Airplane and Belt Conveyor

[ThreeWheels]

A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

[vided]

i'm going with a i don't think so :p

[MarkLawson]

Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.

[vided]

:banghead::banghead::banghead:

[Bob Denman]

Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.
:agree: Without movement through the air; the wings provide no lift...

[PrairieSpyder]

Nope. It's not a matter of the speed of the wheels turning, but of the rate of airflow over/under the wings that make the plane fly.


:agree: Without movement through the air; the wings provide no lift...

:agree: They tested this on Mythbusters.

[aeroshots]

Yes it can. https://www.google.com/search?q=vertical+lift+airplane&rlz=1T4GUEA_enUS598US599&tbm=isch&tbo=u&source=univ&sa=X&ei=xtkjVa-bFMTnsAX2h4DQAQ&ved=0CCEQsAQ&biw=1350&bih=610


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:yes:

[MarkLawson]

Yes it can. https://www.google.com/search?q=vertical+lift+airplane&rlz=1T4GUEA_enUS598US599&tbm=isch&tbo=u&source=univ&sa=X&ei=xtkjVa-bFMTnsAX2h4DQAQ&ved=0CCEQsAQ&biw=1350&bih=610


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:yes:

Hadn't considered that possibility!

[Bob Denman]

:shocked: Okay... you caught us with a trick question! :clap:

[ThreeWheels]

:shocked: Okay... you caught us with a trick question! :clap:

It's not a trick. VTOL is not part of the original question.

[Bob Denman]

A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

It doesn't mention HOW it must take off; it just misdirects us, by making us think about the obvious...
We were all drawn to the issue of the wings not having airflow over them...
...While forgetting about the other methods of lift that are available! :clap:

[aeroshots]

It's not a trick. VTOL is not part of the original question.

O, okay sorry. I was trying a good humored yet accurate answer to a humorous yet interesting question.:opps: You did say plane four times in your question, but I missed the VTOL exemption. I guessed I missed your point in the question. So, what is the answer?:D

[Chupaca]

to late to give an opinion....great question food for tought answer should have been polled or given in a few days...:thumbup: but I'll keep my three wheels on the ground...:roflblack::roflblack:

[jcthorne]

The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.

Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.

[Bob Denman]

But it's not moving forward; the conveyer belt is counteracting it's forward speed, by running in the opposite direction.
It'll just sit there... :shocked:

Unless it's a Harrier!

https://www.youtube.com/watch?feature=player_detailpage&v=2pweY5y5eRI

[PrairieSpyder]

The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.

Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.


It's not the air through the engine that causes lift, but air moving over the wings. The plane has to move forward through the air in order to achieve lift. It the plane can't move through the air, it won't fly!

[bscrive]

The plane is accelerating with regard to the runway, moving or not. It does not use the wheels as motive force, rather the acceleration of air through the engines provide thrust which happens regardless of the speed of the wheels turning. The belt movement has no net effect other than the minimal rolling resistance of the wheels.

Yes the plane will take off in normal fashion and will move forward at its normal acceleration and lift rates.

:agree: We are not talking about a car where the mode of forward movement is the wheels.

[Bob Denman]

.................................................. .....................................Lift... :D
:agree: The turbines provide the thrust; the wings provide the...

[jcthorne]

But it's not moving forward; the conveyer belt is counteracting it's forward speed, by running in the opposite direction.
It'll just sit there... :shocked:

Unless it's a Harrier!

https://www.youtube.com/watch?feature=player_detailpage&v=2pweY5y5eRI

The counter direction conveyer has no effect once the engines are providing enough thrust to overcome rolling resistance of the wheels. It cannot 'counter' the forward acceleration that is the direct effect of the rearward acceleration of the air through the engines. This is nothing like a car that uses the wheels to generate the forward thrust.

[jcthorne]

It's not the air through the engine that causes lift, but air moving over the wings. The plane has to move forward through the air in order to achieve lift. It the plane can't move through the air, it won't fly!


Its the acceleration of the air through the engines that provides the forward movement. The plane DOES move forward regardless of the speed of the conveyor belt. Therefore the plane achieves lift in the normal manner.

[Bob Denman]

:shocked: oops...
Good Point!
I stand corrected, and bow to your problem-solving skillset... :bowdown:

[PrairieSpyder]

A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.

Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.

[aeroshots]

This is more enjoyable that I first thought, thanks.

So lets consider take off speed of a DC-9 is 140 Kts IAS for a given weight and atmospheric conditions. With zero wind and a normal runway (not one with a conveyer belt);) its ground speed/(wheel speed if measured) will be 140 Kts GS for the given conditions. I know, there are other factors that relate to GS, but to keep it simple please humor me. In said example with the conveyer belt runway, the runway will correct for the speed of the "plane" (as I understand the riddle). One would need to ascertain if "plane" speed in this riddle is measured at the wheels or at the pitot tube (i.e. airspeed). If at the wheels then when the IAS reaches take off speed of 140 Kts the wheel speed would be 280 Kts because the runway would be matching the wheel speed thereby doubling it again and again to infinity. The airplane still takes off when it reaches 140 Kts IAS.

