1504

Item 1504

OTHER: Rotor Concept - Traversing Ideal Twist - Simplistic Method

Overview:

For one conceptual means of utilizing reverse velocity see OTHER: Rotor Concept - Rotor X Wing - Traversing Twist - Overview.

For one proposed method of implementing the above conceptual means see below

Method of Implementation:

Blade Segment

The above is a short length of extruded aluminum NACA 0012. It represents a segment. The segments rotate about the blade's spar, which will be located in the round hole.

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The blade segment on the right is 'hanging' in its mean position. It is lightly held in this position by the elastomeric bearing (not shown), which is located between the spar and the blade. Forward velocity air will rotate the segment in one direction, whereas reverse velocity air will rotate the segment in the other direct.

The width and radial position of the spar key sets the two pitch angles to which the segment will rotate. It may be a different angle for forward and for reverse.

The forward velocity angle is set by conventional pitch control means since the spar key rotates with the spar.

The angle between the forward velocity angle and the reverse velocity angle may have to be variable to suit different flight conditions.

More on Method of Implementation:

The blade spar is a round extremely rigid beam.

It can be rotated approximately 30º by pitch change, which originates at the collective and cyclic sticks. This is identical to a conventional rotor control.

The skin, core and leading edge weights assemblage is conventional, except that it is cut up into dozens segments approximately 2" long each.

Each segment has its own elastomeric bearing and this bearing allows the segment to rotate about the spar through an arc of 180º or less.

This elastomeric bearing has a spring effect that wants to center the segment at approximately the midpoint of its arc of rotation.

All of the segments are installed on the spar so that from a distance the blade looks like a conventional blade, except that there appears to be parallel chordwise lines at approximately 2" centers down the length of the span.

When installed in the rotor the 'spring' of the elastomeric causes the trailing edge of all the segments to point straight down.each blade has its trailing edge(s) pointing down.

Every blade element can have its trailing edge rotated forward and up 90º plus backward and up 90º.

At both 90º locations the blade segment comes up against a stop on the spar and it can rotate no further.

When these blades are rotated about the mast during hover the airflow past the segments will cause their trailing edges to rise and trail.

At some speed below RRPM all the segments will have come up against the stop.

As the collective is raised the pitch of the spar and all the segments will acquire an angle of attack and this will lift the helicopter.

During hover the rotor looks no different from a conventional rotor.

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Forward Flight:

As the forward velocity of the craft increases the root of the retreating blade will stop experiencing any airflow and the segment at the root will become vertical due to the spring action of the bearing.

As the forward velocity is further increased the location of zero air flow on the retreating side will move further out the blade and more of the segments near the root will assume a vertical orientation.

Meanwhile the segment at the root will rotate in the opposite direction because it is experiencing reverse velocity.

Current Concern: On the retreating side at mu >0 and <1 a change of the blade's pitch will result in angle of attack in the reverse flow region increasing or decreasing while the angle of attack in the forward flow region changing in the opposite direction.

Random Notes:

The segments will only be unaligned with the adjacent segments when the airflow at that segment is very slow. Therefore, this misalignment is not aerodynamically detrimental.

Piezoelectric actuators could vary the angle of the two rotational stops in each element.

Or ~ 3-position magnetic control could position one segment in relation to its adjacent segment.

The blade could have built in twist by tapering the width of the 'key' in the spar so that it is wider at the root then it is at the tip. This will give the root end segments less angular rotation than the tip end elements.

The centering spring in each element is a natural characteristic of the segments elastomeric bearing.

The rate at which the element will oscillate is equal to the rotors rpm.

As the forward speed of the craft increases the RRPM will be slowed down. (see Large Chord and Low Tip Speed). Also, the diameter of the area of reverse velocity will increase. In other words, the maximum oscillation rate of the elements will be less for those elements near the tip than those near the root.

Element Tab Stops:

Each element will have a rotation stop on each side. These will probably consist of overlapping taps seating into pocketa at the trailing edge of each segment, since the trailing edge has the longest moment arm. These stops will come up against stops in the adjacent elements an thereby assure that the trailing edges of all elements are inline when the airfoil is subjected to forward or reverse velocity.

Perhaps angled sides on the elements should be used as a replacement for the tabs. Airflow over the angled sides, particularly at high mu might help (or might hinder) the rotation at the front and the aft if the disk.

The tab may still be required to give a precise alignment between elements.

Smoother Flight:

The spar's pitch rotation stops and/or the element tab stops might be given resiliency. This might provide some semblance of the 'freewing' and thereby reduce the strength of perturbations on the craft's components and occupants.

Independent Root & Tip:

Independant root and tip control could be considered for inclusion in the future.

Concerns:

Size of rotational arc of segments:

The angle of rotation can be fixed by the width of the so-called keys, which are located at each segment along the full length of the spar. In addition the width of the key can be tapered so that the arc of rotation is greater for the elements at the tip end and less for the elements at the root end. However ther is no provision for varying the size of these arcs during flight.

Possible Solutions:

Using piezoelectric devices to change the width of the 'keys'.
Using piezoelectric devices on both sides of the 'keys' so that the forward velocity pitch angle and the reverse velocity pitch angle can be change independently.
For twin latterly located rotors; fix the pitch of the blades when on the retreating side and only control the pitch on the advancing side.
For twin latterly located rotors; fix the retreating pitch of the blades when on the retreating side and only control the advancing pitch on the retreating side and the advancing pitch (there only is an advancing pitch of course) on the advancing side.

Will the spar be strong and rigid enough?

Consider a large tip weight so that centrifugal force will significantly contribute. A lightweight axially wound spar will allow for a larger tip weight while adding to the rigidity of the blade.

Initially Displayed: March 26, 2006 ~ Displayed on PPRuNe and on Rotary Wing Forum: April 8, 2006~ Last Revision: August 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 them. ~ 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.