Missile energy (split)

Moderator note: split from http://forums.eagle.ru/showthread.php?t=92564

/E

I'm really trying to walk away but I'm a geek and a nerd in a Forums... it's like bringing an alcoholic to the bar :D

More and more often I forget people don't hear my inner monolog and I forget to explain my point

Uhuh :D

Using my original thought that missiles do reach the maximum speed on their own power ( which I still believe is true for most missiles) I meant it if the missile goes faster because the launch vehicle, instead of the missile flying its max mach, the missile would be flying at 2 or 3 mach above that, fins glowing red and nose cone just coming apart, then it entering lower , more denser air, airframe soft like the skin of the SR-71 and the missile just breaking or blowing apart. So that is what I meant when I ask if the missiles would be able to pull g or break.

Not really. The average AAM transits through high speed faster than most people realize. It isn't going to be melting down or having severe thermal issues - nowhere in the literature does such a consideration appear. ANd I think the fact that heat seekers will track right though their Mach 3 peak speaks for itself when it comes to thermal problems (the noise of the IRdome would be too much if what you said was true), and missiles with the more aerodynamic radomes will have even less trouble.

So to sum ti all; you all are saying that the missile range is increased and it has more energy at impact on a non maneuvering target at a specific altitude because it goes faster if the launching aircraft is going faster. So and Aircraft going at mach 2 will add that much energy to the missiles top speed. That is what I get you guys are saying.

Correct. Not only are we saying it, it's supported by a lot of literature, not to mention 'just physics' and mentions from RL pilots :D

I say range and energy at the target are increase not because maximum speed changes, I think is because the missile was at that maximum speed for longer. Traveling at maximum mach speed for longer, reaching the target at faster speed and traveling longer distance.

It reaches a higher peak speed, which does mean that it travels a higher speed longer. What you are calling 'max speed' is something that the missile will never reach - it just doesn't have enough fuel in that little rocket.

So, instead of the missile being at max mach for 1 second ( like when launch from an aircraft below mach) to the missile being at maximum mach speed fro 5 second when launch from a supersonic aircraft. So to me, the way I see it, the kinetic energy was the same, but the missile was able to use it before drag reduce the speed.

Which is incorrect. The missile will be accelerating when its fuel runs out. The faster it's going, the less it accelerates (because drag force increases as speed increases), but it will still accelerate beyond the speed it would reach if you launch it at M0.9. Take a 120, which can hit maybe 3.3M at altitude from a 0.9M launch. Launch it at 2.0M and it will hit 4.5M.

As for statements like 'the kinetic energy was the same', I throw the book of physics at you :P

Cool, I love to learn stuff, so physics.

So what is that, Jules right? Ok so how many Jules at launch speed? I guess I need to learn how to get Jules in the first place. Please teach sir

Joules are nothing but a unit. You can express energy in whatever units you want (that make sense), such as lbf, which is how we commonly express thrust in north america.

One way to express kinetic energy is E = 0.5mv^2. But this is a snapshot. If you want to examine how a missile works, you need to do more work than this.

To keep things very naive and simple though, that is also the kinetic energy of the missile at *launch*. If you launch from a hover/the ground/whatever, then v^2=0, so the whole thing is zero to begin with.

If you launch at Mach 2, or about say 700m/s, then v^2 is pretty large, and the missile's kinetic energy is pretty large before it even begins accelerating.

In both cases, the potential energy stored in the rocket is added to the kinetic energy at launch, subject to drag and all this other fun stuff that makes things non-linear.

Cool, I love to learn stuff, so physics.

So what is that, Jules right? Ok so how many Jules at launch speed? I guess I need to learn how to get Jules in the first place. Please teach sir

Love nerd talk, just wish I could remember things.

Love nerd talk, just wish I could remember things.

:megalol:

You can express energy in whatever units you want (that make sense), such as lbf, which is how we commonly express thrust in north america.

Ouch. :)

Ouch. :)

What he said. :D

Uh oh, engineering instincts kicking in!

Joules are nothing but a unit.

