Item 1070
MAKE: UniCopter ~
Rotor - Blade - NACA 00xx - Spar - RootThis page is being replaced by;
MAKE: UniCopter ~ Rotor - Blade - NACA 00xx - Spar - RootThis page is associated with the spar on pages
1082.html and 1054.html.
Drawing:
There is a mockup of the threading of the top semicircular arraignment on
DESIGN: UniCopter ~ Rotor - Blade - VR-7mod - Spar, and pictures of the Bo105 blade root on DESIGN: UniCopter ~ Rotor - Blade - General - Root
Half circumference ie 5.1603". At NACA 0021, which is approximately 12" from the pins, the chord is 8", which mean that the front 25% is 2". Actually, it is slightly more because of the curvature. This means maybe that the spar can be about 4" wide at the root.
The pins are at 15º intervals therefore the carbon fiber width it the ID> of the pin holder plate is
5.1603" / (180º / 15º) = 0.4300". The number of strands per pin is 0.4300" / 0.0238" = 18.
To sum the moment arm lengths, in the flapwise direction, of the two alternate pin arraignments:
|
|
|
Upper - Semi circle: |
Lower Curve: |
|
|
Location |
Vertical distance |
Vertical distance |
|
|
Center |
2.13" * 1 = 2.13" |
1.67" |
|
|
1st from center |
2.05 * 2 = 4.1" |
1.63 |
|
|
2nd from center |
1.84 * 2 = 3.68" |
1.52 |
|
|
3rd from center |
1.5 * 2 = 3.0" |
1.32 |
|
|
4th from center |
1.06 * 2 = 2.12" |
1.03 |
|
|
Sum: |
8.58" ~~ 15.03 / 9 = 1.67 avg. * 2 = 3.34" |
7.17" |
The circular arraignment will be the strongest.
Loading on Bolts:
Ultimate Radial moment = square root (4,5122 + 42,8462) = 43,082 lb-in. (191,638 N) ~ from DESIGN: UniCopter ~ Rotor - Disk - Blade Forces
AN bolts have a minimum tensile strength of 125,000 psi.
NAS 1103 - NAS 1106 bolts have a minimum tensile strength of 160,000 psi.
5/16" AN bolt; S = F/A; F = S x A; F = 125,000 psi for an AN bolt * 22/7 * (5/32)2 ; = 9591 lbs.
9591 lbs. x 9 bolts * 3.34" [circular arraingment used] = 288,305 lbs
NAS 1103 - NAS 1106 have a minimum tensile strength of 160,000 psi.
All of the loading cancellations MUST be checked and revised.
Areas of metal must be higher where there is no carbon so that the bolts can be fully tightened.
Thoughts re Construction of Spar:
The top and the bottom flange are produced separately. See:
DESIGN: UniCopter ~ Special Tool - Rotor - Blade - SparTape Lengths:
(if tape were to be used, which it is not)If the blade has a span of 8'-6" then the longest tape will be about 17'-3" long.
If the tape has a thickness of 0.0013" and the blade thickness increases by this amount for every 3.5" movement toward the root then each tape will be 7" shorter than the previous one.
Heat Bar Profile:
Not used.The heat bar to have a spiral profile so that it can be used an all span locations by shifting it slightly in a chordwise direction.
The root end will have an outside radius of
2.38"/2 = 1.19" and this will have a circumference of 180º.The largest radius will be at the back of the spar at the tip end. It will be 51.2686"
Does cured epoxy have any flex? Re slightly changing the curvature of the curve for perfect fit.
Cut and remove the cross threads from the unidirectional prepreg after it has been placed under tension. This should give straighter threads and a therefore stronger spar.
Have more loops over upper bolts than quarter ones and side ones.
Winding about pins:
Tow:
Layers:
If the spar at the root is 4.382" wide and the diameter of a tow is d = 2 x root(A / pi) = 0.0268".
There will be 4.382 / 0.0268 = 163 tow. 1773 / 163 = 11 layers.
High Stiffness:
High Modulus. The stiffness of steel is only 29 msi
Spacer: to take clamping pressure:
Outer ring around wound pins, with saw tooth inner diameter. Epoxied into place.
Or instead of one ring, use10 identical segments (wedges).
Notes:
Consider affixing tabs to the inside of the spar to hold the spar while grinding it's sides. Then grind the two sides of the spar to size. Then grind the inside of the spar to size, removing the tabs as well.
Weigh all 12 spar-halves to make sure that they are identical.
Balance all 12 spar-halves to make sure that they are identical.
Check the natural bend to make sure that they all are identical.
Back to top | UniCopter Home Page
Last Revised: June 21, 2004