wing levelers

Ron Webb wrote:
How can you tell whether you are straight and level? If
you're in a balanced turn, your accelerometer (which actually measures net
force) will believe you are straight and level.

And a GPS won't help much at all, mostly because its response rate is too
slow.

Frank


As I see it, accelerometers and GPS together are all that's needed. If the
vectors from all 3 accelerometers are in the right direction, and the
average GPS heading is not moving much- you're straight and level.

My GPS updates about once per second. That's plenty fast enough.Once every
10 seconds would work.When flying, do you react to every bounce, or just
ride with the flow and provide general guidance? I don't know about you, but
I try to stay relaxed.

The GPS does too make the differance between a really sticky problem and a
slam dunk.
I'm betting your practical experience was before $50 GPS and $3
accelerometers? (say, 5 years ago). Am I right?

Nope... I finished on my MTech thesis the year before last, designing a
system to automatically measure ocean waves. I used the ADXL202
accelerometers you've mentioned here, plus 3 magnetometers to measure
attitude, plus some digital filtering and stuff. Ocean waves, being in
constant variable motion, is probably a tougher environment than an
aircraft. And, as someone else suggested, I guess that an aircraft
system could be designed as a pilot aid rather than pilot replacement.

Your GPS can't tell you whether you're straight and level, only whether
you're straight. Whilst we're talking GPS, some interesting work was
done using GPS to measure attitude using 3 antennas about a foot apart.
This sounded like it had real promise.

Maybe we have bumpier bumps here, or maybe you fly something with a high
wing loading, or whatever, but in the circumstances where an active wing
leveler would be useful, I think it would need to react accurately and
correctly within (say) 0.1 seconds to be useful. And would need to not
need to be reset more than (say) once in 20 minutes. I just can't see
that with a 1-second GPS update of position and track (not airspeed or
heading). If there's no bumps, then manual aileron trim will do the
trick just as well.

Frank

Your GPS can't tell you whether you're straight and level, only whether
you're straight.

Agreed.

But if the GPS says I'm straight (over a 10 second average) and the
accelerometer says the roll axis vector is pointed toward the floor of the
aircraft, then it seems to me I'm straight (otherwise the heading would be
changing) and level - since if there is no heading change the only vector
remaining is G.

-----BEGIN PGP SIGNED MESSAGE-----
Hash: SHA1

Ron,

Try adding in some cross controll input & acelerometer error Bzzzzt. The
deal is that over time, any acelerometer, even 3 axix will accumulate
error, and ignoring your idea of non-realtime GPS directional input for
the moment, what you need is a leaky integrator. To accomplish this, you
need to be able to sense the horizon in an accelerated frame of
reference. You can accomplish this in a number of ways. The two that
come readily to mind are magnetometers & solid state or otherwise steam
gage type gyros. Sadly, this last requirement for instrumentation is
often where the expense for your system will come in to play.

Evan Carew

Ron Webb wrote:
Your GPS can't tell you whether you're straight and level, only whether
you're straight.


Agreed.

But if the GPS says I'm straight (over a 10 second average) and the
accelerometer says the roll axis vector is pointed toward the floor of the
aircraft, then it seems to me I'm straight (otherwise the heading would be
changing) and level - since if there is no heading change the only vector
remaining is G.



-----BEGIN PGP SIGNATURE-----
Version: GnuPG v1.0.6 (GNU/Linux)
Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org

iD8DBQFCLdNmpxCQXwV2bJARAo9QAJ9IMxPQ/igwTJZ+enML69Su6SRd9QCfbHYp
VCxBa5Nc6LdrmsK+D3W6/Tc=
=JQDQ
-----END PGP SIGNATURE-----