This Should Leave Your Brain In A Knot- Part 2!

[OCBob]

I think Smoke is right. The thrust of the engines is not moving air across the wing surfaces. Nothing is as the plane has a 0 mph ground speed, as the treadmill is keeping the plane stationary on a point on the earth. Without air moving across the wings it's got less chance of getting up than Larry Craig at a strip club.

I really wish I remembered more from physics (hell, I wish I remembered more from last weekend LOL). Seems to me that friction has to come into play here too, this is a complex problem.

Let me go smoke a bowl, I might be back to change my mind LOL.

 

[Roz]

The ONLY purpose for landing gear (wheels) is to prevent damage to the underside of the aircraft and for the aircraft to have something to rest on besides it's belly.

Does anyone truely understand how a plane engine works?

The propeller/turbine is like a screw that threads itself through the air. The wheels could be cinder blocks or dunkin' donuts - it doesn't matter.

The wheels are FREE SPINNING. They spin because the plane moves. The plane doesn't move because the wheels are spinning.

 

[OCBob]

But the question doesn't state wheel speed, it states plane speed. This means that the movement of the "earth" in the opposite direction would cancel out the speed of the plane, keeping it stationary.

Look at it this way, if the treadmill were moving at 200 mph in the easterly direction the plane would need to generate enough thrust to accomplish 400 mph to take off in the westerly. But if you turned it around on the treadmill and faced it easterly it would need to generate 0 thrust of it's own, as it would be flung into the air as a result of the lift generated on it's wings.

Or maybe not? heheheheh

 

[tinygiants]

I understand the thrust against air principal, but now I see smokes point also. His point is that treadmill speed can be increased to the point of equaling the forward thrust. I see his point as requireing the drag in the wheel train to equal the thrust.

If the plane moves forward, then thrust is stronger than drag. Treadmill speeds up to match plane. So it becomes a do loop until the treadmill equals the plane thrust.

The wrench in this debate will come from how is the plane speed measured. Thus determining how fast the runway will be powered. If the plane speed is measured by forward motion, then the treadmill will not effect the overall speed of the plane. If the plane speed is measured relative to the runway, then the engine thrust would ultimately be accounted for as the runway keeps speeding up to compensate for any thrust created motion. This cycle would continue until drag = thrust.

I love good healthy clean debate. It stretches the brain.

 

[popacoll]

plane on conveyor belt question

Of course the plane can't take off, there is no pilot! Do you think a plane flies itself? silly question.....

 

[ntw0rk]

The speed of the treadmill doesn't matter, the aircraft speed relative to the earth does.

 

[Roz]

Alright Smoke (and the rest of the nay-sayers) - maybe this will click.

I'm gonna use the 'coptor in your avi as a reference. Take your helicoptor, and allow it to hover a few inches over the runway/treadmill. Now, lower the rear wheels onto the runway(still hovering - no forward motion), but allow the front wheels to remain in the air. Manuvuer the helicopter forward (NOT UP) - the treadmill will contradict the forward motion of your rear wheels to infinity. BUT the copter still moves FORWARD. Right?

Now, lower the the entire helicopter onto the treadmill (while moving in a forward motion) the 'copter will STILL move forward.

Granted a helicopter and and airplane operate differently, I'm just trying to get everyone past the fact that the plane/'copter WILL move forwards.

With THAT being said - the plane will move forward also - generate lift and take off into FLIGHT.

 

[OCBob]

Yeah Roz, we were just discussing the hover concept over dinner. That might be right, or maybe not hehehe.

 

[FlyingLow]

Sorry Scott, this is not a good example because you are relying on the ground to provide leverage. An aircraft engine doesn't need the ground for leverage, it uses the density of the air. So, independently spinning wheels are merely the bearings that allow the aircraft to move forward, propelled by the engines which are pushing on the air, and therefore not affected by the speed on the runway.

