What-If 0056: "Restraining an Airplane"

What if there was a forum for discussing these?

Moderators: Moderators General, Prelates, Magistrates

thesilv3r
Posts: 9
Joined: Fri Aug 14, 2009 12:33 pm UTC

What-If 0056: "Restraining an Airplane"

Postby thesilv3r » Tue Jul 30, 2013 9:16 am UTC

What-If 56: Restraining an Airplane

If you wanted to anchor an airplane into the ground so it wouldn't be able to take off, what would the rope have to be made out of?
—Connor Childerhose


Image

But what if you wanted to restrain an Aeroplane?

Also, I know braiding/plaiting/twisting is supposed to help the strength of rope, could this be applied here, or would it decrease "thickness" efficiency?

User avatar
Flumble
Yes Man
Posts: 2084
Joined: Sun Aug 05, 2012 9:35 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Flumble » Tue Jul 30, 2013 9:19 am UTC

Too bad Randall didn't go into detail about using bones.

Image

thesilv3r wrote:But what if you wanted to restrain an Aeroplane?

Oh no you don't! We have quite enough of those discussions already.


[edit] I can't seem to resize the image with bbcode
Last edited by Flumble on Tue Jul 30, 2013 9:23 am UTC, edited 1 time in total.

User avatar
rhomboidal
Posts: 791
Joined: Wed Jun 15, 2011 5:25 pm UTC
Contact:

Re: What-If 0056: "Restraining an Airplane"

Postby rhomboidal » Tue Jul 30, 2013 9:22 am UTC

I can't wait to catch the "Cirque Du Sowhale" act at SeaWorld.

Ehsanit
Posts: 50
Joined: Tue Nov 09, 2010 7:53 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Ehsanit » Tue Jul 30, 2013 10:05 am UTC

This is a very important question.
If someone drops an aeroplane, they might never hear it hit the bottom!

User avatar
peewee_RotA
Posts: 504
Joined: Mon Dec 12, 2011 1:19 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby peewee_RotA » Tue Jul 30, 2013 11:34 am UTC

Mythbusters actually tackled both concepts here. The first to discuss is the human hair rope. It comes from relatively short strands braided together. The strength of the hairs themselves are relatively meaningless because the joints are the failure point. They did a lot of braiding and were able to make one that held the weight of a person as they climbed.

The second is a cable strength test. They tried to make a "bat mobile" turn entirely based on a grapple. They had trouble finding any cable in existence that could hand the inertia. This was a very quick yank that began at full speed. Our plain plane (on a plane) would have a gradually increasing speed. But I honestly think that at takeoff speed, and with a weight heavy enough to restrain the plane, all discussed cables and ropes would snap, even at that thickness. Because the thickness is sourced from a catalog of existing cables, I have to have my doubts.
"Vowels have trouble getting married in Canada. They can’t pronounce their O’s."

http://timelesstherpg.wordpress.com/about/

CharlieP
Posts: 397
Joined: Mon Dec 17, 2012 10:22 am UTC
Location: Nottingham, UK

Re: What-If 0056: "Restraining an Airplane"

Postby CharlieP » Tue Jul 30, 2013 11:45 am UTC

thesilv3r wrote:But what if you wanted to restrain an Aeroplane?


Out of interest, what's the historic reason for having two different words in the UK and USA, and which one do other parts of the Anglosphere use?
This is my signature. There are many like it, but this one is mine.

dalcde
Posts: 173
Joined: Fri Apr 06, 2012 5:49 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby dalcde » Tue Jul 30, 2013 11:45 am UTC

Given that individual hairs can support about 50 grams of weight

Liek Srsly?

User avatar
Klear
Posts: 1965
Joined: Sun Jun 13, 2010 8:43 am UTC
Location: Prague

Re: What-If 0056: "Restraining an Airplane"

Postby Klear » Tue Jul 30, 2013 11:56 am UTC

CharlieP wrote:
thesilv3r wrote:But what if you wanted to restrain an Aeroplane?


Out of interest, what's the historic reason for having two different words in the UK and USA, and which one do other parts of the Anglosphere use?


