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Thread: Uncommanded Dive

  1. #11
    Join Date
    Dec 2005
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    Cwmbran, Torfaen, UK
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    713

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    No, Inuss. I hadn't engaged the A/P and the speed was around 120 and accelerating when the nose started to lift. I held it down then raised the nose at about 150 kts with the joystick. Then gear up whilst holding the climb at around 10 deg, retracted the flaps at around 180, then, at around 3000 ft engaged the A/P and Alt Hold mode. Alt window was set to 12000 ft and A/T set at 230. It went into a dive.


    Now, just to complicate matters, initially my B744, A350, A320 and B738 would takeoff normally until I engaged the A/P and Alt Hold, whereupon it would go into an immediate dive.


    So, I deleted my fsx.cfg file and restarted FSX, and changed all the settings back to those previoulsy. I also deleted the joystick assignments for everything except 3 buttons, none of which would change the flight dynamics. Then, my B744 acted as it did in the first paragraph. Now, with the B738, it was the same as the B744 except the nose didn't try to lift at first. However, once in the climb the A/P was engaged the A/C nose pitched up until the aircraft was almost vertical, and, of course, stalled.

    I hope someone has a clue as to what's happening because I don't.

    Going to run some more tests later.

    Allan

  2. #12
    Join Date
    Dec 2005
    Location
    Cwmbran, Torfaen, UK
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    713

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    Decided to go back to first principles.

    Without changing ANY settings from the post above I chose the default A321.

    Set:

    A/P Off
    A/T Off
    Speed set 210
    Alt set 12,000
    ROC 1200 ft/min
    Elevator Trim 0.0 Deg

    Flaps 2

    Set 100% N1.

    At about 150 kts the nose came up sharply of it's own accord and the aircraft pitched up to 30 deg plus. Unable to control it.


    Repeated takeoff with 81% N1 and aircraft took off normally. Was abe to set the nose up angle and engage all aspects of the A/P without problems.





    Repeated the exercise with a 3rd party B738.

    All settings the same.

    Selected 80% N1 but clear the aircraft wasn't going to reach V1 so increased to 100% N1.
    Aircraft took off normally at about 150 kts although it did require a little more joystick input

    In the climb cleaned the aircraft up and engaged the A/P.
    Started to go into a dive although it was easy to control and once controlled the A/P took over normally.



    I'll try the other aircraft later but I still can't understand why I never had these issues in the past.

    Allan

  3. #13
    Join Date
    Jan 2012
    Location
    San Francisco, California
    Posts
    18,142

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    Fuel load? Flaps setting about 5 degrees? At 120 knots you should start feeling the nose rise and takeoff should be around 135-140 knots. Autothrottle should be set for 250 knots until reaching 10,000 feet. Flaps up by 180 knots and gear up after shortly after takeoff. V/S set for 1800. I recommend 92% N1 for takeoff and not 100%.

    All this starting from a fresh new flight and not from a "saved" condition? What airport, weather conditions?

    Keep in mind that max fuel load, airport altitude, and weather conditions will play a roll in how things go after wheels up.
    Last edited by mrzippy; 11-26-2020 at 11:13 AM.
    Mr Zippy Sent from my keyboard using "Whackamole", NudgeAKey + 2 Fingers

    No flight Sim installed until I get a new computer.

  4. #14
    Join Date
    Dec 2005
    Location
    Cwmbran, Torfaen, UK
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    Hi Mrzippy,

    I haven't yet got around to calculating fuel loads. Tried Flaps 5 and 10 deg. Under normal takeoffs I'd never experienced the nose starting to rise and T/O usually 140 kts plus. I set the A/T initially at something like 230 because I've sometimes found it's exceeded 250 before settling back, a result, obviously, of takeoff issues. I clean up by 180 kts.

    Until these problems started I'd always used 100% N1.

