Gazzer

Folks,

I have just put up my OS 91 DF and Ramtec for sale in the uK and have been asked how noisy it is as one guy who is interested has a noise threshold at the club he flies. He said if it was too noisy he would need to go Turbine.

I believe that the turbines are actually noisier than DF but in the air, the quality of sound makes it percievably lower.

Has anyone ever measured the noises from both and compared??

Gazzer

Gordon Mc

My Feedback: (11)

The way I (mis ?)understand it, the turbine does in fact generate higher noise levels, but the frequency that the noise is at causes it to attenuate much faster with distance - whether in real terms or only our ability to discern the noise, I don't know. That's just for the noise from the turbine itself ; the noise from the pipe can be an altogether different matter.

We did some tests at one club that I joined, to see whether noise was likely to be a problem for the nearby housing estate. Close up, it was found that the turbine bust the club's permitted noise levels - but when the club president walked out to the club's boundary line and I flew the aircraft around for a while, he indicated that he was amazed how quiet the turbine was. We pointed out to the club that while most of the turbines behaved that way, there were some that were still very loud at distance (e.g. one of Tam's F4's generated so much noise with one of the early/experimented bifurcated pipes, that it generated more complaints about noise in one day than the club had in the entire 10 years of its history[X(])

I believe that that club consequently drafted an addendum to their noise-limit rules, indicating that turbines would be permitted to bust the noise limits for the normal (3-meter distance?) test, but would be individually assesed by a club officer for the in-flight noise level.

Gordon

Wayne22

My Feedback: (2)

ours was 114 db 10 from the tailpipe on the ground....but at 30' (from the side) it could not be heard over the ambient background noise......only way to tell it was running was watching the grass being blown down behind it. We did not take readings at any other orientation.

1Eye

My Feedback: (2)

For noise measuring purposes we arbitrarily adopted the IMAC noise measuring standard which can be found at <http://www.mini-iac.com/Portals/57ad...Schematic.pdf>. The obvious change was to orient the sound meter perpendicular to the noisy end of the plane. Sound levels from runups were captured with a Radio Shack sound meter. The meter has a high/peak level indication - this didn't require observers to stand in the plane of (turbine) rotation during the runup.

For grins, we took sound readings of two models:
The first (probably worse case) was one of my dogmeat ByroBlaster Enforcers - the measured sound level at full wick using the IMAC setup was 108dBA and, as you might expect, was fairly annoying. In the air it's persceived sound level is not as bad but frequency/pitch level could be an issue for some.
The second was a BobCat with a JetCat P-120 turbine - the measured sound level at full wick was just nudging 102dBA. And, as most of you know, the in-flight noise levels from turbine-powered models are usually not an issue. We have not taken measurements on fully enclosed installations yet - maybe I'll drag my Bandit out and get a baseline for it.

Air temperature and relative humidity both affect how sound travels. But as most of you know, every 3dB change in measured sound level up or down equates to either a doubling or halving, respectively, of perceived sound level by the human ear. So, by comparing the ByroBlaster and BobCat examples above - a 6dB difference, the BobCat emanated 1/4 the sound of the Enforcer!! [X(] The reciprocal suggests the Enforcer is 4 times louder! Yeowww ... you could sure tell the difference.

Independent of what are "good" or "bad" sound levels, in the absence of any other standard I think the IMAC sound measuring standard (i.e., orientation and distances, etc.) is the one to use.

Mike