1516

Item 1516

OTHER: Rotor Concept - Reverse Velocity Utilization - Traversing Root Pitch Axis

Objective:

To provide a simple means for the root end of a blade to utilize the reverse airflow, when the blade is on the retreating side during forward flight.

Simply, the direction of the aerodynamic drag on the root end of the blade sets the position of the root end so as to provide lift at the root end.

Means of Achieving Objective:

The root's pitch axis (spar) is able to cyclically position itself at 25% of the chord and at 75% of the chord.

The cyclical repositioning of the blade on the spar is done automatically by the direction that the free airflow pushes (drag) on the blade.

This is done so that the pitch axis is at 25% of the chord length back from the edge of the blade that is receiving the incoming airflow.

Lift is achieved by the blade's curved slot moving in respect to the curved spar. This will result in the blade having a positive pitch when experiencing conventional airflow and a negative pitch when experiencing reverse airflow.

X-section of Blade's Root:

During cruise the blade is moving forward and back, in resect to the spar, at a rate of once per rotor revolution.

Note that the external profile of the illustrated airfoil is not intended to represent an actual one.

Note that there is probably no reason for the pitch to be as large as 12º during reverse velocity flow. However, it will be preferable to have the feathering axis near 25% of chord, therefore, consider the round spar in the option below.

A torque tube might be located within the spar to control the pitch at the tip of the blade.

An Explanation of the Invention:

A blade that is located in airflow is subjected to drag (profile and Induced). This drag is attempting to force the blade rearward.

On a conventional blade the spar, which is attached to the rotorhub, resists any movement.

On this blade;

The spar has a horizontal rectangular cross-section. It is located in a blade that has a rectangular inner hollow slot at it's root end. This slot is wider than the spar and this allows the blade's root to move forward and aft along the chord line. The slide distance is 50% of the blade's chord and thereby allows the spar to be located at 25% of the chord and at 75% of the chord. This means that the spar can be located at 25% of chord from the edge of the blade that is receiving the airflow. In other words, the blade's root can horizontally oscillate, at a rate of 1/rev., on the spar during cruise or remain in one location during hover.
The 'blade sliding on the spar' arraignment only extends from the root toward the tip for a distance of R * mu [Rotor radius * Advance ratio]. The amount of 'sliding' gets proportionately smaller when moving from root to this location mentioned in the preceding sentence.
The OD of the spar and the ID of the blade's inner hollow have a concave profile. Therefore the pitch of the blade will oscillate between positive and negative, during cruise. For example say +12º to -12º.
This change of location of the blade on the spar is achieved by the force of the free airflow on the root end of the blade.
The location of change on the rotor's disk (azimuth) is automatically determined by the very flow of the air that the blade is working on.
When there is zero airflow at the root the pitch axis will be at 50% of chord. This is due to the 'springiness' of the blade's composite construction.
Alternatively, the 'home' position of the pitch axis might be located closer to 25% of forward velocity chord. One reason for this alternative is that the profile of the airfoil may be such as to have a higher drag in reverse velocity.
A damper may be incorporated to control the oscillations of the blade root about the spar root.

Note that there is full cyclical and collective control for the tip end of the blades by rotating the spar in a conventional manner.

Construction:

Spar.

The spar is rigid in respect to in-plane and out-of-plane bending and torsion.

Skin.

The skin is rigid in respect to out-of-plane bending but is flexible in respect to in-plane bending and torsion.

Core.

For an electric rotorcraft, consider the possibility of making the core as a capacitor.

Application:

This invention was primarily intended for low cost and perhaps expendable UAVs. However, it may work successfully during autorotation, and thus be viable for manned craft, particularly if the root was given some collective control.

Active Root Control:

A separate adjustable control might be considered for the root.

This control might operate by limiting the range of blade traverse across the spar, in one or both directions

This control might have no reason to operate at a rate as high as 1P. Therefore it might be quite simple

It might change the number of degrees between the two boundaries or it might maintain the same range of movement but shift the range more positive or more negative.

Notes:

Should there be a damper at the root to stabilize the oscillation of the blade on the spar?

Should or could there be a controllable device to assist the drag induced oscillation?

