It has been suggested that this might be handy for best-glide in case of engine failure.
None of the King ones allow this. They energise all servos, or none. I wonder if the GFC700 or the DFC90 allow this?
One could achieve it on a King AP by having a switch which removes power from the clutch of the roll servo. The autopilot computer cannot tell the servo is not actually functioning. Illegal, of course.
The other thing is that the most time for finding a field is arguably the “lowest sink” speed (which is slightly below Vbg), not Vbg itself which is useful only if you are trying to glide for the maximum distance.
Cobham a.k.a S-Tec a.k.a. Genesys System 30 ALT and System 60 PSS are pitch-only devices, which can be installed either alone or as add-ons to roll channel autopilots (see the autopilot selection guide)
Good question, I have not tried that with the DFC90 … ! I think it should work, but nor sure. Achima? Jonzarno?
What I would do in case of engine failure:
- select nearest airport, press direct in GPSS mode of A/P
- use IAS mode for best glide speed, in my case 88 KIAS
I was told that from a certification standpoint an autopilot is not allowed to do pitch control when it doesn’t also perform roll control.
None of the APs I dealt with allow this. In real life, CWS accomplishes the job. If you only need standard rate turns, twist the heading knob, if you need steeper and/or faster turns, use CWS.
Dunno. I’m flying on Tuesday and will try it if I remember.
In the best glide scenario, the DFC 90 more or less holds best glide because the envelope protection lowers the nose to prevent the stall although using IAS at best glide is, of course, better practice.
Dynon Skyview is doing that. Not certified indeed, but about the same functionality than the most advanced fully digital certified autopilots.
Achima, in the SR22 the DFC90/100 does not have CWS. But of course you can steer it with the Heading Bug.
I was told that from a certification standpoint an autopilot is not allowed to do pitch control when it doesn’t also perform roll control.
How is that? If it was true, then something like System 60PSS would be forbidden.
Cobham a.k.a S-Tec a.k.a. Genesys System 30 ALT and System 60 PSS are pitch-only devices
Yeah, but at least 60PSS doesn’t have an IAS hold mode, as it doesn’t even know what IAS is…
As promised, I tried this today with the DFC 90 in my Cirrus.
What happens is that, if you engage any altitude or climb / descent mode, roll steering also engages and, although you can overpower the autopilot, it does remain engaged.
Yes, now I remember … have flown only five hours in three months, couldn’t remember!
Thanks!
