Let's say you had a giant treadmill with an airplane on it

[regionaltard]

In this case, it is right. That column, "Ask the Pilot" on Salon.com is by Patrick Smith, a regional Captain turned legacy furloughed F/O.


He brings lots of experience in his columns. They are all excellent, and he thoroughly does his research if he's presenting a question (as in this case).



You're right, everyone needs to be careful when finding answers on the internet.

But in this case, that column and that pilot are a good, credible source.

Then the only thing that sets him apart from everyone else offering an opinion here is that he's getting paid and we're wasting time.

 

[Longhorn]

This is turning into the greatest thread of all time.

Keep it up!!

 

[jeroom]

You guys are torturing me here....Can't even drink my beer correctly reading this stuff....

Damn!!... where's my Ipod? Where did I put my Ipod?...

 

[Occam's Razor]

If the airplane will fly, Midway airport wants to talk to you!

Get rid of that short-a$$ set of 30's era runways, and install a pair of threadmills!

Pos-and-hold...run 'em up...and launch!

It'd work, right?

 

[FlyinScotsman]

Why on earth are we discussing this one again??? And FS, I thought you were smarter than this
You guys are thinking as if the engine produces forward motion via the wheels. The wheels are only there to make it easier for the engine and propeller to pull the airplane on the ground, guys... Well, and for somewhat smoother landings, I guess...
Look at it this way (using a small SE prop for ease of understanding):

You are standing in front of the airplane, holding it by the propeller blades. YES, the engine is off!!! Wheels are on a threadmill, brakes released. And yes, YOU are standing on solid ground.
The threadmill starts up, slowly at first, then faster and faster. Initially, you'll feel a tug, as the wheels start spinning, but you'll find that it's actually not that hard keeping the airplane still as the wheels go faster and faster. Yes, I know, eventually you'll get to the point that you can't hold it any longer, but that is at a much higher wheelspeed than you apparently think.
Now realize how much more pulling power that engine and propeller has. It'll easily overcome the small amount of friction the threadmill is exerting on the wheels. Thus, the airplane will move forward on the threadmill, and it will become airborne at normal indicated airspeed. TIRE speed will be way higher than normal, but assuming the tires will withstand those speeds, the airplane will be airborne LONG before the friction from the threadmill is at the point of countering thrust.

Yes, I am an idiot, but I believe I stated that earlier.

I think it is these long azz days. 11+hrs yesterday!

I got up this morning at 430am and was shaving, thinking about this stooooooopid question. All of a sudden I felt very dumb. I got it, I totally got it.

Like I said I am an idiot.

 

[orangeskysurfer]

yall gotta me kinda confused wid all this pilot mumbo jumbo.. but i got me a airboat back at the trayler with big block 350 chevy on da back. yall saying if i go fast enuff i could go up in the air? See i dont reckon i could do thiis cause when i put the throttle up so far past about where my nee is about.. the tork of my engine would make me go sidways and id be gettin all wet with the alligators. now if i put a hifallootin jet engine on dere i reckon i might not have that tork and id be goin reel reel fast. maybe then i could be kinda like yall pilot folk. ill run down to walmart tomorra and pick me up one of them treadmills and ill try it out.. see if i cant geterdun.. suzys always tellin me i shoudl have been a airline pilot cause they make the big bucks, but i was never one of them smart kinds

 

[Leroy Smith]

I thought I would dust off this old gem to kill the PIC thread.

Let's say you had a giant treadmill with an airplane on it.

As you add power and begin to move for the takoff roll, the treadmill speeds up and keeps the plane in the same relative position. As the plane goes faster, the treadmill speeds up, always maintaining the aircraft's relative position.

Would you ever be able to take off?

GO!!

Mr. Vane, you are my new Evil-Genius hero. "Scott Hall" is far more prolific, but this was just pure, unadultarated divine inspiration.

Bravo, Thank You, and may God have mercy on your soul!

 

[PCL_128]

If the airplane will fly, Midway airport wants to talk to you!

Get rid of that short-a$$ set of 30's era runways, and install a pair of threadmills!

Pos-and-hold...run 'em up...and launch!

It'd work, right?

No, because the runway length required for takeoff doesn't change. You'd need to have a treadmill that is just as long as the current runways.

 

[JimNtexas]

another way to look at is an airboat in a river. The thrust of the airboat is from an airplane propeller.

Aim the airboat up river and give her all she's got. If the river keeps accelerating downstream as you speed up going upstream. Will you move?

If the top end of the airboat is 100kts, and the river is flowing at 100 kts the other way, will you have moved past the dock you just left on the shoreline?

That analogy is incorrect. If you are in an airplane that lifts off at 100kts, and you point that airplane into a 100kt headwind then it will take off with a zero length ground roll.

Boats don't rise up off the water, unless they are flying boats.

The acceleration of our airplane with respect to the surface of the earth on the threadmill is given by:

A = F/M

where A is the acceleration in length/time squared, M is the mass of the airplane, and F is the net horizontal force on the airplane. The net horizontal force on the airplane is the thrust from the engines minus aerodynamic drag and rolling resistance.


To hold the airplane still with full thrust from the motors, some equal and opposite force must oppose the thrust of the motors.

 

[runwayjockey]

Since when did wheel speed equate to lift generated? The plane will not fly with no relative wind!