1496

Item 1496

DESIGN: Single-Bladed All Electric Rotor (SBAER) - Disk - Vibration - Rotor Induced

Objective:

To understand and then minimize the 1P rotor-induced vibrations.

Thoughts about Different Realms of Flight ~ February 6, 2006

Vibration and the single-bladed rotor:

During Hover:

It should be easy to balance the rotor for hover, at a specific gross weight.

1/ For Thrust: Set the arm length of the counterweight so that the centrifugal force of it and that of the blade offset the thrust of the blade.

2/ For Drag: Place a fixed counterweight on a short arm where the arm is in the plane of rotation and is normal to the pitch axis. This arm will lead the item with the greatest drag (blade or counterweight) by 90º.

3/ For Cyclical Corollas: There is none.

4/ For Acceleration and Deceleration about the Mast's Axis: There is none.

5/ For Acceleration and Deceleration about the Teeter Axis: There is none.

6/ For Acceleration and Deceleration about the Pitch Axis: There is none.

All should work well.

During Vertical Climb, Vertical Descent, or Hover at a Gross Weight that Differs from the Specified Weight:

This should be easy.

1/ For Thrust: The concept of shifting the mass of the blade and the counterweight outward toward the tip of the blade to compensate for the increased inward pull of the blade's thrust has been addressed Michael Gluhareff's patent, Vladimiro Lidak's patent, and the idea previous put forth on my web site. They all should theoretically work.

2/ For Drag: Michael Gluhareff addressed this by using the small counterweight mentioned above. However, he linked the arm length of this counterweight to the pitch of the blade. In other words, the flapping of the blade moves the main counterweight, and the pitching of the blade moves the small counterweight. What Vladimiro Lidak has done is unknown. The static mast will be subjected to a torsion load but it will be a constant one.

3/ For Cyclical Corollas: There is none.

4/ For Acceleration and Deceleration about the Mast's Axis: There is none.

5/ For Acceleration and Deceleration about the Teeter Axis: There is none.

6/ For Acceleration and Deceleration about the Pitch Axis: There is none.

All should work well.

During Forward Flight:

This will be difficult.

1/ For Thrust: Symmetry of lift implies that the thrust will be equal about the disk. Therefore the concepts to balance thrust, mentioned above in vertical climb, should work.

2/ For Drag: The interesting part. If the arm length of the small counterweight were to be set by the pitch of the blade, as has been done by Gluhareff, there is a problem. This is because we know that the blade pitch is a lot higher on the retreating side then it is on the advancing side. Yet we also know that the drag on the retreating side is no higher than the drag on the advancing side. In fact, it might be slightly less. Therefore, we got vibration, 'cause the compensation for drag is greatest on the side that has the least drag. This is because it is the angle of attack that generates the induced drag.

3/ For Cyclical Corollas: ??

4/ For Acceleration and Deceleration about the Mast's Axis: ??

5/ For Acceleration and Deceleration about the Teeter Axis: ??

6/ For Acceleration and Deceleration about the Pitch Axis: ??

However, all maybe made to work well. Simply link the arm of the small counterweight to the blade's mean Angle of Attack, instead of to its pitch.

Thrust:

Lift is countered by centrifugal force.

Pull is countered by offset centrifugal force.

Static Balance and Dynamic Balance about the Teeter Axis.

If the blade-cw unit is in static balance when at rest, then at hover what amount of offset of the blade-cw centroid is required? In addition, will the gyroscopic precession of the motor reduce this?

Static Balance and Dynamic Balance about the Pitch Axis.

If the blade-cw unit is in static balance when at rest, then at hover what amount of offset of the blade-cw centroid is required? IF the profile drag of the CW and the profile + induced drag is equal during hover at a specific gross weight then no offset will be required.

Musings on the single-blade rotor and 1P vibration.

If the rotor has a teetering hinge, and the crossbar is underslung, and the crossbar has a precone, then it might be roughly correct to say that a small amount of teetering will not change the length of the blade's and the counterweight's moment arms. In other words, the centrifugal (centripetal) forces of the blade and the counterweigh will remain in balance.

However, the thrust of the single blade is normal to the plane of the blade. If the blade has a coning angle, then this thrust will have a lift component and a rotating horizontal component (pull). The pull will result in an imbalance between the two centrifugal forces and therefor a 1P horizontal vibration.

A potential solution is to eliminate the undersling and precone from the teetering rotor. This way, the moment arms of the blade and the counterweight will decrease in unison. To overcome the inequality resulting from the horizontal component of thrust and any flapping within the blade, this teetering rotor might be given a reverse cone. This will result in the moment arm of the counterweight decreasing at a slightly faster rate than that of the blade.

