Impossible catch

[Michi.G85]

I just noticed a strange behaviour in the Hornet (possibly any fast mover). Curious if it is possible to shoot my own jettisoned fuel tank somehow I never was able to catch up with a free falling tank or in this matter any stores. Even when dropped at angels 40 and 90° upwards and then going 90° downwards it is impossible to get faster then the falling items - even with AB. It seems like a strange bug, where the stores can reach up to Mach 1.3 just by pure gravity. Einstein would have loved this...

Edited December 3, 2024 by Michi.G85

[Vakarian]

Hmmm, it seems it's not just the stores, I've seen on a few times that when I get shot down my wreck ends up smashing at the ground supersonic. It's been a while since I've sat through a physics class in the school, but that doesn't sound plausible. It's almost like the falling object doesn't have any drag whatsoever and just keeps accelerating at the steady pace.

I'll spend an evening trying to reproduce this now that I've seen I'm not the only one to observe it

[PawlaczGMD]

Yeah, that's definitely wrong. Dumb bombs terminal velocity is subsonic. Empty fuel tanks would be slower than that. 

[silverdevil]

that's funny because i got shot-down in a dogfight and ejected. i looked around for my AC and never saw where it was.

[silverdevil]

12 hours ago, Michi.G85 said:

Einstein would have loved this...

LOL

time to start riding the train more herr einstein.

[Michi.G85]

9 hours ago, Vakarian said:

Hmmm, it seems it's not just the stores, I've seen on a few times that when I get shot down my wreck ends up smashing at the ground supersonic. It's been a while since I've sat through a physics class in the school, but that doesn't sound plausible. It's almost like the falling object doesn't have any drag whatsoever and just keeps accelerating at the steady pace.

I'll spend an evening trying to reproduce this now that I've seen I'm not the only one to observe it

Or - just my 2 Cents - the stores are somehow still (invisibly) connected to the airframe and accelerate accordingly.

[Vakarian]

Bear in mind, I did no calculations prior to see if this is possible or not, but my gut feeling tells me that something is wrong. 

In this scenario, I've first jettisoned all stores (with a bit of fumbling in the cockpit) So I had fueltanks and Mk-82s being jettisoned. Both objects reached speeds well over Mach 1 before impacting the ground. Drop tanks reached ~900kts (M1.35), Mk-82s reached ~780kts (M1.18) before impact. That seems crazy high.

My aircraft after being destroyed (I've also shut down the engine to minimize its impact) first fumbles in the air, maintaining ~180-200kts of speed and then when it turns near vertical with the nose pointing upwards it just starts accelerating without stop, reaching 600+kts before impacting the ground.

Attached are tacview file showing the ordnance speeds and a track file in which you can see the aircraft speed before impacting the ground.

 

There's also another track where I've tried to be as fast as possible before getting destroyed. Regardless, when I got shot, aircraft started to tumble and lost a lot of speed (~400kts -> 180kts) but again, as soon as the nose pointed up it started accelerating and impacting the ground at ~680kts.

 

Can someone smarter than me double check this? Is this legit or is something off with the physics?

aVeryFastCrash_startSpeedHigh.trk Tacview-20241203-202018-DCS-crashTest.zip.acmi aVeryFastCrash.trk

[PawlaczGMD]

14 minutes ago, Vakarian said:

Bear in mind, I did no calculations prior to see if this is possible or not, but my gut feeling tells me that something is wrong. 

In this scenario, I've first jettisoned all stores (with a bit of fumbling in the cockpit) So I had fueltanks and Mk-82s being jettisoned. Both objects reached speeds well over Mach 1 before impacting the ground. Drop tanks reached ~900kts (M1.35), Mk-82s reached ~780kts (M1.18) before impact. That seems crazy high.

My aircraft after being destroyed (I've also shut down the engine to minimize its impact) first fumbles in the air, maintaining ~180-200kts of speed and then when it turns near vertical with the nose pointing upwards it just starts accelerating without stop, reaching 600+kts before impacting the ground.

Attached are tacview file showing the ordnance speeds and a track file in which you can see the aircraft speed before impacting the ground.

 

There's also another track where I've tried to be as fast as possible before getting destroyed. Regardless, when I got shot, aircraft started to tumble and lost a lot of speed (~400kts -> 180kts) but again, as soon as the nose pointed up it started accelerating and impacting the ground at ~680kts.

 

Can someone smarter than me double check this? Is this legit or is something off with the physics?

aVeryFastCrash_startSpeedHigh.trk 245.67 kB · 0 downloads Tacview-20241203-202018-DCS-crashTest.zip.acmi 126.07 kB · 0 downloads aVeryFastCrash.trk 276.86 kB · 0 downloads

can you compare jettisoning the mk82 vs dropping it on a target? I assume the physics of a normal drop are correct to at least roughly match real ballistics and depression angles.

[Vakarian]

Yeah, sure. Give me a moment

[Vakarian]

Well, at least this case is logical to me. Regardless if the bombs are jettisoned or dropped in a CCRP attack, they both behave the same. When dropped from 32000ft, they reach ~780kts (M1.17) on impact. 

Now, whether this is correct or not, I'm not completely sure but same as before, gut feeling is that this is wrong. I really don't think that the free falling object is capable of accelerating on the way down and reaching M1.0+ speeds near or at ground level. 

 

jettisonAndAttackDrop.trk Tacview-20241203-211342-DCS-crashTest.zip.acmi

[silverdevil]

according to some docs i found sponsored by the US navy, a free fall bomb should never reach this speed.

"It is here referred to as “terminal velocity” and depends on mass and shape of the bomb. How closely a bomb can approach its (computed) terminal velocity depends on the altitude from which it is dropped. A bomb of about 550 pounds gross weight has a terminal velocity of 918 feet per second."

