How about go old normal one object A pushing object B. In this case the wheel is pushing on the axle.
How about go old normal one object A pushing object B. In this case the wheel is pushing on the axle.
- Mar 20, 2000
- 102,402
- 8,572
- 126
without electro-magnetic, the atoms would all just collapse into a big morass.
without strong nuclear, the protons wouldn't bind together and all we'd have is hydrogen.
i'm not really sure what weak nuclear's effect is, binding quarks i guess.
and without gravity, well, the plane would just hover above the runway. er, conveyor belt. and then there is no question the plane would take off.
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
1) The rotational energy in the wheels does not contribute to linear forces in the plane, other than a neglible amount due to bearing drag against the axles.
2) The wheel speed is bounded by 2x the take off velocity of the model of plane in question. The plane will be at it's equilibrium velocity when the wheels reach that speed. For example a 747 will have a forward air speed of 180 mph, a wheel speed of 360 mph, and the treadmill will have a speed of -180 mph at the moment the pilot points the nose up.
The plane pushes on the wheel horizontally through its axle, while the contact patch resists that forward movement tangent to the wheel surface, this causes a net torque and allows the wheel to rotate at the speed that the plane moves forward. The treadmill then pulls the wheel from its contact patch in the opposite direction of the force applied through the foward movement of the axle, adding to the wheel speed.
Push a toy car with sticky wheels (no sliding) on a sheet of paper on a table. Pull the paper out from under the car at the same time you are pushing the car forward. You have forces acting on the wheel. Add up the velocities. The wheels spin faster and the cars forward movement doesn't change.
This is true for the energy applied to the treadmill. Not true for the planes engines.
It doesn't matter. There is no force exerted by the wheels which counteracts the thrust created by the propeller. So, let's go over this. There is the force of gravity on the plane. There is the (variable) force of lift from the wings. There is a very large component of force forward due to the propeller..... and that's all. The bearing has prevented the rotational motion of the wheels from translating to the body of the plane, so there is no force in the reverse direction.
Again your an idiot. Bearing reduce the friction but they don't have anything to do with the force required to change the speed of a wheel. Just like changing the speed of a car requires an input of energy so does changes the rotational speed of a wheel.
Ok we are talking about different case. I'm assuming that the treadmill will matches the speed of the plane relative to the treadmill.
OK, imagine you have a bearing in your hand with an axle going through the center. Now, spin the axle in your hands... does the bearing move forwards or backwards?
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
That falls under electromagnetic force. The force of the electron bonds in molecular structures in each object binding and repelling keeps the lattice structure of the substance tight and rigid.
The electron bonds of +/- attractions holding two molecules close together resist any collision with other materials, like a net, and the resulting elastic movement between bonds and friction between molecules creates heat energy at the site of the collision.
Unless of course you have enough kinetic energy, ie: a bullet, the resulting molecule and bond collisions is greater than the stored electron energy, thus ripping about the molecular structure on a grand scale, and visibly distorting the object. You can also have an object with a very strong molecular structure collide with a weak structure, and like a baseball through a house of cards or a key across a paint job, the weaker structure will yield because its bonds are very weak.
All forces except for gravity that we experience on a daily basis are due to electromagnetic attraction and repulsion. This is what makes our world solid and allows Newtonian mechanics to exist.
Cerpin Taxt
Lifer
- Feb 23, 2005
- 11,940
- 542
- 126
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
Same effect as yanking a sheet of paper out from under a toy car as you push it with your hand. The speed of the wheels IS the speed of the plane relative to the treadmill. If the plane is moving 180 mph along a stationary treadmill, you would increase the speed of the treadmill to -180 mph, correct? Treadmill matches the speed of the plane, but in opposite direction. This is similar to two people in a western gun fight back to back and pacing away from each other at the same speed. Both of them moving at equal speeds in opposite directions will result in doubling the speed that the distance between them increases. The plane and treadmill can both always be the same exact speed but in opposite directions, and the plane, and a fixed point on the treadmill will move apart from each other at twice that speed, both covering the same distance from a fixed starting point on the ground.
