will it take off?

[patrick_g]

Regarding the bowline... Besides there being both a cowboy bowline and a sailor bowline (AKA innie and outie) there are several variants of bowlines like the tugboat bowline, anchor bowline etc.

The reason (excuse) for my bowline example was to OPEN SOME MINDS to possibilities beyond ones own self inflicted myopia. This holds for the classroom example as well as the will it fly thing.

You may note that some of us are still doggedly (and relatively mindlessly) holding onto one position or the other, clutching to their hearts, assumptions (not necessarily stated in the problem but just plucked from somewhere) and think those of opposite persuasion are daft at best.

Guys, get over it, depending on assumptions and definitions, EITHER can be right OR wrong. Until and unless all the definitions and assumptions are teased out and agreed upon, arguing at cross purposes just wastes time.

Once you accept the MAGIC CONVEYOR the plane is doomed by the laws of physics to never take off. So long as you conveniently restate the problem in your own terms to nullify the magic conveyor (voiding the contract so to speak) you can easily make the plane take off.

This was a thought experiment not a trial such as performed by the Myth Busters whose truck pulling the "conveyor" was NOT equivalent to a MAGIC CONVEYOR. A comparison of apples to light bulbs. The one has NO BEARING on the other.

There currently exists no technology to even get close to building an actual real conveyor that will interfere with the take off of an airplane capable of taking off with no conveyor involved. So, for any realists with limited imagination and limited visualization ability who can't wrap their minds around the concept of the "MAGIC CONVEYOR", clearly the plane will always take off. For the rest of us who can grasp the concept of the "MAGIC CONVEYOR" we can see that the plane could theoretically be prohibited from taking off. This second position has absolutely nothing to do with reality and is just the result of applying simple physics to a theoretical situation to determine what would happen IF a "MAGIC CONVEYOR" could be built.

Now, as regards the helo on the turntable. If the turn table rotates at the same speed as the rotor but in opposite direction then the blade is standing still in the air mass and the relative wind over the blades is zero and so there is zero lift. Collective and cyclic pitch are not effective in the least when there is no airflow over the airfoil.

The model with the little engine mounted to the rotor has been around for decades and decades in one form or another. I have even flown a freeflight lampshade with a model airplane engine mounted vertically. You need fins inside the "duct" to cancel torque induced rotation or centrifugal force can increase to the point of disturbing fuel flow.

Pat

 

[RobS]

Just to throw a stick in the ocean of theoretics:

Replace the wheels with skis (or ice skates) and ice the belt. There just went all the energy being applied to spinning up wheels, etc.

Harry K

Ah, but are you using the special, frictionless skis or the regular ones? In physics class we always joked about the frictionless pulleys and massless string at the campus bookstore. Never found that aisle...

 

[Egon]

Darned, and here I thought a car on the dyno was going to go somewhere!!

 

[RobS]

Regarding the bowline... Besides there being both a cowboy bowline and a sailor bowline (AKA innie and outie) there are several variants of bowlines like the tugboat bowline, anchor bowline etc.


Pat

As a young boy scout I was taught the traditional rabbit/hole method of tying a bowline (I have no idea which version). I always struggled with that method then along came a wise scoutmaster who proclaimed that you will have no time for a rabbit/hole when you are dangling off the side of a cliff. He taught a one handed version that allowed you to keep one hand on the long end of the rope at all times. Quick too. To this day, I cannot tie a bowline using the rabbit/hole but can tie one in the dark without ever removing my hands from the rope using his method.

 

[SPYDERLK]

Just to throw a stick in the ocean of theoretics:

Replace the wheels with skis (or ice skates) and ice the belt. There just went all the energy being applied to spinning up wheels, etc.

Harry K

nope. wheels are an unambiguous stipulation of the original boundary conditions. But, while were playing why dont we fool with things that arent stipulated. What about gravity? no gravity no downforce on the conveyor, no traction. The wheels are skis. You can get enuf lift even sitting still for a takeoff just by blowing air over the wings. but why is there air?
larry

 

[SPYDERLK]

There currently exists no technology to even get close to building an actual real conveyor that will interfere with the take off of an airplane capable of taking off with no conveyor involved.
Pat

I would think yould disagree with this statement.
larry

 

[Iplayfarmer]

Regarding the bowline... Besides there being both a cowboy bowline and a sailor bowline (AKA innie and outie) there are several variants of bowlines like the tugboat bowline, anchor bowline etc.

The reason (excuse) for my bowline example was to OPEN SOME MINDS to possibilities beyond ones own self inflicted myopia. This holds for the classroom example as well as the will it fly thing.

You may note that some of us are still doggedly (and relatively mindlessly) holding onto one position or the other, clutching to their hearts, assumptions (not necessarily stated in the problem but just plucked from somewhere) and think those of opposite persuasion are daft at best.

