Gyroplane noise

[SandL]

Can the forum suggest the best way of reducing gyroplane noise

I have a rotax 2 stroke turning a 3 blade wooden prop at about 5-6,000 rpm
friends have an RAF subaru
I have also seen odd shaped prop tips do they work ?

I have heard of people adding a carb silencer but some say it only adds weight and chokes the engine, it's the prop that makes the noise.
I am sure there are knowlagable people on the forum, so please can I take your advice.
I may have to relocate my gyro and need to have a low noise footprint.
I guess wind carries noise and that trees shelter and absorb it, yet buildings (hangers reflect it , am I right ?
Thanks
Peter

[Master Roda]

A 4 stroke is really the way to go. Everything else is a band-aid for the problem. I suppose redirecting the exhaust may work. Reduce RPMS (however that may be). Some props are noisier than others, but I can't recommend any.

[SandL]

Thanks
But changing engines to change base airfields seems an expensive way to go
I have also heard that a VW 4stroke can be a little noisy
noise is a very interesting issue , I do not phone the rail company every time a train goes past, nor do I complain about farmers cutting fields, yet a quite mosquito in a quiet hotel room can drive me mad !
Even the mrs asked wants to complain about the extra doing aeros ner by on a quiet sunday afternoon, yet she does not mind the red arrows or a para motor flying over.
I think part of the problem is that the tone and volume changes often during FW aeros and gyros doing hops. whilst a PPG passing is a constant noise that we know will be gone shortly.
any more suggestions would be welcome
Thanks

[jebthereb]

They are all just jealous because they are stuck on the ground!!!

[Rotor-Head]

Fly somewhere away from people... Otherwise. Just enjoy it...

[Redbaron]

A slower turning rotor helps. More rpm equals a chop chop sound :-)

[steveb]

Almost all of the 2-stroke microlights in the UK have carb inlet silencers on them - its got to be worth a try as you can pick them up second hand fairly cheaply (I think you need to re-jet the carb too). You can also get a Rotax after-muffler for the exhaust - can't do any harm either (I had one on my Merlin).

When I flew single-seat there were a couple of guys who seemed very pleased with their Prince P-tip props - don't know if you can still get them. It might also be worth having a chat with the guys from Hercules props - they had a good write-up in the LAA mag recently.

As Stan said, the other way to mitigate the issue is to stick to TOPO operations and don't hang around near the airfield.

[ckurz7000]

Originally Posted by Redbaron

A slower turning rotor helps. More rpm equals a chop chop sound :-)

The rotor contributes almost zilch to the overall sound profile. And the chop-chop sound is not caused by rrpm but by each blade traversing the preceding blade's trailing vortex. The main factor causing this is blade loading and high AoA.

-- Chris.

[Gyro28866]

I know my Mac is "LOUD", so I try to avoid flying around the pattern.
I do have one ole feller, about 2 miles north of the airfield (which is a friend) that whenI see him reclining on his front porch (taking a nap) I will climb up to about 1500' and set up a decendong power off turn, which puts me rounding out over his front yard. As I pour the throttle back to her, and make a little, no a lot of noise, it wakes him up and brings him out of his rocker.
All in good fun! of course.

[Vance]

Hello Peter,

Many years ago someone decided racing vehicles needed to be quiet and each racing organization came up with different rules. Most used a DB meter and it did not take long to see that where the sound was measured on the race track and what was around the meter made a lot of difference.

We could get something to pass at the shop and then it would not pass at the race track.

In my opinion the sound energy has little to do with how irritating it is.

I find the high energy high notes of a two stroke particularly annoying and yet they are the easiest to reduce the sound energy on.

Because two strokes don’t have valves a lot of noise comes out the inlet side of the engine and in my opinion a well designed inlet silencer can be of great benefit without reducing power.

An air cooled two stroke can sometimes benefit from rubber dampeners between the fins. Most shops that have two stroke dirt bikes will probably have something that will fit. The tighter they fit between the fins the better it works.

In my opinion sound energy is cumulative so any part of it you can take out has value.

In my opinion noise energy is very directional so any time you can direct it away from the listener has value.

I have heard a Rotax powered gyroplane with all the silencers on be very quiet and I liked it. It appeared to have plenty of power and for me the quiet made the gyroplane flight even more magical and appeared effortless.

I don’t know what propeller they were running and I did not see any devices to redirect propeller noise.

I feel a slower larger propeller has the potential to be quieter than a smaller faster turning propeller.

In my experience the propeller tip shape can make a lot of difference in the sound energy.

In my experience uninterrupted air flow to the propeller can make a lot of difference in the sound energy.

It appears to me that when the flow to the propeller is partially blocked it can set up a particularly annoying sound.

Some people like to complain and in my experience there is little you can do other than make friends and take them flying.

I have also found that some people equate a reduction in sound energy to a loss of power even if there is no loss in power.

Thank you, Vance

[phantom]

my dom is the quietest gyro that I have ever had, I use the after muffler and a 3 to 1 gear turning a two blade warp drive prop.

norm

[scott heger]

My open frame 582 Sportcopter noise is about half wind noise, half engine noise when flying at 70MPH. I do not think the noise is all that bad with the stock muffler, 3-1 gear box and 3 blade prop. 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. If I changed to a full face closed motorcycle helmet, most of the problem would be solved, but I enjoy my open faced motocross style helmet (radio headset installed with big mike muff), fresh cooling air and the open air experience and put up with the minimal times I have to talk with control towers or other aircraft.

Scott Heger Laguna Niguel, Ca N86SH

[SandL]

I once heard bar talk about making the prop tips pointed like spitfire wing tips

has anyone any experience in this ?

buying a prince P-tip prop is just marginally less expensive than
buying and learning to fly a turbine helicopter.
Making friends with all the neighbours then knocking them off their deckchairs is an attractive, yet unfortunately an unrealistic option but people are not sitting outside this year as we do not have any warmth or sunlight in the UK right now, but I fancy giving it a try. (wettest summer on record since records began so far) Likewise with offering them a free flight around the local area in my single seat gyro could have interesting results.
Intake mufflers on the bing carbs on my 2 stroke sounds the best option so far yet a quick google suggests that the results are mixed and with rejetting suggests a power reduction. extra weight and reduced power is not a great option.
I have noticed that my wooden prop is slightly out of balance, does anyone think a rebalancing will reduce noise volume?
Thanks

[Redbaron]

Originally Posted by ckurz7000

The rotor contributes almost zilch to the overall sound profile. And the chop-chop sound is not caused by rrpm but by each blade traversing the preceding blade's trailing vortex. The main factor causing this is blade loading and high AoA.

-- Chris.

Thanks for the correction Chris. I disagree that the rotor contributes almost zilch to the sound profile but that's only my opinion. :-) I like to be believe my gyro is pretty stealthy when it comes to sound. Flying the gyrobee and having fun. - YouTube

[eddie]

I believe prop noise is most of the noise heard on the ground,my engine is a subaru that turns a 5 bladed warp drive 5,100 on takeoff.I have been told the high pitch whine is very differunt than other gyros. best regards,eddie...