Is Ukraine about to have a war?

[Winemaker]

Originally Posted by ORAC

Assuming it was a ballistic missile and slowed to zero vertical velocity at its apex and accelerated under gravity to M2.5 - then it would have peaked at just over 50,000ft and fallen for 60 seconds before impact.

Since it’s accelerating under gravity the distance from the launch point is irrelevant, it’s the height from which the descent commenced which determines the terminal velocity.

Actually this is not how it works. A ballistic trajectory is the path of an un-powered projectile that is affected by gravity. The only flight path where the projectile slows to zero vertical velocity is a vertical launch. Yes, the rocket will coast up to some height and then fall down vertically, but any path other than vertical will not do that.

The extreme other example is a projectile (rifle bullet for example) that is fired absolutely horizontally. During its flight the bullet will experience a downward force from gravity of 9.8 m/sec^2. If the bullet is shot from a mountain top, in one second it will fall 9.8 m. Its horizontal velocity will still be very high, reduced only by aerodynamic drag. In fact, if the bullet is fired and a weight is dropped from the same height at the same time of firing, after one second both objects (in a vacuum of course) will have dropped the same amount.

So a ballistic missile that is launched a some none vertical angle will have a component of velocity greater than zero even as it arcs over its highest altitude and down toward the target. The lower the angle of launch the greater the horizontal component of velocity. The velocity of a missile impacting a Soviet airbase will not be from the maximum altitude it reaches unless it's fired straight up (which I suspect is not the case).

Since I'm being pedantic, I'll also point out that a falling object in the atmosphere will reach some terminal velocity, determined by its drag characteristics; for a sky diver it's about 120 mph. I seriously doubt any dropped object in the atmosphere will go supersonic.

[nevillestyke]

Originally Posted by etudiant

What is not clear is what price in blood Ukraine is paying

What IS clear, is that the Ukranians are willing to pay it. Do we see Ukranians jumping off their sunbeds and legging it?
The nuclear threat is still there, as it always was; no change.

[GlobalNav]

Originally Posted by nevillestyke

What IS clear, is that the Ukranians are willing to pay it. Do we see Ukranians jumping off their sunbeds and legging it?
The nuclear threat is still there, as it always was; no change.

Also what’s is clear is that every element of assistance that can be provided to the Undaunted Ukrainians should be. These are freedom loving people who stand for what Americans have claimed to stand for over two centuries. Words are one thing, but actions are the true substance, and we need to do whatever it takes to honor the sacrifices of the Ukrainians and speak/act against the Satan that Russia has become (credit to Pres Reagan).

[soarbum]

Originally Posted by Winemaker

Actually this is not how it works. A ballistic trajectory is the path of an un-powered projectile that is affected by gravity. The only flight path where the projectile slows to zero vertical velocity is a vertical launch. .

Velocity is a vector with components in x,y and z. ORAC clearly referred to zero vertical velocity, ie the z component. If it went up and came back down, then at some point, the vertical component was zero regardless of the shape of the trajectory.

Originally Posted by Winemaker

Since I'm being pedantic, I'll also point out that a falling object in the atmosphere will reach some terminal velocity, determined by its drag characteristics; for a sky diver it's about 120 mph. I seriously doubt any dropped object in the atmosphere will go supersonic.

I don't see why not if the object has a small enough cross section, a large enough mass and some fins to keep the pointy end at the front. Also bear in mind that the air density is much lower during the upper part of the trajectory.

ps: since you mentioned sky divers, low level divers reach 120mph while spread but Felix Baumgartner reached 843.6 mph (Mach 1.25) on his dive

[rattman]

Originally Posted by Winemaker

Since I'm being pedantic, I'll also point out that a falling object in the atmosphere will reach some terminal velocity, determined by its drag characteristics; for a sky diver it's about 120 mph. I seriously doubt any dropped object in the atmosphere will go supersonic.

