The PROS and CONS of helicopters

[Head Turner]

Considering that it takes just one person to complain about helicopter useage to initiate extensive investigative action by the authorities, is it an assumption then, that more people are harmed by the helicopter than are helped.
Considering the recent and ongoing help provided by helicopters in the aftermarth of Katrina and in Parkistan, would it not be best for all if the investigative authorities took a different stance when receiving complaints.
What are your views?

[MCA]

My view is the same people who complain about helicopter noise, find the sound of a helicopter coming down the valley the sweetest sound in the world when they have a broken leg three days walk from civilization. Slightly off topic but… A company I used to work for quite frequently flew climbing party’s into mountain huts, one guide in particular used to use our company helicopters to get to the hut and then he would complain about helicopter noise (to the authorities) when he was climbing! What a W@#$er

[verticalhold]

No problem with them complaining about the noise just so long as they don't expect a free ride to intensive care when they need it. "Have you ever complained about helicopter noise? Blink once for yes, twice for no. Ok your rattly bumpy much slower ground ambulance is over there, Byeeee!":E

[havoc]

Several years ago an Aviation General retired, bought land near Mother Rucker, started a housing sub-division and then complained daily about the flight paths over the area.

They put a 1K no fly around the subdivision. Not much investigating went on there.

More recently (last month) the FAA asked that the several EMS providers keep the airspeed up and altitude (above 1000 ft agl) as long as possible before starting the approach into a down town hospital pad (gound level pad).

The same individual complains on a daily basis, EMS or ENG it does not matter. No other complaints from residents in the area since the pad went into service years ago.

[SilsoeSid]

We had a nice complaint the other month.


At the time we were following a 'sus' vehicle @ 2000', early hours. This vehicle eventually began to drive around the block for 20 mins or so, pax constantly looking up at us. We noticed that the front seat pax had just been on his mobile when we got the call, yes you guessed it,

"We have had a complaint about the Police Helicopter following a vehicle in xxxxx St, is that you?"

"Yes"

Apparently we were preventing them from carrying on their normal 'business'.


Beggars belief don't it!

:mad:
SS

[NickLappos]

I stood as temporary Operations Officer one time in the National Guard unit that flew Hueys around Connecticut, and got a noise complaint one time from a woman who was right under the middle marker at a local airport. She couldn't stand the noise of the guys practicing ILS approaches.

I told her,"Some day you might be on your roof in a flood, and that sound would be very welcomed, woudn't it?"

She said, "I live on a hill"

We all have thin memories when it comes to putting up with annoyances, unless we need them right away. Kipling said it very, very well:

Then it's Tommy this, an' Tommy that, an' "Tommy 'ow's your soul?"
But it's "Thin red line of 'eroes" when the drums begin to roll.."

For it's Tommy this, an' Tommy that an' "Chuck him out, the brute!"
But it's "Saviour of his country," when the guns begins to shoot"

[Above Datums]

I have had the pleasure(?) of living with Fast Jet, Multi engine and Rotary wing aircraft and I can say that Rotary aircraft have to be the least offensive to the ears. OK, so jets scream by and then thier gone but MY GOD what a racket! Rotary aircraft can be noisy but are great to watch, safe to fly and are the ONLY vehicle to have saved more lives then they have claimed. Helicopter are truely brilliant machines (except the Osprey, thats just weird!)

AD

[havoc]

Since each helicopter model has a distinctive sound, maybe part of the investigation should be similar to a line up.

Have a variety of helicopters fly over the complaintants house and have them identify the one that caused the complaint to be filed.

This could be staged out over several days and of course throughout the day and night.

I think they would understand and appreciate a complete investigation of the original complaint.

[Graviman]

As a professional engineer (quite sad really) i have always been suprised by the fact that most tail rotor designs use square tipped rotor blades. Most of the noise that the complainant can hear will be tail rotor generated, since main rotor is sub audible. I accept that fenestrons are not suited to all applications.

