Printable View
im also going to be super nit picky here, and say that at super high treadmill velocities, skin friction of the treadmill will generate a current thats might be significant enough to actually suck the plane to the ground.
high velocity = low pressure = suction
You's guy's is being dumbasses.
Ok, the pilot firewalls the fucker, directing tens of thousands of pounds of thrust AGAINST THE AIR. The conveyor senses this and begins rotating the opposite direction at a speed\acceleration rate equal to that created against the air by the engines. BUT this opposite force IS NOT BEING APPLIED TO THE AIRFRAME. This force is being applied to the fucking wheels, which DO NOT transmit any fucking lateral force to the airframe itself, the force applied by the conveyer can by definition ONLY TURN THE FUCKING WHEELS, not counteract the force against the air emplaced by the engines. These pilots are fucking drunk anyways if they've managed to get themselves in this situation.
yeah but the treadmill will never be going faster than the plane's takeoff speed which is much lower than the velocity needed to do that.Quote:
Originally Posted by pechelman
when the plane lifts off from the runway at 220 mph the wheels will be spinning at 440 mph in one direction and the treadmill will be spinning at 440 mph in the other direction. theoretically
NO, the treadmill will be going 220 mph. the wheels go 440 mph (this statement doesn't even really make sense, but assume you are talking about the tread of the tire) because the plane is going 220 in the opposite direction.Quote:
Originally Posted by AsheanMT
Pechelman, get some rockets and get your ass up here to my clubhouse. We need to get scientific n' shit.
the treadmill will be spinning at the same speed as the tires
No, it doesn't. The treadmill moves at the same speed at the plane. Ignore the tires completely, all that needs to be there is something that allows the plane to move freely forwards with respect to the treadmill, like wheels, skids, maybe it hovers on magnets like those new trains. whatever, it doesn't matter.Quote:
Originally Posted by AsheanMT
either im 100% right, or I dont get it
the turbine applies force to the mass of the plane to make it move
the plane weighs a lot, so that turbine force sees a lot of resistance
since it sees a lot of resistance, the plane accelerates relatively slowly
which in iteself is irrelavant, because the treadmill matches this speed instantly.
im still not seeing how one rationalizes that the plane has relative velocity to anything.
edit: anything related to the earth as a reference frame. lets not get all astronomical here.
uber simplified FBD showing no forces being placed directly opposite those of the engines by the conveyor.
http://www.tetongravity.com/forums/a...1&d=1171930837
It matches the speed, but then what does that mean? The treadmill doesn't put any force on the plane.Quote:
Originally Posted by pechelman
pechelman! Pay attention! Plane velocity is not measured by how fast the wheels are spinning. Plane velocity is measured by how far the plane actually travels in a given period of time. If "shits not moving anywhere," the conveyor belt, by the very fucking premise of the question, is not moving.Quote:
Originally Posted by pechelman
It's all about the interaction of the conveyer at the wheels. The energy goes into turning the wheels, on the free pivot, rather than creating any vector that counteracts the thrust.Quote:
Originally Posted by pechelman
Wrong. Motherfucking wrong.Quote:
Originally Posted by pechelman
The plane fires its engines, which push against the air and the plane starts moving at 1 mph. The treadmill begins moving at 1 mph BECAUSE THE FUCKING TREADMILL MATCHES THE FUCKING PLANES SPEED. PERIOD. Please reread the question until you understand this.
The force from the treadmill cannot push the plane backward since the wheels do not transfer energy to the airplane.
except the treadmill is not moving forwards, and the plane (which is attached to the tires) IS moving forwards.Quote:
Originally Posted by AsheanMT
Ok Pechelman, two fellow enginerds just typed almost the exact same posts. Are you a beleiver yet?:)Quote:
Originally Posted by DJSapp
A car would move forwards on this same treadmill. What's with all this free pivot nonsense???? Has absolutely nothing to do with the problem or the solution to the problem. You fucking engineers are overanalyzing schitt and getting yourselves confused.Quote:
Originally Posted by DJSapp
Correct. The plane IS moving forward and WILL takeoff!Quote:
Originally Posted by focus
....and the wheels will be spinning at twice the speed of the treadmill. :)Quote:
Originally Posted by AsheanMT
That's why dyno shops are so fucking dangerous. Always cars jumping off those fucking things smashing through walls n' shit!! :eek: :rolleyes:Quote:
Originally Posted by focus
how bout this.....
if all those who say no fly are the treadmill
and all those who say will fly are the wheels of the plane
then this thread would be the plane just after takeoff
the thrust is counteracted by the plane's mass.
the problem says the plane and treadmill's velocities are equal, which in my mind, means the plane doesnt move.
nothing that has been so far has made me understand what you guys are saying (right or wrong).
and focus, give me a break.......
I know how a plane's velocity is measured.
Its called a pitot tube.
It measures the different in incident airflow pressure vs ambient pressure.
This difference in pressure is then used to calculate a velocity.
Yes!! Yaaaaaa, you're not a dumbshit!!:yourock: :yourock: :yourock:Quote:
Originally Posted by focus
You fucking idiot -- the treadmill doesn't move backwards unless the car moves forwards. The speedometer will show a speed of 40mph when the car is actually going 20mph (relative to the earth).Quote:
Originally Posted by P_McPoser
But yeah, keep rolling your eyes. Reread the question and report back.
group photo of everyone who posted in this thread:
http://tetongravity.com/forums/attac...chmentid=22114
I'm the handsome fella in the back row all the way on the right:wink:Quote:
Originally Posted by f2f
Velocity is not force. There is an unbalanced force acting on the airplane. The force from the engines is much greater than the friction from the wheels.Quote:
Originally Posted by pechelman
Newtons first law states that an object at rest will remain at rest unless an unbalanced force acts upon it.
