Kinetic energy calculation
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If its a US registered aircraft use American units like pounds, and feet not this pussy stuff like meters and knots
Anyway,
The F4 landing on the carrier is F=MA as the F4 is in fact Aing its F-ing M all the way down the . . deck, forcing the wire to a force greater than the original hook up force.
So there is a secondary accellerating force - whilst the Massive F4 is being ground to a halt by the poor old wire up to and until the Accel Force is dissipated. see that? All due, as you all know, to the fact that you have to apply full chat, in case the `lil ol wire gives or in case you have not hooked up - on touchdown
Sorry to sound so technical - do I get a degree now?
Last edited by Natstrackalpha; 7th Jun 2013 at 22:27.
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Power on arrest
Right, Natstrackalpha,
The wire not only has to absorb the kinetic energy, but also has to do work against the running engines.
The aircraft moves ~100m to stop (?), and has ~10 tons (?) of thrust, so the work done is ~10MJ: a modest, but not insignificant, correction.
You might not get a degree, but that's definitely worth some coursework credit.
The wire not only has to absorb the kinetic energy, but also has to do work against the running engines.
The aircraft moves ~100m to stop (?), and has ~10 tons (?) of thrust, so the work done is ~10MJ: a modest, but not insignificant, correction.
You might not get a degree, but that's definitely worth some coursework credit.
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Since Machinbird's reckoning exercize proposition (KE reckoning when the F-4 was catching the wire) which seemed easy (I used the easiest frame : the Ship), the question of absorbing the Bird's energy came on the table.
I discovered that we have to use a frame independant from the Ship to "stop" the Bird at the same speed that the Ship. But since you are using that frame , new factors (oscillation, first shock, thrust, geometry of wires, position of the Bird, Ship's speed modification, natural wind, crosswind, etc.) appeared of significant possible Megajoules.
I searched too if the frames were galilean, it seems they are.
Which additional terms would help to coherence of different frames and methods?
@ Machinbird and your Navy's apilots Friends
Which shocks did you experience with Ship doing its own wind ? Is it the same - or not - than natural wind? Reckoning and theories must correspond to experience.
I discovered that we have to use a frame independant from the Ship to "stop" the Bird at the same speed that the Ship. But since you are using that frame , new factors (oscillation, first shock, thrust, geometry of wires, position of the Bird, Ship's speed modification, natural wind, crosswind, etc.) appeared of significant possible Megajoules.
I searched too if the frames were galilean, it seems they are.
Which additional terms would help to coherence of different frames and methods?
@ Machinbird and your Navy's apilots Friends
Which shocks did you experience with Ship doing its own wind ? Is it the same - or not - than natural wind? Reckoning and theories must correspond to experience.
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The frames are Galilean: at 200kt, relativistic corrections are at the one-in-a-trillion level.
The only frames that matter are i) that of the deck/concrete on which you stop, and ii) that of the moving air in which you are flying. The ship should be steaming relative to the wind so that its angled deck has a direct headwind of at least 30kt.
You can pick any other frame you'd like too; but you don't need to know what the energies are in any of those.
The only frames that matter are i) that of the deck/concrete on which you stop, and ii) that of the moving air in which you are flying. The ship should be steaming relative to the wind so that its angled deck has a direct headwind of at least 30kt.
You can pick any other frame you'd like too; but you don't need to know what the energies are in any of those.
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F=MA
You might not get a degree, but that's definitely worth some coursework credit.
~10 tons (?) of thrust
Stored energy, how to control it - ans= fly the aircraft.
see? easy!
Last edited by Natstrackalpha; 15th Jun 2013 at 22:14.
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Do I still get some credit for a reasonable guess?
Looking it up, it seems that a Phantom has around 2x12,000lb dry thrust, which I make a total of about 11 tonnes. It also seems that the 100m distance to stop is within about 10%, perhaps a little generous, so 10MJ to run the wire out against the engines is I think within 10% of the total. If it's in afterburner, about 50% more.
That makes sense, given the time it would take to reach 150kts (~75m/s) from a standing start should be about 8s, and it stops in ~2s, so the kinetic energy is about four times the work done by the engines during the stop.
Looking it up, it seems that a Phantom has around 2x12,000lb dry thrust, which I make a total of about 11 tonnes. It also seems that the 100m distance to stop is within about 10%, perhaps a little generous, so 10MJ to run the wire out against the engines is I think within 10% of the total. If it's in afterburner, about 50% more.
That makes sense, given the time it would take to reach 150kts (~75m/s) from a standing start should be about 8s, and it stops in ~2s, so the kinetic energy is about four times the work done by the engines during the stop.
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Heavy landings question
I don't see the energy involved in landing a large aircraft being substantially different from landing a fast aircraft, other than having relatively less specific thrust, and this needing longer to add enough energy to climb away instead.
"Stabilized" to my mind means having steadily declining potential energy and constant kinetic energy: airspeed is steady in gust-free air; rate of descent is steady. The kinetic energy you carry to the ground is then the energy that goes into the air behind the spoilers and alongside the reverse-thrusting engines, and into the brakes. If this "stable" condition isn't met by 1000-2000 feet above the ground, leaving a minimum amount of things to do and avoiding excessive workload near the ground, then you go around and try again.
I'm not sure why your heavy aircraft leaves its steady progress to the ground? Is it a change in wind, or to the degree of a microburst? A change in thrust or drag, or setting up a dutch roll? If none of these things are a big change, and can be quickly countered by the controls and throttles, then the energy is about the same, you're still "stable" in terms of energy, and you should still be safe to land. If you choose to add energy and go around, you need add only a little - just enough per second to overcome the sink rate.
Even as the wheels touch, you're still flying. A fraction of 1% of the energy of the aircraft is sapped away to spin the wheels up, leading to a change by a half of that amount in groundspeed, but you're still almost flying, and still have the whole length of the runway to add power and go around. At that point, if you're happy to decide to brake instead, all the kinetic energy is safely dumped into the wheels and the airflow behind, and you can drive off safely.
"Stabilized" to my mind means having steadily declining potential energy and constant kinetic energy: airspeed is steady in gust-free air; rate of descent is steady. The kinetic energy you carry to the ground is then the energy that goes into the air behind the spoilers and alongside the reverse-thrusting engines, and into the brakes. If this "stable" condition isn't met by 1000-2000 feet above the ground, leaving a minimum amount of things to do and avoiding excessive workload near the ground, then you go around and try again.
I'm not sure why your heavy aircraft leaves its steady progress to the ground? Is it a change in wind, or to the degree of a microburst? A change in thrust or drag, or setting up a dutch roll? If none of these things are a big change, and can be quickly countered by the controls and throttles, then the energy is about the same, you're still "stable" in terms of energy, and you should still be safe to land. If you choose to add energy and go around, you need add only a little - just enough per second to overcome the sink rate.
Even as the wheels touch, you're still flying. A fraction of 1% of the energy of the aircraft is sapped away to spin the wheels up, leading to a change by a half of that amount in groundspeed, but you're still almost flying, and still have the whole length of the runway to add power and go around. At that point, if you're happy to decide to brake instead, all the kinetic energy is safely dumped into the wheels and the airflow behind, and you can drive off safely.