Guys, get over it, depending on assumptions and definitions, EITHER can be right OR wrong. Until and unless all the definitions and assumptions are teased out and agreed upon, arguing at cross purposes just wastes time.

Once you accept the MAGIC CONVEYOR the plane is doomed by the laws of physics to never take off. So long as you conveniently restate the problem in your own terms to nullify the magic conveyor (voiding the contract so to speak) you can easily make the plane take off.

This was a thought experiment not a trial such as performed by the Myth Busters whose truck pulling the "conveyor" was NOT equivalent to a MAGIC CONVEYOR. A comparison of apples to light bulbs. The one has NO BEARING on the other.

There currently exists no technology to even get close to building an actual real conveyor that will interfere with the take off of an airplane capable of taking off with no conveyor involved. So, for any realists with limited imagination and limited visualization ability who can't wrap their minds around the concept of the "MAGIC CONVEYOR", clearly the plane will always take off. For the rest of us who can grasp the concept of the "MAGIC CONVEYOR" we can see that the plane could theoretically be prohibited from taking off. This second position has absolutely nothing to do with reality and is just the result of applying simple physics to a theoretical situation to determine what would happen IF a "MAGIC CONVEYOR" could be built.

Now, as regards the helo on the turntable. If the turn table rotates at the same speed as the rotor but in opposite direction then the blade is standing still in the air mass and the relative wind over the blades is zero and so there is zero lift. Collective and cyclic pitch are not effective in the least when there is no airflow over the airfoil.

The model with the little engine mounted to the rotor has been around for decades and decades in one form or another. I have even flown a freeflight lampshade with a model airplane engine mounted vertically. You need fins inside the "duct" to cancel torque induced rotation or centrifugal force can increase to the point of disturbing fuel flow.

Pat

Despite your long list of qualifications, certifications, and your sophistocated terms, Pat, I'm still going to disagree, even in the "Magic Conveyor" World.

The major falacy that I see in the "It will fly" camp is that they insist on imposing magical properties on the conveyor but at the same time insist on leaving the wheels of the plane in the real world in which we live.

Why are the bearings, etc. of the plane wheels subject to heat, friction, and failure, but the bearings, motors, belts, etc. of the conveyor are not?

More later about how the concept of the magic conveyor is inherently contradictory... I just got asked to make dinner.

 

[bx23barry]

Re: Mythbusters/airplane/treadmill

As stated, I watched Kansas State put the kabosh to previously unbeaten Kansas last night and have not gone back to watch the episode. That will be a project for THIS evening. I had no doubt that the plane would take off though. So.. did anyone go resurrect the old thread yet? lmao Surely there must be a thousand or more "I told you so's" in order...

I told ya so

 

[SFish]

patrick_g:

You said "Again, depending on the definitions of terms and ignoring the current state of the art in building conveyors and airgraft wheels/tires/axles, you picks your definitions and you gets your answer. Either contention can be supported, depending on your assumptions." I am very curious what the assumptions you see that would prevent takeoff.

The original post conditions are a plane on top of a conveyer like device that rolls its surface backward at exactly the speed the plane is moving forward. This is not a complicated device, certainly not magic.

By the way, my favorite teaching bowline is collapsing a slip not (simple noose) made back from the working end after putting the working end through the loop of the noose.

Steve

 

[SPYDERLK]

The major falacy that I see in the "It will fly" camp is that they insist on imposing magical properties on the conveyor but at the same time insist on leaving the wheels of the plane in the real world in which we live.

[[[Why are the bearings, etc. of the plane wheels subject to heat, friction, and failure, but the bearings, motors, belts, etc. of the conveyor are not?]]]

[[[ I dont recall anyone saying that. I doubt that those who understand what is involved here would say it.]]] Actually tho, magical wheels would be wonderful and would assure that the magical conveyor could keep the plane on the ground forever. -- just so the wheels magicalness did not include causing them to be massless, or causing them to have a moment of inertia of zero.
larry

 

[Iplayfarmer]

[[[ I dont recall anyone saying that. I doubt that those who understand what is involved here would say it.]]] Actually tho, magical wheels would be wonderful and would assure that the magical conveyor could keep the plane on the ground forever. -- just so the wheels magicalness did not include causing them to be massless, or causing them to have a moment of inertia of zero.
larry

I'm referring to the implication that the conveyor is able to accelerate infinately assuming that it overcomes the phenomenal friction of it's own bearings but the wheels are not able to overcome the consequent friction on their bearings and somehow the drag pulls the plane backwards overcoming the force of the thrust.

I'm still waitin for the backlash as to how this question is so much different from the "Rooster's Egg" or "Where do you bury the survivors" http://www.tractorbynet.com/forums/owning-operating/90325-will-take-off-82.html#post132104

 

[Egon]

All night I have been lying awake. Sleep would not come. Mayhaps it was the incoming rain. Anyways lots of time to think.

