Why Does this Syrian Mil-8 Hip (Russian helo) Explode in Midair?

[Bill Walker]

Note that in the video, the smoke/fuel trail hangs around quite a while.

Yes, it hangs around, but what is the fuel/air ratio? I suggest it is decreasing as it moves away from the aircraft. It will reach a point where all the barrel bombs in Syria won't ignite it. Maybe that distance is less than the radii of the fire balls. I can think of some really fun experiments to prove or disprove this, if somebody has a whole lot of money.

BTW, smoke from an incomplete combustion (oxygen starved) can also make a nice explosive mixture. There were a few airliner incidents involving smoldering cabin fires that built up hot smoke while in flight, which "flashed over" when the cabin doors were opened admitting oxygen. (See NFPA 921 for a complete description of flash over.)

I bow to my learned colleague's superior knowledge in the fields of intentional explosives. I make my living off the accidental stuff.

 

[robunos]

Be careful what you say.....

http://www.foxnews.com/science/2012/10/22/italian-court-convicts-7-scientists-for-failing-to-predict-earthquake/

....................................................................

cheers,
Robin.

 

[Orionblamblam]

I can think of some really fun experiments to prove or disprove this, if somebody has a whole lot of money.

I sense a "Mythbusters" episode...

BTW, smoke from an incomplete combustion (oxygen starved) can also make a nice explosive mixture. There were a few airliner incidents involving smoldering cabin fires that built up hot smoke while in flight, which "flashed over" when the cabin doors were opened admitting oxygen. (See NFPA 921 for a complete description of flash over.)

Some years back I happened upon a truck full of energetics - fireworks, initially, followed by a lot of hydrocarons [gas? fiberglass? plastic?] - merrily burning away at the side of the road. One of the more interesting phenomena was that the plume of thick black smoke would occasionally turn itself inside out and burst into flame 50 feet up... presumably unburned but vaporized and superheated hydrocarbons were sucked up into the plume, shrouded by CO2 and smoke, exposed suddenly to the air at some point, and would then mix & combust. Entertaining as all getout... but not *explosive.* No supersonic shocks formed, just some rapid deflagration.

I can see a flashover event in a jetliner... packed as they are with burnable, meltable and vaporizable plastics. And while I can see the sudden pressure rise from a flashover causing the fuselage to burst... shredding the craft barrel-bomb style just doesn't make sense to me.

I bow to my learned colleague's superior knowledge in the fields of intentional explosives. I make my living off the accidental stuff.

In better days I was the Junior Blow Stuff Up Guy at United Tech. "Accidental explosions" were really, really bad, while "intentional explosions" were *fun.* It was one of the former that caused United Tech to fold up like a road map.

FYI: timing is everything when it comes to the difference between deflagration and detonation. Example, start with a match, a cup of liquid oxygen and a charcoal briquette:
1) Light charcoal. Pour on LOX. Result: a fast bright fire that eats through your BBQ and scares the people standing around the BBQ.
2) Put briquette into cup, allowing the briquette to soak up the LOX. Throw match at briquette. Result: about half a stick of dynamite, sending chunks of the BBQ into the people standing around, killing many.

Same stuff in the same ratios. Very different results.

 

[Orionblamblam]

Be careful what you say.....

I seem to recall what happened the last time European governments decided to start arresting scientists. The US ended up doing pretty well from the deal. Maybe that'll happen again, though India, China and Brazil might do well of it too.

 

[Bill Walker]

I found this on YouTube, seem to remember several similar experiments in the 1980s? A number of interesting points:

The flimsy sheet metal structure is severly damaged by a relatively small amount of explosive (a few pound, IIRC) WITHOUT any air loads. That spiralling Mi-8 probably already had several parts about to come apart or off before anything blew up.

No big fire ball with this explosion. The Mi-8 could be a small explosion over-pressuring the fuselage, opening it up, then airloads shredding it. The small explosion also ignites the fuel/air mixture that had been building up since the first gunfire strikes, producing the fireballs (which look neat, but aren't needed to shred the airframe). Don't need a barrel bomb, maybe just a hand gernade coming off somebody's belt (which I think was in OBB's original scenario).

On the other hand, a fuel air explosion inside the fuselage could open it up, the inertial loads and q loads from the extreme manuever underway at the time then shred the sheet metal.

<iframe width="420" height="315" src="http://www.youtube.com/embed/wTsKLAnfDuU" frameborder="0" allowfullscreen></iframe>

 

[Orionblamblam]

The flimsy sheet metal structure is severly damaged by a relatively small amount of explosive (a few pound, IIRC) WITHOUT any air loads.

Sure, but it remains in large pieces. In flight, it looks like you'd have pieces of 747 skin the size of houses falling out of the sky.

On the other hand, a fuel air explosion inside the fuselage could open it up, the inertial loads and q loads from the extreme manuever underway at the time then shred the sheet metal.