The word came to England through France, while obviously being derived from Greek. The form "airplane" originated in the UK, but never caught on there, and according to wikipedia it is used in the USA and Canada, while the UK and most of the commonwealth uses aeroplane.

User avatar
Flumble
Yes Man
Posts: 2084
Joined: Sun Aug 05, 2012 9:35 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Flumble » Tue Jul 30, 2013 12:48 pm UTC

dalcde wrote:
Given that individual hairs can support about 50 grams of weight

Liek Srsly?

srsly d00d

Although all internet sources disagree with eachtother, the absolute lower limit I found was 5 gram and the upper limit over 2,4 kilogram. Taking an exponential average*, you end up with a tensile strength of 117 gram.

Sources:
http://en.wikipedia.org/wiki/Ultimate_tensile_strength
http://www.kgbanswers.co.uk/what-is-the ... ir/3434316
http://wiki.answers.com/Q/What_is_the_a ... human_hair
http://hypertextbook.com/facts/1999/BrianLey.shtml


*Image - using e is quite arbitrary but whatever.

User avatar
BrianB
Posts: 94
Joined: Wed Feb 23, 2011 3:50 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby BrianB » Tue Jul 30, 2013 1:09 pm UTC

I think that Randall makes an error in regards to the human hair portion...

Shown in his graphic are 20 people with their hair attached to the plane. While the tensile strength of the combined strands of hair may be able to withstand the pulling force of the jet engines, most certainly the body weight of those 20 people just standing there won't keep the plane from moving. (i.e. no sufficient anchor point)

Conclusion: The tensile strength of the hair from 20 people is enough to allow those people to be dragged down the runway and into the air as the plane takes off.

User avatar
Klear
Posts: 1965
Joined: Sun Jun 13, 2010 8:43 am UTC
Location: Prague

Re: What-If 0056: "Restraining an Airplane"

Postby Klear » Tue Jul 30, 2013 1:18 pm UTC

BrianB wrote:I think that Randall makes an error in regards to the human hair portion...

Shown in his graphic are 20 people with their hair attached to the plane. While the tensile strength of the combined strands of hair may be able to withstand the pulling force of the jet engines, most certainly the body weight of those 20 people just standing there won't keep the plane from moving. (i.e. no sufficient anchor point)

Conclusion: The tensile strength of the hair from 20 people is enough to allow those people to be dragged down the runway and into the air as the plane takes off.


Yeah, I thought the same could happen with the legion of fishermen, though it is a lot of fishermen.

mr_six
Posts: 6
Joined: Tue Apr 16, 2013 4:17 pm UTC
Location: 43.96362 -92.05791

Re: What-If 0056: "Restraining an Airplane"

Postby mr_six » Tue Jul 30, 2013 1:36 pm UTC

Where is 7?

BrianK
Posts: 17
Joined: Tue Jul 30, 2013 1:15 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby BrianK » Tue Jul 30, 2013 1:49 pm UTC

peewee_RotA wrote:Mythbusters actually tackled both concepts here. The first to discuss is the human hair rope. It comes from relatively short strands braided together. The strength of the hairs themselves are relatively meaningless because the joints are the failure point. They did a lot of braiding and were able to make one that held the weight of a person as they climbed.

The second is a cable strength test. They tried to make a "bat mobile" turn entirely based on a grapple. They had trouble finding any cable in existence that could hand the inertia. This was a very quick yank that began at full speed. Our plain plane (on a plane) would have a gradually increasing speed. But I honestly think that at takeoff speed, and with a weight heavy enough to restrain the plane, all discussed cables and ropes would snap, even at that thickness. Because the thickness is sourced from a catalog of existing cables, I have to have my doubts.


The trouble the MythBusters ran into is that as the cables get stronger, they also get stiffer. Stiffer cables stop the car over a shorter distance, so the shock loads go up. They needed to engineer some compliance into the system. A stretchier cable material or a mounting point with some noticable give would have helped a lot.

In rock climbing, for instance, there are actually two different rope categories. Static rope which is meant for climbs where the route is already established and any falls will be relatively short. These ropes are stiff so that you don't expend a lot of energy stretching the rope. Then there is dynamic rope for lead climbing. In lead climbing, the route is not pre-established. The highest anchor point is usually below the climber, so falls are much longer. The rope has to be stretchy to soften the shock load and keep from breaking the climber.