ATACMS is believed to reach mach 3 during its terminal phase

[NutLoose]

Taking out a Russian counter drone system…….. from a drone

Twitter

[NutLoose]

Originally Posted by Winemaker

Since I'm being pedantic, I'll also point out that a falling object in the atmosphere will reach some terminal velocity, determined by its drag characteristics; for a sky diver it's about 120 mph. I seriously doubt any dropped object in the atmosphere will go supersonic.

That is totally height dependent, the higher you go, the thinner the atmosphere, the faster you drop.

In 2012, the record for the highest skydive in history was broken by Felix Baumgartner in what’s been considered as the greatest marketing stunt in history! People from around the globe stopped everything to watch a YouTube live stream of Baumgartner stepping out of his Red Bull capsule from the stunning altitude of 127,852 feet! Baumgartner’s jump would set records for the highest skydive in history, fastest freefall speed (843.6 mph or Mach 1.25), and become the first man to break the sound barrier without vehicular power. Additionally, Baumgartner broke the records for vertical freefall distance with a drogue parachute, and vertical speed without a drogue.

https://www.skydivetecumseh.com/2020...ve-in-history/

[fdr]

Existential threats

Russia's contempt to the safety of the Zaphorisia NPP is a existential threat to Europe, Central Asia and southern Russia, as well as China and North Asia.

At what point do the adults get off their backsides and place a protective force around the NPP to stop Russia causing mayhem to themselves and all others.

[Winemaker]

Originally Posted by rattman

ATACMS is believed to reach mach 3 during its terminal phase

I agree. That velocity is not achieved from simple acceleration due to gravity. A large component of that is its initial velocity, which is what I was attempting to explain.

[Winemaker]

Originally Posted by soarbum

Velocity is a vector with components in x,y and z. ORAC clearly referred to zero vertical velocity, ie the z component. If it went up and came back down, then at some point, the vertical component was zero regardless of the shape of the trajectory.



I don't see why not if the object has a small enough cross section, a large enough mass and some fins to keep the pointy end at the front. Also bear in mind that the air density is much lower during the upper part of the trajectory.

ps: since you mentioned sky divers, low level divers reach 120mph while spread but Felix Baumgartner reached 843.6 mph (Mach 1.25) on his dive

Yes, he did. With decreasing altitude there is increasing air density, hence more drag. He slowed down at lower altitude. The comment I was responding to implied that every projectile on a ballistic path achieves some zero vertical speed then plummets to the ground with a final velocity depending on its maximum altitude. This is true for a vertical shot, but with any horizontal component there is a vector that does not go to zero at maximum altitude and carries a horizontal component that determines, with the altitude, the final velocity of the projectile. This is energy imparted to the projectile at launch and it does not vanish as the projectile achieves its maximum height, except for drag.

[Winemaker]

That is totally height dependent, the higher you go, the thinner the atmosphere, the faster you drop.

Again, I agree, except that we don't live in a vacuum. The lower you go the slower you go until you hit the ocean, when you stop. The final velocity of the rocket at impact is not only dependent on its maximum altitude during flight. This is a vector thing.

[fdr]

Originally Posted by NutLoose

And the other side of the hedge is……

https://twitter.com/bhginee/status/1557396938307391488

Russia's latest submarine commander.

Still as a means of avoiding arty, his posture was pure genius, could be new

Guinness

ad. Now, is it possible to get the whole Russian army to emulate the latest anti-arty technique and park all of their mighty scotts pines T-72's in the sea of Azov? In one chicken fowl swoop they would save Russian lives of those that can swim, and save Russia from the antics of the gang that couldn't shoot straight.

[Beamr]

I am no marine warfare expert, but that sub (if it is a sub as suggested) seems to be rather close to the shore. I've no idea what are the capabilities of UKR Navy against submarines nowadays, but they did sink Moskva and other vessels.