Have a listen to a Grob Demona light plank some time. The use of elliptically tapered blades makes a serious difference to the noise signature of the machine. Perhaps future legislation is required to make manufacturers consider consider this aspect at the design stage. In the auto/truck industry, we are quite use to being constrained by both noise and exhaust emissions. It makes for a better product in my view - especially if you have to live in Los Angeles or London...

Mart

[Farmer 1]

Graviman,

From dead ahead, I think you'll find most of the noise is from the main rotor, as in the Huey, for instance. Not sure if that's the case with the Chinook, though.

[heliduck]

Farmer 1,
I agree that the main rotor "vortex interference" causes most of the oncoming noise in the big machines. I spent many years as a loader driver for AG ops & used to have a quick nap on top of the water tank between loads on occasion. The noise of the 206 tail rotor when the machine was on its way back for another load would wake me up in time to start the pump & get the fuel hose before the machine even came into view!!

[NickLappos]

There are two basic sources of noise from a rotor, either main or tail:

1) Pressure noise, caused by its motion thru the air, and determined by its tip speed, the thickness of the airfoil and the planform (the shape, as in swept, square, cranked, etc.) The faster the tip speed and the thicker the blade the more the noise (duh!) In most flyovers, pressure noise is the chief source of noise.

2) Blade-Vortex Interaction (BVI)- Caused when a section of the rotor blade passes thru a spot of disturbed air from another source, usually causing the blade to momentarily get a lot faster, sometimes making Pop sound. BVI is often caused by the preceeding blade, occur mostly in slight descent (vortex drops as it is pushed away from the blade) and occur mostly to blades that are already going pretty fast. On some helos in approach, BVI is the main source of noise.

A Huey is the poster child for BVI noise, since its rotor is going very fast (to squeeze enough lift from the two blades) and the space between the blades is almost perfect to make the Pop at moderate speeds.

Making a low noise helicopter is an art, and costs weight and performance. A slow main rotor is great, but it stalls at low speed, weighs more and doesn't autorotate as well.

[Dave_Jackson]

Eliminate the tail-rotor and you reduce noise.
Implement Stepniewski's Slowed Rotor Intermeshing configuration (ABC - Synchropter) (http://www.unicopter.com/1093.html) and you really reduce noise.

Hi Nick ~ Just a continuation from a debate on another forum. :cool:

[bullshitproof]

You are bang on the money their head turner, but unfortunatly untill they bring a drug out to counteract jealousy we are stuck with it.

[Hilico]

Had a Chinook heading towards Harwich from the Clacton direction a couple of weeks ago. While it was still over the estuary it sounded like someone practicing flamenco dancing on the conservatory roof. By the time it got directly overhead, though, I could barely hear it.

[bullshitproof]

And is that not the case with most europien laws aviation or other wise we set up a body to police them where most ignore them.

[Graviman]

At some risk of off-topic posting:

"Making a low noise helicopter is an art, and costs weight and performance. A slow main rotor is great, but it stalls at low speed, weighs more and doesn't autorotate as well."

I have often wondered whether a hybrid powertrain would help with this. The downside is definately cost, bearing in mind the objective here is to reduce noise complaints. A high RPM electric motor (ie light weight - ideally a disk design) is used in parallel with the turbine. A minimum mass set of LiMH batteries, optimised for high power/weight is also required. We are talking a few seconds worth of power only - energy/weight or range is normally the limiting factor for batts.

The motor provides a very fast transient RRPM response, when collective requires, to overcome turbine lag. This could allow improved cruise efficiency in addition to low noise. The fast RRPM response still allows good manouvreing margin, without any pilot flight mode selection. Without doing the sums in detail, my guess is that the performance advantage would more than make up for weight penalty. Long term cost (other than fuel savings) is harder to estimate, but turbine would not need to operate so near to its TET limit which must be good.

In combination with weak collective servo additional benefits might be fast automatic entry into autorotation. There may even be some energy reserve, pending calculations, that gives the pilot more options. It may even help overcome the H-V curve limitations, by providing enough power for a controlled landing.