JMHO

OP what say you?:dontknow:

IAS = indicated airspeed
GS = Ground speed

[ARCTIC]

A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.

Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.


I wonder how many forums have had this very same question asked and how many hours have been devoted to arguing about it.


Here's the correct answer:

The wheels under a typical airplane are nothing more than nearly frictionless free spinning wheels. The airplane gets ZERO propulsion from the wheels. The airplane is drug through the air by the thrust created by the propeller. The airplane WILL TAKE OFF!!! If the wind was blowing hard enough an airplane could take off with no groundspeed whatsoever (think about that one for a while). It's all about the air movement NOTHING about the ground affects it.

Added thought here: The belt cannot overcome the forward motion of the airplane AND the conveyor moving in the opposite direction is going to cause a wind to assist in the plane's takeoff.

[jcthorne]

A plane cannot fly without achieving a certain AIRSPEED. The contact with the ground and the speed at which it travels relative to the ground is irrelevant.

Consider a glider. After it is aloft, it gets lift by having air flow over it's wings. An engine is not required. Thrust comes from gravity.


ehh, ok. The conveyor belt does not have any effect on airspeed either. Same point as I previously spoke. The plane achieves lift and forward speed in the normal manner. The conveyor belt is irrelevant.

[ThreeWheels]

This is more enjoyable that I first thought, thanks.

OP what say you?:dontknow:



I say, thank you, that's the purpose of this discussion.

As to the answer, some of you are correct, and others are not.
I won't end the thread prematurely.
If this thread remains active, the answer will be revealed at Spyder Quest in September of 2015.
Provided, of course, that I have enough beer.............................................. ........

[Bob Denman]

:D This was a heckuva lot more fun, than I originally thought...

Thanks! :clap: :ohyea::yes::ohyea:

[jcthorne]

I wonder how many forums have had this very same question asked and how many hours have been devoted to arguing about it.



It takes time to explain the laws of physics to those uneducated in the subject. They are not always easy concepts to understand. And this riddle tires to throw an irrelevant curve ball into the mix. Your answer may have explained it better than I did.

[Bob Denman]

But... Once in a while; the Pig DOES learn to whistle! :thumbup:

[vided]

http://www.spyderlovers.com/forums/attachment.php?attachmentid=104949&stc=1

[ARtraveler]

:coffee::coffee:

I hope this is technical enough for the Technicality Police. :roflblack::roflblack:

I will watch this one. Don't feel like math this morning. :yes:

[spydaman60]

I say, thank you, that's the purpose of this discussion.

As to the answer, some of you are correct, and others are not.
I won't end the thread prematurely.
If this thread remains active, the answer will be revealed at Spyder Quest in September of 2015.
Provided, of course, that I have enough beer.............................................. ........you and bridgett missed farkle bingo last year and that would be the perfect spot for the answer steve. ps. i won't ask where you and bridget were!:roflblack:
:roflblack::roflblack:

[aeroshots]

Not going to Spyderfest so I'll summarize my view and close with this.

Even if said plane requires forward motion to create lift, i.e. not VTO capable it will still take off. It will move forward due to its thrust being independent to its wheels. Again, the conveyer runway will match the rotation speed of the wheels into infinity or until the airplane reaches take off speed. Then airborne.:clap:

If the conveyer were successful in its attempt to keep the plane motionless, then grounded I say, GROUNDED. Unless of course the headwind were equal to the take off speed of said plane then the plane would hover above the conveyer and thumb its nose at said naughty conveyer runway for delaying its scheduled departure time and inconveniencing the passengers.:mad:

My personal conclusion is Yes and No.nojoke
I'm 100% confident in my conclusion. :roflblack:

[Yazz]

Arggg! Aeroshots, we posted at the same time, saying the same thing different ways. You said it better!

Leaving this in through...

Take a piece of lined paper and cut it in half lengthwise. Hold the paper under your lower lip and blow. That is the principle of lift which gets airplanes in the air and keeps them there.

[Bob Denman]

:yikes: Paper cut on my lower lip now... :banghead:
As I leak blood onto my collar; I'm left to ponder flight...

http://www.spyderlovers.com/forums/attachment.php?attachmentid=104955&stc=1

[ottawa-rider]

The plane will take off when its AIRSPEED reaches what the pilot call V2 or take-off speed.

The speed of the conveyor or its direction will not affect the plane's ability to reach that speed since it is not attached to the conveyor.

As has been said above, the only force acting on the plane is from the thrust of its prop or jet engine.

The only impact of the counter rotating conveyor will be a small amount of friction.

[ottawa-rider]

Seems like we are all tripping over each other trying to say the same thing.

