B436

OTHER: ~ Rotor Concept - Independent Root & Tip (IRAT)

~ Proposed means of achieving Active Blade Twist ~

Overview:

A rotor that has two flight-control mechanisms. One controls the root pitch of the blades and the other controls the tip pitch of the blades. In other words, the blades have in-flight adjustable (active) twist.

[Independent Root & Tip] is a means of applying [Active Blade Twist], however since IRAT it has its own sub-groups they have both been put on the same hierarchical level.

Advantages:

See; OTHER: Rotor Concept - Active Blade Twist (ABT) ~ Advantages

Range of Pitch Amplitude and Frequency:

See; OTHER: Rotor Concept - Active Blade Twist (ABT) ~ Range

Detailed Explanation of Independent Root and Tip Method:

There are two pitch controllers per rotor, one for the roots of the blades and the other for the tips of the blades. The blade's spar and skin have in-plane and out-of-plane rigidity (no lead/lag or flapping), but the skin (and in some methods the spar) are flexible in torsion (twistable about the feathering axis).

The root pitch of the blade is determined by the pilot's collective and the craft's forward velocity. The tip pitch of the blade is varied by the pilot's cyclic, with additional partial input from the pilot's collective.

During hover, the blades at 90º azimuth will have maximum negative twist and the blades at 270º azimuth will have a slightly less negative twist. This is done to improve the figure of merit.

During fast forward flight, the root of the retreating blades have a large negative pitch (positive twist) to eliminate any negative thrust from the region of reverse airflow. This additional lift on the retreating side, plus ABC, during fast forward flight eliminates any requirement for negative lift on the advancing tip and any possibility of retreating tip stall. In addition, this negative pitch will help provide air to the upper portion of the propeller.

The root of the retreating blade during forward flight will be experiencing reverse airflow. At speeds below mu (tip speed ratio) = 1, the tip of the retreating blade will be experiencing conventional airflow. This means there is a location on the blade that is experiencing no airflow. The RRPM of the rotor is a constant therefore as the forward velocity of the craft changes, this location of no-airflow will relocate along the span of the blade. As the forward velocity changes, the Independent Root and Tip Control will cause the positive pitch at the tip and the negative pitch at the root to change. This change of root and tip pitches is done so that the location of the zero angle of attack is always located at a location close to the location of no-airflow. The angle of attack, the air velocity and the thrust will increase as the spanwise distance from this no-airflow location increases; in both directions. See sketch.

During autorotation, the blades at all azimuths have a small positive twist. The roots will have negative pitch and the tips will have positive pitch. This is similar to the gyrocopter, which always operates in an autorotative mode.

This control method is to be used in conjunction with; Reverse Velocity Utilization (RVU), Absolutely Rigid Rotors (ARR), Advancing Blade Concept (ABC), and DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed

Proposed Methods of Applying Independent Root & Tip:

	OTHER: Rotor Concept - Independent Root & Tip - Torque Tube Method	1096
	OTHER: Rotor Concept - Independent Root & Tip - Floating Root Method	1371
	OTHER: Rotor Concept - Independent Root & Tip - Aerodynamic Tip Method	1375
	OTHER: Rotor Concept - Independent Root & Tip - Reverse Pitch Rotor	1357
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	Current Method Under Development for the UniCopter; -
	UniCopter ~ Control - Flight - Independent Root & Tip (IRAT) ~ Torque Tube Method

Notes

Forces and Moment Acronyms Used Below:

CF ~ Centrifugal force; on spar and skin (plus core).
IP ~ In-plane moments; on spar and skin (plus core).
OP ~ Out-of-plane moments; on skin.
TF ~ Torsional moment; on control(s); (due to pitching moments and bearing friction)

General:

The optimum method will be the Torque Tube Method where all the major loads are on the root bearing and root control. The root control will probably require power assist. The tip control will only be required to handle a percentage of the TF and this will be done without any power assist. The problem appears to be that of having a very strong spar, which could be twisted with minimal force. Plus, a torsion tube, from the hub to the tip, which will very strongly resist twisting. This is the method that is currently being developed for prototyping. See; UniCopter - Rotor - Blade - NACA 00xx

Possible Methods:

The Torque Tube Method is currently being developed for the UniCopter.

