Topic: Can this airplane lift off?

[Soos]

Are some people suggesting that the lift gained by an airplane is actually wind coming back from the prop?

You move enough air, it doesn't matter where it comes from.
And "normal" plane would not lift due to the wing size VS. the weight and the amount of air the motor can move.

But in theory, yes a motor can lift a plane simply by the air it moves.




Therapy... I don't need therapy, just hand me my bottle of pills......
Funny how you can get thrown in jail for smoking herb, but they tell you it's ok to go to a "legal" dealer, AKA pharmacist get some stuff that REALLY messes with you,  and it's OK to go to work....



l8r

[Bob Wessner]

Soos,

What if the plane had a pusher prop?

[Soos]

Then you would have to move MASSIVE amounts of air to even HOPE to get enough air flowing over the wings.

I doubt that setup would be able to.

[mystic_1]

I dont know what "!=" means.   I gather he was just using the ! .

So this leaves me wondering what he intended, one is correct, one is incorrect...

I Goggled !=. "Google does this.

Your search - != - did not match any documents.

Interesting, is he just emphasizing that he believes airspeed and ground speed are always equal? 

Sorry, != is programming notation for "not equal" since the real "not equal" symbol ≠ doesn't appear in standard ASCII.

In other words, "!=" == "≠".



mystic_1

[MCRider]

Are some people suggesting that the lift gained by an airplane is actually wind coming back from the prop?

You move enough air, it doesn't matter where it comes from.
And "normal" plane would not lift due to the wing size VS. the weight and the amount of air the motor can move.

But in theory, yes a motor can lift a plane simply by the air it moves.




Therapy... I don't need therapy, just hand me my bottle of pills......
Funny how you can get thrown in jail for smoking herb, but they tell you it's ok to go to a "legal" dealer, AKA pharmacist get some stuff that REALLY messes with you,  and it's OK to go to work....



l8r

Stunt planes fly vertical. No wing lift there, all prop. But remember that props (rotary wing) works the same way fixed wings do. Low pressure on one side, high pressure on the other. Mass moves into the low pressure. How much air is moved is not the goal. Creating sufficient low pressure is. And the amount of air moved is the side effect.

[bunghole]

Funny how you can get thrown in jail for smoking herb, but they tell you it's ok to go to a "legal" dealer, AKA pharmacist get some stuff that REALLY messes with you,  and it's OK to go to work....



l8r

Move to California.  I buy my weed in store that exists just to sell weed.  Pretty soon the whole developed world will be like that and a thread like this might get to a half a page before we forgot what we were discussing

[kslrr]

This entire community needs group therapy.

We have issues.

Yes, the "therapy" is the old bikes we work on and the "group" is this site.

[Gordon]

This is officially my new favorite thread of all time!!

I think this needs to be "stickied" at the top of the page and all prospective new forum members should be forced to read it from beginning to end before being allowed to post just so they know what they're getting into.

[DammitDan]

I'm amazed that I actually made it far enough in to contribute something.  I assumed "Surely by page 4 everyone would be in agreement!"  I was wrong 

Here's my explanation:

Tie a rope to the front of a wagon.  Put a conveyor belt under the wagon moving backwards.  Turn the conveyor belt on and start pulling the rope.  Which way does the wagon travel?

Now turn it around.  Take a long stick and push the wagon from the back with the conveyor belt turned on.  Which way does the wagon travel?

It doesn't matter how fast the conveyor belt is traveling, because the thrust acting on the wagon isn't attached to the wheels, it's attached to the rope or stick (a.k.a. the propeller on an airplane).

On an airplane, this rope/stick is the propeller.

[markb]

Well Dammit Dan,
(Might be a pun there)
Best explanation I've heard yet.  I was hung up on the plane being held stationary by the conveyor but that can't happen if the wheels are able to roll.  Can I change my vote yes?
Thanks for the physics lesson guys!

[Gordon]

Tie a rope to the front of a wagon.  Put a conveyor belt under the wagon moving backwards.  Turn the conveyor belt on and start pulling the rope.  Which way does the wagon travel?

Now turn it around.  Take a long stick and push the wagon from the back with the conveyor belt turned on.  Which way does the wagon travel?

It doesn't matter how fast the conveyor belt is traveling, because the thrust acting on the wagon isn't attached to the wheels, it's attached to the rope or stick (a.k.a. the propeller on an airplane).

On an airplane, this rope/stick is the propeller.

I've tried multiple times to explain this in as many ways as I could possibly think of, and have come to the conclusion that those who haven't gotten it yet never will.  But it's still fun!  

The forward movement of the plane is not dependent on what the ground beneath it is doing, because the propeller or jet generating the thrust that is moving the plane is completely independent of the ground.

