1184

Item 1184

OTHER: Flight Dynamics - Control - Yaw Control for Twin Rotor Configurations

Overview:

This concept is only applicable to twin rotor helicopters, which also have Independent Root & Tip Control, including Reverse Velocity Utilization.

A practical application will (hopefully) be the UniCopter.

Note:

Operationally, it is identical to the use of tip-brakes on the Gyrodyne RON-1 coaxial helicopter. In the Gyrodyne, the yaw in one direction is caused by increasing the drag on the rotor that is turning in the opposite direction. The concept on this page achieves the same results, but by a different mechanical means.

Firstly, it should be noted that the primary reasons for having Independent Root and Tip Control are;

to put the roots of the retreating blades into a negative pitch at high speeds. This causes additional lift from the reverse airflow over this portion of the blades.
High pitch at the blade roots during hover increases the efficiency of the rotor.

Instead of incorporating tip-brakes, this concept works by adjusting the root-pitch and the tip-pitch of the blades on the appropriate rotor, only. The root-pitch at all azimuths will be lowered toward and into negative pitch. At the same time, the tip-pitch at all azimuths will be increased. This way the total thrust of the rotor will not change, but its induced drag will increase.
Since the two features, mentioned above, are already incorporated into the rotors, the ability to provide yaw is basically a 'freebie'. It could also result in a very strong yaw authority, and this has been a concern with some twin rotor helicopters.

Coaxial, Interleaving and Intermeshing Configurations (w/ differential rotor collective):

Coaxials achieve yaw by varying the drag (and lift) between the two counter-rotating rotors. In autorotation, the application of the pedals or the yaw control linkages must be reversed. The method on this page will eliminate the current need for reversal of yaw inputs.

The Intermeshing configuration has Obliquity and rotates outside forward therefor rotation of the craft about the Y-axis will probably want to drop the nose. However, this can probably be compensated for by having a slightly stronger lateral dihedral on the other rotor.
The Interleaving configuration might rotate about a vertical axis that is laterally disposed from the centerline of the craft.

Yaw - Pitch Cross-coupling on Intermeshing Configuration:

The rotor-disks are sloped down to the sides and the rotors are turning outside forward. The increased drag in one rotor will cause the craft to rotate about the oblique axis of this rotor and this will probably result in a slow downward pitch of the craft's nose. The automatic addition of a little cyclic thrust at 180º azimuth on one or both rotors should resolve this problem.

Potential Concerns:

Autorotation: Concern re intermeshing configuration; OTHER: Aerodynamics ~ General - Autorotation ~ Synchropter Directional Stability

Will this method exert enough yaw at full negative root pitch? Yes, if the root pitch is able to have a high negative value. In addition, the Twin Vertical Stabilizers and Variable Vertical Fin should be considered.

Partial pedal input is only reducing positive root pitch and slightly increasing tip pitch. Will this cause additional drag, or must the root pitch be negative before the drag increases? There must be some increase in drag during positive root pitch, because high twist is considered more efficient. Perhaps the change of root pitch could be made non-linear with the pedal depression, so that more root pitch change per pedal travel takes place in the initial pedal travel.

Will the performance and handling be identical in autorotation?

Related Pages at This Site:

OTHER: Rotor Concept - Active Blade Twist
OTHER: Rotor Concept - Independent Root & Tip Control
OTHER: Rotor Concept - Reverse Velocity Utilization
OTHER: Flight Dnamics - Control - Variable Vertical Fin is a means of improving yaw authority on intermeshing helicopters. Make mention of the ability to have Differential Longitudinal Cyclic. This method may reduce the need for such a large rudder on the Flettner, Kaman and Kellett helicopters

DESIGN: UniCopter ~ Rotor - Disk - Large Chord & Low Tip Speed
DESIGN: Dragonfly ~ Control - Flight - Directional - by Collective Pitch Differential

Alternative Method:

DESIGN: UniCopter ~ Rotor - Disk - Autorotation Yaw by Separate Root and Tip Control

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Initially displayed: May 17, 2003 ~ Posed on PPRuNe: June 4, 2003 ~ Posted on Eng-Tips: June 4, 2003: Last Revised: March 27, 2006

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.