Notices
Like Tree198Likes

Fun physics question.

Old 01-20-2019, 08:16 PM
  #1061  
Senior Member
 
Join Date: Nov 2009
Location: Jax, Fl
Posts: 4,069
Default

if a 747 with out wings and fuel assumes that a person with long hair and lipstick in high heels might be good at place kicking a football???? is dada art? or is super realism a philosophy?
fijon is offline  
Old 01-20-2019, 08:17 PM
  #1062  
Senior Member
 
Join Date: Jan 2007
Location: NSW Australia
Posts: 4,808
Default

For all the people that want to cloud the question to suit themselves, the parameters are given, the only thing different to a "normal" 747 takeoff is given, the wheels are on a conveyer designed to match the speed of the wheels, that's it, nothing more, nothing less, whether it has fuel, is painted red or has a Chinese pilot are not part of the question and never will be.
fijon likes this.
noelm is offline  
Old 01-20-2019, 08:36 PM
  #1063  
Senior MemberCaptains Club Member
 
Join Date: Nov 2005
Location: Paradise, FL
Posts: 1,280
Default

Originally Posted by noelm View Post
For all the people that want to cloud the question to suit themselves, the parameters are given, the only thing different to a "normal" 747 takeoff is given, the wheels are on a conveyer designed to match the speed of the wheels, that's it, nothing more, nothing less, whether it has fuel, is painted red or has a Chinese pilot are not part of the question and never will be.
...and therein lies the answer - the conveyor matching the speed of the wheels makes the conveyor go an equal speed in the other direction, doubling the wheel speed. But the plane takes off because the airspeed remains the same as with a static runway.
WaterDamage is offline  
Old 01-20-2019, 09:32 PM
  #1064  
Senior Member
 
Join Date: Dec 2014
Posts: 1,054
Default

Originally Posted by noelm View Post

here's another one WHAT CHAIN? don't add irrelevant shit.
It's not irrelevant, it's just an attempt to help folks realize that the conveyor belt and wheels moving in opposite directions at equal speed work exactly the same way a chain would, namely that both deny any forward motion to the airplane regardless of how much thrust is applied by the plane's engines. If you can't see that I can't help you. I can try to show you, but I can't make you see. There are some things that can't be fixed.
flcatcher1 is offline  
Old 01-20-2019, 09:55 PM
  #1065  
Senior Member
 
Join Date: Jan 2007
Location: NSW Australia
Posts: 4,808
Default

No, you can't make me see, because it's not right, the speed of wheels on a plane have no influence on whether the plane can fly or not, they are not attached to the means of propulsion in any way shape or form, as mentioned many times, the wheels can be skids, tanks are a couple of sticks, the wheel speed relative to the conveyer is not in the equation, the wheel speed relative to the ground beside the conveyer is important, you are confusing a car with driven wheels on a conveyer to a plane with free spinning wheels.
noelm is offline  
Old 01-20-2019, 10:18 PM
  #1066  
Senior Member
 
Join Date: Mar 2016
Location: The South Coast
Posts: 733
Default

Originally Posted by noelm View Post
For all the people that want to cloud the question to suit themselves, the parameters are given, the only thing different to a "normal" 747 takeoff is given, the wheels are on a conveyer designed to match the speed of the wheels, that's it, nothing more, nothing less, whether it has fuel, is painted red or has a Chinese pilot are not part of the question and never will be.
I find the "you're making all these assumptions" argument against takeoff somewhat humorous.

I'm thinking back to studying physics and seeing problems like "Given X, Y, and Z, can an observer tell A, B, or C?"

Pretty sure if I'd answered "there's no way to know because the observer could have just been stabbed in the neck and be losing consciousness at this exact moment, you haven't ruled out that possibility" I wouldn't have done especially well in school.

The question only becomes a question if we assume the plane could fly if the treadmill replaces a normal runway. Otherwise you get sidetracked by ideas like "can the treadmill run backwards?"

Because if it's really low friction, which seems possible given that we're supposed to imagine that it can perfectly and instantly match the speed of the wheels, then we need to know the length of the treadmill and whether it can move in either direction. After all, the wheels don't NEED to turn for the plane to move. If you've ever seen a tundra plane landing on a frozen lake (yes, I'm Canadian) you may have seen wheels that don't rotate on contact with a surface. A treadmill as long as a runway, with lower friction than whatever is inherent in the wheels, would allow the plane to accelerate smoothly down the runway and take off, without spinning the tires at all.

