I didn’t say it IS thrust but it defines the thrust. Let me ask you a question; If you blocked the jet nozzle so there was no exhaust, what would the net thrust be?
as i mentioned before in previous post it would be contained, counteracting itself but if you put the engine up against a wall it would move away from the wall initially and you wouldnt have felt any air out the back because the wall was there but the ac would move. it’s not the force hitting the wall what moves the plane its the force acting in the opposite direction that pushes the plane forward. one force trying to push the wall over but cant because it is fixed and the opposite force pushes the plane away and getting some movement because is not fixed. there are two forces so to speak one action in the direction of the plane and the other opposite towards the wall, if the engine was open on both side and the explosion was in the middle.you would have equal force/thrust coming out each side.
vy
How does any of that contradict what I have said?
Not a matter of contradicting, just clarification of direction (pardon the pun if it scraped by as one). The forward thrust is gone, used up/traded off/converted to movement by the planes forward movement. The rest is what the plane didn’t use because of the mass of the ac and found it’s way out of the combustion chamber in another direction albeit the exhaust hole.
vy VY
No, sorry. None of that makes any sense. With full-coverage thrust reversers deployed, there never was any forward thrust. There is backward thrust because the output of the engine has been redirected in the forward direction. If you had a 100% efficient ducting system you could direct 100% of the engine’s output to backward thrust.
You seem to be confused about what happens to the forward force on the turbine blades, combustion chambers and other engine components. This force is cancelled by the force on the thrust reversers (essentially exerting a net stretching force on the entire engine), but this happens entirely within the engine. No forward force is transmitted to the airplane and converted/“absorbed by the mass”/etc. With the thrust reversers deployed, the engines pull backwards on the airplane. That’s all there is to it.
The net force on the engine is distributed around the thrust reverser outlets and exerted by the pressure of the air leaving them.
basically If there was a flat surface for the reverse thrust the exhaust would be directed upwards. the buckets have to be curved to take advantage of that upward thrust which hits the curve in the metal knocking the plane in a backwards direction.. whats not used is just waste air bouncing of the buckets.. it’s the air hitting the metal curve on the bucket that tries to push the plane in that direction. after it comes off the buckets it’s job is done, it has no more effect on the ac. Hold a piece of paper in your hands and blow on it, is it the air coming back to you that is pushing the paper or the air going towards it?
vyVY
Are you trying to ask questions here or are you lecturing us?
I think he understands it well enough. He’s just using terms in an unusual way. To him exhaust is wasted energy because it represents an area of the engine that doesn’t have anything “pushing” on it. But that overlooks or plays down the fact the exhaust is necessary for a net thrust vector to exist. With no exhaust there is no movement so it is not wasted at all, it is necessary.
If you read my posts you would see when i had my eureka moment , when I grasped what I was trying to figure out. now because I am explaining what I understand you want to put me back into question mode?
vy VY
stand in front of an engine and throw a 100 mph ball at the bucket the ac wouldnt go back 100 mph it may go back 10 mph and the ball will come back at you 90 mph. if you keep throwing the ball, gradually the ball will rebound back a less speeds because the plane is using more of the energy, so less and less of the energy is wasted if it was possible from the ball to get the plane going backward at 100 mph, the ball would never come back towards you. but the plane would still be going backwards..
Thats what I see in my head
vyVY
btw when I say wasted I mean the ac couldn’t use it to it’s full potential because of the mass of the plane, it used what it could for that particular time frame and accelerates/decelerates, as time passes it will be able to absorb more the faster it is pushed. if 10 mph of the 100 mph is attained then it will take another 10 or 15 so to speak and speed increases or decreases 20 -25 mph…I think it works exponentially.
vyVY
That’s not what is happening though. You are standing IN the engine and throwing the balls at the buckets. The balls are always bouncing off the buckets at the same speed relative to you. I think now that you don’t quite have it right in your head.
None of your post immediately above mine makes any sense to me. I’m not sure if that’s a failure of you to explain or me to grasp what you are saying.
I think I know what he’s saying. I think.
He is saying that if the engine is producing 100 mph exhaust, then the plane does not immediately accelerate to 100 mph, but rather takes some finite amount of time, and that when the plane’s velocity is less than 100 mph some of the exhaust energy is “wasted” because the mass of the plane prevents it from accelerating to 100 mph immediately. Or something to that effect.
This is not accurate.
To a first approximation, the engine’s thrust does not depend on the airplane’s speed, and the airplane’s rate of acceleration (i.e. rate of energy “absorption”) does not depend on the speed either (ignoring air resistance). Yes, it takes a certain amount of time for the plane to accelerate, but this does not mean any energy is wasted. The engine produces thrust by ejecting gases at 100 mph, relative to the speed of the plane! Ejecting gas at 100 mph produces a certain reactive force, and this force is constant regardless of how fast the airplane is going. And this force always accelerates the plane by the same amount, regardless of whether it is going 0 mph or 200 mph (again, ignoring air resistance and other such things).
