Rocket.

Discussion in 'Free Thoughts' started by TheFrogger, Jul 11, 2018.

  1. TheFrogger Valued Senior Member

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    Has anyone noticed how when a rocket is launched, there is quite a moment when the engines are fired, but the rocket remains. The rocket and the Earth are one.
     
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  3. Gawdzilla Sama Valued Senior Member

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    Thrust does have to develop. This is not rocket science.
     
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  5. TheFrogger Valued Senior Member

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    A rocket? The Earth!
     
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  7. Gawdzilla Sama Valued Senior Member

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    Pancakes? Truffles!
     
  8. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    I have no idea what you mean by this statement. Could you elaborate why you think that the time after ignition but before the rocket moves is special in some way?
     
  9. Michael 345 Bali 1 week here 2 to go Valued Senior Member

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    Could it be that the stupid people who launch rockets hold them down with massive clamps?

    I don't know but holding down rockets until the full thrust has built up enough to lift the rocket would perhaps stop the rocket tipping over if only partial thrust was applied

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  10. TheFrogger Valued Senior Member

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    They do the same with planes. The brakes are applied, after-burners ignited until thrust is achieved, then the brakes released. ☺

    The above philosophy does not only apply to the Earth. It could also apply to it's satellite (Mooney.)
     
    Last edited: Jul 11, 2018
  11. Gawdzilla Sama Valued Senior Member

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    If you're on a USN carrier they push a button. That plane is going SOMEWHERE, in whole or parts.
     
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  12. origin In a democracy you deserve the leaders you elect. Valued Senior Member

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    I see that "TheFrogger" use to be known as "Counter", that explains the odd posts.
    Goodbye.
     
  13. TheFrogger Valued Senior Member

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    Hello. ☺

    James R has amalgamated the accounts. I wasn't banned. ☺
     
  14. Michael 345 Bali 1 week here 2 to go Valued Senior Member

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    So the point of the original post was.....?

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  15. billvon Valued Senior Member

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    Correct. It takes a short time (seconds) for the engines to throttle up to takeoff power. In some cases, as in the Apollo moon missions, the rocket actually had to sit there for nine seconds until it was light enough to take off. (i.e. thrust exceeded weight.)
    Usually not. Most planes don't have afterburners, and most aircraft don't hold brakes at any point during the takeoff. It's most often used when you need every inch of runway.
    You didn't list a philosophy.
     
  16. TheFrogger Valued Senior Member

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    Rocket=Mooney.
     
  17. billvon Valued Senior Member

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    Mooney=doctor killer.
     
  18. DaveC426913 Valued Senior Member

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    Oh. That makes so much sense now. I wondered about the recent uptick in ... whatever that is.
     
  19. RainbowSingularity Valued Senior Member

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    what DO rockets study in science class ?
     
  20. Michael 345 Bali 1 week here 2 to go Valued Senior Member

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    Fireworks

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  21. Gawdzilla Sama Valued Senior Member

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    Well, this thread never got off the ground. We need a steely-eyed moderator man right now.
     
  22. Kittamaru Suppose it makes sense. Wearing a bit thin. Valued Senior Member

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    Are you referring, perhaps, to the moments of equilibrium in which the effect of gravity on the mass of the rocket is in balance with the force of thrust from its engines?

    I believe this is done in a specific sequence to avoid both having the rocket fall and smash the exhaust nozzles on the ground and to prevent ripping the launch platform apart - taking the Falcon Heavy as an example, I believe that if those engines all spooled up to maximum thrust before the clamps were released, it'd either rip the tower apart, or torque the rocket in some horrific way. It is a terrific amount of thrust being utilized, after all.

    As for the rocket tipping - that's been an interesting dilemma since rocketry originated; stabilizing the thing when the fulcrum point is, essentially, at the very bottom with all the mass suspended above it. It's why most (maybe all?) modern rockets use gimbaled exhaust nozzles, allowing for basic thrust vectoring to help keep it stable.

    Er, most aircraft don't have afterburners at all; for that matter, there are very few planes with afterburners where the wheel brakes would be able to hold the plane back at maximum afterburner. You may be thinking of a carrier launched aircraft (which is held in place by a catapult). Typically, AB use is situation dependent; though there are some exceptions:

    The F/A-18 Hornet always launches with afterburner. This accomplishes a couple things, chief among them being a test of the afterburner system, and getting the rather heavy craft in the air more quickly. On a land-based launch, they typically come up to what is called "military power", which is the maximum throttle setting without engaging the afterburner, and then punch in the afterburners during the roll out (typically to half afterburn). Carrier operations are similar - the burner is kicked in about halfway down the deck during a catapult launch, then pulled back to military power once you've cleared the flight deck. At night, afterburners are kicked on prior to the catapult firing to ensure they are functioning properly, then pulled back once you've cleared the deck.

    Afterburners are also often used during carrier landings - upon touching the deck, the pilots will punch the throttle so that, if they miss the arresting wires, they have sufficient thrust to take back off and circle around - after all, rolling off the end of a flight deck tends to end poorly if you haven't built enough velocity to get airborne again.

    According to F-16 pilots, they typically use afterburners for takeoff whenever their expected takeoff roll is more than 50% of the available runway - usually, this is when they are heavily loaded with fuel (both wing tanks) and ordinance - granted, this is an aircraft that can put out more pounds of thrust than the total weight of the aircraft itself.

    A big consideration for all of this is the thrust ratio - an aircraft in motion can go faster faster than a stationary one - this is because of the ramjet effect on the air intake - at several hundred knots, you are shoving vastly more air into the engine intake than you are at a standstill. Modern aircraft computers continually adjust the fuel/air mixture to optimize performance; firing an afterburner on takeoff gets you to rotation speed faster, and I'd imagine the key there is you do not want to find yourself at a point halfway down the runway where you are accelerating too slowly to take off before you run out of tarmac, but are going too fast to stop before the end of the runway.
     

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