|
|
#21
11-23-2005, 10:12 AM
|
|||
|
|||
Re: think about this...
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] If the plane is not moving, no air is being forced under its wings. If no air is being forced under its wings, there is no lift. So it stays grounded. [/ QUOTE ] When did I say the plane wasn't moving? [/ QUOTE ] you essentially gave us two velocity vectors of equal magnitude that work in exactly opposite directions. the plane has zero velocity relative to somebody standing on the ground observing it. it is going nowhere. i think. [/ QUOTE ] Everyone seems to be figuring this from the standpoint that the plane's wheels are where the thrust is comming from. The wheels do not push the plane forward, the props do. [/ QUOTE ] Why is that relevant? The thrust from the props = X. The "thrust" from the moving conveyor-runway = -X. The aircraft is not moving relative to the air. Hence, no airspeed, so no lift. 
|
|
#22
11-23-2005, 10:13 AM
|
|||
|
|||
|
Re: think about this...
so do you get it now?
|
|
#23
11-23-2005, 10:13 AM
|
|||
|
|||
|
Re: think about this...
[ QUOTE ]
The thrust from the props = X. The "thrust" from the moving conveyor-runway = -X. [/ QUOTE ] this is wrong.
|
|
#24
11-23-2005, 10:13 AM
|
|||
|
|||
|
Re: think about this...
[ QUOTE ]
Everyone seems to be figuring this from the standpoint that the plane's wheels are where the thrust is comming from. The wheels do not push the plane forward, the props do. [/ QUOTE ] no. I understand what causes the plane to move forward.
|
|
#25
11-23-2005, 10:18 AM
|
|||
|
|||
|
Re: think about this...
What everyone is missing is that the plane is attached to a hook on a launching arm, and the runway is oiled and there is a very low coefficient of friction. The wheels are just spinning wildly, it just happens to be the same speed as the conveyor belt. I hope this makes it easier to understand. [img]/images/graemlins/grin.gif[/img]
Cheers, Rube Goldberg
|
|
#26
11-23-2005, 10:22 AM
|
|||
|
|||
|
Re: think about this...
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] If the plane is not moving, no air is being forced under its wings. If no air is being forced under its wings, there is no lift. So it stays grounded. [/ QUOTE ] When did I say the plane wasn't moving? [/ QUOTE ] you essentially gave us two velocity vectors of equal magnitude that work in exactly opposite directions. the plane has zero velocity relative to somebody standing on the ground observing it. it is going nowhere. i think. [/ QUOTE ] Everyone seems to be figuring this from the standpoint that the plane's wheels are where the thrust is comming from. The wheels do not push the plane forward, the props do. [/ QUOTE ] Why is that relevant? The thrust from the props = X. The "thrust" from the moving conveyor-runway = -X. The aircraft is not moving relative to the air. Hence, no airspeed, so no lift. [/ QUOTE ] I agree, ground speed has nothing to do with it. It's all about airspeed (the speed at which air passes over the wing). Nothing else matters. If an plane is moving forward at 50 MPH into a headwind of 100 MPH, the net airspeed is 150 MPH BUT the plane would actually be moving backwards at a rate of 50 MPH groundspeed....
|
|
#27
11-23-2005, 10:27 AM
|
|||
|
|||
|
Re: think about this...
[ QUOTE ]
[ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] [ QUOTE ] If the plane is not moving, no air is being forced under its wings. If no air is being forced under its wings, there is no lift. So it stays grounded. [/ QUOTE ] When did I say the plane wasn't moving? [/ QUOTE ] you essentially gave us two velocity vectors of equal magnitude that work in exactly opposite directions. the plane has zero velocity relative to somebody standing on the ground observing it. it is going nowhere. i think. [/ QUOTE ] Everyone seems to be figuring this from the standpoint that the plane's wheels are where the thrust is comming from. The wheels do not push the plane forward, the props do. [/ QUOTE ] Why is that relevant? The thrust from the props = X. The "thrust" from the moving conveyor-runway = -X. The aircraft is not moving relative to the air. Hence, no airspeed, so no lift. [/ QUOTE ] I agree, ground speed has nothing to do with it. It's all about airspeed (the speed at which air passes over the wing). Nothing else matters. If an plane is moving forward at 50 MPH into a headwind of 100 MPH, the net airspeed is 150 MPH BUT the plane would actually be moving backwards at a rate of 50 MPH groundspeed.... [/ QUOTE ] too bad, i'm right.
|
|
#28
11-23-2005, 10:29 AM
|
|||
|
|||
|
Re: think about this...
[ QUOTE ]
i'm right. [/ QUOTE ] this is true - you seem to be the only one grasping it so far. out of curiosity, what is your job/major?
|
|
#30
11-23-2005, 10:38 AM
|
|||
|
|||
|
Re: think about this...
If a plane (specifically its wings) is traveling with zero speed with respect to the air, then there can be no lift. If the props are forcing air over the wings, there can be lift (though then the plane is not traveling with zero speed wrt the air, so we don't contradict the above). If you have some VTOL capabilities (really just VT) you could take off. I think in the scenario you described, you cannot, though I am not sure how much air the props push over the wings.
The discussion in this thread makes me think perhaps your phrasing is awkward.
|
 |
|
|
Linear Mode
