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60something · 10-09-2011, 06:59 AM

There seems to be two camps developing, designwise, single layer rotor array, vs stacked rotors. Any thoughts on what if any difference flows from the two approaches? It would seem single layer would give finer mixing control (with the right programming!) but it certainly ups the mechanical complexity.

brtmac · 10-10-2011, 05:06 PM

Stacked loses efficiency. The lower rotors are in the turbulent airflow of the upper rotor. Plus, that air is already moving downwards pretty quickly so the lower props can only add a fraction of the thrust. It's similar to how a prop plane loses thrust as it increases speed.

You could do things like use lower pitched props on the top and higher pitch props on the bottom to help even things out, but you still have the turbulence to contend with.

10-09-2011, 06:59 AM	#21 (permalink)
60something Registered Users Join Date: Aug 2010	There seems to be two camps developing, designwise, single layer rotor array, vs stacked rotors. Any thoughts on what if any difference flows from the two approaches? It would seem single layer would give finer mixing control (with the right programming!) but it certainly ups the mechanical complexity. __________________ Schluter Champion, Kavan Allouette, TRex550E-FB, HC500SE, CloneT450pro-4bladed, Blade 400, WK 4F200, Xaircraft X650, and a CB180D, usually in a tree.

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10-10-2011, 05:06 PM	#22 (permalink)
brtmac Registered Users Join Date: May 2008	Stacked loses efficiency. The lower rotors are in the turbulent airflow of the upper rotor. Plus, that air is already moving downwards pretty quickly so the lower props can only add a fraction of the thrust. It's similar to how a prop plane loses thrust as it increases speed. You could do things like use lower pitched props on the top and higher pitch props on the bottom to help even things out, but you still have the turbulence to contend with.

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