In order to analyse the noise produced by different propellers, a series of propeller noise comparison tests were carried out on Wednesday 25^th May 2005.

Model: Pilatus ARTF

Engine: SC .61 mounted inverted

Silencer: Standard with silicone exhaust adaptor pointing downwards

                                                                                                                                                    Noise Readings Table

Propeller	Size	Revs	Front On	Rear On	Side On Left	Side On Right
Master Airscrew	12×8	10500	86	76	81	80
APC	12×8	9700	82	74	81	80
Bolly	12.5×8	9600	84	72	80	79
Graupner	12.5×6	10300	87	72	82	81
Master Airscrew 3 Blade	12×8 equivalent	11300	86	76	84	83

 

Air tests were conducted by completing identical full power vertical climbs into wind using the Master Airscrew 12×8, APC 12×8 and Master Airscrew 3 Blade equivalent.

There was NO discernible difference in performance, and as the APC 12×8 was turning at 800 rpm less, the conclusion was that the THRUST generated was very similar.

General Observations

• Propeller noise is the biggest factor (closely followed by exhaust noise) which is shown above by the highest decibels being produced by the frontal readings.

• Increased revs does not necessarily equate to higher airspeed (see 3 blade rpm).

• Propeller tip speed has a lot to do with noise generation indeed some clubs recommend keeping the revs below 10000rpm to reduce noise output.

• 3 blade propellers are not necessarily the answer for noise reduction.

• To the human ear, each increase of 3db is double the noise.

Conclusions

The above results are quite conclusive in our view APC propellers are definitely the quietest on the market and substantially reduce noise output.

In this test and for this model, after keeping all other factors identical (airframe, silencer, fuel etc), only fitting the APC meets the D of E recommended noise limits – maximum of 82dBa at 7 metres