12/12/2007 - the Conveyor Belt myth will be busted

I think that after we end this conversation, the next person who asks about a plane on a conveyor belt needs to get beaten with a conveyor belt.
 
Kent - my posts have been mostly tongue in cheek ... I was poking fun at myself, because I started the floatplane conveyor analogy post ...
 
gkainz said:
Kent - my posts have been mostly tongue in cheek ... I was poking fun at myself, because I started the floatplane conveyor analogy post ...
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Phew! I was afraid I'd confused someone.

The smilies are right over there ;) --------->

(at least when you're writing a post...)
 
KennyFlys said:
Drag. Actually, drag in the form of friction.

In order for any airplane to begin the takeoff roll, it must overcome the drag of the wheels on the runway. That drag varies only by how much weight is placed on the wheels and the traction the wheels have on the runway.

As the plane begins to roll on the conveyor and the conveyor is moving the opposite direction the initial drag is overcome but there continues to be drag. Eliminate the thrust, drag will stop the plane. In order for the plane to take off, there has to be sufficient thrust to overcome not only the initial drag but the continued drag as the conveyor rolls the opposite direction.

I don't know if anyone is considering fluid drag or not. The force I'm looking at is friction which must be overcome with ever increasing thrust.
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Ken drag is not a factor. even if you took a plane on a solid runway held the stick forward so the wheels stayed on the ground you would accelerate as fast as the plane could go or there abouts. So a Lancair would be doing 300 kts on the ground yet it only needs 70 or so to lift off. If you factored in friction it may only get up to 290 kts but it still only needs 70 to lift off. Take even your brakes held on, full throttle and let them up just a little and your moving. Friction is not a factor.

Dan
 
mikea said:
Greg, when the floatplane is using "80 knots worth of thrust to counteract the current, exactly what force is propelling it? Did the plane drop a outboard prop into the water somewhere and not tell us? It's amazing that you set up the PERFECT analogy as to why the plane DOES fly and use that to deny it. The THRUST holds it by moving AIR backwards. THAT IS YOUR AIR TO FLY WITH.

The perfect analogy is that a floatplane CAN take off into a opposing current. You have to move your frame of reference from the shore (where it won't move) to the relative air (where it IS moving.) Even better than the conveyor belt, whre the wheels have no friction, the skis have lots of friction and water drag to overcome.
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Once the float plane is in the current and has enough force to produce movement relative to the current it will step up and have less friction. Once up on step it will accelerate as the drag from the water will be quite low. As a matter of fact the faster the water goes the higher up the plane will be out of the water.

Dan
 
t0r0nad0 said:
I think that after we end this conversation, the next person who asks about a plane on a conveyor belt needs to get beaten with a conveyor belt.
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No no not until all the unbelievers have been converted. Have a heart, you don't want some pilot out there thinking he can not take off if he happens to run across a conveyor belt runway.

Dan:goofy:
 
Greebo said:
It means it doesn't matter.

ALL that matters is airspeed.

There really is no real physical way for a conveyor belt to affect enough force on the airplane to stop the airplane from moving forward *relative to the air*.

Honest.

I mean it.

Tie a rope to a tree. Stand on a treadmill facing the tree. Turn on the treadmill REALLY really fast, and hold onto the rope and pull forward. You'll fall down.

Now do it wearing roller skates. You'll be pulled forward by your force on the rope.

The propeller is your arms and the wind is the rope.

Get it?
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I heard that somewhere....

060303.gif

http://www.straightdope.com/columns/060203.html
http://www.straightdope.com/columns/060303.html
 
KennyFlys said:
Tell ya what, you line up the terms as you wish. You're sure hell getting more out of that question than I am. I really don't give a crap any longer. As far as I'm concerned, Ed, Jasson and now Kent can...


GO TAKE A FLYING FORNICATION THROUGH A ROLLING DONUT!

This was not what I initially wanted to say but I had a reluctant change of heart. Please read my other post regarding going against the grain.

Now, I'll happily take the ban and go on my merry way. Merry Christmas.
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LOL. Wow, man. Aside from the chat convo, I don't see why you'd get so mad.
 
KennyFlys said:
The moment three people made personal attacks.
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Was that before or after you surgically remove your forum credibility by deleting all your messages in this thread? At least, that's how it looks. Before then, it was just discussion. But now... geesh.
 
Chairboy said:
Was that before or after you surgically remove your forum credibility by deleting all your messages in this thread? At least, that's how it looks. Before then, it was just discussion. But now... geesh.
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I got tired of the personal attacks rather than simply arguing the terms of the experiment or possible outcome. Apparently, my attempt to disagree was fodder for something other than argument of the results.

I removed my points and those with the attacks can stand on their own.

Credibility? That counts only when I react to a given situation in real life while following a solidly established set of rules in a checklist.
 
So, would a donut take off from a treadmill?
 