Tie a box to the treadmill and butt it up against the back of the plane, free to coast on its wheels. Move the plane 1 meter forward in 1 second, and move the treadmill 1 meter in one second. The box and plane will both be 1 meter from their starting positions and 2 meters apart from each other. The wheels on the plane will have traveled at a speed of 2 meters per second in 1 second.
Make sense yet?
Imagine holding an axle with two wheels attached on either end. Rest the wheels on a treadmill and keep your hand steady. The wheels will rotate as the axle stays stationary, correct?
Now push the axle forward with your hand. The axle and wheels will move forward and the wheels will spin faster than before, even though the treadmill is going in the opposite direction.
This is how the airplane is able to take off. Instead of your arm pushing an axle, it is a plane engine pushing a plane. Both are not being pushed by the wheels.
Now push the axle forward with your hand. The axle and wheels will move forward and the wheels will spin faster than before, even though the treadmill is going in the opposite direction.
This is how the airplane is able to take off. Instead of your arm pushing an axle, it is a plane engine pushing a plane. Both are not being pushed by the wheels.
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
Planes do not 'move air' or 'blow air across the wings'. Planes push themselves against the air with thrust far less than the weight of the plane, relying on the forward motion of the wings through the air to generate lift. It's like sweeping your hand through the water at the right angle; with only movement in the horizontal plane your hand feels an upforce due to principles of fluid dynamics (of which aerodynamics is a specific class of fluid dynamics that deals with air and flight, particularly in the Earth's atmosphere).
There are few exceptions, such as the F-15 which has a thrust to weight ratio so high that it can pretty much fly like a rocket on thrust alone, even accelerating straight up. It doesn't really even need wings other than for directional control. An F-15 has almost 60,000 lbs of thrust and the unarmed plane weights 30,000 lbs with 2,000 lbs of JP8 in the tanks. Compare that to a 747 which is 800,000 lbs and generates about 220,000 lbs of thrust. This is why the 747 has such large wings and relys on wing lift rather than engine power. You could not fly a 747 straight up or perform a loop, it would start to stall out and lose air speed and level itself out.
If you've heard of the term 'stall speed' this has nothing to do with the engines, but with the speed at which the lift generated by the wing design is no longer greater than or equal to the weight of the plane. The engines only need be powerful enough to overcome air resistance drag encountered by the plane as it keeps the planes forward velocity greater than or equal to the stall speed. As the wings attached to the plane are forced through the air by that forward motion, they manipulate the air in a way that produces lift in the same way as the hand in water example. Variable geometry such as flaps, and angle of attack also come into play as much as the shape of the fixed portion of the wing.
In this case the treadmill's movement simply slips against the wheel bearings and rotates the wheels faster, the plane is still able to push itself against the surrounding air with it's engines and gain the required forward speed for the wing design to work. On a 747, the wings generate enough lift to reach equillibrium against the 800,000 lb weight of the plane with only 180 mph of forward movement. At this point there is no weight on the landing gears.
Think about a plane, with rockets instead of turbofans, out in space. Spin the wheels up as fast as you can in either direction at any speed you want. Even give the plane a push backwards so that it may continue backwards indefinately. Ignite the rocket engines, and the plane will slow down, then reverse direction and start heading forward, regardless of what the wheels are doing. A turbofan jet engine pushes on the surrounding air in an enclosed atmosphere in the same way that a rocket pushes itself on the rocket exhaust byproducts.
What the wheels are doing or what they are in contact with absolutely do not matter, provided they are rolling or not snagging on something, in which case they would just be torn off by the jet thrust. The wheels free spinning on any surface at any speed have little effect on the acceleration of the plane in the horizontal plane. The constant force of the engines will eventually accelerate the plane to its stall speed and beyond and cause the plane to lift off the ground. If the plane was kept still and started going backwards on the conveyer (no rolling of the wheels occuring), it would just take longer and take more runway, because with constant acceleration, it would have to go from -180 mph to +180 mph instead of 0 to 180 mph. It would still be the same force, the same power output, just applied over a longer time to overcome rearward inertia first.
