Q:
I know the answer.... do you..
A plane is standing on a runway that can move (like a giant conveyor
belt). This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly.
Will the plane be able to take off? and Why...
Discuss...........
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1977 280ZTurbo /intercooled
13.02@105
South east Z shoot out 7 Link
A:
Yes:
An aircraft is not propelled by the wheels, only by the engines. The speed of the aircraft depends on thrust.
The conveyor will have almost no affect on the speed of the aircraft (other than the very small amount of resistance put up by the additional speed of the wheels). The aircraft will continue to move forward at the same speed as it would have without the conveyor, creating the necessary lift.
NOW: Consider a craft that generates its initial speed from a motor connected to the wheels. In this case, the aircraft would be unable to take off, because the craft would not move (similar to a car on a giant dyno), thus creating no lift.
What do I win?
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
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NISMO Transmission mount
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A:
Presicely, of course it will take off (though it will take longer than usual).
A:
i say no it wont take off...
why?
cause its not the engines that make the plane go up, its the lift over the wing...and if the airplane isnt moving against the wind, no wind is traveling over the wing, thus no lift...
if you look at the position of the airplane against a backdrop, if this worked, the airplane would be stationary, even though the wheels are turing at 200mph+......
now what do i win?!?
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
Very clever Keane.. You are correct sir.. You win.. uh.. heh.. uhh.. I will have to get back to you on that......
-----------------------------------------------------------------------------------------------
1977 280ZTurbo /intercooled
13.02@105
South east Z shoot out 7 Link
A:
The Law of Physics, according to me.. will ensure that the plane does not take off, it will remain stationary.. (I know thats wrong - but it seemed right to me)
Will have a hard think about what you posted Keane, sounds good but my head hurts already..
Post Edited (Oct 31, 19:19pm)
A:
AH! you're right! i just thought about it!!!!
the engines are propelling the aircraft, not power to the wheels... the wheels are just kinda a "medium" in a way...
ok....yeah---nevermind...
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
Doesn't matter, the plane would stay stationary... The plane would pick up speed at the wheels, however it would stay in the same spot, similiar to a person running over a treadmill. You could be going 10mph in a treadmill, but the gym doesnt move does it?
Lift is dependent on the speed of the airfoil through the air, not the speed of the wheels... The wheels could be rotating at a speed equivalent to 300mph, however the conveyor would cause the airplane to remain stationary relative to the air and therefore no air movement over the airfoil and hence no lift produced.
No lift = no take off...
If the conveyor suddenly stopped however, the plane would get off.
84 300zx AE
A:
uk:
think of it this way, what is causing the airplane to move WITHOUT the conveyor?
In a CAR, it is the wheels spinning. The Wheels make direct contact to the ground, so speed is measured as the distance moved (relative to the ground)/time.
In an airplane, it is the Propellors/jets/etc moving. This makes contact with the air only, so speed is measured as the distance moved (relative to the surrounding air)/time.
Without the conveyor, both speeds are equal. What the conveyor does is move the 'ground' separate from the air, thus making them different reference points.
In an airplane, ONLY the speed that matters toward lift, is the air speed.
Edit: TXT, see this same post as well.
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
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Unothadox UD Pulley
NISMO Transmission mount
RPS Sport Street Clutch w/ RPS Segmented Flywheel
Post Edited (Nov 9, 11:53am)
A:
Righto nevermind, the jet engines would cause air to move over the airfoil... causing lift.
84 300zx AE
A:
Thanks Keane - I wish you were my Physics teacher, I always loved the subject but he wasn't too good at explaining things in simple terms like you just did.
Post Edited (Oct 31, 19:19pm)
A:
the propellors just make the plane move so air can go over the wings.......planes will not fly without air over the wings....no air speed no fly...jets same way...engines are just a means to an end....propulsion creates air flow and then lift...
1976 280z 2+2 - Risen from the dead - garaged since 1988. Pallnet Fuel Rail and guage - ES rack and front bushings - 260Z 4Speed - Arizona Z Car Clutch - H4 Lights - Lots more to come...
A:
What about this one...
You're driving a car inside of a wind tunnel that is 5 miles long. The wind in the tunnel is going exactly 50mph. If you are driving the same direction as the wind, at exactly the same speed, and you roll down the window and stick your hand out, will you feel any wind?
Lead, Follow, or get out of the way!
A:
Aces: No, because you are travelling 0 mph relative to the air, even though you are 50 mph relative to the ground.
1990 NA 300zx 2+0
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Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
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A:
And Keane gets it once again...
--------------------------------------
1990 300zx NA
- Custom Exhaust
- JWT Pop Charger
A:
Since I've taken off an airplane at zero groundpeed, I can say for damn sure that it is easily doable.
A:
Hybrid, the airplane is NOT taking off at zero ground speed. It is taking off at the normal speed. The wheels on the other hand, are travelling twice the speed (1x for the forward motion, 1x for the belt).
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
Unothadox UD Pulley
NISMO Transmission mount
RPS Sport Street Clutch w/ RPS Segmented Flywheel
A:
Keane, yes, it DID take off with zero groundspeed, the wheels did not even spin at all. The same would be true in the conveyor belt example since WIND was not specified. Given enough wind a plane does not need to "roll" for takeoff to gain enough airspeed...
A:
Yes, I understand how YOU did take off at Zero Groundspeed, but in this situation, groundspeed is not 0. In this case, wind is considered 0 (a default value, when none is given).
"Groundspeed" should be measured agnostic of the conveyor, that is, to the ground underneath the conveyor belt. Air movement is considered to be 0 (for the problem's sake).
The engines propel the plane against the air, the wheels will just spin really fast, causing no signifigant loss in speed (other than the wheel bearing's friction ).
1990 NA 300zx 2+0
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Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
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A:
No, it will just loop around and around,
my proof: remember this:
Astro from the Jetsons:
"YES I will finish what I sta"
.
1977 280Z blue 2+2,
1973 240z
1977 280Z coupe in restoration progress
Post Edited (Nov 9, 12:39pm)
A:
no!
no no no!
you are wrong!!!
the airplane wouldnt move at all!!!
if you set an airplane down with ZERO wind on the belt...and the airplane is NOT moving...
you apply full thorttle at the engines, the airplane starts moving relative to the ground...then the belt starts going in the opposite direction at the same rate...
THE AIRPLANE WOULDNT MOVE....given ZERO wind, there is NO LIFT being created...
the only way hybrid took off with ZERO ground speed was if the wind was blowing around 70mph in a small cessna 172 facing the airplane directly....
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
bubbleguinea: i am pretty sure you have misunderstood the situation (same as hybrid).
Draw out a force diagram, and you should understand it better.
1990 NA 300zx 2+0
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A:
wait---i reject my last comment...
to put it simple ::::::::::
IF there is an outside force acting on the airplane, that is NOT TOUCHING THE BELT, the thing will move....IF THE WHEELS are the way it moves, it WONT move....
the engines are not touching the belt, so they are not affected..
the reason ASTRO doesnt move is because his feet are touching the belt...