User avatar
Red Hal
Magically Delicious
Posts: 1445
Joined: Wed Nov 28, 2007 2:42 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Red Hal » Tue Jul 30, 2013 2:40 pm UTC

In the hospital after eating 9.
Lost Greatest Silent Baby X Y Z. "There is no one who loves pain itself, who seeks after it and wants to have it, simply because it is pain..."

DanD
Posts: 316
Joined: Tue Oct 05, 2010 12:42 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby DanD » Tue Jul 30, 2013 2:52 pm UTC

thesilv3r wrote:What-If 56: Restraining an Airplane


Also, I know braiding/plaiting/twisting is supposed to help the strength of rope, could this be applied here, or would it decrease "thickness" efficiency?


Braiding or twisting increases the strength because it improves force transfer between individual fibers, which are typically considerably shorter than the overall cable. Even in cases where the individual strands are as long as the cable (wire cable, some synthetics), if an individual fiber breaks, this allows the load to be transferred to the remainder more efficiently.

It doesn't do anything to increase the actual fiber strength, however.

DanD
Posts: 316
Joined: Tue Oct 05, 2010 12:42 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby DanD » Tue Jul 30, 2013 2:55 pm UTC

peewee_RotA wrote:The second is a cable strength test. They tried to make a "bat mobile" turn entirely based on a grapple. They had trouble finding any cable in existence that could hand the inertia. This was a very quick yank that began at full speed. Our plain plane (on a plane) would have a gradually increasing speed. But I honestly think that at takeoff speed, and with a weight heavy enough to restrain the plane, all discussed cables and ropes would snap, even at that thickness. Because the thickness is sourced from a catalog of existing cables, I have to have my doubts.


If you were attempting to restrain the plane from moving at all, then the static load rating of the cable is plenty. If you're attempting to jerk the plane to a halt just before takeoff, then you're probably correct, but I also suspect the cable would damage the plane sufficiently that it would still be unable to take off.

mr_six
Posts: 6
Joined: Tue Apr 16, 2013 4:17 pm UTC
Location: 43.96362 -92.05791

Re: What-If 0056: "Restraining an Airplane"

Postby mr_six » Tue Jul 30, 2013 3:24 pm UTC

Red Hal wrote:In the hospital after eating 9.


Har Har Har

User avatar
cellocgw
Posts: 1956
Joined: Sat Jun 21, 2008 7:40 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby cellocgw » Tue Jul 30, 2013 4:49 pm UTC

The drawback to using a whale as counterweight is you never know when it's going to turn into petunias.
https://app.box.com/witthoftresume
Former OTTer
Vote cellocgw for President 2020. #ScienceintheWhiteHouse http://cellocgw.wordpress.com
"The Planck length is 3.81779e-33 picas." -- keithl
" Earth weighs almost exactly π milliJupiters" -- what-if #146, note 7

User avatar
Klear
Posts: 1965
Joined: Sun Jun 13, 2010 8:43 am UTC
Location: Prague

Re: What-If 0056: "Restraining an Airplane"

Postby Klear » Tue Jul 30, 2013 5:01 pm UTC

cellocgw wrote:The drawback to using a whale as counterweight is you never know when it's going to turn into petunias.


...or a nuclear warhead.

User avatar
PinkShinyRose
Posts: 833
Joined: Mon Nov 05, 2012 6:54 pm UTC
Location: the Netherlands

Re: What-If 0056: "Restraining an Airplane"

Postby PinkShinyRose » Tue Jul 30, 2013 5:44 pm UTC

DanD wrote:
peewee_RotA wrote:The second is a cable strength test. They tried to make a "bat mobile" turn entirely based on a grapple. They had trouble finding any cable in existence that could hand the inertia. This was a very quick yank that began at full speed. Our plain plane (on a plane) would have a gradually increasing speed. But I honestly think that at takeoff speed, and with a weight heavy enough to restrain the plane, all discussed cables and ropes would snap, even at that thickness. Because the thickness is sourced from a catalog of existing cables, I have to have my doubts.


