As I said Ron, it integrates accelerations and moments (probably should say
'or')

I believe it gets angular moments from a small mems device that deflects
under twist, however, opposing
accelerometers separated by a distance accomplish the same. I've never
looked at a schematic. The gizmo is a very small mass on some kind of
spring or lever (thus you have the force and the mass, so the deflection
gives you acceleration).

It does *not* use the principle of rigidity in space provided by a spinning
gyroscope in which conservation of angular momentum resists a change in its
spin axis.

No one is suggestion that you use a camera to provide a backup flight
instrument. The only purpose of my post
was to site the minor physics gaff. Its the old teacher's assistant in me I
guess. Someone else can chain onto this and tell me I am misusing the term
'moment'

It *is* interesting to me that consumer electronics provide this capability.
Between the camera, and the more expensive R/C helicopters which have a
stability augmentation system like a yaw damper (which uses an actual
spinning gyro)
this stuff is coming into reach of a cockpit mountable capability.

A bigger crime to be debated is the "psuedo" panel display afforded by some
of the handheld GPS units.
It derives bearing and attitude information from the apparant change in
flight path. I have heard folks speculate
that this could be used in instrument flight after failure of the AI/HI?
I might open up a thread to see how that debate unfolds. It would certainly
be more interesting than the essays on tort reform and having your mom sew
epaulets on your Sport's pilot shirt that are all the rage on the other
forums.

Regards
Todd



"Ron Garret" wrote in message
...
In article ,
"Todd W. Deckard" wrote:

Actually, Ron you can derive a very accurate attitude reference from only
accelerometer(s).

I doubt that very much. You need roll rate information from somewhere.
Do you have a reference?

In any case, even if you can do it with just accelerometers, you need
very good accelerometers and you need an integrator, neither of which
this camera is likely to have. It almost certainly has a single
accelerometer and no integrator. All it will tell you is the apparent
acceleration, not your actual attitude.

This is how the AHRS units in a Garmin G1000 work for example. They
integrate accelerations and moments
using small very accurate mechanical sensors.

Yes, but some of those sensors are gyros. They are solid-state gyros,
but they are gyros nonetheless. (The gyros may themselves be built out
of accelerometers as components, but one way or another you have to
sense rotation rate in order to build an AHRS.)

Now, I cannot vouch for using a camera as an inflight reference :^)
However, I have wondered if some sort of
"solid state" package (or something based on the small RC helicopter
gyros)
could be built that could provide
an attitude reference that you could even velcro to the glare shield.

Yes, such things exist (e.g.
http://www.icarusinstruments.com/microEFIS.html). But they are
expensive because they require multiple sensors and sophisticated
electronics to do the integration.

Maybe the camera is proof we would be close.

No, this is exactly my point. What this camera is doing is (almost
certainly -- I haven't actually looked at its technical specs) NOT the
same as an AHRS despite the fact that their behavior is superficially
similar, particularly when you are not in an airplane. That is exactly
why I think it's important to warn pilots away from trying to use this
device as a backup AI. It will almost certainly kill you.

rg