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
Yep. I think ya got it!
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
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NISMO Transmission mount
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A:
see, thats what i thought at first..i didnt think that the whole point of an engine is to move air In, then thrust it out...
the airplane doesnt take off cause of its ground speed, it takes off cause the engines propel it through the AIR not racing on the ground...
and the air is seperate from the belt!
ha!
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
LOL, Keane. If you asked then question then you can set the parameters. Otherwise everything not mentioned is fair game for the rest of us to consider.
If I get to choose what's not stated, I choose my plane and my conditions and my location. People that do not pose the question do not get a say in other initial real possible conditions.
A:
HOWEVER!!! it would take a hellava long runway for the airplane to take off, right? your ground speed still has to get up to the correct speed for takeoff depending on what airplane you are in...
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
this is too easy-- it doesnt say that the engines are running or even turned on, it doesnt say there is a pilot! of course it cant take off it is sitting stationary not in flight rediness mode. if i put my zx on a treadmill and turn on the treadmill even though my zx may get thinner and weigh less when its done ,it will not have gone anywhere. ( just to be car related) hehe!!!
____________________________________
1980 280ZX coupe
2001 maxima
1994 F150 4x4 van works custom truck
170000 and never needed mech repairs
1996 ford explorer -they cant all be good
A:
there are too many variables! agh!
but yes, in theory, it would take off.
==============================================
High Performance NA L28 engine, Performance Suspension, Full Interior, 2500lbs, and room for 3 HOT girls in the car!
shift_2+2
13.9 @102.7 on 205mm street tires and 110 octane :-)
A:
but where would it go? ( just another riddle to wrap your brain around)
____________________________________
1980 280ZX coupe
2001 maxima
1994 F150 4x4 van works custom truck
170000 and never needed mech repairs
1996 ford explorer -they cant all be good
A:
It's a silly question to even consider wheel rotation at all for an aircraft as some limiting factor. As silly as that movie "Pearl Harbor" where the CGI planes would screach their tires as they begin a takeoff run Now that was just too damn funny!
A:
bubble, the distance to take off would be the same.
The aircraft would take off EXACTLY like it would without the conveyor. The conveyor has no affect on the aircraft beyond the minimal drag from the wheel bearings. This drag is most likely too small to make the signifigant digits anyway.
Hybrid: That is just being pedantic for the cause of not admitting defeat.
ZXToy: WTF? Dallas.
1990 NA 300zx 2+0
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Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
Unothadox UD Pulley
NISMO Transmission mount
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A:
"Hybrid: That is just being pedantic for the cause of not admitting defeat."
Pedantic ?
We had the same conclusion.
A:
For those of you who doubt a plane can take off with 0 ground speed.
http://plawner.org/video/zagi_and_mirage_2000_slope_flight.wmv
No engines, no propulsion, just wind in your face standing on a hill.
06 Lemanz Sunset Track Z
Best car I ever bought.
IHI Turbos comming soon.
A:
Quote:
It's a silly question to even consider wheel rotation at all for an aircraft as some limiting factor. As silly as that movie "Pearl Harbor" where the CGI planes would screach their tires as they begin a takeoff run Now that was just too damn funny!
--Never saw pearl harbor, but I will say this: Wheel bearing resistance causes a force against the forward motion of the craft. It is so minute that it can be ignored, but I figured I would mention it for accuracy.
Quote:
"Hybrid: That is just being pedantic for the cause of not admitting defeat."
Pedantic ?
We had the same conclusion.
You implied that you believed the craft would have 0 groundspeed, which is not true in this situation.
The crafts taking off from stop (with wind) is pretty cool though.
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
Unothadox UD Pulley
NISMO Transmission mount
RPS Sport Street Clutch w/ RPS Segmented Flywheel
A:
Don't forget that
L=1/2 rho v^2 S CL
so you will need an airspeed to cause a takeoff
If the aircraft accelerated and the tread mill counteraccted the relative position of the aircraft is the same (relative to the observer from far away). But there will be an airflow over the aircraft because the air will stick to the treadmill (due to viscosity effects). Thus at some point there will be enough airflow going over the aircrfat for it to takeoff, which it will do vertically at first and then will proceed forward (in the direction of trust).
======
'74 2+2 -- MSA sway bars, Illuminas, Eibach Progressive, Energy Suspension
L28 with MN47, 240Z rods, milled down dished pistons (11.6:1 CR) and 240sx tranny
======
committing suicide in small managable payments
A:
Quote:
If the aircraft accelerated and the tread mill counteraccted the relative position of the aircraft is the same (relative to the observer from far away). But there will be an airflow over the aircraft because the air will stick to the treadmill (due to viscosity effects). Thus at some point there will be enough airflow going over the aircrfat for it to takeoff, which it will do vertically at first and then will proceed forward (in the direction of trust).
False, the tread mill will never counteract the force of the engines. It will attempt to, but only provide a force against the wheels. Meanwhile, the engines will be providing the groundspeed, because there is no direct corrolation between wheel speed and ground speed.
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
Unothadox UD Pulley
NISMO Transmission mount
RPS Sport Street Clutch w/ RPS Segmented Flywheel
A:
Keane,
No, I simply implied that it's possible to even takeoff with zero groundspeed (as I have done personally in an airplane and the cute video showed). Groundspeed is irrelevant to actual flight.
I believe it was you that decided to use the pedantic phrase "measured agnostic of the conveyor" to say that ground means the ground. That was funny stuff.
Yea, it flies just the same no mater how complicated people try to make the problem.
A:
Ah, I misunderstood your point. Thanks.
My "agnostic to the conveyor" comment was to point out that in a zero wind situation, ground speed would be the same as without the conveyor.
1990 NA 300zx 2+0
Aztec Red, Grey cloth interior
Specialty Z Quad Tipped Exhaust w/ Resonated H Pipe
JWT Pop Charger
Z1 Motorsports Steel Driveshaft
Unothadox UD Pulley
NISMO Transmission mount
RPS Sport Street Clutch w/ RPS Segmented Flywheel
A:
datto dont do riddles
73' 240z: F54 4.2L, OS Giken LY DOHC Crossflow head, 17:3comp.ratio, N33, Tripple SU's, T10 Hybrid Draw-Through TT @ 47pds, Roots&Centrifugal Type supercharger, 3-2-1 headers, Centerforce 4 clutch, 6oz flywheel, R300 differential, Super-Hicas
A:
Which is fine as this riddle was solved some 20 posts ago.