Someone used the analogy of a boat, with a traditional submerged propeller, travelling upstream on a fast-moving river.  This is not a good analogy for an airplane, because the boat is dependent on the surface it's on for it's thrust.  Take that traditional submerged propeller boat and swap it out with a swamp boat that has a large fan pushing it through the air and over the surface of the water, and you have a good analogy.  That swamp boat could easily travel upstream on a fast moving river because it's pushing itself through the air rather than through the fast-moving water.

[Inigo Montoya]

Yeah a regular boat drives itself similar to a car. At least some of us get it!

[HavocTurbo]

Tie a rope to the front of a wagon.  Put a conveyor belt under the wagon moving backwards.  Turn the conveyor belt on and start pulling the rope.  Which way does the wagon travel?

Now turn it around.  Take a long stick and push the wagon from the back with the conveyor belt turned on.  Which way does the wagon travel?

It doesn't matter how fast the conveyor belt is traveling, because the thrust acting on the wagon isn't attached to the wheels, it's attached to the rope or stick (a.k.a. the propeller on an airplane).

On an airplane, this rope/stick is the propeller.

I've tried multiple times to explain this in as many ways as I could possibly think of, and have come to the conclusion that those who haven't gotten it yet never will.  But it's still fun!  

The forward movement of the plane is not dependent on what the ground beneath it is doing, because the propeller or jet generating the thrust that is moving the plane is completely independent of the ground.

Someone used the analogy of a boat, with a traditional submerged propeller, travelling upstream on a fast-moving river.  This is not a good analogy for an airplane, because the boat is dependent on the surface it's on for it's thrust.  Take that traditional submerged propeller boat and swap it out with a swamp boat that has a large fan pushing it through the air and over the surface of the water, and you have a good analogy.  That swamp boat could easily travel upstream on a fast moving river because it's pushing itself through the air rather than through the fast-moving water.

That was me.... and I said propeller boat, meaning the swamp boats.... so now not only did I misunderstand you.... but you misunderstood me!!!!

Makes us even right?....... right? 

[TwoTired]

You folks seem mechanically-minded...

There is an airplane on a runway. The runway is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

Can this airplane take off?

Discuss.

Sounds like an engineering question....

Here are the givens:
Airplane = A
Runway = R
Conveyor belt = C  (C=R)
Wheel speed = WS
Conveyor Speed = CS (Where CS = WS-WS)
Take off speed  = TOS
TOS is a direct function of A's design, which is an unknown variable and not given in support of the following question. (airplane could be a glider, or VTOL capable)
No external effects are are defined or placed for the A in the the equation.  There is no link between A,  and R, C, WS, or CS.  You even have to make assumptions about gravity.

The question makes the reader toil over facts given which are irrelevant to A's capability or the forces placed upon it.  In fact, the sentences before the question actually have nothing to do with the ending question.

If the plane is capable of flight, it can take off.  If incapable, it will not.  You can decide on either depending on which assumptions you make about A and forces placed upon it. 

Essential missing data:
Does it have thrust against an air medium?  (Is there an air medium?) Are the wings strong enough to support the rest of the plane?  Are the wheels even free to rotate about an axis attached to the plane.  (parking brake applied?  If so, neither the wheels or the conveyor surface moves.)

In the end, the real question becomes, do you want the plane to fly or not?  Is your glass half empty or half full?  You can manufacture either answer depending on the assumptions made, none of which are supported or presented in the original post.

In fact, the question has no relevance to being mechanically minded, either.  It is a psychology question to gauge a person' optimism or pessimism.

If you answer no, you're a pessimist.
If you answer yes, you're an optimist.

Unless you have a fear of flying...  Then a plane that can't fly is considered a good thing.  Ain't it great that it can't crash and kill the occupants.  That's optimism!

Cheers,

[333]

Well Dammit Dan,
(Might be a pun there)
Best explanation I've heard yet.  I was hung up on the plane being held stationary by the conveyor but that can't happen if the wheels are able to roll.  Can I change my vote yes?
Thanks for the physics lesson guys!

And it only took 11 pages.

[Steve F]

And it only took 11 pages.

Just wait...it's not over yet, since were waiting for certain individuals to get the light bulb over their heads to come on. 

[Duke McDukiedook]

You folks seem mechanically-minded...

There is an airplane on a runway. The runway is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

Can this airplane take off?

Discuss.

Sounds like an engineering question....

Here are the givens:
Airplane = A
Runway = R
Conveyor belt = C  (C=R)
Wheel speed = WS
Conveyor Speed = CS (Where CS = WS-WS)
Take off speed  = TOS
TOS is a direct function of A's design, which is an unknown variable and not given in support of the following question. (airplane could be a glider, or VTOL capable)
No external effects are are defined or placed for the A in the the equation.  There is no link between A,  and R, C, WS, or CS.  You even have to make assumptions about gravity.

