| Qualitative noise data |
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| Four strokes may sound quiet in the air, and be unlikely to give rise to noise complaints, yet they may register quite high readings on decibel testing at 7m. A similar phenomenon has been noted with large 2 strokes, including with petrol engines. This does not appear to be due to greater attenuation of noise with distance in 4 strokes or larger 2 strokes, as the following experiment shows: Aircraft: Dalotel Wot 4 Engine: Super Tigre 91 Super Tigre 51 Prop: 15x10 Master airscrew 11x9 APC Silencer:ST quiet silencer + Irvine Mouse ST quiet + NRD-1000 RPM: 7100 10100 Distance to meter: Dalotel noise Wot 4 noise F L B R F L B R 1 m 97 91 90 94 93 92 87 91 3 m 90 86 78 86 86 87 78 84 7 m 83 80 70 80 80 77 73 77 14 m 77 74 64 74 75 72 66 71 21 m 71 70 61 69 71 69 60 66 28 m 70 69 60 69 68 65 55 62 Taking the 7m readings as a baseline, the following data compare how the readings obtained above differ from those expected by merely increasing distance (given that sound pressure falls according to an inverse square law) Distance to meter: Dalotel noise Wot 4 noise Expected F L B R F L B R 1 m +14 +11 +20 +14 +13 +15 +14 +14 +17 3 m +7 +6 +8 +6 +6 +10 +5 +7 +7 7 m 0 0 0 0 0 0 0 0 0 14 m -6 -6 -6 -6 -5 -5 -7 -6 -6 21 m -12 -10 -9 -11 -9 -8 -13 -11 -9.5 28 m -13 -11 -10 -11 -12 -12 -18 -15 -12 Thus if anything, the noise from the smaller engine attenuates more over distance. Qualitative assessment: The following data illustrates how qualitative assessment of 4 strokes does not always correlate with decibel level. All assessments were done by at least two independent observers: Model Engine Prop RPM Max dB at 7m Qualitative Sopwith Pup Laser 90 14x7 - 83 V.Quiet Magister OS 90 15x6 8000 82.5 V Quiet Quaker Flash Enya 35 11x7 8300 77 V.Quiet Puppeteer Saito 45 12.5x5 9000 78 Quiet Magister Enya 120 15x8 - 83.5 Quiet Moth Minor Enya 120 16x6 - 87 Quiet Richthofen Enya 60 12x6 9300 81 Quiet Tomtit Enya 40 12x5 9300 81 Quiet Stampe Enya 120 16x6 8000 85.5 Quiet Tiger Moth OS 90 15x6 8000 82.5 Quiet Aeromaster OS 90 14x7 8000 85 Quiet Dalotel Enya 46 11x7 8100 78.5 Quiet Sopwith Pup Magnum 30 29.5x6 6500 87.5 Quiet Waco Saito 120 15x6 9000 85 Acceptable Aeronca Champion Laser 90 15x8 - 83.5 Acceptable Aeromaster Saito 80 14x6 9000 86 Acceptable Acrowot OS 90 14x7 8500 83.5 Acceptable Waco Saito 120 15x6 9000 87 Noisy Aeromaster Saito 80 12x7 10500 87 Noisy Mystic Enya 120R 14x11 8000 87.5 Noisy |