Any pilots want to weigh in on the Myth Busters BS about an airplane taking off from a conveyor belt runway?
The original myth is: Can a airplane take off from a conveyor belt runway?
Logic suggests and the intent of the original problem is: that the rolling runway will result in zero ground speed, thus zero air speed. Aeronautical engineers will immediately see why the plane will not fly.... zero air speed means no flow of air over the lift surface (wing) thus no lift.
I find it fascinating that this years old problem is still controversial.
They clearly caused the air plane to have ground and air speed... Myth conditions were not met... test failed due to inability to create the original problem's conditions... They are now idiots in my mind... Their elation at busting the myth shows they do not understand the original problem and they are blissfully unaware of aerodynamics...
More sad is the string of Internet arguments over this simple problem.
Comments?
BTW I have successfully landed an airplane with zero ground speed and zero landing roll. I was flying a Rally 2B ultralight...stall speed 28 knots. Any pilots want to describe for the audience how that was possible?
I'm both. Haven't seen the episode in question and will try and have a look later today. If the conveyor belt is going fast enough, I don't see why it wouldn't fly, but not sure of the premise yet.
Agree about the idiot part. Keep in mind it's entertainment and not science. Many uncontrolled variables in most episodes, for example.
BTW, had a touchdown in the 737 just this week at less than 100 knots ground speed. With a little more wind, it could have been zero also!
More sad is the string of Internet arguments over this simple problem.
Comments?
First, I don't understand what your position is.
Second, this is likely to turn into another "string of internet arguments over this simple problem" (unless you can explain the answer, whatever you believe it to be, with such clarity that everyone agrees with you).
And no, I'm not going to join the rhetoric beyond this. Good luck though.
Any pilots want to weigh in on the Myth Busters BS about an airplane taking off from a conveyor belt runway?
The original myth is: Can a airplane take off from a conveyor belt runway?
Logic suggests and the intent of the original problem is: that the rolling runway will result in zero ground speed, thus zero air speed. Aeronautical engineers will immediately see why the plane will not fly.... zero air speed means no flow of air over the lift surface (wing) thus no lift.
I find it fascinating that this years old problem is still controversial.
They clearly caused the air plane to have ground and air speed... Myth conditions were not met... test failed due to inability to create the original problem's conditions... They are now idiots in my mind... Their elation at busting the myth shows they do not understand the original problem and they are blissfully unaware of aerodynamics...
More sad is the string of Internet arguments over this simple problem.
Comments?
BTW I have successfully landed an airplane with zero ground speed and zero landing roll. I was flying a Rally 2B ultralight...stall speed 28 knots. Any pilots want to describe for the audience how that was possible?
I have flown a small airplane, but to me if there is air, and you have lift, you should fly regardless of the moving belt as long as you have foward motion. Or am I completely unaware of the issue. heheheh
Totally irrelevant to our Smart dilemma but it does pass the time while we wait . . . and wait . . . and wait . . .
OK, looked at the short clip and some of the replies. If I understand the problem correctly, the idea is that you place the aircraft on a conveyor which is moving at the aircraft's lift-off speed; the theory being that it will not fly as it will never generate lift. Lots, and I do mean lots, of misunderstanding of aerodynamics and physics in the replies and probably in the full episode as well. Will have to keep an eye out for a re-run.
Two BIG issues here. First, unlike your car (if you ever get it ) airplanes do not have power to the wheels. Airplane wheels are for rolling and stopping. The forces provided by the prop or jet engine move the airplane forward - thrust. You can pull the rug out all you want and the wheels will just spin in place. (Friction is never zero so eventually the airplane will begin to creep in the direction of the rug's motion, given no thrust, or more correctly, thrust less than the residual friction.)
Secondly, lift is produced by air moving over the airfoil of the wing. Seems like most responders understand this concept. To get the air moving, you simply have to get the airplane going forward which is not a problem because the thrust provided by the engine is more than enough to overcome the small amount of extra drag caused by the moving carpet. The speed of the conveyor is irrelevant to the test as long as the wheels are allowed to spin freely.
It should have been totally expected that the airplane would fly. After all, its what they do.
Tomorrow's topic: landing and taking off in a headwind. Now go hit those books, Smartians.
You can move the conveyor belt as fast or slow as you want. Unless you have a string holding the plane back, it will still move forward due to trust. Even with the string attached, the air movement will cause the plane to create lift. Wheels are not what causes a plane to fly, You could just as easily fly off a snow covered mountain with skis on the plane.
Fred,
I have watched the ground moving forward in my Dad's Cesna 120 due to a head wind that was stronger than our air speed speed and have seen a Piper Cub land moving backwards on a runway.
