Kris^

My Feedback: (1)

I've been seeing a lot of posts/emails lately on the lists and forums, concerning about how people are running 150-210cc engines, on canisters and 3-bladed propellors, and are STILL too noisey for their local fields noise regulations, or for IMAC competition. I've seen some really quiet setups for all these engines, and my personal aircraft have always been quieter than "the other guys", so it strikes me that there is something wrong when bolt-on systems are easily available, yet the flyer still can't get his plane quiet.

I'd like to open up this thread for suggestions, combinations, and ideas about how to get our planes QUIETER, with no loss of performance. The bolt-on systems exist, or have been built and reviewed, and for certain there are quiet propellers out there, so WHY are people having problems getting them quieter? I'm sure a lot of it has to do with controlling the left stick, but todays 40-50% planes are really tough to quieten to a reasonable level. So. . is it an attitude problem, a physics problem, or a combination of the two, and what SHOULD we be doing about it, if anything.

Please, no flame attacks or product "issues". I just think it's time someone brought this out, and we all had a big happy discussion about it, and figured out some solutions as well as learned a bit from the guys who REALLY know about it. The truth is, no matter where you fly, sooner or later you are going to go someplace where your plane MUST be quiet. . .Joe Nall is a great example of this, and the fine folks down there are really "encouraging" people to address the issue. Seems we should all take a step forward and do it as a matter of course, rather than have it dictated to us after it's almost too late.

JohnVH

My Feedback: (38)

Is there really a problem? all the 100's and 150's on cans are pretty quiet I thought... I know mine on stock exhuast are loud but Im not competing, and our fields dont care how loud they are.... I personally like them loud.

Be interesting to see what can be done, How quiet can they really get??? Maybe its time to start buying stock in the LiPoly industry

Kris^

My Feedback: (1)

Well, John, when one of THESE posts hits the email lists :

"anyone running a zdz 210 on a 3 blade that is happy with the noise
reduction. I have a rcs 34X12 wood prop turning 5400 rpm and it is
way too loud. I have not put a db meter on it but I'm positive that
I'm over 100db."

I start to look for answers. . like WHY is he "noisey" when his setup is reputedly very quiet. . I've several of these big Yaks that were nice and quiet, as well as a big Raven, with the same engine setup, that is so quiet it's silly. So. . what to do, where to go, and how to start getting the word OUT in a concise, cohesive manner? thus, this thread.

Personally I'd prefer to see a big 3-blade on the front of the plane, and will suggest it to him. . but in the meantime, its not a bad idea to keep this subject in the forefront of engine-related forums.

JohnVH

My Feedback: (38)

Maybe its the 200+ engines? The bigger the louder? Good question.

Thanks

Diablo-RCU

My Feedback: (1)

Could be the RCS prop? Or maybe he has in-cowl mufflers. Where I fly (three clubs around Chicago and Northwest Indiana), noise just isn't an issue. The only ones with cans in the fuselage and three blade props are a handful of the guys flying on the IMAC circuit.

Flyfalcons

Do what the full scale Europeans do and run even higher blade count (4 or more). No matter what you do with the exhaust, the prop will be a considerable source of noise.

PlaneKrazee

My Feedback: (14)

The quietest large plane I have seen is a JTec 40% arf with a ZDZ160 champion running the cannisters from RC Showcase. The owner loves the plane and even though it measures over 100 db it sounds much quieter than any of the muffled 40 size planes at the field.

I would like to see someone make a motor box/muffler chamber similar to the Air Hobbies design. Make it larger and add baffles then take in-cowl mufflers and have them dump into this chamber and exit out the bottom of the motor box. One of the problems will be to make a system light and strong.

Kris, your 110 engines would be a good candidates for this setup as they weigh less and the extra weight would not be as much of a factor as with other engine brands.

Shortman

My Feedback: (21)

Best way for quieting is coming, Brushless motors

Kris^

My Feedback: (1)

You will still have gear drives and prop noise, shortman, and the prop is probably 80% of the noise during a ground test, and when they rip in flight you'll never hear the exhaust of an engine.

Skypilot. . do you have any idea how TIRED I am of R&D work? I'm about burnt out on it, to be truthful. BUT, I have an exhaust that I am designing that is specificaly designed for flat twins, using a 2-1 collector/header assembly into a common muffler. I've actualy tried a similar design in the past, with no muffling, and realized a tremendous increase in performance in a BME 5.8, of some 600+ rpm. I have so much going on, with 2 40% planes, 3 projects on the building boards, and having to work for a living on top of it, that I have little time for my passion for R&D. Maybe somethign will come out of this thread.

Here's some ideas I've been considering, other than the new "exhaust" style:

Re-engineer the props to make them "rip proof". Basically the props load goes up exponentially with rpm, but the speed only increases in a linear progression. Even unloaded, it should be possible to design a prop that will run into a "wall" as it starts to go transonic at about .75-.8 mach, requiring a tremendous increase in power to push it past "the wall". Developing a prop to achieve this would get rid of all but the most blatant prop rip. A second consideration would be to reduce blade size in close to the hub, and increase chord and narrow the airfoil to keep the same rpm, but give the prop more "area" to grab air. By increasing pitch slightly, and not depending so much on the airfoil itself to provide thrust, prop rpm's could be kept constant or dropped slightly as pitch is increased. With a narrower cross-section, transonic noise tendencies would also be reduced. The result would be a prop turning about the same rpm, less cavitation or rip as the speed increases, a wider footprint to pull the air with, slightly higher loading as the props speed increases, and slightly more speed as the plane gets up to speed and the prop unloads a bit.

I've seen no measurable difference in a "double-swept rounded tip" and "squared off tip" for tendency to get noisy and rip. I've modified the rounded tip props to square tips. . no difference as far as I could tell, and the plane flew the same with either design. What's needed is a totally swept tip,like on the Apache helicopter rotor blades, to reduce turbulence at the tip. Prince Propellers tried this a few years ago, using downward swept tips, but once they went transonic they were louder than conventional props. . NOT a desirable thing. A wider, flatter, and radically swept tip, to reduce turbulence and cavitation, would markedly lower the total noise signature of the props.

Lastly, make the props more efficient at 60% mach, set the plane up to use them at that speed at cruise-full power, and design the airplane with a specific engine/prop/rpm combination in mind. The days of blasting around with open diverters are almost over. . better exhausts will come out, and the only step left is propeller design. Some people just need to knuckle down and do it. Unfortunately. . . . .I don't have time.

Just some ideas

PlaneKrazee

My Feedback: (14)

Shortman,

I think you're right! One and a half pounds for the motor/gearbox and five pounds of lipo batteries should do it.

The batteries need to become more reasonably priced with a standardized safe charge method. I don't like the idea of charging assemblies of 3s4p packs without removing them from parallel.