Missile Velocity

[S77th-GOYA]

I recently read a debate on whether or not a real life missile's speed can simply be added to the launching aircraft's speed to give the actual top speed of the missile. An example of a theoretical launch of an AMRAAM from an SR-71 at Mach 3.3 and an altitude of angels 80 was given.

 

One side argued that yes, you simply add the velocities and the 120 has a speed of ~Mach 7 at engine termination.

 

THe other side said that no, the 120 would reach a terminal velocity where thrust equals drag at Mach 4, saying that is a design limit.

 

To me, without knowing the thrust of the missile's engine and the drag coefficient, one cannot confidently choose either side of the argument. Obviously the thrust is quite large compared to the mass but at speeds around Mach 7, even a missile with very small drag coefficient would be experiencing strong drag forces. But without better data, I can't say.

 

Anyone have any thoughts on the matter?

[nellen_mellen]

Being as I'm taking an advanced physics course at uni. right now, I might be able to lend an answer.

 

If we were to release the missile from the rail, into the moving air around the aircraft, without its engine igniting, what would eventually happen (think of bomb releases).

 

The missile would slow down because its no longer being carried (since its not connected to the aircraft which is producing thrust to sustain its airspeed) and its not producing any force to overcome the forces of drag induced by the air coming towards it. This deceleration will continue until it reaches its terminal velocity, or hits the ground (terminal velocity will occur when the missile will also be falling straight down).

 

The reasoning that says that the missile will attain its designed velocity (mach 4) plus its launch velocity (mach 3.3) does not take into account the drag that already has to be overcome at the time of launch by the missile.

 

When the missile is launched, it will accelerate only if the thrust of its engine can overcome the drag induced by the speed of the oncoming air.

 

I know it sounds crazy, but it applies to anything that is being removed from the aircraft or launched from it.

 

So, take a bullet from an on-board cannon, for example. If the aircraft is traveling with an oncoming wind speed greater than the maximum velocity of the fired bullets, the bullet will slow down once they enter the airstream.

 

Now, its true that the bullets will be able to leave the barrel of the gun, since there is some boundary layer flow around the surfaces of an aircraft, in which the air is moving slower.

 

Once any projectile/object enters the full force of the surrounding airflow, and it doesn't have any provisional force (thrust) acting on it to over come the force of the airflow, it will decelerate.

 

Now, I should mention that there is an interesting fact about aircraft that fly at high altitude and "high mach speed" that will probably negate this observation about bullets/missiles slowing down.

 

When people say that an aircraft like the SR-71 or the Mig-25 or the XB-70 is flying at mach 2.5-mach 3.3 at high altitude, you have to be a bit cautious about what that speed really means.

 

These speeds are the speed relative to the ground, not the speed relative to the airflow around the aircraft. And since we know that at high altitude, the air is much, much thinner, the airflow around these aircraft at high altitude and "high mach relative to ground" is not as fast as the ground speed.

 

This is why in some sims, when you try to fly at say, 60k feet, and your airspeed indicator is measuring in ground speed, you could be flying at something like "400mph" and be stalling.

[D-Scythe]

I recently read a debate on whether or not a real life missile's speed can simply be added to the launching aircraft's speed to give the actual top speed of the missile. An example of a theoretical launch of an AMRAAM from an SR-71 at Mach 3.3 and an altitude of angels 80 was given.

 

One side argued that yes, you simply add the velocities and the 120 has a speed of ~Mach 7 at engine termination.

 

THe other side said that no, the 120 would reach a terminal velocity where thrust equals drag at Mach 4, saying that is a design limit.

 

To me, without knowing the thrust of the missile's engine and the drag coefficient, one cannot confidently choose either side of the argument. Obviously the thrust is quite large compared to the mass but at speeds around Mach 7, even a missile with very small drag coefficient would be experiencing strong drag forces. But without better data, I can't say.

 

Anyone have any thoughts on the matter?

 

Drag also varies with altitude - with less air to put up resistance, it is very possible for the AIM-120 to reach higher speeds. It really becomes a question of altitude. At the SR-71's cruise altitude (~80-90 000ft), I'd imagine the AMRAAM would easily exceed it's design limit of Mach 4. An AIM-120 could theoretically reach Mach 10+ if launched from the space shuttle in orbit.

[3Sqn_Sven]

And of course, If you carried AMRAAMs on an X-wing and released it during Hyperspace, the missile would travel at Lach 4.5 (Like Mach, but light speed)....

