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Flying at high altitudes

shervink99

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#1
A month ago I went to Italy, and naturally I brought my drone with me. I think mountains are some of the most spectacular things you can capture from a drone. The footage is below.

Now, since this turned out great, I would like to climb a bigger mountain in the summer, like 4000 meters or so. Would the altitude be a problem? Pressure and such isn't exactly the same up there. Any physicists out there? Or anyone with more experience than me?

 

zocalo

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#3
I regularly fly up around 3500 m, with no problems. Flight time is perhaps slightly reduced.
The Mavic 2 is rated to 5000m above sea level, so 4000m should be perfectly OK. People have apparently gone a good deal higher than that (almost certainly not legally), and although it's not entirely clear how modified those drones were it's very likely that the 5000m is just what DJI considers "safe" rather than an enforced ceiling and the drone would be able to operate higher if pushed and conditions were good.

Air pressure (and hence temperature) drops with altitude, so you'll have colder batteries and the thinner air means that the motors will have to work harder to keep the drone in the air. You'll also typically get higher windspeeds than at sea level, which will again reduce battery life, so expect flight times to be further reduced accordingly.

Check the wind conditions with something like UAV Forecast before you fly, keep an eye on the battery life indicator, make sure you have plenty of battery to RTH, and you should be fine.
 

4wd

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#4
As the air gets thinner it will be more difficult to counter the wind and maintain stability.
Clearly there won't be a specific altitude above which it just can't work, but a gradual lack of control and potential for things to suddenly go wrong.
I've seen video of a short Phantom 2 flight near the top of Everest, more recent models have far more power and better stability.
 

Jackcutrone

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#5
On the winds are higher at higher altitudes note, best to fly into the wind outbound do on the return you are not fighting the wind. You may want to check an aviation winds aloft forecast to get an idea of the feasibility of flying at all.
 

Cymruflyer

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#6
In a nut shell, the higher you go, the thinner the air. Thinner air means reduced performance, which means the props are not biting into as much or as thick air as at sea level. This means the motors will work harder to maintain the same or similar performance the higher you go.

Then there is density Altitude to consider, which means the air gets even thinner at the same altitude, the higher the ambient temperature is. For non aviation type, this is an example, but remember, just an example so don't take the numbers to be exact because it is just to give you an idea. If you had performance XXX at 5,000 ft at 50F degrees and XX at 7,000 ft at 50F and X at 8,500 ft at 50F. If you were at 5,000 ft and the temp increased to say 70F, then you are now at an effective, higher altitude regarding performance, so it now might be like XX but still at 5,000 ft. And if the temp went up to say 90F you may find your performance even lower so it might now only be X.

As a real example, say you have a fully loaded old 747 ready to take off for England from Denver airport which is a mile high but lets call it 5,000ft. As long as it took of with a 12,00ft runway early in the morning when the days summer temps are still cool, it could safely get off the ground and fly to England. However, if there were any flight delays due to mechanical issues or a late arriving connecting flight with a lot of passengers for England, and the temps now got up to 80F, that flight would have to be cancelled because the density altitude would be too great to allow for a safe take off. There would just not be enough runway left for the aircraft to lift off safely at those higher ambient temps because the air became too thin and did not allow enough performance of the aircraft to be able to take off.

Your drone does not need runway of course so that is not a problem for take off, but the air is thinner at altitude and the warmer the air, the more thin or less dense it becomes, so efficiency of the props is reduced further, meaning more work for the motors to do to get the drone off the ground.

You might find that you could lift a 1lb weight at sea level with your drone, but at 9,000ft on a warm day, those props and motors could run as long as you want and the drone would not be lifting off. Since the motors are having to work harder, you will find your batteries diminish more quickly than at sea level. That is something to keep in mind while flying at high altitude, the drone will not have the same performance as you expect at lower levels or sea level and by that I also mean battery time per flight. So if you expect 22 mins of flight for safe flight and home to land, don't expect that to be the case at high altitude. Fly as if you only had half the battery life each time, despite what your percentage numbers are showing you, and that might keep you safer to get back to home point. Hope this explains things for you. Okay, maybe that wasn't a nut shell, but in a coconut shell...
 
