Coaxial Inefficiency

[Debian Dog]

I was looking at many of the new multicopters and notice a lot of them are coaxial (2 motors on one arm) and was wondering if they somehow solved inefficiency or that you just understand you will get less flight time. Or is there something blatantly obvious I am missing?

 

[Droider]

Its all about requirements. You may loose 5/10% but it more than makes up for it in lots of other ways.. My opinion. I fly Y6 and X4 machines in the UK for a living. I am building a XM flat 6 just to make sure I aint missing out on something ;-)

Dave

 

[gtranquilla]

There is a very detailed scientific analysis that has been done by one of the universities on counter-rotating coax ducted fan efficiency.
And Howard Hughes engineers worked this all out with counter-rotating aircraft propellers back in the 40's claiming it was more efficient that using separate motor/prop assemblies...
but then HH flew the experimental plane and crashed it... and the program was then permanently grounded etc.
Variable pitch control on at least one of the coax props eliminated the inherent inefficiencies.

 

[jhardway]

also you are talking about a fixed wing airplane oppose to a helicopter. I like the coaxial mainly for redundancy but do not know how much more energy they take to lift copters, however with that said considering the upper motor is doing a lot of the work, by the time the thrust gets to the bottom propeller there should not be a lot of energy need to spin that prop until its need from something the upper motor has not given.

I would like to know efficiency ratio.

There is a very detailed scientific analysis that has been done by one of the universities on counter-rotating coax ducted fan efficiency.
And Howard Hughes engineers worked this all out with counter-rotating aircraft propellers back in the 40's claiming it was more efficient that using separate motor/prop assemblies...
but then HH flew the experimental plane and crashed it... and the program was then permanently grounded etc.
Variable pitch control on at least one of the coax props eliminated the inherent inefficiencies.

 

[Cuba59]

Its all about requirements. You may loose 5/10% but it more than makes up for it in lots of other ways.. My opinion. I fly Y6 and X4 machines in the UK for a living. I am building a XM flat 6 just to make sure I aint missing out on something ;-)

Dave

if we talking heavy X8 it can take from 10-15% more power than a regular octo or quad, BUT it gives much better yaw stability. thats bec. the airspeed is much higher going through the coax props than a regular octo

 

[Bartman]

there are a lot of variables....what props did he use? same pitch top and bottom?