corsair01

Need your help guys.

I'm flying a 73 inch ultimate with a DA50. Last weekend we had noise test at our club. The max. noise we may produce is 86 dB. My plane was measured a 95 dB. I have to do something about this but don't know what. I'm using a DA50 with a MTW muffler. For prop I use a 22/10 Mezjlik (carbon) and gives about 6800 RPM on the ground. I'm going to try to bring my air intake into the fuselage and perhaps a 3-blade prop but I don't know if it will be enough.
!!! HELP PLEASE !!!!! I am desperate. [&o]

Thanks on advance
Ronny

Kweasel

My Feedback: (29)

Get a big muffler, soft mount, reduce prop diameter and increase pitch. 86db will be tough but not impossible.

Mrt1750

My Feedback: (1)

Need more info from you how far was the measurement taking from 3 meters or 7 meters on your side of the pond my understanding is that readings are taking from 7 meters.

I'm going to go on that assumption for now, no way your plane can be that noisy at 7meters with your set up. Put the cowl on a 23 inch two bladed prop, and check everything inside the air frame for something rattling around.

95 to 98 DB reading is what I'm getting at 3 meters with 80 cc motors and your type of setup, MTW or KS with header.

Hope this helps.

Thanks

corsair01

Thx guys,

Measurement was at 7 meters. What do you mean with checking the inside ? It's a wooden frame covered with oracover and almost empty . See the picture. Don't you thing that bringing the air intake into the fuselage would help. When my engine has enough gallons I will switch to a bigger prop. (Maybe a 21/10 3-blade). I will have to try untill I get to 86 dB.

rmh

you will kill the power with large prop and three blades are worse.
I have a new 23" (actually it is more like 22.5") from RCShowcase which is quiet and pulls very well -it is the 23x12 ZM -the pitch is a fooler - it revs about same as the Mejzlic 22x10 but very quiet -no rip - look at the tips in their picture of it..

crhammond

My Feedback: (21)

I am using a DA50, Slimline non-smoke Pitts muffler and Mejzlik 20x12 3-blade. A Mejzlik 23x8 is 2db louder (in general going from 3 to 2 blades adds 2 to 3 db at WOT.) At 6400 RPM from 7.5m over grass with the meter set to dbA and slow response I am at 90 db (our limint is 92db.) If you are over cement you will be at least 3-4 db louder. It will honestly be hard to make 86 at 7M... a canister will help but the prop is going to be an issue. On planes that just can't make the readings at our club we let people fly after coaching them to manage the throttle... if they rip the prop in the air and crack WOT too often they are grounded.

Make sure nothing rattles on the plane as that can make a huge difference - make sure all cables, hatches, cowl etc have been secured. Any hatches, cowl etc should have silicone, rubber or some other dampening material to reduce noise.

Interestingly enough my DA100, Slimline smoke in-cowl mufflers with Mej 25x12 3-blade at 6300 RPM is only 87 db! I believe vibration is the main difference - the airfame is not generating near as much noise as it's fully sheeted (Cap580.) The H9 Extra 260 is all covering - it resonates like mad. I also have a composite Sukhoi with a Evolution 58 that resonates so much it can't pass a sound test... its like 103db!!! I bet I could make 86 on the 580 with DA100 with a little work.

If you're going for quiet I believe Mejzlik is the best based on my testing (we tested a LOT of props.) The best way to get quiet is with a higher pitched carbon 3 blade. It will keep RPM's down and massively reduce tip speeds. I really like the performance of the 3-blades. Maybe they don't pull as hard but they are very smooth... one drawback is you'll have noticably less braking effect on downlines and when slowing for landing but you'll get used to it.

Chris.

rmh

The new ZM props are quieter - they also are listed as having higher pitches - which makes sense - performance is stil about the same bit you can't get em to RIP-- My 42%, 39 lb pig is turning a ZM30x14 at 66-6700 in the air level flight and still quiet - will also stop start vertically and accelerate up - I also prefer Mezjlic to any of the wood stuff - in holding noise down
The wood props I have run are all noisy -if allowed to run at full throttle in level flight .
coupled with the big JMB cans -very quiet --same thing on my 80 single on the 26x12 - no rip -it gets louder but never that friggen blatt from the tips going into spank mode.

Pelle Gris

A friend of mine flies a 220cm cap equipped with a BFM 51 (german manufactured gasser), tuned pipe, rubber mount, intake air taken from within the fuselage, Mejzlik 21x12 3-blade prop. Measures 86,5dBA at 3 meters. With a 23x10 Mejzlik it measured 93,5dBA at 3 meter.

corsair01

Thanks guys,

What 3-bladed prop do you think would fit on my DA-50 (It turns a 22/10 Mezjlik at 6800 RPM) For the 3-bladed I would prefer a Mezjlik to, but because they are very expensive I don't want to test around untill I found the good one.

MalteS

An 21x12 should do it. Should turn around 62-6300
This is an emhw Ulti? I have one as well. Mine should be <84db in 7m with 3W56 twin and engel 3blade 22x10@7100umin. Motor is soft mounted...
hints:
Make sure the wing cords are tight and attach felt (or something like this) to the wings and the elevator. Another noise source is the upper wing canopy since the steel staves may get play and produce noise.

corsair01

Thanks MalteS,
Yes, it's a Weiershauser Ultimate, BTW a wonderful plane. I see you live in Bocholt, I believe it's not so far from where I live. I live near Maaseik, and do most of my shoppings by W&W modellbau in Haaren. Maybe you go there to ?

