Hello guys,

I've been testing my drone in slightly sub-freeze temperatures and normal winds. I have 2 questions about operating at high altitude and flying in sub-zero:

1) What would you recommend as a max altitude (speaking >500 m) you are comfortable flying in?
2) No doubt wind is stronger and temperatures even lower at high altitude but how much exactly? Is there a rule-of-thumb or a formula for the fall of temperature. Let's assume 0 °C ground temperature. Since my drone doesn't have an onboard outside temperature sensor, what would the temperature be at 500 m / 1000 m /... ?
How much stronger will the wind be?

Alex

I am a qualified private pilot and so will attempt to answer your questions!

dan_vector Posted at 2017-12-24 03:23
I am a qualified private pilot and so will attempt to answer your questions!

Thank you sir!

I am a qualified private pilot and so will attempt to answer your questions!
1) It does depend on the aircraft and if icing conditions are present. Unpressurised aircraft max ceiling will be 12,000ft at 1013mb. If icing conditions are not present (basically visual moisture and a heavy dew point then I would be happy to fly at that altitude. Again there many things to consider. Most private flying will occur at less than 6,000ft as the climb to altitude as well as the decent would take a long time as well as the piston engines becoming less efficient at too high an altitude. Another reason is that as you ascend further the airspace gets more and more controlled (away from airfields) due to the increasing commercial activity.

2) The International Standard Atmosphere (ISA) or rule of thumb is for every 1000ft of altitude gained you will drop 1.98 celcius. Unless you hit an inversion where the temperature can increase again however that isn't really a concern for drone pilots! So basically if it was 0c on the ground then at 1000ft you could expect it to be almost -2c all things being equal.

Wind also strengthens as you increase in altitude (less surface friction and less dense air as altitude increases) but this is a bit harder to predict. You can find wind/altitude charts online which will forecast what the wind will be.  Basically wind will veer and increase as you ascend and back and decrease as you decend.

dan_vector Posted at 2017-12-24 03:33
I am a qualified private pilot and so will attempt to answer your questions!
1) It does depend on the aircraft and if icing conditions are present. Unpressurised aircraft max ceiling will be 12,000ft at 1013mb. If icing conditions are not present (basically visual moisture and a heavy dew point then I would be happy to fly at that altitude. Again there many things to consider. Most private flying will occur at less than 6,000ft as the climb to altitude as well as the decent would take a long time as well as the piston engines becoming less efficient at too high an altitude. Another reason is that as you ascend further the airspace gets more and more controlled (away from airfields) due to the increasing commercial activity.

Thank you for the comprehensive answers. The Mavic Pro manual states a Max Service Ceiling Above Sea Level at 16404 feet (5000 m) which would take around 16 minutes to reach in sport mode (5 m/s max climb speed) and almost 28 minutes for a controlled descend back to sea level which exceeds the maximum flight time! My scenario could look something like this:

- taking off a mountain at around 6560 ft (2000 m)
- reaching 10.000 ft altitude after 3.4 minutes
- 12 minutes effective flight time at this altitude
- vertical descend at max. speed [without cutting the rotors ;) ] in 5.6 minutes

Ground level (let's say weather station is at 2000 ft ) temperature should then be a warm 16 °C (!) to not exceed DJIs recommended operating temperature range which is 0-40 °C for the aircraft itself. If I understood you correctly, a plus of 8000 ft altitude would mean ca. 16 °C lower temerature.

Very interesting result, didn't think the temp changes are that extreme! This means only low altitude flights this winter with the Mavic.

If flying on a regular basis consider a battery warming piece of kit , they sell them and they connect to the charging unit.  also consider the Insulation stickers.

remember when flying in below zero weather the battery will drain quickly and also what I find is the ( I use and P{ple I pad Pro )  device for the go app can sometimes just turn off on you  even with a decent charge still remaining .  I use a hand warmer that is activated by the air and attach it to the back of the I pad . Also keep the I pad nice in warm in  a heating pad seems to help as well, just make sure not to hot .

As far as winds go , past 20 mph and it becomes challenging. and much less fun flying , If you loose GPS assist and are not an experienced RC flyer , you will have your hands full !! .  Keep in mind the aircraft will get down wind  FAST and be sure you leave yourself plenty of time and more importantly battery life to make it back.  One time I got to far down wind and just barley made it back .  Try to  keep your flying  upwind if possible  and then coming back is a breeze ( pun intended )

Once had my AC go 93 mph coming back going  with  the AC going downwind, and the speed was climbing , so be careful of high winds.

