coaxial adds unnecessary complexity and loss.
=Specific Thrust is function of propeller Disc Loading...That's about 30 lbs of static thrust per HP.
So a 600 lb MTOW heli would require about 20 HP to hover?
If yes, bring it on!
They do have side advantage of opposing gyroscopic forces, which may be desireable.Coaxial systems are typically envisioned to recover swirl loses, but at low disk loading swirl loses are very small. From "Fundamentals of Helicopter Dynamics" by C. Venkatesan, page 23 - typical single rotor helicopter has about 1% swirl loss - there is not too much to recover. From the same book - non uniform inflow is responsible with 5-7% loses.
From "Principles of helicopter aerodynamics" by J Gordon Leishman, page 101, non-separated coaxial has 41% increase in induced power vs separate rotors.
So my opinion is - coaxial adds unnecessary complexity and loss. It's better to use a single rotor and straightening vanes to get rid of the torque.
=low disc loading (15 kG/m^2) =16 kG/kW !!!==Specific Thrust is function of propeller Disc Loading...
iff you have the same DL=15 kG/m^2 (i.e. 20*1 m^2=20 m^2) you can achive 300 kG
of thrust force.
-in auer KASPERWING (20 HP) we have 80 kG of thrust...(D=1.3 m)