1220

Item 1220

DESIGN: UniCopter ~ Rotor - Disk - Blade to Blade Clearance - 4-blade Rotors

Two intermeshing rotor disks with 4 blades each.

Picture:

Front of craft

Rear of craft
Four blades per rotor ~ Maximum chord is 15" at 24" radius
Trailing edge proximity: (shown in picture) Port blade is at 300º azimuth. Starboard blade is at 345º azimuth. Pitch on both blades is about -6º, which is +6º because of the reverse velocity. This will be of interest during fast forward and autorotation.	Leading edge proximity: I don't think that this will be a problem. Look at again, just to be sure
Trailing edge proximity: Blade is at 292.5º azimuth. I.e. the trail edge is over the other hub Pitch on blade is about +18º. This can be increased to about 21º by trimming 1/2" off the top rim of the hub. This will be of interest during hover and climb.
The blade will be modified to increase the root chord, plus decrease the widest chord and move it outward.

Drawing:

This blade planform is different from that in the above picture. The final planform will probably be somewhere between the two.

From the drawing ~ The center to center vertical distance between blades, including 3º pre-cone, at the widest location of the chord on the upper blade is 5.0867". The obliquity is 9º.

Other thoughts;

Move the widest chord further out the span ??

Have separate root control and set to zero pitch on retreating blade root?

Have the blade come all the way in to the root. Make the skin out of flexible fiberglass and have the trailing root corner activated by a ring out side or inside the hub.

It looks like increasing the pre-cone and decreasing the mastVmast angle will reduce the blade-to-blade clearance. See DESIGN: UniCopter ~ Rotor - Disk - Pre-cone ~ Thoughts re Angle: Have done in FORM, below

FORM: Rotor - Disk - Interaction: This is the current thinking, re dimensions.

Inputs: The number of blades per rotor is 4, the stagger is 27", the obliquity is 7º, the precone is 4º, the decone is 0º, the disk radius is 9'-6", and the azimuth of the port blade is variable.

Output: It calculates the radius of the crossover on each blade and the vertical center to center distance between blades at this location.

Notes:

From the above form ~ using 4 blades per rotor, 27" stagger, 7° obliquity, 4º precone, 9'-6" radius, and at various azimuths. They do not include the gap increase due to the coning angle.

The vertical ctr. to ctr. distance when the upper blade is at azimuth 90º is 5.18".
The minimum vertical ctr. to ctr. distance is 3.3" at 117° azimuth. The radius is 26.0"
The minimum horizontal hub to blade ctr, to ctr. distance is 24.2" at 104° azimuth.
The port blade azimuth is 120 degrees when it is over the 27" radius of the starboard blade (the location on the starboard blade that passes over the port mast). The vertical ctr-ctr. distance is 3.32"

Azimuth of upper blade. ⁽²⁾	Azimuth of lower blade. ⁽²⁾	Distance out upper blade from center of its hub.	Vertical ctr. to ctr. distance between the feathering axis of both blades.	Vertical ctr. to ctr. distance between the feathering axis of both blades. ⁽³⁾
270º	45º	30.0"	5.18"	6.11"
285º	330º	26.9"	3.59"	4.18"
300º	345º	30.0"	3.32"	3.77"
315º	0º	42.4"	4.07"	4.07"
330º	15º	100.7"	9.71"	9.71"
330.9º ⁽¹⁾	15.9º	113.7"	10.9"	10.9"

(1) Any greater and the 9'-6"R. (114") blades do not overlap.

(2) The actual azimuth angles above are based on taking the FORM's inside-forward (breaststroke) rotation angles and subtracting 180º to get the azimuth of the blade for outside forward.

Does the above give enough clearance??? NO A little Curved Anhedral should/would be nice

(3) Decone set at -2º from 0º, and precone increased by 2º to 6º. These values will be similar to those that would come from anhedral.

Additional Notes:

Note: The height of the rotor hubs will be greater than the height of the blade, as shown in its cross-section.

Interaction on Full Scale Mockup:

Parameters: March 25, 2004 ~ Radius = 108", Root chord = 17", Tip chord = 6". On drawing 0884.dc

Azimuth of Port Rotor Blade:	Azimuth of Starboard Rotor Blade:	Climb: (> + pitch)	Autorotation: (> - pitch)
180.0	225.0	OK	OK
191.25	216.25
202.5	247.5	(1)	OK
213.75	258.75	(2)
225.0	270.0	(3)	OK
247.5	292.5	(4)	OK
270.0	315.0	OK	OK
292.5	337.5	OK	(5)
315.0	360.0	OK	OK
337.5	022.5	OK	OK
360.0	040.0	OK	OK

Trailing edge of starboard just not touching leading edge of port. Check either side. Trim 7" off the root of the leading edge may do it.

Trailing edge of starboard is hitting the extension of port hub. Trim 7" off the root of the trailing edge.

1" on port leading edge AND 1" on starboard trailing edge. Check either side. Trim 9" off the root of the trailing edge. or Trim 3" of the root of the leading edge and trailing edge.

Conflict with starboard trailing edge and port hub. The intended lowering of hub by 0.5" should solve this. Check either side

Serious interaction between port leading edge and starboard trailing edge. Trim 9" off the root of the trailing edge.

Trimming 8" off the root of the leading and trailing edges.

The angled trim off of the leading edge and the trailing edge may have to be the same so as to not change the aerodynamic pitching force.

June 22, 2005 ~ Consider having the chord at the very root as great as is possible. In addition have the root pitch axis at 50% of chord. This will allow the root to contribute more toward the lift, be it advancing or retreating.

Notes on the Airfoil Planform on the Drawing:

R = 9'-0" (108"), plus 3" tip

Chord at root = 15"". Shape is circular. OD of pultruded carbon spar is 2.50".

Chord at tip = 5.8124". Airfoil at tip is NACA 0006. Thickness at root is 0.3487".

Widest physical chord is 10.9166" and it is located at 49" radius. This is not very wide, even for four blades.

Thickness increases from 0"0 ID at tip to 2.0" at root therefor the change in thickness is approximately 2.00" / 108" = 0.0185" per inch of span.

The thickness at 49" span is 0.3487" + (0.0185 * 59) = 1.4402"

1.4402" / 10.9166" = 0.1319 Therefor the airfoil at 49" radius is NACA 0013.19

The maximum allowable angle on both blades appears to be 25º when the mast to mast angle is 18º, see drawing 1220.dc. Rounding the intersection of the trailing edge lines will give a little more.

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Last Revised: February 6, 2007