Mart

[NickLappos]

Mart,
Look in Stepniewski and Keys where they explain how rotor stall works. The issue is that if you slow down the rotor enough, you raise the control loads (amount of stall) and thie requires beefier control components (servos to blade horn) or lower lives. Often, maneuver requirements occur in a split second, with no time to recover rpm.
A better way might be to have a high lift device on the blade, so that it reacts to the need quickly. The piezoelectric flaps come close.

[IFMU]

Dave_Jackson said:
Eliminate the tail-rotor and you reduce noise.
Implement Stepniewski's Slowed Rotor Intermeshing configuration (ABC - Synchropter) and you really reduce noise.

Graviman said:
"Making a low noise helicopter is an art, and costs weight and performance. A slow main rotor is great, but it stalls at low speed, weighs more and doesn't autorotate as well."

Guys, this ignores one facet of human behavior. People who are prone to be POed at aviation don't have to hear the hear anything to be POed. If they can see it that's enough. My old glider club got complaints about violating the airspace over somebody's house. Of course the towplane can generate a lot of ire amongst the aviation haters, but interestingly enough it's about the same if you tow right over somebody's house or are coming back at 3000 agl and low power. They just have to see you. And, stepping out of the plank world, helicopters can operate lower altitudes and land anywhere. That makes them easier to see. So, even if somebody invents a rotorless Stepniewski rotation antigravity silent vortex generator powered helicopter, somebody is going to complain about it. I think it is how these miserable people get some of the meaning for their lives.

-- IFMU

[Graviman]

"Often, maneuver requirements occur in a split second, with no time to recover rpm."

Good point well made, Nick. The limiting factor could well be the need for say a fast roll for collision avoidance. Maybe variable camber blades are the future then, makes sense since twist ideally already needs to vary. Perhaps the limitations of a machine with a need for manouvre thrust overhead is just something we have to accept.


"... even if somebody invents a rotorless Stepniewski rotation antigravity silent vortex generator powered helicopter, somebody is going to complain about it."

Yes this does ring very true. An EMS machine overflew the cottage today. Naturally i had a look to see what the machine was, but the noise was not that bad. Didn't immediately recognise it: looked a bit like a 117, only with a fenestron. I guess it is just a question of whether you like the noise or not...

Mart

[havoc]

Install a noise cancellation system on the aircraft, would that then create positive calls from those that complain?

[Thomas coupling]

Pro's: flexible and versatile.

Con's: noisy / expensive / noisy / expensive.

[Head Turner]

What really is most upsetting and shows what an ass the legal systems are, is that as a pilot in command you are assumed 'guilty' until you have proved otherwise. Twice I have been investigated and hounded by the authority until in both instances I was able to prove quite clearly my 'not guilty' verdict.
But this was after days of harrassing questioning and an attitude by the investigating officer that one way or the other I was going to be found guilty of the aledged offence. In both cases the 'reporter' was not subsequently charged the cost of the investigation.

Investigating officers ought to present a copy of 'Kiplings' poem so very well presented above to any 'reporter'. That may well save aviation, and therefore us from even more expenses and the harrassment.

[Graviman]

"Install a noise cancellation system on the aircraft..."

Des'nay work! Qinetic (UK equivalent of DARPA) wasted lots of money to find out what most engineers already know, with the pointless NXT system (albeit their objective was internal noise). If you could design a system than radiated a phased array of acoustic sources, the power requirement, or system mass, is rediculous. It would at any rate only work on the lower frequencies

The best you can ever do is to minimise the noise sources, then absorb as much of it as you can. Maybe some research into compliant rotor tips, with viscous damping, is required. Rotor blade damping makes sense anyway, to my mind, to reduce aeroflex vibration sources...

Mart

[Dave_Jackson]

Mart,

An external noise project was tested during the Vietnam War. They used a "radiated phased array of acoustic sources" to try and overcome the noise of the rotors during an attack. However, it did not work.

This experiment was depicted during a stealth attack in the movie 'Apocalypse Now'. :D