SUBSONIC AVIATION SECRET ( part 1. of 3 )
A way to further refine traditional propellers
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Treat the blades like wings and your
propeller will
a) be grateful
b) boost your engine power
for “absolutely nothing”
c) increase top speed
d) become silent
e) save fuel
Traditional Propellers’ Efficiency by Speed Range:
Range 1.
Blades work like blades – those of a compressor. Deep blade stall, poor efficiency
Good thrust possible. Low speed.
Range 2.
Blades work like wings – high efficiency
Range 3.
Windmilling and negative thrust growing.
SUBSONIC AVIATION SECRET ( part 2. of 3 )
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Warping – Heritage of the Wrights
(continued)
Remember, the Wright brothers started really to fly when they started warping their wings.
(The Wright brothers used wing warping for roll control on their 1901 and 1902 gliders and on the successful 1903 flyer. (Wikipedia))
• The airflow followed the wing surface and got warped itself;
• As a resistance to “getting warped” the airflow pushed back, and that helped to roll and/or to stabilize the aircraft.
Some known facts and some new lessons:
A. Propeller blades work in a warped airflow;
(Warped airflow = the vector of resulting speed has a changing direction along the propeller radius.)
B. Propeller blades have a warped surface, which is fully aligned with the warped airflow around them, for maximal efficiency;
(Alignment ensures the blades can produce maximal thrust and zero blade-stall.)
C. Unfortunately “B” remains true for DESIGN SPEED only;
(As the airspeed will change the way the flow is warped along the prop-radius will change too. So the alignment with the blade surface will partially be lost.)
D. Thus for speeds other than the design speed the maximal thrust and zero blade-stall will be lost – unless. Unless the alignment between the blade surface and the airflow is (somehow, still) sustained.
E. The Solution (See next post.)
SUBSONIC AVIATION SECRET ( part 3. of 3 )
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IMPLEMENTING THE IDEAL PROPELLER BLADE
( Images in this post are all clippings from the eBook downloadable at
https://stallfreepropellers.com/ )
WARPING – HERITAGE OF THE WRIGHTS
(continued)
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G. The Solution
• All equations of geometry, which describe how the airflow speed is changing along the propeller radius, are known. That means
• we have the mathematical description of the warping airflow both along the propeller radius, and around the propeller blades. (This is a 3D system. See the insert.)
• Now the task is to create a mechanical structure – a new blade ! – which can be warped exactly the same way the airflow is warping.
• The new blade will have no exact design speed, as it will be capable of retaining full alignment between the blade surface (a 3D surface!) and the airflow, both along the propeller radius and around the blades – at all subsonic (and reasonable) values of axial speed.
H. The new blade concept has practical implementation displayed at the www.stallfreepropellers.com website. This is still a concept, but attached documentation (free eBook)
• has all details to check if the mathematical equations valid for the airflow geometry (the Simple Blade Element Theory applied in 3D) are identical with those describing the configuration (and movements too) of the surface of the new blade structure. Both radially and around the blade sections;
• has all details to carry out a
PROTOTYPING PROJECT
PROPELLER DESIGN
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The basic Blade Element Theory (BET) is applied in 3D.
The simple BET is based on a triangle of speed vectors of the airflow.
Assumptions:
1. Lift to Drag ratio is optimal always, when
Blade Angle = ( Angle of Resulting Wind + AOAopt )
2. Optimal AOA = AOAopt = a small value (about 4 Degrees), which can be neglected for a first stage design of blade geometry without a risk of any greater errors. Therefore we use
Blade Angle = Angle of Resulting Wind
3. 3D image of the vector triangles (built along the propeller radius) will always contain the 3D IMAGE OF AN IDEAL PROPELLER BLADE;
4. Surface of an ideal propeller blade is
a) a twisted (warped) surface, where the
b) degree of warping is a function of both the axial speed and the propeller RPM.
5. A propeller with ideal blades will always produce maximal thrust and efficiency, and minimal (near zero) blade stall AT ALL VALUES OF AXIAL SPEED below the sound barrier.