correct as-is AIM-120 Range?

[SharpeXB]

Seems amazing to me that at 30,000' doing Mach 1.6 an AIM-120C has a range of only about 10 miles against a cold target, does that seem right? It's a WVR weapon at this point. 

[Hulkbust44]

Cold? absolutely, here your target is at mach 1.1
Granted the LARs in DCS are too conservative last I checked.

[SharpeXB]

1 hour ago, Hulkbust44 said:

Cold? absolutely, here your target is at mach 1.1
Granted the LARs in DCS are too conservative last I checked.

But I’m traveling faster than the target by 340kts. I get it that this means a shorter range but… seems amazing. Does the missile get a vote here or do you have to pull along side the bandit and throw it at em? It’s as if the aircraft speed is more important than the missile speed. 
This did end up as a dual kill ;-D

Edited February 7, 2023 by SharpeXB

[GGTharos]

39 minutes ago, SharpeXB said:

But I’m traveling faster than the target by 340kts. I get it that this means a shorter range but… seems amazing. Does the missile get a vote here or do you have to pull along side the bandit and throw it at em? It’s as if the aircraft speed is more important than the missile speed. 
This did end up as a dual kill ;-D

 

Ok, do the math.  He's 14nm ahead of you, doing about 11nm/min.   You're doing 16m/min and that missile is going to do an average of 20nm/min (this is distance dependent - there's a peak, then the further you go, the smaller it gets).   So what do you think, can your 120 cover the necessary 25nm over that one minute?

It helps to think of missile flight time instead of range, you can compute the range quickly if you know the flight time and the average speed for that time.

[Tholozor]

Exactly. The missile doesn't have to cover the range at which you fire it: it has to cover the range needed to intercept.

[SharpeXB]

16 minutes ago, GGTharos said:

Ok, do the math.  He's 14nm ahead of you, doing about 11nm/min.   You're doing 16m/min and that missile is going to do an average of 20nm/min (this is distance dependent - there's a peak, then the further you go, the smaller it gets).   So what do you think, can your 120 cover the necessary 25nm over that one minute?

It helps to think of missile flight time instead of range, you can compute the range quickly if you know the flight time and the average speed for that time.

Oh I get it. Just seems funny to see this depicted so clearly in front of me. 

[Ghosty141]

Just as an additional datapoint, I saw this video (don't worry I timestamped it):

No idea if the data can be trusted since it's not blurred which is odd since they are usually quite secretive when it comes to ranges etc.

Lets assume the F22 flies at the same altitude (40k ft) as the target with comparable speed (since Vc = 1460kts, 1460kts/2=730knts should be fine since it's head on). I replicated this scenario in DCS and it matches quite well. I'm a bit slower (only have the hornet :/) but Vc is close and altitude is basically the same. Looking at the radar, the range of the AMRAAM matches the one in video.

Looks like ED comes quite close!

[MARLAN_]

Just a feeling, but it seems like atmospheric drag affects missiles too much in DCS, high altitude ranges seem fine to me though.

[GGTharos]

Maybe you could back up the feeling with some drag force calculations

[Hobel]

vor 5 Stunden schrieb GGTharos:

Maybe you could back up the feeling with some drag force calculations

I must say I have the same feeling.
High seems good Low a bit too much?

As I said, I only have a feeling, but of course I don't have any proof.

an idea.

if you drop an MK-84 from 40,000ft at 1.0M.

does the bomb accelerate to impact?
or approximately how fast should it hit?

 

in DCS it looks like this

DCS MK84.acmi

[Pavlin_33]

4 hours ago, Hobel said:

I must say I have the same feeling.
High seems good Low a bit too much?

As I said, I only have a feeling, but of course I don't have any proof.

an idea.

if you drop an MK-84 from 40,000ft at 1.0M.

does the bomb accelerate to impact?
or approximately how fast should it hit?

 

in DCS it looks like this

DCS MK84.acmi 91.34 kB · 2 downloads

Feelings are not reliable. That's why we invented science.

The bomb will decelerate to its terminal velocity. At this speed it will impact the target. If there was no air, the bomb would continue to increase its speed until impact.

P.S. Termnial veolcity is the speed at which the force of air resistance (drag) will be the same as the force of gravity. It depends of the object's shape. That's why a feather falls slower than a hammer.

P.P.S. What happens in the track? I am away from DCS.

Edited February 18, 2023 by Pavlin_33

[Default774]

6 minutes ago, Pavlin_33 said:

P.P.S. What happens in the track? I am away from DCS.

Bomb accelerates from mach 1 at release to almost mach 1.3 at impact

[Pavlin_33]

5 minutes ago, Default774 said:

Bomb accelerates from mach 1 at release to almost mach 1.3 at impact

That's very weird. It implies that the bomb's terminal velocity is above Mach 1.0, which I find hard to believe. Quick search yields that a t.v. of a bullet is around 200mph/320kph. I can't imagine that a MK84 would have much higher than that.

[Hobel]

Am 18.2.2023 um 14:01 schrieb Pavlin_33:

Feelings are not reliable. That's why we invented science.

I have not claimed anything else. 

Am 18.2.2023 um 14:21 schrieb Pavlin_33:

That's very weird. It implies that the bomb's terminal velocity is above Mach 1.0, which I find hard to believe.

