Very heady technical conversation.
I had an iced up Pitot tube WITH a fully functioning heat and my G600 indicated it but my attitude indication never was effected. I maintained Straight and level and also descended without problem. A standby Vac AI was also referenced. the VSI which is part of the G600 also worked. So the descent was not an issue. When I got to a warmer alt the airspeed came back.
From a pilots perspective I would not want a system that shuts my primary display down because my ASI went blank.
Looks like Aspen is fixing the pitot dependency: https://www.ainonline.com/aviation-news/general-aviation/2018-07-23/aspen-avionics-max-imizes-evolution-displays
as indicated by Peter this is part of the certification.
I think it’s clear that it is somehow a certification requirement (otherwise nobody in their right mind would be implementing it that way) but does anybody know exactly why?
But presumably you need to work out where ‘down’ is over a period of time?
Yes – you assume that, in the long term, flight will have zero acceleration, and you simply sense gravity. That is what every mechanical AI does.
QuoteNo! You don’t integrate the acceleration sensors, you just take their direction (in 3D space) to erect the gyro. Much like the blade vanes do in a mechanical gyro.
But presumably you need to work out where ‘down’ is over a period of time?
Now what is the failure rate of a MEMS gyro that cannot be detected by other means (i.e. a chip falling off the board by noticing a failure of response on the I2C, SPI or whatever bus is used to attach the sensor)? And what is the probability of the pitot icing closed or the GPS loosing signal for some time? I bet there are several orders of magnitude in between. Now if you use these checks to draw Xes instead of the attitude indicator, then almost always this will not be due to faulty MEMS output, but because of faulty check signals! That is, you’ve reduced the highly reliable MEMS sensor reliability to the lower reliability of the pitot and/or the GPS!
Totally agree, as indicated by Peter this is part of the certification. Nobody seems to have found an alternative means of compliance which the rule makers can live with, as they all use the same principle.
The one glass-panel aircraft I’ve flown was an aerobatic super-Decathlon and on landing I noticed the AI was off by about 30 degrees. I don’t remember who made the panel.
This is quite common if you actually did aerobatics. I did some projects on aerobatic aircraft with AHRS systems and found most systems don’t make up for their claimed specifications in aerobatics.
I understand correctly will be related to the noice, specified by 0.03 sqrt(Hz) dps… which to be honest I don’t know quite how to interpret.
No, bias free noise is not much of a problem. The bias drifts by typically 0.03°/s if you change temperature by 1°C. This then gets integrated to arrive at ° output.
And you’d need to integrate the gravity direction sensors, but I would have though that would be much easier to do.
No! You don’t integrate the acceleration sensors, you just take their direction (in 3D space) to erect the gyro. Much like the blade vanes do in a mechanical gyro.
So assuming you can keep the temperature stable, you’re interested in the drift which if I understand correctly will be related to the noice, specified by 0.03 sqrt(Hz) dps… which to be honest I don’t know quite how to interpret.
And you’d need to integrate the gravity direction sensors, but I would have though that would be much easier to do.
The one glass-panel aircraft I’ve flown was an aerobatic super-Decathlon and on landing I noticed the AI was off by about 30 degrees. I don’t remember who made the panel.
