New Counter-rotating propfan


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26 May 2006
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Rolls-Royce's jet engine book that is available online on scribd here
notifies how propfans especially have good use from counter-rotating since the load factor per turbine (propfan's turbine) stage can be high then, meaning you only need a single turbine stage per "prop" and it gets simple, light and reliable.
Scimitar sweeping the blades, plus forward fan blade vortex recovery in the aft fan by using forward swept aft fan blades?
Read the link that he found the images from. The design of the blades as shown negates the need to use a fan shroud. It has many of the advantages of the ducting without the ducting. It's quite an interesting concept.
An IDBP would be based on the same
principles as those of an IDP (Inherently Ducted Prop-fan), except for
one major difference: In an IDBP (Inherently Ducted Bi-prop), to enhance
structural integrity, pairs of the
blades of the downstream propeller
would be connected by the winglets. This
arrangement is particularly suitable for
high solidity installations and can reduce
overall weight and drag as compared to a
rotating shroud concept.

From Hesham's NASA link:-

It's a fantastic idea to add winglets to prop blades (perpendicular to the plane of the disk) but this could be applied to all sort of props including helo rotors. But I don't like the idea of joining the blades with the winglets so much as this would rule out any possibility of viable pitch blades but that always seems to go once a prop becomes a prop-fan or ducted, for no adequately explained reason.

Very interesting find none the less.

Cheers, Woody

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