OTHER: Helicopter - Inside - Interleaving - Enhanced Dihedral Rotors & More ~ Nemesis
For the fun of it and as time will allow, consider 'fleshing' this idea out using criteria from; Prouty's example helicopter, the V-22 Tilt Rotor, or the VTOL Heavy Lift Rotorcraft.
Drawing of Very-Light Rotorcraft and Heavy Rotorcraft Configurations:
Currently, this drawing is also used on Nemesis.html
This drawing is also used on Nemesis.html
Note re Dihedral: It may be better if the 'masts' are vertical. This is because the cone of both rotors should provide lateral stability, particularly since the outside blades are providing most of the lift (i.e. the greatest pitch). In this arraignment the tips will be above the roots of the other rotor's blades. Perhaps with a 1ºto 2º greater pre-cone.
Note re Dihedral and Yaw Control: The application of left pedal will cause forward cyclic on the starboard rotor and aft cyclic on the port rotor. The precone angle of 1.5º times the moment arm length between the rotorhub and the fuselage will generate a CCW rotation. However, the obliquity of 5º times the moment arm length between the centers of thrust and the centers of the rotorhubs will create a CW rotation.
Note re Yaw Control: the use of twin propulsors may provide for reverse thrust on ether of the propulsors. A single propulsor might be provided with horizontal cyclic pitch control for positive and negative thrust on port and starboard.
Rotation - Outside Forward
The tips of the retreating blades pass under the roots of the blades on the other rotor. In other words, the blade roots are not located in the downwash from the blade tips of the other rotor. In addition, the tip is retreating and the craft has (ABC), therefor the thrust is minimal.
When electrical root control and electrical active blade twist is implemented the hubs will be smaller and less restrictive to airflow.
The obliquity is 5º, or less.
The precone is 1.5º, or less.
The maximum tip speed ratio (mu) might be 0.67 for a Very Light helicopter and on up past an mu of 1.0 for a Heavy Helicopter. Note that a high mu does not necessarily mean an exceptionally fast forward speed due to the slow rotational speed of the rotors.
Locate the single, or dual, pusher prop(s) behind the fuselage or under the rotorhubs.
By increasing the stagger from that of the Intermeshing UniCopter, Momentum Theory shows a reduction in the horsepower required for hover by 12%. The Blade Element Theory shows an increase. There must be an error in the coding.
Consider placing an airfoil over the short spars to the rotors. The airfoil might be rotateable, so that it assists with lift during forward flight and has minimum drag during hover.
If the engine(s) are located in the fuselage then use a 1:1 miter gear at the rotorheads and locate the reductions in the fuselage to keep the parasitic drag to a minimum. Alternatively, if the horizontal thrust is to be located under the rotorheads then consider placing the engines at this location.
High Speed Flight:
Reverse Pitch Rotor Concept will be required.
- Consider using a turbofan engine under both rotors. The engine could be similar to that used on the F-35 fighters in that it would have a PTO for driving the rotor. It would probably have a have a high bypass fan. For this speed the
M] 0.9 (979 fps).
The tip-speed-ratio [mu] is 2.
The centerline of the fuselage is located at 0.65 R at 270º azimuth.
- The tip speed at 90º azimuth is Mach [
- The craft's air speed is 2/3 * 979 = 653 fps = 445 mph = 387 knots.
- The velocities of the blade tips are 326 f/s.
- The resultant air velocities at;
- Azimuth = 90º, R = 1.0 is +979 fps.
- Azimuth = 90º, R = 0.0 is +653 fps.
- Azimuth = 270º, R = 0.0 is -653 fps.
- Azimuth = 270º, R = 0.65 is -441 fps.
- Azimuth = 270º, R = 1.0 is -326 fps.
At cruise speeds below 445 mph the downwash on the fuselage will be even less.
OTHER: Helicopter - Inside - Interleaving - Downwash in Hover
When high amplitude piezoelectric devices significantly improve, it should be possible to further improve the downwash distribution on the retreating blade. At 270º azimuth it will be possible to have a positive root pitch, a zero mid-span pitch and a positive tip pitch. This will further minimized the downwash on the fuselage.
