High wind and RTH

[Dbez1]

I admit I didn’t read all the responses, so I apologize if this is redundant but in this situation, just tap on the map in the lower left hand corner, put it in sport mode, and bring it back. I have never found the map to fail me. Ezpz unless you are low on battery. You might also consider VLOS, but that’s an entirely different conversation.

 

[Deleted member 103366]

Sar104 I have been thinking about what you have been saying about the maximum speed during RTH and something might just be beginning to get into my head.
Are you saying
1) that in entirely automated RTH, the maximum ground speed is 8m/s?
2) in terms of airspeed the drone will fly as fast as is necessary, up to its maximum possible airspeed, in an attempt to achieve a ground speed of 8m/s and that this maximum airspeed is or includes the maximum airspeed available in sport mode?

 

[sar104]

Sar104 I have been thinking about what you have been saying about the maximum speed during RTH and something might just be beginning to get into my head.
Are you saying
1) that in entirely automated RTH, the maximum ground speed is 8m/s?
2) in terms of airspeed the drone will fly as fast as is necessary, up to its maximum possible airspeed, in an attempt to achieve a ground speed of 8m/s and that this maximum airspeed is or includes the maximum airspeed available in sport mode?

(1) is correct. (2) is incorrect. It is limited to the maximum pitch available in P mode, which is set in FW. Pitch determines airspeed, and is the more fundamental quantity, but that means that it is therefore limited to the maximum airspeed in P mode, not S mode.

 

[scro]

@PhiliusFoggg when you say you've "pushed" the drone to get it to go faster during RTH was that in P mode or S mode?

 

[Deleted member 103366]

Sar104 thanks, I need to think on this

Scro, I am fairly sure I have RTH'd whilst in both those modes and possibly in C mode as well but the last set were in S mode.
I will leave things there for the moment whilst I think things over.

 

[scro]

It would make sense if you were in S mode when you could "push" the drone faster than what it was achieving on RTH. However, pushing in P mode would presumably not get it to go any faster that RTH speed.

I'm still sans-drone so can't play about to see what happens.

Another thing to consider: the MM has a max airspeed, dictated by max tilt angle, for each mode. For S mode it also has a max groundspeed, dictated by firmware. Does P mode have a max groundspeed limit too? Ie in P mode while flying downwind, can you exceed 8m/s?

 

[Deleted member 103366]

Scro your first sentence corresponds to my undertanding but seems contrary to SAR104's explanation of my "2)". This is what I need to think about.
However, I think you have highlighted maybe the root of the problem, what precisely is meant by "flight speed" and "speed" etc?
To my mind the meaning of "air speed" and "ground speed" are clear and unambiguous, the former is relative to the air, the latter is relative to the ground. "Flight speed" and or "speed " are ambiguous.
I know it would 'look bad' but I think it would be better if the writers of the manual rigourously applied specific terms to specific things.
For example if they are writing about ground speed they should write "......ground speed of *m/s" etc.
As my old man said "call a spade a spade".
Of course, it could be that my definitions are out of date/fashion and DJI's writers' write using new definitions.......

 

[sar104]

Sar104 thanks, I need to think on this

Scro, I am fairly sure I have RTH'd whilst in both those modes and possibly in C mode as well but the last set were in S mode.
I will leave things there for the moment whilst I think things over.

It doesn't matter which mode you are in to start with - once the aircraft mode switches to RTH then the P mode flight parameters are in effect.

 

[old man mavic]

@PhiliusFoggg my fellow flyer with the greatest of respect ,when a RTH is initiated whether by design or because of some problem the drone, irrespective of any wind regardless of direction or speed ,will only fly home in normal P mode ,if you then cancel the RTH, you can then fly it home manually in any mode you choose, it might be better to stay in P mode and just reduce height to achieve forwards momentum, or maybe sport mode will be better as well as reduced height ,the spin off of using sport mode is increased battery drain

 

[sar104]

It would make sense if you were in S mode when you could "push" the drone faster than what it was achieving on RTH. However, pushing in P mode would presumably not get it to go any faster that RTH speed.

I'm still sans-drone so can't play about to see what happens.

Another thing to consider: the MM has a max airspeed, dictated by max tilt angle, for each mode. For S mode it also has a max groundspeed, dictated by firmware. Does P mode have a max groundspeed limit too? Ie in P mode while flying downwind, can you exceed 8m/s?

These are all in the published specifications:

• Max Speed (near sea level, no wind)

13 m/s (S Mode)
8 m/s (P Mode)
4 m/s (C Mode)​

• Max Tilt Angle

30° (S Mode)
20° (P Mode)
20° (C Mode)​

 

[BokiFly]

Is greater speed in S mode achieved only with greater tilt angle, or motors run faster also?
Considering that tilt angle is the same for C and P mode then different speed is probably achieved with different motors speed.

