Physics
Postmaster
Joined: Aug 2004
Posts: 4,004
Likes: 1
From: North of Boston MA
Originally Posted by BrianA
If your treadmill allows the plane to achieve forward velocity and matches AIRSPEED with a counter acting GROUNDSPEED as seen on the treadmill, then yes the plane will fly, because it is free to achieve whatever airspeed it wants, the wheels are simply spinning faster than they would on a fixed runway.
If the conveyor is such that is offsets the airplane's GROUNDSPEED with an equal and oppostie GROUNDSPEED, the plan would sit motionless and never take off.
So if the plane tried to move forward (relative to the ground) at 10 mph, the conveyor belt would automatically adjust and run 10 mph in the opposite direction so that the plane never moved.
groundspeed / airspeed : THAT DISTINCTION is the key to understanding it all.
If the conveyor is such that is offsets the airplane's GROUNDSPEED with an equal and oppostie GROUNDSPEED, the plan would sit motionless and never take off.
So if the plane tried to move forward (relative to the ground) at 10 mph, the conveyor belt would automatically adjust and run 10 mph in the opposite direction so that the plane never moved.
groundspeed / airspeed : THAT DISTINCTION is the key to understanding it all.
Airspeed is strictly a measure of air past the wing. A plane that is parked into a 50 knot headwind has an airspeed of 50 knots (yes it does
) and a groundspeed of 0. A plane flying at 50 knot airspeed into a 50 knot headwind has an airspeed of 50 knot but a groundspeed of 0. Turn it around 180° and the plane with the same 50 knot airspeed now has a ground speed of 100 knots. Some small planes (Cessna 152, Piper Cubs) can be flown slow enough that in a strong headwind they will fly backward, relative to the ground. As far as the plane knows, it still has enough relative wind to maintain lift and thus fly.
That is why takeoffs and landings are always made on the runway that is most into the wind. It makes your takeoff and landing distance much shorter. Aircraft carriers turn into the wind and adjust their thru the water speed to make a 30 knot or so headwind. Makes it much easier on the catapults when launching and greatly slows the relative speed on landing.
Oh well, I have a plane to catch. I wonder if Logan Airport (KBOS) has a conveyor we can borrow this morning.
Merry Christmas all.....
Ray
FTE Leadership Emeritus
Joined: Jan 2003
Posts: 161,999
Likes: 75
From: 3rd Rock
Originally Posted by andym
I just can't believe an FTE moderator would pull that kind of stunt.
Just because he is a moderator does not mean....he does not have an opinion, nor is allowed to speak it.
Last edited by IB Tim; Dec 16, 2005 at 07:25 AM.
"Mifflin Clay"
Joined: Jul 2005
Posts: 3,177
Likes: 4
From: Mifflin, PA
Originally Posted by Nitramjr
Actually, that is exactly the trap to this question. The conveyor would not care one bit about airspeed or groundspeed. Once the wheels start rotating and the conveyor started moving, their speed (of the wheels and conveyor)would only be relative to each other and have nothing to do with the airspeed or the groundspeed of the plane. Either way of looking at it, the planes engines thrust against air and the plane moves forward. There is nothing holding it back.
Airspeed is strictly a measure of air past the wing. A plane that is parked into a 50 knot headwind has an airspeed of 50 knots (yes it does ) and a groundspeed of 0. A plane flying at 50 knot airspeed into a 50 knot headwind has an airspeed of 50 knot but a groundspeed of 0. Turn it around 180° and the plane with the same 50 knot airspeed now has a ground speed of 100 knots.
Some small planes (Cessna 152, Piper Cubs) can be flown slow enough that in a strong headwind they will fly backward, relative to the ground. As far as the plane knows, it still has enough relative wind to maintain lift and thus fly.
That is why takeoffs and landings are always made on the runway that is most into the wind. It makes your takeoff and landing distance much shorter. Aircraft carriers turn into the wind and adjust their thru the water speed to make a 30 knot or so headwind. Makes it much easier on the catapults when launching and greatly slows the relative speed on landing.
Oh well, I have a plane to catch. I wonder if Logan Airport (KBOS) has a conveyor we can borrow this morning.
Merry Christmas all.....
Ray
Airspeed is strictly a measure of air past the wing. A plane that is parked into a 50 knot headwind has an airspeed of 50 knots (yes it does
) and a groundspeed of 0. A plane flying at 50 knot airspeed into a 50 knot headwind has an airspeed of 50 knot but a groundspeed of 0. Turn it around 180° and the plane with the same 50 knot airspeed now has a ground speed of 100 knots. Some small planes (Cessna 152, Piper Cubs) can be flown slow enough that in a strong headwind they will fly backward, relative to the ground. As far as the plane knows, it still has enough relative wind to maintain lift and thus fly.
That is why takeoffs and landings are always made on the runway that is most into the wind. It makes your takeoff and landing distance much shorter. Aircraft carriers turn into the wind and adjust their thru the water speed to make a 30 knot or so headwind. Makes it much easier on the catapults when launching and greatly slows the relative speed on landing.
Oh well, I have a plane to catch. I wonder if Logan Airport (KBOS) has a conveyor we can borrow this morning.
Merry Christmas all.....
Ray
Post Fiend
Joined: Mar 2002
Posts: 19,402
Likes: 38
From: Bonita Springs FL
Originally Posted by Tim Lamkin
Seems to me, he was, and is speaking his point, something you or any member can.... and often do.
Just because he is a moderator does not mean....he does not have an opinion, nor is allowed to speak it.
Just because he is a moderator does not mean....he does not have an opinion, nor is allowed to speak it.
Posting Guru
Joined: Aug 2000
Posts: 2,416
Likes: 4
From: PacNW
{Taking off Mod hat}
Good lord! 13 pages of this stuff, amazing! Bottom line as long as the conveyer is long enough for the plane to get up enough airspeed of course it will fly. Best analogy I can think of, take a conventional dragster and put it 1/4 mile track made of ice. It'll never move because the power is being applied to the wheels and they can't overcome the lack of friction it takes for forward momentum. Now take a jet dragster and put it on the same track. It'll shoot off like a...well...a jet. Why? Because it's not using friction to move forward it's using thrust, the wheels don't have to spin at all.
{Putting Mod hat back on}
Merry Xmas everyone!
Good lord! 13 pages of this stuff, amazing! Bottom line as long as the conveyer is long enough for the plane to get up enough airspeed of course it will fly. Best analogy I can think of, take a conventional dragster and put it 1/4 mile track made of ice. It'll never move because the power is being applied to the wheels and they can't overcome the lack of friction it takes for forward momentum. Now take a jet dragster and put it on the same track. It'll shoot off like a...well...a jet. Why? Because it's not using friction to move forward it's using thrust, the wheels don't have to spin at all.
{Putting Mod hat back on}
Merry Xmas everyone!
Last edited by Bill_Beyer; Dec 24, 2005 at 02:11 PM.
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