Last night watched a Swedish cop show on TV, (wife loves them because they have subtitles).
Some guy was murdered by tying him to a helicopter rotor blade about half way along it. Then spinning it up to full speed. Poor bastards head flew off with bright streamers of blood.

I seriously doubt this is possible, what's the breaking strain of the neck?
How fast would the rotors have to spin to achieve that much G?
And how much vibration would having one rotor so much heavier than the other 2 cause?
I think the rotor assemble would fly apart before the guys neck gave way.
Any thoughts, serious observations?

Maybe you should ring myth busters and get them to tie poor buster to the blade and see what happens.

The neck comes apart very easily, have you ever spun a snake by its tail then whipped it.

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decrepit said..

I think the rotor assemble would fly apart before the guys neck gave way.

I'm not a doctor but I think this would happen ^

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lotofwind said..
Maybe you should ring myth busters and get them to tie poor buster to the blade and see what happens.

The neck comes apart very easily, have you ever spun a snake by its tail then whipped it.

Gee, I must've pissed you off.

^^^^^^,
This was the last Myth test buster was part of RIP Buster
Pretty awesome slo-mo vid.

Serious imbalance issues on the rotor for sure, likely some kind of override that would cut power? I suspect the guy would be dead due to brain embolism first, but I doubt the rotor assembly would hold together long enough for decapitation.

As Australians many of us are of course uniquely qualified to answer this exact scenario via direct working experience with mums Hills Hoist. The workable solution that every 6 year old knew up until about 1980 was to put another person on the opposite rotor.

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decrepit said..
Last night watched a Swedish cop show on TV, (wife loves them because they have subtitles).
Some guy was murdered by tying him to a helicopter rotor blade about half way along it. Then spinning it up to full speed. Poor bastards head flew off with bright streamers of blood.

I seriously doubt this is possible, what's the breaking strain of the neck?
How fast would the rotors have to spin to achieve that much G?
And how much vibration would having one rotor so much heavier than the other 2 cause?
I think the rotor assemble would fly apart before the guys neck gave way.
Any thoughts, serious observations?

You would have to be a very bored villain to go to the trouble to attach someone securely to a helicopter's rotor blade. I guess everyone gets bored in their job

but you would think there would be easier ways.

Hey, Dimitri, attach this guy to the rotor, but can you weigh him exactly and attach a bag with the same weight in it to the other side. Make sure you glue them with epoxy or something in case the rope slips off too early.

Main rotor rotates at 3-400rpm, but with that type of imbalance you would never get there. The aircraft would tip over well before then. Even 100grams out of balance gives a very rough ground bounce at max rpm and they are talking 80kgs outboard from the hub.
And no, there is no automatic depower feature on a helicopter due to imbalance. There is actually no system that will automatically reduce the power, govern the power, yes but not reduce it. It's not something you really want at several 1000ft, or worse, 50ft.

Yep, that was my feeling exactly. If the rotor doesn't break away, the whole craft would turn over.
It's very bad script writing, thought the Scandinavians were better than that.

At least it provoked some thought in at least one viewer. The equation for the centripetal acceleration is easy v*v/r and the force at the end of the rotor is getting up over 800G. You'd think that would pull the head off, but maybe not, because while the head might be getting 800G, 2mm further in the force is 799G, etc. Guaranteed stroke and blood leaking out of any orifices in the skull.

It made me wonder if any of the proposed tourist space stations are going to use rotation to create artificial gravity. You could put a couple of pods at either end of of a 200m rope and slowly bring them up to spin around the central point. With a 30s period of rotation you get about 0.5G. But docking would be hard.

A helicopter blade has very little cantilever strength. Duck taping an 80 kg person to it would possibly cause it to fail before it even did one turn. The blades hold the helicopter by being in tension. The blades form a shallow cone when flying. That 800g at the tip provides the necessary tension.

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Paradox said..
As Australians many of us are of course uniquely qualified to answer this exact scenario via direct working experience with mums Hills Hoist. The workable solution that every 6 year old knew up until about 1980 was to put another person on the opposite rotor.