[cool_t]

I recently read a debate on whether or not a real life missile's speed can simply be added to the launching aircraft's speed to give the actual top speed of the missile. An example of a theoretical launch of an AMRAAM from an SR-71 at Mach 3.3 and an altitude of angels 80 was given.

 

One side argued that yes, you simply add the velocities and the 120 has a speed of ~Mach 7 at engine termination.

 

THe other side said that no, the 120 would reach a terminal velocity where thrust equals drag at Mach 4, saying that is a design limit.

 

To me, without knowing the thrust of the missile's engine and the drag coefficient, one cannot confidently choose either side of the argument. Obviously the thrust is quite large compared to the mass but at speeds around Mach 7, even a missile with very small drag coefficient would be experiencing strong drag forces. But without better data, I can't say.

 

Anyone have any thoughts on the matter?

 

 

Ok,

 

(ALT)(Launch Platform + Speed + Missile/Speed) = Xspeed

 

 

Here is the link again. Its like saying "If a space craft is traveling at the speed of light and you throw a rock from the space craft, the rock is going faster than the speed of light."

 

HERE IS A GOOD SOURCE LINK!!!!!!!!

 

http://www.nasa.gov/centers/dryden/news/FactSheets/FS-093-DFRC.html

 

 

:book:

[britgliderpilot]

Being as I'm taking an advanced physics course at uni. right now, I might be able to lend an answer.

 

And it's all pretty good, but about this bit . . . .

 

When people say that an aircraft like the SR-71 or the Mig-25 or the XB-70 is flying at mach 2.5-mach 3.3 at high altitude, you have to be a bit cautious about what that speed really means.

 

These speeds are the speed relative to the ground, not the speed relative to the airflow around the aircraft. And since we know that at high altitude, the air is much, much thinner, the airflow around these aircraft at high altitude and "high mach relative to ground" is not as fast as the ground speed.

 

This is why in some sims, when you try to fly at say, 60k feet, and your airspeed indicator is measuring in ground speed, you could be flying at something like "400mph" and be stalling.

 

I know what you mean, but I think you've got it down wrong ;)

 

You can't give a Mach number relative to the ground. Mach number is always specific to the fluid through which the object is travelling, which is subject to variations like pressure and density.

 

So Mach 1 at high altitude will be at a lower true airspeed than Mach 1 at ground level.

 

However, lift is a function of air density in the other direction - so you'll need a higher true airspeed to produce the same amount of lift at high altitude.

 

Example - the U2 flying at 70,000 feet could turn so that the inner wingtip would be travelling below stall speed, and the outer wingtip would be producing Mach waves.

 

Freaky, no?

[britgliderpilot]

I recently read a debate on whether or not a real life missile's speed can simply be added to the launching aircraft's speed to give the actual top speed of the missile. An example of a theoretical launch of an AMRAAM from an SR-71 at Mach 3.3 and an altitude of angels 80 was given.

 

One side argued that yes, you simply add the velocities and the 120 has a speed of ~Mach 7 at engine termination.

 

THe other side said that no, the 120 would reach a terminal velocity where thrust equals drag at Mach 4, saying that is a design limit.

 

To me, without knowing the thrust of the missile's engine and the drag coefficient, one cannot confidently choose either side of the argument. Obviously the thrust is quite large compared to the mass but at speeds around Mach 7, even a missile with very small drag coefficient would be experiencing strong drag forces. But without better data, I can't say.

 

Anyone have any thoughts on the matter?

 

I'm with Goya.

 

It depends what is limiting the missile's top speed - whether it's aerodynamics or motor burn time.

 

If aerodynamics are limiting the missile top speed, the missile will accelerate away from the aircraft and when thrust from the motor = drag, stop accelerating. It'll then cruise along at that speed until the motor burns out, at which point it will complete the flight on it's stored kinetic energy.

 

If motor burn time is limiting the missile's top speed (i.e. there's so much thrust that drag won't build up to similar levels until silly speeds), then the missile will just keep on accelerating for as long as the motor burns.

 

 

If Case 1 - Aerodynamically limited top speed - is true, then the missile will only ever accelerate to it's nominal top speed, call it Mach 4.

 

If Case 2 - Motor Burn Time limited top speed - is true, then the missile could end up at Mach 7 from an aircraft launching at Mach 3.

 

 

. . . . but without thrust information and drag coefficients (which vary going from supersonic to hypersonic, IIRC), you simply can't tell.

 

I personally would lean towards Case 2 . . . . but I have precisely zero information to support that!