The problem then is related to the centrifugal force of the blade being above the teetering hinge and the centrifugal force of the counterweight being below the teetering hinge. This vertical offset of the two forces will result in a 1P vibration. Will It ??? Why since the rotor is gimbaled?

The solution to this might be to have the blade and the counterweigh flap on separate hinges. Both pair of hinges will be located on a common axis, which is the same location as the teetering hinge on the above rotor w/o undersling. The final component is a connection between the rotor and the counterweight 'grips' so that when the blade cones up the counterweight cones up also. This connection (partial gear interface) could be given a ratio to provide the desired differential coning rate between the conning of the blade and the conning of the counterweight.

Hover should be a simple solution, since the coning angle is a constant. The above may well be a solution for vertical climb. However, forward flight will probably generate a number of additional vibratory concerns, partially due to drag.

Friday, January 20, 2006 ~ Currently the optimum solution appears to be Option #1 on page 1490.html

What will the utilization of a CVJ do, if anything? Nothing. Since the mast is not rotating just use a single universal joint.

Drag:

Profile is created by the blade and by the power-arm.

Induced is created by the blade, when it has an angle of attack and is producing lift.

Initial Assumption:

The initial criterion is that the drag of the rotor and the counterweight (motor and powertrain etc.) is in balance during hover at GW. In other words the profile drag of the blade and the profile drag of the counterweight ar in balance

Drag on the rotor can be balanced for; one level of thrust and zero forward velocity. The designer will work to minimize the profile drag of the counterweight and arms, therefore the preceding statement assumes that there is an angle of attack, within the operational range of rotor that will allow this balance.

This may be more of a problem when a motor and powertrain, with its higher profile drag, is substituted for a simple and ideal counterweight.


Drag resulting from rotational velocity:
Drag resulting from forward velocity:
	Profile drag:
	Induced drag:
		Advancing side:
		Retreating side:
		End on:
			Tangential velocity:

In-plane Hub Shear:

Resulting from Climb, Forward Flight and Autorotation:

Vertical climb will increase the pitch of the blade, which in turn, will increase the blade to motor drag ratio. This will result in a constant increase in the torsion moment and a 1P shear oscillation.

~ Can the change in the blade's pitch or in the drive torque cause something to move the hub off the center of the mast in a direction that is normal to the blade's span? Delta3 does, but in the wrong direction.

An increase in the pitch will increase the induced drag, BUT the change in pitch will cause the blade to flap up and this reduce the increase in the angle of attack and therefor the increase in the induced drag. In addition, the upward flapping of the blade, and the associated downward 'flapping' of the motor, will reduce the arm lengths of the moments of inertial and this will want to speed up the RRPM due to the Coriolis effect. However it accelerates both the blade and the rotor but only the blade is subjected to the increased induced drag. NO

Idea: Consider giving the teetering guide at the bottom of the hub a slight angle about the azimuth of rotation in respect to the teetering axis azimuth. This will cause a reduction in the pitch of the blade as flaps up (This is a fourth style of delta3, plus mass offset) and in addition it will shift the mass of the entire rotor in a chordwise direction to ward the leading edge. This may take care of Hub Shear during Hover and Autorotation, However, it will not take care of the imbalance in drag during forward flight. Perhaps forward flight is not a major concern. WRONG. It will shift the mass of the entire rotor in a chordwise direction to ward the TRAILING edge and this is bad. See delt3 page.

The profile drag of the blade will probably be less the drag of the powertrain, how ever, the induced drag of the blade will increase as the pitch of the blade increases. In addition, all drags are going to increase (x²) as the advancing side and decrease on the retreating side (x²) as the craft's forward speed increases. If the parasitic drag of the counterweight (motor & power-train) is designed to match the profile and induced drag of the blade during 'mean' pitch then it will be greater than and less than the blade during different blade pitches.

Idea: Higher pitch will require more power from the rotor. Therefore consider streamlining the power train and the have an 'air-scoop' proportionately open for cooling of the motor as the power demand increase. This 'scoop' on the counterweight side of the rotor may provide a required function and counterweight the increasing profile drag of the blade during high pitch.

Idea: Can a needed mass on the rotor, such as small capacitor etc. be located on an arm. This mass might be repositioned by the pitch of the blade so as to locate this mass in an optimal location to offset the 1P vibration of the varying unequal drag.

As the forward velocity increase (I suspect ~ at this point) that the drag of the CW will increase faster than that of the blade, when they are on the advancing side. This is because the forward velocity/ rotational velocity ratio is increasing faster at the root than at the tip.

Another Idea: Place a moveable airfoil about the motor - powertrain assembly. As the blade flaps up have this airfoil pitch up. This will increase the total lift of the rotor slightly while it is increasing drag in proportion to the increasing drag at the blade.