Keeping in mind in an area with lots of trees or buildings can significantly reduce  the perceived wind speeds at ground level , what I do when I get to my cruising altitude is turn around and fly back a bit if going against the winds, If I can't get above 8 mph I know it is very windy up there and don't go that far away if I need to fly with the  wind because coming back is difficult  .Also when flying at full bore downwind and find the AC going like 60 MPH( or more, my record was 93 mph)   you know that you have strong tailwind and will need to fight this coming back.  This all becomes second nature after flying for a while .  



What is the law regarding max  altitude for RC aircraft in Germany ???
I  personally do not fly above 400 feet for the most part in my area becasue of proximity to an airport several mile away.  Now if I am in a deserted area away from civilization I may bring it above that point but do cautiously and with a spotter.  That altitude  being somewhere between the 400 foot and the max allowed by the firmware , dont do it often but not going to lie and say I never have done so.  Funny when I flew RC  Sailplanes  for many years no one ever said a word  about altitude and we were significantly above 400 feet all the time .

donnie w

Donnie * Posted at 2017-12-24 07:09
If flying on a regular basis consider a battery warming piece of kit , they sell them and they connect to the charging unit.  also consider the Insulation stickers.

remember when flying in below zero weather the battery will drain quickly and also what I find is the ( I use and P{ple I pad Pro )  device for the go app can sometimes just turn off on you  even with a decent charge still remaining .  I use a hand warmer that is activated by the air and attach it to the back of the I pad . Also keep the I pad nice in warm in  a heating pad seems to help as well, just make sure not to hot .

Thats for the input donnie!
I already thought about  getting insulated, maybe even heated battery pouches to keep the batteries warm and ready to go. So far what I did is let the mavic heat up and hover for a couple of minutes till the battery temp rised before going full throttle. The max altitude for multicopters in Germany is currently 100 m or 328 ft unless you have a permission to go higher OR if you are at a model airfield. Over 2500 ft you'd be entering controlled airspace. (whole another topic)
I can understand the government is concerned about multicopter because they are so easy to fly etc. But yeah I've flown various RC helicopters before and you could even now do whatever the heck you want. Considering UACs like the Mavic are high end flying computers and much more safe to fly than a full manual rc heli going at crazy speeds without any collision warning / GPS / autoland / redundant systems. The newest 100 m height restriction is plain stupid as lots of objects are higher than that. Minimal height for safety reasons would be nice though.

ShortRouter Posted at 2017-12-24 05:18
Thank you for the comprehensive answers. The Mavic Pro manual states a Max Service Ceiling Above Sea Level at 16404 feet (5000 m) which would take around 16 minutes to reach in sport mode (5 m/s max climb speed) and almost 28 minutes for a controlled descend back to sea level which exceeds the maximum flight time! My scenario could look something like this:

- taking off a mountain at around 6560 ft (2000 m)

In addition to dan's comments, another thing to keep in mind is that the climb rate won't remain constant as you go up. As you ascend into thinner air, the climb is going to slow down, though with an electric aircraft I couldn't really say by how much.

But, to take an example, my piston fixed wing climbs at about 1700/1800 fpm at sea level, but that drops to about 900fpm max at my airport's 6300' elevation. At 10,000' above sea level, it can just barely do 500fpm.

That of course includes the loss of power in the engine itself due to altitude effects which you won't have with an electric, not accounting for possibly reduced power from a cooling battery...

So just to keep that in mind, don't be surprised if the climb to your altitude takes longer than a simple calculation would say.....

ShortRouter Posted at 2017-12-24 09:05
Thats for the input donnie!
I already thought about  getting insulated, maybe even heated battery pouches to keep the batteries warm and ready to go. So far what I did is let the mavic heat up and hover for a couple of minutes till the battery temp rised before going full throttle. The max altitude for multicopters in Germany is currently 100 m or 328 ft unless you have a permission to go higher OR if you are at a model airfield. Over 2500 ft you'd be entering controlled airspace. (whole another topic)
I can understand the government is concerned about multicopter because they are so easy to fly etc. But yeah I've flown various RC helicopters before and you could even now do whatever the heck you want. Considering UACs like the Mavic are high end flying computers and much more safe to fly than a full manual rc heli going at crazy speeds without any collision warning / GPS / autoland / redundant systems. The newest 100 m height restriction is plain stupid as lots of objects are higher than that. Minimal height for safety reasons would be nice though.