--------------------------------------
1990 300zx NA
- Custom Exhaust
- JWT Pop Charger
A:
If you have enough airflow you can make a brick lift up
======
'74 2+2 -- MSA sway bars, Illuminas, Eibach Progressive, Energy Suspension
L28 with MN47, 240Z rods, milled down dished pistons (11.6:1 CR) and 240sx tranny
======
committing suicide in small managable payments
A:
Keane, yea, groundspeed would of course be the same with or without the conveyor (since the air is the same speed as the planet in a no wind condition). If you need 70kts airspeed for takeoff then you will be moving over the planet at 70kts no matter what the wheels are doing.
A:
it would be like a car being pulled by a chain, no matter how fast the wheels are turning or how fast the conveter belt is going the only thing that matters is how fast the chain is pulling.
---
Justin T
72 240Z L28, 5-speed
77 280Z 5-speed (t-boned 8-25-04)
80 280ZX automatic(retired)
A:
It would take a little bit longer to take off since the greater friction caused by the wheels and the conveyor moving at double the normal speed would result in a slight counteraction to the thrust generated by the engines. It may only be a couple feet difference but it would not be exactly the same as if there were no conveyor.
1972 240Z always in progress
***WARNING*** MY POSTS MAY CONTAIN SARCASM
A:
OK, most commercial Turbine engine aircraft take-off at ~140-160 mph.
Most land at 120- 140 mph.
So lets say the aircraft throttles up and starts moving forward. At the same time the conveyor senses the forward motion of the aircraft and starts moving the conveyor at the same speed of the wheels but in the opposite direction. So the wheels start spinning at twice the normal speed.
Would the plane take-off? Yes, because the speed of the wheels has nothing to do with lift over the wings and the take-off roll.
What would really happen? The tires on an aircraft are speed rated like any other tire. At 250-275 mph the tires would overheat and blow the thermal fuses from the rims since the rated speed of the tire was exceeded by about 50-70 mph. The tires would deflate in about 5 seconds and then pieces would start flying off. Depending where the engines were located on the aircraft it may ingest them and cause the engines to fail if they're mounted to the fuselage att he rear. If there mounted on the wings then that wouldn't happen. Regardless of where the engines are mounted the flaps would be damaged thereby destroyng the additional lift required for take-off on most aircraft.
The aircraft would crash and burn, therefore, the answer to your question is:
NO, the aircraft would not fly.
I have a few mods
A:
Man, talk about beating a dead horse...
--------------------------------------
1990 300zx NA
- Custom Exhaust
- JWT Pop Charger
A:
A plane taking off with 0 ground speed
_____________________________________________________
'76 280Z w/Shaved Head and Illuminas
'83 280zxt w/RUST
A:
The JSF!.... Joint Strike Fighter!!
73' 240z: F54 4.2L, OS Giken LY DOHC Crossflow head, 17:3comp.ratio, N33, Tripple SU's, T10 Hybrid Draw-Through TT @ 47pds, Roots&Centrifugal Type supercharger, 3-2-1 headers, Centerforce 4 clutch, 6oz flywheel, R300 differential, Super-Hicas
A:
Not the same at all... Instead of producing lift, it is using the jet engines to create a force parallel to gravity to lift it off the ground...
In this case though, like I said, although the plane has 0 ground speed, the jet engines are pulling air around the airfoil which will cause lift.
84 300zx AE
A:
All I have to say about this post is look at any plane that can do a vertical take off and you will have your answer.
Progress:
Z32 Had to sell for DD 06 Sentra :(
S30 one of these days I will get around to putting it all back together.
A:
Best looking plane ever:
A-10 Warthog. I love the sight of this thing!
Don't want to see this in your rear view mirror:
********************
1975 280Z (Stock)
303 Emerald Green
A:
Author: Zolorin
Date: Nov 9, 2:54pm
"If you have enough airflow you can make a brick lift up"
Yes the Air Force proved that with the F4 Phantom!!! haha
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
A:
"If you have enough airflow you can make a brick lift up"
Zolorin, actually airflow makes a lot more drag than lift on a brick.
If you have enough "power" (not airflow) you can make anything fly (as NASA demonstrated with the Apollo project). Same as with the F-104 Starfighter or the SR-71, they had POWER but airflow (drag) was the actually the enemy.
A:
No airspeed, no lift, no flight. Where is tkr514 for some "insight" HA.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
"No airspeed, no lift, no flight"
Gee, you'd better get right down to NASA and tell them that flight is impossible without aispeed and aerodynamic lift. I'm sure that they would like to know that...
A:
HybridZ-
Umm how much thrust do the Titans engines produce?
How much thrust do a boeing 747s jet engines produce?
Which direction to a 747s jet engines point relative to the earth? Perpendicular or parallel?
84 300zx AE
A:
My god man......
1) why the hell don't aircraft carriers have "treadmills" then...IT WON'T WORK show me Proof
THE ONLY WAY IT WILL WORK, is if the thrust is diverted toward the ground, giving up lift
A:
"1) why the hell don't aircraft carriers have "treadmills" then"
What kind of logic is that?
I don't know the answer, but my guess would be:
Maintaining a treadmill the size of a freaking aircraft carrier would cost WAY more than the slingshot method they currently use.
--------------------------------------
1990 300zx NA
- Custom Exhaust
- JWT Pop Charger
A:
Are we still argueing about this?
If you are I have other questions for you, I know the answers do you?
Whats heavier, a pound of rocks or a pound of feathers?
If your running on a treadmill and it stops while your in mid-air, will you go flying off the front of it? (Test this its cool)
And lastly, if two pennys leave a table at the exact same time, one is dropped just barely off the edge and one is propelled flat off the table to 10 feet away, assuming they hit nothing else in the way, which will hit the floor first?
06 Lemanz Sunset Track Z
Best car I ever bought.
IHI Turbos comming soon.
A:
Whats heavier, a pound of rocks or a pound of feathers?
They weigh the same
If your running on a treadmill and it stops while your in mid-air, will you go flying off the front of it? (Test this its cool)
No, but it's gonna hurt when you land (edit: actually it won't hurt at all)
And lastly, if two pennys leave a table at the exact same time, one is dropped just barely off the edge and one is propelled flat off the table to 10 feet away, assuming they hit nothing else in the way, which will hit the floor first?
Should land at the same time as a penny will not generate much lift
--------------------------------------
1990 300zx NA
- Custom Exhaust
- JWT Pop Charger
Post Edited (Nov 10, 8:39am)
A:
Umm how much thrust do the Titans engines produce?Less than a 747
How much thrust do a boeing 747s jet engines produce? More than a Titan.
"Which direction to a 747s jet engines point relative to the earth? Perpendicular or parallel?" The 747 engines point "up" for takeoff and parallel in flight and down in a descent.
Not sure what you're tying to get at with those questions ...
A:
The plane will still take off on account of the wheels are just for wheels...something to plant on terra firma..the engines, if they are running that is..will overcome the air density/resistance and the plane will take off because the engines provide forward AIR thrust...not forward traction as on car wheels..and the thrust will provide the airspeed to create lift..Harriers and the J-Strike fighter take off vertically with tons of downward thrust...then adjust accordingly for forward thrust and lift...rockets are just slow burning, (comparatively speaking), controlled bullets...