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Walt

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#7
The Mavic 2 is rated to 5000m above sea level, so 4000m should be perfectly OK. People have apparently gone a good deal higher than that (almost certainly not legally), and although it's not entirely clear how modified those drones were it's very likely that the 5000m is just what DJI considers "safe" rather than an enforced ceiling and the drone would be able to operate higher if pushed and conditions were good.

Air pressure (and hence temperature) drops with altitude, so you'll have colder batteries and the thinner air means that the motors will have to work harder to keep the drone in the air. You'll also typically get higher windspeeds than at sea level, which will again reduce battery life, so expect flight times to be further reduced accordingly.

Check the wind conditions with something like UAV Forecast before you fly, keep an eye on the battery life indicator, make sure you have plenty of battery to RTH, and you should be fine.
Thanks for this information.
I want to take my drone up to 5000' over the next couple of days. Estimated temperature at that elevation will be 10 degrees F. Do you use anything to reduce the chance of ice formation on your propellers?
 

Cymruflyer

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#8
Thanks for this information.
I want to take my drone up to 5000' over the next couple of days. Estimated temperature at that elevation will be 10 degrees F. Do you use anything to reduce the chance of ice formation on your propellers?
Ice forming has to do with Dew Point temperature and ambient temperature and nothing to do solely with altitude and temp.

Check your dew point temps, when they are showing as the same or very close to your ambient air temp then you are in a prime situation for icing, regardless of your altitude, be it 2,000 ft or 8,000 ft. The further apart your ambient temp is to your dew point temp, the less likely you are to come into icing conditions.

In general, the higher the altitude, the colder and dryer the air, but that is in general. Therefore, in general, you should not be concerned with icing of props. Icing conditions do not happen too often, but when flying real aircraft, you may experience icing conditions in summer as well as in winter seasons, it is not just a winter thing or just an altitude thing.
 
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lolo780

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#9
Make sure to use props with a higher pitch than stock M1P props. Platinum or M2 (with rears trimmed) work well.
 

Walt

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#10
Ice forming has to do with Dew Point temperature and ambient temperature and nothing to do solely with altitude and temp.

Check your dew point temps, when they are showing as the same or very close to your ambient air temp then you are in a prime situation for icing, regardless of your altitude, be it 2,000 ft or 8,000 ft. The further apart your ambient temp is to your dew point temp, the less likely you are to come into icing conditions.

In general, the higher the altitude, the colder and dryer the air, but that is in general. Therefore, in general, you should not be concerned with icing of props. Icing conditions do not happen too often, but when flying real aircraft, you may experience icing conditions in summer as well as in winter seasons, it is not just a winter thing or just an altitude thing.
Thank you very much for this response!
 

Cymruflyer

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#11
Make sure to use props with a higher pitch than stock M1P props. Platinum or M2 (with rears trimmed) work well.
I would not suggest simply using high pitch props because an aircraft is set up to optimize the engine and if present, reduction drive, to diameter of prop, number of blades and the pitch setting. Unless you have a variable pitch prop but then you need to change engine setting as you use this.

I would think the engineers must have chosen a set prop diameter and pitch to optimally work with the motors and the max. rpm they produce to get the best possible performance out of the total match on the drone. Changing prop size or pitch of prop could do things to the motors you are not aware of and possibly cause damage over time. An increase in prop pitch puts added strain on a motor and it takes the motor more effort when spooling up from stop, which may possibly put more strain on the motor.

If you are a tech type who is able to calculate the differences, if they are valid on a drone (I don't know) regarding different pitch settings of props, then change what you know is safe for long term use, if not I would suggest staying with what they designed the drone to use.
 