The location on the span of the blade where the blade becomes a conventional one on out to the tip is the location at 270º azimuth where the airflow is 0 fps during cruise. I.e. If mu = .5 during cruise then this transition location will be 0.5 R.

The 'leading' and 'trailing' gaps between the blade and it's spar will decrease when moving from the root to the transition location.

The control of this blade might be by Independent Root and Tip ~ Floating Root Method.

Pilot originated cyclic and collective control is totally or primarily realized at the tips of the blades.

With 3-blade and 4-blade rotors the motion of the root during cruise may not cause a longitudinal vibration. From the perspective of mass, note that the skin is moving but not the spar.

The thinking is that the root skin of the blade is predominantly fiberglass. The elasticity of the fiberglass will want to center the root on the spar. However, the elasticity will be quite weak in-plane and therefore give little resistance to the in-plane flexing.

Pitch Angle: (crude approximations)

Notes:

The tip cyclic control is 1/rev.
The root pitch is the tip pitch adjusted by the range of the Traversing Root Pitch.
The range of the Traversing Root Pitch might be +6 to -16 (not the +12 to -12 in the above sketch).

During Hover:

Azimuth	Tip pitch:	Root pitch:
0º ~ aft	4º	4º + 6º = 10º
90º ~ advancing	4º	4º + 6º = 10º
180º ~ forward	4º	4º + 6º = 10º
270º ~ retreating	4º	4º + 6º = 10º

During Cruise:

Azimuth	Tip pitch:	Root pitch:
0º ~ aft	4º	4º + 6º = 10º
90º ~ advancing	2º	2º + 6º = 8º
180º ~ forward	4º	4º + 6º = 10º ⁽¹⁾
270º ~ retreating	6º	6º - 16º = -10º ⁽¹⁾

More Notes:

The aerodynamic pitch angle will be somewhat less because the airflow at these azimuths is not parallel to the chord.

Option A:

A means of achieving the same operation but utilizing a different mechanism. In this option the the root of the blade is attached to a rocker arm. The movement of this arm about the root pivot gives the same action as the original idea, in that the blade oscillates back and forth about the spar in the same path.

The advantages of this option are that;

A rolling action of a bearing at the root pivot replaces the sliding action on the spar.
The spar can now be round.
The spar, or the arm, can be used to limit the travel distance.
The travel limit might be variable in flight by varying the position of the for and aft stops that the arm comes to rest against.

Note that unlike the initial idea, this root pitch change is totally independent from the tip pitch change.

The spar would have its pitch changed in the conventional manner by the cyclic and collective controls. As above, this will set the pitch of the tip end of the blade.

The pivot point at the bottom of the rocker arm could be given controllable horizontal movement. This would provide root pitch control when the root is subjected to forward velocity and when it is subjected to reverse velocity.

Option B:

Possible Concerns:

Will there be a problem with stability or vibration?

Will the drag be sufficient to 'slide' the skin on the spar?

Will the small amount of drag at root during hover be sufficient to position the blade on the spar? Perhaps the blade and it's root must be manufactured with a positional preference for forward velocity.

Potential Applications:

Interleaving - R/C Electric - UAV

Additional Considerations ~ February 26, 2007:

Consider actively increasing the thickness at the temporary leading edges by the spar's movement to that edge. The intent is to make the profile a little more like that of a conventional airfoil ~ if it helps at all.

Possible method: ~ If the drag force is sufficiently strong, between the blade and its spar, then this force might be used by a mechanical, hydraulic or aerodynamic means etc. to alternately increase the thickness at the temporary leading edges.

Consider actively increasing the weight at the temporary leading edges (somehow) by the spar's movement to that edge.

Perhaps these two considerations can be achieved by a common activity.

_________________________

This subject is expanded on web page; OTHER: Rotor Concept - Reverse Velocity Utilization - Traversing Root Pitch Axis - Leading and Trailing Edge Exchanging ~ May 19, 2007

This is a means (a sub-set) of providing OTHER: Rotor Concept - Independent Root & Tip - Floating Root Method

Initially displayed: June 24, 2006 ~ Displayed on PPRuNe; June 24, 2006 ~ Last Revision: January 16, 2008

The above application of reverse velocity utilization in the main rotor(s) of a helicopter 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.