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Why inceased power consumption upwind?

Dronedevices

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Does anyone know why the power consumption in sport mode at full speed is about 15% higher (from radar readings) when going upwind vs no wind at all, even though the tilt angle is the same at the maximum tilt angle of 35°? Using the moving slab of air concept shouldn't the power consumption be the same, but reduced speed over ground upwind? Is it due to turbulence and leveling adjustments? As we know, down wind consumption is much less with the reduced tilt angle limited by the 40 mph maximum over ground (all observations done with latest firmware, no changes).
 
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Doug Lare

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If you're going against the wind, your Mavic needs more power to continue forward motion. It would seem your maximum tilt angle is at maximum, as you stated, therefore more power is required to maintain that angle of attack. As I recall, when piloting my full sized plane, we could use a particular angle of attack, at a particular engine RPM, maintain altitude and actually drift backwards in the wind. Granted, it was a pretty stiff wind, more than what you'd fly your Mavic in, but the same principle.
 

tcope

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Air has resistance. Every try to run up wind when it's blowing 20mph... not as easy as running downwind when it's blowing.
 

Dronedevices

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If you're going against the wind, your Mavic needs more power to continue forward motion. It would seem your maximum tilt angle is at maximum, as you stated, therefore more power is required to maintain that angle of attack. As I recall, when piloting my full sized plane, we could use a particular angle of attack, at a particular engine RPM, maintain altitude and actually drift backwards in the wind. Granted, it was a pretty stiff wind, more than what you'd fly your Mavic in, but the same principle.
Thanks for your comment. If it does require more power for the same tilt angle upwind I would agree, but I still don't understand why it would require more power to maintain the same tilt angle (again using the moving slab of air concept)?
 

Just_nick

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You can imagine air as a fluid, and upwind is a denser fluid. To move through a denser fluid requires more energy by both the propellers and the body itself.
 

Dronedevices

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Air has resistance. Every try to run up wind when it's blowing 20mph... not as easy as running downwind when it's blowing.

Thank you for your comment. I agree with that, but using the moving slab of air concept the power consumption should be the same, but reduced speed over ground upwind, and as you mention the down wind consumption is much less with the reduced tilt angle limited by the 40 mph maximum over ground.
 

tcope

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Thanks for your comment. If it does require more power for the same tilt angle upwind I would agree, but I still don't understand why it would require more power to maintain the same tilt angle (again using the moving slab of air concept)?
The more angle, the faster the props need to spin to maintain the same altitude. Faster spin means more power drain. If they did not spin faster, the Mavic would loose altitude because of the increased angle.
 

Dronedevices

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The more angle, the faster the props need to spin to maintain the same altitude. Faster spin means more power drain. If they did not spin faster, the Mavic would loose altitude because of the increased angle.
Thank you for your comment. I also agree with that, but using the moving slab of air concept shouldn't the power consumption be the same, but only reduced speed over ground upwind?
 

Dronedevices

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The more angle, the faster the props need to spin to maintain the same altitude. Faster spin means more power drain. If they did not spin faster, the Mavic would loose altitude because of the increased angle.
But angle stays the same at 35°, upwind and no wind? I used an inclinometer visible to video to verify the angle.
 
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tcope

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But angle stays the same at 35°, upwind and no wind? I used an inclinometer visible to video to verify the angle.
If that were correct, then the only way to move the Mavic faster would be to increase propeller speed. That uses more power. Air is an object, just like water. As I said above, walking against a 20mph wind requires more energy/effort then walking into no wind or a tail wind. Leaning forward makes this more efficient but means you need to move faster in order to maintain that lean.

Bottom line, flying into the wind requires more power because of the resistance of the air against a moving object.

If you are _really_ looking for an easy answer, look at it this way. Push an object in space and it will continue to move as long as there is no resistance. Introduce resistance and it will slow down. The more resistance, the slower it will move. Same with the Mavic. The more air being forced against it, the slower it will move. So more power is needed to overcome that resistance. All other things. That is a bottom line. Nothing will change this.