Quote:
Originally Posted by mikea View Post
Greg, when the floatplane is using "80 knots worth of thrust to counteract the current, exactly what force is propelling it? Did the plane drop a outboard prop into the water somewhere and not tell us? It's amazing that you set up the PERFECT analogy as to why the plane DOES fly and use that to deny it. The THRUST holds it by moving AIR backwards. THAT IS YOUR AIR TO FLY WITH.

The perfect analogy is that a floatplane CAN take off into a opposing current. You have to move your frame of reference from the shore (where it won't move) to the relative air (where it IS moving.) Even better than the conveyor belt, whre the wheels have no friction, the skis have lots of friction and water drag to overcome.

stingray said:
Once the float plane is in the current and has enough force to produce movement relative to the current it will step up and have less friction. Once up on step it will accelerate as the drag from the water will be quite low. As a matter of fact the faster the water goes the higher up the plane will be out of the water.

Dan
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I know my quotes are hosed, but c'est la vi ... the prop is pulling the air to achieve a relative stationary position in respect to the bank, earth, whatever, but does that not also produce 0 knots of air over the wing? The prop does not provide (all) the airflow over the wing to produce lift. It's relative wind, or movement thru the air. Whatever your prop or power setting might be to hold a relative stationary position in a flowing river would produce (other than prop wash) 0 knots of relative wind over the wing, would it not?
 
what if a super cub on skis was taking off during an avalanche?
 
Who would win? Ditka or a conveyor belt?
 
:( The worst part is that tomorrow morning, this thread will be locked, and we were all having fun (well, all but one of us).

Threads like this made me a sad panda.
306_panda_dance.gif
 
SkyHog said:
:( The worst part is that tomorrow morning, this thread will be locked, and we were all having fun (well, all but one of us).

Threads like this made me a sad panda.
306_panda_dance.gif
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No hot linking form that site apparently. We can't see the panda. I'll just have to imagine it, sorta of like when Cartman imagined Kyle doing something in imagination land.

OFF TOPIC SOUTH PARK QUESTION FOR NICK: Did you see the Guitar Queero episode? CLASSIC!
 
smigaldi said:
No hot linking form that site apparently. We can't see the panda. I'll just have to imagine it, sorta of like when Cartman imagined Kyle doing something in imagination land.

OFF TOPIC SOUTH PARK QUESTION FOR NICK: Did you see the Guitar Queero episode? CLASSIC!
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not nick, but yes its hilarious. i can't wait for some heroin and rehab hero
 
gkainz said:
Quote:
Originally Posted by mikea View Post
Greg, when the floatplane is using "80 knots worth of thrust to counteract the current, exactly what force is propelling it? Did the plane drop a outboard prop into the water somewhere and not tell us? It's amazing that you set up the PERFECT analogy as to why the plane DOES fly and use that to deny it. The THRUST holds it by moving AIR backwards. THAT IS YOUR AIR TO FLY WITH.

The perfect analogy is that a floatplane CAN take off into a opposing current. You have to move your frame of reference from the shore (where it won't move) to the relative air (where it IS moving.) Even better than the conveyor belt, whre the wheels have no friction, the skis have lots of friction and water drag to overcome.


I know my quotes are hosed, but c'est la vi ... the prop is pulling the air to achieve a relative stationary position in respect to the bank, earth, whatever, but does that not also produce 0 knots of air over the wing? The prop does not provide (all) the airflow over the wing to produce lift. It's relative wind, or movement thru the air. Whatever your prop or power setting might be to hold a relative stationary position in a flowing river would produce (other than prop wash) 0 knots of relative wind over the wing, would it not?
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It would, but have you not sat on the ramp full throttle and rocked the plane. Just sitting there it shakes to beat the band.If you can hold the plane stationary (to the shore) in a moving current you can rock the wings and get up on step. (The water is moving at some speed below the floats). Once on top you have less drag than you did before. Less drag means you will now move forward. I would even think that just holding the plane stationary the floats would come up on their own, but I am not a seaplane pilot.

Dan
 
Great episodes! I love the end, very unexpected!

Stupid hotlinking....I'll fix
 
SkyHog said:
Here - sad Panda:
306_panda_dance.gif
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Full name=Sad Sexual Harassment Panda !!

Who lives in the east 'neath the willow tree
Sexual Harassment Panda!
Who explains sexual harassment to you and me
Sexual Harassment Panda!
Don't say that don't touch there
Don't be nasty says the silly bear
He's come to tell you what's right and wrong
Sexual Harassment Panda!
 
You have reached ONE MILLION POINTS!

You...are...***s!

Great ep... ;)
 
Someone help me out here. I get the flying fornication bit, but I am somewhat puzzled by the rolling donut concept.....

Pete
 
Basically, the question revolves around the amount of energy (measured in calories) stored in fried pastry and its interaction with kinetic energy (which a rolling donut would have).
 
Chairboy said:
Was that before or after you surgically remove your forum credibility by deleting all your messages in this thread? At least, that's how it looks. Before then, it was just discussion. But now... geesh.
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Maybe, just maybe, he finally realized that he was wrong? Too bad he's given up figuring out why like a good CFI should.

