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#### manolis

##### Well-Known Member
Hello Dusan.

You write:
"Automatic variable pitch propellers were developed since 1930, based on centrifugal/aerodynamic forces; Why reinvent the wheel? "

At https://www.pattakon.com/Pitch/US_2416516_Aeromatic.pdf it is the US patent granted for the Aeromatic propellers:

The Aeromatic design seems too heavy (count the number of heavy bearings required) and too complicated for the Portable Flyer.

This is why.

Thanks
Manolis Pattakos

#### Steve C

##### Well-Known Member
Not only that, but the blades are very heavy. I've had one in my hands.

I do like the idea though.

#### jedi

##### Well-Known Member
Can any one give a simple explanation of how the Aeromatic prop functions?

#### BJC

##### Well-Known Member
HBA Supporter
Centrifugal force of the weights creates a force that balances against the aerodynamic force on the blade.

BJC

#### manolis

##### Well-Known Member
Hello all.

The following explain how the PatPitch works.

Starting with a regular tetrahedron (Fig. 1)

a wire-frame is formed following four from its six edges (Fig. 2).

A characteristic of the tetrahedron is that each pair of “opposite” (non intersecting) edges are skew lines.

Looking from a viewpoint on the line connecting the midpoints of the AC and BD line segments, the angle between the edges AC and BD appears orthogonal (90 degrees, Fig. 3):

In Fig. 4 two collinear forces F and –F load the pair of skew edges / arms AC and BD of the wire frame of Figs. 2 and 3; the wire frame is considered inflexible.

With the edges / arms AB and CD of the wire frame being flexible, Fig. 5 shows the deformation of the wire-frame due to the forces F and –F of Fig. 4.

Looking from a viewpoint on the line connecting the midpoints of the AC and BD line segments, the angle between the edges AC and BD is now far from orthogonal (it is shown as 75 degrees); that is, the loading of the wire frame by the F, -F forces causes an angular deformation.

The line segment AB connecting the ends of the one flexible arm and the line segment CD connecting the ends of the other flexible arm are skew lines.

When looked from a viewpoint on the line MN connecting their midpoints (M is the midpoint of the line segment AB, N is the midpoint of the line segment CD), they form a wide (substantially different than zero) angle.

Exploiting this kind of angular deformation, the propeller of Fig. 6 is made (the blades are properly sliced / cut to fit in the drawing).

It comprises two wire frames (as those of Figs. 2 to 5, red in the following animation) and two blades.

Each wire-frame is secured by one of its arms on the propeller shaft, and by the opposite (skew) arm on a blade; the remaining pair of “free” flexible arms of the wire-frame gives angular flexibility to the connection between the propeller shaft and the blade.

Compare the “mechanism” of the Aeromatic propellers with the “mechanism” (?) of the PatPitch propeller, their weights, the space requirements, their costs, etc...

And think the advantages the PatPitch propellers can bring to Flying Devices like the Ehang 841 (here are the proppellers they used, the older design at left, the last design at right):

the air taxis in general, the drones (big and small ones), etc, etc.

Thanks
Manolis Pattakos

#### WonderousMountain

##### Well-Known Member
Your torsion bar autospring is very interesting, and