The spar and skin twist. A torque tube passes up the middle of a spar. The spar is rigid in all respects except twist.

For Blade details see; UniCopter - Rotor - Blade - NACA 00xx

For Flight-Control details see; UniCopter - Control - Flight - Independent Root & Tip

The Floating Root Method is the second choice, if the above fails. This method is simply an Absolutely Rigid Rotor with the ability to twist the skin at the root. The probable disadvantage of this method compared to the one above is that this will almost certainly require power assist for both the tip and the root controls. Whereas, hopefully, the first will not require power assist for the tip control. The tip controller handles all loads. The spar accepts the CF, IP and OP. The blade tip is rigidly affixed to the spar. The root of the blade rotates axially about the spare. The skin of the blade twists in 'basically' a linear fashion between the tip and the root.

The Aerodynamic Tip Method The skin of the blade at the root is rigidly affixed to the spar. The spar rotates and with it the root. Together they handle the inner span portion of the IP and OP. The root pitch handles all of the CF. The airfoil at the tip rotates about the spar. The skin of the blade twists in 'basically' a linear fashion between the tip and the root. The tip of the blade handles the outer span portion of the in-plane and out-of-plane moments.

The spar is rigidly attached to the rotorhub and does not rotate or twist. It accepts the IP and OP. The root control and root bearing handles all the CF. The tip of the blade rotates about the spar. It is rotated by a tortionally rigid torque tube, possibly located inside the spare. The root of the blade rotates on a radial elastomeric bearing about the spar. The skin of blade skin rotates on angular contact bearings about the spar. The skin of the blade twists in 'basically' a linear fashion between the tip and the root. The in-plane, out-of-plane loads are transmitted from the bearings, located along the blade span, to the spar. The friction will be handled by the root and the tip controls.

Notes:

Thoughts:

If there is not to be active twist then the single cyclic control system and pitch bearings will be subjected to the maximum loads. This is basically the Absolutely Rigid Rotors.

Therefore, why not skirt the root with a flexible skin and give it a separate 1P controller? This is the Floating Root Method #4 above.

Therefore, why not let the root, via a stronger flexible skin, handle the centrifugal force?

Therefore, why not let the root, via a very stronger flexible skin, handle all the major loads?

Hence, active blade twist.

I am going with (1). Rotation of the tip should not involve any friction but their will be a force required to twist the spar and skin. If Torque Tube Method: does not work then look into the Floating Root Method

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An alternative to this mechanical method is the electro-mechanical, as covered on ~ OTHER: Rotor Concept - Electrical Twisting of Spar. If and when functionally possible, the electro-mechanical method might be cheaper and functionally better than this mechanical torque tube method.

Related Pages at This Site:

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

Related Web Pages at Outside Sites:

IVOPROP In-flight Adjustable Ultralight Props . This shows the validity and ability to twist carbon blades. I think :)

Airfoil Design and Rotorcraft Performance Excellent paper covering L/D ratio at points (ψ, r) on rotor disk. I have hard copy.

Extension-Twist Coupled Laminates

449 more pages on the subject

Air Muscle; http://www.efunda.com/sponsors/inventables/AirMuscle/AirMuscle_Intro.cfm

Controllable Twist Rotor: ~ American Helicopter Society

http://www.vtol.org/cgi-bin/dbsearch/ahsdbsearch?session=294513147&task=search&q=%22Controllable+Twist+Rotor%22

http://www.vtol.org/cgi-bin/dbsearch/ahsdbsearch?session=294513147&task=abstract&l=18

http://www.vtol.org/cgi-bin/dbsearch/ahsdbsearch?session=294513147&task=abstract&l=23

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Initially displayed: July 26, 2002 ~ Last Revised: October 15, 2007

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.