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  1. #1
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    Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hello,

    I'm seeking help for proper use of auto throttle with Project Magenta.

    Setup :
    - Project Magenta with FDS MCP hardware
    - FSX default 737-800

    I'm trying to achieve for sample a TO/GA procedure take off with A/T.

    I must do something wrong, here is what i do :

    Aircraft fully loaded.

    - CDU preflight complete and correct
    - Lined up on the runway
    - FD on, YD on, A/T on
    - Flap 5
    - MCP speed set to V2
    - Runway heading on MCP, ALT 10.000 set for sample

    Takeoff clairance :
    - Move throttle to stabilize 40% N1 brakes applied
    - Release break, push N1 button on MCP, MCP speed set automaticly to V2+20
    - Throttle goes automaticlaly to power set by CDU, approx 97-98% let say

    - Taking off

    Airbone the aircraft just go through 200 kts in a few seconds, in fact i just have time to retract gear and the i got to set Flap 1 and Flap 0 with no delay.

    No way of holding v2 + 20 speed here with autothrottle, it simply don't care, just staying at approx 97-98% thrust.

    The FD command a very high pitch to limit acceleration, i guess too much for passenger confort, it sometimes lead to more than 5.000 feet V/S.

    I try to set MCP speed to 250 kts, nothing. It just passes 250 kts and accelerate, stuck to full thrust.

    The only way of keeping below 250 kts is to disengage A/T for me and manage thrust manually, wich result in a low thrust as 60-70% in climb.

    I guess the default 737 is totally overpowered in FSX, still why does not the A/T command thrust decrease to maintain speed ?

    Do i make something wrong ?
    I follow a tutorial based on the PDMG 737 so not sure what i'm missing here.

    Or does PM autopilot has an issue with A/T ?

    Thank you if you think you can give an advice in any way !
    Comma

  2. #2
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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hi, I will admit to not knowing PM at all but N1 mode does not hold a speed, and if the CDU has 98% N1 set, then the throttles go to 98% and stay there regardless of speed. In my sim I use TO/GA mode and the throttles go to the CDU set RPM and then the plane varies the climb rate to keep the speed down to the MCP speed then the autopilot changes to SPEED mode, then the throttles come back to maintain the speed.

    So try reassigning your button to TO/GA instead of N1.

    Hope that helps... Andy



    edit... there is no button on the MCP for TO/GA, you will have to assign one.

  3. #3
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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hi Andy,

    I think when the aircraft is airbone and N1 set with V2+20 speed on the MCP the LVL CH activate itself.

    So i guess there is a major problem with FSX 737 model (and POSKY wich does exactly the same) with wich i have to command let say a 35 pitch in order to maintain correct speed.

    I would think a fully loaded 737 would have kind of more difficulties to accelerate in climb than to have to reduce so much thrust in order to keep a speed restriction.

    I'm confused with TO/GA mode button. Is there one on real aircraft ? PM documentation if i remember do not talk about a TO/GA mode in other word than the N1 pushbutton procedure on takeoff. I certainly missed something.

    I remember trying a TO/GA FSX button assignement with no result in PM behaviour, so i thought this was not used for PM.

    Very confusing...

    Comma

    PS : Anyone using FSX with PM for a 737 sim ? If so which aircraft model do you use ?

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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hi, you said that "you" have to pull up to 35 degrees? that tells me that the autopilot is NOT engaged ?, just autothrottle, or you would not be able to pull up yourself. not shure I understood what you said??

    I fly the default FSX 737 and it does climb REALLY fast with full power. My CDU picks 84% N1 for climb and with A/T and A/P engaged it will climb at 250KTS and 2000-3500 fpm rate, then if you slow down the MCP speed to say 220kts it pitches up really far untill the speed comes down.
    But if I use N1 mode even at 84% and level off the plane will go past 450kts in a hurry.(bell clacking after 340kts)

    The TO/GA switch on a 737 is under the throttle handle mounted vertically, right behind the hinge point for the thrust reverser lever, you really can't see it good in a normal picture of the cabin or the throttles.
    search some pics and you will find it.

    I just re-read your first post and your checklist does not show "autopilot on".
    when you engage TO/GA on the runway the thrust is set. then after you rotate and are at 500 feet or so you engage autopilot and then the LVL-CH mode takes over and the plane should climb out at the MCP speed.

    OK...I'll stop rambling and wait for another reply.
    I will stay with you till you get it sorted out...Andy

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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Andy you are actually right, i do not engage autopilot, but i understand that A/T and A/P are two different systems, the thing is i might not use them well.

    I certainly have A/T engaged without A/P with success in final approach for sample. Well i think so.

    I like to fly the SID "by hand" but i thought i could do it with help of A/T. I understand that the only command the FD can show me is to add pitch in order to reduce speed, so i think that is the N1 part i don't get really, in fact i should be using SPEED mode instead of N1 + LVL CHG during my climb if i want to achieve my speed with A/T and without A/P.

