1355

Item 1355

MAKE: UniCopter ~ Rotor - Blade - NACA 00xx - Spar - Root Flange

Overview:

XXX

Drawing:

This drawing is currently a portion of the drawing on, DESIGN: UniCopter ~ Rotor - Blade - NACA 00xx - Profiles (x-sections) It is only partially completed.

The thinking is to make a male part, then female mold(s), then insert an uncured mixture of chopped carbon and epoxy into the mold. Perhaps a small amount of filament winding can be included. The part cannot be made from aluminum.

It will be rotated 22.5º so that it can be split vertically, with four bolts on each side.

Drawing is probably to be revised. See this pages starting notes.

The following two pages will have pictures that are somewhat related to this spar root. DESIGN: UniCopter ~ Rotor - Blade - VR-7mod - Spar, and pictures of the Bo105 blade root on DESIGN: UniCopter ~ Rotor - Blade - General - Root

Bill of Material 1355

This page is associated with the spar on pages 1082.html and 1054.html.

New Thoughts related to decreasing the length (spanwise) of the bolts and the wrap around the bolts: October 14, 2005

Concern; The wrapping of all the spar's tows over the root pins will result in an excessive length on the span axis at the location of the bearings.

The centrifugal effect is less than normal because of the slower RRPM. Therefor the spar can provide in-plane and out-of-plane strength without having to have all the tows go over the root pins and contribute resisting the centrifugal effect.

Re the mockup: the plasticine has been removed and the curvatures on the particleboard changed. It appears that with different radiusing of the particleboard the tow lay-up can move out from the pin centerline or inward toward the pin centerline.

The spar - root flange might be further reduced by having the first layer of tow not wrap around the pins but wrap across the root of the spar and return to the tip on the other side. There would have to be a rootward extension of the flange at the center so that the opening would be left for the torque tube shaft.

Once the spar was cured some of the root end of the wrap around the pins could be ground off to reduce the spanwise length of the root wrapping. This weakening of the centrifugal resistance but cutting some of the tow ends is probably not a concern.

Notes:

Think about how to put a cap over the bolts and threads. This cap is intended to take the forces out to the rim of the spar so that for any radial moments the moment arm from bolts to rim is as large as possible. This cap may be combined with the pitch arm.

The ID circumference at the root is 2.5 * 22/7 = 7.85". The OD circumference, with a 0.25" wall thickness, at the root is 3.0 * 22/7 = 9.43". The area of carbon thread at the root is ((3.0 / 2)² * 22/7) - ((2.5 / 2)² * 22/7) = 2.16 sq-in.

Alternatively;

The ID circumference at the root is 2.5 * 22/7 = 7.85". The OD circumference, with a 0..1875" wall thickness, at the root is 2.875 * 22/7 = 9.03". The area of carbon thread at the root is ((3.0 / 2)² * 22/7) - ((2.5 / 2)² * 22/7) = 1.58 sq-in.

The width of the threads per layer on each side of the pin is 0.4911'. Therefore the number of strands per pin is 0.4911" / 0.0238" = 20.6

Loading on Bolts:

Note that the loading is mainly centrifugal force. The radial bearing(s) will take most of the thrust and lead/lag.

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.

1/4" AN bolt; S = F/A; F = S x A; F = 125,000 psi for an AN bolt * 22/7 * (1/8)² ; = 6138 lbs.

6,1381 lbs. x 8 bolts = 49,107 lbs

NAS 1103 - NAS 1106 have a minimum tensile strength of 160,000 psi. This will give 49,107 * (160/125) = 62,875 lbs.

The bolts may have to be increased in diameter. All of the loading cancellations MUST be checked and revised.

Areas of this flange must be higher where there is no carbon tow so that the bolts can be fully tightened.

The bolts must be separated from the carbon tow [For more detailed information see ~ FWCS p.9-17] and this will consume a portion of the critical space.

To sum the moment arms, in the flapwise direction; for radial loads on bolts:

		Upper - Semi circle:
	Location of bolt:	Vertical distance between bolt and rim directly below
	Top Center	2.1875" * 1 bolt = 2.1875"
	22.5º from top center	1.7228 * 2 bolts= 3.4456"
	Sum:	5.63"

Ultimate Radial moment = ????? = ???? lb-in. (???? N) ~ from DESIGN: UniCopter ~ Rotor - Disk - Blade Forces I do not think that this has yet been revised.

The following has to be reviewed and revised or eliminated.
Thoughts re Construction of Spar:

Does cured epoxy have any flex? Re slightly changing the curvature of the curve for perfect fit.

Have more loops over upper bolts than quarter ones and side ones.

Winding about pins:

Tow:

See; OTHER: Composite - General - 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.