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Item 0036

OTHER: Helicopter - Inside - Single-Bladed All Electric Rotor (SBAER) - Principal Assembly

Concerns:

Conclusion:

As with the Mapleseed, it appears that the Single-Bladed Rotor Configuration is good for vertical flight, including hover; however, it is not good for forward (horizontal) flight.

Rotor Induced Vibrations due to; Thrust, Drag, Corollas & ???

See page; DESIGN: Single-Bladed All Electric Rotor - Disk - Vibration - Rotor Induced

Vibration will probably be the biggest, and perhaps insurmountable, concern.

And the varying drag may be the main cause.
In addition, to have forward flight the angle of attack must be reduced on the advancing blade and increased on the retreating blade. Since pitch is set by torque, it means that the torque must be reduced when the blade is advancing and increased when the blade is retreating. I.e 1P tortional vibration. In addition, the two rotors will be going in and out of phase.

Using the motor for the counterweight may very likely result in a drag that is excessive

Note that Gluhareff's patent US 2,944,610 has to do with reducing the drag of the counterweight and his counterweight is not excessively bulky. The high weight of the motor and powertrain will mean a shorter moment arm on the current concept and this may help.

The control response may be so fast that Hiller paddles or gyro bars may be required. Delta3 may help, but it has its own problem of offsetting the rotor's mass in the correct direction. Another option is to use electrical gyroscopes.

This may be the biggest problem at present: The drag of the blade will vary as the pitch is changed, however the drag of the counterweight will remain constant. See Drag on Forces & Moments. Enclose the CW arm assembly in an NACA 0025 to 0033 airfoil. Allow this airfoil to freely pivot about the arm so that the drag will always be at a minimum and its angle of attack will not be detrimental to autorotation.

The remaining 2P vibration is small but at 18.7 cycles/second it is in the objectionable range See; http://www.unicopter.com/1059.html

Idea: Could a short fixed pitch airfoil be located on the counterweight arm and near the mast? This airfoil will give a constant lift about the azimuth during hover but it will provide a varying lift between the advancing and the retreating sides during forward flight. This variation will increase as the forward velocity of the craft increases.

Does a 1-blade Rotor have a Better Figure of Merit than a 2-blade Rotor ???

Unlike a second blade, the motor and reducer cause additional drag without generating additional lift.

Perhaps this can only be shown by comparative testing.

Sub Assemblies:

Disk

Information:

See 139 page technical report; Single Bladed Torqueless Helicopter Design by Martinus Maria Klijn. It is located in [Single-bladed All Electric Rotor] binder.

Features of the Rotor:

There are not any clutches between the rotor and the motor:

This means that the motor's rpm [Ω_MOT] always has a direct relationship to the rotor's rpm [Ω_ROT].

The use of Gyroscopic Precession: Do the force and moment calculations some time and/or experiment

An electric motor is substituted for the single-blade's counterweight. The axis of the motor shaft intersects the Z-axis of the rotor hub. As the motor rotates about the mast, the gyroscopic precession resulting from this rotation combined with the rotation of the motor plus power train results in an upward force on the 'counterweight' arm.

This has been tested and confirmed by placing a bicycle wheel at the end of a pole. The axle of the wheel is in alingment with the length of the pole. Pictorially similar to a parasol. The wheel is then spun, the end of the pole opposite the wheel is held and the pole is extended out horizontally from the persons standing body. When the person vertically rotates in one direction the wheel and pole want to climb. When the person rotates in the opposite direction the wheel and pole want to descend. The desired climbing takes place when, from the person's perspective, the wheel is rotating CW and the person is turning CCW, when view from above.

This lift from this gyroscopic precession can be used to;

Reduce the weight of the craft slightly by reducing the weight of the counterweight (motor etc) and the tip weight. (note that both must be reduced because the horizontal component of the centrifugal force must remain in balance)

Reduce the weight of the craft slightly by reducing the arm length of the counterweight and reducing the tip weight. (note that both must be reduced because the horizontal component of the centrifugal force must remain in balance)

Leave the weight as they are and allow the motors lift to reduce the coning angle. This reduction in the coning angle will reduce the compensation for the teetering; the ideas of which are covered on the page Hub.

Of course, there will also be gyroscopic precession of the rotor when the disk is tilted. It looks like an upward flap will accelerate the rotor very slightly and a downward flap will decelerate the rotor slightly. Will this acceleration/deceleration, which will have a 1P-yaw oscillation present a problem? With twin rotors that are not synchronized the two oscillations could go in and out of phase.

The Use of Pitch - Torque Coupling:

The blade's pitch [θ] has a direct relationship with the torque being applied to the rotor [Q_ROT]

Pitch - Flap Coupling:

The blade's pitch [θ], obviously, has a direct relationship with the blade' flap [β]. This will have a 90º-phase lag unless a hub spring or flapping hinge offset is incorporated into the rotor.

Relationships:

Ω_MOT ≈ Ω_ROT.

Q_ROT≈ θ.

T ≈ Ω_MOT * θ The rotor thrust has a relationship with the rotor speed and the pitch angle (actually the angle of attack and forward velocity etc.)

GP ≈ Ω_ROT. The gyroscopic precession will have a relationship with the rotor speed.

θ ≈ β. With delay of 1/4 rotor revolution.

Just to record a thought, which currently may not work:

Locate the crown gear below the pinion. Rotate the motor and the pinion in the opposite direction, so that the rotor still turns in the previous direction. Replace the elastomeric pitch bearing on the blade side of the hub with a 'rigid' connection. Provide the blade with approximately -10º of twist. The torque about the pitch axis that the powertrain imparts to the split blade spar on the CW side of the 'rigid connection will result in a positive pitch change at the tip of the blade. In other words, motor torque in the opposite direction will case a blade pitch change in the desired direction. In other words the elastomeric bearing has be replaced by a torsionally elasticity in the blade's spar(s). An obvious problem with this is that the gyroscopic precession within the motor will now want to lower the motor in stead of raising it.

Cross-couplings:

Roll-Yaw: With inside forward rotor rotation (breaststroke) the input of Roll (by dissimilar lift) will result in some yaw due to the higher drag on the rotation of one rotor. This should be ok since the craft will yaw in the same direction as the roll. Consider the possibility of spiral dive.

Mathamatics:

For blade element method, the centripetal force F acting on a body of mass M is given by the equation F = (Mv²)/r, where v is its velocity and r is the radius of its path. [F is in pounds], [M is in slugs (1 slug = 32.175 lbs)], [v² is in ft/sec.], [r is in feet].

T = 2 * ρ * V² * A, [in pounds]. Thrust can be resolved into 'Lift' and 'Pull'.

Safety:

The flight controls and the low disk loading will result in an automatic entry into autorotation, plus a slow descent rate and soft landing. A device to recover the rotors' inertia or a device to apply short duration torque could be incorporated. This default pitch of this device is set to that which is required for autorotation.

Work to do:

Study more about forces, moments and the resulting vibrations.

Pitch-Torque coupling device

Controller and control logic.

Composite blade and arms

Last Revised: September 12, 2008