Ahh, not again....
zadnji put kad sam bil u ovoj temi se grdo zavrsilo
Ugl ispocetka sam tvrdil da avion nebu poletel, al istina je da hoce
Ako je brzina nula, onda zadatak nema smisla te je hipotetsko pitanje.Izvorno postao ::diaboliq::
Posto ljepo pise (bar u orginalnom textu na Engleskom) da se prati brzina aviona, koji se krece po traci, kao sto je i poznato avion ce se kretat bez obzira kaj se ispod njega vrti traka, jer je snaga avionskih motora jaca od trenja koje se desava izmedju kotaca i trake, a koje bi eventualno sprijecilo, usporilo avion da se krece.
Ono kaj ljude uvijek buni kod obog, je to kaj avion ima dvije brzine:
groundspeed - brzina kojom se krece avion po pisti
airspeed - brzina kojom se avion krece kroz zrak
Evo C/P s jednog foruma:
As has been explained, its all about the airspeed. All the conveyor does is alter the ground speed. Assuming the wheel friction is relatively low, which it would be in practice, you can roll the conveyor backwards as fast as you like and the relative ground speed increases but the airspeed stays the same. Lift is proportional to the square of the airspeed, how fast the wheels are spinning doesn't come into the job.
Look at it this way:
1. The pilot is sitting in his aeroplane finishing his sandwiches on a calm, windless day without realising that someone had replaced the runway with a conveyor.
2. The conveyor starts rolling backwards.
3. He is a bit surprised as his plane begins to move backwards, but he screws the lid on his flask and releases the wheel brakes.
4. The friction in the wheel bearings means the plane continues to move backwards.
5. The pilot has a bite of his chocolate biscuit and pushes the throttle forward till the forward thrust is equal and opposite to the friction in the wheel bearings. The aeroplane is now standing on the conveyor, which is rolling backwards while the planes wheels are spinning round. The ground speed is now negative but the airspeed is still zero.
6. The conveyor speed increases and if we assume the friction in the wheels also increases then pilot needs to increase the throttle a bit. He doesn’t need much power as the friction in the wheel bearings still isn’t that high (its actually probably lower than the initial static friction). The conveyor operator can increase the conveyor speed as much as he likes and all the pilot has to do is ensure the thrust overcomes the wheel bearing friction. Assuming the bearings don’t cook, the wheel bearing friction will not get that high and so the pilot won’t need much thrust.
7. The pilot finishes his biscuit, has another sip of tea from his flask and opens the throttle.
8. The plane now accelerates down the runway no problem and the airspeed increases.
9. The conveyor speed can be increased but it makes little difference as all it does is change the ground speed and hence the friction in the wheel bearings slightly.
10. The aeroplane reaches its take-off airspeed and the pilot pulls back on the stick and flies off into the sunset.
Dakle avion leti
Evo jos dokaza:
http://youtube.com/watch?v=IZGdUAiMcPs
http://youtube.com/watch?v=mAA_WbgyD8I
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