See how smart you guys really are?

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A plane is standing on a runway that can move (some sort of variable speed band conveyer). The plane moves in one direction, while the conveyer moves in the opposite direction. This conveyer has a control system that tracks the plane speed and tunes the speed of the conveyer to be exactly the same (but in opposite direction).

-The plane is not a harrier or osprey


The question is:

Will the plane take off. Yes or No?

posted by  Enthusiast

I hate riddles,but I'm bored...so I think the plane may take off, but it might not be able to continue its flight(unless its on the ground)

posted by  jollyroger

That doesnt make much since but you have to give reasons why

posted by  Enthusiast

I say no. Not sure if it's a riddle and the answer turns out to be that the plane didn't have any fuel. Logically, however, the plane needs speed to create lift, so it's like running on a treadmill; there's no wind, so it's not getting lift.

posted by  chris_knows

I'm going to say no just because there's got to be something not right with that.

posted by  SyntheticTrust

Yes. Common sense would tell you that if the conveyor is moving in the opposite direction, it will act just as if the plane were moving forward. The wheels will turn (normally), speed up and take off.

posted by  97Talonchik

The wheels will go twice as fast but that's about it, i.e. the plane will take off as normal (maybe a bit more thrust due to wheel bearing friction)?

posted by  Wally

That is a moronic question on many levels that you obviously gave little thought or effort to and cannot be answered as posed. Why?

1. Because we don't know which direction the aircraft is moving, we can't draw a conclusion if it will take off. If said aircraft is moving in reverse we know it won't take off.

2. Before you start typing, wait. One reason we don't know which direction the aircraft is moving in is because we don't know it it's moving under its own power or being pushed/pulled. Once again you expect us to guess before we can draw a conclusion.

3. Assuming the aircraft is moving forward, we still don't know if it'll ever gain enough airspeed to takeoff, because among other reasons...

4. We don't know what type of hypothetical aircraft we're talking about, except that it's not a Harrier or Osprey. On the other hand, it could still be some sort of VTOL aircraft (thank you Nikola Tesla) because there are literally hundreds of designs. But I digress...

5. And that airspeed is an extremely important factor in whether or not the aircraft will rotate. After all, a Piper Cub will rotate at about 60 mph where an SR-71 needs an airspeed of, well I don't know if that's been declassified so I'd better not say anything more than FAST. And yes, I have experience working on Habus.

6. We also don't know at what speed or what direction the wind is blowing in relation to the aircraft. There's a reason the aircraft always takeoff into the wind, or as close as possible to it.

7. So as you can see, I could keep going for day picking apart this feeble attempt at a question, but here is the answer you're most likely looking for.


Assuming that the aircraft is moving forward, and assuming the flight controls are positioned for takeoff (takeoff trim), and assuming the aircraft is under it's own power, and assuming it's not over the max takeoff weight, and assuming that all other flight parameters are met, the speed of the runway (or lack thereof) has nothing to do with if the aircraft will rotate and fly. Ground speed is immaterial as is wheel speed. The only thing that matters if everything else is in place is airspeed, and a moving runway does not provide airspeed. Happy?





Now I have a question for you. Is this for your third grade science project or what, because that's about the level of difficulty of this question?


P.S. You forgot one answer on your poll. Make one that says "This is a stupid question that can't be answered because the person asking it has no f*cking clue."

posted by  vwhobo

Thinking about this question on a deeper level is hurting my neurons. My head hurts. I never liked word problems. I always end up with more questions than answers. Now I'm going to be thinking of this in my sleep.

