Which EFIS for IFR

[the_other_dougreeves]

Originally Posted by dav1111

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.

Interesting, but I'm not sure that I'd be worried about 2.5 deg of pitch if I lost the pitot.

TODR

[rpellicciotti]

It does appear that the information that was presented on the conference call that I attended about the Chelton system was inaccurate. I posted a correction on the GRT user groups list. It seems that this was a problem with the older/ experimental Chelton system and not their current offerings. I apologize for the confusion.

[Jamie]

Wow, did you know that in a certified, vaccum driven ship if you lose the vacuum pump you'll lose the attitude indicator AND the directional gyro?

Ok, all scarcasm aside...knowing the limitations of your EFIS system is the same as knowing the limitations of a vacuum-driven system in a store bought airplane.

Know your airplane's systems and failure modes...no matter what system you put in. There is nothing wrong with one system being dependent upon another as long as you realize that. Dynon's limitations are very well spelled out in the manuals. I'm sure the other vendors limitations are too.

[breister]

Hmmm, I know for a fact that the Dynon D-180 has an internal method of correction based on simple gravity (or more likely, "weighted average accelleration"), because if I start it up "tilted" and hold it steady during the initialization, it shows the correct attitude.

Yes, I know the cheapie AHRS systems are subject to some error over time if uncorrected, but I'll bet that unless you do inverted acrobatics in the weather with a blocked pitot tube it will still be accurate enough to navigate by.

Know your systems, and have redundant independent attitude indicators.

[the_other_dougreeves]

Originally Posted by Jamie

Know your airplane's systems and failure modes...no matter what system you put in. There is nothing wrong with one system being dependent upon another as long as you realize that.

Well said. Know how it fails and what it's going to do when it fails. Doesn't matter whether it's an alternator light or UAL232.

TODR

[grantcarruthers]

My only concern is how do you know WHEN it's lying to you, that's often the killer. A partial vacuum failure is 10 times harder to catch than a complete failure. If you follow the lying attitude just long enough you're really confused and heaeded for an upset. If it croaks and falls over dead you're still under control when you figure somethings up.

My real question is how big an error can it feed you. A 2 degree pitch error isn't going to kill you before you figure there's a problem. a slow 20 degree bank error could.

A 2.5 degree pitch error is a heck of a lot better than the lies the vacuum based systems can tell in a deadly and convincing manner.

I will follow Pauls advice and plan for failure with non-dependent backups.

[w1curtis]

Originally Posted by SteinAir

....I've said it before and I'll say it again. If anyone thinks that the $2K AHRS systems are equivalent to Cheltons, Xbow or Garmins certified stuff then I have a bunch of beachfront property and bridges for sale - cheap! There is NO free lunch here - one of these days I think I better just put an article together on AHRS to try and dispell all the half truths and misinformation.

Well, there is Chelton, and then there is Chelton.

This is partially Chelton's own fault. There ARE two different Chelton's; their experimental Sport and their Certified FlightLogic systems. For so long now they obfuscated the issue and have tried to convince buyers that the experimental Sport was the "same" as their certified FlightLogic systems. Now it is coming back on them. The simple matter is that they are NOT the same. Just look at the below temperature specs for the certified and the experimental systems. This is but one of the many differences. There may be some level of the same software, but the two hardware platforms are totally different. There is NOTHING certified about the Pinpoint AHRS and I would not rate it any better (or worse) than the AHRS from the other experimental EFIS systems--with the exception of the G900X. The Crossbow GA-500 included with the certified FlightLogic systems is certified, the Pinpoint is not. The original poster may have related information about the Pinpoint system that does NOT apply to the certified FlightLogic EFIS.

Experimental
http://www.cheltonflightsystems.com/...uct-specs.html
Operating temperature: -30 deg. to +50 deg. C (internally fan cooled)

Certified
http://www.cheltonflightsystems.com/...pecs_tech.html
Operating temperature: -55 to +80 degrees C (internally fan cooled)

Experimental


Certified

[SteinAir]

Originally Posted by breister

.......I'll bet that unless you do inverted acrobatics in the weather with a blocked pitot tube it will still be accurate enough to navigate by.

I'll take that bet. Instead of "betting", I've actually flown my Dynon with the Pitot tube blocked - more than once....care to "bet" on the outcome? Let me know what we're betting on, and I'll take you up on it. I know one thing....I wouldn't bet my life on it - or even a beer!

Cheers,
Stein

[Rainier Lamers]

Originally Posted by breister

Hmmm, I know for a fact that the Dynon D-180 has an internal method of correction based on simple gravity (or more likely, "weighted average accelleration"), because if I start it up "tilted" and hold it steady during the initialization, it shows the correct attitude.

Yes, I know the cheapie AHRS systems are subject to some error over time if uncorrected, but I'll bet that unless you do inverted acrobatics in the weather with a blocked pitot tube it will still be accurate enough to navigate by.

Know your systems, and have redundant independent attitude indicators.

What you are describing forms the bases of ANY attitude system including a vacuum driven system (it's called the pendulous erection mechanism).
Unfortunately on its own it is COMPLETELY useless as any form of attitude system in an aircraft. Not even as itsy bitsy backup of whatever sort.
It's purpose is to very slowly apply a force to the indicated horizon to level it.
This is the reason why many simpler systems will show straight and level after a while if you perform a continuous banked turn.
Any modern solid state or moving gyro based system that I am aware of uses accelerometers in place of the pendulous unit to effectively replace this function. Some simpler electric gyros even use simple mercury switches to do the same thing.
I am sorry, but describing this as some form of "backup" simply does not wash...
If it did, you could simply use a piece of string with a weight at the end and you don't have to pay lots of $$$ to people like us for fancy gyros.

Rainier
CEO MGL Avionics

[az_gila]

Originally Posted by SteinAir

I'll take that bet. Instead of "betting", I've actually flown my Dynon with the Pitot tube blocked - more than once....care to "bet" on the outcome? Let me know what we're betting on, and I'll take you up on it. I know one thing....I wouldn't bet my life on it - or even a beer!

Cheers,
Stein

Stein,

You need to add "REMOVE PITOT COVER" to your check list.....

gil A