Gyroplane noise

[NoWingsAttached]

Man, you folks who have noise problems...I feel for ya. But everyone around my local airport, and my house, and all points in between and everywhere else have nothing but great things to say about my gyros. The cops love em. Them neighbors love em. Even when I run out of gas land in someone's backyard - they love em. i have had weddings and funerals both wave at me. On the same day. Boaters stand up and wave furiously. Lately everyone has been asking why I have not been seen barnstorming the lakes around here and ducking down behind the dams for the past couple of months.

Maybe it's just a Georgia thing. We love gyros in this neck of the woods, anyway.

[gyronutjoe]

My local grass airport banned gyrocopters because of a noisy helicopter. Oh if anyone knows how to get the ban removed. Its called Buchan Airport, Sarasota Co. Fl.

[NoWingsAttached]

Move it to West Georgia

[perbgyro]

Originally Posted by scott heger

... When transmitting on the radio the easiest way to hear me clearly is to lower the power setting and speed to about 40-50 mph or less to reduce wind and engine noise.

Glad to hear someone else has that problem! I have to do the same.

Originally Posted by scott heger

If I changed to a full face closed motorcycle helmet, most of the problem would be solved

Not solved. I use a full face helmet and if you hear what the mic picks up, it's loud! It even has a foam cover on it.

I'm experimenting with a throat mic to see if that helps. The CEP headset was the only way to hear the radio without blasting me ears.

[SandL]

Redbarron your gyrobee is real quiet, and produces a low note
can we ask what engine, prop, prop RPM and silancing you have please

and any audio tweeking for the video ?

is this the quietest powered gyro on the planet ?

What's the trick ?

[Redbaron]

Originally Posted by SandL

Redbarron your gyrobee is real quiet, and produces a low note
can we ask what engine, prop, prop RPM and silancing you have please

Engine is a rotax 447 with a 2.58 to 1 gearbox swinging a 2 blade 60x36 Tennessee prop.
Stock side mount exhaust.

Here's a quote I found from the designers website.

" The engine, reduction drive, and prop are well-matched, yielding very close to an optimum static thrust coefficient. What that means is that a 40 hp engine provides plenty of power for the aircraft. The Gyrobee cruises at 50 mph at only 5000 rpm (about 30 hp), which is excellent for any gyro, let alone an ultralight. Because the engine size is modest and cruise rpm is low, the Gyrobee is a very quiet gyro - also very unusual. I am often asked about the use of larger engines. While the Gyrobee would accommodate a 503 or larger engine if you used light blades, the power is not needed and can only get you in trouble!"

http://taggart.glg.msu.edu/gyro/gbfeatr.htm

[BEN S]

Gyronutjoe..
I looked up your airport on Airnav. It is a publicly owned airport....to answer your question, Get an N Number and fly legally and they CAN NOT stop you from flying there. If they have accepted a single penny of FAA funding it is my understanding that they can't keep you out.
Ben S

[robert mckenny]

I was told by the rotex dealer. if you put a silencer you do not have to re jet the carburetors and if you put a cone on the propeller it'll be much quieter.

[gyroplanes]

SnoBird had a Charger Stealth model gyro. It was the standard Rotax 582 open frame gyro with modifications to meet and exceed strict European (France?) noise regulations.

The 582 was equipped with the intake silencer and after muffler, it helped a bit.
The main difference was a higher ratio redrive (IIRC around 3:1) and (2) 3 bladed IVO props run on the same prop flange and staggered, creating a 6 bladed prop.

Reduction of prop tip speed is essential. Using as few a blades as possible is desirable, but not practical in a pusher configuration.

Most of the aircraft's noise is propeller caused. Vortices created at the prop tips interact with each other and, more importantly, air frame structure, causing a "siren" effect.

Ever notice how pusher aircraft sound so much alike?

McCulloch, Cessna Skymasters, Republic Seabees's all make a lot of noise and most offend longer due to their slower speed.