Digressing...I'm missing key elements of the question here. Are you asking if the plane would take off on it's own just by being on the conveyor belt or are we to assume you are asking if just by being on the conveyor belt would make the plane take off. You need thrust to actually take off, right? But I keep reading this problem and then second guessing myself. If the plane is moving in one direction and the conveyor in the other at the exact same speed, the plane would be fixed in one spot, but would there be enough forward thrust to take off? Screw it, I'm going to bed. :ohcrap:

posted by  97Talonchik

This question has been debated many times on TEH INTARWEBS, and the answer is always that it won't take off. Simply put, the plane is technically not moving, which means there is no air going under the wings at high speeds to create the lift. The wheels have no bearing on takeoff, being that they do not actually provide any propulsion, they just allow the plane to be moved by the engine's thrust, which creates the windspeed under the wings, so if the plane is not moving, no take off.

posted by  dodgerforlife

Of course the plane would move and takeoff, the ground has nothing to do with thrust or air displacement.

posted by  Wally

i say no!
a plane needs air under the wings to provide 'lift'!
(i havnt read other peoples remarks so if its similar,,,,coincidence!)

posted by  True_Brit

The plane isn't moving... it's technically sitting motionless. The thrust produced by the engines is what provides forward movement, not the wheels, and since whatever thrust is being produced is being matched by the conveyor belt running in the opposite direction, the plane isn't moving forward, thereby not "gathering" air under it's wings.

posted by  dodgerforlife

If the conveyor is moving at one speed one way, and the the plane is moving the opposite direction at the same speed, then of course it won't lift off. The plane is standing still with its wheels moving frantically.

posted by  Mathew

Are you guys for real? What are the wheels on a plane for? That's right they are there to reduce friction. The condition clearly states the conveyor moves in an opposite direction to the plane, unless the brakes are lock on, the wheels will merely rotate faster.

Think of you with a piece of string attached to an object with wheels on a conveyer moving counter. The object will stay where it is because the string restrains it. When you pull on the string the object will move forward with about the same effort as with a stationary conveyor, only the friction of the wheel bearings adding extra drag.

posted by  Wally

If you read the conditions, it's that the conveyor ALWAYS matches the speed of the movement of the plane. The thrust from the engines which would naturally provide the forward movement of the plane is negated, therefore there is no way the plane will lift.

posted by  dodgerforlife

I give up. By your thinking you can lift yourself up by the bootstraps.

posted by  Wally

....a plane needs lift to fly. A plane that is stationary does not produce lift. Said plane will not fly. Simple enough?

posted by  dodgerforlife

Good luck trying to explain such a simple concept to a bunch of apparent idiots. There are a couple of people involved in this thread that I've been mistakenly giving too much intellectual credit to for the last few years. Let me give it one last shot.




If the vehicle in question was wheel propelled, such as a car, is would not gain any forward speed. The vehicle would be powered forward and at the same time the roadway would move in the opposite direction, negating any acceleration.

Now here's a newsflash for many of you. AIRPLANES ARE NOT WHEEL DRIVEN. The thrust from the engine(s), whether they are jets, fans or props, moves the airframe forward. The only thing the wheels do is keep the landing gear from dragging on the ground (and obviously the nose gear steers). If the aircraft requires an airspeed of 100 mph to takeoff, once the airframe reached a speed of 100 mph it would take off, even though the wheels would be spinning at 200 mph. Simply put, ground speed of the tires does not equal airspeed of the airframe.

Really children, this is all third grade stuff. I understand that none of you have the aviation training and experience that I do or the engineering training and experience that Wally has, but it also seems you don't have the common sense of my nephew's pet rock.




Now something to really drive home how ignorant you all are. The Earth rotates easterly (as viewed on our maps) at approximately 1,000 mph. If an aircraft requires an airspeed of 200 mph to takeoff and is taking off in an easterly direction, does it really have to accelerate to 1,200 mph before it can take off... Or will it take off automatically because it already has 800 mph more airspeed than it needs? :banghead:

posted by  vwhobo

The only outstanding simplicity, or simpleton, here is you. Because of that, you get your very own resonse. Sit down and actually read your own posts on this subject. You contradict yourself in every one. You yourself said that forward motion is caused by the thrust of the engines and not by the wheels, so... Explain to us all in great detail why there will be no airspeed as thrust is applied. The engines are pushing the airframe, not turning the wheels.