- Have extreme taper.
- Implement ABC to put most of the lift on the advancing halves of the disks.
- Implement RVU with;
- The wide root of the blade at 270º azimuth being slightly negative (i.e. generating lift from reverse velocity.)
- The narrow tip of the blade at 270º azimuth being very slightly positive (i.e. generating a little negative lift from reverse velocity.)
Yaw: Dissimilar rotor collective with rotor lateral cyclic.
~ or ~
Small Craft: The single pusher propeller, located at aft of fuselage, to have lateral cyclic.
Large Craft: Opposed thrust of the two laterally displaced pusher propellers.
If propellers are to be used and they are to be located under the rotorhubs then there will probably be a conflict with the retreating blade tips at 270º azimuth. The question must then be asked; is the reduction of stagger over that of a conventional interleaving configuration, which is realized from the dihedral rotor, worth the necessity of using smaller diameter propellers. The smaller diameter turbofans will replace the pusher propellers if the Reverse Pitch Rotor Concept is viable.
To minimize the hover downwash over the fuselage, on a Heavy helicopter, the Electrical Twisting of Spar type of Active Blade Twist could be implemented. In actual fact, this azimuth-element grid of active variable pitch will be good for everything but washing dishes.
Tall pylons that are required to create a vertical gap for the blade tips of the other rotor may reduce the Aeroelastic stability. The Absolutely Rigid Rotor combined with a 'throat' on the pylon, to re-direct an excessively divergent tip, might reduce the length of the pylon.
Modified Arraignment ~ Conventional Interleaving Configuration but with Regular Dihedral:
The rotors in the draw at the top or this page have a 1.5º precone, an obliquity of +5.0º, the advancing blades at 90º ψ is 6.5º above the horizontal, the retreating blade at 270º ψ are 3.5º below the horizontal, and the blades at 180º and 0º ψ are 1.5º above the horizontal.
This modified arraignment gives up the reduced stagger to get larger diameter propellers mounted under the rotorhub.
would be 3Ί above the horizontal.
Perhaps a 3.0º precone, a +3.0º obliquity, the advancing blades at 90º ψ at 6º above the horizontal, and the blades at 180º and 0º ψ are 3.0º above the horizontal, might be a more advantageous alternative. This will give a 3º 'type of flapback' which should improve the longitudinal stability with the rigid rotors.
See; DESIGN: Nemesis ~ Rotor - Disk - Enhanced Dihedral Consider moving the above Dihedral information to this page.
- To have the retreating blades at 270º ψ of 4-blade rotors operate in the same plane without conflict, the stagger would have to be Radius + 20%.
- In this alternative situation, with the same 1.5º precone, the obliquity would be +1.5º and the advancing blades at 90º ψ
Rotors and turbofans could be moved closer to the fuselage than shown.
Related Pages at This Site:
OTHER: Aerodynamic - Rotor Disk - Dual Configuration - Interleaving
OTHER: Helicopter - Outside - Intermeshing - Stepniewski (concept)
OTHER: Helicopter - Inside - Interleaving - with Canard
OTHER: Rotor Concept - Independent Root & Tip - Reverse Pitch Rotor
OTHER: Helicopter - Inside - Interleaving - Morphing
Some Interleaving Configuration notes.
Single (large) - Sikorsky's Reverse Velocity Rotorcraft Proposal
OTHER: Helicopter - Inside - Interleaving - Very-Light Rotorcraft
Related Outside Material:
See NACA TM 858 'The Focke Helicopter'. Have hard copy.
Same Page ~ Different Craft: ~ SynchroLite ~ UniCopter
Introduction Page | SynchroLite Home Page | Electrotor Home Page | UniCopter Home Page | Nemesis Home Page | AeroVantage Home Page
Initially displayed: March 25, 2005 ~ Posted on PPRuNe; March 26, 2005; on rec.aviation.rotorcraft; August 4, 2005 ~ Latest 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 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.