Propeller Structure Inspired by the Blade Element Method of Design

Blade Skeleton Motion Cycle (from feather to max twist)

Above, controlled deformation of a Stage 1. Design propeller blade is shown

(Skeleton parts simultaneously rotated around two perpendicular axes)

Blade Element Fig. 1.

Speed vectors on a propeller blade section – basic arrangement according to the Blade Element Theory

Blade Element Fig. 1.

Blade Element Fig. 2.

Vector arrays

Blade Element Fig. 2.

First an array of vector-triangles is built along the propeller radius for one value of the axial speed. Then another array for a different speed – and so forth for several values. A pattern will appear. This pattern can be emulated by elements (rods) of a blade skeleton.

Blade Element Fig. 3.

Blade design

Blade Element Fig. 3.

In the above manner a blade skeleton of pivoting rods is built, which is capable to retain similarity of blade geometry to the geometry of arrays of the vector-triangles throughout their motion.

Smart morphing propeller blades reshape propulsion characteristics

By using special blade geometry, it is possible to build fans and propellers that have, instead of one, several design speeds. By adding the classic variable pitch technology, the resulting efficiency curve of such fans and propellers can be made quite flat (which is good) and – low (this is bad). Going somewhere below 80%. With most part of the chart staying below 60%.

Thus, the working speed range is made wider, with the price paid in the loss of a single optimal speed. Forget about the 90% plus efficiency peaks of propellers with clean blade geometry.

The conceptual Stallfree technology makes it possible to retain the clean blade geometry (of either fans or propellers), throughout the whole subsonic speed-range, and – mainly – to keep the peak value of efficiency. The expected (resulting) efficiency curve will be as flat as ever – but this time with a plateau spanning high, near the optimum level.

https://www.youtube.com/watch?v=i-6cRVGvFas
https://youtu.be/i-6cRVGvFas

Known fact:
· Traditional propellers’ working range becomes significantly wider if they are installed and used in contra-rotating arrangement.
But:
· Contra props are noisy.

„… Contra-rotating propeller configuration is an exceptionally complex design case, concerning its acoustic prediction…”

„Since the late 1970’s there were initiatives of developing prop-fans, mainly due to their superior fuel efficiency compared with jet and turbo-fan engine. One of the major flaws with prop-fan is their acoustic signature.
The high noise level …”

„… The high noise level imposes restriction on using prop-fan both due to its ground acoustic footprint and high cabin noise level.
Nowadays … „

„… Nowadays with the renewed interest with prop-fan and open-rotor configuration, the goal of designing efficient, practical prop-fan, with low environmental impact is still relevant.”
Ohad Gur: Toward Optimal Design of Contra-Rotating Propulsion System – Practical Acoustic Analysis (https://www.researchgate.net/publication/339659399_Toward_Optimal_Design_of_Contra-Rotating_Propulsion_System_-Practical_Acoustic_Analysis)

Of course, tests and measurements will be necessary, but still, there are strong chances the SFP will be quieter than the traditional contra-rotating propellers:

1. Due to higher predicted efficiency there remains less energy for the losses and (among losses) less energy to be converted to noise;
2. To achieve wider working range SFP-s don’t have to be used in contra-rotating arrangement – which is inherently prone to high level of noise;