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B777-200ER VNAV

Controlling your aircraft, using the autopilot etc.

B777-200ER VNAV

Postby johnmalkovich » Thu Sep 22, 2011 1:47 pm

Is VNAV successfully implemented in 2.4 version and how exactly should I program it for instance from the route manager?
I just don't know how to use it. VNAV would not bring me to the cruise altitude specified in the route manager.
Thank you in advance.
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Re: B777-200ER VNAV

Postby ThorstenB » Sat Sep 24, 2011 8:21 pm

No and yes. VNAV on the 777 currently just sets a fixed altitude 35000ft. However, you can use LNAV + ALTITUDE HOLD.
The FlightGear GPS directly drives the autopilot's target altitude. So, when you cross a waypoint with the GPS/route manager enabled, you'll see the selected autopilot target altitude being updated according to the altitude given for each waypoint (this is actually hard-coded in the FG binary). That's why LNAV + ALT HOLD really works like LNAV + VNAV...
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Re: B777-200ER VNAV

Postby johnmalkovich » Sun Sep 25, 2011 8:10 am

Thank you Thorsten. That's what I already use and it works perfectly. More precisely, I use FLCH which then switches automatically to ALT HOLD when it reaches the desired FL. However, I am trying to figure out the difference between FLCH/ALT HOLD and VNAV. Can you enlighten me?
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Re: B777-200ER VNAV

Postby ThorstenB » Sun Sep 25, 2011 9:53 am

Well, VNAV doesn't really make sense right now - it's not really implemented. What I meant is that using the combination of LNAV + ALT HOLD/FLCH does exactly what the combination of LNAV+VNAV would be supposed to do in a real A/C. And In real world, ALT HOLD should not be affected by LNAV - as it is now. So, it's best to forget about VNAV - maybe until FG2.6.0 or so... ;-)
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Re: B777-200ER VNAV

Postby johnmalkovich » Tue Sep 27, 2011 10:41 pm

Roger. Thank you.
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Re: B777-200ER VNAV

Postby Hooray » Sat Oct 15, 2011 3:59 pm

Update: We are planning on implementing the VNAV-related autopilot/PID controller logics for the 777: http://wiki.flightgear.org/Talk:Boeing_777-200
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