1494

Item 1494

DESIGN: Single-Bladed All Electric Rotor- Rotor Hub - Delta3 by Tipping of Hub

Notes: ~ It looks like delta3 will be a disadvantage in respect to drag induced vibration.

See following remarks in red italic.

I assume that the (profile + induced) drag of the blade and the (profile) drag of the counterweight can be balanced for one specific flight condition; for instance ~ hover at gross weight. However, with higher angles of attack the drag of the blade will exceed the drag of the CW, and with low angles of attack it will be less.

Based upon the imperfect criteria that;

The flap angle exactly duplicates the pitch angle but 90º later, and
The angle of attack has a fixed relationship with the pitch

I hoped that the lateral weight offset of the blade-CW unit would counter the increase force of drag. Unfortunately, the above two points are not true and worse yet, the lateral weight shif is in the opposite direction of what is desired..

Objectives:

To reduce the fast response of teetering rotors on very light helicopters.

To offset the additional drag of the blade when it's pitch is high. In other words, minimize the 1P vibration due to unequal drag between the blade and the counterweight. This may be the opposite of what is desired if the delta3 is setup to remove pitch as the blade flaps up.

Assumptions:

That the greatest positive discrepancy between blade drag and CW drag will be experienced when the blade's angle of attack is high.

That the high angle of attack will be experienced when;

The pitch-angle is constantly high (vertical climb).
When the pitch-angle is cyclically increasing (forward flight).

Situation 1. can probably be satisfied by having the centroid of the blade offset from the mast at an azimuth 90º ahead of the blade.

Situation 2. can probably be satisfied by having the centroid of the blade offset from the mast at an azimuth 90º ahead of the blade's maximum pitch azimuth. Not the blade's maximum flap azimuth.

This means that the movement of the centroid can be coupled with the blade flapping for situation 1. But not for situation 2. Unfortunately, delta3 will not even work for situation 1 since delta3 moves the centroid in the reverse direction for the direction that it should be moved.

How can the movement of the centroid be linked to the pitch (not the flap)? [centroid - pitch coupling]

Idea: A torque - pitch coupling exists so couple the centroid to the torque.

Method: Have a +/- 12" arm extend down from the blade-arm unit. At the bottom of this arm locate a small counterweight. When the blade pitches up it will move this small counterweight forward. In addition, when the blade pitches down the small counterweight will swing to the other side of the mast and thereby offset the now higher drag of the primary counterweight (motor & powertrain).

Will the acceleration and deceleration of the small counterweight require that the azimuth of its operation be changed?

Picture:

Bottom views of single-bladed rotor hub.


Delta3 angle = 0º (i.e. no delta3)	Delta3 angle = 30º (approximately) The delta3 in this picture (view of the bottom of the hub and blade) is pointing the wrong way. The guide tracks should be pointing toward the blade's trailing edge, not its leading edge. Retake the above picture, some time.

Notes:

CW rotation of the guide tracks (when viewed from above) will cause upward flapping to;

Remove some of the pitch. Similar to the Robinson rotor hubs, this should make this light rotor easier for the pilot to control.

Move the mass of the rotor chordwise in the direction of the blade's trailing edge, in respect to the mast. This may mean that the centrifugal force of the blade, due to its offset from the hub, may work WITH the increased drag of the blade and make the 1P vibration worse. See calculations below for arm of mass and centrifugal force.

Construction:

The bottom of the hub housing consists of a ring, which rotates with the housing about the static mast. A bearing and seal are located on the inner diameter of this ring and they are in contact with the large diameter folded down ring of the universal joint's upper yoke.

A pair of guide bars are attached to this lower ring. Between the guide bars is a needle bearing and inside the needle bearing is the static mast. The guide bars thereby control the angle of the teetering in respect to a line normal to the blade' feathering axis.

Calculations re Centrifugal Force Normal to the Pitch Axis:

Assumptions:

The maximum teeter is 10º.

The delta3 angle is 20º.

The undersling is 2.9".

The weight of the Rotor (Principal Assembly) is 30 pounds. From DESIGN: Single-Bladed All Electric Rotor - Disk - Forces, Moments & Vibration

The rotational speed of the rotor is 560 RPM

Calculation:

Horizontal movement due to 10º teeter; sin(A) = a/c, a = sin(A) * c = sin(10) * 2.9 = 0.1736 * 2.9 = 0.5"

Normal to pitch axis due to 20º delta3; sin(A) = a/c, a = sin(A) * c = sin(20) * 0.5 = 0.3425 * 0.5 = 0.17"

F = (M * Ω² * R) / 2. Where [F is in pounds], [M is in slugs], [Ω is in rad per sec.], [R is blade radius, in feet].

Mass M; = 30 lbs / 32.16 = 0.933 slug

Rotational speed in radians Ω; 6.283 rads per revolution * 560 RRPM / 60 sec per min = 58.64

Radius of mass R; = 0.17" / 12 in per ft = 0.014 ft.

Force F; = (M * Ω² * R) = 0.933 * 58.64² * 0.014 ft = 45.45 lbs.

Initially displayed: January 29, 2006 ~ Last Revised: February 3, 2006

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.