[jonnysevel]

The counter direction conveyer has no effect once the engines are providing enough thrust to overcome rolling resistance of the wheels. It cannot 'counter' the forward acceleration that is the direct effect of the rearward acceleration of the air through the engines. This is nothing like a car that uses the wheels to generate the forward thrust.


:agree: Absolutely correct! not a case of relative motion.. If the wheels were providing the propulsion then that would be a different story

[jaherbst]

A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

NO

Jack

[bruiser]

The airline will charge passengers a fee for the conveyor.

The aircraft will become airborne as long as the engine(s) provide enough reaction force, thrust, to overcome aircraft weight, thrust to weight ratio, and forward speed to provide wing lift. The overall effect of the conveyor is nil.

[Bob Denman]

Let me see if this is the right way of looking at this... :banghead:
The Turbines are providing their thrust against the atmosphere...
The conveyor is working against the speed attained by the wheels...

While there are opposing forces working hard; they're not opposing each other...
It should (might, maybe, sort of, could...) take off; once the wings are providing enough lift...

I need some Aspirin, and a handgun! :shocked:

[ARtraveler]

Let me see if this is the right way of looking at this... :banghead:
The Turbines are providing their thrust against the atmosphere...
The conveyor is working against the speed attained by the wheels...

While there are opposing forces working hard; they're not opposing each other...
It should (might, maybe, sort of, could...) take off; once the wings are providing enough lift...

I need some Aspirin, and a handgun! :shocked:

Please fax me some Aspirin. I will see what else I can find. :roflblack:

[Yazz]

A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

No or yes...

The conveyer belt is moving as fast backwards as the plane is moving forwards, which means the plane has it's engines spooled up but it's going nowhere.

The plane has to reach the proper airspeed to take off, not how fast the wheels are going, or the thrust output, but how much air is flowing over the wings.

Refer back to blowing on a piece of paper, make sure you have parental guidance.

This may be a trick question. Something about a light plane and strong headwinds, in that case, it can be done.

[BajaRon]

I wish I'd gotten in on this earlier. But you guys have it nailed as it is airspeed, not ground speed that creates lift.

If takeoff speed is reached at 100 mph AIR SPEED, the plane could actually achieve liftoff at zero ground speed in a 100 mph wind. Of course it could not maintain it without forward thrust because once it left the ground the wind would begin to push it backwards (ground speed) which would reduce air speed to below the needed 100 mph to maintain sufficient lift to keep the plane in the air.

Very clever though. Pointing the reader to a ground speed question when the answer lies in the arena of air speed. I love it! :thumbup:

[jcthorne]

No or yes...

The conveyer belt is moving as fast backwards as the plane is moving forwards, which means the plane has it's engines spooled up but it's going nowhere.

The plane has to reach the proper airspeed to take off, not how fast the wheels are going, or the thrust output, but how much air is flowing over the wings.

Refer back to blowing on a piece of paper, make sure you have parental guidance.

This may be a trick question. Something about a light plane and strong headwinds, in that case, it can be done.

Your first sentence contradicted itself. Either you say the plane is moving forward under power (correct) or you say it is NOT moving forward (incorrect for this scenario).

The air is flowing over the wings based on the aircraft's speed relative to the earth. And that is the same as without the conveyor. The conveyor is detached from the plane and does not act on it. Makes no difference HOW fast the conveyor belt is moving, it does not affect the speed of the plane.

[bruiser]

F=ma

Basic physics. If the aircraft is static, that is, no forward motion, then it remains static. However, if you add thrust or acceleration as a constant, then the aircraft will move forward because force is overcoming mass creating velocity. If that force is great enough and constant to overcome the mass (aircraft) then lift will be achieved. The only constant force acting to keep mass in place is gravity. Gravity acts in only one direction, down. By providing rearward thrust, the mass has to move forward, overcoming the downward acceleration of gravity.

If you are running on a treadmill, your mass is constant to the speed of the treadmill because the downward force of gravity is holding you in position so you don't move forward. Now, if someone comes from behind and pushes you forward with enough force to overcome gravity you will move forward (probably falling on your face) regardless of the speed of the treadmill. If you increase the speed of the treadmill, but don't increase your pace relative, force from the treadmill will propel you backwards because that force is great enough to overcome mass.

[Magdave]

Turn the plane around on the runway. It will take off in half the time. Assuming the runway rolling direction is 1 way of course.:thumbup:

[Magdave]

Your first sentence contradicted itself. Either you say the plane is moving forward under power (correct) or you say it is NOT moving forward (incorrect for this scenario).

The air is flowing over the wings based on the aircraft's speed relative to the earth. And that is the same as without the conveyor. The conveyor is detached from the plane and does not act on it. Makes no difference HOW fast the conveyor belt is moving, it does not affect the speed of the plane.