Don't you thing a 21x12 3-blade would be to much for the DA50. I was thinking about an 21x10 ????

MalteS

21x10 will probably give you not enough speed. 21x12 is o.k. but Mejizlik could have too wide blades. I would go for a engel (www.engel-mt.de) They have a narrow blade that is more silent than a wide one.
Since my LHS is 2minutes by car W&W is not an option for me (about 1,5h drive).

corsair01

Mejzlik has a 21 x 11.5N 3-blade. It's a narrow prop and recommended by other. Maybe I'll try that one.

corsair01

Got an answer from DA, they recommended a 20x12 3-blade. It's getting more and more difficult now to select the right prop now.

MalteS

Then I'd say: if Mejzilik go with the 20x12. If this prop turns 6400 you have well reduced the tip speed (and this is the most important thing)
BUT:
This will not get you 9dB noise reduction!
I've gone through this with my plane. Its not a single adjustment.
1) Really tight wing cords are mandatory, at least for the measurement since the get loose over time. If they get loose noise and servo gear slop is the result.
2) Apply all this felt stuff.
3) Soft mounting of the engine could be required. However from the clearence of the DA to the canopy that I've seen in some german forums I doubt that soft mounting is easy.
4) In your pictures I've noticed that you have 2 cannopy screws only. This could be another noise source.

It is a difficult but not impossible job...

yakka

I was thinking of getting a DA100 for a composite ARF yak-55. But we have an 82db limit at our club. From what I have read here it's worth even trying to attempt.

BaldEagel

Yakka

Have a look at Pe Rievers site in the Netherlands he has to comply with an 80Db limit, you can also find him under the "MVVS Support Forum"

Mike

rmh

I went thru this routine --in making the 94 DB required for pattern flying
the engine - a ZDZ40F3A which is one using a different ignition curve and runs very well in light shell composite models
These types ring like a brass banjo -you have to tap around the model with your fingers till you find and stop any plink plink or rattle
THEN----- a looong pipe and a higher pitched prop - I used the new ZDZ 20x12 wooden prop which is quite a surprise- it is very quiet and the shape and stiffness are different -in comparing with other wood props.
So -when applying what Ed and I found on this model - the same work is required on larger engines /models

rubber/loose or shaky mounts are -quite frankly a double edged sword and I won't use em - and yes I know about the rotating plates and shock absorber types - that is all old hat.
A mount that is progressively distributing the load thru the fuselage is still the best approach - -iTis really "mass balancing "
the front of a fuselage can easily be induced to ring at various rpm THAT is the big problem -and each design is it's own problems to sort out -use longerons or strakes to stop these vibes.

NM2K

My Feedback: (14)

Find another club or obtain your own flying field. 86db is ridiculously low. Conversation is typically at 85db. After everyone spends mucho money complying with this sound level, the community will stick kick you off your field. BTDT too many damned times to count.


Ed Cregger

Rcpilot

My Feedback: (78)

Our club has a 92dB limit at 3 meters measured on the concrete runway.

It's been a rule for several years, but we didn't worry about it too much because the club is well over a mile from the nearest house. And it's just one house that nobody lives in to my knowledge. Next closest homes are well over 2 miles away.

Recently, a developer starting building $1 million dollar homes about 1/2 mile from the club. [:@]

Now the club officers have the sound meters out and are checking planes. It sucks. It won't be long before one of those rich lawyers or doctors decides that his Sunday morning coffee and paper would be better without the buzz of our engines.

I've been telling people for years that it's not just the prop/engine. Airframe vibration contributes to noise in a much bigger way than most guys realize. But, I was an idiot for saying it 3 yrs ago. I guess thats why I'm a member of the Idiots Club.

I feel your pain. 86db is really strict. I'm afraid my latest project is going to get red flagged. It's a side dump muffler on a 75cc engine with a 24-10 Xoar prop. I haven't started it or had it sound checked yet, but I'm guessing that side dump muffler is going to be loud as hell. I'll probably end up having a pitts muffler custom fabbed for it--or worse case, a cannister. The problem is--it's a Husky conversion engine. Any exhaust I put on it will have to be custom manufacturered at a premium cost. []

Keep your flying wires tight and run your servo extensions inside a tube instead of letting them bounce around inside the fuse and vibrate on the covering. Keep your wheel collars snugged up to prevent wheel vibration on the axles. Lower the RPM--already been covered by previous posters in this thread. Secure your cowl with rubber isolators t prevent vibration resonence. (sp?)

Good luck. Post back and let us know what you did to quiet the plane.

Tired Old Man

My Feedback: (1)

I have a feeling that your propeller choice will be a big downer as well.

As for moving the air intake inside the airframe I doubt you'll gain what you're looking for. The three noise makers are exhaust, airframe, and propeller. I've watched planes fly where I could not hear the engine or propeller because of the drumming of the airframe. That was a U-Can Do with a Saito 1.50 on the nose. OTH, with a well designed muffler and airframe I've stood next to an airframe where the only noise you heard was from the propeller. I don't think we want to spend that much to reach that goal, though.........

I'm with Dick on this one. Look for ways to make the airframe more rigid, experiment with some props, and use big cans.