[supersport396_2000]

There is a plane on a runway with 2,000lbs of birds onboard, the plane cannot take off because of the weight of the birds. If the birds all hovered inside the plane could it now take off?

 

[Dan72]

Yes, until they hit the back wall of the cabin, rejoining the weight of the plane.


Go stand on a scale. You weight x lbs. Now jump in the air. What does the scale do? It goes to 0, right?

 

[Chevelle408]

Yes, until they hit the back wall of the cabin, rejoining the weight of the plane.

The birds wouldn't hit the back of the plane, because they are moving at the same speed as the plane.

 

[Derek69SS]

This reminds me of the pilot guy on "The Red Green Show" who built a trailer with wings to tow behind his airplane for hauling things that were too heavy for his plane to carry

 

[Derek69SS]

The birds wouldn't hit the back of the plane, because they are moving at the same speed as the plane.

This depends on how quickly the plane accellerates.

Ever ridden in a car fast enough to push you back into the seat?

 

[Dan72]

Quote:
Originally Posted by zachs chevelle
The birds wouldn't hit the back of the plane, because they are moving at the same speed as the plane.


Derek:

This depends on how quickly the plane accellerates.

Ever ridden in a car fast enough to push you back into the seat?

Exactly, takeoff implies acceleration. When they are flying, they cease to be a part of the plane, and the plane moves independant of the birds. Hence, they can certainly slam into the back of the plane.

Believe me, I know about Conservation of Momentum, I've been arguing about its existance...

 

[Derek69SS]

...the plane moves independant of the birds. Hence, they can certainly slam into the back of the plane...

...but the air the birds are flying in moves WITH the plane, so they don't have to fly as fast as the plane goes, just fast enough to overcome the mass / accelleration.

 

[supersport396_2000]

This depends on how quickly the plane accellerates.

Ever ridden in a car fast enough to push you back into the seat?

It doesnt really put you back in the seat, the seat hits you. The car accelerates,not you. You dont accelerate till the seat hits you and pushes you foward.

The birds wouldn't hit the back of the plane, because they are moving at the same speed as the plane.

The birds are still sitting still while the plane moves around them, so unless they start moving foward at the same rate as the plane they would hit the back of the plane.

 

[Chevelle408]

It's like throwing a feather up in the air of a moving train. The feather would reamin the same speed and move with train. I've asked 3 different physics teachers about this and that's how they say it works.

 

[6t7gto]

just like when a fly is buzzing around inside your car and you are going down the freeway.
david

 

[supersport396_2000]

But they started off NOT moving foward, then the plane moves so they bird will have to move along with them, if not they'll hit the back of the plane.

 

[1966_L78]

It's like throwing a feather up in the air of a moving train. The feather would reamin the same speed and move with train. I've asked 3 different physics teachers about this and that's how they say it works.

Not exactly... Ever had anything hanging from your rearview mirror? When you accelarate, you can see the object swing back... Its not the speed, its the accelaration... Eventually, the birds would be able to stay in the same place, but during the initial accelaration of the plane, they would need something to accelarate them (either flying, or the back wall of the plane, etc)... Its also why you need seatbelts in your car...

 

[Dan72]

Correct, in the case of the feather the feather is ALREADY moving at the same speed as the train...

 

[allengator]

Ya'll are missing the point.....

When a bird flaps his wings he exerts downward pressure. This is equal to or greater than the weight of bird....

It's easier to think of like this.... picture a model helicoper sitting on a bathroom scale in a sealed box.... say the model weighs 2 pounds. if you start the motor and hover the plane just above the scale (but not touching it) the scale would still read 2 pounds.... 2 pounds of thrust are needed to keep the helicoper aloft...

The plane would be no better off if the birds were flying or perched....

 

[Dan72]

Believe it or not, I did think (wonder) about that.

Does this qualify as a trick question?


So to further qualify my original example, the scale first climbs above your weight as your jump generates thrust in excess of your weight, then after your launch your thrust goes to 0, your momentum carries you up then you fall, but the scale goes to 0 when thrust ceases.

 

[allengator]

So to further qualify my original example, the scale first climbs above your weight as your jump generates thrust in excess of your weight, then after your launch your thrust goes to 0, your momentum carries you up then you fall, but the scale goes to 0 when thrust ceases.

This example would be a plane full of KANGAROOS.... ha!
But you cant get anything for free...!
Just as you state about jumping on a scale... its going to average out....
Any benefit gained by the short period of the airborn jump would be lost by having to overcome the GAIN experienced just prior to the jump (thrust)...

It's fun to think about! But again.. nothing is free, it all averages out!!

 

[Derek69SS]

OK, now a plane with a midget, a hooker, and a priest is flying at the speed of light over the top of a conveyor belt... Does it crash?

 

[depley]

for those who think the plane can take off I am almost positive you also think you could jump up in the air right at impact of a crashing airplane to save yourselves

 

[supersport396_2000]

Ya'll are missing the point.....

When a bird flaps his wings he exerts downward pressure. This is equal to or greater than the weight of bird....

It's easier to think of like this.... picture a model helicoper sitting on a bathroom scale in a sealed box.... say the model weighs 2 pounds. if you start the motor and hover the plane just above the scale (but not touching it) the scale would still read 2 pounds.... 2 pounds of thrust are needed to keep the helicoper aloft...

The plane would be no better off if the birds were flying or perched....

The helicopter produces lift by means of an airfoil sucking the rotor and helicopter up (think rotating wings). Just a guess but maybe 30% is actual downward force, the rest is actual lift, the birds on the other hand produce the hovering lift from downward pressure and also some airfoil type lift.

 

[Finally]

Well if it did get off the ground it would soon crash. Birds cr** while they fly. All those piles of cr** in the plane would add to weight and down she comes! So there!