 

[scro]

Those are the max speeds for "no wind". Whereas what I was wanting to get clear in my head is whether the stated P and C mode max speeds also apply if there is wind. I expect they do, as I know from experimentation that in S mode both the ground and air speed are limited to 13m/s max. i.e. a tailwind won't make your ground speed go any higher than this, but a headwind can limit your max ground speed to lower than this.

@BokiFly These are the max tilt angles for each mode. In C mode it probably rarely uses the full 20deg tilt, unless it is quite windy. There will be a slight increase in motor speed associated with increase in tilt angle. When hovering all the available thrust for a given motor speed is used to support the weight of the drone. When the drone tilts forward to start moving the thrust vector is now no longer vertical - ie some of that thrust is directed backwards so as to push the drone forward. Hence a little bit more overall thrust, ie more motor speed, will be required to ensure there is the same vertical component supporting the drone. The increase is proportional to the tan of the tilt angle. At 90deg tilt the extra thrust required is infinite since you no longer have a vertical component. That's why tilt angles are limited - tilt too far and you start to fall out of the sky.

 

[slup]

These are all in the published specifications:

• Max Speed (near sea level, no wind)

13 m/s (S Mode)​

8 m/s (P Mode)​

4 m/s (C Mode)​

• Max Tilt Angle

30° (S Mode)​

20° (P Mode)​

20° (C Mode)​

Just too elaborate a bit out from the Mini specs that sar104 attached ... & in manual control

The priority here (kind of), between the tilt angle & max speed ... is speed.

If flying with a moderate wind in for instance P-mode the AC will keep a max ground speed of 8m/s ... and keep it there by significantly lowering the tilt angle. The AC will not, in this case, utilize the full tilt of the available 20 degrees ... which would lead to a higher speed then spec.

If instead letting the AC fight a headwind it will again try to reach the speed of 8m/s ... but depending on the headwind the AC will utilize a steeper tilt, once reaching max speed the AC will settle with that needed tilt angle ... which can be less than the maximum 20 degrees.

If the headwind increases, the AC will further increase the tilt angle ... if needed, all the way to max 20 degrees. If max speed then isn't reached, the AC will remain with max tilt of 20 degrees but the speed will be lower than those max 8m/s.

With a still increasing headwind, with the AC tilting to the max, the AC eventually stops full fighting & if wind is strong enough the AC will start to drift down wind with full 20 degree tilt.

If going with Sport mode exactly the same will happen but the speed & tilt specs will be different ...

When RTH is activated the same behavior will repeat as described above with specs equal to P-mode.


As a side note ... & for time being, only for the MA1 which I fly with.

The specs for the MA1 in
P-mode: max 8m/s, max 25 degree tilt
Sport mode: max 19m/s, max 35 degree tilt

With manual control you can think that it wouldn't tilt more then 25 degree in P-mode to achieve the 8m/s speed ... but it does. Even though in P-mode & not manage to achieve the prioritized max speed of 8m/s due to a headwind ... it starts to utilize tilt angles steeper than the specified 25 degrees in order to maintain the speed to P-mode spec.

This was unexpected & came as a surprise when I first saw it in the flight log ... but have since then seen it repeatedly, the MA1 utilize Sport mode tilt spec in P-mode but only up to reaching the specified max speed of 8m/s. Have not a clue if this behavior is used in RTH also ... or if this applies to other DJI models.

And it's also a lesson learned for me ... because if I'm in P-mode trying to fight a to strong headwind & can't make way, the tilt is probably already utilizing the Sport mode tilt of 35 degrees ... & by switching to Sport I doesn't gain anything, the only tool a have left then is to drop height!

 

[scro]

@slup Interesting observations on the MA1 behaviours when fighting a headwind! I have a suspicion the MM doesn't do this, and hence exacerbates it's inferior resistance to wind compared to the MA1. I need to get a working MM back in my possession to test ?.

Another thing I'd be interested to get to the bottom of is when in RTH mode is the tilt strictly limited to 20deg, or can you apply stick input and get the aircraft to tilt further? If so, how much further can it tilt, and do you need to have been in S mode prior to initiating RTH, or not? That is what I was aiming at in post #26, but I may not have been clear enough in my wording.

 

[slup]

@slup Interesting observations on the MA1 behaviours when fighting a headwind! I have a suspicion the MM doesn't do this, and hence exacerbates it's inferior resistance to wind compared to the MA1. I need to get a working MM back in my possession to test ?.

Another thing I'd be interested to get to the bottom of is when in RTH mode is the tilt strictly limited to 20deg, or can you apply stick input and get the aircraft to tilt further? If so, how much further can it tilt, and do you need to have been in S mode prior to initiating RTH, or not? That is what I was aiming at in post #26, but I may not have been clear enough in my wording.

Well to comment your post ... & to show that the MA1's behavior to utilize the Sport mode tilt also applies to RTH ... but if this is equal to the Mini I can't say though ... but certainly gives Mini owners excuses to fly some more in order to test ?

This is from a RTH with a MA1 with a head/side wind coming in from the right... before RTH it was in P-mode.