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0

[ARCTIC]

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0

The treadmill would instantly go to Infiniti mph as the plane pulled itself forward by the propeller as it overcame the initial pullback of the friction created by the wheel bearings beginning to spin. Not sure what kind of drag a greased axle could create but the treadmill would probably break at some point less than infinity and the tires and bearings on the plane might last longer than the treadmill. If BRP manufactured the treadmill it would overheat and go into limp mode long before it created issues for the airplanes tires:roflblack:

[Explorer]

1. The plane will take off.
2. The air speed and true ground speed will be the same.
3. The conveyor will have to be almost as long as a runway.
4. At lift off the conveyor will be moving at the lift off speed, of the plane, but the wheels will be spinning at 2X that speed.
5. Of course the tires may blow or the wheel bearings seize, due to the heat generated by 2X normal rotation of the wheels. In which case, "Houston We Have A Problem".
Roger

[jcthorne]

In the original scenario the plane speed = 0. The relative motion to the earth below the wing tips is 0


In the original question the plane moves, not zero, and the conveyer belt moves at the same speed in the opposite direction. Both are moving relative to the earth and in opposite directions. None the less, the plane is moving as a result of its engines providing thrust and thus air flow over the wing and lift.

I think i liked Arctic's explanation best though.

[Magdave]

In the original question the plane moves, not zero, and the conveyer belt moves at the same speed in the opposite direction. Both are moving relative to the earth and in opposite directions. None the less, the plane is moving as a result of its engines providing thrust and thus air flow over the wing and lift.

I think i liked Arctic's explanation best though.

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?

[ARCTIC]

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?

I'll anchor a plane stationary to the ground, pitch the props to full dig and bring the engine up to full RPM's. You walk around back behind the wings and tell me if you feel any wind :roflblack::roflblack::roflblack:

[aeroshots]

:opps:thought I was done posting here:D
I can't control my typing thumb. Since the trend seems to be that lift is related to the aircraft movement relative to the ground/earth, I must interject. The aircraft movement relative to the ground has nothing to do with producing lift. The cord line of the wings angle of attack to the relative wind produces lift. An airplane can fly controlled backwards over the ground and I assure you if it is below the critical angle of attack it remains airborne and it's producing lift.

[BajaRon]

:opps:thought I was done posting here:D
I can't control my typing thumb. Since the trend seems to be that lift is related to the aircraft movement relative to the ground/earth, I must interject. The aircraft movement relative to the ground has nothing to do with producing lift. The cord line of the wings angle of attack to the relative wind produces lift. An airplane can fly controlled backwards over the ground and I assure you if it is below the critical angle of attack it remains airborne and it's producing lift.

Very true! In the right conditions an airplane can fly with a negative ground speed. Especially smaller airplanes that need less airspeed to maintain flight.

The stall warning device has no idea what your ground speed is. That should tell you something!

[Bob Denman]

:gaah: Okay...

...It's time to decide this; once and for all! :banghead:

We'll need an airplane, a BIG conveyor belt, and... :D

[ursamajor35126]

This ought to answer the question!
https://www.youtube.com/watch?v=YORCk1BN7QY

[Bob Denman]

Thanks! :D

:clap::clap::clap::clap::clap::clap: :2thumbs:

[ThreeWheels]

This ought to answer the question!

Sorry, no.

[Magdave]

That will only work on a forward prop plane pushing wind over the wings. Not a jet. It sure seemed to me it was moving faster than the belt was pulled. Look at the pylons move as the belt is pulled:dontknow:

[jcthorne]

There is no lift, no air going over the wing the plane is stationary relative to the earth. If the wing tips are wider that the belt you would see no positional difference relative to the ground. Engine speed has nothing to do with it. It is like a car being Dyno tuned. Is it moving?


Lets back up. Do you agree that the engines provide thrust which is a large force pushing forward on the aircraft? If so, what force do you believe is counter acting that to keep the plane at rest?

A car on a dyno will move ALOT if its not strapped down while applying the large force to the rollers. The plane is not strapped down but neither is it applying force to the belt (rollers on a dyno) as the wheels are not driven. But this has nothing to do with the aircraft scenario, the wheels to conveyor belt interface is not applying any meaningful force to the plane or the belt. Also the speed and direction of the conveyor has no bearing on the ambient air, for this example its assumed stationary, ie no wind.

The engines push the plane forward with sufficient force to bring it up to speed. The speed (relative to the earth, not the belt) is the same as the air speed over the wing, that creates the lift. The width of the belt and thus relative position of the wing tips have no bearing on this. The plane moves through the stationary air.

I am really trying here and not doing a very good job explaining it. If I come off sounding condescending, it absolutely is not my intent, just friendly conversation on a technical subject.

