Is This The Dumb Question Department?

[sar104]

I’ll go fly today and send you the log that’s np.

It may be only able to overcome 24 mph winds and maintain full speed but it doesn’t make sense that a craft that can reach speeds of up to 40 MPH as you say can only withstand winds of 24 MPH. Going 0 mph into a headwind of 40 mph is the exact same thing as going 40 MPH in no wind

I'm not arguing about what makes sense - I'm telling you how the aircraft is configured. And having examined multiple flight logs where the aircraft has been blown downwind, I can guarantee that it really is set up that way. You could try setting the wind parameter to 100 and then check whether it can hold in 40 mph winds. I won't be trying that test.

 

[Former Member]

Yea but there’s also less air resistance for the same reason. I’m in Salt Lake City and regularly take off in the mountains at 8000-10000 feet in the mountains and then go up even higher and I find that the drone actually flies better at those high altitudes. It takes less to build up inertia and then it just kinda coasts. Harder to stop though. I always thought this was also why jets climb to high altitudes as well?

I was surprised looking at my flight records that my longest flights (in the 25 min range for MP) were when I climbed a couple 1000” feet and also were among my furthest flights.

Coming from the reciprocating world, I was taught that a recip engine is less efficient at higher altitudes. On a drone, I would think that the props would have to spin alot faster to offset the loss of lift able to be generated in thinner air.

 

[sar104]

Yea but there’s also less air resistance for the same reason. I’m in Salt Lake City and regularly take off in the mountains at 8000-10000 feet in the mountains and then go up even higher and I find that the drone actually flies better at those high altitudes. It takes less to build up inertia and then it just kinda coasts. Harder to stop though. I always thought this was also why jets climb to high altitudes as well?

I was surprised looking at my flight records that my longest flights (in the 25 min range for MP) were when I climbed a couple 1000” feet and also were among my furthest flights.

Airliners are optimized for higher altitudes because drag scales with air density.

 

[Former Member]

Airliners are optimized for higher altitudes because drag scales with air density.

Do the jet engines produce the same HP at ground level as they do at altitude?

 

[brett8883]

I'm not arguing about what makes sense - I'm telling you how the aircraft is configured. And having examined multiple flight logs where the aircraft has been blown downwind, I can guarantee that it really is set up that way. You could try setting the wind parameter to 100 and then check whether it can hold in 40 mph winds. I won't be trying that test.

I've actually already done this test.

You can see I am in a canyon where the canyon walls are over 1 mile high to reduce the effect of cross wind. I start out flying towards the home point and then turn away from it. With a tail wind I get it up to 60 fairly easily. I turn around cause I quickly lose radio reception and come back into the wind. I am able to only get it up to 30 MPH in that direction.

I then turn with my back to the wind again and sit in a hover for a few seconds clearly showing the Flight controller is able to keep me in place at these high winds. After a false start I am able to reach 69 mph for a short time.

So you can see that the wind is about 30-35 MPH here.

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[sar104]

Do the jet engines produce the same HP at ground level as they do at altitude?

Thrust and power go down, but efficiency goes up.

 

[Former Member]

Thrust and power go down, but efficiency goes up.

How do you think Mavics perform as altitude increases?

 

[sar104]

I've actually already done this test.

You can see I am in a canyon where the canyon walls are over 1 mile high to reduce the effect of cross wind. I start out flying towards the home point and then turn away from it. With a tail wind I get it up to 60 fairly easily. I turn around cause I quickly lose radio reception and come back into the wind. I am able to only get it up to 30 MPH in that direction.

I then turn with my back to the wind again and sit in a hover for a few seconds clearly showing the Flight controller is able to keep me in place at these high winds. After a false start I am able to reach 69 mph for a short time.

So you can see that the wind is about 30-35 MPH here.

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I can't tell much without the log, but if you were in sport mode and actually have the max tilt set to 60° then the maximum wind holding speed will be commensurately higher than with the default settings, even if you didn't change the wind resistance parameter.

 

[sar104]

How do you think Mavics perform as altitude increases?

For propellers, thrust, power and efficiency go down with altitude.

 

[Former Member]

For propellers, thrust, power and efficiency go down with altitude.

So would it make sense that the higher up a pilot launches his drone, he/she could possibly experience lower speed, lift, and flight time?

 

[Former Member]

For propellers, thrust, power and efficiency go down with altitude.

Thank you for all your invaluable input.

 

[brett8883]

I can't tell much without the log, but if you were in sport mode and actually have the max tilt set to 60° then the maximum wind holding speed will be commensurately higher than with the default settings, even if you didn't change the wind resistance parameter.

Kk I get your point there. There’s not enough wind today to see what wind resistance it has with a normal sport tilt parameter so I’ll do the flight with 60 tilt and send you the fight data tonight.

It’ll have to be a different day that I test the hovering in high wind conditions but just so I’m straight you are saying that the Mavics ability to hover in wind is greater in sport mode than any other mode?

