G1000 upgrade to WAAS/EGNOS: LPV, KAP 140, and capturing vertical path

PetitCessnaVoyageur wrote:

Does that mean that during the upgrade of KAP140 DA42, Diamond accepted to lose roll steering to get AP coupling vertical LPV ?

I don’t see why. The KAP 140 has separate analogue roll steering inputs, distinct from the course deviation inputs.

I thought all analog autopilots got roll steering via a faked heading bug input.

AIUI the roll steering converters work by converting ARINC429 roll angle values into a fake heading bug voltage.

Peter wrote:

I thought all analog autopilots got roll steering via a faked heading bug input.

Actually, KAP140 is digital autopilot

PetitCessnaVoyageur wrote:

Does that mean that during the upgrade of KAP140 DA42, Diamond accepted to lose roll steering to get AP coupling vertical LPV ?

No. You have roll steering when flying coupled LPV approach.

Peter wrote:

I thought all analog autopilots got roll steering via a faked heading bug input.

I guess most do, but not the KAP140. With the G1000+KAP140 combination, the A/P is in NAV mode — not HDG mode — when you are following a flight plan from the G1000. Roll steering is applied for fly-by at waypoints.

Emir wrote:

Actually, KAP140 is digital autopilot

Begs the question why it’s then wandering all over the place ! I have always assumed that it was analog so I’ve been cutting it some slack

Actually, KAP140 is digital autopilot

We did that before many times, e.g. here

The KAP140 is dated from 1998. Like the KFC225, it has an analog roll steering input for a KLN94. Line IM I would be amazed if any source other than a KLN94 would use this interface, but it is possible.

The KFC225 has ARINC429 roll steering. This, like the above, is used in the NAV mode. But the KAP140 has no ARINC429 functionality.

Yes it probably has a digital control loop (like the KFC225). It would be interesting if it has the same problems as the KFC225. It is a long story but basically it is to do with poor processing of the ex-KI256 pitch and roll signals. I recently received some info on this from “old” insiders. It is probable that the reason why the KAP140 doesn’t burn out its servos like the KFC225 does is because it uses different servos and they just happen to not have the stupidly bodged current limit circuit.

I posted about autopilot ages here.

Peter wrote:

The KAP140 is dated from 1998. Like the KFC225, it has an analog roll steering input for a KLN94.

Yes – AFAIK those two have the same connection to KLN94.

Peter wrote:

But the KAP140 has no ARINC429 functionality.

I’m not sure about this. Or to be more precise with G1000 installation there might be something like GAD29 to fill this gap. Do you have some more info on this topic?

Yes, see this post where I posted the KAP140 IM and search it for “arinc”

Or you can start at the back and look at the signals.

AFAIK the KLN94 roll steering interface is undocumented as to voltage levels etc, but it is years since I last looked into it. I was going to connect it up on my plane but in the end never bothered. From vague memory I never found anybody who had it connected (and was sure about that) and who could comment on whether it does anything useful. The KLN94-KFC225 nomal analog (NAV mode) interface works fine for any kind of flying in the real world. In the future when I get a new WAAS GPS I will connect its ARINC429 stream to the two SN3500 EHSIs and the(ir) analog roll steering output can drive the KFC225.