chop chop chop

December 28, 2005 8:47 PM

Imagine what it might feel like to get hit in the head by a rotating helicopter blade. Johnny Lowe found out two days ago -- and has survived to earn the nickname "Chopper".
posted by soiled cowboy (25 comments total)

"I don't think it's really sunk in for him. He's talking about being back at work tomorrow. He's a pretty stubborn little bugger. "

...Or maybe he's not all there because he was hit in the head by a helicopter blade
posted by saraswati at 9:02 PM on December 28, 2005

Quite amazing. Reminds me of the strange tale of Phineas Gage, who survived a railroad spike through the head. The only ill effect, according to his friends and family, was that ol' Phin turned into an ornery old cuss.
posted by Dr. Wu at 9:09 PM on December 28, 2005

I doubt the blades were spinning at full force when he was hit, it was probably the first time around.
posted by Citizen Premier at 9:23 PM on December 28, 2005

Things didn't turn out as well for that one zombie in the original Dawn of the Dead.
posted by maxsparber at 9:33 PM on December 28, 2005

Hmmm, I never knew Vic Morrow was the father of Jennifer Jason Leigh.
posted by strangeleftydoublethink at 9:43 PM on December 28, 2005

Props on this post, sc.
I crack myself up sometime.
posted by rob511 at 9:43 PM on December 28, 2005

Ever wonder what causes that distinctive helicopter sound, that rotor "chop - chop - chop"? It's because at flight speed the ends of the rotors are traveling faster than the speed of sound and what you hear is the series of sonic booms as the sound wave from the leading end of the rotor reaches your ears. Anyone hit by a rotor is not likely to survive. This guy is exceedingly fortunate.

One day in April 1968 I saw the result of a UH-1 rotor catching a guy who was trying to escape a damaged ship as it made an emergency landing at Cu Chi, Viet Nam. It's one of the saddest memories of many sad days.
posted by X4ster at 9:50 PM on December 28, 2005

I've seen the footage of Vic Morrow and the kids getting hit by the helicopter, but cannot remember it. The image was too appalling for my mind to maintain.
posted by maxsparber at 9:58 PM on December 28, 2005

makes me want a couple of aspirin just thinking about it
posted by pyramid termite at 10:02 PM on December 28, 2005

No kidding, I can feel my skull geting crushed right now. It hurts. I'm thinking the blades were beyond the first go around. They did have to take his scalp off. And he won't get it back for a couple months. The story is sort of light on details though. It's pretty incredible that he was able to walk inside and call for help.
posted by panoptican at 10:26 PM on December 28, 2005

okay, so now New Zealand and Australia have their Choppers.

inspiring story. I think not having a scalp is a pretty damned good reason not to make it into work.
posted by Busithoth at 10:27 PM on December 28, 2005

Helicopter rotors are only near sonic when they're the advancing blades during forward flight:

To keep generating lift, the retreating blade has to move backward faster than the rotorcraft is moving forward. The airflow in the inner portion of the retreating blade is then reversed and would flow from the trailing edge of the blade to the leading edge. As airspeed increases, the area of reversed flow on the retreating blade gets bigger, and the airspeed of the rest of the blade keeps getting smaller. At some point, the retreating blade cannot make enough lift to keep the helicopter flying because its airspeed is too low. The helicopter is caught between the need to keep positive airspeed on the retreating blade and the need to keep the tip of the advancing blade below Mach 1. These two requirements limit the theoretical maximum speed of a helicopter to significantly below Mach 0.5, or half the speed of sound. This is why the current world helicopter speed record is only 249.10mph (400.87km/h).
posted by marvin at 10:38 PM on December 28, 2005

Ever wonder what causes that distinctive helicopter sound, that rotor "chop - chop - chop"? It's because at flight speed the ends of the rotors are traveling faster than the speed of sound and what you hear is the series of sonic booms as the sound wave from the leading end of the rotor reaches your ears.

No, they do not. Neither do propeller blades or jet engine blades. When the airflow around the blade approaches trans-sonic, there is a great increase in drag and a decrease in generated lift. No conventional blades are strong enough to withstand the resultant loads. That is one of the reasons why you don't see helicopters flying faster than about 400 km/h, propeller driven supersonic planes, or why people spend so much time trying to design inlet ducts for supersonic jets that would slow down the incoming airflow to sub-sonic velocities before it reaches the compressor.

