Thrust = Weight

Richard

Richard

Final Approach
Joined
Feb 27, 2005
Messages
9,076
Location
West Coast Resistance
Display Name
Ack...city life
If you don't agree, explain how a kite requires a counterforce (usually a weight) against the winds to stay aloft.
 
Richard said:
If you don't agree, explain how a kite requires a counterforce (usually a weight) against the winds to stay aloft.
Click to expand...

A kite is a heavier-than-air craft that depends on wind to overcome gravity to fly. To stay aloft, most kites make use of an airfoil, a shape or surface that deflects airflow to produce different air pressures.

The basic principle of kite flying has to do with a difference in air pressure. When air moves quickly over a surface, the pressure is decreased. When air moves more slowly, the pressure is increased.

Thrust and lift are the forces that make kites fly. Thrust is created by the wind, so the speed of the wind affects how well a kite flies. Lift is produced when the bridle and line hold a kite at an angle to the wind. The correct angle causes the air to move more slowly across the face of the kite and pushes the kite upward. At the same time, air moves move quickly across the back of the kite and reduces pressure to create lift.

Drag; determined by the weight, design and the set of the bridle line of the kite, and gravity pulls down on the kite. A kite must have more lift than drag to fly; however, some drag is needed to add stability.
 
As the story goes Benjamin Franklin was trying to get his kite flying, and he was having some trouble. His wife, seeing this, yelled out the window, you need more tail. Ben yelled back: Make up your mind lady. Last night when I mentioned that, you said go fly a kite! :dunno:
 
Let'sgoflying! said:
is part of this thread missing?
Click to expand...

Yeah, the part that makes sense!:rolleyes:

OK upon further reading, the original post actually does make sense, I just missed the question. And to that (the question) I would answer...

A kite is nothing more than a tethered airfoil. Assuming that by "weight" you mean the force on the tether (an untethered kite is either a glider or a parachute), that force is opposing the drag created by the kite plus the lift beyond the weight of the kite itself. With a tethered airfoil, I'm having trouble identifying a component properly labeled "thrust" although it must be present and equal to the kite's drag. Certainly this "thrust" must come from part of the tension on the tether, but as I said some (most?) of that tension is opposing the kite's drag (induced and parasite). Given the typical kite's poor L/D most of that will be induced which would go to zero if the kite weren't generating any lift.

How exactly did you arrive at the notion that thrust equals weight? I can't think of any situation where that's true except when an object in freefall has reached "terminal velocity".
 
Last edited:
lancefisher said:
How exactly did you arrive at the notion that thrust equals weight? I can't think of any situation where that's true except when an object in freefall has reached "terminal velocity".
Click to expand...

I was trying to relate it to the usual lift/weight/thrust/drag thingy, but need help.
 
Well, I don't actually think weight = thrust. I too was trying to tie it to the 4 forces concept. I was hoping someone could explain how a kite is kept aloft.

Consider, a pilot who has no knowledge--at whatever level--beyond what is commonly explained in a ground school for the PPL. One day, he sees a kite and starts to wonder how the 'thrust' is produced. How would you explain it to him?

Expanding on the lo L/D as mentioned by Lance, does that still hold for the inflatable (semi-rigid leading edge) gliding parachutes? This is close to, or parallel to the discussion of thrust in a glider which has a hi L/D.
 
Last edited:
lancefisher said:
How exactly did you arrive at the notion that thrust equals weight? I can't think of any situation where that's true except when an object in freefall has reached "terminal velocity".
Click to expand...
A helicopter hovering? :dunno:
 
Everskyward said:
A helicopter hovering? :dunno:
Click to expand...

Maybe, but the vertical "thrust" of a helicopter is usually called lift. Maybe a powerful jet that's climbing vertically and holding a near constant airspeed would be a better example of thrust = weight.
 
lancefisher said:
Maybe, but the vertical "thrust" of a helicopter is usually called lift. Maybe a powerful jet that's climbing vertically and holding a near constant airspeed would be a better example of thrust = weight.
Click to expand...

Especially if that airspeed is a constant zero.
 
You must log in or register to reply here.
Back
Top