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lolo780

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#12
Platinum props work well on on any M1 so you can't go wrong with those.

Efficiency at sea level is excellent:

At high altitude the Platinum props will maintain efficiency of 20 watt seconds per vertical meter where stock M1P props drop off due to maximum motor speed.



Fixed props will perform the best up high.
 
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#13
I routinely fly at an altitude of 4300 ft up to about +/- 5000 ft in cold weather and have never noticed any problems even when flying at temperature of -30 deg C. As mentioned above if the temperature were higher say 40 deg C then those altitudes might be more challenging.
 

FoxhallGH

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#16
Master Airscrew 'Stealth' props are a great alternative for high-altitude flying, because these prop's (designed for Mavic Pro) are a courser pitch. Standard Mavic Pro prop's are 8330 (8.3" diameter x 3.0" pitch), whereas the MA prop's are 8344 (8.3" diameter x 4.4" pitch). These prop's already display better efficiency at normal flying altitudes (by extending flight times by a couple of minutes), so with the courser pitch, they have to be a big help up the mountain!

DJI Mavic Pro & Platinum STEALTH Upgrade Propellers - x4 Orange

MavPro_MA.jpg
 

Mitchell99

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#17
Here is another way to explain it... First thing is for someone to understand what components make up lift. I teach the lift equation to help identify those components. Lift = CL * 1/2P * S * V2 .... CL = Coefficient of Lift. 1/2P = 1/2 Air Pressure. S = Surface Area. V2 = Velocity squared.
So to increase lift you need to increase one of the components and as others decrease others will need to compensate for the loss to create the same amount of lift. We can discuss each and how they can be affected.
First, Air Pressure. There is not anything we can do to affect the air pressure but knowing generalities will help. As you go higher in altitude or the temperature increases the air pressure decreases and therefore will decrease lift with all others being the same. One way you can determine what kind of altitude you will be finding out the Density Altitude at the location you will be flying at. High, Hot, and Heavy will be a worst case scenario.
Next, Coefficient of Lift. This can also simply put at the angle of attack that the airfoil creates. I'm not going to get is to the intricacies of angle of attack, induced flow, ground effect and other factors. With other factors remaining the same you could produce more lift by increasing the angle or bite of the prop. This also has its down side because you can get to the point where the blade will stall and produce no lift. Increasing the pitch or bite will also increase the amount of power needed to turn the props, although at higher altitude the air has less pressure and will allow for a higher angle of attack.
Surface area. If you were able to increase the surface are of the props wither by making them wider or longer an increase in lift would increase but the added weight of the props will again cause strain on the engines.
Last is the Velocity. Most important to note is that velocity is squared so any increase or decrease in RPM of the motors will effect the lift. Most drone use this to affect flight because it is the only way lift can be changed with fixed pitch props.

At high altitude your motors will have to work harder and will diminish your battery life to maintain the safe lift for your drone. You may also notice the drone will not react as quickly and may become a little sluggish. You will also have an increased susceptibility to vortex ring state if you decent vertically at a high rate of decent.

Those using the fixed props are most likely getting better flying characteristics due to a slight increase in surface area or pitch in the prop. It would be interesting to hear if anyone has used any other props at higher altitudes and what increases in lift resulted. However I would use caution as the increases may cause undue wear and strain on the motors.
 

FoxhallGH

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#18
Hmmm - or - it could just be that due to the thinner air, the prop's will have less resistance and therefore the rpm will be greater. A big advantage of electric motors, is they don't care if they have air or not. They will spin faster in lower pressure air, but won't work harder because the higher speed v's lower air pressure - balances the load on the motors. As the air pressure diminishes, the motor rpm is going to increase toward a point where it spins as fast as it's capable of (in a theoretical vacuum). So therefore, if you are maxed out in rpm, the thing that's going to give the prop' more 'bite' is the pitch.
 

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