And the same goes for you - do you have proof of this?  I think the speed is more than reasonable, the bomb has very little air resistance and is enormously heavy.

[Dragon1-1]

A bomb's terminal velocity is indeed supersonic. This is not uncommon, particularly with objects that are very dense. If you go fast enough, you can do pretty amazing things with dumb bombs.

[Pavlin_33]

1 hour ago, Hobel said:

I have not claimed anything else. 

And the same goes for you - do you have proof of this?  I think the speed is more than reasonable, the bomb has very little air resistance and is enormously heavy.

 

1 hour ago, Dragon1-1 said:

A bomb's terminal velocity is indeed supersonic. This is not uncommon, particularly with objects that are very dense. If you go fast enough, you can do pretty amazing things with dumb bombs.

Just to make it clear: weight has nothing to do with terminal velocity. I know it's counter-intuitive, that's why I mentioned the hammer and feather example.

I don't really have proof strictly speaking, but you can't expect a similarly-shaped object (bullet-bomb) to have air resistance order of magnitude less.

Having said that, I am yet to verify how much would a bomb-shaped object accelerate/decelerate.

 

[Mad_Shell]

12 minutes ago, Pavlin_33 said:

Just to make it clear: weight has nothing to do with terminal velocity. I know it's counter-intuitive, that's why I mentioned the hammer and feather example.

Weight is definitely in the equation for terminal velocity of an object. As said above in the thread, terminal velocity is achieved when air resistance is equal to the force of gravity applied to the object (this force is also called... weight). And the weight is propotrionnal to the mass of the object (9.81 * mass, to be exact).

That explains why 2 objects having the exact same shape, but different masses, will have different terminal velocities.

To come back to the bombs, they generally have a high density and a better aerodynamic shape than bullets, being more elongated, so it really wouldn't surprise me if their terminal velocity is supersonic. 

[Dragon1-1]

14 minutes ago, Pavlin_33 said:

Just to make it clear: weight has nothing to do with terminal velocity.

Come again? The hammer and feather example pretty much shows that weight does have everything to do with terminal velocity. Literally, here's the equation from Wikipedia:

Weigh is m*g, it's right there. Also note the air density, rho. At high altitudes, terminal velocity of anything in general is stupidly high, because the air isn't very dense. Clearing Mach 1 isn't so hard up there, and the bomb will do most of its accelerating in thin air. By the time it gets down, it'll be going too fast to appreciably slow down. Also note the total area, A, which actually works against the bomb, but due to square-cube law the ratio of bomb's weight to its frontal area is much higher.

Terminal velocity is weird because if you account for drag, the primary school way of thinking about how things fall comes apart. Both mass and size do, in fact, play a role in how things fall in situations where drag can't be disregarded.

[Pavlin_33]

2 hours ago, Mad_Shell said:

Weight is definitely in the equation for terminal velocity of an object. As said above in the thread, terminal velocity is achieved when air resistance is equal to the force of gravity applied to the object (this force is also called... weight). And the weight is propotrionnal to the mass of the object (9.81 * mass, to be exact).

That explains why 2 objects having the exact same shape, but different masses, will have different terminal velocities.

To come back to the bombs, they generally have a high density and a better aerodynamic shape than bullets, being more elongated, so it really wouldn't surprise me if their terminal velocity is supersonic. 

 

2 hours ago, Dragon1-1 said:

Come again? The hammer and feather example pretty much shows that weight does have everything to do with terminal velocity. Literally, here's the equation from Wikipedia:

Weigh is m*g, it's right there. Also note the air density, rho. At high altitudes, terminal velocity of anything in general is stupidly high, because the air isn't very dense. Clearing Mach 1 isn't so hard up there, and the bomb will do most of its accelerating in thin air. By the time it gets down, it'll be going too fast to appreciably slow down. Also note the total area, A, which actually works against the bomb, but due to square-cube law the ratio of bomb's weight to its frontal area is much higher.

Terminal velocity is weird because if you account for drag, the primary school way of thinking about how things fall comes apart. Both mass and size do, in fact, play a role in how things fall in situations where drag can't be disregarded.

I stand corrected. Mass is a factor determining terminal velocity: increase in mass, increases V _c

Thank you for pointing this out.

I could not find a valid reference for it's terminal velocity nor for its drag coefficient.
There is this paper here about Mk-82, but I think that C_d that coefficient seems too low, for some reason.

Edited February 19, 2023 by Pavlin_33

[Dragon1-1]

Modern bombs are really not that draggy. They weigh a lot, and that cause the whole ship to require more AoA and become more draggy, but once released, their shape is close to optimal for the speeds they fly at. A bullet is less aerodynamic because it generally can't have a boattail this long because of muzzle ballistics, notice how long the bomb's tail is. A short tail would be a significant contributor to drag due to turbulent flow behind it, the shape of the Mk82 is specifically designed to minimize that effect.

Also to keep in mind, this is a subsonic Cd. Supersonic will be higher due to nose shape, although probably not by that much.

[GGTharos]

Terminal velocity for a given bomb is easy to approximate if you want to look up the appropriate coefficients etc.   Back-of-the envelope kind of calculation ... no I'm not doing it