Airplane / Treadmill Voting Booth

**huck4bucks** · 02-19-2007, 11:22 PM

I'm still shaking my head at the jackassery in the thread next door. Once the answer is decided once and for all, this thread should prove to be a roster of who knows what the heck they're talking about and who is a blathering idiot.

So please, everyone put your pride in your pocket, run to the fridge and grab a beer, re-read the problem, and post your vote here.

**Big Blue** · 02-19-2007, 11:50 PM

I still have no idea why there's even a debate about this. And I still can't fathom how anyone with an engineering degree didn't get this right immediately. The plane will not only take off, but there will be only a minimal difference in the time it takes versus a normal takeoff. If you still don't understand this problem, please go take a physics class.

**summit** · 02-20-2007, 02:15 AM

holy shit OF COURSE THE FUCKING PLANE TAKES OFF

unless you have the stickiest treadmill surface and tires one could imagine and the plane is above max takeoff weight...

If you still don't get it (like the guy above) remember, the turbofans are NOT driving the wheels. the wheels turn because the airplane is moving relative to the surface they are touching and there is friction between them.

A car on the treadmill would remain stationary relative to its starting location. Put a turbofan engine on the car and it will fly off the fucking treadmill.

**summit** · 02-20-2007, 02:19 AM

Originally Posted by Iowntheskies

Wind == 0
Airspeed != 0
Indicated Groundspeed (relative to the moving treadmill surface (ie if you had a speedometer hooked up to the aircraft wheels) == 2xAirspeed
True Groundspeed == Airspeed (until rotation when you change your velocity vector)

Stop thinking like a race car driver. The airplane doesn't accelerate based on the normal friction force from its engine powered tires. It goes because of the equal but opposite reaction of blowing all that hot air out of its turbofan engines which directly propel it. However, the treadmill is limited in the force it can apply to the plane by the amount of rolling friction it has with the aircrafts tires.

If you attatched a the plane to a flatbed truck and fired up the engines, the aircrafts groundspeed relative to the surface it rested on (the truck bed) would be zero but the airspeed would not be zero.

Treadmill/wheel speed is irrelevant on the treadmill.

The air is not on the treadmill.

**summit** · 02-20-2007, 02:30 AM

omg i read the other thread... its full of people who think that the pilot left the parking brake on or something... (or they actually believe that the aircraft is propelled by its wheels)

ETA to elaborate on this point the problem says nothing about the plane's velocity being required to be at zero relative to the air (ground, absolute reference frame, etc). the treadmill's ability to slow the plane relative to the ground is limited by its ability to apply force to the plane which is limited by the rolling friction of the wheels. so once again, unless the pilot left the parking brake on, the treadmill is only going to be able to apply a tiny bit of force via friction vs the force applied by the jet engines.

**belgian** · 02-20-2007, 03:55 AM

to clarify. the WHEELS OF AN AIRPLANE ARE NOT POWERED IN ANY WAY. If the airplane was powered via the wheels like a car, then it would not take off, but the wheels are FREE SPINNING so the treadmill could keep accelerating to infinite speeds but as long as the air above remains untouched then the plane WILL TAKE OFF. This is because the jet engines move the air above the treadmill, the only way a plane moves is by moving the AIR. If you claim the plane will not take off because of the treadmill then you must also believe that a plane requires a road through the sky to fly.

Look at it this way, if you strap a rocket to your ass and hop on a treadmill, it doesn't really matter how fast your legs are going and how fast that treadmill is going. As soon as Jimmy lights up that rocket, you're fucking going places.

**MeatPuppet** · 02-20-2007, 04:00 AM

Oh, for God's sake...

**focus** · 02-20-2007, 06:17 AM

Holy jesus christ. I hate to keep getting into this...but people are so retarded. Why can't I just leave them be?

Summit, Belgian, owntheskiesguy -- none of you get it. All three of you are barking up the wrong tree, and really your understanding of the problem isn't that much different.

Meatpuppet -- the question, as it is termed, is answerable.

The treadmill isn't trying to stop the airplane.

If the airplane transmitted power through the wheels to achieve takeoff speed, it could still theoretically take off. (Assuming it was able to push the wheels at twice the speed normally required for takeoff.)

**smitchell333** · 02-20-2007, 07:28 AM

Originally Posted by Summit

holy shit OF COURSE THE FUCKING PLANE TAKES OFF

unless you have the stickiest treadmill surface and tires one could imagine and the plane is above max takeoff weight...

If you still don't get it (like the guy above) remember, the turbofans are NOT driving the wheels. the wheels turn because the airplane is moving relative to the surface they are touching and there is friction between them.

A car on the treadmill would remain stationary relative to its starting location. Put a turbofan engine on the car and it will fly off the fucking treadmill.

Sorry but what makes airplanes fly is not the turbofans, the wheels, etc. It is THE LIFT CREATED BY THE WINGS AT SUFFICIENT AIRSPEED (speed relative to the air). If a glider has no engines it can be made to take off by rolling down a sufficiently steep hill. A fighter on an aircraft carrier is propelled forward initially mostly by catapault.

