24 March 2006

Wop, Wop, Wop......

Our EMS company gives out helicopter lapel pins as an advertising promo.
Some years ago my Mom was wearing one I had given her as she stood in line at a grocery store. The guy in line behind her noticed the pin and asked her about it. When she told him what I did for a living, he asked her how I became a helicopter pilot.
She told him I was Army trained and a Viet Nam veteran, and he said "I was a grunt. You tell him the sound of that Huey headed our way to pull us out of the field was the most wonderful sound in the world!"

And what a sound!
In some ways, like a heartbeat.

I have 3,000 hours beneath the rotor of various models of the UH-1.
The rotor on the UH-1H model Huey was 48 feet 3 inches in diameter.
Each time that two-bladed rotor swung around, 24 feet of it was takin' a huge bite out of the air.
The red-line on the airspeed indicator was 120 knots/138 miles per hour. The rotor itself was turning at over 400 miles per hour at the tip. When it came around on the advancing side, it was going fast enough under some conditions to begin to build up a pressure wave, associated with the speed of sound.
That's what gave the Huey it's distinctive sound signature.

One of the reasons helicopters are not so noisy today is that rotor diameter has been reduced, lessening the speed at the tip. Most manufacturers are making multi-bladed systems, which decrease the amount of work the individual blade needs to do, therefore lowering sound levels.

When you hear a helicopter flying by, in most cases the loudest noise you hear is the tail rotor. It turns at 6-7 times the R.P.M. of the main rotor, and makes a high-pitched hum.

The main rotor is generally the second loudest thing on the helicopter. In most machines it is a lower pitch buzzing sound.

On top of all this you add the noise of the engine. In the case of a turbine, it is barely noticeable on top of rotor noise. In helicopters powered with reciprocating engines you can identify the engine sound, but it generally is not objectionable..........more like the sound of your neighbor mowing his lawn at a distance.

I was always aware of the noise footprint of the Huey. It was such a noisy machine, when I flew over cities or late at night, I tried to fly at altititudes that would dissipate the noise.
When I hear one now.......no matter where I am or what I'm doing, I'll stop to watch it pass.....
everything comes to a stop until the aircraft is out of sight and out of earshot.

The Old Huey is a sweetheart, and I'll love her 'til my dying day.


the golden horse said...

You are so right about the Huey. Living here, I get to hear all kinds of copters, tour, police, traffic, Coast Guard, and of course our wonderful military. The only one I really stop to watch is the Huey. When I hear it over our house, and out of the regular flight paths, you just know it is for a special reason.
When we walk down by the ocean next to the flight paths and see the big C's coming in, all dark with no numbers, you know they are bringing our troops home. Bless them all.

Dave Starr said...

In 1965 I received a "Greeting" letter from our Uncle. I was already a newly minted private pilot and I knew in the back of my mind that the Army as already looking for WO candidates for rotary wing training. I thought things through and as I always did made exactly the right (or wrong) decision and ran off to the USAF recruiter for a career in aircraft maintenance. (Two tours in SEA but I never served in-country and almost never touched helicopters). I never see a Huey, hear one go by, or listen to Billy Joel

"… They heard the hum of our motors,
They counted the rotors.
And waited for us to arrive..."

without thinking about October, 1965. Thanks for the memories and the remembrance of why those birds mean so much to so many.

Anonymous said...

I live in Australia Melbourne. One day I heard a wump wump sound from a long distance away. It gradually got louder and louder until it was deafening. It was two Huey helicopters flying with the Oz air force. I two stood and waited to see where the noise was coming from.