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Thread Killer

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  1. Okay, I must concede. I did check my glider books and indeed, they do not mention thrust. Conceptually, I think that it is useful to call the forward component of lift "thrust" because in reality, that is what moves the glider forward. I think it is a bit harder to visualize where the forward movement comes from when it is described as a small component of the lift - but that is the standard so... I was wrong. I guess.
  2. Welcome to Sailing Anarchy. I feel it fair to point out that you participated in the glider discussion so to claim a hijacking is not quite reasonable in my opinion. an·ar·chy /ˈanərkē/ noun a state of disorder due to absence or nonrecognition of authority.
  3. Thanks, but no. If you can't understand how a glider moves forward through the air, there is no chance you will ever understand how a sailboat sails upwind. I suggest you take your "discussion" to https://www.boatdesign.net/forums/hydrodynamics-aerodynamics/
  4. That's okay. I think that NASA explanation is quite lacking. Whether you want to separate out the forward component of lift and call it thrust, or just forget about it and only use lift, it really doesn't matter. The physics are the same, the power source is the same. It is just semantics.
  5. If gliders only had weight (gravity), lift and drag then they would never move forward. I can agree that thrust is most commonly defined as the forward force produced by some form of engine. If you look up the definition of "thrust" you won't easily find it associated with engineless vehicles. However, in engineless vehicles the forward force is still called thrust. I don't have my glider books at hand right now but I am 99.99% confident that "thrust" is the term used to describe the forward force in gliders. In a glider "thrust" is the forward portion of the lift vector.
  6. Okay, what is the proper word to call the forward force in a glider? I think it is thrust but I am open to being educated. In a Cessna thrust comes from the rotating wings of the propeller acting against the air, their movement through the air being powered via an engine. In a glider the the thrust comes from the wings reacting against the air, powered by gravity. The main difference (other than the obvious) between the two being that the bulk of the lift in the Cessna's case is being used to move the aircraft forward while the bulk of the lift in the glider's case is being used
  7. The lift from a keel does NOT increase righting moment, if it did it would greatly increase leeway. It is the weight of the keel that provides the righting moment, that is why they tend to be made of very heavy materials. A keel does produce thrust, that is how a sailboat is able to sail upwind, by using the keel to react against the water - just like a glider using gravity to react against the air to produce thrust. It does not matter if the water current is moving in one particular direction or not, just like the glider does not care if the airmass is moving up or down or is stationary
  8. Be obtuse if you wish. For a short time I thought you were actually trying to understand these concepts. Apparently you just want to argue. Good luck.
  9. Yeah no shit. The point is that the forward movement of a glider (thrust) comes from gravity. Remove the gravity and you remove the thrust. Doesn't matter if the airmass is rising or not. Gravity is what binds the glider to the Earth so that it can react against the air mass - much in the same way that a sailboat needs a keel to convert the sideways forces of the wind into forward motion.
  10. As a glider pilot, I can absolutely assure you that gliders do in fact fly very nicely in still air. They even will fly in downdrafts and turbulence although those are not as enjoyable.
  11. So I guess you think that gliders can't fly in still air??? Gliders can fly quite nicely without any vertical movement of the air mass, but they can't fly at all without gravity.
  12. It isn't. Gliders use the power of gravity to move forward. Rising air simply allows them to stay aloft longer.
  13. Calculating available power using TWS and projected area of a sail will never work, unless you can account for the energy absorbed by the surrounding air. IOW, it is not possible to only extract energy from the projected sail area.
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