Mini wind resistance - ok for coast flying?

[FoxhallGH]

But I asked that, before continuing, could you please explain what you think it takes for either drone to move upwind, and you haven't done that. I was hoping that the question would get you thinking about my point, which is simply that the only way to move upwind is for the drone to generate lateral thrust that is greater than the force the wind is exerting. And my point which you keep missing is that inertia has absolutely nothing to do with how much lateral thrust a drone can generate.

But I'll try one more time by asking another question: What's the difference, if any, between a drone holding position in a 25 mph wind and flying 25 mph in still air? I think it should be obvious that what you're saying about inertia and acceleration does not answer either question, but if not, there's no point in continuing to argue with you.

Drones generate lateral thrust by tilting, and it doesn't matter if it's still air or windy -- that's the only way a drone can generate lateral thrust. As I said, weight does play an indirect role because they can't tilt to 90-degrees and apply all available power to thrust. They can only tilt to the point that they're still generating enough lift to counteract the drone's weight. And again, the heavier a drone is, the more power that is required to generate lift, leaving less power available for lateral thrust. So, given equal amounts of power, the lighter Japanese Mini is at an advantage, not a disadvantage: It could tilt farther without falling out of the sky, if the programming allowed it. In still air, it should be able to fly faster, and in wind, it should be able to resist higher velocity wind for the same reason. Inertia has nothing to do with it.

Hi RogerDH - first I want to say that I'm not considering this an argument - more of a discussion and a chance to explore this subject (which I'm really enjoying by the way - thank you). So I hope you don't think I'm attacking you or anything ... I thought I had explained what it takes to move a drone through the air and into wind. I'm 100% in agreement with your first paragraph. I'm also in agreement with your second paragraph - which is why a stationary aircraft in a wind-tunnel works the same as a moving aircraft in open air.

Where this departs from the theoretical to the practical, is that your assumption about a drone moving 'forward' into a 'headwind', is entirely correct only IF:
- you have a 100% constant wind speed (i.e. no gusts)
- you have the wind from exactly the same direction all the time
- the Mavic does not yaw in its flight attitude
- the Mavic does not pitch in its flight attitude
- the Mavic is flying at or below its max airspeed for the mode it is in

The practical problem we have is that the wind speed and direction will change and the Mavic will wobble in flight. It only takes a degree of wobble in a gust for different forces to push the Mavic in a different direction. It's at this point that inertia comes in! You are correct in that a light aircraft is more manoeuvrable, but I say again, it works both ways - in that a light aircraft is much more at the mercy of the winds.

It would be interesting to know what the 'power' output of the motors are for the MM and the 2Pro - because then you could get a 'power to weight' ratio for the two airframes. I'm sure if you could track it down, we'd see the M2P having the better P/W ratio. The M2P definitely has more powerful motors and swings props with a larger diameter and larger bite. It has a max speed of 72 km/h (45 mph), where the Mini's top speed is 13 m/sec ( in S mode) = 29 mph. So based on that - and to answer your question ... IF you can point the Mavic Mini directly into a 'constant-non-gusting' 29 mph wind, and the Mavic does manage to stay rock-steady attitude-wise, then it should hold steady in the air.

Just a point about the drone having to adopt a nose-down attitude to fly forward ... Just remember that what it is doing, is tilting itself so gravity can pull it downwards at speed, and then it applies power to push itself up to counteract the downward force of gravity. The resulting vector is forward, at a set speed, and constant altitude (when the tilt angle and the thrust all balance). What is it that determines the angle that the drone needs to be at to get to a certain speed? Its weight - as that is what gravity is acting upon to pull it down. For that reason, the weight/mass does contribute to the speed that the drone can achieve. The drone is effectively falling to get speed, and pulling itself forward & up with its motors to maintain height. The more it weighs, the faster it accelerates into the fall ... I believe that you'll find that in all Mavic's, that max angle forward or backwards, is determined by software. It's also not the case that you can continue to tilt the Mavic over to be vertical to fly into the headwind, as you are then presenting a larger surface area to the wind, and there is a maximum rpm that the motors can turn the props at which means that past a certain speed, the prop's won't push any more air, and in fact, become a barrier to the air. DJI would have determined this spec' in a wind-tunnel and found the angle at which each Mavic model gets the optimum penetration which will determine its max airspeed. There will be a graph of this around somewhere which will look like a curve mapping tilt angle to airspeed (at a constant max rpm) - that will peak at an ideal tilt angle and then drop off as the Mavic over-tilts and becomes a parachute!