However, after his first fornication comment and lack of any thought towards addressing the points raised in the numerous excellent explanations in this thread, I got a bit hot under the hat and said some things that were unproductive. So, Kenny, my apologies for that. I would much rather help you understand the conveyor problem than have a fight. I am left wondering why you never addressed the specific points raised here.

All that said, it bothers me greatly that we have a system (FAA) where a commercial-rated pilot who is close to becoming a flight instructor can have such a fundamental lack of understanding of how an airplane flies. Kenny, I sincerely urge you to postpone your CFI ride until you truly understand the treadmill problem. (What if the examiner asks you the treadmill question on your oral??? :dunno:) There are obviously a lot of people here who are willing to help you out.

I still don't understand what joining the mile high club with a pastry in a Pitts has to do with anything... :dunno:
 
flyingcheesehead said:
All that said, it bothers me greatly that we have a system (FAA) where a commercial-rated pilot who is close to becoming a flight instructor can have such a fundamental lack of understanding of how an airplane flies. Kenny, I sincerely urge you to postpone your CFI ride until you truly understand the treadmill problem.
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I don't think it's fair to say something like that. First, the entire question is a hypothetical. It's not going to make one lick of difference if any of us are right or wrong. Secondly, a number of us have gotten caught up on the question and it's usually worded in a specific vague way to trick you. Is the conveyor moving fast enough to cancel the forward motion or is the conveyor only matching the forward motion speed? As you can see, the answer to the question is different for each of those premises.

Suggesting that someone lacks the ability to perform the duties of a certified flight instructor safely and accurately due to their answer on a hypothetical question that they would never encounter in the real world is over the line in my opinion.

But what do I know, I'm just a 24 year old PP-ASEL who hasn't flown in months. MONTHS! So there's my two cents and .1 on the Hobbs.
 
gkainz said:
I know my quotes are hosed, but c'est la vi ... the prop is pulling the air to achieve a relative stationary position in respect to the bank, earth, whatever, but does that not also produce 0 knots of air over the wing? The prop does not provide (all) the airflow over the wing to produce lift. It's relative wind, or movement thru the air. Whatever your prop or power setting might be to hold a relative stationary position in a flowing river would produce (other than prop wash) 0 knots of relative wind over the wing, would it not?
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Yeah. You can look at it that way for the simplest model.

What I was hinting at is the plane could take off perfectly well without moving relative to a fixed point on the ground if you had sufficient headwind. There's some combination of overcoming the water resistance and headwind which, once the plane left the water would be headwind only.

A J3 that has a Vx of 60(?) MPH would not move relative to a fixed point with a 60 MPH headwind. I've heard that J3 can fly from their tiedowns.

http://youtube.com/watch?v=A8c2gxlw0MU
http://youtube.com/watch?v=x01Qs7dl8jw
 
wbarnhill said:
First, the entire question is a hypothetical. It's not going to make one lick of difference if any of us are right or wrong.
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It does make a difference. It's about understanding the basics of flight. Those that do not understand something like this will never do anything but drive airplanes. If driving them by the readings of a couple gauges is enough for you. That's fine. But most of us on this forum want to fly, we want to be the best pilot we can be, and to do this you need to understand why wheels don't matter.

I've seen some pilots make some pretty sad comments about snow or ice on the runway. They can't quit thinking about the wheels and because of this they do some scary things.

wbarnhill said:
Is the conveyor moving fast enough to cancel the forward motion or is the conveyor only matching the forward motion speed? As you can see, the answer to the question is different for each of those premises.
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Not really. It can't move fast enough to stop you. Your wheels would explode before that point. I consider fire and certain death not the purpose of this question. Don't bend the words to mean something that it's not meant to mean. This question is supposed to help you think about air and not ground. Those that disregard air are the ones who lose control on landing or takeoffs.

wbarnhill said:
Suggesting that someone lacks the ability to perform the duties of a certified flight instructor safely and accurately due to their answer on a hypothetical question that they would never encounter in the real world is over the line in my opinion.
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I don't think so. This question is real. This question applies to a lot of aviation, including snow/ice runways. If you can't understand a basic fundamental of aviation you should not be instructing the fundamentals of aviation to students.

wbarnhill said:
But what do I know, I'm just a 24 year old PP-ASEL who hasn't flown in months. MONTHS! So there's my two cents and .1 on the Hobbs.
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Would you want an instructor teaching you about airplanes that does not understand thrust does not give a flying fornication about the wheels spinning? I sure wouldn't.
 
So if the treadmill is the same length as a runway, why would you want a treadmill? Seems like a dumb topic to get all spun up about.
 
AWACSEng said:
So if the treadmill is the same length as a runway, why would you want a treadmill? Seems like a dumb topic to get all spun up about.
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To me it implies in the question that yes, the airplane really will move forward. However, the point of the treadmill is to fool you into thinking of airplanes like cars.
 
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