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Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
Patrick wrote ...
ok lets consider this a reduced complication scenario.
Each blade is a span, attached ridgedely at one end. and prgressively lifted at the tip, with maximum deflection and local force at the tip.
if considered as above, i should be able to predict "upward" propeller force. if i build a span on my work table, and hang lead weights i should find both breaking and deflection measurements. This of course ignores radial "throwing from the hub" force.
the phrase "exploding from the hub force" also works nicely.
Centrifugal forces should help us here.
The 'forces in a beam' thing will give us the forces in the blade. At hover, total force on each blade is equivalent to total mass divided by number of blades, etc.
Not sure if this 'bending moment and shear force' calculator will be useful, but it looks like it might be worth trying. There's plenty more tutorials on this stuff out there.
Registered Member #3414
Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245
I just want to expand on a point I made above regarding NACA profile or constant section thin airfoil.
Having given this some more thought, I've realised that the typical NACA section used for traditional 'copters was probably chosen to facilitate construction with materials available at the time, ie a steel beam was common in these designs, with other materials. The steel was for strength.
This type of construction necessitates a profile similar to a NACA profile.
If modern materials allow a constant thickness thin airfoil using laminated CF, while maintaining the required strength, then a constant thickness thin airfoil section 'should' be more efficient than a typical NACA profile.
I think the rest of the theory still holds, ie greatest efficiency is achieved just before anything goes supersonic, assuming we do the sums correctly.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
ive made some mods and relearned some 3d tools in autoCAD. Ive made progress on the 14" prop drone which will be flying in 1-2 days.
Ill print a hub and 4 inches (2 inches to the left and right) just to get some lessons learned. With these big or intricate builds, the first few attempts often "fur-ball" on the table.
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Propeller Physics and VABs Program.
