[Rainier Lamers]

Stein I'm quite confused on this. In my simple way of thinking both an autopilot and an AH have to know which way is down. And to do this they must rely on gyros (in the case of the Dynon EFIS and the TruTrak autopilot they're presumably solid state gyros). But all gyros, whether mechanical or solid state, accumulate error. So if the Trutrak does not have aiding how does it deal with this error.

Let me answer that as nobody is comming to the rescue.

In principle few autopilots know which way is up. They operate in the "relative" domain and do not need complex AHRS systems.
A typical horizontal autopilot may need only a single gyro aligned in the yaw axis. It does not need a good gyro and something as basic as a gyro used in a model helicopter (to stabilise the yaw) is quite good enough.
It's only purpose is to monitor left/right yaw and use airlerons or rudder (depending on what the servo controls) to counteract the yaw. If coupled to a GPS you can use this to allow a turn at a defined rate of turn to intercept and lock onto a heading.

A vertical autopilot does not need any servo at all - it just needs to know your current vertical rate of climb or sink, altitude and target altitude. Simpler systems don't even use the vertical rate.

Of course, autopilots like this cannot take over your aircraft and be commanded to fly some impressive aerobatics. Your aircraft needs to be in a stabilized attitude and if you ever get out of that you need to take control from the autopilot because if you don't, you'll need to buy a new plane soon.

Does this help ?

Rainier
CEO MGL Avionics

 

[breister]

I had planned on using a Dynon FLTDEK 180 with their new AP for my -8 for the uncluttered installation, but I am concerned now.

I understand that the EFIS uses pitot pressure for aiding and the risks associated with it. But what concerns me is, if there is loss of pitot pressure, how will Dynon's AP react to that situation? The obvious solution is to use an external AP such as Trio or TruTrak, but I kind of liked the idea of flying a coupled ILS from my SL-30 through the Dynon, but I guess that I could fly the "overlay" from the handheld GPS.

Any thoughts?

Joe Hutchison

Were you planning on having ANY backup attitude instrument? If so, what?

If you choose ANOTHER Dynon, it sounds like you should install a second pitot tube...

 

[breister]

If my ASI reads way low and my AI dissagrees with the trutrak...I'll simply engage the A/P and let it fly the airplane and keep and eye on the altimer...This assumes IFR flight.

Hey Frank, be careful - a BLOCKED Pitot tube (e.g. Pitot Heat fails in visible moisture and hole freezes over) will read exactly the speed you were going before the blockage as long as your altitude remains constant!

 

[Ironflight]

I had planned on using a Dynon FLTDEK 180 with their new AP for my -8 for the uncluttered installation, but I am concerned now.

I understand that the EFIS uses pitot pressure for aiding and the risks associated with it. But what concerns me is, if there is loss of pitot pressure, how will Dynon's AP react to that situation? The obvious solution is to use an external AP such as Trio or TruTrak, but I kind of liked the idea of flying a coupled ILS from my SL-30 through the Dynon, but I guess that I could fly the "overlay" from the handheld GPS.

Any thoughts?

Joe Hutchison

Joe,

This is why I actually don't get terribly excited about a true "all-in-one" box, where the displays, AHRS, autopilot, and GPS are all part of one black box. If you lose it, what have you got left? I DO want all of these items to talk with each other so that when they are all working, I have a nicely integrated cockpit, and th pilot workload is eased with the resulting automation.

In the case of using the Dynon's, you can add a D10A for some redundancy of you have a power loss, but if you lose the pitot tube, you can have funny data from both your primary and backup displays. A more robust solution would be a Tru Trak ADI (or similar solution) to have some unlike redundancy.

As I have mentioned, I have flown Louise's airplane with the D180 getting pitot, and the D10A not getting pitot - there error in the D10A was huge, but not outrageously apparent, except in comparison with the D180 and th outside world. It is my opinion that if the pitot was blocked in flight, and the platform "walked off" in a similar fashion, you would never catch it happening - it would be very similarly insidious as a vacuum driven gyro spinning down.....but that's just my opinion based on a single observation.

Paul

 

[Brantel]

This is why for my planned panel, I have a backup AI device that is independant of the pitot tube and the EFIS.

The Dynon AP function is currently limited in that if you have two efis's on the bus, only one of them can control the AP and to switch to the other requires a reconfiguration of the bus. I am told it can be done in flight but that to do in an emergency might be a problem. Hopefully Dynon makes this more simple in the future.

I don't have the latest pic, I am switching the 496 to below the D180.

 

[frankh]

You would think so

Hey Frank, be careful - a BLOCKED Pitot tube (e.g. Pitot Heat fails in visible moisture and hole freezes over) will read exactly the speed you were going before the blockage as long as your altitude remains constant!

But mine fell to zero..OK must be a leak right?...Well it passed its IFR P/S cert just a month before so I doubt that would be the issue.

For fun I might un hook the Dynon from the pitot tube and fly it around VFR to see how bad the error builds up to replicate Paul's experience.

Frank

 

[Steve Brown]

Mine went to zero as well

But mine fell to zero..OK must be a leak right?...Well it passed its IFR P/S cert just a month before so I doubt that would be the issue........

Frank

But not instantly. IMC, at night, no radar coverage, on the NDB into 1O2. 1990 I think.

First dropped some airspeed. I pushed the nose over. Then dropped some more. I pushed some more, but with growing suspicion. When it dropped to zero, I knew I was still flying so I initially flew the AI, which was telling me that if I didn't pull up I would die soon.

Between a loran with GS readout, the AI, and altimeter, I finished the approach and got down just fine. I vowed never to forget the pitot heat IMC again.

Two weeks ago something interrupted my before-takeoff flow and I forget the pitot heat. While already IMC in conditions conducive to pitot ice, I remembered. This before I lost airspeed, but a reminder of why I don't like single point safety.