OTHER: Helicopter - Inside - Interleaving - Advanced Very-Light Rotorcraft
A small Interleaving helicopter that incorporates the features that are being developed for the Intermeshing UniCopter.
Consider tandem seating. ~ See note below.
See start of tandem seating on drawing 1368-C.dc
Somewhat related craft; the SNCASO Farfadet
Specifications of Craft on Above Drawing:
Targeted at the Very-Light Rotorcraft category.
Gross Weight is 600 kg (1,320 lbs) or less
One or two seats. (side-by-side or tandem)
Rotation - Outside Forward
The tip speed is 450 fpm.
At mu = 0.80 there is very little downwash on the fuselage.
Cruise for the above parameters will be 245mph. 213 knots.
Locate a single pusher prop behind the fuselage or tractor prop in front of the fuselage.
A 3.0º precone and a +3.0º obliquity. The advancing blade at 90º ψ is at 6º above the horizontal. The blade at 180º and 0º ψ is 3.0º above the horizontal. This will give a 3º 'type of flapback' which should improve the longitudinal stability with the rigid rotors. So will the thrust from the propeller.
The close proximity of the blade tip to hub on the other rotor, for approximately 30º of rotation, may reduce the tip vortex and improve the lift fractionally.
Pros and Cons:
Advantages over single rotor:
No power consumed countering single-rotor torque.
Equal or less downwash on fuselage during cruise and low downwash during hover.
Propeller can be incorporated at rear or in front of fuselage to increase forward speed while reducing rotor thrust.
Use of ABC will reduce the downwash on the fuselage and it should reduce vibration.
Advantages over Intermeshing rotors:
Disadvantages over single rotor:
- Possibly greater vibration in hover, however the eight blades will result in a higher frequency and lower amplitude than experienced on a single-rotor craft.
Advancing Blade Concept
Large Chord and Low Tip Speed (including Absolutely Rigid Rotors + Pusher Propeller)
Independent Root & Tip Control (incorporating Reverse Velocity Utilization) ~ Could be included or provisions made for future inclusion.
Just a thought re the Interleaving with a single propulsor: The streamtube of a single, fuselage aligned, propeller (tractor and pusher) MAY add slightly to the free-stream air-velocity that elements of the retreating rotor blades are experiencing. This MIGHT mean that the area of reverse velocity is slightly bigger for a given craft airspeed. I.e. the craft MAY have to operate at a slightly lower mu than convention would suggest.
Power Train Planetary gearbox W/ engine going to pinion planet holder going to propeller and ring gear going to rotors. For idea see; DESIGN: UniCopter ~ Pusher Prop - General - Variable Speed Rotors and Prop
Can it be a two-speed or variable speed rotor using the planetary idea. Collective control on both the rotors and propeller? Use rotor governor?
Perhaps locate a 1:1 miter gears at the rotorheads and locate the reductions in the fuselage to keep the parasitic drag to a minimum.
Flutter: The widest chord is in the area of reverse velocity. There is a potential for instability on the retreating rotor blade caused by reverse flow shifting the aerodynamic center from the 1/4 chord to the 3/4 chord. The flexibility of Active Blade Twist may add to this concern. However this is probably very unlikely because this wide chord is near the line of zero velocity, and the root's pitch control is powered.
A one or two seat Interleaving configuration could utilize identical components as those of the one seat Intermeshing UniCopter.
Independent Root and Tip Control will place the fuselage under the no thrust area during cruise.
4-blade rotors may have a slightly smaller stagger than 3-blade rotors.
3-blade rotors would be more susceptible to vibration at high forward speed, due to lateral dissymmetry of lift at this high forward speed; unless adjusted for, by ABC, or by a future ability for 'azimuth x segment' pitch change. This craft will not be going all that fast.
For more information and 3-blade layout see; Interleaving Configuration
Could use slightly strengthened SynchroLite blades if Absolutely Rigid Rotors is not desired. But what about Corollas and lead/lag?
The propeller might increase the reverse velocity region of the disk area. This is because the propeller is moving a region of the air rearward at a velocity that is greater than the craft's forward velocity. This may not be true for a tractor prop
Flight-Control: It might work well with only a single pitch-control (no root & tip control). HHC might assist with providing a minimal thrust at 270º azimuth, but perhaps it will not be required.
Loads and Moments on Spars: This should not be much more, if any more, than what the wings on a comperable airplane are subjected to except for the large gyroscopic moments created between the two counter-rotating rotors.
- Tandem Seats:
- The craft is intended to be easy to fly. This implies that the hours of flight instruction will be lessened. Therefore the advantage of side-by-side seating is reduced. Tandem seating will be more aerodynamic, plus the back seat space can be used for storage, or equipment for in-flight operations.
- The tandem seating may be aerodynamically better suited to the reverse velocity region and downwash.
- The spars from the fuselage to the two rotors could be twin spars in a 'V' shape in leiu of the single 'I' shape. This may better distribute the downwash on the spar and allow the af leg of the 'A's to take the drive shaft for the engine which will be located further aft.
- The tandem seating will reduce the distance between a puller prop and the nose of the fuselage, plus be more aerodynamic for the prop's airflow.
Yaw Control: If Absolutely Rigid Rotors are incorporated, what means will be employed to effect yaw? Have not thought this through yet; but it appears that opposed longitudinal cyclic and differential collective will not work. Perhaps differential collective, with strong lateral cyclic to maintain a level attitude might work, but the strong downwash over the fuselage will probably generate an unacceptable vibration.
A large intermeshing helicopter will not have this problem. It will have a pair of propellers and they will be located under the rotorheads or side-by-side at the tail of the fuselage.
Consider 'lateral cyclic' on the propeller for yaw control.
Some, many or all the concerns here may be applicable to this craft; OTHER: Nemesis ~ Concerns & Tasks
Related Page at This Site:
OTHER: Helicopter - Inside - Interleaving - Enhanced Dihedral Rotors
Interleaving Configuration for a larger craft with Absolutely Rigid Rotors + Pusher Propeller
Model interleaving helicopter; Rubber-band Powered Model Interleaving Helicopter
Introduction Page | SynchroLite Home Page | Electrotor Home Page | UniCopter Home Page | Nemesis Home Page | AeroVantage Home Page
Initially displayed: October 04, 2004 ~ Latest revision; August 11, 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.