Angle of Attack and Sideslip angle estimation from ArduIMU V2+ and GPS data

Hi, I'm wondering if there's a way to obtain AoA and sideslip angle information from GPS speed data? There is vertical speed and 3d speed so this would probably be able to give me an estimate of the angle of attack, but for sideslip, I would have to have the y-component of the speed. Is there a way to get this from GPS or the IMU unit?

I have also tried it for one whole day but am at a loss of how to get the information to be passed from ArduIMU V2+ to ArduPilot so that I can use XBee to transmit it wirelessly to my GCS. Any clues from any good samaritans out there?

Otherwise, I think I am left with integrating acceleration information from the IMU which will probably be susceptible to a lot of errors, and also since it depends on the 'initial conditions' the errors will accumulate continuously.. :( Any ideas on whether this is a feasible option at all?

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Comment by Hamish on November 29, 2010 at 3:59am
y = v*sin(theta)

y=sidespeed
v=actual speed
theta=angle between actual velocity and direction the plane is pointing

Is what I would do for sideslip. And for AoA I would make myself a little vane connected to a pot, and stick it on the side of my plane. then read the pot value for a brilliantly accurate AoA.

Developer
Comment by Doug Weibel on November 29, 2010 at 8:06am
Unless you are using a magnetometer ArduIMU uses gps ground course to correct for gyro drift in the yaw axis, so there is no way to get an instantaneous estimate of sideslip. Any sideslip is incorporated into the gyro drift correction such that the IMU's output gives you an estimate of ground course and not actual heading.
Comment by Jimbo1981 on November 29, 2010 at 10:29am
Hey Joseph,
I think you mean the flight path angle, because the angle of attack is the angle between the airflow and the wing cord. you can not get that from gps data. the flight path angle is always less, but this you can get from gps.
And side slip is is not easy either! should read up wiki or something like that, because both these info's have nothing to do with gps data. GPS is not the instrument that is used in basic flying. It's extra info for position of the aircraft only
Greet
Comment by Joseph Lum on November 29, 2010 at 7:30pm
Hmm, looks like I have to get a pot for these two readings.. If I'm using ArduPilot, how can I connect the potentiometer signals to my ArduPilot? There are R/C inputs and also servo outputs for the aircraft controls.. Can I use empty channels from these? Or do I have to use another microcontroller? The reason is that I need to synchronize the potentiometer readings to the same timer that I control the aircraft flaps so that I am able to get the dynamics of the aircraft..
Comment by Michael Zaffuto on November 29, 2010 at 7:53pm
An AoA sensor was previously discussed briefly and resulted in this link to Charles River's Albatross

This is his schematic: http://www.charlesriverrc.org/articles/asfwpp/lelke_alb1electronics...
This is his AoA Sensor: http://www.charlesriverrc.org/articles/asfwpp/lelke_launch.htm

Pressing "Back" and "Next" on his site will reveal additional info.

His AoA sensor is a low friction vane with magnets exciting a HoneyWell 91SS12 Hall Effect sensor
providing an analog output voltage to represent angle of attack.
Comment by Joseph Lum on November 29, 2010 at 9:59pm
Hi Hamish, Doug, Jimbo, Michael, thanks all for the help rendered!! I'll take a look at the available sensors for angle of attack and sideslip and try to wire them into my ArduPilot board.. Thanks again!

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