1976 280z 2+2 - Risen from the dead - garaged since 1988. Pallnet Fuel Rail and guage - ES rack and front bushings - 260Z 4Speed - Arizona Z Car Clutch - H4 Lights - Lots more to come...
A:
I can't believe people are still misunderstanding this.
I guess people who are still having trouble are stuck in an automobile mindset, where the thrust is generated at the wheels. The airplane generates thrust at the engine, with the thrust being applied to the air. The spinning of the wheels will not affect the ability of the airplane to move forward, IT'S PUSHING ON THE AIR, NOT THE GROUND. If there is no wind, the airplane will still achieve a normal takeoff airspeed equal to it's ground speed.
Imagine a guy in a wheelchair. He is in a narrow hallway that has handles along the walls. The floor of the hallway is a moving conveyor belt. Can he move forward? YES - IF HE GRABS THE HANDLES ON THE WALL IT DOESN'T MATTER HOW FAST THE CONVEYOR BELT MOVES, HE CAN PULL HIMSELF ALONG BY HAND. In the same way, the airplane is pushing ON THE AIR (like wheelchair man pulls along the handlebars), the wheel speed is IRRELEVANT.
-- Next Up: SCCA ITR 300ZX --
A:
Hybrid77: maybe do a quick net search before you type.
#1 - "Umm how much thrust do the Titans engines produce?Less than a 747"
Titan = approx 1040 tons thrust (assuming NASA rates in METRIC to avoid more stupid mistakes in imperial)
747 = 248,000lbs total thrust = 112.72 tons (assuming 4X Pratt Whitney 4062@62,000lbs; best available engine)
:logic: Titan > 747
#2 - "Which direction do a 747s jet engines point relative to the earth? Perpendicular or parallel?" The 747 engines point "up" for takeoff and parallel in flight and down in a descent."
I sure hope you are trying to be sarcastic, and I posted my rebuttal too soon.
As for the rest of the congregation that are continually stumped by the "aircraft treadmill" riddle; wow, im almost speechless. Please (for your own mental stability) remove all your concerns about all modern technology. Leave us engineers to our designs, and get back to whatever it is that you do well, because grasping simple dynamics;you are not.
A:
lol the problem is people aren't thinking of the wheels as just being dead wheels, they think they are drive wheels.
Now the problem of the wheels blowing out cause of speed ratings could very well be real.
But the wheels on an aircraft don't drive it. They are simply a medium to allow the craft to be moved while on the ground.
Mans Prayer "I'm a man.... But I can change..... If I have too...... I guess"
No matter how good she looks, some other guy is sick and tired of putting up with her.
A:
kind of like training wheels on a bike , right? they turn but they dont propel you forward.
____________________________________
1980 280ZX coupe
2001 maxima
1994 F150 4x4 van works custom truck
170000 and never needed mech repairs
1996 ford explorer -they cant all be good
A:
rockets make thrust because they do not have wings, not much lift gen. Draw a free body diagram and fig yourself. It will not get of the ground, period. If the 747 is not moving relative to the ground it is not gen airspeed, no lift.
It is a bugs bunny question,not a riddle
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
poopy question...
84 300zx AE
Post Edited (Nov 11, 7:55am)
A:
Seems like the question should have been ... 'Can the airplane take off..." not " Will it take off ...."
Under the conditions described, if I understand this 'conveyer' system, the place could take off, if the headwind was as stong or stronger needed to create lift sufficient to allow the airplane to become airborne.
Same as without the conveyor.
'73 2.8 L, Mikunis, 5-speed, 3.7 LSD, Eibacks, Illuminas, Panasports, needs paint
A:
i e-mailed this to my friend that is a capitan of a plane and this is his responce,:No the plane can't take off... it isn't the speed of the wheels in relation
to the runway that matters. What matters is the speed of the wings throught
the relative wind.
A plane can only fly if the airstream above the airfoil is relatively faster
than the airflow below the wing. This is illustrated with bernoulli's
principle... in a nutshell there is no airflow above or below the wing to
create lift, to the average observer, the airplane is stationary.
I must say though... that runway conveyor machine is f*$king fast. Real
f*$king fast.
76 280 all stock exept full bushings,qwuik knuckles,tokico struts&springs,3-2 header,k&n cai,msa sway bars,konig rewinds with toyo proxis ra1.
78 rust bucket. (4 sale!)
2000 v-dub mk4 jetta vr6
2005 titan 4x4 with nismo cai,banks exhus
A:
All I can say is that I don't want to fly with your friend!!
Does he pilot RC planes???
-----------------------------------------
12.804 @ 107.26 mph on crappy street tires with Dual SU Powered 2.9L Stroker!
ZCAR.COM member since Aug 1998
A:
lol...good one Norm...me either...
1976 280z 2+2 - Risen from the dead - garaged since 1988. Pallnet Fuel Rail and guage - ES rack and front bushings - 260Z 4Speed - Arizona Z Car Clutch - H4 Lights - Lots more to come...
A:
he is right, no flight. Why would it. Put the 747 in a wind tunnel with a conveyor belt and it would start flying. F1 cars are tested in this manner to find out down force,(-lift), with wheels turning.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
Huilo - Have you even read (and tried to comprehend) any of the educated posts in this thread?
-- Next Up: SCCA ITR 300ZX --
A:
The popular explanation of lift
Students of physics and aerodynamics are taught that airplanes fly as a result of Bernoulli’s principle, which says that if air speeds up the pressure is lowered. Thus a wing generates lift because the air goes faster over the top creating a region of low pressure, and thus lift. This explanation usually satisfies the curious and few challenge the conclusions. Some may wonder why the air goes faster over the top of the wing and this is where the popular explanation of lift falls apart.
In order to explain why the air goes faster over the top of the wing, many have resorted to the geometric argument that the distance the air must travel is directly related to its speed. The usual claim is that when the air separates at the leading edge, the part that goes over the top must converge at the trailing edge with the part that goes under the bottom. This is the so-called "principle of equal transit times".
As discussed by Gale Craig (Stop Abusing Bernoulli! How Airplanes Really Fly., Regenerative Press, Anderson, Indiana, 1997), let us assume that this argument were true. The average speeds of the air over and under the wing are easily determined because we can measure the distances and thus the speeds can be calculated. From Bernoulli’s principle, we can then determine the pressure forces and thus lift. If we do a simple calculation we would find that in order to generate the required lift for a typical small airplane, the distance over the top of the wing must be about 50% longer than under the bottom. Figure 1 shows what such an airfoil would look like. Now, imagine what a Boeing 747 wing would have to look like!
Fig 1 Shape of wing predicted by principle of equal transit time.
If we look at the wing of a typical small plane, which has a top surface that is 1.5 - 2.5% longer than the bottom, we discover that a Cessna 172 would have to fly at over 400 mph to generate enough lift. Clearly, something in this description of lift is flawed.
