Deemar,
An interesting argument. We are probably talking about the same thing, but from slightly different perspectives
Let's forget the vectors since; the prop
rotor's thrust and the craft's motion will be vertical during vertical climb, and the
proprotor's thrust and the craft's motion will be horizontal during forward flight.
As you say
"It's the change in momentum that matters." Momentum is the quantity of motion of a moving object, equal to the
product of its mass and its velocity. In other word; the mass can be large and the velocity low, or the mass be small and the velocity large.
As you have said, large rotor is more efficient for hover, but as Mart has said "a more powerful engine is already required for higher speeds".
The 'geometric pitch' of the propeller must be high enough to provide the desired velocity of the craft during forward flight, however as you say, the diameter of the disk should be large to provide efficient lift during hover.
The idea of this thread is to change the 'effective' disk area between hover and cruise so that it is closer to the optimum diameters for both requirements.
In addition and as you have previously said, the proprotor will have to have collective pitch, and the pitch will be much higher during cruise.
slowrotor,
You are probable correct if the intent of this tread was that of conceiving an economical, safe and simple VTOL craft.
Perhaps I should have mentioned at the beginning that the object of this thread's concept is to consider a craft that improves on the shortcomings of the V-22.
The Advancing Blade Concept is a beautiful 'Rotor & Propulsor concept', as a contrast to the tiltrotor's 'PropRotor & Wing concept'. However, it is appearing that the ABC concept
may only be able to provide cruise speeds of 250 knots and higher if a reverse velocity blade can be conceived. At the present time, to my knowledge, any improvement to reverse flow through the blade will create a greater dis-improvement to the forward flow through the blade.
The idea on this thread is just another attempt to get a 'Free Lunch' out of Nick.
Mart,
Dave, i'm amazed Leishman find's time to write all this stuff. Paper printed off for a quiet evening...
It is a very interesting article. Maybe his students do the 'grunt work'.
At the risk of winding Nick up ~ again
, this report could have been done, and should have been done, many, many decades ago if America had not been redirected away from twin main rotors.
Dave