Letters To The Editor: How About Engine Intake Noise?
I've read numerous articles and letters recently about model aircraft noise. I think James Wilson's article "Gopher Canyon" in the August issue was particularly informative.
A lot has been said about propeller noise, airframe noise, and exhaust noise, but I have seen nothing about intake noise. I know intake noise is not insignificant — anyone who has ridden a two-stroke motorcycle with the air cleaner/silencer removed knows how loud the intake can be.
Charts showing noise levels in different quadrants around a model often indicate the highest levels straight ahead. The exhaust usually points rearward, while propeller noise radiates mainly from the tips. Perhaps we have assumed that the noise forward of the model is from the propeller; I think that assumption deserves re‑examination. If propeller noise is such a big factor, why are electrics (which run at similar speeds to glow engines with similar props) so much quieter?
I think it's time intake noise is considered and approaches to reduce it are examined. For front‑intake engines this won't be simple; rear‑intake designs might lend themselves to some interesting noise‑reduction ideas.
Recommended testing
- Compare front‑intake and rear‑intake engines of similar size and power output using the same prop and running at the same RPM.
- Chart the noise‑level distribution around each configuration.
- Determine whether the distributions differ significantly.
- If differences are noticeable, pursue further examination and development.
- Invite engine manufacturers or importers to perform or sponsor such testing and publish their findings.
I hope this provides food for thought to someone who can act on it. We need all the information we can get to make our sport acceptable to the widest audience.
Rick Murray Portland, OR
Editor's note
Testing by North Carolina State University did not agree with the suggestion that intake noise is the dominant forward noise source. See the four‑part report in the December 1989 through March 1990 issues for details.
Historical note
Searching our memory, we recall that Tore Paulsen of Norway used a carburetor muffler on a front‑intake engine at the 1977 RC Aerobatics World Championships in Springfield, OH. His aircraft was noticeably quieter than the others that year. How much of the improvement was attributable to the carburetor muffler is uncertain, but Paulsen clearly paid careful attention to aspects of model aircraft sound.
Transcribed from original scans by AI. Minor OCR errors may remain.