Spinning the wheels faster does not impart any significant drag to the plane in opposition to the engines, that is what the axles and bearings are for. In fact, the faster the plane begins to move foward, the less drag there is on the axles because as the wings build up lift, the weight of the plane decreases and the normal forces involved in friction decrease.
BoomerD
No Lifer
- Feb 26, 2006
- 66,260
- 14,689
- 146
"Splain this to me...if the treadmill moves in reverse fast enough to counter the plane's forward thrust, where is the lift going to come from? Yes, the plane's motors/engines may move it in a forward direction (now countered by the treadmill, the there would be no forward movement through the air to generate the necessary lift....so, everyone who says the plane takes off, what am I missing?
(/me knows zip about physics, but understands mechanics)
(/me knows zip about physics, but understands mechanics)
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
The part I bolded is wrong, that's what is missing.
The treadmill does not act on the plane, it acts on the free spinning wheels, and by doing so imparts little and negligible drag via rolling friction. The planes engines can more than compensate for this rolling friction because they are designed to overcome aerodynamic drag in flight, a force far greater in magnitude than that of the wheel friction while rolling on the ground.
Standing on a treadmill on a skateboard and having someone give you a hard push while someone else cranks the speed up on the treadmill will just smoke the wheels, it wont stop you from flying off the front of the treadmill.
Or as I've said in countless examples, push a toy car or plane across a table on a sheet of paper by applying a constant force with your hand (use a scale between your hand and the car to verify that you hold this pushing force constant). As you push the car, pull the paper out from under it and behind it while watching the scale and observe that the scale reading changes little (ie: the force of the paper going backwards adds little to no rearward force to the vehicle), the car continues moving forward, and the wheels scream for a few seconds. The vehicle continues moving forward.
On a plane, this means lift.
Another example:
You have an aquarium on the front seat of your car (or rear seat, roof, wherever you want).
In the aquarium, you have a fish.
You drive down the road; for the sake of the example, let's say you are going North at a speed of 55 MPH.
With the fish maintaining its position in the aquarium, it is going 55 mph relative to the road, and nominally zero mph relative to the bottom of the aquarium.
If the fish swims North at one half mile per hour, it is doing 55.5 mph relative to the road, and 0.5 mph relative to the bottom of the aquarium.
If you accelerate or decelerate the car in a controlled fashion, and the fish is maintaining position in the aquarium, it doesn't matter: To the fish, the water isn't moving.
The same scenario applies to the air mass that the airplane exists in. The treadmill does not affect the air mass. When propelled from the front by a propeller, of from the rear by a propeller, jet, or rocket, the force is applied to the air mass, not the treadmill belt. The wheels, skis, or skids are only there as a bearing surface. The friction/drag induced by the wheels, skis, or skids has no practical affect to the motivational force applied by the power system of the airplane to the air mass that contains it.
This effect is seen with most takeoffs and landings of all airplanes. Whenever possible, airplanes take-off and land into the wind. This maintains the airspeed but reduces the groundspeed (it reduces the wear & tear on the mechanical parts ... pilots are notoriously cheap). Landing with the wind has the opposite effect; groundspeed increases (airspeed plus the speed of the air mass), but the airspeed (plane relative to the air mass) stays the same.
The apparent wind that the wing sees is all that counts. A treadmill belt does not affect the apparent wind that the wing sees, only the ground speed seen by the wheels when they contact the surface.
There is no "wind" to a flying aircraft; they are part of the air mass, just like the fish is part of the water it is swimming in.
I know this won't clear the issue up with the non-taker-offers, but I thought I'd put it out there for the mearly confused.
Also, just because the statement bothered me ... a propeller does not (and is not supposed to) created enough wind to generate lift to the wings; it provides propulsion by "screwing" itself into the airmass (as pointed out many, many posts ago) just like a trolling (no pun intended) moter clamped to the front of a boat is not supposed to push water under a boat to move it forward .... it "screws" itself into the water to create the propulsion.
FWIW
Scott
You have an aquarium on the front seat of your car (or rear seat, roof, wherever you want).
In the aquarium, you have a fish.
You drive down the road; for the sake of the example, let's say you are going North at a speed of 55 MPH.
With the fish maintaining its position in the aquarium, it is going 55 mph relative to the road, and nominally zero mph relative to the bottom of the aquarium.
