1408

Item 1408

DESIGN: SynchroLite ~ Rotor - Disk - Hub Spring Induced Lead/Lag Mitigation

Preamble ~ Points Related to the Teetering Rotor:

Neither the amount of the undersling nor the angle of pre-cone causes Cyclical Coriolis Effect during hover and vertical climb; if the rotor-disk is normal to the mast.

If the above disk is tilted so that it is no longer normal to the mast then cyclical Corollas effect (Hooke's joint effect) will be experienced.

If the Hooke's joint is then replaced by a true constant velocity joint, the cyclical Corollas effect should be eliminated. This is because the 'theoretical mast' of the rotor is now always normal to the disk.

If a hub spring is then installed into the rotor its resistance to the tilting of the rotor-disk will;

a/ Provide a moment between the rotor and the fuselage for better control ~ GOOD
b/ Introduce cyclical Corollas, because the blades will bow up and down and the tip-path-plane will no longer be normal to the 'theoretical mast'. ~ BAD

Increasing the rigidity in the structure of the blades will allow 4.a/ to take place while reducing the ability of 4.b/ to take place. ~ VERY GOOD

Concern:

Even with extremely rigid blades (Absolutely Rigid Rotor) there will still be some out-of-plane flexure within the blades.

Objective:

This page covers a potential means of overcoming the lead/lag that will result from any Corollas effect resulting from this blade flexure. The objective is to significantly reduce the changes in the distance between the axis of the 'theoretical mast' and the blade's center of mass, as the blade rotates around the mast.

Mitigation of Flap Induced Lead/Lag:

To overcome this the rotor has a pre-cone angle that exceeds the normal coning angle. The mass in each blade will move in the out-of-plane direction during maneuvers, but this movement will normally be between this pre-cone angle and the angle normal to the 'theoretical mast' (90). However, the mass will not move radially in respect to the centerline of the mast. This is because during non-extreme flight maneuvers the blade only bends in a downward direction. As it bends down from the precone angle the curvature of the bend keeps the hub axis to mass distance (radius) a constant.
In other words; The hub spring will resist the upward teeter of the hub at a specific azimuth, say 90º, therefore the increased thrust of the blade at this azimuth will cause the blade to flex upward. The whole blade will not have flapped up, but the tip will have 'bowed' up. This will reduce the distance between the tip and the centerline of the 'theoretical mast' (forget the mast's centerline) and this will result in a Cyclical Coriolis effect. The act of blade 'bowing' instead of hinged 'flapping' should mean that the center of mass has not moved inward as much. In addition, increases in blade rigidity will reduce the 'bow'.

Sketch:

Notes:

Pre-cone = +3º

Coning angle in hover + 20% = 1.8º

Range of flapping (bow) at location of blade mass, the tip can and will be greater) = 3º, with perhaps a 1 or 2º exception during extreme conditions. (i.e. No detrimental effect resulting from overshoot.)

It must be noted that the +/- 1.8º is the flap (blade bow) and that it is in addition to the teetering.

Blade normally operates with negative bow

An advantage of large pre-cone is;

higher blade tips when the craft is on the ground.
Greater blade clearance over the other hub.

The greater the blade's rigidity the less the inplane deflection 'bowing', and this is good.

Adjustables:

Precone angle

Tip weight

Taper

Twist

Blade stiffness

RRPM (slightly)

More Notes:

Taper and twist MAY help by having the center of mass and lift closer to the centerline of the hub to begin with.

Possible or partial solutions, which is intended to reduce the amount of dimensional change between the CG of the blade and the output axis of the CVJ hub.

It is based upon the fact that the blades 'bow' instead of 'flap'. In other words, the out-of-plane bending takes place much further out from the hub. In addition, make the pre-cone angle greater then the hover coning-angle.

With a conventional rotor, which has a cone and pre-cone of 2º, left cyclic will cause; the Port tip to lower and move outward slightly, and the Starboard tip to rise and move inward slightly.

If the natural coning angle during hover is 2º, consider giving the rotor a 4º pre-cone. Left cyclic will cause the Port rotor to provide less thrust. The tip will 'bow' down but because its initial 2º is already below the pre-cone angle of 4º the tip may move inward, if it moves at all in the inplane direction. The Starboard rotor tip will 'unbow' from its 2º position to the 4º position and hopefully it will not move at all in the inplane direction.

The reduction of thrust by the Port rotor will allow the Starboard side of the hub to teeter up a bit more. This should reduce the 'bow' the starboard blade slightly. ~ Good.

The blade can flex out-of-plane so why can't it flex slightly inplane (w/o any coupling?).

Applicable to: SynchroLite ~ Rotor - Hub - 3-blade - Constant Velocity Joint & Hub Spring

Concerns:

That of pitch change on a 'bowed' blade

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Initially displayed: November 4, 2004.. Last Revision: January 10, 2005

The above utility invention is openly and publicly disclosed on the Internet to negate an entity from patenting it, to the exclusion of all others whom may wish to use it. ~ Reference patent law 35 U.S.C. 102 A person shall be entitled to a patent unless - (a) the invention was known ... by others in this country, ..., before the invention thereof by the applicant for patent.