In heavy bombers, always use only 25 or 50 % fuel. That will take you across the map and back.
With the lighter loadout, takeoff is easier. Also, drop a notch or two of flaps when your halfway down the runway, to give you additional lift. Select a runway that doesnt have a hill or a tree at its end

. Dont start climbing immediatly after getting wheels off the ground, start gaining some speed first. If you still have trouble, holler and ill meet you in the TA and well get you going. Or ask any of the trainers.
check out
http://www.netaces.org for tons and tons of info on how to set up game, how to start flying and how to bomb etc etc. Almost any question will get answered there.
Welcome to Aces High

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>S< Schatzi
PS: Dont compare other flying games to Aces High. They are programmed a lot different. As far as i know AH is one of the most realistic (ie difficult) games.
Edit: Make sure your Joystick is set up and calibrated correctly. Check if youre going 100% throttle on takeoff (Easiest way to check this is: Grab a fighter that has WEP - like the P51, go full throttle and press P... if that does give you extra power, your full throttle)
Edit2: Also check if you have ALL engines selected. If not, hit
CTRL E.