The question makes the reader toil over facts given which are irrelevant to A's capability or the forces placed upon it.  In fact, the sentences before the question actually have nothing to do with the ending question.

If the plane is capable of flight, it can take off.  If incapable, it will not.  You can decide on either depending on which assumptions you make about A and forces placed upon it. 

Essential missing data:
Does it have thrust against an air medium?  (Is there an air medium?) Are the wings strong enough to support the rest of the plane?  Are the wheels even free to rotate about an axis attached to the plane.  (parking brake applied?  If so, neither the wheels or the conveyor surface moves.)

In the end, the real question becomes, do you want the plane to fly or not?  Is your glass half empty or half full?  You can manufacture either answer depending on the assumptions made, none of which are supported or presented in the original post.

In fact, the question has no relevance to being mechanically minded, either.  It is a psychology question to gauge a person' optimism or pessimism.

If you answer no, you're a pessimist.
If you answer yes, you're an optimist.

Unless you have a fear of flying...  Then a plane that can't fly is considered a good thing.  Ain't it great that it can't crash and kill the occupants.  That's optimism!

Cheers,

After sleeping on it this is what I can agree with. Not enough information given to come up with and accurate answer, too many assumptions have to be made. Like I said in the beginning, this is a thought problem, meant to excercise the mind.

[333]

And it only took 11 pages.

Just wait...it's not over yet, since were waiting for certain individuals to get the light bulb over their heads to come on. 

And some will never give in and say "I was wrong", regardless of how much proof there is, or how many videos showing that it really will fly.


And I guess we're at 12 pages.

[Duke McDukiedook]

And how many videos not showing the speed of the wheel on the airplane. You cannot relate the video directly to Sochiro's thought problem. They are not the same. The belt in the video does not match the speed of the tire on the plane, the plane wheel goes faster than the belt, obtaining forward motion to provide lift for the wings. Apples and oranges.

That's it, the last comment above and this are my last comments on the problem.
Tawk amongst yooaselves. 

[tsflstb]

Just gotta add my two cents...probably saying the same thing a lot of others are.

If the plane were sitting there like an air hockey puck, any outside force from a propeller would move it forward even if the air hockey table were moving at 500 mph.  It would have an inertial frame of reference to the earth if you assume zero friction.

In real life, the thrust from the plane's propulsion system has to overcome the friction on the wheel bearings, the rolling friction of the wheels, and any multiples of those forces due to acceleration from steady state in the conveyor belt.  If it can do that, the plane can fly.  I think those forces are minimal compared to the thrust most planes are capable of (optimist), so I voted "yes".  

[SD750F]

It is in the way the original question was asked:

There is an airplane on a runway. The runway is like a conveyor belt, and can detect the speed of the wheels of the airplane. When the runway senses the wheels moving, the runway will match the speed of the airplane's wheels, but in the opposite direction.

Can this airplane take off?

the question is clearly referencing the speed of the wheels as the factor to determine the speed of the conveyor. Now if there was a reference to a fixed object on the ground, such and no speed in reference to, then there would be no airflow (except for the very minimal near the wings root cause by the propeller) to produce lift. BUT THE ORIGINAL QUESTION DID NOT MAKE THIS EXCEPTION.

So the plane will fly and the wheels will be free spinning at two times the equivalent speed the the particular aircraft requires for take off.

Scott

[mystic_1]

The belt in the video does not match the speed of the tire on the plane, the plane wheel goes faster than the belt, obtaining forward motion to provide lift for the wings.

This statement assumes that the wheels are powered when in fact they are not.  The wheels are free-spinning and by definition will always turn at whatever speed of the surface they are in contact with.

The plane moves forward because of thrust derived from propeller acting against the atmosphere.

mystic_1

[Gordon]

The belt in the video does not match the speed of the tire on the plane, the plane wheel goes faster than the belt, obtaining forward motion to provide lift for the wings.

This statement assumes that the wheels are powered when in fact they are not.  The wheels are free-spinning and by definition will always turn at whatever speed of the surface they are in contact with.

The plane moves forward because of thrust derived from propeller acting against the atmosphere.

mystic_1

Give up, man.  He's a lost cause.

[alltherightpills]

This is sooo much better than a politics/gun thread.  I love it.

[bunghole]

Hmmmm......

Upon re-reading the original wording of the question...

Wouldn't the conveyor and therefore the wheel speed accelerate to infinity.  Each time the plane moved forward relative to the ground (not the conveyor), the conveyor would sense an increase in speed and then match that speed.  The friction of the wheel bearings (no matter how small) would eventually overcome the ability of the plane to move forward relative to the atmosphere.  Granted, the bearings would burn up and be destroyed in short order.