Mini wind resistance - ok for coast flying?

[DanMan32]

I agree there are ways to get out of trouble with wind by not using RTH, use RTH only to change heading towards you, descend to lower winds, or just land where you can.
The problem occurs when you start losing signal in the process of recovery. That automatically triggers RTH, which puts you back in trouble both in higher altitude with higher winds, and limited speed.

Even an experienced pilot could be caught off-guard with higher winds that originally thought.

So, have RTH try to use the target airspeed (which DJI may need to rethink for max efficiency), but go to higher speed/attack angle if GPS shows it's not making headway.

I'm surprised we haven't seen this much trouble with winds with the other models. Perhaps that's because RTH in the others can handle winds to the point that if winds were higher, most would instinctively know not to fly. 18mph isn't much, and could be easily encountered at higher altitudes where the ground winds are moderate.

 

[FoxhallGH]

I agree there are ways to get out of trouble with wind by not using RTH, use RTH only to change heading towards you, descend to lower winds, or just land where you can.
The problem occurs when you start losing signal in the process of recovery. That automatically triggers RTH, which puts you back in trouble both in higher altitude with higher winds, and limited speed.

Even an experienced pilot could be caught off-guard with higher winds that originally thought.

So, have RTH try to use the target airspeed (which DJI may need to rethink for max efficiency), but go to higher speed/attack angle if GPS shows it's not making headway.

I'm surprised we haven't seen this much trouble with winds with the other models. Perhaps that's because RTH in the others can handle winds to the point that if winds were higher, most would instinctively know not to fly. 18mph isn't much, and could be easily encountered at higher altitudes where the ground winds are moderate.

It's actually not surprising when you consider that the Mavic Air is almost twice the weight [430g] of the Mavic Mini ... A heavier drone will hold it's position in wind much better than a lightweight one will - especially in gusty conditions. Mavic Pro weighs in at 734g and Mavic 2 Pro 907g ...

A simple example of this is to take two feathers - tape a coin to one - and drop them from the same height while standing in a wind. See which one lands closest to your feet. ?

The experienced pilot will tend to not get caught out, because their experience tells them when they should and shouldn't put their drone up in the first place ...

 

[Ian in London]

Yep, that seems to be a common misconception. If you had a Mini and a Mavic Pro sitting on a table and it got windy, it's intuitively obvious that the Mini will get blown off the table first. However, applying that intuition to what happens in the air is fallacious. Sitting on the table, the resistance to the force of the wind is the friction with the table, which is directly proportional to the weight of the drone. However, when it's in the air flying, the only resistance to wind drag is thrust, i.e. the same two forces that limit top speed. Any drone with a higher thrust-to-drag ratio than the Mini will handle higher winds than the Mini, regardless of weight.

Precisely. Hence the Mavic Air slices through wind way above it's spec'd maximum...

 

[Ian in London]

Just one more comment to RTH and sports mode:
If the MM gets blown away the best you can do is switching to sports mode, lowering altitude as much as possible and flying home manually, as stated before.
However, at low altitude the risk for connection loss is increasing dramatically and the worst case would be loosing the connection. Same problem is in case you get aware that you cannot reach your location (e.g. because battery is empty) and you decide for intentionally landing at a foreign but easy to find place. Risk is extremely high that the connection will break prior to landing.
In such cases the MM will automatically initate a RTH, increase altitude again up to the pre-programmed level and therefore get blown away again. I have actually no solution on how to prevent this. For the bigger Mavics there is a GO4 option for connection loss handling, where you can slelect between landing in place or issuing RTH. This could save your MM in such situations, too.

Very good point on the remote landing. I wonder if hitting the 'autoland' function would make it continue landing even if it subsequently lost signal? I'll test that one out the next time I'm out flying....
Ian

 

[netsonic]

Very good point on the remote landing. I wonder if hitting the 'autoland' function would make it continue landing even if it subsequently lost signal?

No Ian, without a working connection, you cannot transmit the command and the Mini will use the RTH triggered by the loss of signal.

This is the default and there is no alternative. Bigger Mavics have the option in the DJI Go 4 App to Hoover in place if the signal is lost, but the DJI Fly App does not have this option. It's the classic Chicken or Egg scenario.

 

[GerdS]

No Ian, without a working connection, you cannot transmit the command and the Mini will use the RTH triggered by the loss of signal.

The idea is pressing the landing button already before the MM is low enough for loosing connection. The question is, what will happen when connection is lost during landing? Will the MM continue the already running landing operation or will it fall back into RTH and climb again?

