they just need filtering and smoothing. The DAT pitch/roll data will be far more accurate than any effort to extract pitch from video. Also, how are you ascertaining that the upwind data are obtained flying directly into the wind? If it isn't then you need to account for roll as well.

Power goes approximately with thrust to the power of 3/2, and thrust varies inversely with cosθ, so power is somewhat sensitive to angle at these kinds of tilts. A back of the envelope approach suggests that a 2° change around 35° should result in around a 5% change in power.

View attachment 30953

Thanks for the information!

 

[Dronedevices]

I suspect you weren't taking advantage of the MotorPower calcs available in CsvView/DatCon. E.g. Motor:Watts:Avg:All is smoothed power signal for the motors. To include the MotorPower calcs go to the menu bar and select DatCon Fields -> MotorPower. The pitch signal shouldn't be too noisy. Here is an example of some data I took when trying to figure out the wind calcs that are done on the Mavic (and other platforms) and then recorded in the .DAT. There are 4 cycles, each with 1) a leg flying away from the HP with full elevator, 2) some rotating to gauge the wind speed, and 3) a leg returning to the HP using RTH. Here is one of those cycles. Outbound has a ground speed of 9 m/s, pitch -9.3 and motorWatts 81. The teal background represents the RTH where ground speed has increased to 10, pitch to -13.5, and motorWatts to 86.

View attachment 30949

That's best looking cycle and is the 2nd out of the 4 cycles. The first 2 cycles are the same path out and back, while the last 2 cycles were a path ortogonal to the first 2.
View attachment 30948

Note, that the ground speed under RTH is always 10 m/s but the pitch and motorWatts varies to meet that requirement.

This data/experiment isn't quite what's needed to answer @Dronedevices 's question. But, it could be a good start.

I recorded the measured power from the displayed map option for "radar" which shows the power consumption along it's circumference, which I can compare with speed, etc., also rpm from the controller. The power readings are fairly accurate, although I wanted it in data form with more information from the .DAT files instead, but if I remember correctly even the Motor:Watts:Avg:All and the pitch was too noisy. Thanks for showing me your data as an example, it's very clean! I'll have to take another look at trying to use CsvView/DatCon.

 

[BudWalker]

I recorded the measured power from the displayed map option for "radar" which shows the power consumption along it's circumference, which I can compare with speed, etc., also rpm from the controller. The power readings are fairly accurate, although I wanted it in data form with more information from the .DAT files instead, but if I remember correctly even the Motor:Watts:Avg:All and the pitch was too noisy. Thanks for showing me your data as an example, it's very clean! I'll have to take another look at trying to use CsvView/DatCon.

Maybe you were thinking of the basic motor data which is pretty noisy. The MotorPower calcs that I mentioned

was added a versions back to help the Battery/Motor/distance guys (the Batterians) . Like you they needed to see smoothed data.

BTW, the motor power consumption should be dependent just on tilt angle - given that air density and altitude are constant. Probably what you're seeing is that pitch is being adjusted to meet variations in elevator input and/or ground speed.

 

[Kilrah]

BTW, the motor power consumption should be dependent just on tilt angle - given that air density and altitude is constant.

Thank you, way too few people understand that!

 

[Qoncussion]

For every action - there is an equal and opposite reaction. Physics.

 

[sar104]

BTW, the motor power consumption should be dependent just on tilt angle - given that air density and altitude are constant. Probably what you're seeing is that pitch is being adjusted to meet variations in elevator input and/or ground speed.

Thank you, way too few people understand that!

With one additional qualification - steady-state flight - because the vertical aerodynamic forces (i.e. lift) vary with airspeed.

 

[BudWalker]

With one additional qualification - steady-state flight - because the vertical aerodynamic forces (i.e. lift) vary with airspeed.

But.. is there any lift to be dependent on airspeed? Is lift generated by a quad moving horizontally? Isn't it all about vertical thrust which has to be exactly the weight of the AC if the altitude is constant?

 

[Dronedevices]

Maybe you were thinking of the basic motor data which is pretty noisy. The MotorPower calcs that I mentioned
View attachment 30963
was added a versions back to help the Battery/Motor/distance guys (the Batterians) . Like you they needed to see smoothed data.

BTW, the motor power consumption should be dependent just on tilt angle - given that air density and altitude are constant. Probably what you're seeing is that pitch is being adjusted to meet variations in elevator input and/or ground speed.

Thanks, I think I did, but I'll have to check again. It's great that this is available!

 

[sar104]

But.. is there any lift to be dependent on airspeed? Is lift generated by a quad moving horizontally? Isn't it all about vertical thrust which has to be exactly the weight of the AC if the altitude is constant?

I'd be very surprised if any of these aircraft are aerodynamically neutral with horizontal airflow. And I recall a couple of studies that showed that flight time increased with airspeed, at least for moderate airspeeds, also suggesting that the fuselage generates some lift.

So yes, the balance that you describe is correct, but it is vertical component of thrust plus lift equals weight for steady, constant-altitude flight.

 

[Dronedevices]

But.. is there any lift to be dependent on airspeed? Is lift generated by a quad moving horizontally? Isn't it all about vertical thrust which has to be exactly the weight of the AC if the altitude is constant?

Interestingly the power consumption doesn't go up much, if at all up to 20 mph air speed. I believe this is due to the added lift from the propeller blades which sides are rotating into the wind (this added effect is also use when sailing close upwind) and makes up for the added form drag from the drone's body, and at higher speeds with more tilt this drone body is the opposite of a lifting body.

 

[sar104]

Another consideration is that the power/thrust relationship varies with airspeed normal to the props, which obviously changes with horizontal airspeed. Again - that doesn't change the conclusion that for steady-state flight at constant altitude, thrust and power are single-valued functions of pitch, but it does introduce other variables during acceleration/deceleration.

 

[sar104]

Interestingly the power consumption doesn't go up much, if at all up to 20 mph air speed. I believe this is due to the added lift from the propeller blades which sides are rotating into the wind (this added effect is also use when sailing close upwind) and makes up for the added form drag from the drone's body.

That effect is countered, at least to some extent, by the rearward moving phase with reduced lift. I suspect that fuselage aerodynamics and propeller efficiency with incoming airspeed dominate, unless I'm missing something obvious.

 

[Dronedevices]

That effect is countered, at least to some extent, by the rearward moving phase with reduced lift. I suspect that fuselage aerodynamics and propeller efficiency with incoming airspeed dominate, unless I'm missing something obvious.

I agree, although the rearward moving phase also has less forward drag (backward vector), along with less lift.