P.S. For all the non-knowers and pretenders like you, it's not "air under the wings" that pushes up an airplane, it's lack of pressure above the wings that makes it fly. That's why it's called lift. :banghead:

posted by  vwhobo

Okay, I can understand what you two are saying. I guess I took a little different approach to the problem...which I should have explained further. So I apologize for that, but there is an instance in which the plane will not take off. Maybe I shouldn't have attempted this a little on the tipsy side...

If the conveyor system can exactly match the plane, including the thrust the engines are putting out(which I do realize would take an almost unimaginable belt speed, but this whole concept is a little on the far side), then there is no movement in regards to the air, which means the plane would never reach the air speed necessary to take off. I guess the approach that I should have taken was that it's just matching the wheel speed, which means the plane would still gather air speed, and would take off eventually, I will agree to that.

posted by  dodgerforlife

You're still wrong, so you still "shouldn't have attempted this". It doesn't matter what speed the conveyer is moving, the tires are rolling on the conveyer. The engine thrust is pushing the AIRFRAME forward. The speed of the conveyer has no bearing on the airframe's speed. Get it through your head, the wheels are free to turn. It is not ground speed that allows an aircraft to fly, it is airspeed.

posted by  vwhobo

All correct and interesting information, but in what way does it address the "question" and how did you vote in the poll?

posted by  vwhobo

At the risk of entering into this game late, yes the plane would take off because an airplane's engines allow the craft to gain speed by pulling through the air, not along the ground. Put simply, anyway. The wheels would spin very quickly and might make some interesting noises, but that's about it.
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posted by  hondaman

I think I'm starting to see how it would take off...After checking it out on Youtube, it's much easier to visualize. It doesn't matter what speed the belt is spinning at, the plane can still take off (provided that there's enough runway)

http://youtube.com/watch?v=IZGdUAiMcPs
For anyone else who couldn't entirely understand how the plane takes off.


BTW Hobo, the SR-71 has been declassified, the take-off speed is 200 knots according to google.

posted by  chris_knows

All I'll tell you is don't take everything you read about the SR-71 as gospel. If you pay attention, anytime you read something about it's specifications from a reputable source, you'll see the words "publicized specs" or something of that nature. There IS a reason for that. :wink2:

And yes, 200 knots would be a realistic takeoff speed under certain circumstances.

posted by  vwhobo

I know some stuff is probably estimated, but the take-off speed isn't an exact speed, is it?

posted by  chris_knows

You don't get it Chris. It has nothing to do with knowing what the specifications are, it has to do with what has been released to the public versus actual specifications. For example, I can assure you that there's technology used on that particular aircraft that is still top secret.

Try this on for size. Last year Renault won the F1 Constructors Championship. Do you think because 2006 is over and a new season is starting, they're going to tell everybody everything about last year's car just because some of the technology isn't carried over? Not on your life. Same deal.

posted by  vwhobo

I understand what you mean, but the only publicized specification on the site (http://www.marchfield.org/sr71a.htm) is the top speed. I see why they wouldn't want to release any information though.

posted by  chris_knows

Have it your way, but remind me again how much direct experience you have with the SR-71 and the United States Air Force. You want to argue semantics, I'm trying to deal in facts. Just because that's the only place that states it, doesn't mean that that's the only spec that is for public consumption. The fact is that much of the information that has been declassified and released to the public is not the actual information or specification.

Trust me, I have friends, acquaintances and customers who were maintainers, pilots and navigators on them, including don't forget myself. Just because you read it on the internet, doesn't make it a fact. And don't for a minute think I'm saying that none of the information is correct. I'm saying not all of it.

posted by  vwhobo

I saw an SR-71 at an aviation museum once. It was quite large.

That's my random tangent for the day.
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posted by  hondaman

just out of curiosity for your answer, can you explain to me how this proves the plane would take off? If that person showed a video of a plane on a conveyor and that person showed the plane not taking off, would that person still have been correct in that planes do not take off on conveyors?

posted by  salimander13

I'm not trying to argue anything really...I know since the information is classified, it might not be true. However, take-off speed on that plane can probably be anywhere from 150-250 knots under the same weather conditions...No...I understood how it happened, but couldn't actually see how it happens. The video just proves what I know, making it easier to understand.

posted by  chris_knows

NVM after reading vwhobo's argument.

posted by  Bronxie

Vwhobo: Are you saying that despite the fact the plane isn't making forward progress on the ground, the body of the plane is stll gaining airspeed depending on the speed of the conveyor belt and that is entirely independent of the wheels making forward progress?