The problem as I see it there is that the chopper isn't moving *that* fast. It was apparently structurally intact until it went foom... the rotors were still on, for instance. A fuel burst could certainly pop the fuselage, and winds would splay it... but to shred it this completely? Dubious.


Clearly the only way to resolve this is to start blowing up Syrian helicopters.

 

[Bill Walker]

Clearly the only way to resolve this is to start blowing up Syrian helicopters.

Agreed. Do you know anyone at Myth Busters?

As an old mentor of mine used to say: "when the going gets tough, the tough get empirical".

 

[Bill Walker]

Posting after more time to reflect.

In flight, it looks like you'd have pieces of 747 skin the size of houses falling out of the sky.

That's house sized pieces before the air loads get to them. Look for videos of the wreckage recovery of the Air India 747 bombing back in the 1980s, and you see suitcase sized pieces of skin after a few kg of explosive in flight (plus maybe a high speed water impact, I admit). Scale that down to an Mil-8, and the pieces might approach the resolution of this crappy video.

The problem as I see it there is that the chopper isn't moving *that* fast. It was apparently structurally intact until it went foom... the rotors were still on, for instance. A fuel burst could certainly pop the fuselage, and winds would splay it... but to shred it this completely? Dubious.

Not just speed, but yaw rate combined with side slip angle and maybe some negative g. I bet the Mil structural guys never had this load case on their to-do list.

I'm surprised nobody has come up with the "but Russian helicopters are built like farm tractors" arguement yet. I have the dubious honour of having worked on both helicopters and farm tractors for several decades, and got to crawl through an Mi-24 a few years back at a European client. For a helicopter, the Mils are very well built. For a farm tractor, they are just a flimsy bit of tinfoil.

 

[SOC]

Clearly the only way to resolve this is to start blowing up Syrian helicopters.

I fully support this investigative methodology.

 

[Bill Walker]

Clearly the only way to resolve this is to start blowing up Syrian helicopters.

I fully support this investigative methodology.

Here, I've done step one. Now somebody can raise the funds, and then we will carry on.

 

[Orionblamblam]

Feh. They want *millions* for those helicopters. We are in a time of economic strictures, and should demonstrate some fiscal responsibility. This can be done by rather than buying and blowing up helicopters, simply skipping step one and just blow up the helicopters. There are quite a number of operators of such choppers who I'm sure wouldn't mind... Syria, Iran, North Korea, etc. Simply send techs onboard these choppers and plant "test equipment." Since this is SCIENCE this means we should bracket the output of the "test equipment." Some will get no more than a small firecracker. To save further on expense, some will get merely detonators, but attached to host-nation-provided "barrel bombs." Some will get atomic demolitions munitions. I'm not sure if there is a need to go all the way to 150 kiloton thermonuclear "test equipment," but it's a discussion worth having.

 

[SOC]

Feh. They want *millions* for those helicopters.

I can think of someone to foot the bill. Reparations to the scientific community and whatnot.

I'm not sure if there is a need to go all the way to 150 kiloton thermonuclear "test equipment," but it's a discussion worth having.

See, if you could get me some k-switches...

 

[Bill Walker]

I'm not sure if there is a need to go all the way to 150 kiloton thermonuclear "test equipment," but it's a discussion worth having.

A quick review of the available literature in the field shows that the Myth Buster guys always go a little over the top if they debunk the original myth. I strongly recommend we collect some data at around the 150 Kton point, and keep it in the can in case we need it.

 

[Orionblamblam]

I thought this might be educational: a rare video of a sizable unintentional gas explosion. This is relevant to the discussion of the "fuel mist" hypothesis. Note that a gas leak would probably produce a better bang than a mist of fuel due to better fuel/oxygen mixing and faster flame propagation. Even so, the explosion has a heck of a lot of heaving force, but not a lot of brissance... the building bursts, but it does so almost sedately.

http://www.youtube.com/watch?v=ldNRcuIT0J0

 

[kcran567]

What about this theory: the Mi-8 chopper is getting churned around like a paint can, or a vodka tonic shaken in ice (not stirred), as the chopper is struggling for control, its churning around fuel inside, increasing the surface area of the fuel. On the outside, there is fuel leaking, and the rotors are still spinning around a fuel air mixture, fire, spark or bullet ignition and BLAMMO the thing goes off like a shaken Molotov cocktail.

 

[Broncazonk]

What about this theory: the Mi-8 chopper is getting churned around like a paint can, or a vodka tonic shaken in ice (not stirred), as the chopper is struggling for control, its churning around fuel inside, increasing the surface area of the fuel. On the outside, there is fuel leaking, and the rotors are still spinning around a fuel air mixture, fire, spark or bullet ignition and BLAMMO the thing goes off like a shaken Molotov cocktail.

Well, that's what I was thinking. Regardless, it really is an amazing, and very unsual event.

Bronc