 

[netsonic]

Hey @GerdS, check post #20 on page one. Let's say that if it's low on battery (under 20%), it will definitely land.

 

[FoxhallGH]

Yep, that seems to be a common misconception. If you had a Mini and a Mavic Pro sitting on a table and it got windy, it's intuitively obvious that the Mini will get blown off the table first. However, applying that intuition to what happens in the air is fallacious. Sitting on the table, the resistance to the force of the wind is the friction with the table, which is directly proportional to the weight of the drone. However, when it's in the air flying, the only resistance to wind drag is thrust, i.e. the same two forces that limit top speed. Any drone with a higher thrust-to-drag ratio than the Mini will handle higher winds than the Mini, regardless of weight.

You have forgotten something basic here I'm sorry @RogerDH ... The good old F=MA [Force = Mass x Accelleration] equation rears its head here ... The lower the 'Mass' (weight), the less 'Force' is required to push it around. The problem the Mini has is that due to its low 'Mass', the slightest misalignment with the wind can force it off track very easily. IF you were able to have your MM tracking directly into wind for mile after mile and never needed to deviate from course, then yes - you can withstand a direct head-wind up to about 18 mph - But as soon as the nose goes up, down, left or right - that would be it, the low mass of the Mini will allow it to be pushed around and put in an attitude where it's no longer penetrating the airflow, but going with it. Heavier drones are more immune to this because their weight gives them 'Inertia' and the Inertia helps withstand the force of the gusts to the extent that the drone has time - and less movement - to react to.
Your sitting on the table analogy has some merit RogerDH, but it completely ignores Physics.
Don't forget the age-old diagram that's been around since the Brothers Wright - that shows the forces acting on an aircraft in flight ... That down-pointing arrow is not to be ignored!

 

[Drony_Drone]

So anyone in UK flown over the sea for lighthouses, or mouth of rivers where ships come in etc?

How does MM cope, I know depending on wind, but in general?

 

[RogerDH]

You have forgotten something basic here I'm sorry @RogerDH ... The good old F=MA [Force = Mass x Accelleration] equation rears its head here ... The lower the 'Mass' (weight), the less 'Force' is required to push it around. The problem the Mini has is that due to its low 'Mass', the slightest misalignment with the wind can force it off track very easily. IF you were able to have your MM tracking directly into wind for mile after mile and never needed to deviate from course, then yes - you can withstand a direct head-wind up to about 18 mph - But as soon as the nose goes up, down, left or right - that would be it, the low mass of the Mini will allow it to be pushed around and put in an attitude where it's no longer penetrating the airflow, but going with it. Heavier drones are more immune to this because their weight gives them 'Inertia' and the Inertia helps withstand the force of the gusts to the extent that the drone has time - and less movement - to react to.
Your sitting on the table analogy has some merit RogerDH, but it completely ignores Physics.
Don't forget the age-old diagram that's been around since the Brothers Wright - that shows the forces acting on an aircraft in flight ... That down-pointing arrow is not to be ignored!

View attachment 92123

F=ma means that with a sudden gust of wind, a lighter drone will react with a higher acceleration. But that just means that, if the wind force is not resisted, the heavier drone will take a little longer to get up to the speed of the wind. On the other hand, if both drones immediately counteract that sudden drag with similar thrust, the heavier drone will be slower to react to that force, too, so I'd call that a wash. It's still thrust versus drag to determine whether the drone can make progress versus the wind.

I now think that weight does indirectly have something to do with it, but it's kind of the opposite of your theory. Suppose that the 200g Japanese version of the Mini can deliver the same power to the props as the 249g standard version. (That's not necessarily true, but let's assume it is.) Which version would have better resistance to the wind? I believe that theoretically, the Japanese version should be able to achieve a higher airspeed than the standard, because less power required to generate lift means more power available for thrust, and I believe that would mean it could make progress against higher winds (assuming that the extra available power was exploited with a higher pitch angle).

 

[GerdS]

Hey @GerdS, check post #20 on page one. Let's say that if it's low on battery (under 20%), it will definitely land.

It will land for sure on low battery, but that was not my question. The question is, will it also land with a full battery if commanded to do so and the connection goes lost during the landing process?

 

[RogerDH]

It will land for sure on low battery, but that was not my question. The question is, will it also land with a full battery if commanded to do so and the connection goes lost during the landing process?

I forget who it was, but one user reported (and rightly complained about, I think) that the Mini would abort a Land command and execute RTH if it lost connection on the way down.