But, who says the separated air must meet at the trailing edge at the same time? Figure 2 shows the airflow over a wing in a simulated wind tunnel. In the simulation, colored smoke is introduced periodically. One can see that the air that goes over the top of the wing gets to the trailing edge considerably before the air that goes under the wing. In fact, close inspection shows that the air going under the wing is slowed down from the "free-stream" velocity of the air. So much for the principle of equal transit times.
Fig 2 Simulation of the airflow over a wing in a wind tunnel,
with colored "smoke" to show the acceleration and deceleration of the air.
The popular explanation also implies that inverted flight is impossible. It certainly does not address acrobatic airplanes, with symmetric wings (the top and bottom surfaces are the same shape), or how a wing adjusts for the great changes in load such as when pulling out of a dive or in a steep turn?
So, why has the popular explanation prevailed for so long? One answer is that the Bernoulli principle is easy to understand. There is nothing wrong with the Bernoulli principle, or with the statement that the air goes faster over the top of the wing. But, as the above discussion suggests, our understanding is not complete with this explanation. The problem is that we are missing a vital piece when we apply Bernoulli’s principle. We can calculate the pressures around the wing if we know the speed of the air over and under the wing, but how do we determine the speed?
Another fundamental shortcoming of the popular explanation is that it ignores the work that is done. Lift requires power (which is work per time). As will be seen later, an understanding of power is key to the understanding of many of the interesting phenomena of lift.
Newton’s laws and lift
So, how does a wing generate lift? To begin to understand lift we must return to high school physics and review Newton’s first and third laws. (We will introduce Newton’s second law a little later.) Newton’s first law states a body at rest will remain at rest, or a body in motion will continue in straight-line motion unless subjected to an external applied force. That means, if one sees a bend in the flow of air, or if air originally at rest is accelerated into motion, there is a force acting on it. Newton’s third law states that for every action there is an equal and opposite reaction. As an example, an object sitting on a table exerts a force on the table (its weight) and the table puts an equal and opposite force on the object to hold it up. In order to generate lift a wing must do something to the air. What the wing does to the air is the action while lift is the reaction.
Let’s compare two figures used to show streams of air (streamlines) over a wing. In figure 3 the air comes straight at the wing, bends around it, and then leaves straight behind the wing. We have all seen similar pictures, even in flight manuals. But, the air leaves the wing exactly as it appeared ahead of the wing. There is no net action on the air so there can be no lift! Figure 4 shows the streamlines, as they should be drawn. The air passes over the wing and is bent down. The bending of the air is the action. The reaction is the lift on the wing.
Fig 3 Common depiction of airflow over a wing. This wing has no lift.
Fig 4 True airflow over a wing with lift, showing upwash and downwash.
The wing as a pump
As Newton’s laws suggests, the wing must change something of the air to get lift. Changes in the air’s momentum will result in forces on the wing. To generate lift a wing must divert air down; lots of air.
The lift of a wing is equal to the change in momentum of the air it is diverting down. Momentum is the product of mass and velocity. The lift of a wing is proportional to the amount of air diverted down times the downward velocity of that air. Its that simple. (Here we have used an alternate form of Newton’s second law that relates the acceleration of an object to its mass and to the force on it; F=ma) For more lift the wing can either divert more air (mass) or increase its downward velocity. This downward velocity behind the wing is called "downwash". Figure 5 shows how the downwash appears to the pilot (or in a wind tunnel). The figure also shows how the downwash appears to an observer on the ground watching the wing go by. To the pilot the air is coming off the wing at roughly the angle of attack. To the observer on the ground, if he or she could see the air, it would be coming off the wing almost vertically. The greater the angle of attack, the greater the vertical velocity. Likewise, for the same angle of attack, the greater the speed of the wing the greater the vertical velocity. Both the increase in the speed and the increase of the angle of attack increase the length of the vertical arrow. It is this vertical velocity that gives the wing lift.
Fig 5 How downwash appears to a pilot and to an observer on the ground.
As stated, an observer on the ground would see the air going almost straight down behind the plane. This can be demonstrated by observing the tight column of air behind a propeller, a household fan, or under the rotors of a helicopter; all of which are rotating wings. If the air were coming off the blades at an angle the air would produce a cone rather than a tight column. If a plane were to fly over a very large scale, the scale would register the weight of the plane.
If we estimate that the average vertical component of the downwash of a Cessna 172 traveling at 110 knots to be about 9 knots, then to generate the needed 2,300 lbs of lift the wing pumps a whopping 2.5 ton/sec of air! In fact, as will be discussed later, this estimate may be as much as a factor of two too low. The amount of air pumped down for a Boeing 747 to create lift for its roughly 800,000 pounds takeoff weight is incredible indeed.
Pumping, or diverting, so much air down is a strong argument against lift being just a surface effect as implied by the popular explanation. In fact, in order to pump 2.5 ton/sec the wing of the Cessna 172 must accelerate all of the air within 9 feet above the wing. (Air weighs about 2 pounds per cubic yard at sea level.) Figure 6 illustrates the effect of the air being diverted down from a wing. A huge hole is punched through the fog by the downwash from the airplane that has just flown over it.
Fig 6 Downwash and wing vortices in the fog.
(Photographer Paul Bowen, courtesy of Cessna Aircraft, Co.)
So how does a thin wing divert so much air? When the air is bent around the top of the wing, it pulls on the air above it accelerating that air down, otherwise there would be voids in the air left above the wing. Air is pulled from above to prevent voids. This pulling causes the pressure to become lower above the wing. It is the acceleration of the air above the wing in the downward direction that gives lift. (Why the wing bends the air with enough force to generate lift will be discussed in the next section.)
As seen in figure 4, a complication in the picture of a wing is the effect of "upwash" at the leading edge of the wing. As the wing moves along, air is not only diverted down at the rear of the wing, but air is pulled up at the leading edge. This upwash actually contributes to negative lift and more air must be diverted down to compensate for it. This will be discussed later when we consider ground effect.
Normally, one looks at the air flowing over the wing in the frame of reference of the wing. In other words, to the pilot the air is moving and the wing is standing still. We have already stated that an observer on the ground would see the air coming off the wing almost vertically. But what is the air doing above and below the wing? Figure 7 shows an instantaneous snapshot of how air molecules are moving as a wing passes by. Remember in this figure the air is initially at rest and it is the wing moving. Ahead of the leading edge, air is moving up (upwash). At the trailing edge, air is diverted down (downwash). Over the top the air is accelerated towards the trailing edge. Underneath, the air is accelerated forward slightly, if at all.
Fig 7 Direction of air movement around a wing
as seen by an observer on the ground.
In the mathematical aerodynamics description of lift this rotation of the air around the wing gives rise to the "bound vortex" or "circulation" model. The advent of this model, and the complicated mathematical manipulations associated with it, leads to the direct understanding of forces on a wing. But, the mathematics required typically takes students in aerodynamics some time to master.