 

 

edit - Had better add that the aerodynamic limit is always present . . . launching from an aircraft at Mach 3, you might find where it is.

[GGTharos]

No, LAW 2 is a nice starting point for the nuances of aerodynamics. Or rather, while the law holds true, it's rather misleadingly skimpy.

 

In any case, yes, launch velocity affects missile velocity and thus range, and we have minizap which can simulate this. No, it isn't getting fixed any time soon.

 

In any case, drag builds up with speed, so the faster you're going when you launch the missile, the more you go into a land of diminishing returns (at silly speeds that is) within the atmosphere. In addition, high speeds are associated with heating issues, and the airflow might be such that the missile becomes uncontrollable. So the 'design limit' being mach 4 is a reasonable argument, for two reasons:

 

Not many aircraft will launch the missile with a start velocity much higher than mach 1.5 at high altitude, and, the materials the missile is made of have certain thermal limits, both externally and internally (for example, radar efficiency decreases as temperature increases).

[Guest PKM]

If Case 1 - Aerodynamically limited top speed - is true, then the missile will only ever accelerate to it's nominal top speed, call it Mach 4.

 

If Case 2 - Motor Burn Time limited top speed - is true, then the missile could end up at Mach 7 from an aircraft launching at Mach 3.

 

Both these answers are wrong.

 

Newton's Laws of Motion.

 

1, Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

 

2, The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector.

 

3, For every action there is an equal and opposite reaction.

 

laws 1&2 will answer your question. Law 2 gives you the mathmatical solution to answer your question.

[Camoman]

And of course, If you carried AMRAAMs on an X-wing and released it during Hyperspace, the missile would travel at Lach 4.5 (Like Mach, but light speed)....

 

:megalol:

After a nite of selling piss to retards in the bottleshop at least sum1 still made me laugh. Cheers bud.

[Guest PKM]

No, LAW 2 is a nice starting point for the nuances of aerodynamics. Or rather, while the law holds true, it's rather misleadingly skimpy.

 

Law2 is the MOST important law of motion and it's not misleadingly skimpy. Everything that flies is designed around that law.

 

In any case, yes, launch velocity affects missile velocity and thus range, and we have minizap which can simulate this. No, it isn't getting fixed any time soon.

 

In any case, drag builds up with speed, so the faster you're going when you launch the missile, the more you go into a land of diminishing returns (at silly speeds that is) within the atmosphere. In addition, high speeds are associated with heating issues, and the airflow might be such that the missile becomes uncontrollable. So the 'design limit' being mach 4 is a reasonable argument, for two reasons:

 

Friction/heat is also a factor of height, The thicker the atmosphere the more friction which equals more heat.

 

Not many aircraft will launch the missile with a start velocity much higher than mach 1.5 at high altitude, and, the materials the missile is made of have certain thermal limits, both externally and internally (for example, radar efficiency decreases as temperature increases).

 

See above. On the note of limits, many systems and weapons supersede there actual given limits, it allows for human error and reliability.

[Guest PKM]

One side argued that yes, you simply add the velocities and the 120 has a speed of ~Mach 7 at engine termination.

 

This would be the exact case if the missile was launched in a vacuum like space.

 

THe other side said that no, the 120 would reach a terminal velocity where thrust equals drag at Mach 4, saying that is a design limit.

 

This should say "the 120 would reach a terminal velocity where thrust equals drag".

 

The drag that would be induced in the mesosphere would be substantially less than the troposphere, less drag equals a higher speed terminal velocity.

[S77th-GOYA]

The drag that would be induced in the mesosphere would be substantially less than the troposphere, less drag equals a higher speed terminal velocity.

 

That is accurate. However air density is not as important a factor in determining drag as velocity.

 

 

Notice that velocity is squared in the drag equation.

 

The only thing I can see that might give any real insight to an answer is that if pilots are trained to increase speed before a launch to increase range.

 

GG, I assume minizap takes drag into account. How were the drag coefficients for different missiles determined?

[3Sqn_Sven]

:megalol:

After a nite of selling piss to retards in the bottleshop at least sum1 still made me laugh. Cheers bud.

 

Ah yes, my old job. Well no worries man, glad I could help! Never been good at maths, pull trigger missile goes boom, but the thread needed a bit of humour. How goes the application? I'm moving to newie in a few weeks, starting early (was meant to be next year).

 

I'm done hijacking the thread btw Goya, but good question and a few interesting answers.

