|
Post by Windknot on Feb 2, 2006 13:32:18 GMT -5
What? Is the Sexyloops board up and running? What the hell am I doing here then?
If you asked this question in the sixties you'd probably get 90% of 14 year old boys giving the correct answer. Back then they'd not only know what an aileron was, but what it did.
|
|
|
Post by ScottRods on Feb 2, 2006 13:37:03 GMT -5
The plane would take off if sufficient belt speed existed. The movement of the belt and the planes engines running will create airflow. Which will draw air over towards the wings from the front. If sufficient airflow is created, lift will occur when the airflow over the wings is less than the airflow under the wings (Bernoulii's principle).
|
|
|
Post by ScottRods on Feb 2, 2006 13:38:22 GMT -5
this is like being inside a plane at 340mph and you jump into the air, do you shoot to the back of the plane? Why not. Surely the plane moved forward in the microseconds you were in the air??
|
|
|
Post by ScottRods on Feb 2, 2006 13:38:58 GMT -5
or you walk forwards down towards the front of the plane - are you effectively walking at 344mph??
|
|
|
Post by flounder on Feb 2, 2006 14:07:03 GMT -5
The aircraft would take off as the wheels are not the driving force of the aircraft, the engines are. The wheels would rotate at whatever speed the convayor belt would go at and therefore would not slow down the aircraft. The engines 'push' against the air and therefore move it suffiently forward enough to create lift and thus making it take off. Basic prinicples of flight
|
|
|
Post by Dom on Feb 2, 2006 14:13:36 GMT -5
Scottrods. You don't fly to the back of the plane because you are travelling as fast as the plane. If you run forwards, you are running at say 4mph relative to the plane, or 344mph relative to the ground. It is all relative. (someone did a theory about this sort of thing I believe )
|
|
|
Post by elwyman on Feb 2, 2006 14:36:18 GMT -5
The answer is obviously no!
As someone said at the start of the thread, the plane doen't move relative to the ground and its airspeed is therefore 0 - if it doesn't move there is no uplift on the wing to make it fly. Unless it's a harrier jet.
It's like a treadmill, as TP said.
|
|
|
Post by flounder on Feb 2, 2006 14:55:05 GMT -5
As someone said at the start of the thread, the plane doen't move relative to the ground and its airspeed is therefore 0 - if it doesn't move there is no uplift on the wing to make it fly. But it would move because the engines (either prop or jet) would 'push' the jet along. The wheels are only there to facilitate the movement along the ground. They are not the driving force of the aircraft therefore could move slower of faster then the aircraft moves.
|
|
|
Post by dunc85 on Feb 2, 2006 14:55:17 GMT -5
It's like a treadmill, as TP said. But it's not! On a treadmill, you are powered by your legs. But with the plane, the wheels are just not affected by the conveyor, they just spin freely. The power, and forward thrust, comes from the engines.
|
|
|
Post by clockwork on Feb 2, 2006 14:58:17 GMT -5
The answer is obviously no! As someone said at the start of the thread, the plane doen't move relative to the ground and its airspeed is therefore 0 - if it doesn't move there is no uplift on the wing to make it fly. Unless it's a harrier jet. It's like a treadmill, as TP said. Oh it most certainly does move forward.. Why do people focus on the moving conveyor?? it is such an obvious red herring question, when the penny finally drops with you "no" people there will be some red faces listen very carrrfully I will sayy zis ooonly wunce more The conveyor does not have any pull on the plane it will not move backwards and the wheel will spin in free motion very fast Me roller skates moving pavement under me me remaining stationary with wheels spinning. me with big jet pack switched on me flying up the pavement byeeeeeeeeeeeeeeeeeeeeeeeeeeeee
|
|
|
Post by flounder on Feb 2, 2006 14:59:58 GMT -5
Exactly clockwork. Oh by the way. I work on aircraft lol
|
|
|
Post by Cumbrian on Feb 2, 2006 15:16:43 GMT -5
Here are my thoughts, for what they are worth ... For a plane to take off there must be sufficient forward thrust to overcome air resistance and resistance between the wheels and the runway (conveyor). In normal circumstances there will always be a nett forward thrust such that the plane will accelerate (Newton: f=ma). If there is no acceleration then the plane could never reach take-off speed. Given there is always acceleration and that the runway is long enough then the plane will eventually reach take-off speed (varies with wind conditions). – speed at which there is sufficient lift for take-off. If the plane can take off normally (i.e. generate sufficient thrust), what would be effect of this moving conveyor? The speed of the conveyor will increase as the speed of the plane increases. Thus as the forward speed of the plane increases thus the speed at which the wheels rotate will double. However, if the dynamic friction between the wheels and the conveyor is constant then no matter at what speed the wheels are turning there would be no increase in friction as the speed of the aeroplane (and conveyor) increases, so the plane would take of irrespective of the conveyor (in fact as speed increases then friction would reduce due to the effect of lift on the wings). The conveyor has no added effect once the plane has started moving forward. Notes: Static friction is greater than dynamic friction (it takes a greater force to start a body in motion than to keep it in motion once moving) Friction is independent of speed once an object is moving. Faster does not mean more friction. See: hypertextbook.com/physics/mechanics/friction/Given that I was always better at Statics than Dynamics the above could be flawed, I am willing to learn ... but PLEASE let's not turn this into a war as on the old forum and the "Dynamics of Fly Casting", Airflo vs Sexyloops - what an introduction to a forum that was (and you think some disputes are bad now ;D )
|
|
|
Post by "Squatter" on Feb 2, 2006 16:24:07 GMT -5
Ok try this one out..........................
