airplane riddle (taken from another board) - Page 3

Doug Taylor · November 27th, 2005, 17:33

If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.

Philip · November 27th, 2005, 17:35

Quote:

Originally Posted by skywestseth

Okay it looks like after two pages of this going on the main question was sort of lost....it says in the question quoted right above here ...that the "plane" or aircraft speed would be identically matched by the treadmill...

so the answer is no it will not take off or accelerate....

by jacetheace

In my opinion Jacetheace spelled it out right here....

uhhhhh what does the speed that the wheels are spinning have to do with anything?
Why do you think the airplane isn't going to move just because the treadmill matches the speed?

Philip · November 27th, 2005, 17:36

Quote:

Originally Posted by Doug Taylor

If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.

logic, psh.

JaceTheAce · November 27th, 2005, 17:44

Quote:

Originally Posted by Doug Taylor

If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps?

The same logic applies to the airplane question.

It will slowly stop descending, then hover, then ascend up via the 150 fps...

BUT!

...........that is a helicopter who's lift is created 100% by it's thrust. It doesn't need relative wind. An airplane needs relative wind.

Here's another question: Will an airplane take off with a special humungous fan that creates a tailwind always exceeding it's stall speed? Keep in mind the fan adjusts the wind speed to exceed the airplanes ability to go faster than the relative wind.

JaceTheAce · November 27th, 2005, 17:47

Quote:

Originally Posted by Philip

uhhhhh what does the speed that the wheels are spinning have to do with anything?
Why do you think the airplane isn't going to move just because the treadmill matches the speed?

The treadmill would have to have an infinite speed in which case the airplane's tire would blow at one point anyway

JaceTheAce · November 27th, 2005, 17:55

Wait a minute... I'm actually thinking right now. The treadmill won't be able to defy the forces of propellar thrust; only the force created by a car's engine propelling a wheel to try to counteract the treadmill's force.

Propellar thrust is associated with relative wind (which is at a standstill and not affected by the treadmill) whereas a car wheel is directly affected by the treadmill (because it's directly planted onto it). Since the airplane's wheel is not associated with the counteracting forces of the treadmill, it will takeoff!

So basically the only way this would work is if there's the tailwind fan analogy I made above (to counteract against the thrust).

Oh man I feel like a dumba$$ lol.

SteveC · November 27th, 2005, 18:15

Quote:

Originally Posted by Chris_Ford

....Now get cracking on how a spring gets heavier when stretched

Start a new thread...

BrknWing4 · November 27th, 2005, 23:32

Discovery Channel "Myth Busters" here we come!!!

moxiepilot · November 28th, 2005, 00:15

Quote:

Originally Posted by BrknWing4

Discovery Channel "Myth Busters" here we come!!!

good idea.

JaceTheAce · November 28th, 2005, 01:24

Quote:

Originally Posted by moxiepilot

good idea.

The could use a Piper Cub

I'm sure it's wheel span is as wide as a treadmill and speed won't exceed the treadmill's speed

jk

JaceTheAce · November 28th, 2005, 01:38

And here we have a Physics forum discussing the same thing! Good answers...

http://forum.physorg.com/index.php?showtopic=2417&st=0

And another forum:

http://www.mikeportnoy.com/forum/tm....&key=&#1077146

Berkut · November 28th, 2005, 02:56

One of the posts on that physics forum cracked me up:

"Those who think that the airplane will take off are REALLY REALLY freaking ignorants and should not be on this forum."

B767Driver · November 28th, 2005, 09:12

I'm not a physics major...but I'll chime in.

I'll say the airplane will not fly. My thinking...taxi an airplane up an inclined plane. Use just enough power to keep it stationary...i.e. not rolling backwards. Let's say it takes 2000 rpm just to keep it from rolling back down the inclined plane. The airplane is still stationary...no way it can take off.

If the airplane is stationary on the conveyor...and while there's lots of work going on below the wing...there's no work being done on the wing.

