Item 1039
DESIGN: UniCopter ~
Rotor - Blade - General - SparWorking with the strength of the spar re webs and deflection etc.
Outside Helicopters:
Sikorsky ABC:
The spar thickness at the root is over 1.6" and tapers to 0.075" at the tip.
Spar Material Selection ~ from 'Development of the ABC Rotor' Presentation:
"To minimize deflections, a higher modulus material was required. As Figure 5 shows, there is little to chose among the three state-of-the-art materials (steel, aluminum, and titanium) from the standpoint of specific stiffness. However titanium does have a strength to weight advantage."
"Figure 5; Comparative Stiffness:
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Carbon Fiber Composite |
330 x 106 |
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Boron Fiber Composite |
275 x 106 |
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Steel |
110 x 106 |
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Titanium |
100 x 106 |
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Aluminum |
100 x 106 |
My comment; Carbon fiber is by far the better and pultruded unidirectional might be even better that the value shown above.
Blade Loading:
Blade forces at the elements come from:
DESIGN: UniCopter ~ Rotor Disk - Blade Forces
Material Properties:
Graphlite Carbon Rod:
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320,000 psi |
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21.4 msi |
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275,000 psi |
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20.5 msi |
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1.3 % |
Unidirectional Carbon Tape:
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Tensile Strength: |
450,000 psi |
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Tensile Modulus: |
msi |
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Compressive Strength: |
psi |
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Compressive Modulus: |
msi |
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Ultimate Tensile Strain: |
% |
Carbon Tow:
(sized with an epoxy)|
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Tensile Strength: |
500,000 psi |
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Tensile Modulus: |
32 msi |
FORM: Rotor - Blade - Spar ~ UniCopter: This form calculates the;
Notes:
The blade's radius [
Modulus of Elasticity [E] is 330,000
Pultruded:
It is claimed that pultruded carbon is 4-5 times stronger than unidirectional tape. If this is so then the amount of material could be reduced by 4. As well, the remaining material will have large centroids between the upper and lower spars, which will give even greater strength. This will reduce the material cost and the amount of machining - if it is true.
distrbution_of_thrust()
incrimental_increase_in_spar_dimensions()
Area of upper web
Area of lower web
Total Area
Distance from Neutral Axis to Extreme Fiber
Currently the sizing of the spar is based on the the width and thickness of the top and bottom flange and the centroids distance increasing at a constant rate from tip to root.
I = moment_of_inertia_for_spar()
Z = section_modulus_for_spar()
kk = radius_of_gyration_for_spar()
TD = deflection_in_beams(R, Elements)
[Source ~ MH p.239] Case 12: ~ Fixed at One End, Intermediate Load. General formula for maximum deflection at end. Y = ((W * l ^ 2) / (6 * E * I)) * (2 * l + 3 * b)
It appears that the deflection at the tip at 1G is ??" and at 10G it is ??"
Miscellaneous:
The NACA 00xx will have equal moment arm length to the upper flange and to the lower. The NACA 230xx will have a shorter moment arm to the lower flange then to the top and this might be better, since the upper is in compression.
This is a long way off. They have started to produce artificial silk and it is stated that silk is 10x stronger than steel by weight.
Other Web Pages:
Langley Tech Report:
Gretchen B. Murri, T. Kevin O'Brien and Carl Q. Rousseau, Fatigue Life Methodology for Tapered Composite Flexbeam Laminates , American Helicopter Society 53rd Annual Forum , Virginia Beach, VA, April 29--May 1, 1997, pp. 13 , Also published as NASA TM-112860. (2MB).
Format(s):
Postscript, or PDF
EVALUATION OF CARBON-ROD REINFORCED CRIPPLING STRENGTH SPECIMENS
http://techreports.larc.nasa.gov/ltrs/PDF/1999/aiaa/NASA-aiaa-99-1282.pdf
Design and Evaluation of a Bolted Joint for a Discrete Carbon-Epoxy Rod-Reinforced Hat Section
http://techreports.larc.nasa.gov/ltrs/PDF/NASA-96-tm110277.pdf
Related Patents:
US 3,943,020 ~ Filament wound blade and method for manufacturing same
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Last Revised: March 13, 2005