I have a few obvious questions,
did you actually engage the autopilot and auto throttles?
did you check your fuel state?
is it possible you have a malfunction enabled, even by accident ( it sounds somewhat like an autotirm problem)
is it possible your joystic calibration is off and causing a fight with auto trim?
Try reducing your rate of climb as well.

As in real life, a/c like the 757 will NOT maintain a 2500 fpm rate of climb at altitude esp with a full fuel load.

You need to begin reducing this in steps. At fl 300 I would think you should be at no more than 1500 fpm, probably less.

That's why it's trying to raise its nose to an impossble angle and stalling out. Even so it shouldn't be happening as low as 6000 ft.

Also in the cruise you should be using mach not ias. At fl 300 you should be going for something like .75 - .78 mach. If you use ias at high alt you are likely to run into overspeed problems.

I think it would be cool if you could make the autopilot prioritize functions, like NOT holding a VS setting if it means a loss in airspeed when IAS hold is on. I guess it's not possible since the autopilot doesn't control speed by pitch.

While nearly every commercial aircraft will pop right off the runway, none can maintain that kind of climb rate. In anything bigger than an RJ85 (BAe-146) you need to keep the climbrate down around 2,000 feet a minute. Why? In a word, thrust. At sea level your engines can and will let you zoom it up to 6k or so, but after that those engines choke for air. Less dense air means less thrust, less lift, and a higher angle of attack on the wings. Eventually the thing will stall out due to a lack of airspeed. The engines can't produce enough power to keep you at 275 knots and climbing at 2,500 ft/min.

Some notes....

1: You can't turn on the autopilot while you're still on the runway. It'll stall out after getting airborne.
2: 2,000 ft/min is too high a climb-rate for nearly every AC. For reference, I've stalled the default 737 at 265 knots with 20 degrees nose up trying to climb too fast. Airliners need more airspeed to avoid a stall than any other plane out there.
3: Set the altitude, NOT the climb-rate-hold, and leave the rest to the computer.
4: By setting the airspeed to 260 knots you probably won't have to touch the throttle once until you begin the approach.


General procedure....
1: Set heading bug for your desired heading after takeoff
2: Set course OBS needle to runway heading
3: Set autopilot for desired speed (less than 250 kts below 10k) and altitude. Do not manually set the VS-hold
4: Set flaps to takeoff norm and takeoff manually
5: Engage autopilot after picking up some speed to avoid a stall and retracting flaps
6: Watch the aircraft until it settles on base course (set with the heading bug)
7: Reset airspeed to 265 knots after passing 10k feet
8: Do not mess with the climb rate unless the aircraft's angle is getting to be too high. The nose will come up to some absurd angle while the speed drops off slowly. If this happens, kill the autopilot and manually get it back under control


Enjoy!
---------------
Hoot

Quote:


You may have initiated a looming stall (when pitching up 20 degrees at that speed), but at 265 IAS you're still flying...