Thrust is measured in pounds
Ground Speed is measured in miles per hour
Air speed in Knots per hour
Lift is measured in pounds per square (Sq) inch or sq foot
Drag is measured in pounds per sq inch or sq foot
Thrust must overcome drag
Lift must overcome gravity
The "problem" is intended to demonstrate that lift is required to generate flight and that thrust is not the only dynamic in play on an airplane
But it is a bit of a mobious loop or an enigma for an engineer... the simple math of it...(if the speed of the rolling road is constantly increased) causes a point where thrust exceeds the weight of the craft and thus it is now theoretically flying
If an object with wheels is on a rolling conveyor belt (rolling road) the amount of thrust needed to maintain the item in a static or fixed location relative to the ground would also keep that object in the same relative position in the air surrounding it... if the speed of the rolling road is increased the thrust must be increased to overcome the drag in the spinning wheels and maintain the item in it's fixed, static location with zero ground speed and zero air speed
No matter how fast the rolling road is moved, and no matter how much thrust is applied to keep the item in the same location, there will never be any air flow over the wings generating enough lift for flight.
We can cheat this with a aircraft that does not require wing lift. However that object is more appropriately called a missile or rocket and "flight" is a function of more thrust then drag
No string is needed.....
Just an understanding that for a wing to generate any lift it must have a flow of air over and under it
When on a bicycle and peddling in a gear that propels you forward at 25 MPH (thrust) the air resistance on your body and bike is drag
Using the same gears and energy (thrust) on a stationary bicycle, there is a 25 MPH indication of the free spinning wheel...but zero ground or air speed and no air resistance or drag
If we set up a conveyor at the equator that is 32000 miles ling and have it saying equal to the speed of the earths rotation in the opposite direction and have the nose of the aircraft pointed in a Westerly direction...
Thrust is measured in pounds
Ground Speed is measured in miles per hour
Air speed in Knots per hour
Actually, the term Knots includes the per hour part. So its just knots.
Lift is measured in pounds per square (Sq) inch or sq foot
Actually, it is just pounds. If the number of pounds of lift is greater than the weight of the airplane, you're climbing.
Drag is measured in pounds per sq inch or sq foot
Also just pounds.
Thrust must overcome drag
Lift must overcome gravity
The "problem" is intended to demonstrate that lift is required to generate flight and that thrust is not the only dynamic in play on an airplane
But it is a bit of a mobious loop or an enigma for an engineer... the simple math of it...(if the speed of the rolling road is constantly increased) causes a point where thrust exceeds the weight of the craft and thus it is now theoretically flying
As you correctly pointed out above, Thrust must overcome drag and Lift must overcome weight. Thrust exceeding the weight of the aircraft only means that you can accelerate vertically once you are off the ground. Otherwise, they are not related.
If an object with wheels is on a rolling conveyor belt (rolling road) the amount of thrust needed to maintain the item in a static or fixed location relative to the ground would also keep that object in the same relative position in the air surrounding it... if the speed of the rolling road is increased the thrust must be increased to overcome the drag in the spinning wheels and maintain the item in it's fixed, static location with zero ground speed and zero air speed
No matter how fast the rolling road is moved, and no matter how much thrust is applied to keep the item in the same location, there will never be any air flow over the wings generating enough lift for flight.
True enough. One could apply just enough thrust to keep the airplane motionless against the moving belt. Except the amount of thrust needed to overcome the friction of the freely spinning wheels is negligible and as soon as you add more power (thrust) you get a positive lateral acceleration up until you reach flying speed.
We can cheat this with a aircraft that does not require wing lift. However that object is more appropriately called a missile or rocket and "flight" is a function of more thrust then drag
No string is needed.....
Just an understanding that for a wing to generate any lift it must have a flow of air over and under it
Yes!
When on a bicycle and peddling in a gear that propels you forward at 25 MPH (thrust) the air resistance on your body and bike is drag
Correct again.
Using the same gears and energy (thrust) on a stationary bicycle, there is a 25 MPH indication of the free spinning wheel...but zero ground or air speed and no air resistance or drag
Ah, except the wheel is NOT free spinning in this example. You are having to work to move the wheel against the conveyor belt. The difference is that on a bicycle (stationary or otherwise) propulsion is provided by the interaction between the wheel and the surface upon which it is riding. In the airplane, propulsion is provided independent of the surface. The thrust is coming from the engine/propeller and the interaction with the runway surface is inconsequential.
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) airplanes do not have power to the wheels. Airplane wheels are for rolling and stopping. The forces provided by the prop or jet engine move the airplane forward - thrust. You can pull the rug out all you want and the wheels will just spin in place. (Friction is never zero so eventually the airplane will begin to creep in the direction of the rug's motion, given no thrust, or more correctly, thrust less than the residual friction.) 
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