The only way to avoid progressing into infinite layers of ridiculousness with interpreting questions like this is to assume the plane is a plane, the treadmill is a treadmill, the wheels are wheels, and everything behaves like it ordinarily does. The wheels don't reach infinite speed, the bearings don't get white hot and explode and cause the plane to crash. The plane isn't held perfectly in place on account of the perfect theoretical treadmill. The wheels just spin up and the plane takes off.

If you want to interpret the whole thing as a riddle with a "gotcha" answer, then sure, if you define the wheel speed in narrow enough terms you can insist that it results in an artificial state of a plane which can't move. But in reality, if you put a plane on a treadmill and spin the treadmill backwards as the plane spools up, it just flies away.
noelm and STIPulation like this.
cracked_ribs is offline  
Old 01-21-2019, 12:46 AM
  #1067  
Senior Member
 
Join Date: Jan 2007
Location: NSW Australia
Posts: 4,808
Default

Probably one of the most sane posts so far.
noelm is offline  
Old 01-21-2019, 04:43 AM
  #1068  
Senior MemberCaptains Club Member
 
Join Date: Nov 2001
Location: Greensboro, NC
Posts: 3,741
Default

Originally Posted by Mr. Demeanor View Post
I say yes.
The wheels are needed to establish movement of the aircraft to get air flow over the wings to get lift. The power to initiate the movement is from engine thrust. If the AC doesn't move then no lift.
If the 747 we're standing vertical and the engines at Max thrust would the plane fly? A resounding no. If the plane were on it's belly with no wheels and at Max thrust would it fly? NO.
If the 747 was on a conveyor that immediatly cancelled any forward movement of the aircraft even tho at Max thrust would it fly. No air and lift from the wings so no. Thrust all one wants but if no movement no takeoff.

If the plane was on a normal conveyor on it's belly, no wheels at Max thrust would it fly?? Absolutely.
Landing would be challenging tho.
round2it is offline  
Old 01-21-2019, 05:01 AM
  #1069  
Senior Member
 
Join Date: Jan 2006
Location: Sunny florida
Posts: 23,034
Default

Originally Posted by km1125 View Post
Assume, assume, assume.

You have to make a lot of assumptions to answer the problem "Yes". You have to make no assumptions to answer the problem "No". Just read the problem.
If the plane takes of vertically, then it can take off. You "assume" it's a rolling take-off. Yes, it's poorly worded question.

CAN the plane take off? Yes. WILL the plane take off? The crux of the discussion.

Someone needs to dumb this question down and use it as an example at teachers college...Many (not all) teachers MAY benefit from it.
billinstuart is offline  
Old 01-21-2019, 05:22 AM
  #1070  
Senior Member
 
Join Date: Feb 2010
Location: Palm Beach Gardens FL
Posts: 1,535
Default

When the airflow over the wings reaches 140 mph the wings will create lift and the 747 will begin to fly. Wheels, runways, conveyor belts make absolutely no difference. 140 = flight. Period.
Fiberglass1 Inc is offline  
Old 01-21-2019, 05:33 AM
  #1071  
Admirals ClubCaptains Club Member Admiral's Club Member
THT sponsor
 
Join Date: Aug 2003
Location: Sarasota FL
Posts: 7,038
Default

Originally Posted by Fiberglass1 Inc View Post
When the airflow over the wings reaches 140 mph the wings will create lift and the 747 will begin to fly. Wheels, runways, conveyor belts make absolutely no difference. 140 = flight. Period.
When the plane hits 140 MPH air speed (assuming no wind)
the tires would be turning 140 MPH Faster then the conveyor belt.
(nothing stopping that from happening)

To some, they see no issue with the plane wheels turning faster then the conveyor belt.
To others, they say, the problem states the conveyor belt has to be turning the exact same speed as the plane tires. (which is an impossibility if the plane is moving on the treadmill)

Last edited by ken2; 01-21-2019 at 06:08 AM.
ken2 is offline  
Old 01-21-2019, 06:00 AM
  #1072  
Senior MemberCaptains Club Member
 
Join Date: Nov 2001
Location: Greensboro, NC
Posts: 3,741
Default

How would the wind be moving 140mph over the wing? The plane won't be moving as the conveyor cancels the forward motion.

If the plane was standing verically would it fly? No because the aircraft would not be moving to get the airflow over the wing.