Our Hills Hoist survived several sessions of spinning with 4 x uni students + 4 x goon bags on the arms

well....... it survived better than the students

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Mr Milk said..
It made me wonder if any of the proposed tourist space stations are going to use rotation to create artificial gravity. You could put a couple of pods at either end of of a 200m rope and slowly bring them up to spin around the central point. With a 30s period of rotation you get about 0.5G. But docking would be hard.

The concept is pretty well established and almost any realistic sci fi movie or book has a version. Go all the way back to Asimov and Rendezvous With Rama and you will find either whole massive spinning cylinders with the internal surface as a "ground" or as you suggest seperate spinning pods, like they had in Passengers or The Martian. Access through a central zero G docking point by matching roll rate and you can climb or elevator down to the gravity section.

The Expanse series is probably the best in dealing with all the issues. In smaller spinning craft coriolis effect makes the experience difficult, but the issue is solved during space travel as if you have an appropriate drive, you just set thrust at a comfortable G and build the ship with down being toward the thrust.

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Paradox said..

Mr Milk said..
It made me wonder if any of the proposed tourist space stations are going to use rotation to create artificial gravity. You could put a couple of pods at either end of of a 200m rope and slowly bring them up to spin around the central point. With a 30s period of rotation you get about 0.5G. But docking would be hard.

The concept is pretty well established and almost any realistic sci fi movie or book has a version. Go all the way back to Asimov and Rendezvous With Rama and you will find either whole massive spinning cylinders with the internal surface as a "ground" or as you suggest seperate spinning pods, like they had in Passengers or The Martian. Access through a central zero G docking point by matching roll rate and you can climb or elevator down to the gravity section.

The Expanse series is probably the best in dealing with all the issues. In smaller spinning craft coriolis effect makes the experience difficult, but the issue is solved during space travel as if you have an appropriate drive, you just set thrust at a comfortable G and build the ship with down being toward the thrust.

The issue is solved during sace travel? After 1 year at 9.8 m/sec.sec you,re going 9.8 ?60 ?60 ?24 ?365 = 30
9052800 m/sec! Light speed! And still haven't got anywhere interesting. How fast do you want to go?

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Ian K said..>>> The issue is solved during sace travel? After 1 year at 9.8 m/sec.sec you,re going 9.8 ?60 ?60 ?24 ?365 = 30
9052800 m/sec! Light speed! And still haven't got anywhere interesting. How fast do you want to go?

Be OK for a trip to the moon, You'd probably go with a compromise, start of with 1G then slowly drop that to 1moon G by the time you get there, a nice slow adjustment.

So accelerate at 1 g for half the distance and brake at 1g for the 2nd half. That's the way modern man drives his 4wd to the next red light. Why not?
At plus and minus 1 g you'll get to the moon in 3 1/2 hrs. If you want to minimise the consumption of rocket fuel it'll take 3 days.

Actually that would not be possible for the head to fly off, but if the person were an inbred or a leper(leprosy) then it now has some real credibility.
If the person had bone structure problems, that would become a mass of baggy flesh with bits of snapped bone in it.
Of the physics, the rhythmic harmonics of the weight of the person would require counterbalancing the other blades or the helicopter would rattle to pieces and turn over.

E.g. Ordinary Light aircraft have +/- G force ratings and are normally 2/-2 or utility classification 4.5/-4.5
Aerobatics aircraft for simple level are around 4/-4
medium level 6/-6
and advanced 9/-9 G forces
WW2 fighters and other military prop aircraft are round 11/-11 G forces rating.

The most in a simulator a human has "survived" is said to be 40 G
but most people rate in basic unprotected terms of blood flow only 6 G.

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nicephotog said..
Actually that would not be possible for the head to fly off, but if the person were an inbred or a leper(leprosy) then it now has some real credibility.

The thing about body parts coming off with leprosy is a myth, but I am intrigued about how inbred you need to be in order to have bits drop off

nicephotog, the head was over half way along the rotor, that's over 400G, if the head weighs 1kg that's 400kg hanging off the head. I'm not sure you are correct saying the head wouldn't fly off.
And there was no sign of a counterbalance, so it must have been trick photography of some sort.

