1193

Item 1193

DESIGN: Dragonfly ~ Rotor - Hub - Load Distribution:

To calculate the blade generated forces on the hub components, plus to pass the force values on to the Power Train.

August 28, 2003 ~ Is there any advantage to lowering the tie-bars? December 31, 2004 It appears that the lower the tie-bar(s) the greater the deviance from the desired geometric movements.

Source of Blade Values:

The intent is to use blade generated values of ever increasing accuracy, as they become available. The sequence of the source for these values is as follows. The arrow indicates the currently used source of values

DESIGN: Dragonfly ~ Rotor ~ Hub - Blade Generated Forces - Preliminary,

DESIGN: Dragonfly ~ Rotor - Hub -Blade Generated Forces - Intermediate

A future Dragonfly page; comparable to; DESIGN: SynchroLite ~ Rotor - Blade - Composite - VR-7b - Centers, Radii & Moments

January 9, 2005 ~ See the sketch at the bottom of this page for perhaps a better understanding of the loads and moments from an Offset Teetering Rotor

Sketch of Forces Vectors and Moment Arms:

It is assumed that there is a virtual hinge just outboard of the feathering bearings.

Values for above drawing:

Symbol:	Value:	Description:
Blade Forces:
F	3,285 lbf.	Centrifugal force at 100% RRPM
T	92 lbs	Thrust at Hover
W	5 lbs.	Weight of a blade
Q	732 in-lbs	Torque delivered to one of the 6 blades
D	732/.75R=10 lbf	The profile and induced drag of one blade.
Arm Lengths:
U	1"	Undersling
d	1.58"	Vertical distance from feathering axis to tie-rod.
e	13.5"	Offset from virtual teetering hinge (center of mast) to actual teetering hinge.
r_LD	62"	Distance from flapping hinge to blade's aerodynamic center.
r_M	27.5"	Distance from flapping hinge to blade's center of mass.
β₀	2º or 1.58º ?	Coning angle, at hover.
β	12º	Maximum angle of flap.
r₁	1.5"	The horizontal distance between the blade axis and the hub head bearing.
r₂	2.5"	The horizontal distance between the blade axis and the flap/drag bearing.
d_PB	2.5"	The distance between the pitch bearing sets.

Note: The above loads are based on 100% RRPM and the craft is hovering.

The Limit Load Factor and Safety Factor are added at each specific requirement (bearing etc.).

Forces at Select Locations:

Positive values are outward, upward & in the direction of rotation.

For factors see; Limit Load Factors and Safety Factors.

States:

Q ⁽²⁾

C ⁽⁵⁾

⁽²⁾

lbf

lb-ft

lbs

lbf

Highest Thrust: (4*GW) ⁽³⁾

3,285

368

61 ?

-5

-x

Highest RRPM: (200%) ^{(3) (4)}

13,140

61 ?

-5

40 ?

Hover at !00% RRPM: ⁽⁶⁾

3,285

>61

-5

10⁽¹⁾

+2014⁽¹⁰⁾

+1418

Zero Thrust at !00% RRPM:

3,285

>>61

-5

10⁽¹⁾

1006⁽⁶⁾

1273⁽⁶⁾

At rest at 0% RRPM:

-5

-27

+54

+27

-5

Autorotation:

3,285

92 ?

-5

⁽⁸⁾

Negative G: (-0.25*GW)

3,285

-23

>732

-5

⁽⁹⁾

(1) The power will be less than maximum therefore the drag will be less.

(2) Moment about the center of the mast.

(3) At Limit Load Factor.

(5) Total, before being divided between C1 and C2.

(6) Assumes that there is a vertical hinge and thereby splits the force according to the 'U' and 'd' ratio.

(7) Assumes full torque. 298

(8) I believe that the force here will be positive; and not excessively large.

(9) The centrifugal force, due to the offset flapping hinge, and the positive pitch, even at the lowest collective setting, will resist this force from going negative. An exception to this could be a fast and excessive unloading of the rotor (bunt-over?).

(10) Shouldn't this be less than B2 because the 'pushing' of the blade is offsetting some of the centrifugal force???

Also calculate the loads on the components when the rotor is subjected to the maximum flap of 12º. Take this data from 1139.html

Notes:

The fact that the three blades are 'tied together' will probably increase the loads considerably on the flap bearing. This may, or may not?, be particularly true in respect to what the lead/lag forces are.

(4) By including a rotor governor, the LLF of many rotor hub components might be reduced from 4 to say 3, since the maximum centrifugal force will be less. This may reduce the crafts basic weight for FAR 103 compliance while adding to the Safety Weight.

Because the craft is non-certified and an ultralight perhaps the Safety Factor should be reduced slightly ???

Notes:

The offset is 13.5"

The undersling is 2.6284"

The centrifugal force is 3,577 lbs

The average coning angle is 1.47º

The flap angle is 15º

Articulated Rotor:

Moment: 3.577 lbs * 3.158" = 11,296 in-lb
Moment: 3.577 lbs * 3.827" = 13,689 in-lb
Total moment: 11,296 in-lb + 13,689 in-lb = 24,985 in-lb = 2,082 lb-ft.

Offset Teetering Rotor:

Moment: 1014 lbs * 13.5" = 13,689 in-lb
Moment: 837 lbs * 13.5" = 11,300 in-lb
Total moment: 13,869 in-lb + 11,300 in-lb = 25,169 in-lb = 2,097 lb-ft.

Back to top | Dragonfly Home Page

Last Revised: January 9, 2005