I have a Neptune Seaplane that I'd like to use either an OS .46AX OR an OS .55AX. The prop I can use need to be 11' max because of clearance issue. Now, I will fly in a place where the noise 'could' be an issue. I'd like to know which of theses two motor could be the quiter of the two with either a 11 X ? OR a three blade prop on the 55AX ? My friend use a 55AX and it seem much less noisy than my 46AX. Of course brand of propeller and size will be the key here but let me know what I can use to produce the less noise.

Thanks,
Séb

My three blade prop is a little quieter but to really reduce noise try putting a mousse can mufler on the model. They are easy to build and I found they really help.

http://www.uoguelph.ca/~antoon/hobby/mcm.htm

The OS PowerBox mufflers are pretty quiet. But, the problem you will run into with a 11" prop is prop noise related to higher RPM. The higher RPM's relate to more noise, and it's pretty hard to get away from that with the smaller diameter props. The three blade prop may be the best solution, with either engine.

The 46 ax with an 11x5 or 11x6 prop and the stock muffler isn't really that loud. The 55AX will be underpropped in that range, and you'll have a lot of prop noise added. With the 55AX, you could go with an 11x8, but you still risk being underpropped. I'd go with the 46 ax in your situation.

Brad

SebM:

Propellers get noisy mainly when the tips reach the speed of sound (M=1).

Try the combination that produces the lowest tip speed, which means lower rpm for a 11" diameter propeller.

I suggest using the 46 engine with a 11 x 6.

Check these interesting articles:

http://www.lcrc.org/stu22.htm

http://findarticles.com/p/articles/m...g=rbxcra.2.a.2

http://findarticles.com/p/articles/m...g=artBody;col1

http://findarticles.com/p/articles/m...g=rbxcra.2.a.2

Regards!

I have noticed that APC props are quieter than either MAS or Zingers...
I would suggest an 11x7 APC on the .55 or an 11x6 on the .46

All of theses suggestions seems to be for two blades prop. What about a three blades prop on either engine ??

Séb

By all means use a three bladed prop with the 55 and keep the rpm down to around 10,000

http://www3.towerhobbies.com/cgi-bin...&I=LXAA35&P=ML
http://www3.towerhobbies.com/cgi-bin...?&I=LXAA36&P=7

Most of us don't use three bladed props. They tend to be less efficient. In your case however, they might be a good answer. Running the numbers on Thrusthp, assuming the OS 55 AX will turn a 12x6 prop in the 13000 rpm range (typical in my experience), that will produce a static thrust of aproximately 9.92 lbs. Using the three bladed 11x6, for the same power rating, you should get about 12, 750 rpm (much lower tip speed so less noise), and just about 10 lbs of thrust. In both cases, top speed is about 72 mph (that's not real world speed, as its dependent on air frame drag).

Bottom line, the three bladed 11x6 should be comparable to the two bladed 12x6 with the 55AX, so go for it.

Brad

Sources of noise:

http://www.lcrc.org/stu20.htm

Thanks a LOT guys,

Séb

I agree. I have/had a 46AX and a 55AX. The 46 screams with an 11" prop. The 55 has a bit more low end grunt and doesn't make such a whiny scream and would be great with a 3 blade prop. Would look more scale, too.