# Case: Plane and Conveyor Belt

viper040 Trainee

I read this on another website, so was wondering what your opinions are in regards to it.

A plane is standing on a runway that can move (some sort of band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in the opposite direction). Can the plane take off?

Some people are arguing that it will take-off and some say it won't take off.

## 6 Responses

CRJCapt Chief Captain

The aircraft will not takeoff.

Let's put it in clearer terms:

Airspeed coordination
A Cessna 172 is on the deck of an aircraft carrier that is moving opposite the direction of takeoff, at a rate equal to the airspeed of the aircraft. At liftoff, the airspeed of the aircraft will have to be 60 KIAS. To obtain 60 KIAS, the aircraft would have to travel across the deck at 120 knots. 60 knots would give an airspeed of zero, an additional 60 knots is required for lift off. An aircraft wouldn't normally be able to travel at twice it's takeoff speed on the ground.

Ground speed coordination
A Cessna 172 is on the deck of an aircraft carrier that is moving opposite the direction of takeoff, at a rate equal to the ground speed of the aircraft. The aircraft would never obtain the required airspeed of 60 KIAS for takeoff. The speed of the ship(runway) would offset the ground speed of the aircraft producing a indicated airspeed of zero, no liftoff.

At a ground speed of 60 knots(ship at 60 knots opposite)= zero airspeed.
At a ground speed of 120 knots(ship at 120 knots opposite)=zero airspeed.[/b]

Drew B (belgeode) Chief Captain

It will not take off cause ostensibly the plane is NOT moving enough to generate the airspeed necessary.

The conveyor is moving OPPOSITE at the same rate of speed as the plane is travelling... it is no different than running on a treadmill... you go nowhere.

That is why Aircraft carriers travel at 30 knots INTO the wind... so that when the catapult launches the aircraft it needs LESS space to achieve correct takeoff speed.

It is not the physical speed the wheels travel at, but the speed the air flows over and under the airfoils that generates the proper lift.

That's my 2 cents.

Doyley Captain

lol no offense to you viper040 but I can't believe people are even arguing about. They are some of the most stupid comments on that blog I've ever seen. 😂😂

Doyley Captain

CRJCapt wrote:

The aircraft will not takeoff.

Let's put it in clearer terms:

Airspeed coordination
A Cessna 172 is on the deck of an aircraft carrier that is moving opposite the direction of takeoff, at a rate equal to the airspeed of the aircraft. At liftoff, the airspeed of the aircraft will have to be 60 KIAS. To obtain 60 KIAS, the aircraft would have to travel across the deck at 120 knots. 60 knots would give an airspeed of zero, an additional 60 knots is required for lift off. An aircraft wouldn't normally be able to travel at twice it's takeoff speed on the ground.

Ground speed coordination
A Cessna 172 is on the deck of an aircraft carrier that is moving opposite the direction of takeoff, at a rate equal to the ground speed of the aircraft. The aircraft would never obtain the required airspeed of 60 KIAS for takeoff. The speed of the ship(runway) would offset the ground speed of the aircraft producing a indicated airspeed of zero, no liftoff.

At a ground speed of 60 knots(ship at 60 knots opposite)= zero airspeed.
At a ground speed of 120 knots(ship at 120 knots opposite)=zero airspeed.[/b]

Reminds me of a couple of vids I made not long back.

viper040 Trainee

I haven't made no comments myself, all I know is it was discussed on Fspassengers website, airliners.net and also between engineers.

From the blog:

But of course cars and planes don't work the same way. A car's wheels are its means of propulsion--they push the road backwards (relatively speaking), and the car moves forward. In contrast, a plane's wheels aren't motorized; their purpose is to reduce friction during takeoff (and add it, by braking, when landing). What gets a plane moving are its propellers or jet turbines, which shove the air backward and thereby impel the plane forward. What the wheels, conveyor belt, etc, are up to is largely irrelevant. Let me repeat: Once the pilot fires up the engines, the plane moves forward at pretty much the usual speed relative to the ground--and more importantly the air--regardless of how fast the conveyor belt is moving backward. This generates lift on the wings, and the plane takes off. All the conveyor belt does is, as you correctly conclude, make the plane's wheels spin madly.

Cheeks Chief Captain

Something like an F-15 or Mig-29 would make it but if they don't 😳 😳

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