I see no flying machine in this scenario.

SteveC · November 28th, 2005, 09:39

Quote:

Originally Posted by B767Driver

I'm not a physics major...but I'll chime in.

I'll say the airplane will not fly. My thinking...taxi an airplane up an inclined plane. Use just enough power to keep it stationary...i.e. not rolling backwards. Let's say it takes 2000 rpm just to keep it from rolling back down the inclined plane. The airplane is still stationary...no way it can take off.

If the airplane is stationary on the conveyor...and while there's lots of work going on below the wing...there's no work being done on the wing.

I see no flying machine in this scenario.

Bzzzt! Thanks for playing. Better luck next time, and be sure to visit our sponsors!

(j/k)

Rick Durden talks about this scenario in this week's AvWeb. See his article here.

JaceTheAce · November 28th, 2005, 11:42

Quote:

Originally Posted by SteveC

Bzzzt! Thanks for playing. Better luck next time, and be sure to visit our sponsors!

(j/k)

Rick Durden talks about this scenario in this week's AvWeb. See his article here.

Good article!

B767Driver · November 28th, 2005, 14:03

Quote:

Originally Posted by SteveC

Rick Durden talks about this scenario in this week's AvWeb. See his article here.

Okay the author has lost me with this info

[/quote]

My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.

[/quote]

...so is the airplane advancing forward on the conveyor? If so...this is a poorly worded deal.

SteveC · November 28th, 2005, 14:06

Quote:

Originally Posted by B767Driver

...so is the airplane advancing forward on the conveyor? If so...this is a poorly worded deal.

Yes to both!

E_Dawg · November 28th, 2005, 19:12

I'll keep this thread in mind next time I take off on a giant converyor belt.

skywestseth · November 28th, 2005, 20:13

Quote:

I'll keep this thread in mind next time I take off on a giant converyor belt.

Doug Taylor · November 28th, 2005, 22:16

Might be a good episode for that show "Myth Busters"!

pullup · November 29th, 2005, 00:38

Quote:

Originally Posted by B767Driver

Okay the author has lost me with this info

My comment: Notice that the question does not state that the conveyor's movement keeps the airplane over the starting position relative to the ground, just that it moves in the direction opposite to any movement of the airplane.

...so is the airplane advancing forward on the conveyor? If so...this is a poorly worded deal.

It's not poorly worded. The treadmill will match the planes speed. So when the plane is at rest the treadmill will not be going. However, when it reaches 1mph, the treadmill will be going 1 mph in the opposite direction. Result? The plane is still going 1 mph forward but the wheels are spinning at 2 mph. When the plane accelerates up to 100 mph, the wheels are now going 200 mph.

It's not that hard people

pullup · November 29th, 2005, 00:42

By some peoples theories, the plane would never move. So if you were coming in to land at 100 mph, on a treadmill going 100mph backwards, would you stop instantly? NOPE! you would continue your normal landing roll excpet your wheels are going twice as fast. Your roll may be shortened by the added friction effects in the wheel bearings, etc but you get the big picture (hopefully)

JaceTheAce · November 29th, 2005, 11:14

Check this out (stolen from another forum):

KLB · November 29th, 2005, 12:25

but the conveyer belt is changing its speed in order to keep the plane in the same position. true, if the plane can move forward and produce lift over the wings, enough for takeoff then yes it will get off the ground. however, if the plane does not move forward, which is what i gather from the riddle, then no, it will not take off.