But an average helicopter weighs 1.5 tonnes. If the rotor hub is as high as the width of the landing skids an out of balance force of 750 kg will topple it. Just under 10g for an 80kg person. He'll probably hit the ground on the upswing, chew his way out of the duck tape and make a triumphant return in the sequel.

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decrepit said..
nicephotog, the head was over half way along the rotor, that's over 400G, if the head weighs 1kg that's 400kg hanging off the head. I'm not sure you are correct saying the head wouldn't fly off.
And there was no sign of a counterbalance, so it must have been trick photography of some sort.

...but you'd also have to have whatever he was tied on by to be able to hold the 400kg.

Not sure how you tie a body to relatively thin, shiny rotor blade.

Duct tape ?

no this was thick rope, and at least they showed where the ropes had cut into the body, but no where near enough. It didn't show the ropes anchored back to the hub either. Unless they'd done that everything would just have slid off the rotor arm.

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nicephotog said..
The most in a simulator a human has "survived" is said to be 40 G
but most people rate in basic unprotected terms of blood flow only 6 G.

Can't find the exact thing I'm thinking of right now, but a race car driver walked away from a 70G crash... but that was peak load of course over a very short time. Basilar skull fractures (used to?) kill a lot of racers, as the G forces on the crash would literally try to pull the head off the neck and the base of the skull would break away. The HANS device was developed to combat this.

They experienced with prone and supine piloting positions in WW2 and later, and pilots can maintain much higher G-loading that regular seating positions... can't find the specific thing I was thinking about on that either

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Carantoc said..

decrepit said..
nicephotog, the head was over half way along the rotor, that's over 400G, if the head weighs 1kg that's 400kg hanging off the head. I'm not sure you are correct saying the head wouldn't fly off.
And there was no sign of a counterbalance, so it must have been trick photography of some sort.

...but you'd also have to have whatever he was tied on by to be able to hold the 400kg.

Not sure how you tie a body to relatively thin, shiny rotor blade.

Duct tape ?

Are all helicopter blades thin? (relative or not). I remember seeing one in real life and thinking it was more of a small wing than anything, but I do remember thinking that the rotors on Skippy seemed small and thin.

Maybe the Swedish program was a version of Skippy and the murderers just stuck the already deceased victim to the chopper and blamed the kangaroo?

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Carantoc said..

decrepit said..
nicephotog, the head was over half way along the rotor, that's over 400G, if the head weighs 1kg that's 400kg hanging off the head. I'm not sure you are correct saying the head wouldn't fly off.
And there was no sign of a counterbalance, so it must have been trick photography of some sort.

...but you'd also have to have whatever he was tied on by to be able to hold the 400kg.

Not sure how you tie a body to relatively thin, shiny rotor blade.

Duct tape ?

If the head will be 400kg, the body would be well over 5 tonnes. I think the body is could fly off the blade before the head comes off.

whatever happens it's not going to look anything like the serials sequence.

Is nobody worried that decrepit knows how heavy human heads are ?

Movie science is always good fun. Like the scene in ghost ship where he's working on the ocean going tug engine, that would look more at home on a 40ft cabin cruiser.

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Carantoc said..
Is nobody worried that decrepit knows how heavy human heads are ?

Well I'm not, Didn't I say about?
Somewhere from the depths of my memory this number sort of jumped out

Hmm, Mr Google says I'm out by a factor of 2

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With the brain, teeth, eyes, muscle and skull, the adult head weighs in at 8 to 12 pounds (3.62 to 5.44 kg).

So you can say 200kg not 400, still wouldn't want that hanging off my head!

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decrepit said..
Hmm, Mr Google says I'm out by a factor of 2

With the brain, teeth, eyes, muscle and skull, the adult head weighs in at 8 to 12 pounds (3.62 to 5.44 kg).

So you can say 200kg not 400, still wouldn't want that hanging off my head!

There was this episode of taskmaster where they had to figure it out, with varied success.

taskmaster.fandom.com/wiki/Scientifically_work_out_how_much_Alex%27s_feet_and_head_weigh