AIR Glide S

On Friday, 23 October 2015 00:27:41 UTC+3, wrote:

bruce, i think you might be assuming the butterfly is merely doing dead reckoning, but what it's doing is more complex than that. it uses an extended kalman filter (EKF), which is a type of software algorithm that is good for estimating the state of something that cannot be directly measured (the motion of the glider, in this case). the EKF takes various data steams as input: accelerometer, gyroscope, static pressure, pitot pressure, magnetometer (compass), and time. what it outputs is an estimate of the motion of the glider.

now, if the EKF only had acceleration and time as inputs, it would need an extremely accurate accelerometer and clock, as you have surmised. acceleration is relative, so even small errors in acceleration will snowball over time into large errors when doing dead reckoning this way.

fortunately, the EKF has much more data to work with. since it also has access to measurements that are absolute (heading, altitude, airspeed), it can integrate all the data in a way that makes the accelerometer error much less significant. since acceleration is only one piece of the puzzle, it has less influence on the overall motion estimate, and therefore the drift you would expect with dead reckoning is diminished.

thanks to the power of the EKF, an extremely accurate IMU (accelerometer, gyro) is not necessary. i wouldn't be surprised if the butterfly has an IMU of similar quality as that of a smartphone.

Kalman (and EKF) is a process that you run into pretty much everywhere. It's quite elementary way of correct predicted state of something on basis of comparing previous predicted state to current observations. It doesn't do theh inertial navigation itself, it's just way of polishing things numerically. For example, if airspeed measurement is systematically too small, Kalman filter corrects that error (this is maybe too elementary example, reality is more complex for sure). I think important part of achieving this state of inertial navigation (without GPS) is by using measured TAS.

On Friday, October 23, 2015 at 12:57:08 AM UTC-7, krasw wrote:
Kalman (and EKF) is a process that you run into pretty much everywhere. It's quite elementary way of correct predicted state of something on basis of comparing previous predicted state to current observations. It doesn't do theh inertial navigation itself, it's just way of polishing things numerically. For example, if airspeed measurement is systematically too small, Kalman filter corrects that error (this is maybe too elementary example, reality is more complex for sure). I think important part of achieving this state of inertial navigation (without GPS) is by using measured TAS.

TAS (calculated, not measured) is probably the most important input to the algorithm, but navigation without GPS cannot be done without heading information as well. interestingly, accurate heading cannot be computed without at least a rough idea of where you are on the planet due to magnetic declination. so this system would not work as well (in most places) without an initial GPS fix. this purely academic though because any navigation system would be useless without at least knowing the starting point.

also interesting is that having a rough idea of where you are also improves the accuracy of the accelerometer because the force of gravity differs depending on where you are on the planet. remember that at rest, an accelerometer will always show roughly 9.8m/s^2 in the downward direction.

I would assume that the two most common mounting locations of the ISU would be forward of the instrument panel, or behind the pilot's seat. I'm leaning towards installing mine forward of the instrument panel, but the nearby radio concerns me. Behind the pilot's seat would be a less convenient installation, and its proximity to the speaker and the steel spar pin present interference issues as well.

Any installation advice from people with either setup?

Thanks!
Chris Fleming

Mine, in an ASW20, is mounted forward of the instrument panel on the
opposite side from the radio. I've had no interference issues. Love the
instrument.






At 09:01 05 July 2016, Fox Two wrote:
I would assume that the two most common mounting locations of the ISU
would=
be forward of the instrument panel, or behind the pilot's seat. I'm
leanin=
g towards installing mine forward of the instrument panel, but the nearby
r=
adio concerns me. Behind the pilot's seat would be a less convenient
instal=
lation, and its proximity to the speaker and the steel spar pin present
int=
erference issues as well.=20

Any installation advice from people with either setup?

Thanks!
Chris Fleming

It's not on the longitudinal axis (you installed it off-center)? Does that cause any roll issues on the artificial horizon?

On Tuesday, July 5, 2016 at 8:31:23 AM UTC-7, Fox Two wrote:
It's not on the longitudinal axis (you installed it off-center)? Does that cause any roll issues on the artificial horizon?

Mine is forward of the instrument panel, essentially over the right knee. Transponder and radio "guts" are not on that side. It appears to work fine there. Have not flown much IFR with it but appears the AHRS is fully functional.

A note that closing the canopy (if the instrument panel tilts with it) immediately after power up helps the Air S calibrate. Look for the three dots in the upper R of the AHRS display prior to launch. Without at least one (prefer two) dots, you won't get the sort of wind reporting the Air is famous for.

At the moment (could be fixed with software) if you're at a contest that demands disabling the AHRS the entire funtionality of the ISU is lost, seriously compromising the vario.
Had originally thought the AHRS screen would be the only loss.
I will send an e-mail to Air support about this.
Jim

If it does I haven't noticed but there again have done little IFR but have
flown with the horizon on without noting any issues.



At 15:31 05 July 2016, Fox Two wrote:
It's not on the longitudinal axis (you installed it off-center)? Does
that
cause any roll issues on the artificial horizon?

On Tuesday, July 5, 2016 at 2:01:15 AM UTC-7, Fox Two wrote:
I would assume that the two most common mounting locations of the ISU would be forward of the instrument panel, or behind the pilot's seat. I'm leaning towards installing mine forward of the instrument panel, but the nearby radio concerns me. Behind the pilot's seat would be a less convenient installation, and its proximity to the speaker and the steel spar pin present interference issues as well.

Any installation advice from people with either setup?

Thanks!
Chris Fleming

I mounted mine on CL forward of the instrument panel under the glare shield as far from anything else as I could. No problems due to mounting location..