1164

Item 1164

DESIGN: Dragonfly ~ Rotor - Disk - Blade to Hub Clearance

Going to use dissimilar lateral cyclic to negate contact. ~ See note on 1176.html Why is this here. It should be more relevant to 1160.

Initial (approximate) Calculations:

FORM: Rotor - Disk - Interaction

The following is the vertical center-to-center distance between the centerlines of the overlapping blades. The masts' angle [V<] is 22º and the Stagger [d_s]is 2.0' (24")

The vertical distance dimension does not take into account; the teetering angle, coning angle, blade thickness, grip thickness, twist, offset or the trailing edge during a high angle of pitch.

Azimuth of Port Rotor:	Azimuth of Starboard Rotor:	Vertical Distance:	Radius of Intersection on Lower Blade:
90º	270º	4.58"	0.0"
95º	155º	4.22	2.2"
100º	160º	4.03"	4.2"
104º	164º	3.97"	5.8"
105º	160º	3.97"	6.2"
106º	166º	3.97"	6.6"
110º	170º	4.0"	8.3"
115º	175º	4. 22"	10.8"
120º	180º	4.58"	13.9"
125º	185º	5.18"	18.0"
130º	190º	6.17"	24.0"

Note the least clearance is at 105º, it is not when the blade is directly over the other mast.

The offset is 13.5". The blade attachment pin is at 20". The full blade chord starts at approximately 31"

Changing only the angle from 22º to 24º will change the Vertical Distance at azimuth 105º from 4.0' to 4.32"

Changing only the stagger from 24" to 27" will change the Vertical Distance at azimuth 105º from 3.97" to 4.46"

Changing both the above two lines will change the Vertical Distance at azimuth 105º from 3.97' to 4.86"

Look at the bottom of DESIGN: Dragonfly ~ Rotor - Disk - Blade to Blade Clearance (3 blades) to see what changes in V-angle and stagger do at blade tip.

Second (more accurate) Calculations:

Drawing:

Notes about drawing:

The 'V' angle between the two masts is 22º.

The stagger is 24". It is the distance between the two virtual teetering hinges.

The undersling from the actual teetering hinges to the feathering axis is 1.0"

The coning angle is 1.6879º.

The negative flap is -10º down from the coning angle. Note that the maximum lateral pitch is to be approximately +8 to -8 degrees. Going with -8º of maximum inward lateral flap; and with -6º of maximum inward lateral pitch.

The drawing shows the lowest portion of the blade (in red) at 0.5" below the blade's centerline.

With the port rotor at 90º azimuth, its grip will contact the top of the starboard hub (dark blue) at 3.3" out from the center of the hub. __________________________

It appears that the grips will clear the other hub at both of the curved lines between the arms. The grip passage line cuts the outer curved line in plan view but the curved line is located half way down the hub and this is radiused.

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Clearance (based on the bottom of blade being 0.5" below its feathering hinge) over the hub's arms (and yokes).

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Calculations with 8º maximum flap lateral and 10º maximum flap longitudinal.

Note that the allowable lateral cyclic will probably be a maximum of 6º (coaxial ABC was 6.25º), but the amount of flap before coming up against a hard stop or the other rotor must be more.

At azimuth 90º with precone and no flap, the feathering axis to horizon is 11.0 + 1.6879 = 12.6879º.

At azimuth 120º with precone and no flap, the feathering axis to horizon is sin(120) * 12.6879 = 10.9880º.

At azimuth 120º the flap will be 8º + (2/3 * (10 - 8)) = 8.6667º

At azimuth 120º with precone and -8.º of flap, the feathering axis to horizon is 10.9880 - 8.6667 = 2.3213º.

It looks like the blade will just kiss touch the yoke. Therefore limit the inward lateral cyclic, and if necessary increase the outward lateral cyclic.

Go with 22º V and 24" stagger. In addition, seriously consider 6 or 7º maximum flap and/or hub spring.

The actual clearance should be over the grip and the grip is higher than the yoke when it is flapped up. For 'partial' solution see; DESIGN: Dragonfly ~ Rotor - Hub - Assembly LAYOUT (w/ Flap and Lead/Lag) ~ Modifications Required

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This chart is not complete, and may not even be needed.

Azimuth:	Relative Elevation:	Azimuth of Starboard Blade:	Radius of Contact: ⁽¹⁾
90º	3.80"	120º	2.80"
95º	3.79"
100º	3.74"
105º	3.67"
110º	3.57"
115º	3.44"
120º	3.29"
125º	3.11"
180º	0.00"

(1) The radius on the starboard rotor hub that just touches the bottom of the port blade (ie. 1/2" below feathering axis). Note that this is based on the top of the hub being level (not dipping by 0.5" in the center).

Mockup:

The above-calculated dimensions can be now crossed checked against actual measurements from the mockup.

Same Page ~ Different Craft: ~ SynchroLite ~ UniCopter

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Last Revised: November 22, 2003