I hope I said that correctly.

posted by  Bronxie

OK its seems there is a problem with the plane wheels being passive devices, so lets make them powered too; here's the analogy. You're running on a treadmill and the faster you run the faster the conveyor moves. Now strap a rocket to your arse and ignite it.... how long do you think it will take for you to splat on the opposite wall. :laughing:

Edit: I decided to consult the internet and found this rather passionate explanation: http://www.meignorant.com/plane_Moz?page=1

posted by  Wally

Almost. The aircraft would in fact be making progress on the ground and in the air because of the forward thrust of the engine(s). The only place it would appear to not make progress is on the conveyer belt... Or actually it would seem to make twice as much progress, depending on your point of view. Because I understand the concept of what is hypothetically taking place here, I know that the wheels would be turning at twice the airspeed, so I see it as making twice the progress on the conveyer. The most important thing to realize is that the forward motion of the aircraft is entirely independent of the rotational speed of the wheels. I think that’s been mentioned a time or two already.

I still can't comprehend why the simplicity of this entire scenario escapes so many people.

posted by  vwhobo

Gee, he seems a frustrated as I am right now. At least I know there are four people in the virtual world (Moz, Wally, my wife and I) who get it. :banghead:

EDIT: I just drank a beer and read the comments on that video. Some of those people make the ignoramuses on this forum look like Albert Einstein... Or maybe Nikola Tesla.

http://www.poster.net/einstein-albert/einstein-albert-do-not-worry-9900884. jpg http://www.teslasociety.com/teslapic00.jpg

posted by  vwhobo

The way I figured it out is simple. The plane's engines are creating a force, I know it's low, but for simplicity's sake lets call it 100 Newtons. The friction from the wheels and air is so small in this problem that they are negligible. Therefore the plane is creating a force of 100N, and with no force pushing it in the opposite direction, the plane will accelerate.

It may be wrong, but it makes sense to me.

posted by  giant016

obviously the plane will take off, reguardless of what the ground does, because it depends on wind spead, generated by the prop, or jet engine, or whatever, to force air over the wings to generate lift.

posted by  dvdrose18

Your conclusion is correct, but not for the right reason. The engine(s) create thrust that accelerates the airframe forward and provides airspeed. They DO NOT force air over the wings to generate lift.

Disclaimer: Unless you're extremly well versed, don't bother talking to me about BLC systems. All they do is assist with lift to lower takeoff and landing speeds and do not create enough airflow to allow an aircraft to rotate.

posted by  vwhobo

i worded it wrong, the engine pushes some air backwords, but the laws of conservation of energy determine that the plane must also move forward, through the airframe, this forward motion through the air causes a type of vacuum force over the top of the wings that lifts the plane upward. so the engine isnt like blowing over the wings, it is pulling/pushing the plane through the air.

posted by  dvdrose18

Pretty simple to demonstrate:- while travelling along in the car put your arm horizonatlly out the window with a flat hand, fingers together, palm down.... the tendancy will be for the arm to rise.

And yes pick your moment when it's safe to do so.

posted by  Wally

Three guys finishing their meal and ask for the bill, the waiter tells them that the bill come to a total of $30, each of the guys take out $ 10 and give to the waiter, the teller tells the waiter: you over charged them mate, the bill should really be $ 25 and not $ 30, here $ 5 to give them back,on the way back to the table the waiter decided not to tell about the mistake and only give them back one dollar each and pocket the remaining $ 2.