Philip · November 29th, 2005, 13:25

dammit I wish I could edit my post and delete this so it haunts you all for life

November 27th, 2005, 17:33	#51
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 39,271 Blog Entries: 1	If a helicopter is on the surface of a giant elevator descending at 150 fps, the pilot moves the collective to produce a 150 fps climb, will it remain on the elevator, hover, or climb at 150 fps? The same logic applies to the airplane question. __________________ Doug Taylor http://76school.flyblog.com (old!) http://30west.flyblog.com (updated 11/28)

November 27th, 2005, 17:55	#56
JaceTheAce Old Skool Join Date: Sep 2001 Location: San Diego, CA Posts: 7,236	Wait a minute... I'm actually thinking right now. The treadmill won't be able to defy the forces of propellar thrust; only the force created by a car's engine propelling a wheel to try to counteract the treadmill's force. Propellar thrust is associated with relative wind (which is at a standstill and not affected by the treadmill) whereas a car wheel is directly affected by the treadmill (because it's directly planted onto it). Since the airplane's wheel is not associated with the counteracting forces of the treadmill, it will takeoff! So basically the only way this would work is if there's the tailwind fan analogy I made above (to counteract against the thrust). Oh man I feel like a dumba$$ lol. __________________ Dash 8 FO "Time spent flying is not deducted from one's lifespan."

November 28th, 2005, 01:38	#61
JaceTheAce Old Skool Join Date: Sep 2001 Location: San Diego, CA Posts: 7,236	And here we have a Physics forum discussing the same thing! Good answers... http://forum.physorg.com/index.php?showtopic=2417&st=0 And another forum: http://www.mikeportnoy.com/forum/tm....&key=&#1077146 __________________ Dash 8 FO "Time spent flying is not deducted from one's lifespan."

November 28th, 2005, 02:56	#62
Berkut Senior Member Join Date: Oct 2000 Location: Murfreesboro, TN USA Posts: 886	One of the posts on that physics forum cracked me up: "Those who think that the airplane will take off are REALLY REALLY freaking ignorants and should not be on this forum." __________________ When seconds count, the police are only minutes away

November 28th, 2005, 19:12	#68
E_Dawg Moderator Join Date: Apr 2002 Location: chicago Posts: 4,123	I'll keep this thread in mind next time I take off on a giant converyor belt. __________________ Yeah, I just stare at my desk; but it looks like I'm working. I do that for probably another hour after lunch, too. I'd say in a given week I probably only do about fifteen minutes of real, actual, work.

November 27th, 2005, 23:32	#58
BrknWing4 Newbie Join Date: May 2005 Location: Spotsylvania, VA Posts: 18	Discovery Channel "Myth Busters" here we come!!!

November 28th, 2005, 09:12	#63
B767Driver Old Skool Join Date: Sep 2003 Posts: 1,830	I'm not a physics major...but I'll chime in. I'll say the airplane will not fly. My thinking...taxi an airplane up an inclined plane. Use just enough power to keep it stationary...i.e. not rolling backwards. Let's say it takes 2000 rpm just to keep it from rolling back down the inclined plane. The airplane is still stationary...no way it can take off. If the airplane is stationary on the conveyor...and while there's lots of work going on below the wing...there's no work being done on the wing. I see no flying machine in this scenario.

November 28th, 2005, 22:16	#70
Doug Taylor Agent Smith Join Date: Dec 1969 Location: KSDL Posts: 39,271 Blog Entries: 1	Might be a good episode for that show "Myth Busters"! __________________ Doug Taylor http://76school.flyblog.com (old!) http://30west.flyblog.com (updated 11/28)

November 29th, 2005, 11:14	#73
JaceTheAce Old Skool Join Date: Sep 2001 Location: San Diego, CA Posts: 7,236	Check this out (stolen from another forum): __________________ Dash 8 FO "Time spent flying is not deducted from one's lifespan."

November 29th, 2005, 12:25	#74
KLB Old Skool Join Date: May 2005 Location: DFW Posts: 2,413	okay but the conveyer belt is changing its speed in order to keep the plane in the same position. true, if the plane can move forward and produce lift over the wings, enough for takeoff then yes it will get off the ground. however, if the plane does not move forward, which is what i gather from the riddle, then no, it will not take off.

November 29th, 2005, 13:25	#75
Philip Senior Member Join Date: Oct 2005 Location: KAPA Posts: 1,315	dammit I wish I could edit my post and delete this so it haunts you all for life

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