One observation that can be made from figure 7 is that the top surface of the wing does much more to move the air than the bottom. So the top is the more critical surface. Thus, airplanes can carry external stores, such as drop tanks, under the wings but not on top where they would interfere with lift. That is also why wing struts under the wing are common but struts on the top of the wing have been historically rare. A strut, or any obstruction, on the top of the wing would interfere with the lift.
Air has viscosity
The natural question is "how does the wing divert the air down?" When a moving fluid, such as air or water, comes into contact with a curved surface it will try to follow that surface. To demonstrate this effect, hold a water glass horizontally under a faucet such that a small stream of water just touches the side of the glass. Instead of flowing straight down, the presence of the glass causes the water to wrap around the glass as is shown in figure 8. This tendency of fluids to follow a curved surface is known as the Coanda effect. From Newton’s first law we know that for the fluid to bend there must be a force acting on it. From Newton’s third law we know that the fluid must put an equal and opposite force on the object which caused the fluid to bend.
Fig 8 Coanda effect.
Why should a fluid follow a curved surface? The answer is viscosity; the resistance to flow which also gives the air a kind of "stickiness". Viscosity in air is very small but it is enough for the air molecules to want to stick to the surface. At the surface the relative velocity between the surface and the nearest air molecules is exactly zero. (That is why one cannot hose the dust off of a car and why there is dust on the backside of the fans in a wind tunnel.) Just above the surface the fluid has some small velocity. The farther one goes from the surface the faster the fluid is moving until the external velocity is reached (note that this occurs in less than an inch). Because the fluid near the surface has a change in velocity, the fluid flow is bent towards the surface. Unless the bend is too tight, the fluid will follow the surface. This volume of air around the wing that appears to be partially stuck to the wing is called the "boundary layer".
Lift as a function of angle of attack
There are many types of wing: conventional, symmetric, conventional in inverted flight, the early biplane wings that looked like warped boards, and even the proverbial "barn door". In all cases, the wing is forcing the air down, or more accurately pulling air down from above. What each of these wings have in common is an angle of attack with respect to the oncoming air. It is this angle of attack that is the primary parameter in determining lift. The inverted wing can be explained by its angle of attack, despite the apparent contradiction with the popular explanation involving the Bernoulli principle. A pilot adjusts the angle of attack to adjust the lift for the speed and load. The popular explanation of lift which focuses on the shape of the wing gives the pilot only the speed to adjust.
To better understand the role of the angle of attack it is useful to introduce an "effective" angle of attack, defined such that the angle of the wing to the oncoming air that gives zero lift is defined to be zero degrees. If one then changes the angle of attack both up and down one finds that the lift is proportional to the angle. Figure 9 shows the coefficient of lift (lift normalized for the size of the wing) for a typical wing as a function of the effective angle of attack. A similar lift versus angle of attack relationship is found for all wings, independent of their design. This is true for the wing of a 747 or a barn door. The role of the angle of attack is more important than the details of the airfoil’s shape in understanding lift.
Fig 9 Coefficient of lift versus the effective angle of attack.
Typically, the lift begins to decrease at an angle of attack of about 15 degrees. The forces necessary to bend the air to such a steep angle are greater than the viscosity of the air will support, and the air begins to separate from the wing. This separation of the airflow from the top of the wing is a stall.
The wing as air "scoop"
We now would like to introduce a new mental image of a wing. One is used to thinking of a wing as a thin blade that slices though the air and develops lift somewhat by magic. The new image that we would like you to adopt is that of the wing as a scoop diverting a certain amount of air from the horizontal to roughly the angle of attack, as depicted in figure 10. The scoop can be pictured as an invisible structure put on the wing at the factory. The length of the scoop is equal to the length of the wing and the height is somewhat related to the chord length (distance from the leading edge of the wing to the trailing edge). The amount of air intercepted by this scoop is proportional to the speed of the plane and the density of the air, and nothing else.
Fig 10 The wing as a scoop.
As stated before, the lift of a wing is proportional to the amount of air diverted down times the vertical velocity of that air. As a plane increases speed, the scoop diverted more air. Since the load on the wing, which is the weight of the plane, does not increase the vertical speed of the diverted air must be decreased proportionately. Thus, the angle of attack is reduced to maintain a constant lift. When the plane goes higher, the air becomes less dense so the scoop diverts less air for the same speed. Thus, to compensate the angle of attack must be increased. The concepts of this section will be used to understand lift in a way not possible with the popular explanation.
Lift requires power
When a plane passes overhead the formerly still air ends up with a downward velocity. Thus, the air is left in motion after the plane leaves. The air has been given energy. Power is energy, or work, per time. So, lift must require power. This power is supplied by the airplane’s engine (or by gravity and thermals for a sailplane).
How much power will we need to fly? The power needed for lift is the work (energy) per unit time and so is proportional to the amount of air diverted down times the velocity squared of that diverted air. We have already stated that the lift of a wing is proportional to the amount of air diverted down times the downward velocity of that air. Thus, the power needed to lift the airplane is proportional to the load (or weight) times the vertical velocity of the air. If the speed of the plane is doubled the amount of air diverted down doubles. Thus the angle of attack must be reduced to give a vertical velocity that is half the original to give the same lift. The power required for lift has been cut in half. This shows that the power required for lift becomes less as the airplane's speed increases. In fact, we have shown that this power to create lift is proportional to one over the speed of the plane.
But, we all know that to go faster (in cruise) we must apply more power. So there must be more to power than the power required for lift. The power associated with lift, described above, is often called the "induced" power. Power is also needed to overcome what is called "parasitic" drag, which is the drag associated with moving the wheels, struts, antenna, etc. through the air. The energy the airplane imparts to an air molecule on impact is proportional to the speed squared. The number of molecules struck per time is proportional to the speed. Thus the parasitic power required to overcome parasitic drag increases as the speed cubed.
Figure 11 shows the power curves for induced power, parasitic power, and total power which is the sum of induced power and parasitic power. Again, the induced power goes as one over the speed and the parasitic power goes as the speed cubed. At low speed the power requirements of flight are dominated by the induced power. The slower one flies the less air is diverted and thus the angle of attack must be increased to maintain lift. Pilots practice flying on the "backside of the power curve" so that they recognizes that the angle of attack and the power required to stay in the air at very low speeds are considerable.
Fig 11 Power requirements versus speed.
At cruise, the power requirement is dominated by parasitic power. Since this goes as the speed cubed an increase in engine size gives one a faster rate of climb but does little to improve the cruise speed of the plane.