Since the treadmill negates any ground and airspeed = plane cannot take off.

Lets say as an alternative that 300 MPH winds came across the plane as it ran on the treadmill - then yes it would take off.

**focus** · 02-20-2007, 07:40 AM

Originally Posted by Big Blue

If you still don't understand this problem, please go take a physics class.

I think that's part of the issue here. It isn't a physics problem so much as a logic problem.

**Brock Landers** · 02-20-2007, 08:07 AM

Originally Posted by smitchell333

Sorry but what makes airplanes fly is not the turbofans, the wheels, etc. It is THE LIFT CREATED BY THE WINGS AT SUFFICIENT AIRSPEED (speed relative to the air). If a glider has no engines it can be made to take off by rolling down a sufficiently steep hill. A fighter on an aircraft carrier is propelled forward initially mostly by catapault.

Since the treadmill negates any ground and airspeed = plane cannot take off.

Lets say as an alternative that 300 MPH winds came across the plane as it ran on the treadmill - then yes it would take off.

Exactly.

The jet engines only create the forward thrust that moves the plane forward, moving air over the wings. This air moving over the wings creates a lower pressure on top of the wing and the air underneath moves up to take its place. While doing this, it pulls the plane up with it. The whole concept of plane lift is with the air moving over the wings. The jet engines only provide a means to achieve this ridiculously high amount of lift.

A spaceship is a bit different- it uses an incredible amount of energy to thrust the spaceship away from the Earth. Once it is out of the atmosphere most of the fuel is spent and it is weightless, in orbit anyway. Any excess fuel is used to control the landing (when it lands it uses the same concept as an airplane- lift on the wings)

If this plane is on a treadmill, the jet engines give it a forward thrust of say 300 mph (thrust isnt measured in mph but to make it easy). The FRICTION of the wheels on the treadmill only means the wheels will turn. If there was no friction there would be no equal/opposite force pushing back on the plane allowing it to move (Newtons first law of motion). The friction isnt really very important though. Since the treadmill is moving at the opposite velocity (same speed, opposite direction) the relative speed of the plane is 0. When they test car engines they are put on a treadmill, and the speedometer says 60mph or whatever but the car goes nowhere. Same here- the wheels have no bearing on the plane other than to keep it standing and allow it to move(back to Newtons first law). Since the jet engines are pushing with a thrust of 300mph, and the effects of the treadmill are keeping the plane still (0 mph) there is no air moving over the wings. The whole point of flight is to get air moving over the wings.

If jet engines were what makes the plane fly, then drag racing cars would fly. They have jet powered engines (or similarly powerful) but no airflow, so they stay on the ground. Much like this plane.

**dbp** · 02-20-2007, 08:10 AM

Originally Posted by smitchell333

Sorry but what makes airplanes fly is not the turbofans, the wheels, etc. It is THE LIFT CREATED BY THE WINGS AT SUFFICIENT AIRSPEED (speed relative to the air). If a glider has no engines it can be made to take off by rolling down a sufficiently steep hill. A fighter on an aircraft carrier is propelled forward initially mostly by catapault.

Since the treadmill negates any ground and airspeed = plane cannot take off.

Lets say as an alternative that 300 MPH winds came across the plane as it ran on the treadmill - then yes it would take off.

Why? Why am I posting in this thread?

As I said in that other thread, everybody (on both sides of this discussion) knows what makes an airplane fly. Thanks. The point of contention is whether the plane will move forward to create the airspeed. The turbofans do make the airplane move down the runway/threadmill.

**Brock Landers** · 02-20-2007, 08:14 AM

Originally Posted by dbp

Why? Why am I posting in this thread?

As I said in that other thread, everybody (on both sides of this discussion) knows what makes an airplane fly. Thanks. The point of contention is whether the plane will move forward to create the airspeed. The turbofans do make the airplane move down the runway/threadmill.

Question in this poll was if the plane would take off. Im assuming that means fly.

**dbp** · 02-20-2007, 08:21 AM

Originally Posted by Brock Landers

Question in this poll was if the plane would take off. Im assuming that means fly.

Yes, and the plane has to move forward in order to take off (assuming no headwind). I think the original question almost assumes you know this. Whether it moves forward is the only "crux" of the problem.

**focus** · 02-20-2007, 08:38 AM

Originally Posted by Brock Landers

...the relative speed of the plane is 0. When they test car engines they are put on a treadmill, and the speedometer says 60mph or whatever but the car goes nowhere..... the effects of the treadmill are keeping the plane still (0 mph) there is no air moving over the wings.

This is where you're retarded.

The treadmill doesn't measure the wheelspeed of the plane. It measures the forward progress of the plane. It isn't hooked up to the speedometer, like in your car engine test, it's hooked up to how fast the plane is going relative to the earth. This speed is not necessarilly the same as that shown on the speedometer. If you've ever driven on icy roads you'd know this.

