I have been trying to evaluate the stress on aluminium propeller:
Diameter: 78", 2600RPM
Have fed load numbers from here, applied distributed mass model onto the blades.
Static Thrust (2600 rpm):
MT 2-blade, 83" composite, 920 pounds
MT 3-blade, 80" composite, 900 pounds
McCauley 2-blade, 82" aluminium, 860 pounds
McCauley 3-blade, 78" aluminium, 825 pounds
The results are rather scary - 30 MPa out of 55 max, for 6061 class Aluminium (the visual deformation is increased 20x for better representation), resulting in +-1cm vertical bending.
Is this normal?
Is there any info on industry's practice for safety margin (numbers show its less that 50%)? Or any kind of test procedures applicable to manufacturers?
The shear stresses are negligible - 150 Pa out of 150 MPa
The two propeller case is really scary looking
Below is a distributed mass (375Kg) - 80% of Max. yield stress
And centrifugal force - over-stressed by 200%:
Finally, a combined non-Linear analysis (incl. torque) - over-stressed by 250%: (notice that everything not in blue will bend and likely crack, with only the blade tips surviving the torture)