Hi folks,
I just installed an airspeed sensor on my new APM 2.5.. I have enabled it in mission planner and it seems to be workig well? But when I click on enable airspeed the horizon pitches up and down depending on the airspeed reading, so if I blow down the tube the artificial horizon pitches down and if in stabilize or another autopilot mode, the plane tries to compensate by raising the nose? Is this normal?
Replies
It is perfectly normal for the pitch to be slightly erratic without a GPS lock while using a airspeed sensor. You will probably notice that while the airplane is sitting still in zero wind the airspeed will jump around a few m/s. That is because it takes very little pressure difference to change a couple m/s while near zero. Once the aircraft is above 5-10 m/s it takes a larger change in pressure to increase/decrease the speed.
The reason why this affects your pitch before GPS lock is because it feeds into AHRS. I do not know all the technical terms but basically since there isn't a GPS lock it uses the airspeed to help in accelerometer/acceleration correction. I know there are people that understand the code better than I do that could explain it, I am more familiar with Piccolo. Bottom line is what you are seeing is normal and not a problem :)
I've experienced the same problem for some time now.
I have the same problem. When GPS fix is obtained the problem goes away, and when GPS fix is lost, then it appears again. If the GPS fix is lost for some reason during the flight, then the autopilot would try to stall the plane so that it would not fly far away?
Hi Dean.
You right, the airspeed should not affect pitch indication but your fault rang a bell with me. Im sure I had that when I first plugged it in and I have a vague memory it was some obscure parameter. Sorry cant be more accurate.
Have just checked it again and the horizon is not affected by blowing in but the elevator does react in auto modes (not stabilize).
On this subject, my pitot was pissing air out everywhere when I first got it so took it apart to have a look.
Here is my fix.
http://diydrones.com/forum/topics/pitot-tube-question
(on my sons I.D. – Leo Hogg).
Vince