Think this through. If the plane is going zero mph, then the treadmill MUST be going zero mph. (The treadmill is NOT TURNING if the plane is not moving forwards! It can't! It matches forward speed, and that's all.) If the treadmill is going zero mph, and the plane is going zero mph, then where is all that force generated by the jet engines (or wheels, or whatever mode of propulsion/conveyence you choose) going????

**DJSapp** · 02-20-2007, 10:09 AM

Well, I was just next door and proved that if the treadmill was moving at the speed of light*, the plane still has a net force pushing it forward, thus creating airflow and lift.

The problem has two major points to it:

1. Aircrafts use engines to push air. Pushing against air means that once the airplane is at 35,000 ft, it doesn't need wheels to propel it forward (duh).

2. Maintain a constant frame of reference throughout the problem. If you change where you measure speed during a problem, you must adjust all of your calculations accordingly. I.E. if you measure airframe speed to begin with, you cannot arbitrarly switch to wheel speed without compensating.

Just curious for all of those on the non-fly side, how much physics education do you have? Any, High School, College, Masters, PhD?

*Yes, I know this breaks the rules as stated in the question, but I'm tired of arguing the finer points of basic physics and just beating the 'no flyers' with their own made up rules.

**maniloff** · 02-20-2007, 10:21 AM

Originally Posted by DJSapp

Just curious for all of those on the non-fly side, how much physics education do you have? Any, High School, College, Masters, PhD?

Bachelor's in physics from a fancy-schmancy school, then a few years working as a hacky pseudo-physicist.

Originally Posted by DJSapp

2. Maintain a constant frame of reference throughout the problem. If you change where you measure speed during a problem, you must adjust all of your calculations accordingly. I.E. if you measure airframe speed to begin with, you cannot arbitrarly switch to wheel speed without compensating.

You're spot on that the tough thing about problems like this (and undergrad mechanics courses) is dealing with multiple frames of reference.

**lemon boy** · 02-20-2007, 10:23 AM

Holy cow, it simply boggles the mind that otherwise intelligent people don't think that the plane will take off.

These same people must think that if you erected a giant verticle treadmill next to the space shuttle and attached little wheels to the booster rockets and had the treadmill spin at whatever speed the stupid problem said that the space shuttle wouldn't take off. A tip for you: the shuttle generates enough thrust on takeoff to acheive escape velocity, it easily can acheive the thrust necessary to counteract some wheelspin, hell...the bearings could be frozen and it'd still take off...just like a plane.

**Tippster** · 02-20-2007, 10:25 AM

Whole bunch of Maggots (not Focus) = not thinking clearly. So sad.

The treadmill cannot keep the plane from moving forward.

**philippeR** · 02-20-2007, 10:33 AM

another plane on treadmill thread ! Just what this board needed !

Here's another question :
How many votes would it takes for the plane to be standing still ? Discuss.

**Viva** · 02-20-2007, 10:35 AM

Originally Posted by DJSapp

Well, I was just next door and proved that if the treadmill was moving at the speed of light*, the plane still has a net force pushing it forward, thus creating airflow and lift.

Problem here is that the treadmill will become smaller as it approaches the speed of light and when that happens, the airplane falls off.

Jet Blue passengers, fucked again...

**maniloff** · 02-20-2007, 10:38 AM

I see a couple ways to approach this problem.

One is to ask if it's possible - if the treadmill could indeed spin such that the plane's ground speed was zero even though it's treadmill speed is nonzero.

The other is to assume a magical supertreadmill that does keep the plane's ground speed zero regardless of the plane's treadmill speed. I read the original question as assuming such a supertreadmill.

With that assumption and the assumption that the speed of the air relative to the ground is zero, then the speed of the plane relative to the air is zero. That means no lift, and thus no takeoff.

If you don't make both of those assumptions, then you would find that the plane's airspeed is nonzero, so takeoff would be possible.

**pechelman** · 02-20-2007, 10:42 AM

wow do we really need 2 threads on this

**lemon boy** · 02-20-2007, 10:44 AM

well, in favor of this thread is that so far it doesn't have a giant snapper like the other one, NSFW threads are not so great at work even if they're interesting.

Focus, just to be clear w/o reading the entirety of the other thread: you do think the plane will take off correct?

**focus** · 02-20-2007, 10:45 AM

Originally Posted by maniloff

I see a couple ways to approach this problem.

One is to ask if it's possible - if the treadmill could indeed spin such that the plane's ground speed was zero even though it's treadmill speed is nonzero.

The other is to assume a magical supertreadmill that does keep the plane's ground speed zero regardless of the plane's treadmill speed. I read the original question as assuming such a supertreadmill.

With that assumption and the assumption that the speed of the air relative to the ground is zero, then the speed of the plane relative to the air is zero. That means no lift, and thus no takeoff.

If you don't make both of those assumptions, then you would find that the plane's airspeed is nonzero, so takeoff would be possible.

What boggles my mind is that, with all that education, you are incapable of reading the question correctly.