On preview: Marvin provides a second reason why helicopters are slow.
posted by c13 at 10:44 PM on December 28, 2005

I guess a good link would be http://en.wikipedia.org/wiki/Helicopter , under "Limitations" section, or the entry on propellers elsewhere in wiki. I'll quote some:
A propeller's performance suffers as the blade speed exceeds the speed of sound. As the relative air speed at the blade is rotation speed plus axial speed, a propeller blade tip will reach sonic speed sometime before the rest of the aircraft (with a theoretical blade the maximum aircraft speed is about 845 km/h (Mach 0.7) at sea-level, in reality it is rather lower). When a blade tip becomes supersonic, drag and torque resistance increase suddenly and shock waves form creating a sharp increase in noise. Aircraft with conventional propellers, therefore, do not usually fly faster than Mach 0.6. There are certain propeller-driven aircraft, usually military, which do operate at Mach 0.8 or higher, although there is considerable fall off in efficiency.
posted by c13 at 10:51 PM on December 28, 2005

Rotten.com has some pictures (Warning: Index page, following pages are NOT WORK SAFE, NOT MIND SAFE) of what happens when the guy hit by the rotors *doesn't* survive.
posted by mrbill at 11:38 PM on December 28, 2005

Marvin & c13,
I conceed that you are correct about aircraft speeds. My comment wasn't in regard to the forward speed of the airframe but the rotational speed of the tips of the rotors. How fast is the tip of a thirty foot rotor blade moving at a thousand RPM? During those military days I was told that the tip of the rotor blade was traveling at a supersonic speed.
posted by X4ster at 11:50 PM on December 28, 2005

Ach , this is nothing.

When i was a laddie we used to catch helicopter rotors with our teeth every morning

AND WE WERE GRATEFUL.
posted by sgt.serenity at 1:56 AM on December 29, 2005

X4ster : A 30 foot diameter blade tip will travel (pi * d) = 94 feet every revolution. At 1000 RPM, that's 1571 feet every second, which is about one and a half times the speed of sound.
posted by ny_scotsman at 7:56 AM on December 29, 2005

Re: Phineas Gage, you can see his skull and the tamping iron that went through it at the Warren Anatomical Museum at Harvard's Countway Medical Library on the Longwood campus in Boston. It's a neat tiny museum with a lot of gross human parts, a cast of Coleridge's head, and so forth.
posted by nflorin at 8:32 AM on December 29, 2005

Note to self : Never click on rotten.com links.
posted by maxsparber at 8:37 AM on December 29, 2005

At 1000 RPM, that's 1571 feet every second, which is about one and a half times the speed of sound.

Well, then, it must not be turning that fast.
posted by deadfather at 8:41 AM on December 29, 2005

I know that propellors at their tips do not go supersonic. I know this from my schooling. I couldn't refute much of this though because I wasn't aware of many of the details of helicopters. But I highly doubt the main rotors are spinning at 1000 RPM. One site I found said 289 RPM.

Even if you have an RPM/rotor length that makes the tips travelling at the speed of sound, you also have to consider whether or not the tips are swept. If they are swept then they can spin faster before the tip 'sees' mach speed. But engineers try and avoid having the propellor speeds get even near mach 1 (maybe 90%?) because the drag leading up to mach 1 can be quite substantial.
posted by Phantomx at 3:05 PM on December 29, 2005

Having totally derailed the thread, I didn't want trivialize your experinces X4ster.
posted by marvin at 4:27 PM on December 29, 2005

Update in today's NZ Herald gives a bit of detail on the experimental procedure used on "Chopper":

Doctors removed about half of Mr Lowe's skull to create room for the swelling. It is being preserved and will be stitched back on in about 12 weeks' time.

(And no, the surgeon's name is not Michael Hfuhruhurr.
posted by rob511 at 6:26 PM on December 29, 2005

From what I've seen on TV the characteristic whop whop sound seems to be around 10Hz... which means 300 RPM for a two bladed chopper. That would put the blade tip speed around half the speed of sound which seems to fit in with the numbers above.
posted by ny_scotsman at 8:43 AM on December 30, 2005