We are surrounded by the force of gravity – example: banana falls from banana tree… The force of gravity brings everything “down”. To fly “up” we need lifting force greater than gravity
Lift force “up” can be created by for example:
– airplane wings
– helicopter rotary wings
– hot air inside a balloon
– rocket engine
Firstly, airplane wings work only from a certain speed, for each individual design. Airplane is not flying when it’s on the ground, it must accelerate to a certain speed. When the aircraft flies too slowly – it start to fall like a stone. Aircrafts have minimum speed. Below this speed they fall. The landing must be done at a certain speed.
Second, since the wings work from a certain speed, to give airplane speed to fly we need some kind of motor – most often it is the internal combustion engine, but I’ve seen electric Extra 330 so future brings new inventions. There is a whole family of jet engines: a rocket engine, jet engine, Pulsejet, motorjet, turbojet engine, double-flow turbojet engine, turbofan engine. Passenger aircraft manufacturers such as “Boeing / Airbus” are the most turbofan engines.
Third, airplane fly forward. There is no “reverse gear”, we can reverse on the ground while taxiing back but we cannot fly standard airplane backwards, it won’t work this way. In some machines we can enable “thrust reversel” but it’s used to support braking during landing as an additional help for the brakes in the wheels
Fourth, aircraft have air cruising speed and the ground speed. What is going on? A simple example – a kite. Kite is flying but at the same time … it looks like it’s hanging in the same place. Relative to the movement of air masses kite is flying at a certain speed but kite relative to the ground stays in place on the cable. If passenger plane flies at 900 km/h (ASI = airspeed indicator) and has a front head wind blowing 200km/h then the speed of the aircraft relative to the air is still 900km/h but ground speed (GS = groundspeed) is 700km/h. This also works the other way. Flying with the wind = flying faster relative to the ground. That’s why we’re landing and making takeoffs into the wind to reduce necessary landing speed. The same with aircraft carriers – the aircraft carrier speed + wind is added to the speed of starting jet. With sufficiently strong hurricane winds, the plane can fly 200km/h but looking relative to the ground it may stay in place or even fly backwards. Here is an example of practical use: due to the strong jet stream of air over the ocean flights from America to Europe can be faster than flying in the opposite direction on the same road, the same day, even though the same distance thanks to wind currents.
Fifth, the wing of the aircraft needs air to work. Air with specific density. The air density varies in depending on the altitude. As we are in the mountains at high altitude above sea level, the air is a bit thinner in density. At very high altitudes the air is too thin for airplanes or helicopters. To clarify – helicopter blades are type of rotating wings. They generates a lifting force by rotation. Each type of aircraft has a predetermined maximum altitude at which we can still fly. Above that we simply can’t fly, because it is impossible – just as you can swim in the water but not in the air. Aircrafts are flying in the air, but not in the vacuum of space. In the space ordinary plane does not fly.
“Invisible plane” is often mistaken with the concept of “aircraft invisible to radar” . There are aircraft designed to have a reduced radar echo compared to normal machines. As a result, these airplanes are “undetectable” for radar. These aircraft are however clearly visible to the human eye …
Flaps, Slots and aerodynamic brakes
To allow slower flight ability for takeoff and more important – slower approach and shorter landing distance some aircraft are equipped with special flaps on the rear edge of the wings and slots on the front of the wings. During takeoff and landing pilot can extend them – thanks to them aircraft can fly slower. This can be easily observed when landing a passenger plane – wings during landing changes its shape into the shape of teardrop – front and rear edge of the wing bends down.
Flaps and slots reduce the required length of airports needed to start and landing, the plane can land on shorter runways. Retracted flaps, slots and landing gear greatly increase air drag of the whole machine. The greater the air drag, the greater is also the amount of energy needed to move the aircraft, which generates as a consequence of higher fuel consumption. During normal flight pilot hides flaps as they are not needed and hide landing gear to reduce additional drag.
I emphasize that I wrote everything in simple language. I have used a number of simplifications and generalizations. Below is only a brief introduction to each topic, because those topics can be found online in more easily accessible and well-made articles by other people.