Problems with Autopilot system

[FGRA]

Please, help me out...
My problem is related with the Autopilot system. When I engage the Autopilot master switch flying on Cessna or Laserjet  (I had not tested in others) only the Heading mode works properly. The automatic vertical speed and the altitude hold don

[Kaworu]

At what speed did you engage the autopilot? Auto pilot's generally don't work at low speeds- It's best to hand fly things until you are into your climb, and within your glideslope(that works for me!)

[beaky]

Two important things:

Proper power setting for the climb

Proper airspeed for the climb

If you want to climb and continue climbing, you must add power. How much depends on the aircraft, its weight, and how far you want to go (distance-wise) during your climb. Without more power, the AP, being basically a very stupid if skilled pilot, will try to increase the angle of attack to get the vertical speed you've dialed in, which will cause the plane to swoop up and then stall.

You should also know the airspeed the airplane "likes" to climb at... for a Cessna 172, for example, normal cruise climb is about 80 knots. This is how you can find the power setting that's correct: increase power until you see the recommended airspeed and the vertical speed you're looking for, and you will find the plane climbs in a stable fashion, without lifting the nose up more and more.

Also... make sure your vertical speed setting is within reasonable limits. A C-172 is not likely to give you more than 800 fpm in a climb, and if you ask for more, it will swoop up and stall on you, for sure. For heavies, 1000 fpm is reasonable under most circumstances.

[Orlaam]

Perhaps you aren't setting the proper mode to engage.  In the default planes, you select a positive amount in the radio panel where the AP is located.  So set the V/S to maybe +500 FPM (feet per minute) in the Cessna on the ground and that way it's ready for you.  Dial in the altitude you want (e.g., 7000 feet) in the same panel.  Then when you take-off, turn the AP on and push HDG and VS, which are located in the same panel as the AP.  This is usually the radio panel on default planes.  Depending on weather and weight, you may only be able to climb at 100 feet per minute.  You must maintain around 80 knots in the Cessna 172.

The larger Cessna 208 will climb at probably 750 or more.  The Boeing MS give you are terrible, as are almost all the default planes.  They don't represent any realistic aspect of the real-world plane, but they're good to learn the basics.  A real 737-400 for example will actually climb out 2500 to 4000 feet per minute.  Again this is dependent on weather, altitude, and weight, but a sea level 737 from LAX will easily climb at 4000 feet a minute if doing a short hop to maybe LAS.  The higher you go, the lower the nose must be, therefore as you get around 10,000 feet you may only be climbing at 2500 feet a minute.  Just depends on certain factors.

Sounds to me like you're climbing at too high a rate to maintain the climb and the default AP won't correct for that like a VNAV equipped plane.  You are responsible to watch over the AP and make sure it doesn't let the plane stall.  If your speed starts dropping below say 70 knots in the Cessna and the climb rate is moving up past 750 feet per minute, you better turn off the AP and get control.