If you _really_ are looking for the tech answer:

Newton's laws of motion - Wikipedia
 

Doug Lare

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Thanks for your comment. If it does require more power for the same tilt angle upwind I would agree, but I still don't understand why it would require more power to maintain the same tilt angle (again using the moving slab of air concept)?
If you maintain a particular power setting, in which your tilt is at maximum, your ground speed will be reduced by the mph of the wind you are going into. As an example, you are doing 20 mph at your particular power setting, in zero wind, then using the same power setting but going into a 10mph headwind, your ground speed will be 10mph. If you want to maintain your 20mph, you need more forward stick. your tilt, already at max, will remain the same, but your power consumption increase dramatically
 

Big Fil

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What is stick order and ground speed setpoint?
It means that when you move the stick it is a command to the flight controller to determine the pitch angle and motor RPM to get to the ground speed being commanded by the stick input.
 
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Dronedevices

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If you maintain a particular power setting, in which your tilt is at maximum, your ground speed will be reduced by the mph of the wind you are going into. As an example, you are doing 20 mph at your particular power setting, in zero wind, then using the same power setting but going into a 10mph headwind, your ground speed will be 10mph. If you want to maintain your 20mph, you need more forward stick. your tilt, already at max, will remain the same, but your power consumption increase dramatically
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.
 
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Kilrah

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Easy - the angle isn't the same. What did you use to measure it?
 

synaesthesia

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I'm not entirely sure what you mean by the "moving slab of air concept", and this quick Google search seems to indicate it only exists on this page on the entire internet...

Anyway...

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?
It seems here that angle is not a factor, you're stating angle is the same in both instances, thus the angle is irrelevant to the discussion. It doesn't deviate between observations. So the question as I understand it is "why is the power drain higher when flying into the wind?".

If you are travelling forwards at 10 m/s in no wind, you are using the power required to move forwards at 10 m/s.

If you are travelling forwards at 10 m/s against 10 m/s wind, you are using the power required to move forwards at 20 m/s plus any additional power required for corrections to keep the drone stable.

As you move faster relative to the air around you, exponentially more power is required to maintain that speed because of air resistance.
 

Dronedevices

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Easy - the angle isn't the same. What did you use to measure it?
I basically used a protractor (marked measuring stick out of carbon fiber) mounted a little distance out in front of the camera to focus on. Then I flew over extended flat farm fields with distant horizons in our area, which I used as the level (background) in upwind, crosswind, no wind and downwind tests (full stick sport mode). I also statically bench measured the angle of the drone with the protractor still attached and camera on. Angles were the same 35˚ for upwind and no wind, but more power consumption upwind (makes no sense), less angle for downwind with least power consumption (makes sense).
 
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Dronedevices

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I'm not entirely sure what you mean by the "moving slab of air concept", and this quick Google search seems to indicate it only exists on this page on the entire internet...

Anyway...



It seems here that angle is not a factor, you're stating angle is the same in both instances, thus the angle is irrelevant to the discussion. It doesn't deviate between observations. So the question as I understand it is "why is the power drain higher when flying into the wind?".

If you are travelling forwards at 10 m/s in no wind, you are using the power required to move forwards at 10 m/s.

If you are travelling forwards at 10 m/s against 10 m/s wind, you are using the power required to move forwards at 20 m/s plus any additional power required for corrections to keep the drone stable.

As you move faster relative to the air around you, exponentially more power is required to maintain that speed because of air resistance.
I agree with your analysis, but I'm using the same stick power full forward in sport mode which puts the drone at 35˚ (less downwind only*) and the speed (air speed not relative to the ground or GPS) should be the same no matter which direction I fly within a moving air mass or slab of moving air (*except downwind were the maximum speed is set to 40 mph, GPS ground speed in firmware). If this is the case, then the power should be the same for upwind an no wind (air mass not moving relative to ground), but it isn't? May be it's the changes in micro wind speed (turbulence) as well as gusts which do show as small power fluctuations, which all require more power to keep the drone at the same speed an altitude. One note, is that at a continuous angle 35˚ if the power consumption is increased (in clam air) the drone will gain speed and altitude.
 

Kilrah

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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.
 

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