I know that you have seen some of those old videos of the early aircraft carriers, when the wind was right, and the speed of the carrier was fast enough, the planes could get lift with very little forward speed relative to the deck, sometimes none. That is really no different than what we are faced with here, except that the wheels will be spinning faster as the plane achieves lift. The key is relative speed. The aircraft speed relative to the moving runway is not important, nor is it (necessarily) important to the relative speed of the ground, (depending on wind speed, as you stated earlier) it only matters relative to the air itself.

This is very different. The carrier moving forward with the winds will provide lift. But in that case the plane is not moving. Now takeaway the wind. Have the carrier start to move backward at the same exact speed as the airplane. The carrier moves backward while the plane moves forward. However the 2 are exactly matched as per the problem. So while the wheels are picking up speed to move, the carrier is moving the opposite direction. The plane increases it speed to 50 mph and the carrier moves backward at 50 mph. Once you run out of carrier then the plane will just fall into the water. At the same spot it started.

I already said if there is enough wind then there will be lift. The engines are not providing lift, the wings are. The engines only push the aircraft forward, fast enough to cause enough wind to pass over the wings.

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The helicopter would move forward. But thrust is different. The blades in a helicopter act as wings. The wings in a helicopter are already flying. The forward motion of the cyclic tilts the tip path plane down thus changing where lift is located. The movements are not due to the down wash. Rotor-speed stays the same in flight. A jet engine increases thrust to move the airplane. A helicopter just changes the pitch of the blade. You can't compare the two unless you put the airplane in flight first.

Let me ask this question. If the same problem was applied to a car with wings then would the car fly? I'm guessing yall's answer would be no due to the fact that the wheels are being driven by the motor. I understand that on the jet the engines are not turning the wheels. But the energy is transferred there.

Engine applies thrust to the airplane.
Airplane starts to move forward.
The forward energy of the airplane is transferred to the wheels.
The wheels start to turn.
At the exact same time the ground starts to move in the opposite direction.

 

[FlyingLow]

Someone needs to get myth busters on this one.

 

[Roz]

Someone needs to get myth busters on this one.

:dontknow: :dontknow: :rock: :rock:

 

[ntw0rk]

Someone needs to get myth busters on this one.

Hahah!!! That's what I told Jimi last night!

In your example about the carrier above; this would be true if you were relying on the deck to provide the leverage for forward motion. But you are not, the propulsion is from the thrust of the engines.

I say that if the deck was long enough, the aircraft would be able to get enough forward speed to achieve liftoff simply because it is NOT dependent on the carrier deck for forward propulsion!

 

[FlyingLow]

In your example about the carrier above; this would be true if you were relying on the deck to provide the leverage for forward motion. But you are not, the propulsion is from the thrust of the engines.

Right. But the thrust from the engines is transferred to the wheels which provide the leverage. An airplane without wheels might move forward, but not enough to get takeoff speeds. If the plane were not moving but the carrier was then the plane would move backward. Now apply some thrust to the engines. The plane would start to move forward on the wheels. It doesn't matter where the force is coming from. The end result is the wheels on the plane move. The plane moves forward on the wheels. The thrust provided is pushing the airplane on the wheels. It is not moving it through the air (well it is literally). The engines are just pushing the plane. If it pushes it fast enough it will fly. But it is pushing the airplane on the wheels. The plane is connected to the ground by the wheels until it gets enough airspeed. Until the right airspeed is reached the airplane is just a big piece of metal on wheels. Those wheels might be turning but if the ground is moving in the opposite direction then no forward movement is actually achieved.

 

[ntw0rk]

Right. But the thrust from the engines is transferred to the wheels which provide the leverage. An airplane without wheels might move forward, but not enough to get takeoff speeds. If the plane were not moving but the carrier was then the plane would move backward. Now apply some thrust to the engines. The plane would start to move forward on the wheels. It doesn't matter where the force is coming from. The end result is the wheels on the plane move. The plane moves forward on the wheels. The thrust provided is pushing the airplane on the wheels. It is not moving it through the air (well it is literally). The engines are just pushing the plane. If it pushes it fast enough it will fly. But it is pushing the airplane on the wheels. The plane is connected to the ground by the wheels until it gets enough airspeed. Until the right airspeed is reached the airplane is just a big piece of metal on wheels. Those wheels might be turning but if the ground is moving in the opposite direction then no forward movement is actually achieved.