F=MA
Since the plane has an unbalanced force acting upon it, the plane will accelerate.
edited for quote clearity
This is not possible without a force acting opposite the thrust. F=MA. You've got the M, but no A, only A is being created by the engines. You're stuck on overcoming the inertia, but it is overcome instantly, or else the wheels or conveyer wouldn't start to turn at all.Quote:
Originally Posted by pechelman
No, that's how you estimate the plane's velocity. Next time you're driving on an icy road, floor the gas pedal. The speedometer needle will jump, but that doesn't mean the car's actually going that speed. A speedometer is a tool used to estimate a car's velocity -- similar to your pitot tube.Quote:
Originally Posted by pechelman
Velocity is, by definition, the distance traveled by some unit of time. Velocity has absofuckingloooootely nothing to do with incident airflow pressure, ambient pressure, or wheel speed.
You're having a bad thinking day -- it's ok. Just don't ask for any more breaks.
Fuck This, I'm gonna go skiing. I'll check on you tards later.
Not to rain on your parade there, but IAS is typically what is used.Quote:
Originally Posted by focus
...and the beatings from the engineers continue...
I said the exact same thing 13 months ago.Quote:
Originally Posted by AsheanMT
Which begs the question, why am I still arguing about it now?
....:confused:
It isn't my parade, it's pechelmans.Quote:
Originally Posted by P_McPoser
And tell me, does it matter? IAS -- Indicated Air Speed, is by its name an estimation of velocity. Same principle, just insert IAS where pitot tube was.
Whoa, how the fuck did I miss that? Thanks for crowning yourself dumbass of the year with that remark. I guess I can no longer perform my function as a ventilation engineer since you decided to rewrite the laws of thermodynamics right there.Quote:
Originally Posted by focus
Guess I can no longer measure air veloticies by measuring Velocity Pressures or anything.
Nevermind, thought you were claiming IAS was useless. I was just saying that's what's used. And for aircraft/boats etc, yes, it's an estimate dependent on either windspeed or current. So no argument there. :)Quote:
Originally Posted by focus
My above post, however, still stands. I can measure AIR VELOCITY (as in wind speed) very accurately with a pitot tube.
Absofuckingloootely was overstating it. The point remains. Pressures, airspeeds, etc. are not what the treadmill is measuring. Measuring them is a tool for estimating velocity. Just a tool. The plane's actual velocity is something that may or may not be reflected by these measurements. The treadmill is measuring the PLANE'S (or cars) actual velocity, not airspeed, not pressures, not wheel speed. Dumbass of the year? I'll wear it. Doesn't change the fact that you still don't seem to fucking get it.Quote:
Originally Posted by P_McPoser
;)
edit: do you get it? I don't know, and I'm not going to reread all your posts right now. Maybe I'm arguing with the wrong guy. It still blows my mind that people who work with this stuff, have degrees in this stuff, can't read the question correctly and can't fit their minds around the concept. All you engineers (the ones handing out "beatings") are overanalyzing the crap out of this thing.
Quote:
Originally Posted by pechelman
A car propels itself by pushing against the ground. An airplane propels itself by pushing against the air. An airplane overcomes gravity by creating a pressure differential between the top and the bottom of the wings. Airflow is required for this.
The question, as it is asked, is unanswerable. There is simply not enough information provided. Everybody is (mostly unknowingly) inserting their own information into this question to make it answerable. Insert different information, get different answers.
Since the engines provide thrust, the plane will move forward unless another force counteracts the engine's thrust. The other force, in this example, is generated by the treadmill and transmitted to the plane through friction. It can be assumed that the wheels are spinning at the same speed as the belt on the treadmill, so there is no kinetic friction between the wheels and the treadmill; only static friction. So the only other place kinetic friction could result in a force being exerted on the plane is in the bearings. Frictionless bearings=plane takes off normally, assuming the treadmill is long enough and the tires don't fly apart due to inertial forces.
If the bearings are of this earth and are affected by friction: then, if the thrust provided by the engines is sufficient to accelerate the plane to a speed that creates enough airflow across the wings to create enough lift for the plane to take off...the plane takes off. But, if the counteracting force generated by the friction in the bearings is not able to be overcome by the engines...it doesn't.
As I said, the question, as it is presented, is unanswerable. More information has to be introduced and people are unconsciously doing this based on perceived characteristics of devices(i.e. a treadmill makes objects remain stationary/jet engine makes airplane take off) without really considering the individual forces involved.
I'm sure there are dozens of engineers and pilots just sitting back and laughing at this discussion.
Isn't the force vector from most planes engines not stictly horizontal? I thought they actually pointed down a bit. If this is true, a non vectored thrurst plane with enough thrust could leave the ground even if it was stationary given MEGA-powerful jets.
:eek:
Also I'm no expert on bearings but I'm pretty sure their friction would increase with velocity in the real world, due to heat expansion, chattering of the inner components, ect(likely not continuously). I know physics texts say that static and kinetic frictions are constant but in real world applications the friction due to systems of stuff probably isn't. So it is possible to have a treadmill spinning super-duper-mega fast that could provide enough drag to counter the thrust forward. The bearings would probably fail long before this though!
:tongue:
Hang out for a second pechel, I'll help explain it.Quote:
Originally Posted by pechelman
Your statement "if the plane isn't allowed to move forward..." Why do you believe that this is true?