 

[GerdS]

I forget who it was, but one user reported (and rightly complained about, I think) that the Mini would abort a Land command and execute RTH if it lost connection on the way down.

I gues it's worth to be simulated, but too bad, weather forecast here is so bad that I doubt to be able to do so this week.

But if I can, I would look for a good place to land, go away for about 40m (safe RTH distance), take off there, fly the MM to the intended place in about 20m altitude while also going to there, tap onto the landing button and then power off the remote. This way I can observe what the MM is doing and if it will start RTH I still can power on the remote and take over control again before landing.

 

[Ian in London]

No Ian, without a working connection, you cannot transmit the command and the Mini will use the RTH triggered by the loss of signal.

This is the default and there is no alternative. Bigger Mavics have the option in the DJI Go 4 App to Hoover in place if the signal is lost, but the DJI Fly App does not have this option. It's the classic Chicken or Egg scenario.

As @GerdS mentions, my idea is to instruct the remote landing before loss of signal. If it's really going wrong and you need to land, hitting the autoland would be the sensible route as long as it doesn't break that command if it subsequently loses connection. Will test that out next week when I have a day off..... Unless someone already knows the answer for definite.

Ian.

 

[GerdS]

I had luck today, the forecast was wrong and at least it didn't rain and there was almost no wind, so I was able to test.

1. I took off from a safe place for RTH landing.
2. I flew away for about 70m to another place which is safe to land.
3. I tested RTH to find out if it would just land or return, it returned to the first place, so distance was sufficient.
4. After cancelling RTH I flew back to the second place at an altitude of about 40m.
5. I pressed the "landing" button within the Fly app and the MM begun descending.
6. Immediately I powered off the remote and waited for about 10s.
7. The MM continued descending.
8 I turned on the remote again. After getting connected the MM stopped descending and initiated a RTH which I was able to cancel.

So the "landing" function can indeed be used in emmergency situations for automatic landing at a safe remote place in case you cannot fly back against a strong headwind.

If this happens to you then:
1. Switch to Sports mode and fly against the wind until you see a safe and easy to find place for emmergency landing. Ideally this place is a bit shielded against the wind e.g. by trees or similar.
2. Descend manually as far as possible as long as the radio connection is stable, means as long as there is nothing between you and the MM in direct sight.
3. Look downwards to ensure a space with at least 10m in diameter around the assumed landing place is safe for landing.
4. Then use the "landing" button within the Fly app for automatic landing.
5. Observe the landing as long as possible before connection will break up.
6. Power off the remote and go to the landing place for retrieving your MM.

 

[netsonic]

Spot on, my friend. I am however a bit sorry that you did not manage to let it land completely. For me it's unclear what happens if it believes that the spot is not suitable for landing and remains hoovering at 0.5 m above ground.

 

[Ian in London]

Spot on, my friend. I am however a bit sorry that you did not manage to let it land completely. For me it's unclear what happens if it believes that the spot is not suitable for landing and remains hoovering at 0.5 m above ground.

That's a good point! And would be difficult to test as it would mean risking the Mini in order to see if it lands in an unsuitable spot, althoughlong grass would probably fall into that category. I might try that this weekend.

Ian

 

[GerdS]

Maybe the MM will hoovering sligtly above ground instead of immediately landing, but it will stay there then until emmergency landing because of battery low.
I was not willing to endanger my MM by landing on ground today, as it was raining before, the ground was very muddy and my shoes still look like after a walk through a freshly plowed field, although I stayed on a tarred dirt road. So I preferred takoff from hand and hand-catching.
But feel free to repeat my test in a better envoironment including touch down and let us know if there was a problem.

 

[lannes]

I would hope that if RTH is activated the MM should go into its best power mode possible to come home by calculating battery etc.

That the problem with the MM RTH, it defaults to P-mode which has a top speed of 18mph which is sometimes not powerful enough to fight a headwind

It can only handle a Beaufort scale of 4

Beaufort scale - Wikipedia

en.wikipedia.org

 

[Drony_Drone]

That the problem with the MM RTH, it defaults to P-mode which has a top speed of 18mph which is sometimes not powerful enough to fight a headwind

It can only handle a Beaufort scale of 4

Beaufort scale - Wikipedia

en.wikipedia.org

What do other Mavic do, in the sport mode for RTH or just that they can handle it’s ok in the normal mode?

If so then DJI need to look into this and think about the MM capabilities and maybe up the RTH to best possible mode to attempt to get home?