I'm happy to be proved wrong, but I still believe that the standard Mavic Mini, and the Japanese Mavic mini - will demonstrate similar top speeds. Mainly because of the software setting to limit the tilt to fly forward. If it's using the same motors and prop's, and the cross-sectional area presented to the wind is the same, then it's difficult to see how it could fly faster. Again, I suggest that it would accelerate to its top speed faster than the standard model - but the same limitations apply when it gets there ... In fact, thinking about what I've said above ... If you agree that forward flight of a Mavic is a balance between gravity pulling it down and the 4-prop's pushing it up and forward, then since the weight/mass is lower with the Japanese MM, then you could be right to assume that model as actually not capable of the same forward top-speed as the standard model? It would be interesting to see an S-Mode drag race between the two ...

FPV racing drones are the extreme example of this, as they are light-weight and have powerful motors that have a very high rpm - so they can literally turn 90 degrees up/down/sideways and push themselves through the air. If you can increase the rpm of the motors that the Mavic Mini has, and override the software that determines the forward tilt. That would get you a faster drone, but it would not help in gusty winds as the MM's mass would still be too light. A typical FPV racing drone starts around 300g before you add the battery and prop's.

 

[RogerDH]

Hi RogerDH - first I want to say that I'm not considering this an argument - more of a discussion and a chance to explore this subject (which I'm really enjoying by the way - thank you). So I hope you don't think I'm attacking you or anything ... I thought I had explained what it takes to move a drone through the air and into wind. I'm 100% in agreement with your first paragraph. I'm also in agreement with your second paragraph - which is why a stationary aircraft in a wind-tunnel works the same as a moving aircraft in open air.

Where this departs from the theoretical to the practical, is that your assumption about a drone moving 'forward' into a 'headwind', is entirely correct only IF:
- you have a 100% constant wind speed (i.e. no gusts)
- you have the wind from exactly the same direction all the time
- the Mavic does not yaw in its flight attitude
- the Mavic does not pitch in its flight attitude
- the Mavic is flying at or below its max airspeed for the mode it is in

The practical problem we have is that the wind speed and direction will change and the Mavic will wobble in flight. It only takes a degree of wobble in a gust for different forces to push the Mavic in a different direction. It's at this point that inertia comes in! You are correct in that a light aircraft is more manoeuvrable, but I say again, it works both ways - in that a light aircraft is much more at the mercy of the winds.

It would be interesting to know what the 'power' output of the motors are for the MM and the 2Pro - because then you could get a 'power to weight' ratio for the two airframes. I'm sure if you could track it down, we'd see the M2P having the better P/W ratio. The M2P definitely has more powerful motors and swings props with a larger diameter and larger bite. It has a max speed of 72 km/h (45 mph), where the Mini's top speed is 13 m/sec ( in S mode) = 29 mph. So based on that - and to answer your question ... IF you can point the Mavic Mini directly into a 'constant-non-gusting' 29 mph wind, and the Mavic does manage to stay rock-steady attitude-wise, then it should hold steady in the air.

