Hello folks,

I noticed that when I fly the inspire in forward flight and use the rudder stick to turn (yaw) while flying forward, I slowly but surely lose altitude. Big sweeping turns will lose 20m or more sometimes. Is this normal? It doesn't drop like a rock, just steadily drops while turning. In contrast, I don't change altitude really at all when using right stick to roll during the same forward flight.
This is all in "position" mode on the radio BTW.

Thoughts? Thanks!

IMU calibration?

Mowog2 Posted at 2015-5-8 15:57
Simple aerodynamics a turn will increase drag to compensate you need to increase power.

Actually you shouldn,t need to do this with the I1 ... as it should compensate for this and try to maintain its alt.

I keep "pushing the left stick" when I am turning any ways because I am so used to do this ...
However ... My I1 is drifting up and down randomly from time to time even when it is just hovering.
Even so ... It is way more stable then anything I have ever flown before so I can´t really complain.

It would be normal in ATTI mode but in GPS mode, the bird should compensate. I have flown other non-GPS craft and it is normal to lose altitude in turns or even just going fast either forward or reverse not so much because drag changes, but because the thrust of the blades is not perpendicular to the earth when the craft is tilted. The downward force can be estimated knowing the approximate angle (ø)  the blades  are from perpendicular. y= cos (ø) give the fraction of downward force generated at any angle. Roughly, at an angle of 45º, you get only 70% of the downward force you had when level (0º) so you would have to increase power or the craft will descend( it will also be moving pretty fast in the horizontal direction of the tilt). And while the forces involved in propeller-driven systems are quite a bit more complex than this, it serves to provide a basic understanding of the physics. In this instance, if your INSPIRE drops in turns or rapid horizontal flight, you are not getting GPS/Barometric Altimeter compensation. This is abnormal and the bird may need service (unless you are unknowingly in ATTI mode)

My other thought in addition to the above: was there significant WIND at the Inspire's altitude?  Mine has behaved as you describe when there is a strong crosswind and trying to execute the turn requires more compensation than the bird can manage.  Sometimes even if there is very little wind on the ground things can be very different a couple hundred feet up.

If it's not that and continues after an IMU recalibration then it may need to be seen.

Thanks guys I really appreciate the time taken for the thoughtful replies. As a little background: I fly large electric helicopters competitively (sponsored pilot) and am very used to flight characteristics that I would deem "normal" in non-gps capable machines like the need to increase pitch or lift as the attitude of the airframe angles to the earth, so I am able to "fly through" this simply by increasing power to the props as I turn but 2 things bug me about it. 1- It is not really precise 2- I thought that in GPS mode the machine would input the necessary control changes to compensate for the altitude loss.

I really appreciate the perspectives and advice, based on that; here is what I'll do next:

1- IMU calibration. I will do this today. Being completely honest here, I all of the sudden feel like a dork. I haver never done this I just realized. I have calibrated the compass before flight but not the IMU when I received the machine. This could be the source of my trouble for sure.
2- Will also try the maneuver in less windy conditions, it was gusting to about 12mph on the ground when I noticed the problem. And it could have been much stronger at the 30m I was flying at.
3- Problem persists: I'll have it serviced (hopefully doesn't come to that :-)

Thank you,
-Adam

jedijawa Posted at 2015-5-8 22:50
IMU calibration. I will do this today.

When you calibrate the IMU, make sure the Inspire is on a true level surface.  You can download a bubble level to your iPad to check, if you don't have an actual carpenter's level.

PeteGould Posted at 2015-5-9 00:00
When you calibrate the IMU, make sure the Inspire is on a true level surface.  You can download a b ...

I would get an actual spirit level if you want to be absolutely sure. The bubble level apps for Android have the ability to calibrate the app which would lead one to believe that the internal sensors aren't always necessarily spot on. I would guess the same is true for i-devices.

So unless your app is properly calibrated you may not get a true reading from it.

I don't know how accurate the altimeter is in gps mode, no drop during right or left turns.  Full IMU calibration on a level surface.  Check your sensor values on a level surface.

PeteGould Posted at 2015-5-9 00:00
When you calibrate the IMU, make sure the Inspire is on a true level surface.  You can download a b ...

I did my IMU calibration on the table in my living room ... I think it is quite flat ...

w1der Posted at 2015-5-10 03:02
I did my IMU calibration on the table in my living room ... I think it is quite flat ...

lol, same here.  bubble level app, pft, haha!  Id not trust that to be very accurate anyway, whens the last time you calibrated your tablets IMU sensors?

sultangris01@gm Posted at 2015-5-10 03:06
lol, same here.  bubble level app, pft, haha!  Id not trust that to be very accurate anyway, whens  ...

Actually I compared my iPad's bubble level app with a true spirit level and was astonished by how accurate it was.

roy@netraction. Posted at 2015-5-9 07:22
I would get an actual spirit level if you want to be absolutely sure. The bubble level apps for And ...

I wonder if Apple is more accurate than Android or if I just happened to be lucky.  The level in my iPad is absolutely dead-on accurate when measured against a spirit level.

PeteGould Posted at 2015-5-10 03:39
I wonder if Apple is more accurate than Android or if I just happened to be lucky.  The level in m ...

amazing, never used one honestly but i would think it would be subject to the same IMU calibration needs as the inspires sensors, if not moreso for getting tossed and bumped around constantly.  I would doubt its more accurate unless using a cheap android, the high end androids are technically superior to apple.  samsung sells them all their second rate parts and keeps the good stuff for their own products.  Their second rate parts are still much better than the crap they put in the cheaper android devices though, lol,