 

[sar104]

Kk I get your point there. There’s not enough wind today to see what wind resistance it has with a normal sport tilt parameter so I’ll do the flight with 60 tilt and send you the fight data tonight.

It’ll have to be a different day that I test the hovering in high wind conditions but just so I’m straight you are saying that the Mavics ability to hover in wind is greater in sport mode than any other mode?

I don't know whether sport mode makes a difference. It depends on whether the maximum tilt used for resisting the wind is a function of the maximum tilt in the mode in use, or whether it's the same across all modes.

 

[FoxhallGH]

Coming from the reciprocating world, I was taught that a recip engine is less efficient at higher altitudes. On a drone, I would think that the props would have to spin alot faster to offset the loss of lift able to be generated in thinner air.

It's actually a bit simpler than that Rob ... Because the air is thinner at high alt's, there isn't as much 'drag' on the prop' as there is when it's spinning in sea-level air. That means that the motor rpm will increase [as the Mavic's altitude increases], and therefore the prop's will stilll push the same amount of air [by volume] out of the way for each revolution. Although the rpm will be higher, the prop's & motors should be doing the same amount of work, and therefore won't be drawing any more current than normal.

The Mavic motor doesn't need air to run of course, so therefore, at the max. altitude the Mavic is capable of reaching, the prop's will be being spun at the max' rev's that the motors are capable of, and pushing the maximum amount of air available downwards so the drone can maintain a hover. There will be an altitude where these two factors (rpm v's air density), intersect to make a point where the Mavic will just not go any higher ... I don't know if that altitude is what DJI quote as the max. attainable in the spec's. - but if so, it would explain why the Mavic 2 Pro with more powerful motors and courser prop' pitch, has a higher service ceiling than the Mav' Pro (1).

 

[Former Member]

It's actually a bit simpler than that Rob ... Because the air is thinner at high alt's, there isn't as much 'drag' on the prop' as there is when it's spinning in sea-level air. That means that the motor rpm will increase [as the Mavic's altitude increases], and therefore the prop's will stilll push the same amount of air [by volume] out of the way for each revolution. Although the rpm will be higher, the prop's & motors should be doing the same amount of work, and therefore won't be drawing any more current than normal.

The Mavic motor doesn't need air to run of course, so therefore, at the max. altitude the Mavic is capable of reaching, the prop's will be being spun at the max' rev's that the motors are capable of, and pushing the maximum amount of air available downwards so the drone can maintain a hover. There will be an altitude where these two factors (rpm v's air density), intersect to make a point where the Mavic will just not go any higher ... I don't know if that altitude is what DJI quote as the max. attainable in the spec's. - but if so, it would explain why the Mavic 2 Pro with more powerful motors and courser prop' pitch, has a higher service ceiling than the Mav' Pro (1).

Good points. How about the fact that the motors on the Mavic are governed by the ESC, and if the ESC detects excess RPM, it will retard the RPMs until they are with spec? That would result in decreased lift from lower RPMs, and possibly stall the aircraft, depending upon how steep the angle of attack or climb rate is. Fixed pitch props tend to be less efficient at speed than variable pitch props, and since the Mavic has fixed pitch, Im going to guess that at higher altitudes, the ESC will try to compensate for the loss of lift by spinning the motors faster and hotter The IMU will wonder why the Mavic has been climbing at 15,000' MSL for 5 minutes and only attained 300' in additional altitude. By that time, the battery might well be exhausted, and RTH would not be an option, only a controlled crash.

Also, the motors at altitude might not require air but they will get hotter if trying to generate the same amount of lift, as is programmed into the ESC calculations. Thats why I was mentioning in a different thread, that if the Mavic was designed to be flown at sea level, and people are flying it at much higher altitudes, who knows what negative effects they will experience.

Only my speculation, and my experience as a full scale pilot.

Off topic, but I have flown many hours in piston engined and turbocharged aircraft at altitude. My flight experience has been in Mooneys, Cessna 182 RG's, Cessna 210s and other similar higher end private aircraft. Mooneys really shine at higher altitudes, but on approach, you need the speed brakes to slow that pony down. Cessna Skylanes are happy at any altitude, and can take off with most loads, as long as you can get the doors closed. Anyone who has owned or flown a Skylane knows what I mean.

 

[FoxhallGH]

Just so you are aware, an on coming storm can send out a gust front up to 50 miles ahead of itself. Also many real pilots have been caught out by the winds from an approaching storm. They go out in the field, check the wind and see where the storm is. The wind direction seems to be flowing to the storm so the uneducated/inexperienced pilot would assume the storm is moving away from them, so it would be safe to fly upwind.