[Guest PKM]

That is accurate. However air density is not as important a factor in determining drag as velocity.

 

 

Notice that velocity is squared in the drag equation.

 

Air density is drag.

 

I understand what you trying to say but we must accept Newtons law that every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

 

To put this in layman terms the higher you go the less drag, less drag equals more sustained, economic and higher speed.

 

Say you launched a missile at angels 4 mach1 (TGS), and it accelerates to mach 4 burns out and stops at that speed. If you launched the same missile at angels 80 mach1 (TGS), do you think it would reach mach 4 and stop?.

[S77th-GOYA]

Drag is a force.

 

Air density is not a force.

 

And no, if a missile has the thrust to propel itself to M4 at 4000, it should be able to acheive a higher speed at 80,000. That's not really the question.

[Guest PKM]

Drag is a force.

 

Air density is not a force.

 

Air density is not a direct drag force but air density does create the biggest form of atmosphere drag through friction, Hence why we have aerodynamics and fluid dynamics. The real daddy of drag actually lies in the sea. Drag IS created from the density of Earths atmosphere via friction.

 

And no, if a missile has the thrust to propel itself to M4 at 4000, it should be able to acheive a higher speed at 80,000. That's not really the question.

 

The question:

 

I recently read a debate on whether or not a real life missile's speed can simply be added to the launching aircraft's speed to give the actual top speed of the missile. An example of a theoretical launch of an AMRAAM from an SR-71 at Mach 3.3 and an altitude of angels 80 was given.

 

OK we agree a missile will travel faster and further and more economical!, My answer is a blackbird travelling at mach 3.3 at angels 80 that launched a missile that travels at mach 4 would combine and give the missile a total speed of around mach5.5-6.0, but that's a guess

 

My answers are VERY relevant to this question, If I'm misunderstanding you please explain.

[britgliderpilot]

Both these answers are wrong.

 

Newton's Laws of Motion.

 

1, Every object in a state of uniform motion tends to remain in that state of motion unless an external force is applied to it.

 

2, The relationship between an object's mass m, its acceleration a, and the applied force F is F = ma. Acceleration and force are vectors in this law the direction of the force vector is the same as the direction of the acceleration vector.

 

3, For every action there is an equal and opposite reaction.

 

laws 1&2 will answer your question. Law 2 gives you the mathmatical solution to answer your question.

 

I don't see where either of my answers contradicted Newton's laws . . . . and after positing that both my statements are untrue you seem to have stated exactly the same thing a little later on.

 

Care to state your case a little more clearly? ;)

[Guest PKM]

I don't see where either of my answers contradicted Newton's laws . . . . and after positing that both my statements are untrue you seem to have stated exactly the same thing a little later on.

 

Care to state your case a little more clearly?;)

 

Sure can!, BTW I didnt say your answers contradicted newtons laws, I only said that I thought they was wrong.

 

If Case 1 - Aerodynamically limited top speed - is true, then the missile will only ever accelerate to it's nominal top speed, call it Mach 4.

 

This comment is stating that a missile will only travel at mach 4 across the range of atmospheres, It will not speed up or slow down whilst it is in full flight no matter how much or little atmosphere drag is applied, Kinda like throttling.

 

If Case 2 - Motor Burn Time limited top speed - is true, then the missile could end up at Mach 7 from an aircraft launching at Mach 3.

 

This could only be possible in a vacuum.

[eleazar]

ah... physics..... i did it quite bad for my A levels... sian....

 

ok.. back to the main topic.... let's don't talk about missile 1st.. think about a bullet/gun/cannon that is on the aircraft.. if the speed of the bullet hits 1km/min (just for an example), then what will be the speed of the bullet during a dogfight? (ok, bullet is small, so do not consider other facts, we just keep this simple). ok, the speed is still 1km/min, but the question is, to who? if during a dogfight, both aircrafts are at speed of 0.5km/min(just for an example), then for both aircraft, the bullet fly at a speed of 1km/min.. however, to a man who is standing on the ground, who do not move and watch this dog fight.. what will the bullet's speed be? 1.5km/min or 0.5km/min? (if happens that the aircrafts fly horizontally pass by him)

 

ok.. case 2.. droping bombs... the basic of caculation that i learn is simple.. horizontal wise, the speed on the bomb is given by the speed of the aircraft; vertical wise, the speed is the gravitational force that is acting on it.. ( basic caculation )

 

so.. from the 2 examples above, when a missile is lunched from an aircraft, it will have the speed of the aircraft as the initial speed...

