When I was on the airplane and noticed that the pilot open flaps during take-off. Why is that?

We could go deep into aerodynamics to talk about this one, but to keep it simple... Airliner wings are built for high speeds, therefore inefficient at slow speeds. In larger aircraft the wing does not produce enough lift for takeoff at lower speeds. Without enough lift at speeds of 130-150 knots (most smaller airliners) knots, the aircraft would run out of runway before enough speed was obtained for takeoff. Flaps increase the wing area and changes the camber of the wing, which in turn increases the amount of lift. Full flaps aren't used for takeoff like they are for landing because of the dramatic increase in drag, so a happy medium is used.

So, you means is that only open a little flaps during take-off. How much is the best? 5,10,15... And, how much for landing? Because I've always can't land on the runway becasue the plane can't decrease altitude by itself.

Hello Citybus!The amount of flaps to apply for takeoff is dependent on many variables such as:Wind speedAircraft weight (including fuel, baggage, passengers)Atmospheric PressureWeatherUsually, the flight computer will take all these variables into account and spit out the correct flap posistion for that particular takeoff. There will be instances, as for example with the Fokker-100, where the aircraft would be fully loaded and no flaps would be required for takeoff. This is be due to the design of the wing and the amount power the TAY engines generate during the takeoff roll on this particular aircraft.Hope this helps a bit!Sincerely,Dennis D. Mullert

I think you need some of the flight tutorials in FS, they would be very valuable in the flight dynamics issues that flaps address. Even small planes like C172 that I fly use flaps, for the same purposes (limited extension for take-off, full extension for landing).Bruce.

As stated above, it depends. However, many airliners will use between 5 and 15

Whoa. But how come I found it is quite hard to take-off a 747 or 330 with flaps? It always goes over the runway.

In addition to flaps ( usually -10 on the 747-200) you are probably going to need + trim adjustments (+7.5-9.5 again on the 747-200)depending on your gross weight to shorten your run and give yourself a proper AOA. You should be aware that once you get off , you will probably need to adjust your trim as the flaps are reduced and airspeed is gained.

The takeoff distance depends on several factors - one of them is how much the aircraft weighs, which is one of the primary factors in FS2002:If you have a 747 fully loaded with fuel (and with passengers, cargo, etc.) and too little flaps (or no), you will not be traveling fast enough to take off prior to going off the end of the runway. If you have too much flaps, they will add drag, slowing down your acceleration to take off speed, also possibly sending you off the end of the runway.

I'd agree with one of the earlier posts. Go through the lessons on FS2K2. They give a pretty good basic introduction to the principles of flight. And, they're quite good fun. But don't stop asking questions as I'm sure that, just like most of us, the more you learn, the more you'll want to ask.....'but why then in this case?'Enjoy your flying!!!!Best wishes!Gavin

I never know how trim is quantified, you mention +7.5-9.5 for 747 but how does one gauge this. Most trim gauges are ambiguous,e.g. PSS FMS usually recommends 3.2 but how do we set this other than guesswork?I have two proprietory trim gauges which bear no relation to each other - needs some clarification.ken ellis