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Dragonmount

Not quite understanding the Altitude raise/lower/hold options

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I have been trying to learn how to use the autopilot of this aircraft, and for some reason, I just don't seem to understand what exactly I do. I have managed to get it to raise to a starting altitude, but it usually isn't the altitude I thought I had selected, do I use the trim wheel to set all of this up? I've got a lot of experience in Boeing aircraft, mostly PMDG, but this auto pilot is just slightlyconfusing to me.

 

Patrick Boynton

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I have been trying to learn how to use the autopilot of this aircraft, and for some reason, I just don't seem to understand what exactly I do. I have managed to get it to raise to a starting altitude, but it usually isn't the altitude I thought I had selected, do I use the trim wheel to set all of this up? I've got a lot of experience in Boeing aircraft, mostly PMDG, but this auto pilot is just slightlyconfusing to me.

 

Patrick Boynton

 

Hey Patrick,

 

The autopilot isn't as advanced as most, and it follows a different convention than most modern airliners, so it may be confusing at first.  It's all the same at its base, however.

 

First, always make sure your aircraft is in trim before handing it off to the autopilot.  So, after departure, you'll want to trim to maintain about 170 knots in a climb.  Because you're the only one flying the plane (unless you have the assistance of FS2Crew), it may be easier to do the following:

 

Prior to departure, set the initial altitude in the altitude select window, and then select V/S mode (and press ALT SEL afterwards) and roll the V/S / Speed wheel up to 1500.  After departing, trim to the point where you don't need to put pressure on the yoke for your climb, throw the AP on, and it will begin climbing at 1500 fpm.  The 1500 fpm value will generally allow you to slowly increase speed while you retract the flaps, bring the gear up, and reduce to climb power.  Getting close to 170 knots, adjust the vertical speed so that there is little change in your airspeed, and then engage IAS mode (if the airspeed is changing rapidly when you do this, the plane will start "chasing" 170 knots, and if you were aboard the flight as a passenger, you wouldn't appreciate the result).

 

Explanation of climb/descent/altitude modes:

V/S - holds the set vertical speed indefinitely, unless you hit ALT SEL (if ALT SEL is armed, it will be amber)

IAS - adjusts vertical speed to maintain a particular indicated airspeed in a climb or descent - you must set the throttle manually for this - indefinitely, unless ALT SEL is armed

ALT SEL - stops a climb or descent at the pre-selected altitude value and automatically places the aircraft in ALT HOLD at that value

ALT HOLD - holds the current altitude

 

As a matter of best practice, I use:

[Depart]

V/S until I get in a stable condition at 170 knots (after departing, the flaps coming up, gear retracting, and power being reduced to climb would make the AP hunt for 170 - I keep it on V/S until all of that is complete)

IAS to hold 170 knots in the climb

 

-Always ensure ALT SEL is selected, as it will automatically trip off if you change altitude modes-

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Personally I don't bother with VS mode much, on departure I generally hand fly the aircraft (using the flight director in GA mode and NAV) to acceleration altitude , then clean up, trim for approximately 180 kts and hit IAS hold and turn on the AP so it holds 180 KIAS. I set climb power (98.6% prop RPM and EGT at Variable Red Line (VRL)) at acceleration altitude.

 

For descents I select IAS hold mode too, typically at cruise speed in straight and level flight and then reduce power to get my desired vertical speed (my VS target I get from the VNAV page of the FMS).

 

Whenever you enter a new altitude in to the AP, ensure ALT SEL is armed so the AP automatically levels off.

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I thought I'd report in now that I've figured out my problem. In most other airliners I've flown in FSX there is no need to activate the VS if you want to use it. My other issue was finding how to set the VS in the first place. Both have now been solved, thanks for your help.

 

Patrick Boynton

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