They jump in their aircraft and go off flying about upwind with their perceived safe knowledge that the storm was moving away from their airport. They then turn to go home and land and are shocked to see that storm very close to their airport now. How could that be, they wonder and some will not be able to return to land because the storm is now too close to their take off point and growing and getting closer. What was actually happening, was that the storm was growing and moving towards them from winds aloft. However, because it was growing so quickly, it was sucking up all the air around itself as it was building and despite it moving toward their airport, the wind on the ground was moving towards the storm (being sucked in to the base). This makes the pilot on the ground think it was being blown away from them when it was really getting closer.

Some pilots have been killed in a crash when trying to quickly get back to their airport to land before the storm got right overhead, but the gust front shot out and caused them to lose control when trying to come back to land. Now this most probably will not affect any drone flyers, but it is something to bear in mind when flying with a big storm nearby. The ground wind direction will not necessarily be your indication of which way that storm is heading. You too could get caught out, flying upwind with your back to the storm and then before you know it, it might almost be upon you and the wind direction could suddenly change, as that storm suddenly dumps out onto the ground, and you are now well down wind and have a storm almost upon you.

If you are flying with a storm near by, keep checking over your shoulder if it behind you, to see if it is getting closer and larger. And remember that in such conditions, your wind direction could possibly change quickly.

Just to add to your very good meteorlogical explanation @Cymruflyer ... The wind direction toward or away from the approaching storm can be a factor of the type of 'frontal system' that the weather is pushing toward you.

A warm front is warmer air pushing up on-top of cooler air, and causes rain as the warm rising air cools and water condenses out of it. The rising warm air causes a drop in air pressure at the frontal system, and therefore, as you face the approaching front, you'll feel air [wind] rushing from the higher pressure [cooler] zone at your back, to the low pressure [warmer] zone in front of you with a change in wind direction likely when it slides in over your location.

A cold front is more like a giant bulldozer blade, in that it's cold air that slides in under warmer stable air, and tends to lift it straight up to make a very well defined line of thunder-cloud. You'll tend to get more of a breeze coming at you from the front, rising to high-winds as it gets to you.

 

[sar104]

Good points. How about the fact that the motors on the Mavic are governed by the ESC, and if the ESC detects excess RPM, it will retard the RPMs until they are with spec? That would result in decreased lift, ands possibly stall the aircraft. Fixed pitch props tend to be less efficient at speed than variable pitch props, and since the Mavic has fixed pitch, Im going to guess that at higher altitudes, the ESC will try to compensate for the loss of lift by spinning the motors faster and hotter The IMU will wonder why the Mavic has been climbing at 15,000' MSL for 5 minutes and only attained 300' in additional altitude.

Also, the motors at altitude might not require air but they will get hotter if trying to generate the same amount of lift, as is programmed into the ESC calculations? Thats why I was mentioning in a different thread, that if the Mavic was designed at sea level, and people are flying it at much higher altitudes, who knows what negative effects they will experience.

If you can post a mobile device DAT file for an M2P hovering at around sea level then I can compare it to my M2P hovering at 10,000 ft MSL. The DAT file includes motor speeds, voltages and currents, and obviously thrust.

 

[FoxhallGH]

Good points. How about the fact that the motors on the Mavic are governed by the ESC, and if the ESC detects excess RPM, it will retard the RPMs until they are with spec? That would result in decreased lift, ands possibly stall the aircraft. Fixed pitch props tend to be less efficient at speed than variable pitch props, and since the Mavic has fixed pitch, Im going to guess that at higher altitudes, the ESC will try to compensate for the loss of lift by spinning the motors faster and hotter The IMU will wonder why the Mavic has been climbing at 15,000' MSL for 5 minutes and only attained 300' in additional altitude.

Also, the motors at altitude might not require air but they will get hotter if trying to generate the same amount of lift, as is programmed into the ESC calculations? Thats why I was mentioning in a different thread, that if the Mavic was designed at sea level, and people are flying it at much higher altitudes, who knows what negative effects they will experience.

Yes - I think you are right w.r.t. the ESC, but still - you are going to get to that point in the sky where the rev's on the motors are max'd out, and the amount of air available is just enough to keep the Mavic at the hover on full up-stick ... The motors won't actually get much hotter, because though they may be spinning faster, the lack of air means that they are still 'working' the same as if they were spinning slower, in more dense air. There may be some issues with bearings coming under load due to higher rpm, but that would cause minor effect. There's also a marked temperature decrease with altitude. In clear skies, temperature drops 9.8 degrees celcius per 1,000 metres. That means that when flying at high altitudes, the motors are going to be in an environment that will keep them cooler anyway!

 

[FoxhallGH]

If you can post a mobile device DAT file for an M2P hovering at around sea level then I can compare it to my M2P hovering at 10,000 ft MSL. The DAT file includes motor speeds, voltages and currents, and obviously thrust.

Now there's a good experiment ... I'll see what I can do as soon as the winds here get down to flying speed! Thanks ...

 

[sar104]

Now there's a good experiment ... I'll see what I can do as soon as the winds here get down to flying speed! Thanks ...

A previous flight log would be just fine.