Vibration: This is a major subject in itself.

The rotors are not intended to have the same rpm. Therefore any vibration in the rotor will cause a combined pulsation vibration as the rotor go in and out of synchronization. Perhaps mounting the rotors coaxially will result in a cancellation of some of the vibration

The drag will be greater at 90º and 270ºφ then it will be at 0º and 180ºφ, during forward flight.

Idea: The motor will require a flow of cooling air. Consider having the motor and planetary reduce enclosed in an NACA 0033 airfoil skin. Then cut the trail edge off so that a 1" deep slot is exposed. This slot is the area where the cooling air escapes. If a gating device can be located in the airflow and if the opening and closing of the gate can be controlled by the vibration, through the computer, would this vary the drag sufficiently so as to counteract the in-plane vibration?

Can the bending frequency of the non-rotating mast be such that it will counter any in-plane vibration, which is at the frequency of the RRPM?

Friday, February 03, 2006 ~ More musings on the single-blade rotor and 1P vibration resulting from drag.

The drag of the blade might be associated with;

Pitch angle
Angle of attack
Flap (teeter) angle

The pitch angle and the flap angle will be 90º out of phase with each other.

During hover, the drag, pitch, AoA and flap will all be moderate and constant. During vertical climb, the drag, pitch, AoA and flap will all be high and constant. Therefore drag could be associated with any of the other three.

During forward flight and maneuvering, the drag will be most closely associated with angle of attack. Certainly more closely associated than with flap. Probably more closely associated than with pitch. ~ I think, having not looked into.

It appears that the optimal way to offset the 1P vibration caused by drag may be to vary the arm length of a given mass that is 90º ahead of the blade in the tip path plane.

Even if statements 1 and 2 are correct the drag will not be directly correlated with the AoA. This is because the arm length will be correlated with the AoA but the centrifugal force, which is opposing the drag, will not be fully developed as the arm moves out and will have residue as the arm moves in. In other words, the cyclical drag will be slightly ahead of the cyclical centrifugal force.

Also the cyclical Corollas of the change in arm length will extend the time of drag on its increase and shorten the time of drag on is decrease. This may work with the above paragraph to advantage since the drag is also developing slower and receding faster.

The Gluhareff patent 2,475318 appears to tie the arm movement to the pitch angle. How close is the pitch angle to the AoA through the complete rotation.

It also appears that linking to the flap, as was hoped for, by delta3, is not the solution.

Friday, February 03, 2006

A possibly simple solution ~ If it is viable to associate the induced drag with the pitch angle then a likely solution is to make the pitch bearings on both sides of the hub eccentric. In other words, as the pitch increases the total blade-arm unit will advance normal to the blade span in a direction toward the leading edge.

Disadvantages;

The drive shaft must have flexible couplings.

There will be a small vertical movement.

Torsion Moment ~ Rotational Oscillation about the Z-axis:

Causes?

1P changes in the induced drag due to tangential velocity? and angle of attack? AoA is greatest when ????
1P changes in the speed due to the cyclical Corollas effect? Speed is greatest when flap is highest (and lowest if blade flap ever goes negative)

1/ and 2/ may not be at the same azimuths. In fact they may be 90º degrees apart.

Changes to torsion moment due to necessary cyclical differences around the azimuth of the rotor disk during horizontal flight:

Idea: During forward flight the torsional oscillation will be at 1P. The rotors will have a fairly constant RPM, within a narrow range. Therefore could the static mast be firmly mounted at its base and allowed limited rotation at its top (i.e in an elastomeric radial bearing or bushing) and the material and dimensioning of the short mast be tuned so as to nullify the torsional oscillation? Or perhaps it would be better to tune the mast to absorb the vibration plus dampen it so that the oscillation does not be con self-exciting?

This may also result in balancing of the drag at azimuth 90º and 270º during forward flight. There may still be a 2P vibration during forward flight due to the greater drag when the blade & motor are pointing to the sides versis pointing forward and aft. However is this any different from that of a two blade rotor?

Corollas:

I think that this has a total correlation with flapping, however the changes in RRPM will have an effect on drag and this effect on drag will be out of phase with flap:

Inertia:

The effect of acceleration and deceleration that is created by the methods used above to correct the major causes of vibration:

Additional information:

At This Web Site:

OTHER: Helicopter - Inside - Side-by-Side - Single Blade Rotors - Electric

OTHER: Helicopter - Inside - Side-by-Side - Single Blade Rotors - Hub

At Outside Web Sites:

Gluhareff patent US 2,475,318. Have hard copy.

Initially displayed: January 9, 2006 ~ Posted on PPRuNe; January 11, 2006; on Rotary Wing Forum; January 9, 2006 ~ Last Revised: September 12, 2008

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.