Just a point about the drone having to adopt a nose-down attitude to fly forward ... Just remember that what it is doing, is tilting itself so gravity can pull it downwards at speed, and then it applies power to push itself up to counteract the downward force of gravity. The resulting vector is forward, at a set speed, and constant altitude (when the tilt angle and the thrust all balance). What is it that determines the angle that the drone needs to be at to get to a certain speed? Its weight - as that is what gravity is acting upon to pull it down. For that reason, the weight/mass does contribute to the speed that the drone can achieve. The drone is effectively falling to get speed, and pulling itself forward & up with its motors to maintain height. The more it weighs, the faster it accelerates into the fall ... I believe that you'll find that in all Mavic's, that max angle forward or backwards, is determined by software. It's also not the case that you can continue to tilt the Mavic over to be vertical to fly into the headwind, as you are then presenting a larger surface area to the wind, and there is a maximum rpm that the motors can turn the props at which means that past a certain speed, the prop's won't push any more air, and in fact, become a barrier to the air. DJI would have determined this spec' in a wind-tunnel and found the angle at which each Mavic model gets the optimum penetration which will determine its max airspeed. There will be a graph of this around somewhere which will look like a curve mapping tilt angle to airspeed (at a constant max rpm) - that will peak at an ideal tilt angle and then drop off as the Mavic over-tilts and becomes a parachute!

I'm happy to be proved wrong, but I still believe that the standard Mavic Mini, and the Japanese Mavic mini - will demonstrate similar top speeds. Mainly because of the software setting to limit the tilt to fly forward. If it's using the same motors and prop's, and the cross-sectional area presented to the wind is the same, then it's difficult to see how it could fly faster. Again, I suggest that it would accelerate to its top speed faster than the standard model - but the same limitations apply when it gets there ... In fact, thinking about what I've said above ... If you agree that forward flight of a Mavic is a balance between gravity pulling it down and the 4-prop's pushing it up and forward, then since the weight/mass is lower with the Japanese MM, then you could be right to assume that model as actually not capable of the same forward top-speed as the standard model? It would be interesting to see an S-Mode drag race between the two ...

FPV racing drones are the extreme example of this, as they are light-weight and have powerful motors that have a very high rpm - so they can literally turn 90 degrees up/down/sideways and push themselves through the air. If you can increase the rpm of the motors that the Mavic Mini has, and override the software that determines the forward tilt. That would get you a faster drone, but it would not help in gusty winds as the MM's mass would still be too light. A typical FPV racing drone starts around 300g before you add the battery and prop's.

I take it, then, that you agree that to hold position or to move upwind relative to the ground, a drone must generate as much or more thrust than the force the wind is exerting on it. I also take it that you are nonetheless continuing to insist that it's the Mini's smaller inertia (rather than its smaller motors) that somehow or another makes the Mini less capable of doing that than the Pro. I don't need to change your mind, so unless you can give me a logical reason to change mine, let's just leave it at that.

 

[FoxhallGH]

I take it, then, that you agree that to hold position or to move upwind relative to the ground, a drone must generate as much or more thrust than the force the wind is exerting on it. I also take it that you are nonetheless continuing to insist that it's the Mini's smaller inertia (rather than its smaller motors) that somehow or another makes the Mini less capable of doing that than the Pro. I don't need to change your mind, so unless you can give me a logical reason to change mine, let's just leave it at that.

OK - Thanks for the discussion. I've already said that I agree with your first point. And also written a lot about the smaller motors and props on the Mini. And it's the Mini's lower 'Mass' that's behind my point. Inertia comes from Mass. This debate has rather changed in that your original point I responded to and wanted to debate, was regarding the weight of the Mavic and how sitting it on a table wasn't the same as flying it (see post #48), so I'm a bit lost as to where you are going with this anyway ... Fly safe and have fun RogerDH ...

 

[RogerDH]

OK - Thanks for the discussion. I've already said that I agree with your first point. And also written a lot about the smaller motors and props on the Mini. And it's the Mini's lower 'Mass' that's behind my point. Inertia comes from Mass. This debate has rather changed in that your original point I responded to and wanted to debate, was regarding the weight of the Mavic and how sitting it on a table wasn't the same as flying it (see post #48), so I'm a bit lost as to where you are going with this anyway ... Fly safe and have fun RogerDH ...