Twitter

[DaveReidUK]

Originally Posted by Winemaker

I agree. That velocity is not achieved from simple acceleration due to gravity. A large component of that is its initial velocity, which is what I was attempting to explain.

I'd quit while you're ahead ...

[ORAC]

For those that want to play there is a calculator at the bottom.

Weight of an ATACMS is 3690lbs and drag coefficient is below 0.7. Have to guess at the cross section, I put in 3ft. Gave a terminal velocity of 3100 f/s - between M2.5 and M3.0.

https://www.grc.nasa.gov/www/k-12/rocket/termvr.html

For those that doubt that missiles go supersonic on descent I refer you back to the Falcon 9 video and the double crack boom on landing - and that after burning back down range to the launch site and a long deceleration burn during the descent to reduce horizontal speed.to zero and reduce vertical speed prior to the last second landing burn.

[NutLoose]

Originally Posted by Winemaker

Again, I agree, except that we don't live in a vacuum. The lower you go the slower you go until you hit the ocean, when you stop. The final velocity of the rocket at impact is not only dependent on its maximum altitude during flight. This is a vector thing.

But again you are using freefall NOT powered, by your logic the fastest aircraft in the world would max out at 120MPH

[Beamr]

military aviation content is a bit hard to come by, but here's a little something to keep the thread on topic.

Twitter

Twitter

Twitter

[Timmy Tomkins]

6 Minutes in May

Originally Posted by DaveReidUK

About 10 years ago, I had the privilege of seeing the late, great Warren Clarke playing Churchill in "Three Days in May", a dramatisation of events in 1940 when Britain teetered on the brink of giving in to Hitler.

I can't vouch for how historically accurate it was, but by all accounts it was a close-run thing.

Nichols Shakespeare wrote a historically accurate account of just how close it was " 6 Minutes in May" a gripping read, even though you know the outcome. Well recommended.

[Just This Once...]

Originally Posted by Winemaker

Since I'm being pedantic, I'll also point out that a falling object in the atmosphere will reach some terminal velocity, determined by its drag characteristics; for a sky diver it's about 120 mph. I seriously doubt any dropped object in the atmosphere will go supersonic.

Just to bring this sub-forum back to its roots and noting that many of us have dropped stuff from altitude, we can categorically assert that stores can go supersonic with ease when dropped from the high block on a level delivery profile. If not effectively mitigated this can be rather problematic for guided bombs as their control surfaces tend not to work (in a rather dramatic way) when Ernst Mach comes-a-knocking.

With the reference to parachuting one should express some sympathy for those whose job entails leaving an aircraft at altitude that flies at an IAS with a parachute that effectively, at opening, respects TAS. Even with an aircraft that can drop safely from (for example) 135kts from the 30-block, with the relative comfort of a static-line delivery, will find themselves at 0.4~0.5M as the canopy inflates. All that energy from the rapid deceleration is taken by the crotch straps. When you have to drop with a delayed canopy, higher, faster and with large amounts of equipment, the careful packing of manhood is as much of a priority as the chutes.

[soarbum]

Originally Posted by Winemaker

That velocity is not achieved from simple acceleration due to gravity. A large component of that is its initial velocity

Lets put some numbers on that claim to see how it smells.

Firstly, lets assume that at the apex of its flight (that point where its vertical velocity IS zero), the rocket motor has finished burning.
The energy in the system is the kinetic energy due to its momentarily horizontally velocity plus the potential energy from having climbed that high.
If it travelled 200km over 30min, horizontal velocity averages 400kmph or 111m/s.
The kinetic energy due to its velocity at the apex is 0.5mv^2, roughly 6.2e3 x m, where m is the mass of the missile with no fuel left.
(the horizontal velocity at the apex won't exactly equal the average velocity but it will be of that order)

The energy in the system when it hits the ground at Mach 2.5 (3087kmph) is 367.6e3 x m

The initial velocity gets it up there but the velocity at impact is very much caused by "simple acceleration due to gravity"