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Stall while engaging autopilot (Read 141 times)
centurion88
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Stall while engaging autopilot
Oct 25th, 2019 at 5:45pm
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Hi!
  I have trouble taking off manually. Every time when I switch the autopilot on CMD mode, it swiftly pulls the yoke,causing a wide attack angal and a high vspeed, which made the jet stall in a low altitude and eventually crash.
  I've already set a low vspeed(about 100) in the APFDS panel, but it doesn't work. I wonder whether you met such problem and how can I solve it. Thanks. Undecided
  
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Markoz
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Re: Stall while engaging autopilot
Reply #1 - Oct 26th, 2019 at 1:58am
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My suggestion would be to select the VS button, then set the VS to ~1000fpm, before takeoff, so that when you engage the AP in CMD mode, the nose will not "swiftly pull up". I do this, as it allows the L-1011 to both gain speed, and to not have too high of an AOA, to cause it to stall. It is surprising what the VS can get to by the time you turn the AP on, especially if you have too much nose up trim (I have never had to set the trim above 6, even at MTOW).

Another thing you could do, would be to set the AP to CWS mode, and gently lower the nose to attain a reasonable VS, then switch to CMD mode.

Note. The VS button will only become active if the FD switches are set to ON or SYNC.
  

Mark Fletcher



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Markoz
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Re: Stall while engaging autopilot
Reply #2 - Nov 28th, 2019 at 9:46am
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100 KIAS is a very slow speed to have the L-1011 set to when you need to be at 1000ft AGL, and V2+20, and calling "Flaps 4", followed by being at V2+60 to call "Flaps up". Then you need to be at V2+70 to latch IAS (press the IAS button, which is different to using the AS, and AT to maintain v2+70 (or ~230 IAS)) to 3000ft AGL.

Considering that V2 could be as high, or higher, than 160 KIAS (I don't have any tables to go on, so this is only an estimate, and I tend to use 145 as VR, and around 160 as V2, on an L-1011 at MTOW), so therefore, 160+70 (230) might be the best minimum setting to enter into the AS (although I use 220 for the AS, as it is 10 below maximum speed for Flaps 15 (the takeoff setting)). This the basis of my previous response.
  

Mark Fletcher



PC: i7 9700K @ 4.6GHz | 32GB DDR4 | 8GB RTX 2070 | 27" LCD Monitor | 1TB SSD & 2TB HDD | Win 10 Pro 64 - FSX, FSX-SE & P3Dv4.5
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