If you were attempting to restrain the plane from moving at all, then the static load rating of the cable is plenty. If you're attempting to jerk the plane to a halt just before takeoff, then you're probably correct, but I also suspect the cable would damage the plane sufficiently that it would still be unable to take off.


Considering the whale diagram, the aeroplane could not have accelerated that much on that small piece of runway (I don't think one 747 length is sufficient to reach an almost take-off velocity). On the other hand, if the engines were not already generating their full thrust the plane would have been moved backwards by the whales mass...

I'm mostly afraid that if something were to give the aeroplane an extra push away from the whale, the whale would hurt its head :( (I'm also generally opposed to using threatened species as a counterweight in an experiment which has no need for the use of threatened species).

rhetorical
Posts: 103
Joined: Wed Apr 21, 2010 12:44 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby rhetorical » Tue Jul 30, 2013 11:12 pm UTC

Klear wrote:
CharlieP wrote:
thesilv3r wrote:But what if you wanted to restrain an Aeroplane?


Out of interest, what's the historic reason for having two different words in the UK and USA, and which one do other parts of the Anglosphere use?


The word came to England through France, while obviously being derived from Greek. The form "airplane" originated in the UK, but never caught on there, and according to wikipedia it is used in the USA and Canada, while the UK and most of the commonwealth uses aeroplane.


Are they pronounced differently? Air-o-plane?

ijuin
Posts: 934
Joined: Fri Jan 09, 2009 6:02 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby ijuin » Wed Jul 31, 2013 5:27 am UTC

BrianB wrote:I think that Randall makes an error in regards to the human hair portion...

Shown in his graphic are 20 people with their hair attached to the plane. While the tensile strength of the combined strands of hair may be able to withstand the pulling force of the jet engines, most certainly the body weight of those 20 people just standing there won't keep the plane from moving. (i.e. no sufficient anchor point)

Conclusion: The tensile strength of the hair from 20 people is enough to allow those people to be dragged down the runway and into the air as the plane takes off.


Besides the strength of the hair, there's the strength of their scalps to consider. I'm pretty sure that if an equal force is placed on all of the hairs, the whole scalp would separate from the skull before the hairs separated from the scalp.

Speaking of which, I think that the 50 grams (i.e. 0.50 newton) figure is based on how much force is required to pull a hair out of its follicle, rather than the force required to snap the hair itself.

CharlieP
Posts: 397
Joined: Mon Dec 17, 2012 10:22 am UTC
Location: Nottingham, UK

Re: What-If 0056: "Restraining an Airplane"

Postby CharlieP » Wed Jul 31, 2013 8:00 am UTC

rhetorical wrote:
Klear wrote:
CharlieP wrote:
thesilv3r wrote:But what if you wanted to restrain an Aeroplane?


Out of interest, what's the historic reason for having two different words in the UK and USA, and which one do other parts of the Anglosphere use?


The word came to England through France, while obviously being derived from Greek. The form "airplane" originated in the UK, but never caught on there, and according to wikipedia it is used in the USA and Canada, while the UK and most of the commonwealth uses aeroplane.


Are they pronounced differently? Air-o-plane?


More like "air-a-plain" the way I say it. The UK variant, that is.
This is my signature. There are many like it, but this one is mine.

User avatar
Xenomortis
Not actually a special flower.
Posts: 1426
Joined: Thu Oct 11, 2012 8:47 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Xenomortis » Wed Jul 31, 2013 8:40 am UTC

rhetorical wrote:Are they pronounced differently? Air-o-plane?

Yes.
Aeroplane has three syllables to Airplane's two.

CharlieP wrote:More like "air-a-plain" the way I say it. The UK variant, that is.

I'm not sure how much it varies across regional accents.
Image

User avatar
Copper Bezel
Posts: 2426
Joined: Wed Oct 12, 2011 6:35 am UTC
Location: Web exclusive!

Re: What-If 0056: "Restraining an Airplane"

Postby Copper Bezel » Wed Jul 31, 2013 9:17 am UTC

ijuin wrote:Speaking of which, I think that the 50 grams (i.e. 0.50 newton) figure is based on how much force is required to pull a hair out of its follicle, rather than the force required to snap the hair itself.