 

just back to the bullet case, now we change the bullet.. if the black bird is flying at a speed of mach 3.3.. so now, we put a mp44, or any gun which will not give the bullet a flying speed greater than 3.3... so if the bullet DO NOT take the speed of the aircraft as initial speed, it means that when it is shooted out, it will just stay inside the gun and break the gun cos the bullet travels slower than the gun.... but if that is ture...

 

so, my stand is that the missile will take the speed of the aircraft as a initial speed..... but is that simple 4mach + 3.3mach???? if everything works fine and their is no 3rd force (like gravity,air, any funny problem due to production, bla bla bla)

 

 

and the last thing i want to say is that, in the book of "Art of Kill" it has this sayings... lunch your missil at your topspeed, after you lunch it.. reduce speed... so that it will cost more time for enemy's missil to fly to you and wasted it's energy(in a head on case).

[S77th-GOYA]

One thing to keep in mind is that when a figure like range or speed is given for a missile, it is usually the figure for optimal conditions. If a missile is called a Mach 4 missile, it doesn't necessarily mean it can acheive Mach 4 at 1000 feet. That is basic aerodynamics. Just like a 400 MPH WWII fighter can't acheive 400 MPH on the deck.

 

The basic question in this thread is not an either/or choice of the two opinions stated in the first post. Theoretically, a missile might reach equilibrium (drag=thrust) at a lower speed than Mach 7 but still be well above Mach 4.

[britgliderpilot]

This comment is stating that a missile will only travel at mach 4 across the range of atmospheres, It will not speed up or slow down whilst it is in full flight no matter how much or little atmosphere drag is applied, Kinda like throttling.

 

Given that the conditions considered were explicitly stated in the first post, I thought stating how it was affected by varying air density would be unnecessary.

 

Re-read my post - it tells you that a missile will accelerate to that speed, not that it'll suddenly fly at that speed and keep flying at that speed forever.

 

Did I forget to say it'd start decelerating when the motor stopped?

 

 

This could only be possible in a vacuum.

 

In fact - and this is a good one, you'll like this - it's impossible to accelerate to Mach 7 in a vacuum.

 

Taking the post as a whole, rather than skipping through it . . . I still see nothing wrong. Likelihood of a missile reaching Mach 7? Slim. But I lean towards the second case rather than the first.

[Guest PKM]

Given that the conditions considered were explicitly stated in the first post, I thought stating how it was affected by varying air density would be unnecessary.

 

Re-read my post - it tells you that a missile will accelerate to that speed, not that it'll suddenly fly at that speed and keep flying at that speed forever.

 

Did I forget to say it'd start decelerating when the motor stopped?

 

 

 

 

In fact - and this is a good one, you'll like this - it's impossible to accelerate to Mach 7 in a vacuum.

 

Taking the post as a whole, rather than skipping through it . . . I still see nothing wrong. Likelihood of a missile reaching Mach 7? Slim. But I lean towards the second case rather than the first.

 

1, Re read my post. I stated when the missile was in full flight, EG motors lit and at full propulsion not motor stopped and missile gliding under inertia.

 

2, Fluxtuations in atmosphere densitys are very important.

 

3, It's "impossible" to accelerate to mach 7 in a vacuum like space?. So if I lit a rocket in space it would not accelerate?, By the way it's a very common misconception to beleive that rockets dont work in space, Please explain.

 

4, Possibilities of a mach 4 rocket reaching mach 5.5-6.0 in the mesosphere is very high.

[S77th-GOYA]

3, It's "impossible" to accelerate to mach 7 in a vacuum like space?. So if I lit a rocket in space it would not accelerate?, By the way it's a very common misconception to beleive that rockets dont work in space, Please explain.

 

Mach is the speed of sound. What is the speed of sound in a vacuum?

[Mr.Cholmondley-Warner.OBE]

3, It's "impossible" to accelerate to mach 7 in a vacuum like space?. So if I lit a rocket in space it would not accelerate?, By the way it's a very common misconception to beleive that rockets dont work in space, Please explain.

 

How can you suggest that a rocket (or anything for that matter) can travel at ANY Mach number in space?

 

Since Mach is the measurement used for an objects velocity in ratio to the speed of Sound and sound can only travel through a medium such as air, water etc. Can you tell me how sound can travel through a vacuum? Quick Answer - it can't.

 

Speed can be measured in space (usually Km/h), acceleration (in G's) can be measured, but not Mach number.

 

 

 

oops, beaten to it. :megalol: