It’s a very limited way to describe an autopilot anyway, as there are other functions it ignores. For example, a single axis a/p may or may not have heading bug, and that makes a huge difference, and, if it does, it may or may not have roll steering (GPSS)*; and a two axis autopilot may or may not have any kind of adjustable pitch or rate (ie it is only altitude hold), and if it does have pitch it may or may not have rate, GS, IAS etc.
* Then there are a number of ways in which it may or may not interact with VOR/HSI, but that is becoming of historical interest.
Peter wrote:
Does anyone know what exactly is meant by “2 axis” versus “3 axis”?
They refer to pitch, roll and yaw.
Normally the 1st axis is roll, as there are roll axis only AP’s but no pitch only AP’s which work without a roll axis. (Both the STEC 30Alt and PSS 60 need a roll AP to engage, at least in all the installations I’ve seen.
Pitch therefore is the 2nd axis. Yaw the 3rd, a 3 axis AP implies that it has a yaw damper.
There are some folks which think a trim servo will consist a 3rd axis (as sales adds are sometimes written by people who really don’t know what they are doing) but a trim servo does not mean that.
Depends on the detail. For example HBK bought a load of 64MB Sandisk CF cards which have a hardware “lock” in them, which needs extra commands to unlock. That’s what one ex HBK guy told me recently. That’s why progs like winhex cannot copy KLN94 cards…
Peter wrote:
The cards are programmed outside the regular file system, so you cannot just copy and paste a card to make a copy of the unlock card
All I’ve got to say is:
dd if=/dev/sda of=card.img bs=1M
The 2 axis definition leaves a lot of leeway in the a/p capabilities, given that it just means pitch and roll servos are present.
For example, the Stec 30 is a 2-axis a/p but the pitch servo only provides an on/off altitude hold function and no vertical tracking or climb/descent control. The roll control is much more sophisticated ranging from simple heading bug tracking to localizer tracking to horizontal gps flight plan tracking including RNAV approaches via GPSS. Vertical tracking for ILS & gps approaches is still manual.
Martin wrote:
What if one AHRS fails (of two) when you’re in say Australia in an EASA-reg plane?
Your EASA maintenance company (or is it the CAMO?) can approve a local Australian (or FAA or anything) engineer that is legal to work on a “similar” airplane of another registry. Not to be used for routine maintenance (nor “calendar time / hours due”), but for anything unforeseeable, good to go. When the plane comes back to its maintenance base, they “inspect” the work done by the foreigner and release it again (the foreigner already released it).
Yes, “3 axis” means yaw damper.
Does anyone know what exactly is meant by “2 axis” versus “3 axis”?
If you count the number of servos, you have 1 for roll and 1 for pitch, plus 1 for pitch trim if there is pitch autotrim. But both of these are only 2 axis i.e. roll and pitch.
Does “3 axis” mean it has a yaw damper?
I have a late update to post #19 in this thread, from a US based installer:
I wonder whether a European G500 owner would be able to get the unlock card? It would seem to be an essential insurance policy.
Peter wrote:
That sort of service is unbelievably expensive.Somebody must be paying for it. If it’s not you then they must be billing to somebody else’s account, literally or de facto.
Why? You pay travel expenses and a reasonable daily rate, like 400-500 €. Of course it’s not profitable for them but it’s part of the service. If I’m stuck somewhere with a problem that I cannot solve and the only local maintenance looks dodgy, I happily pay the money to have a trustworthy mechanic fly out.
I had one case where I asked them to come and they agreed but after a bit of discussion they realized I should be capable to fix it myself and we talked 3x per day on the phone while I performed the maintenance and they eventually approved it via telephone. We agreed if either side was unsure, they would come out. You can do so much by sending photos and movies via WhatsApp…
