Jean Claude
Junior Member
- Joined
- Jan 2, 2009
- Messages
- 2,589
- Location
- Centre FRANCE
- Aircraft
- I piloted gliders C800, Bijave, C 310, airplanes Piper J3 , PA 28, Jodel D117, DR 220, Cessna 150, C
- Total Flight Time
- About 500 h (FW + ultra light)
Here are the results of my calculations for this four bladed rotor 8.5 x 0.225 m, assuming a total mass of 350 kg,
For 312 rpm pitch setting = -1.2° And at 20 m/s a1=0.3° b1 = 0.5° A.o.A shaft = 22° Rotor drag =1380 N
Such a high rrpm produces very high losses due to friction which requires a large angle of attack of the disc, and a negative pitch setting in compensation.
If you want to use 4 commercial blades of pitch setting suitable for an acceptable efficiency (i.e. about 3°), then each pair carrying only half the load, the rrpm will be about: 315/1.41 = 220 rpm which will not pose any safety problem as long as Mu does not exceed 0.35 (ie here about 125 km/h)
For example, with four bladed 8.5 x 0.225 when the pitch setting is +3°, my calculation gives:
223 rpm at 20 m/s a1=2.2° b1 = 0.7° A.o.A shaft = 9.5° Rotor drag =715 N
But in order for such unstayed blades to maintain their usual coning, it will be necessary to accept an 80 kg rotor and to allow for a few degrees of freedom between the two pairs, otherwise cracks will appear very quickly at the roots
For 312 rpm pitch setting = -1.2° And at 20 m/s a1=0.3° b1 = 0.5° A.o.A shaft = 22° Rotor drag =1380 N
Such a high rrpm produces very high losses due to friction which requires a large angle of attack of the disc, and a negative pitch setting in compensation.
If you want to use 4 commercial blades of pitch setting suitable for an acceptable efficiency (i.e. about 3°), then each pair carrying only half the load, the rrpm will be about: 315/1.41 = 220 rpm which will not pose any safety problem as long as Mu does not exceed 0.35 (ie here about 125 km/h)
For example, with four bladed 8.5 x 0.225 when the pitch setting is +3°, my calculation gives:
223 rpm at 20 m/s a1=2.2° b1 = 0.7° A.o.A shaft = 9.5° Rotor drag =715 N
But in order for such unstayed blades to maintain their usual coning, it will be necessary to accept an 80 kg rotor and to allow for a few degrees of freedom between the two pairs, otherwise cracks will appear very quickly at the roots
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