Why do some airplanes take off with their flaps down?

Answer 1

Almost all aeroplanes do use flaps on take-off.
Flaps, using basic terminology increase the lift of the wing, allowing the airplane to fly at a slower speed.
A slower speed means less time on the ground during take off, and a shorter distance to stop during landing.
Unfortunately the flaps also produce drag so after take-off they retract and allow the airplane to fly faster.
There are usually quite a range of flap settings on most large aircraft and the larger the flap setting the slower speed the airplane can fly, but with the larger setting the drag increases and the ability for the airplane to climb after take-off reduces, so with a large flap setting you get of the ground a bit quicker, especially if your runway is short, but you don't climb as well after take-off.
I should point out that all the airplane performance charts that the pilot uses assumes that an engine fails at the worst possible time, and the airplane can still fly and climb above any obstacles in its way.

Answer 2

If it isnt a short runway then you are probably talking about an aircraft that cruises in excess of 200knots.
Higher speed airfoils are designed to be lower drag and produce plenty of lift at their cruising speed. Slow them down and lift is a bit low so you extend some flap - 10 degrees is common but the aircraft manual will have a spec for the wings on that aircraft. You dont run full flaps because although that gives max lift for that airspeed it also gives maximum drag and you need to achieve adequate air speed before you run out of runway. Commercial jets cruise around 600 and they have complex adjustable airfoils -some military stuff even changes the angle of the wing. Very complex stuff.

As a test I once took a Cessna 150 with full flaps and full power and tried to push it into the runway - it wont do it - it balloons on the high pressure wave under the wing. I started dumping flaps as I was at the 3000 foot marker and 5000 feet - the end of the runway - was coming up fast. Probably get in trouble if you tried that now. I did that around 1968 or 69when we could do things without getting into a P**** match with an official.

Answer 3

Generally speaking, in most planes there are a variety of flap settings. The smaller the plane is, the slower it flies, and the less it needs to change its wing characteristics for takeoff. For example, a Cessna 172 can rotate around 55 knots, and cruises around 105 or so - almost double. Generally speaking, no flaps are needed on takeoff. On the other hand, a big jet airliner may take off in excess of 140 knots and cruise at over 550. In order for the wing to cover the whole range of speeds, it needs to be able to change itself. On nearly all jet airplanes, you need an amount of flap (sometimes half as much as you do on landing) in order to generate that lift at such low speeds.

A good rule of thumb for flaps is the first half gives you more lift than drag (for takeoff) and the second half gives you more drag than lift (for landing).

So, the answer is "because that's the way it is in the operating instructions", but the real explanation is that depending on the kind of airplane, it may simply use an enormous amount of runway or simply be unable to takeoff if it was using no flaps.

Answer 4

On smaller airplanes which the majority of us fly; 20 degrees or so of flaps are used for short or soft fields to get the gear off the terrain. This can become very touchy depending on altitude and cross winds. do so only when needed because this can get you in a world of hurt!

Answer 5

Lowering the flaps changes the aerodynamics of the wing to generate higher levels of lift for slower speeds. Once airborne, the aircraft has sufficient speed to generate lift and therefore the flaps are not required.

Answer 6

All airplanes, (that have adjustable flaps,) take off with them extended to get extra lift at slower speeds. Especially on a shorter runway.

They also land with them extended so they can touch down with a slower forward speed. Helps the plane stop sooner.

You can take off and land with the flaps retracted, but it takes significantly higher airspeed to do it and that would require a really long runway.

Answer 7

Changes in the camber of the wing allowing the aircraft to phantomally change the chordline and angle of attack therefore allowing the aircraft to take off at maximum power and shortest distance. Flaps used on Landing allows the aircraft to come in slower and at a steeper angle so that the main wheels will touch first.

Answer 8

One simple reason...on take-off, with a desired amount of flaps extended (the amount of flaps required depends on aircraft weight, airport altitude/temp. and runway length) you can substantually reduce the take-off roll, by increasing lift and drag.

On the contrary, during an approach to landing, max flaps are usually extended, so a steep approach can be made, without excessive airspeed developed.

Answer 9

Up to a certain point flaps increase lift. So the aircraft will be able to lift off at lower speeds.

Answer 10

Flap extention to a certain degree is to produce more lift and help make take-off faster. Also to make landing less violent. More extended flaps will cause more drag and necessitate more airspeed to attain take-off.