[jcthorne]

That will only work on a forward prop plane pushing wind over the wings. Not a jet. It sure seemed to me it was moving faster than the belt was pulled. Look at the pylons move as the belt is pulled:dontknow:

The lift works the same way no matter if the prop is up front, to the rear or a jet engine. The engine provides thrust, not air over the wings. Look at the size and position of the prop relative to the wing span. If what you say is true, a wingspan not much wider than the prop would lift the plane just as easily. Simply not true. The video shows exactly what happens.


It also does not matter that the conveyor is not exactly the same speed. If it had the effect many hear think it does, if it were even a significant portion of the same speed it would keep the plane from take off. In the video it was obviously a significant percentage of the plane speed and did not reduce lift at all. The plane took off at its normal lift off speed. The pilot even says this and he did not expect it to take off at all.

If all this discussion and a very well done video of the subject cannot convince you, then it seams you will never quite grasp the laws of physics. Stick with what you are good at and I will go back to managing my heard of cats....errr engineers.

[jcthorne]

This ought to answer the question!

Thanks for finding that and posting it. Explained it perfectly. Folks that still do not believe or understand likely think the Apollo lunar landings were a hollywood production too.

[ahh-cool]

I have to put in my .02.
If you don't have airflow surrounding the wings you cannot get lift.

Here is my 4 questions that need to be answered.
1) The airflow over the wing is low pressure. Does it pull the wing up?
2) The airflow under the wing is high pressure. Does it push the wing up?
We know jet engines suck and blow.
3) Low pressure in front of the engine. Is the airplane moving into a vacuum?
4) High pressure behind the engine. Is it pushing it forward?

[bruiser]

The high pressure air above the wing exerts a downward force while the low pressure air below the wing exerts lift. That's the simplest way to explain it.

Jet engines-I worked on them for twenty years. The basic engine consists of a compressor, hot section and turbine. The compressor pulls air in and compresses it to create high pressure air at the back of the compressor. That air moves in to the combustion, or hot section, and is heated. This heated air drives the turbine. All this together creates thrust, which in turn pushes the aircraft forward. The front of the engine does create a vacuum but this has no effect on the movement of the aircraft.

[Magdave]

JC I have been flying planes for years and know very well the principals of lift. You said your self there must be forward velocity of the wing surface to create lift or a force that causes air to pass over the wing in sufficient volume to create it. When this thread started I never though about a front prop air plane or even a dual wing conventional engine but a jet with either wing or tail engines. That scenario would prevent lift because there would be no airflow over the wings to create the Bernoulli effect. Even though the MB video shows it taking off if the belt were moving at the same speed that equaled the thrust of the engine the best that would happen would be for the plane to rise relatively straight up and begin moving forward. Obviously that video does not show that, in fact it shows the plane moving down the belt as the belt was moving slower than the thrust of the plane. If the belt was at the same speed as the thrust of the plane the cones would be stationary. Obviously they were not.:thumbup:

[Magdave]

The high pressure air above the wing exerts a downward force while the low pressure air below the wing exerts lift. That's the simplest way to explain it.

Jet engines-I worked on them for twenty years. The basic engine consists of a compressor, hot section and turbine. The compressor pulls air in and compresses it to create high pressure air at the back of the compressor. That air moves in to the combustion, or hot section, and is heated. This heated air drives the turbine. All this together creates thrust, which in turn pushes the aircraft forward. The front of the engine does create a vacuum but this has no effect on the movement of the aircraft.


https://www.youtube.com/watch?v=5ltjFEei3AI

[bruiser]

Simply put.

[Yazz]

Think Myth Busters is busted.

The ultralight was moving faster than the conveyer belt, it went past the cones. Which meant it was going faster than the conveyer belt and there was wind flowing over the wings. Also, most ultralights are Short Take Off and Landing, STOL.

Would like them to try that with a heavier aircraft like a twin engine plane. Doesn't matter if it's a prop or turbine engine, just something heavier than FAA regulations for an ultralight.

Sorry, but flying an aircraft is all about airspeed. Blow on that piece of paper one more time. You can talk about how much grunt you have under the hood, but that doesn't cut it in aviation. Not going to bore anybody with the physics.

Have flown backwards via ground speed, and had the stick pointed down for landing and gained altitude. Both were weird, but they happened because of the wind currents around the plane.

If you haven't flown an aircraft, you don't know...

[ARCTIC]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.

[Bob Denman]

:shocked: I can't wait for my riding season to start... :D

[bruiser]

https://youtu.be/g8f3Jto_fjU

[Magdave]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.
Actually the prop on that plane probably could not generate enough prop wash to generate lift over those wings without forward movement. The air flow would be close to and around the body not the entire wing. Not enough lift generated over the entire wing and the section close to the body is only partially able to provide lift. The section attached to the body itself will not generate any. See above video. Only 1 side of the wing will get any airflow. It takes 2. To me it is mind blowing that anyone thinks the engine provides enough air flow to provide lift. All it does is provide thrust for the ENTIRE fuselage so it moves forward and creates air flow over the wing surfaces. If it provided enough air flow over the wings by it self you would see all the little planes hop like bunnies around the airport. :roflblack:

[ursamajor35126]

It is absolutely MIND BLOWING that someone could actually think that the conveyor could actually prevent a takeoff.