918fps = 543 knots

https://www.usni.org/magazines/proceedings/1941/december/how-about-penetration-bombs

[Vakarian]

Nice find  

 

I'd just like to stress out that is seems like the issue encompasses more things than just weapons, so in my opinion it would be good to run an small internal analysis to see if there are some things that are "not contributing" in the physics calculations. 

[Gun Jam]

freefall in a 0 drag environment is about 10m/s per second. Does it look like its trying to account for some form of drag??

[Jarlerus]

My guess is that they have a template formula for "dead" items falling, and that the formula is stupid

Faster falling-> hitting ground faster-> Getting despawned faster can also be a factor.

Generally, my guess is that they simplify it to not draw server/client CPU for trivial things

[PawlaczGMD]

4 hours ago, silverdevil said:

according to some docs i found sponsored by the US navy, a free fall bomb should never reach this speed.

"It is here referred to as “terminal velocity” and depends on mass and shape of the bomb. How closely a bomb can approach its (computed) terminal velocity depends on the altitude from which it is dropped. A bomb of about 550 pounds gross weight has a terminal velocity of 918 feet per second."

918fps = 543 knots

https://www.usni.org/magazines/proceedings/1941/december/how-about-penetration-bombs

Yeah, that's concerning, I've found similar figures for terminal velocity. If bombs in DCS break Mach 1, how could bombing be remotely realistic?

For a sanity check, if there was no drag, an object would have to freefall for around 35 seconds to reach sea level Mach 1. It would take 20 000 ft.

So can it reach Mach 1.17 from 32k ft with drag? Uhh, it feels wrong, but it's not impossible at first glance.

[Jarlerus]

Ok, if this doesn't only concern "dead drops" but also live ones, I think it's actually an issue.

[AndyJWest]

17 hours ago, silverdevil said:

according to some docs i found sponsored by the US navy, a free fall bomb should never reach this speed.

"It is here referred to as “terminal velocity” and depends on mass and shape of the bomb. How closely a bomb can approach its (computed) terminal velocity depends on the altitude from which it is dropped. A bomb of about 550 pounds gross weight has a terminal velocity of 918 feet per second."

918fps = 543 knots

https://www.usni.org/magazines/proceedings/1941/december/how-about-penetration-bombs

The data is for typical 1941 bombs. More modern designs will have a higher terminal velocity, given their slender shape.

[Michi.G85]

1 hour ago, AndyJWest said:

The data is for typical 1941 bombs. More modern designs will have a higher terminal velocity, given their slender shape.

This doesn´t explain a tumbling fuel tank though?

[AndyJWest]

38 minutes ago, Michi.G85 said:

This doesn´t explain a tumbling fuel tank though?

I didn't suggest that it does. I was pointing out that terminal velocity data for typical WW2 blunt-bodied bombs is unlikely to be applicable to later designs which were shaped to produce less drag at higher Mach numbers.

[Michi.G85]

22 minutes ago, AndyJWest said:

I didn't suggest that it does. I was pointing out that terminal velocity data for typical WW2 blunt-bodied bombs is unlikely to be applicable to later designs which were shaped to produce less drag at higher Mach numbers.

Either way it seems quite unlikely that a bomb can breach the soundbarrier by itself. If that was so simple, humanity wouldnt have struggled this long with it. And even if: a free falling and thumbling fueltank shoulndn´t be able to go over M1.0 on it´s own. So therefore must be something wrong in the Sim.

[AndyJWest]

23 minutes ago, Michi.G85 said:

Either way it seems quite unlikely that a bomb can breach the soundbarrier by itself. If that was so simple, humanity wouldnt have struggled this long with it. And even if: a free falling and thumbling fueltank shoulndn´t be able to go over M1.0 on it´s own. So therefore must be something wrong in the Sim.

Large specially-designed British bombs (specifically 12,000 lb Tallboys and 20,000 lb Grand Slams) were approaching or possibly exceeding Mach 1 by the end of WW2. And humanity had exceeded the so-called 'sound barrier' long before that, with projectiles (and with the tip of a cracked whip, even earlier). There is a nice photo taken in 1877 by Ernst Mach himself of the shock wave of a supersonic bullet here.

In as much as there ever was a 'sound barrier' for aircraft, it was a controllability problem, not one with the fundamental physics, which was well enough understood in the 1940s.

 

Edited December 4, 2024 by AndyJWest

[Michi.G85]

4 hours ago, AndyJWest said:

Large specially-designed British bombs (specifically 12,000 lb Tallboys and 20,000 lb Grand Slams) were approaching or possibly exceeding Mach 1 by the end of WW2. And humanity had exceeded the so-called 'sound barrier' long before that, with projectiles (and with the tip of a cracked whip, even earlier). There is a nice photo taken in 1877 by Ernst Mach himself of the shock wave of a supersonic bullet here.

In as much as there ever was a 'sound barrier' for aircraft, it was a controllability problem, not one with the fundamental physics, which was well enough understood in the 1940s.

 

I still don´t get why a free falling item is as fast/faster then an aircraft in Afterburner. That can´t be right, can it?

[AndyJWest]

1 minute ago, Michi.G85 said:

I still don´t get why a free falling item is as fast/faster then an aircraft in Afterburner. That can´t be right, can it?

Again, I was commenting on the ballistics of bombs, since Silverdevil seemed to be suggesting that their terminal velocity didn't agree with data. As of right now, nobody seems to have come up with the necessary data for the modern bombs.

If ED haven't modelled the ballistics properly in jettisoned drop tanks, it is of next to no practical significance, as far as I can see.