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Post originally shared at the Vertical Flight Society’s forum on 23 July 2024

More about tiltrotors

Post originally shared at the Vertical Flight Society’s forum on 27 June 2024 (Word document shall be saved to disk in order to have the GIFs run.)

Blade Twist Control

BLADE TWIST CONTROL OF THE PROPELLERS

All the stiff bladed rotors and propellers of today’s aircraft are held hostage by the phantom of DESIGN SPEED. A single speed value, or – for the variable pitch propellers – a narrow speed range where (and only there!) operation without heavy blade stall is possible.

In reality, when you fly speed must change. That is why most rotors and propellers work with significant blade stall, and turn much of the precious engine power into losses.

For most people aviation is a synonym of loud and costly business, where you must pay dearly for the privilege of flying.

A new technology may change all this by eliminating much of the blade stall, and promising some great improvements in rotor/propeller efficiency.

Maybe it is just

TIME TO FLY STALLFREE !!

Even the finest variable pitch propellers tend to become noisy at low speed, and lose thrust at high speed.

Watch the GIF to see why and how this happens :

… or download better quality:

https://onedrive.live.com/?cid=C06DC4A61754F5C0&id=C06DC4A61754F5C0%219926&parId=root&o=OneUp

Scanning the axial speed range of a traditional propeller – download GIF scenario here: 

https://stallfreepropellers.com/wp-content/uploads/2021/08/GIF-Scenario__FN_Flight_XXXIV__-1.docx

Conclusion:

In order to keep full alignment between the resulting wind and blade sections along the whole propeller radius, for all (!) values of the cruising speed, blade surface must twist (not rotate), geometrically following the same function that the vector field follows.

Such twisting means a controlled deformation that widespread blades are not capable of.

Only special morphing blades are suitable.

Those manufactured using the Stallfree Technology.

New Propeller Concept Can Yield Also High Profits. Prototyping Needed. 

Here is a new concept for prototyping :

— unmatched efficiency, speed-range & silent operation are part of the promise ;

— simple math of blade motion & geometry both reduces risk of failure and strengthens chances of success.

Documentation is available for download below.

Get the eBook here :

Technically there are three options to download the eBook. For easy handling and reading get a PDF copy here.

For high quality graphics there are two more options to download the eBook in PPT format. Choose the one more suitable for your computer (The end result in both cases is the same zipped bundle.) :

Standard ZIP file

https://1drv.ms/u/s!AsD1VBemxG3AzTc_E9kRmYLl2vRj?e=9MN8fV

Self-extracting ZIP file

https://1drv.ms/u/s!AsD1VBemxG3AzThCI4S5rO8MwNpW

There are 21 PowerPoint files packed in the bundle. Unzip them into the same library. To start the eBook you shall pick and open the file named “StallFreeProp_Front Page.pptx”. It has an active Contents list consisting of the links pointing to the respective chapters. Use this list to go through the eBook.

(Please contact if any problems occur during download. There should not any.)

. . .

Variable blade twist of rotors and propellers – implementation of an old wish for propulsion in subsonic aviation.

Download better quality:

https://1drv.ms/i/s!AsD1VBemxG3AziogijkzyUx98oqO?e=kg7dKb

HOW EXACTLY THE BLADES OF A PROPELLER SHALL TWIST?

THEORETICALLY. TO ACHIEVE BEST (*) THRUST AT ANY SPEED.

Imagine a working propeller. Observation point is rotating in synchronism with the blades.

One blade is selected. Theoretical blade surface is represented by a set of red bars, all of which are hinged at the axis of rotation of the propeller. This particular arrangement allows all the necessary deformations the blade surface has to be subjected to in order the sections remain aligned with the direction of the resulting wind, while the axial speed keeps changing vigorously. Maintaining this alignment will provide the best (*) thrust at any axial speed.

To avoid clutter AoA is not shown in the chart. (Optimal AoA is a relatively small value (= (4° ±Δ) ), therefore it is possible to graphically neglect it without losing basic correctness of the chart.)

(*)        “Best thrust” means the greatest possible thrust with the lowest drag. Blade sections must work at their maximum Lift to Drag Ratio point. Thus, the propeller itself will work at its maximum efficiency level.

Variable Blade Twist is Next Level Sophistication in Propeller Technology!

Variable Twist is a Morphing Blade Propeller Technology. It helps to

(1.) increase top speed of the aircraft;

(2.) maintain improved propeller efficiency both at low and at high speed;

(3.) expand range of electric aircraft;

(4.) make operation less noisy.

See a new FB post here:

https://www.facebook.com/Stallfree-Propellers-100452335016157

Morphing Blade Propeller Concept

Technology to Improve Efficiency of Aviation Rotors / Fans / Propellers

Works by Reducing Turbulence Caused by the Propeller In the Airflow (Slipstream)

Morphing Blade Propellers

Stage 1. design

Compatible (can be integrated in present day constant-speed units)

Concept ready for prototyping (Description exists, complete with drawings and mathematical support)

Public (presented at the www.stallfreepropellers.com website; commercial use tied to license)

Stage 2. design

Further increases flight efficiency (fuel economy & silent operation)

RPM reduction even more significant   

Thrust vectoring support improved / enhanced 

Electric drive preferred  

Requires modification of the airframe

Not compatible (cannot be integrated in present day constant-speed units)

Concept unfinished (main features are identified, mathematical support and machine design incomplete)

Not public

A Game-Changer

. . .

FB https://www.facebook.com/Stallfree-Propellers-100452335016157/

Morphing cycle of the blades :

Proven & Supported Mathematically

Ready for Prototyping / Implementation

Applicable to

– traditional propeller propulsion systems ,

– turboprops ,

– turbofans .

In contrast to the monolithic blades of recent propellers application of TORSIONAL or MORPHING blades is proposed.

Displacements of all parts involved in the blades’ morphing process are performed

a) during the undisturbed rotation of the propeller,

b) in accordance with functional necessity and/or the pilot’s will. (It is understood the actuator mechanism is controlled by the pilot and/or by an optional automated control system.)

The full morphing cycle of the blades, going through all possible phases of the process, is shown in the below GIF:

Blades have a skeleton and a skin. Skeleton is a set of masts – massive cylindrical or tapered rods made of carbon fibre.

https://1drv.ms/b/s!AsD1VBemxG3AzVAR7g1DPMF80nUX?e=4effCk

These propeller/fan blades twist – not just rotate :

End-product is a kind of wide-range variable pitch propeller.

Given the power and strength of the aircraft with Stallfree propulsion

the whole subsonic speed range can be flown

with the same propeller,

having both a good climb rate and top speed of about 0.8 Mach.

All this at a propeller-efficiency close to its maximum value.

Reasons why the Morphing Blade Propeller / Rotor Family is

Optimal for Tiltrotor Application  

Stage 1. design

1./ Reduced RPM propeller

Noise and vibration down.  

2./ No VRS

No Vortex Ring State happens to morphing blade propellers, as also hover (zero axial speed) is part of the normal speed range of such rotors.

For VRS to form, stall at the base of the blades (in the middle of the rotor disk) is required. These props are free of blade-stall along the whole radius, at any speed below 0,8 Mach.

Stage 2. design

1./ RPM reduction even more significant   

2./ No VRS

(Same as at Stage 1. design.)

3./ No Retreating Blade Stall

Stage 2. design of the morphing blade propeller, physically eliminates the option to form Retreating Blade Stall.

To ensure you receive the free eBook with concept, mathematics, and drawings please, send a message! Comments are appreciated too.

Thank you!

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