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727 Captain >> 727 Captain >> Autopilot use - tutorial by Lou
https://www.captainsim.org/forum/csf.pl?num=1312623303

Message started by Aeroporc on Aug 6th, 2011 at 9:35am

Title: Re: Autopilot use - tutorial by Lou
Post by LOU on Jun 15th, 2014 at 8:07pm
I'm not sure why you are having this problem in AUTO G/S and not in MAN G/S. Once you are on the glide slope switching from AUTO to MAN should not make any difference. Once you are on the glide slope in either mode the dynamics are the same.

One thing that will cause pitch changes is thrust changes. Since this is old school flying there is no auto-thrust so you need to be aware to make smooth & slow changes to power as you capture the G/S. If you are level and doing about 150 kts with flaps 15 approaching the glide slope, as the glide slope comes alive, select gear down. As the G/S is around one dot above, flaps 30 and keep an eye on the speed. The speed bleed to approach speed of let's say 125 to 130 kts should work out just right to see the plane pitch down as the G/S is captured. Make small corrections to the thrust to keep the approach speed of 130 to 125 kts.

The main difference in the 727 and the newer planes (767, 777) is the size of the fan part of the engine. A very small physical movement of the thrust levers on the big fan planes gives you a large thrust change. You may find you will move the thrust levers more distance on the 727 to obtain the desired thrust change. Still, you need to make small actual thrust changes to avoid a pitch change.

I just flew the 727 through several autopilot approaches and even when I was a bit fast with the power changes the plane did pretty well holding the G/S.  Try hand flying the plane through a series of approaches just using raw data from the ADI to hold the G/S (no autopilot) and see how power changes affect the ability to keep the plane on the glide slope. Get the plane on about an eight to ten mile final at the proper approach altitude with flaps 15 and around 150 knots. Save the position/flight so you can repeat the approach over and over until your happy with your performance.

Keep us informed about your progress....  8-)

Lou

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