From where the marker is in the chart it's clearly shown that the tilt angle used to reach the max speed of 8m/s (spec) is greater than the specified max 25 degrees for P-mode (& RTH).

Furthermore, at 458sec I apply nearly full elevator input while in RTH ... the tilt down increases to the max 35 degrees specified for the Sport mode (even though in RTH) & the ground speed increases to 10-13m/s (the wind velocity was pretty high in the flight, between 10-13m/s coming in from front/right side).

 

[BadWolf1]

Is greater speed in S mode achieved only with greater tilt angle, or motors run faster also?
Considering that tilt angle is the same for C and P mode then different speed is probably achieved with different motors speed.

The motors have to run faster when tilted. With the aircraft hovering, flat , the prop forces are vertical and lift = weight.
(I wish I could draw here. Imagine an arrow going straight up - the length if it must is the same as the weight of the aircraft g * mass, so 2.44 newtons )
If you angle the the prop to 20 degrees, the upward force (that arrow) must still be 2.44 newtons - otherwise the aircraft comes down, but the output of the prop is not vertical, it forms the long side of a right angle triangle - the other two sides are upward force (which must equal weight - if it's more we go upwards, and less means downwards ) and forwards force. We know the upward force and the angle so the long side - total prop output - must be 2.44/cos(20) - about 2.6
The short side of that triangle is 2.6*sin(20) of thrust. A helicopter can change the lift by changing the angle of attack of its rotor blades so they can stay at constant speed, a drone has fixed blades so can only vary speed.

If you have a constant airspeed at a given pitch, then drag = thrust, so if you know the weight and pitch you can calculate thrust, if you know airspeed and drag you have your drag coefficient. In theory any given pitch should give the same airspeed in all conditions, and depending how strongly the wind is blowing you might want extra pitch (up to the allowed maximum) to overcome the wind and get the requested ground speed, or less pitch to get the requested speed with wind assistance.

AIUI at full forward stick for a mode, pitch whatever gives you maximum ground speed for that mode or maximum pitch for that mode, which ever comes first.
If you want to fly home faster or use full pitch against the wind switch to S mode (which IIRC takes the drone out of P mode).
I have tried, and while descending the "spare" lift cannot be used as extra thrust,

 

[scro]

... In RTH mode the drone will go up to 30 degrees against the wind. If you want to fly home faster you can switch to P mode - provided that the drone is not already at 30 degrees....

Hi @BadWolf1 Have you actually observed 30deg pitch in either P mode or RTH mode on the Mavic Mini, or is that just an assumption that it'll do that? I ask because I'm trying to understand better how the intricacies of RTH mode work. If you've got flight logs that show that then could you share them, or post screengrabs of the graphs? My suspicion is that only S-mode will give you access to the full 30deg aircraft tilt, and this is implied in the specs given in post #30. Other modes are likely restricted to 20deg tilt. From Slup's flight log extract it is apparent the MA1 can tilt more in RTH mode than in P-mode, and with stick input on top of RTH you can get up to 35deg tilt. Many of the RTH-flyaway stories for the Mini imply that its RTH mode has limited tilt if there is no stick input, with some reports of people claiming that cancelling RTH and switching to S-mode was the only way to make headway against a strong wind.

@slup - just checked the specs for the MA1 and they state only 15deg max tilt in P mode. I, too, had it in my head it was more than that. DJI Mavic Air - Specs, Tutorials & Guides - DJI

 

[BadWolf1]

Hi @BadWolf1 Have you actually observed 30deg pitch in either P mode or RTH mode on the Mavic Mini, or is that just an assumption that it'll do that?

My suspicion is that only S-mode will give you access to the full 30deg aircraft tilt,

30 degrees was @sar104 said above. but I misread this

• Max Speed (near sea level, no wind)

13 m/s (S Mode)
8 m/s (P Mode)
4 m/s (C Mode)

• Max Tilt Angle

30° (S Mode)
20° (P Mode)
20° (C Mode)

I read it as 30 in S & P and 20 in C , but it is 30 in S and 20 in P & C.

I have corrected the original post , as it was mostly about the need to spin the props faster when pitched forward.
My understanding was, and remains, that if you have signal in a headwind, switching to S mode gives you a better chance of overcoming the wind. If P mode could use the maximum pitch it would over come the wind to get some movement in the right direction - so as I understand it it- no you don't get 30 degrees in P (and RTH = P) and only that error suggested you did. Sorry for the mistake !

 

[scro]

No problem... I guessed it was an innocent mistake

I'm also of the understanding that S-mode is the preferred mode in high wind situations. During RTH, and provided you've not lost signal it seems you can change the speed, altitude and orientation of the aircraft with stick input (user manual, pg 14), but the aircraft will continue flying directly towards the recorded home point. I'm not sure what the max speed you can manually induce is during RTH.

 

[sar104]

Is greater speed in S mode achieved only with greater tilt angle, or motors run faster also?
Considering that tilt angle is the same for C and P mode then different speed is probably achieved with different motors speed.

It's just tilt angle. The motors don't seem to have different limits.