Airplane Flight Question - Page 7 - United Bimmer Community

**donald1476** · 11-30-2005, 11:00 PM

Quote:

Originally Posted by delmarco

I think the confusement lies within the improper wording of the sentence and lack of necassary information

The answer depends upon what the speeds are referenced to. Let's say that the speed is S, which is greater than the take off speed for the plane and there is no wind. There are three cases:

1. The speeds of the conveyor and that of the plane are both with respect to the ground, this is the assumed case. In this case the plane will take off and the plane will be traveling at 2S with respect to the conveyor.
(understood and agreed, but this was never part of the initial question, when you say conveyer belt it can mean anydirection when you say threadmill it usually implies the belt is moving opposite to direction the plane moving in)

2. The speed of the conveyor is with respect to the ground and the speed of the plane is with respect to the conveyor. In this case the plane will not move with respect to the ground and it will not take off.(agree with you but confusing-"with respect to the ground" in what direction. why not say "the belt is moving opposite with repect to the plane's movement". Too many "repects" donald, tighten it up buddy )

3. The speed of the plane is with respect to the ground and the speed of the conveyor is with respect to the plane. In this case the plane will take off, but the the conveyor will not be moving with respect to the ground...( Totally confusing. too many "repects" and now you say the belt is not moving but the belt has a speed with repect to the plane. I getting that the belt is moving in the same direction the plane is moving in but slower than the plane???unlike in 1. where the belt and the plane's speed are moving in sync and hence creates a speed for the plane that is 2S???)

If you are confused by that then noone should be listening to your reasoning in the first place.

And I said those are the three possible cases, can you read?

Try replacing respect with reletave, maybe you'll get it then...you dolt.

**delmarco** · 11-30-2005, 11:04 PM

Quote:

Originally Posted by komodo

^^ The original wording didn't say it cancels the speed... it just says the treadmill moves in the opposite direction the same speed.

as the same speed as the wheels or the turbine?
actually...
the plane will never fly in this case.

if belt speed = -300 m/s
and turbine speed = wheel speed since the plane is still on the ground and yes those wheels are important until the plane is in the air

then when
turbine speed = wheel speed = total plane speed on ground = 300 m/s
and belt speed = -300 m/s

300 m/s - 300 m/s = 0 m/s b= final planes velocity and speed on ground!

As long as the plane is on the ground then the wheel MUST be on the conveyer belt which is matching the planes speed AT ALL TIMES so the plane cannot fly unless it moves faster than the belt.

why is this not right and not simple?

witeshark · 11-30-2005, 11:04 PM

If the turbo jets determine the aircraft speed, the wheels and treadmill belt do not matter -- because then the head wind effect is by turbo fan engines ignoring the ground if and only if after take off speed has been acquired

**donald1476** · 11-30-2005, 11:05 PM

Quote:

Originally Posted by Delmarco

as the same speed as the wheels or the turbine?
actually...
the plane will never fly in this case.

if belt speed = -300 m/s
and turbine speed = wheel speed since the plane is still on the ground and yes those wheels are important until the plane is in the air

then when
turbine speed = wheel speed = total plane speed on ground = 300 m/s
and belt speed = -300 m/s

300 m/s - 300 m/s = 0 m/s

why is this not right and not simple?

Planes aren't driven by the wheels, Dr. Delmarco. So then think how much of an effect does the conveyor have on the speed of the plane? NONE. How much faster do the wheels spin? 2X

**delmarco** · 11-30-2005, 11:08 PM

Quote:

Originally Posted by donald1476

Planes aren't driven by the wheels, Dr. Delmarco

I never said that. I said the turbine push is reflected in the wheels as long as the plane is on the ground.

Of course if the plane starts at 0 m/s then gets up to 20 m/s wont the treadmill kick in and cancel out the planes motion before the headwind effect takes over?

Donald be quiet for a moment...i'm trying to understand what Witeshark is saying.

