Autopilot and glideslope?

[francesco.doenz]

Having some fun landing with the autopilot, but when on localizer mode the aircraft does not follow the glideslope automatically, only the lateral guidance, I guess it's a normal limitation of the autopilot? Or it's my fault?

[EnDSchultz]

From Pg. 14 of the Accusim P-51D manual:

A few important notes about the Century III Autopilot:
• LOC NORM must be selected for 20 seconds before the Localizer capture circuit is armed.
• LOC NORM must be selected for 20 seconds before Glideslope capture circuit is armed.
• The Altitude switch must also be depressed in the ALT position at least 20 seconds before the Glideslope capture circuit is armed.
• The Glideslope Deviation Indicator must be deflected upward for at least 20 seconds before the Glideslope capture circuit is armed.

In other words, it looks like you need to be in LOC NORM and ALT hold mode at least 20 seconds before glideslope capture, and you must capture the glideslope from below. I've done this before and you should see the ALT hold switch deactivate automatically upon glideslope intercept. If it doesn't, then I just manually deactivate ALT and hand-fly the glideslope while the autopilot handles lateral guidance. I find flying an ILS in the P-51 in actual instrument conditions fairly challenging, as it is very fast, nimble, and sensitive, which makes it very easy to over-correct deviations.

Hope that helps!

[francesco.doenz]

Thanks for having taken the time to help, yes it worked out following your recommendations, I wonder what the technical reason is for these twenty seconds everywhere! And why you have to catch the slope from below! When I have more time I will experiment!

[francesco.doenz]

Strange, I only succeed in getting the glideslope one out of ten times aproximately, with the glidepath never a problem...what is the most often overseen in this situation of autopilot and ILS? No big deal, because can follow the glideslope manually, but it is intellectually irritating...
Looking forward to any suggestions!

[SanderK]

Make sure the glideslope is active before you activate LOC NORM. The localizer is usually activated further away, so it is an easy mistake to arm LOC NORM too soon.

[Roadburner426]

Yeah the autopilot in the Mustang is a finicky one, and you have to be on your A game to use the auto land. I can always get the runway line up, but I know as soon as I hit that point, and I don't see the plane auto descending I just kick the auto pilot off and guide her in myself. What helped me tremendously is doing a lot of touch and goes using the ILS on a nice weather day, and that gives you an opportunity to mess around with it.

[francesco.doenz]

Thanks for all your inputs! My windows system crashed this WK due to new drivers for Saitek quadrant and I will have to make the great leap into windows ten, will take me I guess a good week at least to get everything working again!