Sea Parrot
 lvl.3
Flight distance : 89154 ft
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Yet again I've read a thread that turned into a fight when posters fight about elevator, aileron and rudder on their Mavic Air....
A Mavic Air doesn't have aileron, elevator or rudder. Those aren't what an aircraft does; they are control surfaces on a fixed-wing aeroplane.
http://www.flyingfear.net/wp-con ... 1/planecontrols.jpg (And this image shows other control surfaces as well).
The threads I've read then degenerate into aileron on a helicopter, and how it isn't the same as aileron on a fixed-wing aircraft, and how that isn't the same as aileron on a quadcopter.
First - I know what I'm talking about. I first flew a real aircraft over 30 years ago. I've owned and maintained my own 2-seater aircraft; I've flown 4-seater aircraft aircraft; I passed my pilot's exams with an overall score of over 95%; on the aircraft(technical) paper I scored 100%. I've also flown real helicopters and have flown RC helicopters (TREX 450 and TREX 500) for 8 years. I've been involved in aviation for a looong time; I've had meaningful conversations about the technical side of piloting aircraft with some well-known test pilots and I learnt a LOT from them. Although I'm not a professional aviator I have been involved in professional aviation for almost 20 years and know the importance of getting terminology absolutely correct. It can be a life-and-death matter (although in this case it isn't).
So - the Mavic Air and it's controls. It's a fully fly-by-wire aircraft. There is no direct link between the sticks and propeller RPM/aileron/elevator/etc. The sticks command the aircraft to give a specific performance; the aircraft is 100% responsible for deciding what RPMs to apply to the motors to provide that performance.
I'll discuss both controller sticks and what they really do. I'm going to assume mode 2 (left stick is up/down, and yaw left/right, right stick is move forward/back and move left/right).
What does the left stick do when moved forward or back? It commands no more and no less than a rate of change of height, apart from two specific cases. Left alone, the aircraft maintains height. Stick moved towards the pilot, it commands a rate of descent proportional (in some way) to it's position. Same for moving away from the pilot. The two specific cases are when the aircraft reaches the maximum height it's allowed to go, in which case it won't increase height. Similarly close to the ground, it will stop the aircraft from descending once it's about 3' from the ground. There is then the "override", if the stick is held back, to make the aircraft land.
Simple - and we all think we know this. But actually we don't - many (most?) pilots think it directly controls the propeller RPM. But it doesn't directly controll the propeller RPM. It indirectly control the RPM. The aircraft will decide what propeller RPM to use to provide the result that the pilot is commanding.
That is a subtle difference and should be thought about. For example - if the aircraft is in an updraft (perhaps a thermal? It's a nice day....) and the left stick isn't being touched, then the aircraft will slightly reduce the propeller RPM so that the height doesn't change.
A more compilcated and interesting situation - "aileron"! Or at least that's what it gets called in the .DAT logs etc. and by some posters here and probably by DJI as well.
The Mavic Air does not have aileron. An aileron is a control surface on a fixed-wing aircraft.
So what do pilots mean by aileron? What does DJI mean by aileron?
When the right stick is moved left or right, the aircraft moves left or right. But the aircraft doesn't have an aileron! So what happens?
The right stick, moving left or right, is commanding the fly-by-wire aircraft to move left or right at a specific rate proportional to the stick position. No more, no less.
To do this the aircraft knows the stick position and knows it should move at some speed left or right. For sake of argument, right stick is moved fully left, commanding the aircraft to move to the left as fast as it can. Some folks call this "aileron"; that's wrong.
To move left from stationary the aircraft will tilt left (increase RPM on both right motors, decrease RPM on both left motors, so that the height doesn't change). The aircraft will then start to move to the left. Whilst the RPM left/right difference is happening, the aircraft will tilt more and more to the left. At some point it will be moving to the left at the rate commanded by the stick. At which point the aircraft will increase RPM on the left motors, decrease RPM on the right motors, such that it maintains the same tilt. Again - no aileron! It's all fly-by-wire and very bloody clever it is to.
Something similar happens with "move forwards", i.e. right stick forwards. In this case it's rear motors increase RPM, front motors decrease RPM, until the required tilt forward angle to provide the commanded speed is reached at which point the aircraft will reduce rear motor RPM, increase front motor RPM to maintain that angle.
It gets more interesting when flying in a gusty wind! If the aircraft is hovering, it knows that it should maintain position/height/heading. But what happens if the aircraft is commanded to fly into a headwind with full right stick forward? This is where the fly-by-wire and intelligence of the aircraft really work. It knows that it's being commanded (in P-mode) to fly at say 20 mph over the ground. But that might mean 40 mph airspeed if it's flying into a 20 mph headwind. So the aircraft will tilt rather more forward than it normally would to achieve 20 mph over the ground, and due to the tilt forward you might get the "forward sensors not working due to headwind" warning.
It's a bloody clever aircraft, but I wish, oh how i wish that DJI and the other pilots here would use the aeronautical terminology correctly.....
Oh - and what do the sticks in mode 2 actually command?
See https://en.wikipedia.org/wiki/Six_degrees_of_freedom
Using precise terminology, i.e. the six degrees of freedom, pitch/roll/yaw/surge/sway/heave :
The left stick moved forward and back controls rate of heave.
The left stick moved left and right controls rate of yaw.
The right stick moved forward and back controls rate of surge.
The right stick moved left and right controls rate of sway.
Of the six degrees of freedom; four of them are commanded by the sticks, i.e. heave, yaw, surge, sway. The two that aren't commanded, but are effectively side-effects of what is being commanded, are pitch and roll.
Edited to add: What about when the aircraft is moving fast forwards and "aileron"  i.e. right stick moved right is applied? In that case the aircraft knows it's commands are to fly as fast as it can forwards and right; the rotor RPMs will momentarily change to tilt the aircraft right-and-forwards to provided the commanded response.
I haven't discussed yaw; that's quite simple; it's a matter of differing RPM and thus torque between the motors that turn clockwise and those that turn anticlockwise. It can do this in such a way that the current aircraft attitude is maintained. (Note I said "attitude" not "altitude"; again please don't confuse these two similar sounding terms!)
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First Officer
lvl.4
Core User of DJI
lvl.1
i.e. right stick moved right is applied? In that case the aircraft knows it's commands are to fly as fast as it can forwards and right; the rotor RPMs will momentarily change to tilt the aircraft right-and-forwards to provided the commanded response.