Nothing much to indicate that if it's the case - I think he calculated it based on the tensile strength. Like Flumble said, there's a lot of variance both in tensile strength figures and in human hair thickness, but going with his lower 200 MPa figure and the lowest thickness for black hair from Flumble's Hypertextbook link gets to almost exactly 50 grams - 2e8 * (2.8e-5^2 * pi) / 9.78 = .05 kg.

Like Flumble said, you can raise that quite a bit by using less conservative figures - Wikipedia has a larger average diameter for hair (not even specifying color) and greater tensile strength that come to 300 grams - but I think Randall would be likely to use the more conservative numbers he encountered, and I think it's too close a match to be a coincidence.

Huh. Not all the characters in the drawing have black hair, though. = )
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

she / her / her

User avatar
Flumble
Yes Man
Posts: 2084
Joined: Sun Aug 05, 2012 9:35 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Flumble » Wed Jul 31, 2013 11:58 am UTC

Time for an EXPERIMENT:
Image

I got a measurement of 70 grams for A strand of caucasian male blonde hair. (I'm not saying it's mine) Above that either the hair had slipped out of my hand or split in half. Given the setup you could say there's a lower margin of -0% and an upper margin of +24%, for using a small lever* and not pulling straight upwards** and not pulling with an equal force*** and pulling it from my head just after washing****. *****


*while the hair is fixed to the side of the platform, this accounts for a difference of less than a gram, as was tested by placing loads at different positions along the platform.
**this account for at most +4% as I can assume I pulled the hair at no more than 15° with respect to the platform normal.
***let's just assume I could've suddenly pulled 20% harder because of my motoric ineptness.
****it is assumed hair that has just been in contact with water and shampoo is equally or less tensile.
*****Yes, it is just one random strand. All the previous error margins are mentioned for testing myself on how many variables I can find and rule out.

User avatar
Klear
Posts: 1965
Joined: Sun Jun 13, 2010 8:43 am UTC
Location: Prague

Re: What-If 0056: "Restraining an Airplane"

Postby Klear » Wed Jul 31, 2013 11:59 am UTC

Xenomortis wrote:
rhetorical wrote:Are they pronounced differently? Air-o-plane?

Yes.
Aeroplane has three syllables to Airplane's two.

CharlieP wrote:More like "air-a-plain" the way I say it. The UK variant, that is.

I'm not sure how much it varies across regional accents.


I learnt to pronounce it from this. Oddly, RHCP are American. I guess they needed the extra syllable for the music to work.

charonme
Posts: 141
Joined: Sun May 18, 2008 11:18 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby charonme » Wed Jul 31, 2013 12:27 pm UTC

a 747's four engines can each generate 281.57 kN of thrust
is that also with air in front and around the engines being completely still or does the air need to move (for example if there was a strong opposite wind or if the plane was already moving forward) for the engines to generate that much thrust?

SemisolidSnake
Posts: 7
Joined: Wed Mar 20, 2013 4:06 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby SemisolidSnake » Wed Jul 31, 2013 4:34 pm UTC

BrianK wrote:
peewee_RotA wrote:Mythbusters actually tackled both concepts here. The first to discuss is the human hair rope. It comes from relatively short strands braided together. The strength of the hairs themselves are relatively meaningless because the joints are the failure point. They did a lot of braiding and were able to make one that held the weight of a person as they climbed.

The second is a cable strength test. They tried to make a "bat mobile" turn entirely based on a grapple. They had trouble finding any cable in existence that could hand the inertia. This was a very quick yank that began at full speed. Our plain plane (on a plane) would have a gradually increasing speed. But I honestly think that at takeoff speed, and with a weight heavy enough to restrain the plane, all discussed cables and ropes would snap, even at that thickness. Because the thickness is sourced from a catalog of existing cables, I have to have my doubts.


The trouble the MythBusters ran into is that as the cables get stronger, they also get stiffer. Stiffer cables stop the car over a shorter distance, so the shock loads go up. They needed to engineer some compliance into the system. A stretchier cable material or a mounting point with some noticable give would have helped a lot.