Now, each guy gave $ 10 and got back one dollar, meaning meal cost $ 9 each multiply 3 is $ 27
plus the two dollars the waiter pocketed come to total of $ 29, right ?
Where is the remaining One Dollar gone??

posted by  GreekWarrior

they paid 30 got the 1 dollar back 27 and the waiter kept 2=25 bucks which was what they owed

posted by  salimander13

But I dont understand why the question cant be answered cause you did. Sorry I didnt think assholes like you would come in here and pick it apart in an attempt to make yourself feel superior and you are correct in the answer. Wheels on an aircraft are in "free spin" and they would just spin twice as fast as they normally would as the plane took off.

Your arguements are stupid though. Why would someone ask a question and then out of nowhere bust out with a ton of other variables that where previously unmentioned and give the question a completely different meaning.

For Example.
Can a cat walk through a solid wall?

YES it can because a magic wizard made into a superheroe.

That would completely defeat the purpose. And no sorry it wasnt on my third grade test. It was on a physics exam and the professor had it wrong. He said the plane wouldnt move cause of the conveyor belt and so no air would act on the wings (assuming there was no extra wind) causing zero lift and no takeoff. I presented to him that a planes wheels do not power it, the prop or jets do and the wheels are in freespin, and the plane would take off while the wheels just spun faster than normal. He asked how i knew this and I told him I owned an airplane he said i was at an unfair advantage and didnt give me my points.

It was just a quick question and dont act like your so high and mighty and above questions like these because I asked an engineer for lockheed and he answered without missing a beat and if he builds and designs these airplanes and didnt get offended by the question than either should you.

posted by  Enthusiast

And you've been here how long? :thumbs:

posted by  Cliffy

Ooohhh...easy answer.

I haven't read the responses or voted yet, so I may be wrong, but I know I'm not...but the plane will take off. If there were a way that the plane wouldn't take off...(i.e. being a wheel driven vehicle..) then the plane wouldn't take off (for long at least) even without the adapting conveyor belt.

I'm such a genius, now lets find out who's dumb.

posted by  My Life, My Era

I'd think that a "genius" would know how to spell the word...:laughing:

posted by  chris_knows

I swear I never read a single post or even the poll results, but I say no

its like running up the down escalator, obviously the plane wont take off, it wont even move, the wheels will spin- but that clearly doesnt affect takeoff

posted by  nighthawk

11 out of 18 people...FAIL.

Car-forums needs a logic sub-forum.

posted by  My Life, My Era

Hobo is right, if the wing is shaped correctly according to Bernoulli's principle, and the plane is moving forward, than the pressure across the top surface and bottom surface will differ. Once the right correction of speed and wing are put together it would seem that this shouldn't be a prob. Refine your question.

posted by  Voda48

*bump* didn't read all the post so if anyone mention this, my bad.

posted by  Voda48

lol! the results aren't surprising.

A monkey wrench thrown into the works... there is debate on Bernoulli's principle, and whether wings actually generate lift based on that or on angle of attack.

http://www.aeronautics.ws/blunders.html

"Moving the airfoil through undisturbed air, as in flight, is not the same as moving the air past the airfoil in a wind tunnel."

I found that site to be interesting reading. It may be off the wall, or it may be factual. But either way, it's interesting.

posted by  ChrisV

I'll have to check it out at home, I like to read the other side to priciples and "proofs".

posted by  Voda48

still not sure where my explanation was wrong, not trying to be a dick, but as an ex physics major, maybe you could explain it in different words? i know the part about the shape of the wings, but isn't vacuum the same thing as a difference in pressure?
edit: i was the ex physics major, i realized it reads a little rough.

posted by  dvdrose18

You mean is it valid to say the wing is sucked up or pushed up? :mrgreen:

posted by  Wally

Is that the only thing that was wrong with my understanding? Isn't it the same thing? The air under the wing is more dense than the air over the wing, so the pressure under the wing will be greater than the pressure over the wing, so the plane will rise if the force is greater than the force of gravity on the plane? Or was my problem just in the way I worded my understanding?

posted by  dvdrose18

I think you are being a bit sensitive:wink2: Tbaxleyjr wouldn't have known you were a physics major.

posted by  Wally

i'm not trying to be sensitive, i am honestly trying to undertand, i like to know if I inproperly misunderstand something. but unfortunately, any tone of voice, nonverbal cues etc. are all lost in written comunication.:cussing: dang, even smilies can be misinterpreted.:banghead:

posted by  dvdrose18

The "improperly misunderstanding" had me for a while. In regard to the puzzle, lift is not at issue, it's whether the plane will standstill or move forward.