:agree:.... the ONLY thing the conveyor does is change the rotational velocity of the wheels. Which has NO relationship to the air speed and therefore the lift. It MAY increase drag slightly because of the increased friction but that is all. What is amazing to me is that even the pilot in the Mythbuster test thought the plane would not fly.... was HE ever surprised!:yikes:

[Magdave]

:agree:.... the ONLY thing the conveyor does is change the rotational velocity of the wheels. Which has NO relationship to the air speed and therefore the lift. It MAY increase drag slightly because of the increased friction but that is all. What is amazing to me is that even the pilot in the Mythbuster test thought the plane would not fly.... was HE ever surprised!:yikes:

Your MB post was so bogus. It is obvious the plane was moving forward look at the cones. the belt was not moving at the same speed as the thrust. Once moving forward the engine thrust and forward movement ( causing air flow on the wings) provided lift on the wings. I have seen those UL planes take off in under 100 yrds at our airport just like it does in the video.:ohyea:

[aeroshots]

https://youtu.be/g8f3Jto_fjU

Awesome no doubt. Here is one that actually impresses me more. Does this change any minds or adjust anyone's thinking relative to prop effect or other factors?

https://www.youtube.com/watch?v=0zDo7hkmCNY

edit -- I just think it is a cool airplane and video. I should know better than to stoke the heat. Good, in a way, to see the passion in this thread.

[ursamajor35126]

:shocked::shocked::banghead::banghead: SMDH!

[Magdave]

Didn't say it wasn't possible with a short forward movement once again a STOL plane. Why doesn't this one magically lift off the ground when the engines are full out. Answer no forward motion to provide airflow over the wings. And for the last time the MB plane WAS moving forward not stationary on the belt.


https://www.youtube.com/watch?v=ncI_2Pc1Ysw

[jcthorne]

JC I have been flying planes for years and know very well the principals of lift. You said your self there must be forward velocity of the wing surface to create lift or a force that causes air to pass over the wing in sufficient volume to create it. When this thread started I never though about a front prop air plane or even a dual wing conventional engine but a jet with either wing or tail engines. That scenario would prevent lift because there would be no airflow over the wings to create the Bernoulli effect. Even though the MB video shows it taking off if the belt were moving at the same speed that equaled the thrust of the engine the best that would happen would be for the plane to rise relatively straight up and begin moving forward. Obviously that video does not show that, in fact it shows the plane moving down the belt as the belt was moving slower than the thrust of the plane. If the belt was at the same speed as the thrust of the plane the cones would be stationary. Obviously they were not.:thumbup:


We are going to have to agree to disagree.

The thrust has no speed, its a force. the belt cannot move slower or faster than thrust, only slower or faster than the plane, which you already stated was not moving.....

The net force on the object causes the mass to accelerate. If the thrust alone is not causing an acceleration of the plane, there must be some other force acting on the plane equal and opposite to the thrust. You have yet to tell me where you think that force is coming from. Hint, its not the wheels. And that is the whole point. The conveyor cannot exert a force on the plane opposite of the thrust applied by whatever type of engine is on the plane. The conveyor also cannot effect the air flow over the wings of the moving plane. Prop or jet makes no difference here.

[jcthorne]

Think Myth Busters is busted.



If you haven't flown an aircraft, you don't know...

No MB was correct and one does not need to fly a plane to understand perfectly well how basic physics works. The vast majority of aeronautical engineers are not pilots.

It is scary to me that there are so many pilots that have no basic understanding of the physics that keep them in the air and how to interact with it. Perhaps pilot education needs to be updated.

[Magdave]

We are going to have to agree to disagree.

The thrust has no speed, its a force. the belt cannot move slower or faster than thrust, only slower or faster than the plane, which you already stated was not moving.....

The net force on the object causes the mass to accelerate. If the thrust alone is not causing an acceleration of the plane, there must be some other force acting on the plane equal and opposite to the thrust. You have yet to tell me where you think that force is coming from. Hint, its not the wheels. And that is the whole point. The conveyor cannot exert a force on the plane opposite of the thrust applied by whatever type of engine is on the plane. The conveyor also cannot effect the air flow over the wings of the moving plane. Prop or jet makes no difference here.

I have consistently stated it is obvious the plane WAS MOVING FORWARD. Look at the MB video again. That is what caused enough airflow over the wings to create lift not the engine. The lift force comes from forward movement of the plane through the air. On a STOL UL it doesn't take much forward movement. If the belt was moving fast enough to keep the plane stationary not enough lift would be generated by the engine alone. That creates dirty air any way. I takes smooth air flow to create lift.