Since we now know how the power requirements vary with speed, we can understand drag, which is a force. Drag is simply power divided by speed. Figure 12 shows the induced, parasitic, and total drag as a function of speed. Here the induced drag varies as one over speed squared and parasitic drag varies as the speed squared. Taking a look at these curves one can deduce a few things about how airplanes are designed. Slower airplanes, such as gliders, are designed to minimize induced drag (or induced power), which dominates at lower speeds. Faster airplanes are more concerned with parasite drag (or parasitic power).
Fig 12 Drag versus speed.
Wing efficiency
At cruise, a non-negligible amount of the drag of a modern wing is induced drag. Parasitic drag, which dominates at cruise, of a Boeing 747 wing is only equivalent to that of a 1/2-inch cable of the same length. One might ask what effects the efficiency of a wing. We saw that the induced power of a wing is proportional to the vertical velocity of the air. If the length of a wing were to be doubled, the size of our scoop would also double, diverting twice as much air. So, for the same lift the vertical velocity (and thus the angle of attack) would have to be halved. Since the induced power is proportional to the vertical velocity of the air, it too is reduced by half. Thus, the lifting efficiency of a wing is proportional to one over the length of the wing. The longer the wing the less induced power required to produce the same lift, though this is achieved with and increase in parasitic drag. Low speed airplanes are effected more by induced drag than fast airplanes and so have longer wings. That is why sailplanes, which fly at low speeds, have such long wings. High-speed fighters, on the other hand, feel the effects of parasite drag more than our low speed trainers. Therefore, fast airplanes have shorter wings to lower parasite drag.
There is a misconception by some that lift does not require power. This comes from aeronautics in the study of the idealized theory of wing sections (airfoils). When dealing with an airfoil, the picture is actually that of a wing with infinite span. Since we have seen that the power necessary for lift is proportional to one over the length of the wing, a wing of infinite span does not require power for lift. If lift did not require power airplanes would have the same range full as they do empty, and helicopters could hover at any altitude and load. Best of all, propellers (which are rotating wings) would not require power to produce thrust. Unfortunately, we live in the real world where both lift and propulsion require power.
Power and wing loading
Let us now consider the relationship between wing loading and power. Does it take more power to fly more passengers and cargo? And, does loading affect stall speed? At a constant speed, if the wing loading is increased the vertical velocity must be increased to compensate. This is done by increasing the angle of attack. If the total weight of the airplane were doubled (say, in a 2g turn) the vertical velocity of the air is doubled to compensate for the increased wing loading. The induced power is proportional to the load times the vertical velocity of the diverted air, which have both doubled. Thus the induced power requirement has increased by a factor of four! The same thing would be true if the airplane’s weight were doubled by adding more fuel, etc.
One way to measure the total power is to look at the rate of fuel consumption. Figure 13 shows the fuel consumption versus gross weight for a large transport airplane traveling at a constant speed (obtained from actual data). Since the speed is constant the change in fuel consumption is due to the change in induced power. The data are fitted by a constant (parasitic power) and a term that goes as the load squared. This second term is just what was predicted in our Newtonian discussion of the effect of load on induced power.
Fig 13 Fuel consumption versus load for a large transport airplane
traveling at a constant speed.
The increase in the angle of attack with increased load has a downside other than just the need for more power. As shown in figure 9 a wing will eventually stall when the air can no longer follow the upper surface. That is, when the critical angle is reached. Figure 14 shows the angle of attack as a function of airspeed for a fixed load and for a 2-g turn. The angle of attack at which the plane stalls is constant and is not a function of wing loading. The stall speed increases as the square root of the load. Thus, increasing the load in a 2-g turn increases the speed at which the wing will stall by 40%. An increase in altitude will further increase the angle of attack in a 2-g turn. This is why pilots practice "accelerated stalls" which illustrates that an airplane can stall at any speed. For any speed there is a load that will induce a stall.
Fig 14 Angle of attack versus speed
for straight and level flight and for a 2-g turn.
Wing vortices
One might ask what the downwash from a wing looks like. The downwash comes off the wing as a sheet and is related to the details on the load distribution on the wing. Figure 15 shows, through condensation, the distribution of lift on an airplane during a high-g maneuver. From the figure one can see that the distribution of load changes from the root of the wing to the tip. Thus, the amount of air in the downwash must also change along the wing. The wing near the root is "scooping" up much more air than the tip. Since the root is diverting so much air the net effect is that the downwash sheet will begin to curl outward around itself, just as the air bends around the top of the wing because of the change in the velocity of the air. This is the wing vortex. The tightness of the curling of the wing vortex is proportional to the rate of change in lift along the wing. At the wing tip the lift must rapidly become zero causing the tightest curl. This is the wing tip vortex and is just a small (though often most visible) part of the wing vortex. Returning to figure 6 one can clearly see the development of the wing vortices in the downwash as well as the wing tip vortices.
Fig 15 Condensation showing the distribution of lift along a wing.
The wingtip vortices are also seen.
(from Patterns in the Sky, J.F. Campbell and J.R. Chambers, NASA SP-514.)
Winglets (those small vertical extensions on the tips of some wings) are used to improve the efficiency of the wing by increasing the effective length of the wing. The lift of a normal wing must go to zero at the tip because the bottom and the top communicate around the end. The winglets blocks this communication so the lift can extend farther out on the wing. Since the efficiency of a wing increases with length, this gives increased efficiency. One caveat is that winglet design is tricky and winglets can actually be detrimental if not properly designed.
Ground effect
Another common phenomenon that is misunderstood is that of ground effect. That is the increased efficiency of a wing when flying within a wing length of the ground. A low-wing airplane will experience a reduction in drag by 50% just before it touches down. There is a great deal of confusion about ground effect. Many pilots (and the FAA VFR Exam-O-Gram No. 47) mistakenly believe that ground effect is the result of air being compressed between the wing and the ground.
To understand ground effect it is necessary to have an understanding of upwash. For the pressures involved in low speed flight, air is considered to be non-compressible. When the air is accelerated over the top of the wing and down, it must be replaced. So some air must shift around the wing (below and forward, and then up) to compensate, similar to the flow of water around a canoe paddle when rowing. This is the cause of upwash.
As stated earlier, upwash is accelerating air in the wrong direction for lift. Thus a greater amount of downwash is necessary to compensate for the upwash as well as to provide the necessary lift. Thus more work is done and more power required. Near the ground the upwash is reduced because the ground inhibits the circulation of the air under the wing. So less downwash is necessary to provide the lift. The angle of attack is reduced and so is the induced power, making the wing more efficient.
Earlier, we estimated that a Cessna 172 flying at 110 knots must divert about 2.5 ton/sec to provide lift. In our calculations we neglected the upwash. From the magnitude of ground effect, it is clear that the amount of air diverted is probably more like 5 ton/sec.
Conclusions
Let us review what we have learned and get some idea of how the physical description has given us a greater ability to understand flight. First what have we learned:
The amount of air diverted by the wing is proportional to the speed of the wing and the air density.
The vertical velocity of the diverted air is proportional to the speed of the wing and the angle of attack.
