JETLAG03
Active Member
- Joined
- Jul 6, 2019
- Messages
- 380
- Location
- france
- Total Flight Time
- 300+ flexwing (pendulaire) newly trained on gyrocopter ((autogire)100h)
Had a few comments about the noise of my BMW K1200RS at full throttle 8500rpm on take off, I have a sabre style propeller.
I have increased the AoA of the prop and hope to reduce to the engine revs to 6000rpm, yet to test.
I did a ground test of the noise using my iphone with the NIOSH app from app store. The dB test was NOT conducted as prescribed for a motorcycle, simply because a motorcycle does not have the big fan spinning at the rear. The iphone was placed on a stand 2 metres from the giro, just in front of the exhaust and well forward of the prop and its wash.
1. With propeller
LAeq 92.2dB
max 103,9 dB
LCpeak 116.6dB
TWA 63.9db
exchange rate 3dB
time weighting - fast
2. without propeller
LAeq 86,4 dB
max 93,5 dB
LCpeak 109.1dB
TWA 57.4db
exchange rate 3dB
time weighting - fast
I was unable to spin the propeller independant of the engine so could not confirm the noise purely from the propeller itself. Maybe some has such data?
Basic data suggests that with the propeller the noise is 10.4dB louder = X2 (ish) than motor only. Probably, I have misunderstood the raw data but suspect that there is little if any benefit to be gained from trying to silence the engine further when a higher level of noise is being produced by the propeller.
Am I right?
Does for example a noise level of 93.5dB get completely masked by another noise level of 103.9dB or do the two noise join together to create one noise greater than the two seperate.
The propeller is close to the gearbox/reducer about 100mm (4") but I cannot move the propeller further back due to the structure of the machine.
I look forward to your comments, please keep any suggestions as simple to understand as possible, I am not as academic as many of you.
thanks
phil
I have increased the AoA of the prop and hope to reduce to the engine revs to 6000rpm, yet to test.
I did a ground test of the noise using my iphone with the NIOSH app from app store. The dB test was NOT conducted as prescribed for a motorcycle, simply because a motorcycle does not have the big fan spinning at the rear. The iphone was placed on a stand 2 metres from the giro, just in front of the exhaust and well forward of the prop and its wash.
1. With propeller
LAeq 92.2dB
max 103,9 dB
LCpeak 116.6dB
TWA 63.9db
exchange rate 3dB
time weighting - fast
2. without propeller
LAeq 86,4 dB
max 93,5 dB
LCpeak 109.1dB
TWA 57.4db
exchange rate 3dB
time weighting - fast
I was unable to spin the propeller independant of the engine so could not confirm the noise purely from the propeller itself. Maybe some has such data?
Basic data suggests that with the propeller the noise is 10.4dB louder = X2 (ish) than motor only. Probably, I have misunderstood the raw data but suspect that there is little if any benefit to be gained from trying to silence the engine further when a higher level of noise is being produced by the propeller.
Am I right?
Does for example a noise level of 93.5dB get completely masked by another noise level of 103.9dB or do the two noise join together to create one noise greater than the two seperate.
The propeller is close to the gearbox/reducer about 100mm (4") but I cannot move the propeller further back due to the structure of the machine.
I look forward to your comments, please keep any suggestions as simple to understand as possible, I am not as academic as many of you.
thanks
phil