Simviation Forum - Stall while on AP ?!?

Apr 24^th, 2003 at 7:56am

giotessari Offline
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Soon after take off (after having assigned the right parameters to all the AP windows, such as altitude, speed etc.) I switch the AP on. Well, the aircraft begins to climb tremedously high with a vertical ratio of 3-4 thousand feet per minute and then stall. There is no way to recover the plane, even if I turn off the AP the plane is unrecoverable going down and up like on a roller coaster until it crasches. Note that the flaps are all up. What the hell is this about ?!??

Giovanni (Italy)

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Reply #1 - Apr 24^th, 2003 at 8:02am

Lethal.Ambition Offline
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It happens to me a lot and i end up reccovering the plane myself.
What i've learned is that when i turn the AP on the runway, the trim messes up, or while climbing it messes up too.

Sometimes i turn it on during climb and it either wants make a 360 on my fokker or it wants to see the core of the earth. Fix it with the trim........take nums lock off and if your plane is going up press the 7 key, if it is going down, press the 1.......it is all opposite but control it, because if you leave it pressed then the plan will get out of control in the other direction. so do it by littles, using the joystick as help too.

I advice you to turn on the AP during crusing altitude, after all, if you were flying online it is never good to do it with AP, ATC sometimes talks faster than your AP can manage!

Oderint Dum Metuant - Let them hate as long as they fear.&&Proud member of the =XE= Xtreme Eagles&&Oderint Dum Metuant&&

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Reply #2 - Apr 24^th, 2003 at 11:55am

giotessari Offline
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Got it. Same thing.... It's worth saying : FS2002 : as real as it gets !

Giovanni (Italy)

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Reply #3 - Apr 24^th, 2003 at 12:54pm

B-DUB Offline
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Remember that your AP needs to be set and you have to fly your aircraft to those parameters. Say the rate of climb on your A/P is set at 2700FPM, then you have to trim your aircraft to 2700FPM, and then turn on the A/P. This way, the A/P doesn't jurk the trim. Same thing for autothrottle. You have to have the speed adjusted to say, 280 knots, and then turn on the autothrottle. You won't hear that many fluctuations in the throttle that way. Fly your aircraft to the parameters you want, and then turn on the A/P.

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Reply #4 - Apr 24^th, 2003 at 1:02pm

Tequila Sunrise Offline
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I had a prob the other night and dont know what to make of it, I had a 727 on aauto at 15,000 climbing at 2500fpm and set for 300knots but I stalled and couldn't get it above 20,000 with auto or manual ???

If someone with multiple personality disorder threatens suicide, is it a hostage situation?

Thou shalt maintain thine airspeed lest the ground shalt rise up and smite thee

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Reply #5 - Apr 24^th, 2003 at 1:44pm

RollerBall Ex Member

Any heavy with full fuel will stall while attempting to climb at a high rate at altitude. A 727 will not maintain a rate of 2500 ft per min with full fuel at 15000ft in real life I wouldn't think. There has been acres of debate on the POSKY forum about this for their planes because they insist quite rightly on trying to create as accurate an fde as possible.

Try reducing you roc to 2000 fpm at 15000, over 25000 probably 1500 fpm poss even less with heavy fuel

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Reply #6 - Apr 24^th, 2003 at 1:49pm

fisharno Offline
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B-DUB is right.

AP will try to do what you tell it, but if the parameters you set aren't feasable, then that's when you run into problems. If you activate the AP too early, the trim will adjust itself all the way, down.... or up.... Anyway, that's what gets the aircraft in trouble. Try setting the verticle airspeed to about 1600 to 1800 fps, for your initial climb. Personally, I think 2700 fps is way too high. You'd have to stay at full throttle just to maintain that type of climb.

I use about 75% throttle at 1800 fps on the C-5 Galaxy, and very seldom need 100% in any situation. Once you've got the gear retracted and flaps up, well into your initial climb, activate the AP and set the climb to 1500 fps. This will give you a smooth transition to the AP parameters, then adjust up as you see fit.

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Reply #7 - Apr 24^th, 2003 at 4:53pm

lib319 Offline
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Hi,

This problem could be related to one I have with the Lear at this thread here;

http://www.simviation.com/cgi-bin/yabb/YaBB.cgi?board=fs2002;action=display;num=...

Although I don't think I ask to much of the AP when climbing 1800 fps there are still problems.

lib

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Reply #8 - Apr 24^th, 2003 at 6:13pm

MattNW Offline
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Indiana

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It might also be related to Force Feedback if your using that. I have that rollercoaster effect problem in any plane when using a FF joystick and AP. I set the AP and then if I touch the stick (even slightly bump it reaching for something) it seems the joystick and the AP fight each other. I found it helps to turn off the control surface forces in the Options/Controls/Forces when on AP and then back on when I turn off the AP for landing.

In Memory of John Consterdine (FS Tipster)1962-2003

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Reply #9 - Apr 25^th, 2003 at 4:05am

giotessari Offline
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MattNW, yes, I have FF Joystick. I thought it could be related to this but wanted to be sure it's nothing to do with the simulation before switching on and off some hardware parameters. I will try what you say.

Giovanni (Italy)

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Reply #10 - Apr 25^th, 2003 at 11:54am

fisharno Offline
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I stand corrected.

I was trying to recreate a Go-Around that I saw this 737 do, yesterday, here in Reno. (45 kt. NW winds, here).

Anyway, it happened to me. I set the AP, as I usually do, and when I engauged it at 8000 ft, it topped out at 6000 fps, then when I tried to manually take it, it dove downwards. I had a heck of a time trying to get the AP to act correctly.

I see what you guys mean.... That's very annoying. Angry

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