The lift is proportional to the amount of air diverted times the vertical velocity of the air.
The power needed for lift is proportional to the lift times the vertical velocity of the air.
Now let us look at some situations from the physical point of view and from the perspective of the popular explanation.
The plane’s speed is reduced. The physical view says that the amount of air diverted is reduced so the angle of attack is increased to compensate. The power needed for lift is also increased. The popular explanation cannot address this.
The load of the plane is increased. The physical view says that the amount of air diverted is the same but the angle of attack must be increased to give additional lift. The power needed for lift has also increased. Again, the popular explanation cannot address this.
A plane flies upside down. The physical view has no problem with this. The plane adjusts the angle of attack of the inverted wing to give the desired lift. The popular explanation implies that inverted flight is impossible.
As one can see, the popular explanation, which fixates on the shape of the wing, may satisfy many but it does not give one the tools to really understand flight. The physical description of lift is easy to understand and much more powerful.
--------------------------------------------------------------------------------
76 280 all stock exept full bushings,qwuik knuckles,tokico struts&springs,3-2 header,k&n cai,msa sway bars,konig rewinds with toyo proxis ra1.
78 rust bucket. (4 sale!)
2000 v-dub mk4 jetta vr6
2005 titan 4x4 with nismo cai,banks exhus
A:
Yeah, like you can do a free body diagram or know how to apply a control volume to such a problem. There is no airflow over the wing, how can there be lift? What is the power to weight ratio of a 747, less than one. It flies cause it has a wing that gen lift.
Like you are Educated? Does a 172 fly through 5 tons of air a sec? At 100mph? Fig the volume at 40ft (wingspan), 10ft tall 150 ft/sec or so. Near five tons? do the math. If you can.
Navier-Stokes equations are for the educated, deflection lift hooha is for guys like you. And all the people who think it would fly.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
educated posts in this thread? that is f'in funny I am laughing at that one. Keep in up, HA.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
Huilo - it is you who cannot grasp the concept that the airplane is indeed moving forward through the air normally, just as it would if there was no conveyor belt. THE WHEELS WILL SPIN FREELY ON THE BELT, there is no rearward force generated at the wheels. Get it?
By the way, was it me you were referring to as uneducated? I'll list my academic record if you'd like.
-- Next Up: SCCA ITR 300ZX --
A:
question stated below
"This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly."
I take this to mean no aircraft movment.
speed of the conveyor to be exactly the same (but
in the opposite direction) instantly."
You think the plane is moving? Ah the disparity between academics and education.
If you would assimilate my posts you would come to the conclusion that I am educated. I know for a fact you can not read.
No movement, no flight as stated by the educated pilot and at least two engineers, myself included.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
Quoting Huilo:
"question stated below
"This conveyor has a control system that tracks the plane's
speed and tunes the speed of the conveyor to be exactly the same (but
in the opposite direction) instantly."
I take this to mean no aircraft movment."
Therein lies the only true statement you have made - you "take this to mean" something, and you're wrong! The conveyor belt is only exerting a normal force on the wheels. It cannot impart a forward or backward force on the airplane because the wheels spin freely on bearings. The brakes are not engaged. Therefore, the force diagram at the wheels would only show a weight force acting downward and a normal reaction acting upward. Where would the rearward force come from to immobilize the airplane? FROM YOUR IMAGINATION!!!
When the conveyor belt is matching the speed of the aircraft, it is simply doubling the rotational speed of the wheels. The airplane is still able to move forward freely, because IT'S PUSHING ON THE AIR!!!
By the way, your own re-statement of the original question proves you do not understand the problem: if the conveyor belt instantaneously matches the velocity of the aircraft, then it would never move in your description because the velocity of the plane is always zero! In fact, the forward velocity of the airplane increases as in any normal case, and the velocity of the conveyor belt is equal and opposite. But it doesn't matter, because the conveyor belt CANNOT IMPART ANY REARWARD FORCE ON THE AIRPLANE!!!!
Sheesh man, I'm finished here. If you can't understand this post, you won't understand anything!
PS - It didn't take a bachelor's in Mechanical Engineering, Masters in Aeronautical Engineering, a pilot's license and a few years designing aircraft and aircraft systems to prove you wrong - but it helped in my case.
-- Next Up: SCCA ITR 300ZX --
A:
You are contradictating your self, "When the conveyor belt is matching the speed of the aircraft, it is simply doubling the rotational speed of the wheels. The airplane is still able to move forward freely. If the speed is macthed by the converoy there is no airspeed.
if the conveyor belt instantaneously matches the velocity of the aircraft, then it would never move in your description because the velocity of the plane is always zero! In fact, the forward velocity of the airplane increases as in any normal case, and the velocity of the conveyor belt is equal and opposite.
all you have proved is that you can not read.
Carry on. I think you are lying
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20
A:
Hulio: Why would even stopping the wheels of the plane cause it not to move? The plane is propelled by the engines, not the wheels!
Also, whoever showed the resistance of the wheels, your calculations are wrong for an important reason:
- You mention the static friction between rubber and concrete (as 2.0?! thats high!). You do not care about THIS friction, you care about the friction between the bearings in the wheels, which I bet would make it a coefficient of about .1 or less. Remember, the wheels aren't dragging, they are moving with the conveyor belt.
The only realistic counter to this has been the person mentioning that the tires would blow up at the speeds.
1990 NA 300zx 2+0
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A:
Huilo - you have failed miserably to understand this scenario, understand the correct logic and engineering principles involved, and to understand the correct explanation of the forces and motion involved.
I am not contradicting myself, if you read AND COMPREHENDED my posts you would see what Keane and I are both trying to tell you, but instead you're telling me I "can't read." You, my friend, are a blockhead - unable to be instructed in this case. I give up!
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A:
A:
"Hybrid: That is just being pedantic for the cause of not admitting defeat."
It's what he does best.
That people argue the point reveals a lot about the people here.
An F15C has a 99.9% rate of climb. There is enough thrust from the engines at mil power to keep the plane aloft WITHOUT the wings, watch one side-slip on the fuselage with the wings perpindicular to the ground and you realize with enough thrust, anything is capable of flight.
I like it when others are deemed pedantic. This is fun!
People Are Idiots, Just look around here and you will see!
Tony D: "Knowledgeable but Caustic"... rationull
My brother from another mother calls himself "Willie D"
A:
Ah grasshopper, now if the thrust is not present and the friction in wheel bearings is neglected, conveyor turned on, the plane will not move.
In dynamics I recall removing forces to get a better pic of the prob.
OK my thick head just cracked, the plane takes off with an increased wheel rev.
things getout of context so quickily it is crazy, I quoted.
The conveyor can not " match" the speed of the plane, period. The plane takes off.
Thanks for the persistance, that is half genius. cmcneil you are well on your way, given accomplishments.
82 zxt 5-spd, oil cooler!
96 240sxes
78/81 jeep j-20