If the conveyor exactly matches the wheel speed as stated in the original post which would negate any movement of the aircraft.

The analogy of runners beside the perfect world conveyor doesn't work if they are not on the conveyor. Put them there and they would not pull the person on the skates anywhere.

Last edited by round2it; 01-21-2019 at 08:49 AM.
round2it is offline  
Old 01-21-2019, 06:26 AM
  #1073  
Senior Member
 
Join Date: Feb 2017
Posts: 1,837
Default

Originally Posted by Fiberglass1 Inc View Post
When the airflow over the wings reaches 140 mph the wings will create lift and the 747 will begin to fly. Wheels, runways, conveyor belts make absolutely no difference. 140 = flight. Period.
Now you're introducing a whole 'nuther aspect. But if your statement is true, then how come planes crash (or make "premature ground contact") when they're still going over 140MPH.
km1125 is offline  
Old 01-21-2019, 07:04 AM
  #1074  
Admirals Club Admiral's Club Member
 
Join Date: Sep 2012
Location: Greenville/MHC, NC
Posts: 2,611
Default

I'm just glad I don't work for some of y'all.
aFORDable is offline  
Old 01-21-2019, 08:12 AM
  #1075  
Senior Member
 
Join Date: Aug 2009
Location: CT
Posts: 4,077
Default

Originally Posted by aFORDable View Post
I'm just glad I don't work for some of y'all.

Don’t kid yourself some of the non-fly brain trust are well versed in modern technology and science. These guys routinely have blood drained off to keep them healthy, have lead tooth fillings and are capable of drawing really complex images on the wall of their caves using a stick of charcoal as an outliner and crushed berries for paint.

Not to mention we can thank them for the sun, they make a few human sacrifices annually to make sure it keeps rising.....
aFORDable likes this.
Mpellet is offline  
Old 01-21-2019, 08:42 AM
  #1076  
Senior Member
 
Join Date: Feb 2017
Posts: 1,837
Default

Originally Posted by Mpellet View Post
Don’t kid yourself some of the non-fly brain trust are well versed in modern technology and science. These guys routinely have blood drained off to keep them healthy, have lead tooth fillings and are capable of drawing really complex images on the wall of their caves using a stick of charcoal as an outliner and crushed berries for paint.

Not to mention we can thank them for the sun, they make a few human sacrifices annually to make sure it keeps rising.....
Your assumption was that he was referring to the 'non-fly' guys. Wrong?
km1125 is offline  
Old 01-21-2019, 08:56 AM
  #1077  
Senior Member
 
Join Date: Mar 2017
Posts: 815
Default

If the plane has no forward momentum it will not takeoff. Imo if the conveyor belt is matching the speed of the acft then the acft would infact be stationary, therefore there would be no airflow over and under the wings to create lift.
the thrust of the engines would not lift the aircraft without the negative airflow over the top of the wings
MercuryMan200 is offline  
Old 01-21-2019, 08:58 AM
  #1078  
Admirals Club Admiral's Club Member
 
Join Date: Feb 2012
Location: Beaufort, NC
Posts: 1,437
Default

The conveyor belt cannot stop the airplane.
STIPulation is online now  
Old 01-21-2019, 09:06 AM
  #1079  
Senior MemberCaptains Club Member
 
Join Date: Feb 2003
Location: PA
Posts: 239
Default

The plane will take off normally. The only difference from a normal takeoff is that the wheels will be spinning twice as fast as normal. It is really that simple.
dmartin is offline  
Old 01-21-2019, 09:08 AM
  #1080  
Senior MemberCaptains Club Member
 
Join Date: Nov 2001
Location: Greensboro, NC
Posts: 3,741
Default

Originally Posted by Mpellet View Post



Don’t kid yourself some of the non-fly brain trust are well versed in modern technology and science. These guys routinely have blood drained off to keep them healthy, have lead tooth fillings and are capable of drawing really complex images on the wall of their caves using a stick of charcoal as an outliner and crushed berries for paint.

Not to mention we can thank them for the sun, they make a few human sacrifices annually to make sure it keeps rising.....
Originally Posted by aFORDable View Post
I'm just glad I don't work for some of y'all.
Originally Posted by seatec View Post
LOL there is a web site describing this thread to a T and they also state that there will always be a know it all stating that the answer is simple and denigrating everybody who doesn't agree.

Congrats. You made the cut.
Yes.
round2it is offline  

Thread Tools
Search this Thread