If the fish swims North at one half mile per hour, it is doing 55.5 mph relative to the road, and 0.5 mph relative to the bottom of the aquarium.
If you accelerate or decelerate the car in a controlled fashion, and the fish is maintaining position in the aquarium, it doesn't matter: To the fish, the water isn't moving.
The same scenario applies to the air mass that the airplane exists in. The treadmill does not affect the air mass. When propelled from the front by a propeller, of from the rear by a propeller, jet, or rocket, the force is applied to the air mass, not the treadmill belt. The wheels, skis, or skids are only there as a bearing surface. The friction/drag induced by the wheels, skis, or skids has no practical affect to the motivational force applied by the power system of the airplane to the air mass that contains it.
This effect is seen with most takeoffs and landings of all airplanes. Whenever possible, airplanes take-off and land into the wind. This maintains the airspeed but reduces the groundspeed (it reduces the wear & tear on the mechanical parts ... pilots are notoriously cheap). Landing with the wind has the opposite effect; groundspeed increases (airspeed plus the speed of the air mass), but the airspeed (plane relative to the air mass) stays the same.
The apparent wind that the wing sees is all that counts. A treadmill belt does not affect the apparent wind that the wing sees, only the ground speed seen by the wheels when they contact the surface.
There is no "wind" to a flying aircraft; they are part of the air mass, just like the fish is part of the water it is swimming in.
I know this won't clear the issue up with the non-taker-offers, but I thought I'd put it out there for the mearly confused.
Also, just because the statement bothered me ... a propeller does not (and is not supposed to) created enough wind to generate lift to the wings; it provides propulsion by "screwing" itself into the airmass (as pointed out many, many posts ago) just like a trolling (no pun intended) moter clamped to the front of a boat is not supposed to push water under a boat to move it forward .... it "screws" itself into the water to create the propulsion.
FWIW
Scott
exdeath
Lifer
- Jan 29, 2004
- 13,679
- 10
- 81
Further proof...
When practicing landing it is common to perform what is called a 'touch and go' where you make a complete landing, all wheels make contact with the ground and begin to roll, but instead of backing off the throttle you keep it full power with the flaps full up holding you down (like a spoiler on a car), rolling down the runway. You can maintain this for the entire length of the runway, with the plane going forward and the ground moving backwards, and rotating the wheels the whole time. This has no effect on the planes forward velocity, and you can pull up and climb away as soon as you reach the end of the runway, or any time you want, with the wheels still freely spinning.
Being in a plane with a stall speed of 150 mph or 300 mph will change the speed at which you roll the wheels along the ground, but again, the speed the wheels are rolling, or that the wheels are even touching the ground, has no effect on the plane mainting its forward velocity under engine power.
When practicing landing it is common to perform what is called a 'touch and go' where you make a complete landing, all wheels make contact with the ground and begin to roll, but instead of backing off the throttle you keep it full power with the flaps full up holding you down (like a spoiler on a car), rolling down the runway. You can maintain this for the entire length of the runway, with the plane going forward and the ground moving backwards, and rotating the wheels the whole time. This has no effect on the planes forward velocity, and you can pull up and climb away as soon as you reach the end of the runway, or any time you want, with the wheels still freely spinning.
Being in a plane with a stall speed of 150 mph or 300 mph will change the speed at which you roll the wheels along the ground, but again, the speed the wheels are rolling, or that the wheels are even touching the ground, has no effect on the plane mainting its forward velocity under engine power.
TRENDING THREADS
-
Discussion Zen 5 Speculation (EPYC Turin and Strix Point/Granite Ridge - Ryzen 9000)- Started by DisEnchantment
- Replies: 25K
-
Discussion Intel Meteor, Arrow, Lunar & Panther Lakes + WCL Discussion Threads
- Started by Tigerick
- Replies: 22K
-
News NVIDIA and Intel to Develop AI Infrastructure and Personal Computing Products- Started by poke01
- Replies: 384
-
Discussion Intel current and future Lakes & Rapids thread- Started by TheF34RChannel
- Replies: 23K
Facebook
Twitter