    I will have to try thi TO/GA function in FSX thing. Maybe that the point.

    Also i will try a SID with A/P engaged to understand how the aircraft behave to maintain the restrictions.

    I'll notify if i sorted this, your advices are much appreciated.

    Thanks for making the effort to handle my so poor english by the way.

  6. #6
    1000+ Poster - Fantastic Contributor Jackpilot's Avatar
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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    You never said anything about aircraft loading. Fuel + payload.
    Very different performance and figures depending on weight and CG.
    Jackpilot
    B737-700 Posky
    FS9/P.Magenta
    without PMSystem

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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    I think what you describe, can be anticipated if the flight model is indeed way off. Your procedure seems correct, the autopilot will be in N1 mode. The A/T and thrust computer will set thrust according to the numbers on the N1 page. You mention this being about 97 or 98 percent. This seems quite correct.

    After liftoff, the flight director should indicate pitch up, which should yield a speed of V2+20, at the current power setting, which is about 98%!. The important part is that to my understanding, in N1 mode the speed is controlled by the pitch angle (normally about 15 to 18 degrees nose up) and NOT by thrust setting. (We just want to get away from the runway to a safe speed and altitude, right? Why decrease thrust? )

    At thrust reduction height, the N1 power setting should decrease to the selected Climb N1 setting. Finally, at acceleration height and if no other mode than N1 is selected, the FD should indicate a slight decrease is pitch, in order to increase the speed for the flap retraction schedule, but the thrust setting should remain at Climb N1.

    I think what you are observing is probably proper Project Magenta AT and thrust computer logic, trying desperatly to give proper values for the incorrect flight model.

    I am desperatily looking for a proper model of the 737 for FSX too. Or otherwise a Quality Testing Guide (QTG) document that is used for certification of the certified training devices. We can then fiddle around in the flight dynamics ourselves until it is perfect!!!

    Kind regards, Roel.

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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Jack is absolutely right...fuel & payload make a huge difference in performance. The default 737 in FSX however seems to be turbocharged or has auxiliary launch rockets on the side

    Not flying right now, but I was using the FS9 PMDG 737 model with FSX and the flight model is much better as many people have found out. PMDG supposedly have an FSX model in the works according to they website, but it seems to be taking forever.

    Maurice

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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hi all,

    Well by saying "Aircraft fully loaded" on my initial post i was meaning "Aircraft 100% payload" (i use Fspassenger X and get at approx of 95% of max TO weight allowed)

    Anyway i ran some test yesterday.

    I did manage to get wanted speed by pressing "ALT MODE" also (without engaging A/P). It turns that after take off the MCP goes in SPEED MODE and FD use V/S mode to command pitch, and it reduce thrust to maintain speed.

    Not sure if this is the correct procedure, but it does the trick to handly the departure with precise A/T control.

    Still i agree with mauriceb, the FSX737 must have some sort of rockets and i should try to pass MACH1 whith it in climb.

    It seems that a lot of cockpit builder did not move from FS9 and PDMG 737 flight model, i wonder if someone is using a strongly tested 737 flight model for FSX with success ?

  10. #10
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    Re: Auto throttle : N1 overspeeding after takeoff, unable to stay under 250 with A/T

    Hi

    Just to clarify this. One or two posters are very much correct re the flight model and weight and balance, but there are some things that I'd advise re ops to get the exact correct operation of the TOGA mode.

    First, don't press N1 on the MCP, this was an old workaround before most people had hardware / throttles, and since then the logics became more refined - it is better to set the TOGA command (if you can [see offset listings]) via a switch or joystick button (can be set from FSUIPC). This puts the MCP into full TOGA logic (you N1 will remain unlit). The FMA will indiacte the TOGA modes as you begin take-off. The FD will command 15 a fixed up until 1000fpm climb is achieved initial. Then it will command V2+20. (speed is controlled via pitch as per other poster comments *not* by the AT in a speed mode) the AT power is effectively locked. At 800ft it will go into ARM (waiting for you to active a speed mode but maintaining T/O power. At 1500ft it will go into N1 / CLB unless you have manually selected N1 or another level change mode prior. Once in a speed mode, set your 210kts, and retract flaps on schedule.

    The toga logic is working correctly in this regard for the 737 / NG. If you are speeding up and everything seems wrong, it points to perhaps the incorrect toga mode initial start (i.e. by pressing the N1 button instead of the proper toga command) or the flight model is just so over-powered we can no longer cope with it *or* your weight and balance is enetred incorrectly in the CDU.

    Regards
    Jonathan Richardson
    Project Magenta
    Jonathan Richardson

  11. Thanks Jackpilot, Melnato thanked for this post
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