Yes lift is caused by less positive pressure on the top of the wing to that under the wing, due to increased velocity pressure and reduced static pressure (the two pressures summimg to total pressure). The velocity pressure increases because the air stream has to go the extra distance in the same time the air passes from front to back under the wing. The wing also provides desirable boundary layers and minimal dynamic/friction losses.

Yes vacuum is considered anything under ambient pressure, but being the physicist you know that most calcs are done in absolute pressure units.

posted by  Wally

i voted no but i also received a D+ in physics.


what if.......there are snakes on the plane?? :hi:

posted by  jackal2000

dang, I'm no english major, but usualy I do better than that:oops:

so once the plane is off the ground, the moving belt is completly out of the picture, not that it realy mattered in the first place. basicaly all energe that was transfered to the plane from the belt is changed into rotational energy in the wheels of the plane. but once the wheels leave the belt, there is no transfer of energy at all to the plane, so the plane will have to move forward. I dont even know what i am saying any more. forget it.:ohcrap:

posted by  dvdrose18

hahaha!!!!!!!!

Damn I wish I was here when all this went down. I only bothered to read 1 and a half pages, so sorry if this has been stated, but the planes engines don't drive the wheels. Therefore, putting a speed on the wheels (as opposed to a force) will not impact the speed of the aircraft as generated by the engine. Remember, that unlike a car, the wheels of an aircraft match the speed of the aircraft (as best they're able), rather than generate it.

posted by  windsonian

uh yeah it'll fly can we all move on with our lives

posted by  BanffAutoSpa_ap

I find it interesting that no one has commented on the information in the link I gave. When flying, air isn't moving, it's stationary; the PLANE is moving. The air doesn't flow faster over the top of the wing, as it's not flowing, unlike in a wind tunnel...

posted by  ChrisV

Honestly I never got to the link, but that makes me want to re-read the question now.



When reading this and thinking about B. Prin. I always relate this to drinking out of a straw. The fluid moves up as a result of the pressure decreasing in your mouth relative to the pressure being applied to the fluid, and not you "sucking" the fluid up. Nice summary of the basic idea (or what we consider a basic idea:thumbs: )

*EDIT*
Rereading the question, the plane in all practical matter would not be moving forward. Correct? Therefore if it is not moving forward, and air is not moving around it (the wings) this would change it, yes?
What if ther was a gust of wind strong enough? Gale force winds or something that would create a pressure difference that relative to the weight would create lift? (like a kite?)

posted by  Voda48

I assume you don't mean the original question? Because the conveyor belt won't stop the plane moving, I thought that was covered ad infinitum.

posted by  windsonian

Ok I'll rephrase that for you, the plane is not moving relative to the ground

posted by  Voda48

Incorrect

posted by  My Life, My Era

Well then correct me

posted by  Voda48

The speed or direction of the conveyor belt has nothing to do with the action of the propeller or jet engine on the fuselage of the aircraft, so it will still move forward. the wheels will just roll.

A wheel driven vehicle would remain stationary, but an airplane would not remain stationary. the thrust of the prop or jet engine would still move it forward as if it were on a normal runway.

As for your thoughts on a straw, the flaw is this: water or fluids are incompressible. Air, however, even though it often acts like a fluid, is in fact very compressible, so it reacts differently in a venturi than actual fluids will, and it will react different over a wing (or should I say, when a wing moves through it). At least this is the information presented by that link.

And I can back it up with a scale model. Any cheap rubber band powered balsa wood airplane or non-powered balsa wood glider has flat wings, yet still flies just fine. Angle of attack is what does it.

http://retrotoys.com/images/JetfireBalsaPlane.jpg

http://www.americanjuniorclassics.com/images/Pursuit-1937-1-640x.jpg

posted by  ChrisV

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