1357

Item 1357

OTHER: Rotor Concept - Independent Root & Tip - Reverse Pitch Rotor

Objective:

To create a Interleaving rotorcraft that is capable of flying at extremely fast forward speeds. The rotors are the sole source of lift in all realms of flight.

Futuristic idea------- ----- Novel idea.

Overview:

Current rotorcraft during forward flight have a small portion of the root end of the retreating blade experiencing a reverse velocity over the airfoil from 'trailing edge' to 'leading edge'. The area of reverse velocity increases as the craft's velocity increases. When the tip speed ratio (mu) = 1 the whole retreating blade at 270º azimuth is experiencing reverse airflow. The flow of air across the airfoil in this reverse direction will cause blade instability and excessive drag. There has been consideration for giving both edges the same profile but this will still result in high drag and probable instability.

The concept on this page uses a conventional airfoil. In addition, it has the airflow always moving from the leading edge of the blade to the trailing edge of the blade, even in the reverse velocity region.

The proposed craft may be the Interleaving Configuration with Enhanced Dihedral Rotors, except that the blades on the retreating sides will be facing forward during cruise. To achieve this, the blades must be capable of active ideal twist during flight.

Notes:

This concept is based on the assumption that the blades are capable of 180º of active twist in one direction.

The following calculations and notes do not consider the effect that the collective and the cyclic will have on the blade pitch. Collective and cyclic values will be a modifier of the pitch values.

For Initial Evaluation Purposes:

Cruise at 434 knots = 500 mph = 733 ft/sec

Cruse mu = 5

Therefore the 'slow' tip speed must be 147 ft/sec

The rotor diameter is 48. This is rough and temporary, based on Prouty's example.

Therefore, the rotor 'slow' speed is 58 rpm. This is really slow. The CarterCopter was 107 rpm at the time that he claims it broke mu = 1.

Drawing:

The amount of active blade twist is the vertical distance between the blue and red lines in the above graphs. There is minimal active twist during hover and cruise, with the maximum active twist during transition.

Speeds:

Forward Velocity | Rotor Speed | Tip Speed Ratio

0 MPH (hover) | RRPM | Mu = 0.0:

The azimuth where the blade touches the arc of zero velocity is 0º. This is at the root and is at all azimuths.

?? MPH (transition) | ?? RRPM | Mu = 0.5:

At no azimuth does the blade tip intersect the arc of zero velocityº.

The azimuth where the center of the span of the blade touches the arc of zero velocity is 270º.

This means the tip pitch of the blade will be 0º at 270º azimuth and the root pitch of the blade will be 180º at 270º azimuth. The pitch of the blade at the center of its span will be 90º at azimuth 270º.

?? MPH (transition) | ?? RRPM | Mu = 1:

The azimuth where the blade tip intersects the arc of zero velocity is 270º.
The azimuth where the center of the span of the blade touches the arc of zero velocity is 220º.
The mean of the above two is approximately 245º azimuth, or larger. This will be the azimuth where the pitch of the blade will be 90º

?? MPH (transition) | ?? RRPM | Mu = 2:

The azimuth where the blade tip intersects the arc of zero velocity is 210º.
The azimuth where the center of the span of the blade touches the arc of zero velocity is 192º.
The mean of the above two is approximately 201º azimuth, or larger. This will be the azimuth where the pitch of the blade will be 90º

?? MPH (transition) | ?? RRPM | Mu = 5: (cruise)

The azimuth where the blade tip intersects the arc of zero velocity is 192º.
The azimuth where the center of the span of the blade touches the arc of zero velocity is 186º.
The mean of the above two is approximately 189º azimuth, or larger. This will be the azimuth where the pitch of the blade will be 90º

Notes:

May require 5 or 6 blades per rotor, to reduce the vibration. This is OK.

There are independent root pitch and tip pitch controls or independent root pitch and active twist controls?

The inclusion of root and tip pitch controls plus active segmental twist will provide better control and reduced vibration

The root pitch will oscillate 180º at a rate equal to, or faster than, the rpm of the rotor, at all mu values.

The tip pitch will oscillate 180º at a rate equal to, or faster than, the rpm of the rotor, when the mu > 1.

The eventual inclusion of segmented blade twist within the span of the blade will be a further improvement.

At 500 mph and the blade at 186º azimuth , the pitch is close to +90º (vertical) however the airflow is nearly parallel to the blade's span, therefor the angle of attack is quite small.

It appears that root pitch and active twist should be the two control inputs, since active twist does not change much during hover and cruise. Tip pitch is therefor the result of root pitch and active twist.

Can rotor rotation be maintained during cruse by the fact that profile drag on the retreating side will be higher than the profile drag on the advancing side? Probably not because ABC will cause a higher induced drag on the retreating side.

Related Web Pages:

Application of the concept on this web page; OTHER: Helicopter - Inside - Interleaving - Enhanced Dihedral Rotors

Information on reverse velocity utilization; OTHER: Rotor Concept - Reverse Velocity Utilization

Possible drive train; DESIGN: UniCopter ~ Pusher Prop - General - Variable Speed Rotors and Propellers

Initially displayed: July14, 2005 ~ Displayed on PPRuNe: December 12, 2006 ~ Last Revised: July 8, 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.