In a nut shell, but not in order:

• Longest propeller possible
  
• As few blades as possible
  
• Greatest clearance to nearby surfaces possible
  
• Slowest tip speed possible

[SandL]

thanks for some really interesting ideas,
Tom, if I switch to a 2 blade, and slow it down am I right to say the pitch would have to be greater to soak up the RPM, I just feel that with a 2 blade and slower rotation , it would be quieter but, unless the pitch is quite different I will be pushing less air behind me. So I climb and cruise slower and use more gas, Is there any advantage other than noise foot print ?
I already have a dropped keel and at the back I can move my HS further away from the prop, but I'm not keen on moving the fin further away as that will be a design change along with a mountain of paper work for the powers that be. a "test flight" a nonstandard insurance quote and, and, and !
Thanks

[WHY]

Lonnie Prince of "Prince P Tips" makes a very basic statement, -----Propellor noise is wasted efficiency. You can't eliminate it but you can cut it down.

Since tip vorticies are a major source of noise, especially when they "slap" some part of the gyro structure, (keel or overhead structure), so-- I wonder, is a Xenon noticably quiter than say a Sparrow Hawk or other airframes with both keel and overhead structure near the prop as well as the rudders ???

Tony

[Vance]

Just to show how theory sometimes does not line up with experience I offer The Predator as an example.

We went from a Prince P tip two blade propeller to a larger Cato three blade propeller with straight tips which according to some of the posts should have been louder because the tip speed is higher and I have more blades with straight tips.

We went from a Lycoming O-290 to an IO-320 B1A. Most people feel a larger displacement and more horsepower should make it louder. Most people feel a larger muffler is required for a larger displacement engine.

The IO-320 has higher compression than the O-290 (8.5 vs. 7.5) and most people feel that generally makes more exhaust noise.

We went from a large round muffler with a single opening to a smaller oval muffler made from thinner material with two openings that equaled the area of the single opening.

In my opinion the smaller muffler should make more noise because we have less volume to manage the sound.

The thinner material and the flat sides should be louder because the noise can go right though the thin material and the flat sides oil can and transmit the sound.

It is an uncomplicated back pressure muffler and the small muffler has close to the same back pressure and combined with less volume should be louder.

The O-290 had an oiled foam element that tends to quiet the inlet noise and the IO-320 has a larger paper element.

I fly a low close pattern a lot and virtually everyone who has an opinion says the new setup is quieter.

She even sounds quieter to me.

I do not have answers, only questions.

Thank you, Vance

[ckurz7000]

It's probably been said before, but whether something is perceived as being noisy has a lot to do with the frequency spectrum of the noise. High frequencies are percieved as disturbing and obnoxious. Low frequencies much less so.

Of wo noise sources emitting the same "noise power" but with different frequency spectra, the one with less high frequency contribution will be perceived as more pleasant sounding and quieter.

Vance, maybe this could be the explanation why the new setup in the Predator is generally judged as being quieter?

Greetings, -- Chris.

P.S.: In Europe you have to have a noise measurement and obtain a noise certificate for your aircraft. Having been at ROTR and listened to Sparrowhawks I am glad we do have regulation putting some kind of emphasis on keeping things quieter

[Vance]

Hello Chris,

That was part of my point.

I did not measure it with a DB meter before or after.

I feel the original question was not about sound energy but rather the annoyance factor on the ground.

I have not let anyone else fly The Predator without me so I have never heard her from the ground.

In my opinion the propeller has a lower note with less treble so it is less annoying.

I feel more blades makes for steadier, less irritating sound.

I worked at having a better air flow to the propeller so The Predator no longer has that interrupted sound.

Craig Catto has experimented with different tip shapes and I have one of the quieter ones.

Sound is very directional and having two smaller outlets that equal the size of the one larger one seems to help.

The O-290 muffler was thicker and double wall and I feel there is some sound energy that comes through the walls of the new muffler. We used to have little turn outs that sent the noise out the side instead of straight but we felt they contributed to our muffler cracks so we cut them off short and straight. The general impression was that the straight down outlets made it louder but she was still quieter than the O-290.

I suspect that The Predator would not pass the European standards.

I work a little at not being annoying and try to follow noise procedures if they have them.

Thank you, Vance

[vickijohnk]

Early 707 and DC8 jet engines had exhaust nozzles that changed the exhaust frequency from low to high because high frequencies didn't travel as far as low frequencies and were perceived as less obnoxious. John K.