In rock climbing, for instance, there are actually two different rope categories. Static rope which is meant for climbs where the route is already established and any falls will be relatively short. These ropes are stiff so that you don't expend a lot of energy stretching the rope. Then there is dynamic rope for lead climbing. In lead climbing, the route is not pre-established. The highest anchor point is usually below the climber, so falls are much longer. The rope has to be stretchy to soften the shock load and keep from breaking the climber.


I actually saw something like this on the episode of Top Gear where they drive to the North Pole. The part about increasing impulse of the applied force, that is. The hosts' truck got stuck, so they hooked up another truck to pull it out. The difference however is that they attached an assembly of bungie cords to the stuck car's front end, then the towing cable (or maybe it was rope) from the bungies to the towing truck. The towing truck then took off at full speed with a lot of slack in the rope. However, when the rope finally went taught, the bungies stretched and increased the impulse so much that the stuck truck just glided out of its hole seemingly effortlessly at probably 1 mph. The towing truck gets to build up momentum while both trucks are protected when the force is finally applied. It worked brilliantly.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26547
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

Re: What-If 0056: "Restraining an Airplane"

Postby gmalivuk » Wed Jul 31, 2013 9:11 pm UTC

charonme wrote:
a 747's four engines can each generate 281.57 kN of thrust
is that also with air in front and around the engines being completely still or does the air need to move (for example if there was a strong opposite wind or if the plane was already moving forward) for the engines to generate that much thrust?
I can't imagine the figure being given for anything other than thrust relative to the surrounding air. So, relative to the ground, it could of course work out differently based on windspeed, but that doesn't seem a very sensible way to report engine strength.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
jjjdavidson
Posts: 652
Joined: Fri Mar 29, 2013 1:40 pm UTC
Location: Outside: The Ozarks, North America ─ OTTside: Lost in the 1400s

Re: What-If 0056: "Restraining an Airplane"

Postby jjjdavidson » Wed Jul 31, 2013 11:04 pm UTC

gmalivuk wrote:
charonme wrote:
a 747's four engines can each generate 281.57 kN of thrust
is that also with air in front and around the engines being completely still or does the air need to move (for example if there was a strong opposite wind or if the plane was already moving forward) for the engines to generate that much thrust?
I can't imagine the figure being given for anything other than thrust relative to the surrounding air. So, relative to the ground, it could of course work out differently based on windspeed, but that doesn't seem a very sensible way to report engine strength.

The thrust acts directly on the plane itself. It has nothing to do with the movement of the surrounding air (except as such movement alters the air flow into the engine, which can affect the engine's efficiency and thus its power).

If you replaced the cabin of a 747 with an air tank, covered the engines to feed air directly from that tank, and hoisted the 747 into low Earth orbit, the engines would generate roughly the same amount of thrust, for the brief time before they self-destructed because all their lubricants boiled away in vacuum. There would be no lift, and no way to steer, because there's no air for the control surfaces, but the plane would still move forward (until it tumbled from lack of stabilization). The thrust comes from the engine's exhaust; like a rocket, it doesn't require something to push against.

User avatar
ucim
Posts: 6595
Joined: Fri Sep 28, 2012 3:23 pm UTC
Location: The One True Thread

Re: What-If 0056: "Restraining an Airplane"

Postby ucim » Wed Jul 31, 2013 11:49 pm UTC

jjjdavidson wrote:The thrust comes from the engine's exhaust; like a rocket, it doesn't require something to push against.
Think of it as the plane pushing against its own exhaust.

Jose
Order of the Sillies, Honoris Causam - bestowed by charlie_grumbles on NP 859 * OTTscar winner: Wordsmith - bestowed by yappobiscuts and the OTT on NP 1832 * Ecclesiastical Calendar of the Order of the Holy Contradiction * Please help addams if you can. She needs all of us.