Here is what is given:
There is air Bernoulli's principal still works The plane is unmodified. The treadmill is setup to track the speed of the airplane(not wheels, not to negate thrust)
What is Assumed:
There is air resistance rolling resistance bearing resistance inertia The "speed measuring device" is interpreted as measuring relative to a static point, or for the sake of this experiment a post at the starting line which is anchored into the ground and cannot and does not move from it's position. The treadmill's belt is perfectly level. The treadmill speed measuring device is a real world model which samples speed every 1/60th of a second. Real World scenario items: Boeing 747-100 with a mechanical weight of 324800 lbs. (Plus the weight of 183,380 L of fuel.. Fully filled) Timken equivalent model LM229110 wheel bearings which has a known coefficient of friction of between 0.0015 and 0.002 The aircraft is fitted with 4 Pratt & Whitney JT9D with 46,985.0691lbs of maximum thrust each. (About 187940lbs of total thrust) Rolling resistance is minimized due to the tires being pressurized to about 3150psi and filled with nitrogen. Due to the pressure there isn't much of a contact patch with the ground. Since the experiment does not call for turning there will be no lateral dynamic friction calculations. Wind is calm and temperature is a balmy 70 degrees Fahrenheit.
Conditions:
The throttle to the 747 is set to full throttle thus unleashing the full 187940lbs of thrust out of the back of the plane. If total static friction = static coefficient of friction in Newtons plus static rolling coefficient of friction in N (f+fR=TìN): f = 0.002N per wheel. There are 16 wheels on a 747 Total static friction = 0.036 Newtons Applied force F = 836kN Rolling Friction fR (derived from reliable rubber tire experiments) = 0.8N per wheel. Total fR = 12.8 Force required to overcome static friction f = 0.036N Force required to overcome static rolling friction fR = 12.8N Total Applied Force required to overcome total friction = 13.196N Since F is significantly greater than Tì, even with a severe margin for error, friction is easily overcome. The aircraft begins to move forward with nothing significant holding it back. As soon as the aircraft begins to move, we now refer to wheel and tire friction as kinetic coefficient of friction (0.0015) and dynamic rolling friction (0.06) As the aircraft begins moving, the sensors measure the speed and begin moving the treadmill in the opposite direction and the same speed as the aircraft relative to the post(static reference point).
Effects:
The aircraft has reached 10mph The sensory device senses this and adjusts the belt speed to 10mph in the opposite direction relative to the post(static reference point) The aircraft's wheels are now spinning at the additive speed of 20mph. The wheel gets it's 20mph from the belt spinning 10mph relative to the static reference point. However the belt is moving 20mph relative to the plane from which it derives it's own speed. The wheel is connected to the plane and is also moving through space. No extra resistance has been encountered. The coefficient of friction of the wheels is now kinetic coefficient of friction, which tends to be significantly lower than static COF. The rolling resistance of the tires is reduced as speed increases as the tire due to rotational velocity becomes harder and pushes up ever so slightly off the belt more lowering the contact patch and lowering rolling friction.
Conclusion:
Nothing to stop us now!
