juance

Hi all:
Last year I started wondering why my Dalton Extra 300 42% was so noisy, and began investigating. I want to share what I've found and how I corrected it.

The equipment I have is DA170 with MTW 3E pipes, 14" headers, 3 bladed Biela prop.

I expected from the beginning that the airplane would be quite, but it really wasn't. The RPM's (never tested though, but you can hear it) never went high enough to cross the high pitch close the supersonic boundary. The noise was around 102 DB !!! Just crazy, on top that I like quiet planes !
The comparison was made with another identical airplane but with a DA150, caniseters and mejzlik 2-bladed. his configuration sounds way quieter a around 93 DB!!
Even at ground idling the sound was intense.. How come ? Well, everything was caused by the drumming of the fuselage, canopy, monokote, thin balsa wood, etc., and the pipes themselves are very thin and create a lot of noise that gets "radiated" 360 degrees !! Yes a perfect sound source (pipes) with a resonator on its surroundings-A gas powered loudspeaker!!! . What I did was to enclose the pipes compartment with styrofoam glued to thin balsa (styrofoam side to the pipes), and also covering any possible area that could resonate (drum) with flooring foam (yes, the same used under wood floors) which is very light and easy to work with, including the engine cowling. Noise now is around 93 DB!!!

I still need to check with another 3-blade propeller if there's a difference in noise, but I am under the impression that Biela is not the quietest one.

Happy flights !

Juan

Leadtrumpet

I am interested in more details on how you used the 'flooring foam' to reduce the drumming? I have a 40% Edge 540 which I would like to quiet down as well. What did you do inside the cowling?

juance

I glued the floor foam directly to the cowling using contact cement. I used stripes on the tight curves.

Leadtrumpet

What is the brand name of the foam that you use? Available at the local Rona or Home Depot?

juance

The one I have is SUPEXBOND. They have distributors in Ontario and Quebec only. I am sure you can get an equivalent one locally with the people doing floors. I tried Homedepot and I didn't see anything similar.
Phone number, in case: 514-288-5288 (MGA Commodities)