User avatar
gmalivuk
GNU Terry Pratchett
Posts: 26547
Joined: Wed Feb 28, 2007 6:02 pm UTC
Location: Here and There
Contact:

Re: What-If 0056: "Restraining an Airplane"

Postby gmalivuk » Thu Aug 01, 2013 5:06 am UTC

Most commercial jets have a high bypass ratio and low specific thrust, which means that in fact much of the thrust does indeed come from the turbofan pushing on regular old air.
Unless stated otherwise, I do not care whether a statement, by itself, constitutes a persuasive political argument. I care whether it's true.
---
If this post has math that doesn't work for you, use TeX the World for Firefox or Chrome

(he/him/his)

User avatar
Davidy
Posts: 221
Joined: Sat Dec 01, 2012 1:18 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby Davidy » Thu Aug 01, 2013 5:12 am UTC

I'd like to see figures for using spider silk or carbon nanotube.
"It's only funny until someone loses an eye, then it's still funny but they can only see it in 2-D."

User avatar
Copper Bezel
Posts: 2426
Joined: Wed Oct 12, 2011 6:35 am UTC
Location: Web exclusive!

Re: What-If 0056: "Restraining an Airplane"

Postby Copper Bezel » Thu Aug 01, 2013 6:33 am UTC

The tensile strengths for both are listed on Wikipedia. For spider silk, the question has apparently been asked before. = ) (Though the method is different and comes to a different figure than Randall's method would.)
So much depends upon a red wheel barrow (>= XXII) but it is not going to be installed.

she / her / her

billy joule
Posts: 54
Joined: Tue Jun 11, 2013 7:14 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby billy joule » Thu Aug 01, 2013 7:16 am UTC

Davidy wrote:I'd like to see figures for using spider silk or carbon nanotube.


Ultimate tensile strength figures from wiki..

Human hair = 380 MPa
Spider silk = 1000 MPa
Carbon Nanotube = 11000 - 63000 MPa

Force/Pressure = Area (load (N)/UTS (Pa))= Required area)

2*sqrt(Area/pi) = cable diameter


Spider silk cable would be 18.9mm diameter
Nanotube would be between 2.4 and 5.7mm
Graphene (greatest UTS on wiki) would be 1.7mm

User avatar
davidstarlingm
Posts: 1255
Joined: Mon Jun 01, 2009 4:33 am UTC

Re: What-If 0056: "Restraining an Airplane"

Postby davidstarlingm » Thu Aug 01, 2013 4:57 pm UTC

charonme wrote:
a 747's four engines can each generate 281.57 kN of thrust
is that also with air in front and around the engines being completely still or does the air need to move (for example if there was a strong opposite wind or if the plane was already moving forward) for the engines to generate that much thrust?

Yeah, I'm unsure whether "maximum thrust" as reported here is the same as static thrust, which is what we're actually interested in for the purposes of restraining a 747.

454Casull
Posts: 5
Joined: Mon Dec 20, 2010 6:23 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby 454Casull » Thu Aug 01, 2013 9:53 pm UTC

The whale can't do acrobatics with only enough hair to string it up in static equilibrium. The dynamic forces experienced during the acrobatic manuevers would certainly be much more than 1 g's worth.

urza9814
Posts: 1
Joined: Fri Aug 02, 2013 7:12 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby urza9814 » Fri Aug 02, 2013 7:16 pm UTC

Klear wrote:
BrianB wrote:I think that Randall makes an error in regards to the human hair portion...

Shown in his graphic are 20 people with their hair attached to the plane. While the tensile strength of the combined strands of hair may be able to withstand the pulling force of the jet engines, most certainly the body weight of those 20 people just standing there won't keep the plane from moving. (i.e. no sufficient anchor point)

Conclusion: The tensile strength of the hair from 20 people is enough to allow those people to be dragged down the runway and into the air as the plane takes off.


Yeah, I thought the same could happen with the legion of fishermen, though it is a lot of fishermen.


More than 50-100lbs and their lines will snap. So unless these are some *seriously* anorexic fishermen, I think they'll be alright ;)

ijuin
Posts: 934
Joined: Fri Jan 09, 2009 6:02 pm UTC

Re: What-If 0056: "Restraining an Airplane"

Postby ijuin » Sun Aug 04, 2013 7:07 am UTC

Good point. Fishing line for rods doesn't come heavier than that not because we can't manufacture it, but because it's preferable for the line to snap than for it to pull your arms out of their sockets or pull you overboard.


Return to “What If?”

Who is online

Users browsing this forum: No registered users and 6 guests