    These problems occur sometimes with fresh flights and sometimes with saved,

    Weather is Fine and airport is Cardiff EGFF, 220 ft AMSL.

    Will gather more information later today.

    Allan

  5. #15
    Join Date
    Dec 2005
    Location
    Cwmbran, Torfaen, UK
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    OK.

    Moved FSX from Program Files (x86) to C:\.

    Default A321
    Summer
    No Weather
    Cardiff (EGFF)
    230ft AMSL
    72m566 Kg Gross Weight
    Flaps 2
    Elevator Trim 0.0 deg
    A/P Settings 230 kts and 9,000 ft at 1,200 fpm

    N1 set at 90%

    Nose did not attempt to pitch up during the T/O roll.
    Rotate at 140 kts.

    Smooth rotation, gear retracted, Aircraft Cleaned up.

    Autopilot at A/T engaged.

    No problems at all.


    So now I've proven that the default aircraft is ok I can now go back to the other aircraft to see if they will perform.

    Thanks for all the inputs. I'll come back sometime soon with results of my checks.

    Allan

  6. #16
    Join Date
    Jun 2017
    Location
    South Florida
    Posts
    3,577

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    Sounds encouraging Allan! Hope the progress continues!

    Rick

  7. #17
    Join Date
    Dec 2005
    Location
    Cwmbran, Torfaen, UK
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    OK, so I repeated the exercise today with the same default A321 and takeoff was perfect.

    Changed to a 3rd party B738 - that I'd flown many times previously - with the same parameters. Takeoff was ok to start with but shortly afterwards the aircraft went into steep climb, then stalled. There was nothing I could do to control it.

    So I went to the default B737-800. Again, same parameters. Takeoff seemed normal, engaged A/T and A/P and aircraft was steady in the climb. So I selected heading mode. The aircraft started a turn and the climb steepened. I could not get the angle of climb down, with the inevitable stall.

    Haven't got a clue what's going on.

  8. #18
    Join Date
    Jun 2017
    Location
    South Florida
    Posts
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    Allan - Do you know how to provide this forum screen prints? Would be nice if you focus'd on just the default B737-800,

    1) Take a screen shot of your panel, just before takeoff

    2) When the unexpected happens, try to get a screen shot of the panel! Don't make a screen shot of the panel after you make any adjustments. Get it just as the event happens!

    This way, we might be able to see what is going on in the cockpit, both pre-takeoff AND at the time the event happens!

    Rick

  9. #19
    Join Date
    Apr 2017
    Location
    Massachusetts
    Posts
    83

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    ac10310, I am wondering if you accidentally set the V-Speed (Vertical Speed) too high. It will cause the aircraft to try to nose up and speed up to match your entry . The default 1800 is safest but I believe I have heard that most Boeing usually go at 2500. Rick's suggestion to take a screen shot of your AP panel is a great idea. I fly the default Boeings and Airbus all the time and do not have issues with using the AP shortly after manual takeoffs.

  10. #20
    Join Date
    Jun 2017
    Location
    South Florida
    Posts
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    Thanks Rich, and Allan, here's what I would like to see on your B737-800. I have two pics, one that will successfully climb to 6000' at 1800'/min, the other will manually climb until you engage the autopilot and then it is going down (to Mother Earth) at a descent rate of 1800'/min!!

    This aircraft will put a smile on your face!
    Click image for larger version. 

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ID:	224031

    This aircraft will ruin you whole day!
    Click image for larger version. 

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ID:	224030

    I know you might think of us not being confident in your flying abilities, but not so, we have no way of telling if your problems could be this simple to fix, or you have additional deep rooted problems with YOUR FSX program. We don't have a crystal ball and if we did, I wouldn't know how to use it, so we have to depend on you as the user and sometimes ask you to provide us with pics such as what I have just posted.

    I hope you can soon resolve the issue as I know things like this are frustrating to say the least!

    Rick
    Last edited by Downwind66; 11-30-2020 at 04:46 PM.

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