newest backup for gyro failure in IMC

[Dave J]

For photography dorks only....

Nikon D3 SLR camera:

http://www.dpreview.com/previews/nikond3/page8.asp
(scroll down to see Virtual Horizon)

It may be time for you Canon users to go Nikon.
After all, can your 1D Mark III save your bacon in hard IMC?


Not yet available at Sporty's.

-- dave j

[Ron Garret]

In article
>,
Dave J > wrote:

> For photography dorks only....
>
> Nikon D3 SLR camera:
>
> http://www.dpreview.com/previews/nikond3/page8.asp
> (scroll down to see Virtual Horizon)
>
> It may be time for you Canon users to go Nikon.
> After all, can your 1D Mark III save your bacon in hard IMC?
>
>
> Not yet available at Sporty's.
>
> -- dave j

It is most unfortunate that they chose an aviation-style display because
this feature is almost certainly implemented with an accelerometer, not
a gyro, so it will not work in an airplane. It will be fooled in
exactly the same way that the human inner-ear is fooled, which is the
reason you need a gyro-based AI (or TC) in the first place. If you try
to use this as a backup AI in IMC you will almost certainly die.

rg

[Todd W. Deckard]

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

This is how the AHRS units in a Garmin G1000 work for example. They
integrate accelerations and moments
using small very accurate mechanical sensors. There is no "spinning"
platform which uses rigidity in space to
provide a reference on these airplanes, except for the backup AI.

The reason your brain is fooled is becuase it uses a fluid pool to sense the
vertical. In the case of an acceleration
the fluid shifts and you mis-interpret this as a change in attitude.

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. Maybe
the camera is proof we would be close.

Regards
Todd

"Ron Garret" > wrote in message
...
>
> It is most unfortunate that they chose an aviation-style display because
> this feature is almost certainly implemented with an accelerometer, not
> a gyro, so it will not work in an airplane. It will be fooled in
> exactly the same way that the human inner-ear is fooled, which is the
> reason you need a gyro-based AI (or TC) in the first place. If you try
> to use this as a backup AI in IMC you will almost certainly die.
>
> rg

[Ron Garret]

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

[Dave J]

> 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.

Yes, I don't think we have any idea how this camera works, but it's a
fair bet that it won't work very well in an aircraft. We'll have to
wait for a pilot to buy one and try it out.

My understanding of gyros, be they mechanical or otherwise, was that
they can indeed work simply by measuring and integrating acceleration.
However, that needs to be angular acceleration, not linear. It was
also my understanding that the solid state accelerometers in GA glass
cockpits are in reality not very good on their own. The attitude
solution displayed is actually computed from the integrated
accelerometer values corrected with magnetometer info, air data info,
and even gps data.

-- dave j

[Todd W. Deckard]

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

[Ron Garret]

In article >,
"Todd W. Deckard" > wrote:

> It *is* interesting to me that consumer electronics provide this capability.

I dunno. Single accelerometers with no integration logic are pretty
cheap. Macbooks have had them for some time now. They are used to park
the hard drive head if you drop the machine. There's also a dashboard
widget you can install that displays the accelerometer reading as a
bubble level, which is kinda cool, and much more appropriate IMO than an
aviation-style display.

http://www.apple.com/downloads/dashboard/calculate_convert/carpentersleve
l.html in case you're interested.


> 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.

Yes. I already noted that such devices are already on the market:

http://www.icarusinstruments.com/microEFIS.html

It costs about $1500 (which, interestingly, is about the same as a
middle-of-the-line Macbook).

> 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 actually tried this a while back in a 182 and a handheld GPS. It
works actually much better than a single accelerometer (which is pretty
much guaranteed to kill you). If you are very, very careful you can
keep the plane kinda sorta level for quite a while. But it's mentally
exhausting, and I certainly would not want to rely on it in IMC.

rg

[Ron Garret]

In article
>,
Dave J > wrote:

> > 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.
>
> Yes, I don't think we have any idea how this camera works, but it's a
> fair bet that it won't work very well in an aircraft. We'll have to
> wait for a pilot to buy one and try it out.
>
> My understanding of gyros, be they mechanical or otherwise, was that
> they can indeed work simply by measuring and integrating acceleration.
> However, that needs to be angular acceleration, not linear. It was
> also my understanding that the solid state accelerometers in GA glass
> cockpits are in reality not very good on their own. The attitude
> solution displayed is actually computed from the integrated
> accelerometer values corrected with magnetometer info, air data info,
> and even gps data.
>
> -- dave j

Yes, I believe that is exactly right. And it is all that complexity
that makes them expensive.

rg

[Dave J]

> 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?

This, however, is something that is easy enough to try, and indeed, I
have done so. (under the hood, with a safety pilot). My unit, a Garmin
196, does not include any attitude information, but it does provide:

"airspeed" -- actually, groundspeed
"heading" -- actually, track (but hey, once you've gone track, you
don't go back)
"altitude" -- GPS derived, but with WAAS, not too bad when I
tried it
turn and bank -- based on rate of turn, see heading above.

My experience is partial panel with this was just as easy, if not
easier to fly than with the same panel of real instruments. Starting
in controlled, stable flight, I was able to perform all maneuvers
necessary for instrument flight (climbs, descents, turns) without any
trouble. It was no more fatiguing than normal partial panel.

Starting from a spin or something, I have my doubts.


-- dave j


> 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.