Blueteeth said:Why do you need a reference? From your first post I was under the impression you needed to know whether the plane was at a constant velocity or not...which is relative, not absolute (which would need an external reference). You didn't mention you needed to measure the velocity.
With an accelerometer, you're looking for 'lack' of acceleration, on any axis. Look at the datasheet for one for an explaination of its operation...think about it, does your 'wii remote' use a reference?...
Blueteeth
dknguyen said:Hi. I was wondering how you determine whether or not you are at constant velocity in an airfact. THe IMU I'm getting comes with accelerometers which I never really planned a use for, but they're there so might as well use them how I can. I was thinking about using them to measure the inclination for the compass whenever the plane is at constant velocity but I am not sure how to determine that.
THe only way I could think of was the measring airspeed with the pitot tube but this is dependent on whether the wind is changing or not since if the wind is slowing down as fast as your plane is speed up you still measure zero speed when you are actually accelerating. Do you just assume the wind is essentially at constant speed (or changing slowly enough to assume that?) Or does it just fall apart?
Let's also ignore the case of the wind accelerating in an axis where the pitot tube doesn't measure airspeed for now...
Yah we all know thatHero999 said:It's a known fact that you can't get the speed of a moving body without referencing it to something else. Whether it be a GPS satellite, the earth (using an accelerometer) or wind speed.
No memtion of finding out what the velocity is.Hi. I was wondering how you determine whether or not you are at constant velocity in an airfact.
jpanhalt said:It is not clear to me what your question is. Are you trying to maintain constant velocity of an aircraft relative to the ground? That is very difficult to do even with a pilot on board and lots of equipment. In fact, in strong up-drafts and down-drafts from storms, it may be both impossible from the standpoint of aircraft performance and dangerous from the standpoint of aircraft design strength.
One usually tries to fly at constant speed relative to the relative wind, i.e., indicated airspeed. Thus, with an up-draft, you can let the airplane rise, which makes passengers and air traffic control nervous, or keep the nose down and reduce power to maintain a constant indicated airspeed. In reality, the pilot does a little of both.
As for ground speed, GPS is probably the most common today. DME, which is a ground-based older system with some similarities to GPS, and Loran (most stations over land have been deactivated now with GPS) have also been used. Celestial navigation can be used, but is pretty uncommon today. The big aircraft also use inertial systems. Last but not least, there is the method of pilotage or dead reckoning, a lost art. John
The reference will be the ground below.dknguyen said:...Worded another way...
I was told by the manufacturer of tilt-compensated compasses that the readings aboard an aircraft will be valid (ie. the inclinometer will be valid) if the aircraft is under conditions of no acceleration. Okay. No acceleration- but I can't figure out if that's no acceleration with respect to the ground, or the surrounding air.
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