**komodo** · 11-30-2005, 11:09 PM

Quote:

Originally Posted by delmarco

but then again if the conveyor belt can match and track the plane's speed then the plane will NOT FLY.

Just because the belt MATCHES the speed of the plane, doesn't mean it's exerting a FORCE to counter the forward motion of the plane.... it's just causing the wheels to spin faster.

You're confusing force and speed.

**donald1476** · 11-30-2005, 11:10 PM

Quote:

Originally Posted by delmarco

I never said that. I said the turbine push is reflected in the wheels as long as the plane is on the ground.

Of course if the plane starts at 0 m/s then gets up to 20 m/s wont the treadmill kick in and cancel out the planes motion before the headwind effect takes over?

Donald be quiet for a moment...i'm trying to understand what Witeshark is saying.

No it isn't "reflected" in the wheels. It wont because the wheels are nothing but friction reducers between the plane and the ground. Read through the thread because it is obvious you haven't. Better yet open your physics book.

**donald1476** · 11-30-2005, 11:13 PM

Here just read this. http://www.avweb.com/news/columns/191034-1.html .
It has been done. End of argument.

**delmarco** · 11-30-2005, 11:15 PM

Quote:

Originally Posted by witeshark

If the turbo jets determine the aircraft speed, the wheels and treadmill belt do not matter -- because then the head wind effect is by turbo fan engines ignoring the ground if and only if after take off speed has been acquired

but takeoff speed can never be achieved if the belt cancels out the intial speeds of the plane...

so at
10am the plane is at 0 m/s, o velocity and 0 displacement
at 10.03am the plane is at 100 m/s, 20 m/s^2, displacement 2000 ft.
at 10.03am the belt kicks in at immediately matches the planes speed at 100 m/s

at 10.04 am the plane is moving at 100 m/s and the belt is moving at - 100 m/s, the planes velocity and displacement is now 0

10.05am the plane looks as if it is not moving but held in place like a runner on threadmill. the planes turbine&wheel speed is now 500 m/s but the beltspeed is at -500 m/s. the plane's speed is 0 m/s.

now in this scenario the belt will increase infinately to match the speed of the turbines via the wheels. if the plane never reached headwind speed before the belt kicks in then the plane will be stuck.

**delmarco** · 11-30-2005, 11:18 PM

matter settled. thanks Donald.
Beer is on me next time we meet!

**komodo** · 11-30-2005, 11:21 PM

Quote:

Originally Posted by delmarco

at 10.03am the belt kicks in at immediately matches the planes speed at 100 m/s

Yes, the belt is moving at 100 m/s, but it isn't exerting enough FORCE on the plane to move it the opposite direction at 100 m/s, it's simply moving that fast.... the jet engines can overcome some spinning wheels.

**donald1476** · 11-30-2005, 11:24 PM

Quote:

Originally Posted by delmarco

matter settled. thanks Donald.
Beer is on me next time we meet!

Good because I'm a heavy drinker.

**delmarco** · 11-30-2005, 11:31 PM

Basically my flaw is that i did not know that a n airplane has
two separate speeds at takeoff
1. air speed (propeller puuling the plane forward)
2. ground speed (wheels that spin but do NOT exert force on the ground)
because of airspeed the wheels never exert force on the ground during takeoff. So the plane is naturally light as a feather at the moment of final per-flight velocity.

that is the key to the solution...think of the conveyor belt as not even being there after the propellers or turbines initiate airspeed.

wow...what an AWESOME thread...I almost didn't sleep tonight had i not gotten that answer....

thanks guys...

**donald1476** · 11-30-2005, 11:35 PM

You are semi-right but I'll leave it at End of argument.

witeshark · 12-01-2005, 12:22 PM

Okay. I have thought it over again. To word what I said before better: If the pilot throttles up the turbo fans to take off thrust, the plane will move ahead and develop take off speed regardless of the movement of the treadmill below. The only effect the latter will have is to cause the landing gear wheels to spin at ridiculous speed as the plane gathers speed and takes off.