Well, I can address your feeling of being lost, anyway, before dropping it. I'm pretty sure I've consistently used the terms "mass" and "weight" correctly in context -- mass when talking about inertia and weight when talking about lift and friction -- so I'm not sure why you keep implying that I don't understand the distinction. You are the one who introduced inertial mass with your F=ma argument, but you haven't actually explained why greater inertial mass enhances a drone's ability to generate thrust against the drag. You seem to accept my own answers to my two questions, yet continue to argue about inertial mass because of its influence on reactions to variable wind forces. In all posts, my point has been that fighting the wind is ultimately a contest between thrust and drag, so thinking that lighter drones are more vulnerable to wind because they are lighter is specious. It's because they are less powerful.

 

[FoxhallGH]

Well, I can address your feeling of being lost, anyway, before dropping it. I'm pretty sure I've consistently used the terms "mass" and "weight" correctly in context -- mass when talking about inertia and weight when talking about lift and friction -- so I'm not sure why you keep implying that I don't understand the distinction. You are the one who introduced inertial mass with your F=ma argument, but you haven't actually explained why greater inertial mass enhances a drone's ability to generate thrust against the drag. You seem to accept my own answers to my two questions, yet continue to argue about inertial mass because of its influence on reactions to variable wind forces. In all posts, my point has been that fighting the wind is ultimately a contest between thrust and drag, so thinking that lighter drones are more vulnerable to wind because they are lighter is specious. It's because they are less powerful.

OK - focussing on just the point you are making above. The Mavic has no propellor to pull or push itself forward through the air. Therefore, it has to use its four lifting prop's and align its fuselage nose-down to get forward movement. My point is that the forward motion is a vector-addition of the Mavic 'falling' under the influence of Gravity, and 'rising' under the influence of the four motors/props. The rate at which the Mavic 'falls' is going to be determined by its Mass/weight. The heavier the Mavic, the faster it accelerates - with the forward horizontal vector being stable when the upward thrust of the motors/prop's matches the acceleration due to gravity. I'm reminded that the late Douglas Adams wrote that "the art of flying is simply to throw yourself at the earth and miss!".
So the heavier the Mavic, the faster it can 'fall' - but the motors need to be powerful enough to arrest that fall. This is another factor that the drone designer will build into the software algorithm to ensure that the Mavic can't go past a certain tilt-angle in forward flight. If it did, it would not be able to pull itself up enough to maintain horizontal flight.

I think we all agree that lighter drones are more vulnerable to wind - but what I have been trying to do (without success I'm sorry), is to explain why that's the case when you compare what happens with a heavier drone ... I believe that until we can find out what actual 'power' rating and/or 'thrust' the motors have on a Mavic Mini, and same for a Mavic 2 Pro - so we can produce a power-to-weight ratio - we can't really appreciate the 'power' difference. The Take-off-Weight of the M2P is 3.6x that of the Mavic Mini - but I doubt that the M2P motors are providing 3.6 times more thrust than the MM motors??? If weight didn't influence the drone's forward speed, then you'd expect that if the power/weight ratio of the two types of drone were similar, you'd see similar top-speed and wind penetration spec's.

This guy did a test where he found that the Mavic [1] Pro could lift a little over 2lbs of dead-weight (2lb 8oz was too much) ... 2.1lbs = 910g. The Mavic Pro has a ToW of 1.62 lbs (734g). The combined weight that could still lift off in this experiment would be around 1.644 Kg. Therefore, that means that each Mavic Pro motor/prop-set is capable of giving 411g of thrust, and the power to weight ratio of the Mavic Pro would be 1644/734 = 2.24 to 1 ... It would be interesting to get these same experimental results done for the Mini and the M2P ...

Can the Mavic Mini lift a weight of 560g??? If so, then the P/W ratio would be the same as the Mavic Pro ...