Muffler Output Port Direction

In another discussion entitled "Prop Noise Comparisons" James Pistorino asks about the prop size vs. noise factor. This got me curious about something else, to which the answer seems intuitive, but I was wondering if anyone had real-world confirmation of this...

For an RC plane/drone flying at a few hundred feet (let's say 200'), using a four-stroke 28cc engine (so as to quantify the data), is there a substantial noise difference (as measured from the ground) between the muffler port exhausting (all assuming horizontal flight) upward, toward the back, or downward?

Does anyone have any real-time experience with this, as opposed to hypothetical extrapolation based on intuitive SWAG with some hyperbole thrown in to sound more credibile?

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Lew Payne May 1, 2010 at 9:22pm

Thanks, guys. I'll keep the RPM range in mind, too.
Ryan April 30, 2010 at 10:59pm

Muffler point upward and low RPM, sub 4000rpm will do the trick just fine - I've done it.
Troy Reabe April 30, 2010 at 8:37pm

Easy way for you to test, lay your model on its side and walk around it 200 feet away and see where the noise is the least. But a good muffuler will do more than port direction. This I can show a 60% reduction in engine noise in a bell 47 when we added the muffuler. We use them for crop dusting which is why we care about the noise

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Muffler Output Port Direction

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