I represent the inuendo of your amplifications sir! Jules is a real good sort! Put up yer dukes! :D

GG is right, the max energy missile can reach is sum of its KE at launch, which depends on aircraft speed at launch, potential energy which depends on aircraft hight at lanuch, and missile rocket fuel (which is constant), and reduction of energy due the drag/air friction.

Energy reduction due to drag theoretically can get higher then energy gained from missile fuel burning meaning there is some max speed launch aircaft can have that when missile is launched it will not accelerate at all, however missile do have this speed limit higher than aircraft :) so this can't happen, not for now at least, who knows what can happen in future.

What will happen in the future is missiles that never miss.

Joules are nothing but a unit. You can express energy in whatever units you want (that make sense), such as lbf, which is how we commonly express thrust in north america.

 

One way to express kinetic energy is E = 0.5mv^2. But this is a snapshot. If you want to examine how a missile works, you need to do more work than this.

 

To keep things very naive and simple though, that is also the kinetic energy of the missile at *launch*. If you launch from a hover/the ground/whatever, then v^2=0, so the whole thing is zero to begin with.

If you launch at Mach 2, or about say 700m/s, then v^2 is pretty large, and the missile's kinetic energy is pretty large before it even begins accelerating.

 

In both cases, the potential energy stored in the rocket is added to the kinetic energy at launch, subject to drag and all this other fun stuff that makes things non-linear.

Cool thanks

E = 0.5mv^2 so m= mass correct. Do we use the mass of the aircraft? The missile being pushed by the aircraft and it is attached to it.

E=0.5 (18143.7)(680.5556)^2

D'oh

I get the mass of an object

If you want to know the kinetic energy of the missile, you need to use the mass and velocity of the missile.

Energy reduction due to drag theoretically can get higher then energy gained from missile fuel burning meaning there is some max speed launch aircaft can have that when missile is launched it will not accelerate at all, however missile do have this speed limit higher than aircraft :) so this can't happen, not for now at least, who knows what can happen in future.

In the future?? I can build you a missile like that right now.. but no one will buy it - who wants a missile that flies slower than a plane anyway..

If you want to know the kinetic energy of the missile, you need to use the mass and velocity of the missile.

So how do you get the mass of the vehicle? It is not just the weight IIUC

If missile x weights 136 kilos, what is its mass?

136 kilos.

(SI unit of mass = gramme :P )

EDIT:

http://en.wikipedia.org/wiki/Gramme

The gram (alternative British English spelling: gramme;[1] SI unit symbol: g) (Greek/Latin root grámma) is a metric system unit of mass.

EDIT 2:

To clarify; weight is when gravity acts on an object, and is the force applied. This is why you, in a 9g turn, is said to weigh nine times as much; the turn causes a gravity-equivalent force of 9g. Your mass is however unchanged. So if you normally weigh 100 kilos, your mass and weight will be 100 kilos. Transport yourself to the moon, and your mass will be 100 kilos still, but your weight is 16.5 kilos.

See how sweet and awesome the metric system is? :)

The missile being pushed by the aircraft and it is attached to it.

This here is important as well: forget the aircraft. The job of the aircraft is to get the missile to a high launch speed, that is all the aircraft itself does. Through being attached to the aircraft it has been given it's speed, so the kinetic energy of the missile at launch (pre-burn) is simply missile mass * v² * ½ .

See how sweet and awesome the metric system is? :)

Keep your "Royal with cheese" I like my quarter pounder :P

Keep your "Royal with cheese" I like my quarter pounder :P

No such thing as a Royal with cheese. Too much Hollywood for you! :P

No such thing as a Royal with cheese. Too much Hollywood for you! :P

LOL; "No, No, is not true, that's impossible" (only real geeks will get that)

So, initially it has 92623.5616 Jules?

D'oh,

I'm completely ruining this thread, sorry.

Where is GG, he is suppose to be trowing books at me about this stuff

He's busy, I'm his sidekick. :P

If you want, I can split the thread up and we can discuss this (very interesting) subject in a new place. :)

I think that would be appropriate, enough people hate me already.

Done. :)

thanks, what next? Is that the correct Jules of a 136 kg missiles flying at mach 2?