Sure, thanks for the reply and information and Merry Christmas

donnie

In regards to potential icing conditions. If the outside air temperature is below freezing point at the altitude you are flying at, and moisture is present i.e cloud mist etc then there is a chance of ice forming on your device which may lead to its loss. How fast ice accumulates is from few seconds to several minutes.

Donnie * Posted at 2017-12-25 05:05
Sure, thanks for the reply and information and Merry Christmas

donnie

Actually, I just noticed my information wasn't explicit enough. The 100 m altitude is AGL which leads be to my new concern: The Mavic doesn't measure actual AGL when terrain changes! At low altitude it uses the ultrasonic / infrared sensors for AGL measurement but otherwise? From my understanding all it does is lock in the takeoff point ASL and define it as 0 AGL. Once I attempt to "climb" a 6000 ft mountain from ground level it will then inevitably refuse to climb any further than the 1640 ft (500 m) "max altitude limit" from my takeoff point... I travel a lot and would like to use my Mavic especially in regions where BLOS flying is permitted.

Lildoo Posted at 2017-12-25 06:42
In regards to potential icing conditions. If the outside air temperature is below freezing point at the altitude you are flying at, and moisture is present i.e cloud mist etc then there is a chance of ice forming on your device which may lead to its loss. How fast ice accumulates is from few seconds to several minutes.

Good point indeed, is there any de-ice agent available which is safe to use on drones? Like those they spray at real big bírds at the airport ;)

ShortRouter Posted at 2017-12-25 11:07
Actually, I just noticed my information wasn't explicit enough. The 100 m altitude is AGL which leads be to my new concern: The Mavic doesn't measure actual AGL when terrain changes! At low altitude it uses the ultrasonic / infrared sensors for AGL measurement but otherwise? From my understanding all it does is lock in the takeoff point ASL and define it as 0 AGL. Once I attempt to "climb" a 6000 ft mountain from ground level it will then inevitably refuse to climb any further than the 1640 ft (500 m) "max altitude limit" from my takeoff point... I travel a lot and would like to use my Mavic especially in regions where BLOS flying is permitted.

That's right and that's what will happen. DJI copters specify the altitude limit as referenced from the takeoff point only - they can't and don't compensate for rising or falling terrain.

In manned aviation, AGL limits have to be managed by the pilot as well, though. So, for example, if you're flying over terrain that has a hard 1000' or above limit, you have to maintain that regardless of the MSL altitude. So if you're about to bust airspace above that terrain to follow that rule, you're responsible for doing it correctly.  

I believe the 400' AGL limit in part 107 does actually mean above ground level under the aircraft, though, so it would be ok to bust 400' above where you took off if the terrain rises in the course of the flight. I admit I haven't read part 107 limitations in detail, tho. I think all it says is "400 AGL", which would of course account for rising or lowering terrain....

Alright thanks for the confirmation. The ATL limit sucks :/

ShortRouter Posted at 2017-12-26 07:21
Alright thanks for the confirmation. The ATL limit sucks :/

Sorry if I burst your bubble but it is because of such sentiments (wish to fly high) that has led to more and more countries banning the flight of drones in scenic areas, treating these as full fledged aircraft.

Call these rules anything you will but because of a few, many are affected and denied opportunities to fly legally.

Mike-the-cat Posted at 2017-12-26 20:38
Sorry if I burst your bubble but it is because of such sentiments (wish to fly high) that has led to more and more countries banning the flight of drones in scenic areas, treating these as full fledged aircraft.

Call these rules anything you will but because of a few, many are affected and denied opportunities to fly legally.

As we discussed AGL could be a few ft while ATL is 5000 ft easily. And this is a SMALL mountain. I live in the alps, come on! Also, once you get to the top of a mountain you can trick the Mavic and do 10 000 ft AGL easily. See the difference? Such ATL limit simply makes no sense. Returning my Mavic and getting another one with old firmware lol.