[jcthorne]

Your MB post was so bogus. It is obvious the plane was moving forward look at the cones. the belt was not moving at the same speed as the thrust. Once moving forward the engine thrust and forward movement ( causing air flow on the wings) provided lift on the wings. I have seen those UL planes take off in under 100 yrds at our airport just like it does in the video.:ohyea:

Of course it was moving forward. the belt is powerless to have any effect on the forward velocity of the plane. The belt could have been going 2 or 3 TIMES the plane's velocity in the opposite direction and the plane would still accelerate forward and take off. UL planes use the same physics as larger ones, they just have more wing area per pound of weight so can take off in less distance.

[Magdave]

Of course it was moving forward. the belt is powerless to have any effect on the forward velocity of the plane. The belt could have been going 2 or 3 TIMES the plane's velocity in the opposite direction and the plane would still accelerate forward and take off. UL planes use the same physics as larger ones, they just have more wing area per pound of weight so can take off in less distance.

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:

[aeroshots]

Didn't say it wasn't possible with a short forward movement once again a STOL plane. Why doesn't this one magically lift off the ground when the engines are full out. Answer no forward motion to provide airflow over the wings. And for the last time the MB plane WAS moving forward not stationary on the belt.
....

Magic plays only a small factor in this example. Because the dude is not holding his tongue in the correct pitch angle relative to the P-factor doubled in a twin engine recip causing right yaw thereby increasing lift created on the left wing. If he had let go of the Cessna it would have rolled clockwise over onto its back. Or if it was filmed south of the equator then we know everything rotates backwards there and this Cessna model must have been equipped with north of the equator props.:yikes:

[aeroshots]

Can you all imagine if the MB pilot had a malfunction during his take off roll that required him to abort the take off? Hint -- what if he applied brakes during an aborted take off while Jeromy continued in his truck?
nojoke

[Yazz]

https://youtu.be/g8f3Jto_fjU

Yup, it's going backwards...

To do that maneuver, the plane has to achieve 0 airspeed vertically, then it slides backwards. Once the nose is pointed down, there is proper airflow over the wings and flight is re-established.

http://en.wikipedia.org/wiki/Tailslide

[jcthorne]

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:

No win, just a discussion. And YES, I fully agree that it requires forward motion for the plane to take off in static air. The prop cannot provide the lift. If the plane were pinned to a long rope, such that it could not move forward, ti would not lift off.

Whew, it is time for spyderfest yet! I need a vacation.

[ARCTIC]

Hmmm I think I get your drift. However I am sure you will agree it takes forward motion to gain lift on a wing. All things being equal if a plane is not moving through clean air it cannot generate lift. In this case the belt moving IS irrelevant because the air is static. That being static allows the prop to pull it forward. Wheel speed is irrelevant. You win. It was an interesting debate though:thumbup:
I saw the light bulb go on! Glad this could be a entertaining cordial discussion:2thumbs:

[Bob Denman]

So if your Spyder is on a treadmill that's going backwards as fast as your wheels are trying to go forward... :D


How long will it take to get to Albuquerque?
http://www.spyderlovers.com/forums/attachment.php?attachmentid=105102&stc=1

[OJ UK]

So if your Spyder is on a treadmill that's going backwards as fast as your wheels are trying to go forward... :D


How long will it take to get to Albuquerque?
http://www.spyderlovers.com/forums/attachment.php?attachmentid=105102&stc=1



Easy one that, Bob....twice the square root of Thursday...:2thumbs:

[bluestratos]

I used to be into large scale Radio Control air craft. If it is a prop driven plane the prop blast can be enough to raise the plane and fly off. If it is a jet there is no air movement until it accelerates. We used to build up to 40lb planes (AMA maximum wieght) and use 20hp engines with huge props. They had enough power to hover vertically like a helipcopter and then accelerate straight up. This requires a very low wieght to horsepower ratio so very diffucult to achieve on full size aircraft but there stunt planes that can do this. The idea of a tread mill would work great since it prevents the plane from moving forward but allows the prop blast to build up until the plane literally would levitat at which point it would shoot forward.

The planes we build were refered to as 3D and used very sofisticated electronics and mutliple high power servos on each control surface to over come the shear power of the prop blast. We flew these with both 2 stroke, fourstroke and electric set ups. The large the aircraft the easier it is to keep the wieght ratio low.

The shape of the wing also has a lot to do with it. A Y-Clark wing has more curve under the wing then over it and generates more lift but it makes inverted flight difficult. Stunt planes either modified or fairly flat surfaces on both sides. The lift is generated by the attitude of the wing and the airlerons. I used to progam the servos to work both in opposite directions or to proved equal movent in both directions which would be controld by a channel on the radio (mine was a 14 channel) or by the elevator. If by a switch this was known as flapperons. This mean no seperate flaps were required.

