rtfm
Gold Member
- Joined
- Mar 24, 2004
- Messages
- 531
- Location
- Brisbane, Australia
- Aircraft
- Robin R2120
- Total Flight Time
- 105
Hi,
My understanding is that if one powers the rotor to (say) 95% of the usual flying RRPM, then there is very little left for the airflow to do, and in fact, very little airflow is required to add the extra 5%. The rotor is still unpowered since it would run on an over-run clutch. Since so little additional assistance is required from the airflow, the rotor flying angle is almost (but not quite) horisontal, reducing drag considerably.
Another benefit is that there is now no danger of blade flap should one lose RRPM, because as soon as the RRPM drops, the sprag clutch engages, and maintains the RRPM at a healthy level. This application of rotor power will inevitably cause some yaw, but that's what the rudder is for. And besides, it is a whole lot better than the alternative of chopping off one's tail feathers.
Well, that's my understanding from reading about Dick De Graw's experiments, anyway. The trick is to tap enough power from the motor in an elegant fashion. Again, according to De Graw, a motor/rotor split of about 7:1 does the trick nicely.
But this still begs the question: if the rotor is flying at nearly horisontal (maybe 2 deg), this will significantly change the rotor thrust vector, and I am concerned about how to calculate this without having to take the gyro for a fly to find out... Vance had some rule-of-thumb numbers, which is a great place to start. I doubt that Hollerman's book will be of any help, since I don't think he discusses partially powered rotors. My big question is: if I get the positioning of the RTV wrong by a bit, will this result in a fun-ending day for me and my family
Regards,
Duncan
My understanding is that if one powers the rotor to (say) 95% of the usual flying RRPM, then there is very little left for the airflow to do, and in fact, very little airflow is required to add the extra 5%. The rotor is still unpowered since it would run on an over-run clutch. Since so little additional assistance is required from the airflow, the rotor flying angle is almost (but not quite) horisontal, reducing drag considerably.
Another benefit is that there is now no danger of blade flap should one lose RRPM, because as soon as the RRPM drops, the sprag clutch engages, and maintains the RRPM at a healthy level. This application of rotor power will inevitably cause some yaw, but that's what the rudder is for. And besides, it is a whole lot better than the alternative of chopping off one's tail feathers.
Well, that's my understanding from reading about Dick De Graw's experiments, anyway. The trick is to tap enough power from the motor in an elegant fashion. Again, according to De Graw, a motor/rotor split of about 7:1 does the trick nicely.
But this still begs the question: if the rotor is flying at nearly horisontal (maybe 2 deg), this will significantly change the rotor thrust vector, and I am concerned about how to calculate this without having to take the gyro for a fly to find out... Vance had some rule-of-thumb numbers, which is a great place to start. I doubt that Hollerman's book will be of any help, since I don't think he discusses partially powered rotors. My big question is: if I get the positioning of the RTV wrong by a bit, will this result in a fun-ending day for me and my family
Regards,
Duncan