Here we have a solution to the worlds shortest runway. Instead of a conveyor belt we use rollers like on a dyno. Run them up to the takeoff rotational speed and then open all the throttles. The plane should instantly raise into the air and fly away. This should really alleviate some of the congestion at real busy airports!

I'm on my way to the patent office, fortunes must await me.

 

[Tororider]

I haven't read the whole thread, but just wanted to make sure that you all saw that the Mythbusters did a show on this myth.

The plane will fly. It will take off like normal. The reason being the plane gets no thrust from its wheels like a car. If you put a car on a treadmill and match the forward speed of the car to the treadmill the car will stay in one spot.

Do the same thing with a plane, try to match the forward speed of a plane to a treadmill and the plane will continue on at the normal speed. Unlike a car a plane gets its thrust from its propeller/jet. I am not sure about the wheels speed, but I would guess the wheels would spin twice as fast as normal until the moment of liftoff. But as proved on Mythbusters, the plane WILL take off.

 

[SPYDERLK]

I'm referring to the implication that the conveyor is able to accelerate infinately assuming that it overcomes the phenomenal friction of it's own bearings but the wheels are not able to overcome the consequent friction on their bearings and somehow the drag pulls the plane backwards overcoming the force of the thrust.

I'm still waitin for the backlash as to how this question is so much different from the "Rooster's Egg" or "Where do you bury the survivors" http://www.tractorbynet.com/forums/owning-operating/90325-will-take-off-82.html#post132104

Inevitably some of the counterforce will be due to friction, but actually the counterforce Pat and I have described comes from inertia - the resistance that the wheel mass has to being rotationally accelerated.

As for the others, Icant see any relation to physics in them, but with the rooster you are dealing with a probabilistic situation. Everything stated is improbable, and if improbability had inertia, a train of astounding events that long may drive the result. Hence the egg would never fall. -- The survivors would be buried in the ground.
larry

 

[kozak]

Plane is stationary therefore.......is NOT fly !! The simple answer is normally correct so......I must be right !!

Vic

 

[Runner]

It is....ALIVE....

I couldn't wait for this thread to be brought back, just so I, as a licensed pilot, could give my opinion that the plane will take off.

 

[David Cockey]

The plane will take off.

Speed relative to air is what matters for lift and thrust, not speed relative to the ground. The airplane accelerates due to the thrust of the jet engines and/or propellers, and when the lift exceeds the weight of the airplane it will lift off. Lets call that air speed Vto. When the plane reaches Vto the conveyor/runway will be moving relative to the airplane with speed 2 X Vto.

Any boundary layer effects from the moving ground (and on an actual airplane designed for normal takeoffs they would be small at the height of the wing) would only increase the speed of the air relative to airplane similar to a light headwind. This actually means the airplane will lift off at a slower speed relative to a fixed reference.

The rolling resistance (force) of tires increases only slightly with speed. So with the runway speed twice normal the power consumed by the tires would be only twice that of a normal takeoff. The power required to overcome the rolling resistance of the tires is very small compared to the power required to overcome the aerodynamic of the lifting wing. Assuming the airplane is "real" there will be plenty of power to overcome the added resistance of the rolling tires. And once the airplane lifts off the rolling resistance vanishes.

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

 

[RobS]

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

Welcome to the board David. As you might imagine, it's all those nuances that have kept this thread alive for as long as it is! Interesting reading, if nothing else.

 

[SPYDERLK]

The plane will take off.

Speed relative to air is what matters for lift and thrust, not speed relative to the ground. The airplane accelerates due to the thrust of the jet engines and/or propellers, and when the lift exceeds the weight of the airplane it will lift off. Lets call that air speed Vto. When the plane reaches Vto the conveyor/runway will be moving relative to the airplane with speed 2 X Vto.

Any boundary layer effects from the moving ground (and on an actual airplane designed for normal takeoffs they would be small at the height of the wing) would only increase the speed of the air relative to airplane similar to a light headwind. This actually means the airplane will lift off at a slower speed relative to a fixed reference.

The rolling resistance (force) of tires increases only slightly with speed. So with the runway speed twice normal the power consumed by the tires would be only twice that of a normal takeoff. The power required to overcome the rolling resistance of the tires is very small compared to the power required to overcome the aerodynamic of the lifting wing. Assuming the airplane is "real" there will be plenty of power to overcome the added resistance of the rolling tires. And once the airplane lifts off the rolling resistance vanishes.

I didn't bother to read all the messages in this string, so I may have missed some claimed nuance. But the basic physics are as above.

Qualifications upon request.

Welcome to the thread David. Nothing wrong with what youve deduced. However, there is another way of looking at this which makes more complete use of the physics. It is essentially an extrapolation of the conveyors effect on the situation. I believe it came up to counter the false claim that the conveyor could have no inhibiting effect on the thrust of the plane. The physics of this counter thrust via rotational acceleration of the wheels is described pretty well starting about 1/3 of the way in the thread in the 300's. I dont believe many understand it.
larry