Friday, February 25, 2011

Introducing the Z83D Scissor Prop

Using the principles of elliptical wing design to protect lift from tip losses and vortex aero to energize flow over a sub-wing, I have invented a new prop optimized for low speed 3D maneuvers and hovering called the Z83D Scissor Propeller.  This prop is an asymmetrical 4-blade, where the leading blades are of both smaller diameter and shallower pitch.  The purpose of the two smaller, leading blades is to create some additional thrust/lift, but in a way so their vortex can be used to energize the airflow over the top of the two, larger, primary blades.   Now there is lift from all four blades, but a useless vortex is only left behind by two.



Here are some initial, empirical test results:

Prop
Volts
Thrust
Amps
T/A
 11x4.7 SF
12.6
40.6
35.4
1.15
11x5.5 APC
12.6
38.8
28.7
1.35
11x5.5 APC + 8x3.8 SF
12.6
44.3
31.2
1.42

The first installed static test shows the Z83D Scissor Prop gives a 23% Thrust/Amp boost over a similar size slow fly propeller, and a 5% advantage over the same APC propeller.  I expect greater gains when used on aircraft with a less draggy engine cowling.

The vortex aero theory behind the Z83DSP is the same used by an Eagle during low speed, high thrust maneuvering:


The Eagle splits his relatively low aspect ratio wing into a procession of high aspect ratio winglets, where each leading edge winglet's vortex rolls over the trailing winglet to energize top flow. There are two complex effects at play at once:

  1. The elliptical plan form of the Eagle's main wing and winglets reduce lift to zero at each fractal tip, maximally separating the bulk of lift from the finite wing tip, and thus, associated vortex losses.  This is the same principal used in any elliptical wing aircraft design, perhaps the most famous of which is the Supermarine Spitfire.
  2. The procession of Eagle winglets, to include several mid-span wrist winglets, use their sub-tip vortices to energize airflow over the trailing winglet.  This probably does not reduce the intensity of the overall wing tip vortex, it simply puts some portion of it to good use.  This is the same principle copied in any vortex aero aircraft wing design, perhaps the most famous of which is the greatest fighter in aviation history, the F-16.

The Z83D Scissor Prop's smaller sub-wing vortex is rolled over the top of, and thus recycled into more lift for, the trailing primary prop blades.  There is probably a more optimal alignment, diameter and pitch ratio than my prototype scissor.

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