When I calibrate my TH compass, should I be pointing the nose of it to true north or magnetic north as I spin the axes? Does it matter?
True North or Magnetic North?
- Thread starter moodman
- Start date
Magnetic North for the compass and True North when calibrating the accelerometers. Reference pages 44 and 45 in this manual.
Edit: one thing not mentioned in the static (stationary) accelerometer calibration is to have as close to perfectly level surface to set the TH on as possible. Most smart phones have a bubble level app built in that works well for this purpose.
The other is the debate on the use of the dynamic (in flight) accelerometer calibration. One condition that negates its feasibility is that it is to be done in a no wind condition. A luxury few of us ever see. Most long time experienced pilots only use the static calibration.
Edit: one thing not mentioned in the static (stationary) accelerometer calibration is to have as close to perfectly level surface to set the TH on as possible. Most smart phones have a bubble level app built in that works well for this purpose.
The other is the debate on the use of the dynamic (in flight) accelerometer calibration. One condition that negates its feasibility is that it is to be done in a no wind condition. A luxury few of us ever see. Most long time experienced pilots only use the static calibration.
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Now that is something... I don't remember ever seeing anything about orientation when doing the accelerometer, just keeping it perfectly level. I find it strangely gratifying to still be learning about an AC I no longer own.
Just follow the Compass needle....! It only
tells where "North" is...
I am surprised that the accelerometer needs any orientation at all. In fact, if there is some link between it and the compass, then I would think they need to be in sync as to what they use as a reference direction. But if the accelerometer and compass use two different standards for their calibration, then wouldn't they get confused? I am reminded of a joint Mars mission between NASA and Europe. It crashed when it got to Mars because NASA used imperial measurements and Europe used metric. The margin of error was small, but it was significant when carried out to many decimal places over a long distance.
So, anyone care to explain why true north is even an issue with the accelerometer?
As for the compass, magnetic north makes sense, but only because every place on earth has a different magnetic north. I have been told that if you move very far from where you last did your calibration, you should do it again, since the magnetic north bearing will change.
But that brings me to yet another question. Why is the compass orientation even important? After all, AFAIK, there isn't anything critical going on that requires a precise bearing in typical flying. For example, if you do a RTH, the bird only knows where it used to be in relation to where it is now. So it will fly back relative to its current position. So, if initially north was calibrated as west, everything would still be magnetically relative to how the compass was calibrated and it wouldn't get lost.
So, anyone care to explain why true north is even an issue with the accelerometer?
As for the compass, magnetic north makes sense, but only because every place on earth has a different magnetic north. I have been told that if you move very far from where you last did your calibration, you should do it again, since the magnetic north bearing will change.
But that brings me to yet another question. Why is the compass orientation even important? After all, AFAIK, there isn't anything critical going on that requires a precise bearing in typical flying. For example, if you do a RTH, the bird only knows where it used to be in relation to where it is now. So it will fly back relative to its current position. So, if initially north was calibrated as west, everything would still be magnetically relative to how the compass was calibrated and it wouldn't get lost.
Moodman!
You wrote: "As for the compass, magnetic north makes sense, but only because every place on earth has a different magnetic north. I have been told that if you move very far from where you last did your calibration, you should do it again, since the magnetic north bearing will change"
You are wrong, very wrong! Pls don't misslead forum readers. The magnetic north is where it is seen from all over the world, wherever you are! It's the magnectic field that differs from place to place and most significant east-west-east. Pls get it right. And RTH depends on GPS coordinates not magnetic north or magnetic fields!
You wrote: "As for the compass, magnetic north makes sense, but only because every place on earth has a different magnetic north. I have been told that if you move very far from where you last did your calibration, you should do it again, since the magnetic north bearing will change"
You are wrong, very wrong! Pls don't misslead forum readers. The magnetic north is where it is seen from all over the world, wherever you are! It's the magnectic field that differs from place to place and most significant east-west-east. Pls get it right. And RTH depends on GPS coordinates not magnetic north or magnetic fields!
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Wasn't intending to mislead anyone. I was speaking from the point of view of the person on earth. Of course, the magnetic pole isn't different (although it does move). But relative to you, wherever you are, it is different. For instance, where I am, the variation (or deviation, depending on your nomenclature) from true north is 8 degrees west. If I drive an hour east, it is 9 degrees.
Technically you are right. But I think most people aren't nitpicking. So, just to be clear, technically PHOTO IS RIGHT!
Technically you are right. But I think most people aren't nitpicking. So, just to be clear, technically PHOTO IS RIGHT!
FlushVision
Premium Pilot
When calibrating my compass I'm not so fussy. So long as my aircraft is pointing in the general direction of North all is well.
I was wondering about the significance of facing true north with the accelerometer also? I can only hypothesize it has to do with being perpendicular to the motion of the earth as it rotates?
Still though, that even seems like a stretch since we and everything else on the earth are sharing the same basic motion of rotation while being relatively stationary.
Still scratching my head on that one.
Still though, that even seems like a stretch since we and everything else on the earth are sharing the same basic motion of rotation while being relatively stationary.
Still scratching my head on that one.
PatR
Premium Pilot
Magnetic declination is the same for everyone that is within a the same declination zone. Declination is what is used to establish true north offsets from magnetic north. It has no bearing on establishing magnetic north. Everyone using a wet compass will see the needle pointing roughly at magnetic north.
Multirotor compasses reference magnetic north, just as the whisky compass in airplanes do. Multirotor makers don’t “swing the compass” to determine variations in accuracy in order to provide offset values as compass accuracy is not a mandated certification requirement as it is with manned aviation products.
Multirotor compasses reference magnetic north, just as the whisky compass in airplanes do. Multirotor makers don’t “swing the compass” to determine variations in accuracy in order to provide offset values as compass accuracy is not a mandated certification requirement as it is with manned aviation products.
PatR
Premium Pilot
As you should be. The accelerometers don’t care which direction the aircraft is facing during calibration, as long as the aircraft is resting right side up and relatively level. They sense forces associated with pitch, roll, yaw, and gravity. Magnetic orientation is not relevant to those.
As we don’t want the secret to get out we won’t mention the H calibrates the accelerometers during every boot up process. That’s why it’s so important not to move the aircraft after power up until the boot up is complete. Imagine needing to have the aircraft facing north for every power up[emoji6]
A few years ago I remember reading on this forum, and I don't recall the member's name, how he always pointed his aircraft to the north when first booting it up...I have been doing this faithfully ever since...is it helping...I don't know...is it hurting...I don't know...one thing I do know...I have never had a compass issue...maybe it is just luck
PatR
Premium Pilot
Phaedrus
Premium Pilot