But see... This would be true IF the wheels were actually doing something, but they DON'T. The wheels only spin because the plane is moving.

 

[Roz]

Engine applies thrust to the airplane.
Airplane starts to move forward.
The forward energy of the airplane is transferred to the wheels.
The wheels start to turn.
At the exact same time the ground starts to move in the opposite direction.

There are two different actions here. We also have two reactions. They are completely separate, and have no direct affect on each other at all. We are talking about cause and affect.

One action is the engine thrusting against the airplane. The reaction is the airplane moving.

The other action is the conveyor moving under the wheels. The reaction is the wheel moving in the opposite direction the belt is moving.

The action of the belt is not physically capable of having any affect on the airplane itself.

Cars/Ram SRT10's rely on TRACION to move - Airplanes move by PROPULSION. Two seperate entities.

 

[bee0912]

kevan this is bull i dont understand anything and yes my head hurts

 

[Kevan]

Have the carrier start to move backward at the same exact speed as the airplane. The carrier moves backward while the plane moves forward. However the 2 are exactly matched as per the problem. So while the wheels are picking up speed to move, the carrier is moving the opposite direction. The plane increases it speed to 50 mph and the carrier moves backward at 50 mph.

Sorry to interject, but that is so damn funny it needs to be repeated.

Carrier....50mph..... same sentence....ROFLCOPTER

 

[ntw0rk]

Sorry to interject, but that is so damn funny it needs to be repeated.

Carrier....50mph..... same sentence....ROFLCOPTER

Why is that funny?

 

[Kevan]

Why is that funny?

An aircraft carrier doing 50mph? That's friggin' hysterical. Top speed for those is, like, 6.
(I know Smoke was only using it as an example....and not living in some kinda fantasy world).


From Rachel:
"Of course the plane doesn't take off. It's pre-flight."

 

[ntw0rk]

An aircraft carrier doing 50mph? That's friggin' hysterical. Top speed for those is, like, 6.
(I know Smoke was only using it as an example....and not living in some kinda fantasy world).


From Rachel:
"Of course the plane doesn't take off. It's pre-flight."

Dude! You need to do more research on Aircraft Carriers!!

George H.W. Bush Construction

Contract awarded January 26, 2001

Seven-year construction timeframe

Keel Laid September 6, 2003

Christened October 7, 2006

Delivery scheduled for late 2008

47,000 tons of structural steel and about a million pounds of aluminum

Modular construction process forms large individual units of the ship much like interlocking building blocks

Units welded together to form a module or superlift weighing up to 900 tons

Capability

Top speed exceeds 30 knots

Powered by two nuclear reactors that can operate for more than 20 years without refueling

Expected to operate as Navy warship for about 50 years

Typical Nimitz-class ship carries 80-plus combat aircraft

Three two-inch diameter arresting wires on the deck bring an airplane going 150 miles per hour to a stop in less than 400 feet

Size

Towers 20 stories above the waterline with a 4.5-acre flight deck

1,092 feet long: nearly as long as the Empire State Building is tall

Four bronze propellers, each 21 feet across and weighing more than 30 tons

Steering accomplished by two rudders, each 29 feet by 22 feet and weighing 50 tons

Four high speed aircraft elevators, each more than 4,000 square feet, bring planes to the flight deck from the hangar below

Capacity

Home to about 6,000 Navy personnel

Enough food and supplies to operate for 90 days: 18,150 meals served daily

Distillation plants providing 400,000 gallons of fresh water from sea water daily, enough for 2,000 homes

Nearly 30,000 light fixtures and 1,600 miles of cable and wiring

1,400 telephones, 14,000 pillowcases and 28,000 sheets