Are any of you aware of an independent, stand-alone, self powered attitude back-up system?

I was looking at the Garmin 495.  Its panel page shows heading, bank angle, and vertical speed.  So I assume with a little concentration, that would allow a guy to approximate straight and level flight.  But there is no “attitude indicator.”

Is there something out there better than the 495?

John Hafen

On 6/4/08 4:50 AM, "Chuck Jensen" <cjensen@dts9000.com> wrote:

If I ever decide to fly in circles for a long time, I will be sure to buy a Chelton.

Chuck Jensen

-----Original Message-----
From: Lancair Mailing List  [mailto:lml@lancaironline.net]On Behalf Of Brent Regan
Sent:  Tuesday, June 03, 2008 7:32 PM
To:  lml@lancaironline.net
Subject: [LML] Re: Selecting an  EFIS

Rick writes:

"... some  EFIS systems (especially the inexpensive ones) derive their attitude depiction  data from GPS and pitot data. In other words, if you lose GPS or your pitot  (blockage, icing, etc.), your ATTITUDE depiction will become INACCURATE.  <snip> The most startling thing that I found out during my research is  that the FAA CERTIFIED, Chelton system does have the problem of inaccurate  attitude data with the lost of pitot input. Their manuals state that the  attitude indication can be off as much as 2.5 degrees when pitot data is not  available....>>>


2.5 degrees ??!!??!!  Horror of horrors!

Rick's post proves two things. One is that a little  knowledge is a dangerous thing. The other is that  if you start with a  conclusion you can find facts that "support" said conclusion.

Now for  some real facts and reason. Most mechanical AH gyroscopic instruments rely on  the gravity to determine which way is up. The influence of this "gravity  vector erection" is small compared to the forces that maintain the gyroscope  "rigid in space".  Imagine a pendulum hanging in a jar of honey.  If  you roll the jar, the pendulum will point in a  new direction for a while  but will, over time, return to pointing straight down. Likewise, if you roll  into a coordinated turn with a mechanical gyro AH and hold the turn for  several minutes the AH will eventually show level flight when you are still  turning. Your inner ear also has this property, but for different  reasons.

When your are in a turn the centripetal force vector and the  gravity force vector combine to create an apparent gravity vector, which is  not vertical (with respect to the earth).

Mechanical gyro AHs, and  apparently GRT, rely on the assumption that, on average, aircraft fly straight  and level.

Now suppose you were a cleaver guy and  you knew the  velocity of the aircraft and the rate of turn (degrees per second) you could  calculate the centripetal force vector and then subtract that from the  apparent gravity vector to get the actual gravity vector. You would know which  way is up regardless of how long you maintain the turn.  Chelton uses a  proprietary algorithm to do this very thing and delivers the resulting  superior performance.  The other benefit of this is that the Chelton  ADAHRS is the only low cost solid state AHRS that does not have a "kill  maneuver" that will cause significant attitude errors (e.g. low rate climbing  turn).

Will the Chelton attitude accuracy degrade with loss of air  data? Yes, but in it's degraded state it still has better performance that its  competitors over its entire operating range.  Rick's assertion that his  GRT AHRS is superior to the CFS ADAHRS because it does not have an air data  "problem" is like saying a car without wheels is superior to a car with wheels  because it does not have a potential  flat  tire "problem".

The bottom line is that the  Chelton  system has undergone extensive certification testing and has  proven its performance. All the other wannabes can claim to be "just as good  or better" but until they prove it  empirically  you should not take  the claims as fact.

Having spent the last 14 years designing, building  and flying cockpit flight information systems and having the experience of  having thousands of these systems deployed I can say that it is never a good  idea to fly actual IMC without mechanical backups and that most experimental  EFIS systems only work great when you don't need them, although many fail that  test as well.

Regards
Brent Regan