Interesting EFIS Observation

[Rainier Lamers]

This system is similar to the new GPS based attitude you can select on our EFIS systems either as sole attitude or as reference for a real AHRS.
Taking advantage of the Swiss made u-Blox GPS receiver the EFIS has access to internals way beyond what is available on NMEA strings, including a very accurate 3D velocity vector.
This means you can create a reasonable AHRS display (very reasonable actually) that is not unlike the aiding information used with some high-end aided gyro based systems (except you ditch the gyros and look directly at the aiding information).
This system too, describes your path though the air and is not capable of showing pitch up near the stall. Of course - that could be faked but we decided to not after our many test flights. The reason for this is that it started making sense rather quickly. It's a case of the pilot understanding what he is seeing and then using it correctly.
In order to avoid infringing patents our system adds other sensor inputs as well and takes advantage of the fast operation of a modern GPS receiver.
As a cross-check to an existing gyro based AHRS it is great (and you don't need an expensive EFIS for this, our little sub-$1000 XTreme can do this as well).
The main reason it is great as a cross check is that it is based on completely different technology and neither suffers from the potential problems of the other.

Rainier
CEO MGL Avionics

Originally Posted by Alan Carroll

Yesterday I went out and tested how a static leak would affect the ADI, by opening the alternate static source I have installed (which vents to the cockpit). The sudden decrease in static pressure caused a pitch up, as Paul noted in the OP. However after about 10-12 seconds the pitch indication stabilized as the instrument adjusted to the new lower pressure. So, ultimately a static leak doesn't seem to pose a problem so long as it is a stable leak. What the ADI cares about it rate of change.

On the other hand I found I could rather easily "fake out" the ADI at speeds as high as 80 knots, by using a very low power setting. This results in nose-up attitude but a nose-down indication on the ADI (due to loss of altitude). The ADI continues to accurately indicate the actual flight path though. Like someone said earlier, you need to understand what this instrument is telling you.

[MikeS]

I've been using the TruTrak ADI with track as my primary attitude indicator for two+ years and lots of bad weather flying. I especially like its instantaneous response in both pitch and bank. Excellent instrument & love it for solid IFR work. If I had room on the panel I suppose another one just like it would be a good back-up, but there's not much to break or wear out with these things.

[Rainier Lamers]

Originally Posted by MikeS

I've been using the TruTrak ADI with track as my primary attitude indicator for two+ years and lots of bad weather flying. I especially like its instantaneous response in both pitch and bank. Excellent instrument & love it for solid IFR work. If I had room on the panel I suppose another one just like it would be a good back-up, but there's not much to break or wear out with these things.

Yes, quite right.
Systems like this have been getting bad publicity, usually from people that have not used them or don't quite understand them.
I was one of them, I am ashamed to say.
It's only after we started experimenting with alternative "pseudo attitude cum flight path" indications that I started realizing that these are just as valuable a pilot aid than anything else in the cockpit and, as usual, if you are a pilot trained in proper use of something like this, you will have zero problems interpreting what this instrument is telling you.
The only thing that needs to be clear is that you are not seeing the aircraft's attitude in the way a gyroscope based system would show but you are rather seeing where you are going using a graphic interpretation, quite regardless of where the aircraft is pointing (the two happen to coincide as long as you fly nicely, but only in this case).

The danger is that some may think that this kind of thing is an attitude indicator. Of course it is not. It's a flight path indicator. As an attitude indicator it is dangerous. Switch your mind so that you see it as flight path and immediately it becomes useful.

Rainier
CEO MGL Avionics

[Alan Carroll]

Originally Posted by Rainier Lamers

The danger is that some may think that this kind of thing is an attitude indicator. Of course it is not. It's a flight path indicator. As an attitude indicator it is dangerous. Switch your mind so that you see it as flight path and immediately it becomes useful.

Rainier - I would agree with this; the ADI tells you very accurately where you're going in 3D, but much less about attitude.

Regarding the Xtreme with GPS only (no AHRS), does it provide climb/descent information or just turn?

[breister]

That's good info Ranier, as always.

As these units mature, I believe we will start seeing messages informing us of the status of each of the inputs, as well as warnings when one or more inputs are, or are suspected of being, degraded. With multiple aiding inputs, a color "condition indicator" may be the simplest way to present overall condition, with a button / page / whatever to inform us of why the EFIS considers current information to be less than optimal when that occurs.

Having the system automatically compare flight parameters between systems could generate cautions and warnings which the pilot could later use to build a set of parameters for their specific aircraft. For example, if your aircraft AHARS attitude at 120 IAS is typically within 15 degrees of GPS flight path, a deviation to 20 degrees might generate a warning of unexpected divergence.

As the systems get more complex, the information to diagnose current status also becomes more complex - and the good old "OFF" flag simply isn't sufficient for determining whether or not an instrument is reliable.

[Rainier Lamers]

Originally Posted by Alan Carroll

Rainier - I would agree with this; the ADI tells you very accurately where you're going in 3D, but much less about attitude.

Regarding the Xtreme with GPS only (no AHRS), does it provide climb/descent information or just turn?

The full monty, so to speak - but it is not dependent on static pressure for this and can in fact operate just fine completely without pressure sensors.
Of course it needs a GPS lock but it differs from a normal GPS system in that it is able to track phase shifts of the received satellite signals relative to another and using a very fast correlator will iteratively work out how your position is changing in 3D space so you have a real 3D vector of very high resolution and is available to good accuracy very quickly after you have changed direction. Due to the tight coupling with the EFIS system it becomes possible to add the other sensor inputs as available to augment the information and derive a pretty convincing "picture" of what the aircraft is doing. The interface between EFIS and GPS has become blurred and in this case they are just two components of the same thing.

Rainier
CEO MGL Avionics

[MikeS]

When I'm in cloud and the ADI says I have a nose up attitude, I accept it as a nose up attitude and act just as I would when using vaccuum gyro instruments. I've not ever had to give the slightest thought to interpreting anything the ADI presents me with. The ADI blends perfectly with the other attitude instruments and actually has eliminated the DG from my scan except as a secondary reference.

> Systems like this have been getting bad publicity, usually from people that have not used them or don't quite understand them.

I've never read anything in any of the forums to make me think there is any bad publicity out there. On the contrary, TruTrak customers seem to be consistently enthusiastic about the products and actually rave about the customer service.

************

Later,

I see the concern is about behavior near the stall. Picturing that in a worst case scenario a plane could be gradually accumulating ice with an iced-up pitot and pilot was paying no attention to GPS speed and the canopy was iced up too - a little red light on the ADI comes on when nearing the stall that would get ones attention. I'm pretty good about not letting things get that far :-)