No further resistance can be gained from the wheels Drag is being experienced as speed increases The aerodynamic drag is being experienced by moving an object through a fluid(atmosphere). This drag also includes the drag force caused by the vector motion translation of lift generated by the wings moving through the air. The aircraft is already designed to overcome this drag. This is a proven fact because we all know that a 747-100 can fly. The aircraft reaches 180mph and lifts off. The minimum speed for lift-off of a 747-100 is 180mph unloaded Once the speed of the air moving over the wings induces the Bernoulli effect so that the force of lift is greater than the force the aircraft exerts on the ground due to gravity, the aircraft will now lift off of the ground. The wheels are now spinning at 360mph As illustrated before, the wheel gets it's speed due to the belt moving in the opposite direction but same speed as the aircraft relative to the static reference point. The speed of the wheel is still well within the mechanical tolerances of all parts involved. Aircraft has now lifted off.
________________________________________________________________________________________
Scenario 2
Here is what is given:
There is air Bernoulli's principal still works The plane is unmodified. The treadmill is setup to track the speed of the airplane(not wheels, not to negate thrust)
What is Assumed:
There is air resistance rolling resistance bearing resistance inertia The "speed measuring device" is interpreted as measuring relative to the aircraft. The treadmill's belt is perfectly level. The treadmill speed measuring device is a real world model which samples speed every 1/60th of a second. Real World scenario items: Boeing 747-100 with a mechanical weight of 324800 lbs. (Plus the weight of 183,380 L of fuel.. Fully filled) Timken equivalent model LM229110 wheel bearings which has a known coefficient of friction of between 0.0015 and 0.002 The aircraft is fitted with 4 Pratt & Whitney JT9D with 46,985.0691lbs of maximum thrust each. (About 187940lbs of total thrust) Rolling resistance is minimized due to the tires being pressurized to about 3150psi and filled with nitrogen. Due to the pressure there isn't much of a contact patch with the ground. Since the experiment does not call for turning there will be no lateral dynamic friction calculations. Wind is calm and temperature is a balmy 70 degrees Fahrenheit.
Conditions:
The throttle to the 747 is set to full throttle thus unleashing the full 187940lbs of thrust out of the back of the plane. If total static friction = static coefficient of friction in Newtons plus static rolling coefficient of friction in N (f+fR=TìN): f = 0.002N per wheel. There are 16 wheels on a 747 Total static friction = 0.036 Newtons Applied force F = 836kN Rolling Friction fR (derived from reliable rubber tire experiments) = 0.8N per wheel. Total fR = 12.8 Force required to overcome static friction f = 0.036N Force required to overcome static rolling friction fR = 12.8N Total Applied Force required to overcome total friction = 13.196N Since F is significantly greater than Tì, even with a severe margin for error, friction is easily overcome. The aircraft begins to move forward with nothing significant holding it back. As soon as the aircraft begins to move, we now refer to wheel and tire friction as kinetic coefficient of friction (0.0015) and dynamic rolling friction (0.06)
Conclusions:
If the speed monitor is measuring relative to the airplane then the belt simply doesn't move since as the plane moves forward, the belt is already moving backwards relative to the plane, in the opposite direction, and the same exact speed. What we're talking about here folks is a normal airplane and a normal tarmac runway. So of course it will fly!!!
Keep on smiling Mike
|
|
|
Post by The Famous Grouse on Feb 2, 2006 16:25:01 GMT -5
The plane would not take off.
In order to fly, the airfoils (wings) of an airplane must generate enough lift to support the weight of the aircraft. The greater the speed of the air moving across the airfoil, the greater the lift that is generated (Bernoulli's principle).
To move air across the airfoil, an airplane creates thrust. It draws itself forward through the air, thus the air passes over the wing.
Assuming no other movement of air is influencing this equation, if a conveyer belt was moving at 60 mph and the aircraft was generating forward thrust such that it was staing in a fixed position on the conveyer belt, there is no air movement over the wing. Hence there is no lift and the airplane would not fly.
As an aside, I have actually flown an airplane backward. I was flying one day in a Cessna 152 and encountered some high winds. Just for fun, I pointed the nose straight into the wind, put the flaps down, and idled the engine.
With the yoke pulled all the way back the airplane would not stall. The wind was moving across my wings at a speed greater than the 50 knot stall speed of the airplane. The airplane simply continued to fly.
But when I looked at the ground, I was moving backward! I was actually flying "in reverse", moving away from the direction I was pointing. Talk about disorienting. I think I'd have been sick if I'd have kept looking down.
This is the difference between airspeed and ground speed. Airspeed is the speed of the air moving across the airfoil. Ground speed is your speed over fixed points on the ground. I was flying at 50 some knots of airspeed and -5 MPH ground speed.
Grouse
|
|
|
Post by Trout on Feb 2, 2006 16:28:08 GMT -5
If the plain is stationary. It aint gonna move!!
|
|