My old exhaust pipes were just plain worn out and needed to be replaced. The new stainless pipes were good but I recently learned about "piccolo pipes" and wanted to try it out. Good progress, and more mods might be coming soon.
Try this addition to your piccolo tube. Install a larger tube over the piccolo tube. The larger tube to be capped off at the bottom end, forcing all of the exhaust to reverse direction in the, exiting up near the bend of the smaller tube. The result is that the exhaust pulses from each of the holes along the length of the piccolo tube exit the larger tube further apart in time. Therefore, instead of hearing hearing one loud, short pop, your
The YO-3A was a propeller reconnaissance plane that flew silently to the ground at 1500 ft. It used a long muffler that fed into a piccolo exhaust tube. That plane was based on a glider and observed troops in Viet Nam who, had they heard it, could certainly shoot it down. Here is a video of the restoration project starting at the muffler: ru-vid.com/video/%D0%B2%D0%B8%D0%B4%D0%B5%D0%BE-rIhK8PWRMbI.html Other quiet features are not discussed in the video except the mention of a three blade variable pitch propeller designed by Swedish Ole Fahlin which replaced a six bladed one. Narco traffickers used q-tips on the end of the propeller blades which was a trick they learned from CIA advisors. You don't want to mess with your propellor but the propellor tips are the source of shock cones. Domestic lawnmowers have crap mufflers and rely on low rpm to keep the noise down. The main acoustic things are not create shock waves in the first place and the next is to set up acoustic negative interference.
Just saw the video. In the piccolo test I could hear the prop causing pressure pulses in the air, I could not in the other ones. Would be interested in seeing what the restriction did to the manifold pressure...if weight was no issue, would a header joining the pipes together be considered...? Thanks for doing this interesting experiment.
That's an interesting observation, thanks for pointing it out. I think you're right, combining the exhaust stack into a single pipe might be worthwhile. I know they do this in Europe where noise concerns are a bigger issue. I never looked at the manifold pressure but intuitively I think the piccolo exhaust would lower the pressure, and impact performance. Combining the exhaust in a Y under the engine, then applying the piccolo modification would yield good results for both noise reduction and higher manifold pressure.
Wicks used to sell piccolo tips that I put on my Glasair. It was definitely quieter, but the holes were bent in the opposite direction to yours. Their explanation wasn’t that wind went down the holes but that the extended hole lips acted like little cowl flaps creating a vacuum reducing back pressure.
Great video. I like the new pipes. They sounded great live at the ultralight strip at Oshkosh today. Thanks for letting us join you on the preflight walk around. It was unexpected and totally appreciated.
