Paul,  I've been toying with an idea for a constant speed/variable
efficiency prop.  Someone stop me if this has already been tried.

Given that:

Prop efficiency depends greatly on disk area (more area=more

efficiency)

Disk area is limited by landing gear lenghts.
A given blade twist is optimum for a certain pitch..

Would it be feasable to build a variable diameter prop?

The blade root would act like a hydraulic plunger and pressurized oil

would

control, to be conservative, a 2.5" radial blade travel.  That's 5

more

inches of diameter.  The blade twist and pitch would be optimized for
cruise.  In fact you could also make the blades twist as they

extended.  You

would of course need to couple them mechanically to keep catastrophic
imbalances from occurring.

A 76" prop for takeoff converting to an 81" prop for cruise would

gain you

14% more disk area. 84" to 89" would net you 12%.  Plus, you could

get the

root of the blade out where it could be more effective.

The only potential drawback is that unobtainium might be needed to
manufacture it.

Chris
microcosman.com

Mark Waldron wrote:

One obvious consideration: provision for landing with a failure of the prop
in the extended mode.  I guess either make sure there's enough clearance for
this one-time event with the given gear configuration, plan to land no-flap,
or just prepare for an exciting event upon touchdown.

Mark Waldron

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