Flaps act like a Y-Clark wing, causing high pressure under the wing resulting in more lift. Very useful for landing at reduced speed, however we used to kit bash some funky old kits and install huge flaps and airlerons then add 120 size instead of the recommend 40 size engines. These, when pointed into the prevailing wind (as all planes do at take off) would go up like a helicopter or even fly backwards if the wind was a bit stronger. This allowed us to do pin point bombing runs, fly up to the circle, drop the flaps, hover over it then drop a small plastic flour filled bomb. On target evertime. Even though these huge Y-Clark wings did not like being inverted flight, the kit bashing allowed it to fly both inverted and knife edge.

So yes, with a prop driven plane, given the right configuration and horsepower the plane can take off without forward motion.

[BajaRon]

I am surprised that this relatively simple questions is giving so many such a difficult time....:dontknow:

[Bob Denman]

http://www.spyderlovers.com/forums/attachment.php?attachmentid=105468&stc=1

[ThreeWheels]

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.

I bet you're thinking "How can that be? It's IMPOSSIBLE for a belt conveyor to match the speed of the plane, and the plane will take off!"
And you'd be right.
Nevertheless, the question is "What If". The question isn't concerned with HOW the belt conveyor matches speed, but asks the question "What if it does?"

It's more an exercise in out of the box thinking. Can you accept a premise that might be counter to your everyday experience. Once the premise is accepted, it's simply a matter of two speeds in opposite direction canceling themselves out. All the talk of planes going faster, wheel speed, friction etc. are accurate, but all irrelevant given the conditions of the question.

Here, I'll give you the exact same question, but in a way that's more plausible to those stuck on the answer:

A float plane is travelling in a river upstream at 20 mph. The river is flowing downstream at 20 mph. Does the plane move relative to someone standing on the riverbank ?

[Magdave]

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.

I bet you're thinking "How can that be? It's IMPOSSIBLE for a belt conveyor to match the speed of the plane, and the plane will take off!"
And you'd be right.
Nevertheless, the question is "What If". The question isn't concerned with HOW the belt conveyor matches speed, but asks the question "What if it does?"

It's more an exercise in out of the box thinking. Can you accept a premise that might be counter to your everyday experience. Once the premise is accepted, it's simply a matter of two speeds in opposite direction canceling themselves out. All the talk of planes going faster, wheel speed, friction etc. are accurate, but all irrelevant given the conditions of the question.

Here, I'll give you the exact same question, but in a way that's more plausible to those stuck on the answer:

A float plane is travelling in a river upstream at 20 mph. The river is flowing downstream at 20 mph. Does the plane move relative to someone standing on the riverbank ?

Wrong The belt speed IS irrelevant all that does is roll the wheels. The wind is static therefore the prop will provide forward thrust. The wheels may be rolling twice as fast as normal at take off but wind speed is what counts not ground speed. it will move down the belt and take off just as the MB video shows. Now if the wind speed moved the same speed as the belt IN THE OPPOSITE direction (same direction as plane is going to take off) it would not provide lift and stall on the ground never to see the sky.:thumbup: The float plane would lift off too even if it did not appear to be moving forward because the prop would provide wind speed over the wing providing lift. I t would eventually over come the river speed to and begin to move just as the plane on the Mythbusters video does.

[aeroshots]

Can you all imagine if the MB pilot had a malfunction during his take off roll that required him to abort the take off? Hint -- what if he applied brakes during an aborted take off while Jeromy continued in his truck?
nojoke

http://cdn-www.airliners.net/aviation-photos/photos/3/7/7/1225773.jpg

[jcthorne]

I was hoping this might pique enough curiosity to keep it active until SpyderQuest.
So I'll just give you all the answer now. I suppose I'll have to buy my own beer in Lake George (sigh).

Drumroll please.................The plane does not take off.
The speed of the belt conveyor is equal and opposite to the speed of the plane. They cancel each other out and the plane doesn't move relative to the earth. If it doesn't move relative to the earth, it's not moving in the air and it doesn't generate lift.




Magdave is right. The speed of the conveyor is irrelevant. Could be going many times the speed of the plane and the plane will still take off. The forward speed of the plane is completely unaffected by the mythical moving runway. It cancels out nothing. The thread died because the issue was determined.

[ThreeWheels]

Magdave is right. The speed of the conveyor is irrelevant. Could be going many times the speed of the plane and the plane will still take off. The forward speed of the plane is completely unaffected by the mythical moving runway. It cancels out nothing. The thread died because the issue was determined.

As I said in my answer. You are discussing physical reality vs a what if scenario. You are saying that the belt conveyor could be going many times the speed of the plane. The question is worded in a way that makes that impossible.

"A plane is standing on a runway that can move (some sort of belt 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 the opposite direction). Can the plane take off?"

The Mythbusters video is also incorrect in that they did not match the speeds.

You may, of course, choose to ignore any and all of the scenario. The simple fact is, you are answering a question different than the one that's postulated.

Nevertheless, I'm thinking it's time to end this before you guys turn this into a silly flame war.