The plane does not accelerate instantaneously to 100 mph, or any other speed, just because it takes a lot of energy to accelerate a plane, more than the engine can produce instantaneously. Nor does the plane’s mass have anything to do with it. A lighter plane and a heavier plane will “absorb” the same amount of energy for the same amount of thrust - it’s just that a lighter plane will be traveling faster for the same amount of energy absorbed.
To reiterate: the velocity of the exhaust gases and the velocity of the plane have nothing to do with (to a 1st approximation) with the amount of acceleration the plane experiences.
An engine can produce X pounds of thrust by ejecting a large amount of gas at 100 mph, or a small amount of gas at 10,000 mph. As long as they both produce the same amount of thrust (the same force), the airplane’s acceleration will be identical.
Oops, I wrote that post in the context of acceleration, when we have been talking about deceleration. The concepts are all the same of course.
actually I wouldn’t be standing or attached to the actual metal of the plane, the combustion happens in suspension or in the space inside the engine, and it’s the force of the explosion that pushes the plane forward. the force in the other direction would push you if you were standing at the exhaust. that’s what I mean by wasted energy, it was not used to push the plane, what was used you will never feel coming out the back you would have to stand in front of the plane and as the plane pushes you you would feel what was used at that particular time. I would have to use two balls (well billions if i wanted to produce the force all around) inside the engine to replicate this. like i said before, if both ends were open you would feel exhaust on both sides. Ill use forward and backward force to demonstrate.. if I am suspended in the middle of the engine, I would have to throw two balls to replicate the combustion, one i.e. 100 mph at the front and another 100 mph to the back.. remember an explosion is in all directions, but we are using the pertinent directions here.the force towards the back was going that way anyway, if there was an engine there or not, and vice versa so it is not used.. but because the aircraft is there( the front of the engine) the force that goes in the forward pushes the aircraft, what comes back and adds to the backward exhaust is what is bounced off the engine pushing it because the plane was too heavy to instantaneously go forward at the 100mph lb thrust so to speak. So instead of 100 mph lbs force out the back you will feel what bounces back also off of the forward force. As the plane arrives at 100 mph, only the backward 100mph force you would feel (or would you? just using to illustrate the point)), because the forward 100mph is going with the ac in that direction, nothing to bounce back off of, the plane is using the full 100mph lbs thrust potential(if that was possible). If all the force of the explosion was in one direction then the other theories would hold water, but as I mentioned earlier combustion knows no specific direction. what it can move it will move and what it cannot is counterbalanced. or is wasted out the back; because of the nature of the combustion (all directions) it could not be used.. there is no free energy, either it’s used or it is not used
vy VY
once again the the thrust reverse issue, the reason that the plane reverses is because as the thrust exits the engine it is counteracted by the bucket, the ac being pushed and pulled so to speak, then the force is captured at the curvature of the buckets, when this force hits/strikes the curve, that is the actual action on the aircraft providing the reverse thrust/the slowing, not before and not after, right at that instant when it hits the curve.what energy that isn’t used up in the curve to push the ac backward is bounced away and that’s what you feel coming back at you,towards the front of the ac, unused breeze so to speak, the actionable part is at the curvature. it there was no curve, the force would go in all directions in a 90 degree angle doing nothing for the ac. just counteracting the forward thrust and basically making 0 movement.
vy VY
Jet engine = renewable high pressure air tank.
use various elbows to direct the tank air where you want it to go. ( Action/reaction. )
Yes, a flat board attached to the air tank 90° stuck in front of the nozzle will try to fly back from the nozzle but not nearly with as much force as if you just turned the exhaust the opposite direction to the motion you are trying to counteract. ( Tank moving FWD. )
No, you’re making a fundamental mistake. It is not the case that some force is used to propel the plane forwards, and some force is used to propel the air backwards (“wasted”). Your idea that the “explosion” is like throwing a ball at 100 mph forwards and another ball at 100 mph backwards, and that the plane only uses some part of the energy of the ball thrown at 100 mph forwards and none of the energy of the ball thrown at 100 mph backwards is wrong. What actually happens is the engine “throws” a ball at 100 mph backwards, and the force required to launch the ball at 100 mph backwards propels the plane forward. The plane is propelled forwards slower than 100 mph at first, but this is just because it is much heavier than the ball - no energy is wasted. As the engine keeps “throwing balls backward”, the plane speeds up.
The plane is propelled forwards because of the air propelled backwards. This is Newton’s 3rd Law of Motion - for every action, there is an equal and opposite reaction. The air being propelled backwards is what exerts the force that moves the plane forward. The air being propelled backwards is not the result of “wasted” force - the very action of propelling the air backwards is what propels the plane forwards.