OTHER: Helicopter - Inside - Side-by-Side - Electric Ultralight & UAV

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• The side-by-side configuration is the most efficient (lift to horsepower) there is. This is particularly important when considering the large weight of today's electrical storage devices. A 10 - 20% mutual efficiency based on the proximity of the rotor disks.
• "The conclusion of this is that the co-axial configuration increases the induced power by 16%, compared to the case of isolated rotors; its effect on the profile power is also negative, and this effect leads us to conclude that the use of co-axial configurations are of no use when power availability is limited" ~ from Journal of the American Helicopter Society's October 2007 article 'On the Possibility of Human-Powered Vertical Flight'.
• See the many Focke-Wulf Fw 61 and Fa 223 pictures of the spar arrangement in the thin German book entitled Die deutschen Hubschrauber - 1928-1945. Also see my notes on this subject.

• Motor failure will result in an automatic entry into autorotation, plus a slow descent rate and soft landing. A device to recover the rotors' inertia or a device to apply short duration torque could be incorporated. This default pitch of this device is set to that which is required for autorotation.
• If the blades are good enough to take bullets in a UAV then they should be good enough to handle manned flight.
• Ballistic parachute can be located on central mast above pilot.
• Excessive teetering: The rotors could contain a fixed azimuth hub spring that would resist a blade from teetering down when approching the X-tube between the two rotors. The rotors will probably be turning outside forward there for a pair of 'ramps' could be located between each foot-to-head tube and the X-tube. This 'ramp' will assure that the tip of a deviant blade will passes over the X-tube.

• If the blades and two-position elastomeric collective are factory produced, then homebuilders can purchase and build all the rest.

• Much of the tubing could be carbon, if there is a need to keep the weight down.
• There could be a tail boom and a nose boom and cables from the two booms hold the rotor side arms and place.
• There could be cables to a central mast and to the undercarriage, if necessary.

• Gross Weight: 550 lbs Or less if possible.
• Rotor Speed: 555 rpm.
• Blade: VR-7, 8'-8" radius, 5.25" chord.
• Collective Angle: 10.7º.
• Total Power: 20 horsepower ~ Momentum theory; 26 horsepower ~ Blade element theory. Why the large difference?
• Disk Loading: 1.16 lb / sq-ft.
• For comparative power requirements between configurations see; DESIGN: UniCopter ~ Electrotor ~ Rotor

• A pair of skids will probably be preferable to the tripod arraignment.

• Rotor supporting arms would swing forward and inward. Both 2-blade rotors would have their blades pointing forward and aft; or perhaps the blade grips might be modified so that all four blades point aft.
• The tail boom is detachable.
• Bowden cables between the mixer box and the rotor will simplify the swinging of the rotor spars.
• This gives a very collapsed configuration for storage and ground transportation.

• A UAV craft provides a safe way to develop and test the craft.
• Low vibration: For a camera mount this configuration should provide the least vibration. This is because there is no rotor to rotor interaction, the downwash is on a fuselage of thin tubing and there is no tail-rotor.
• Sophisticated remote controls, if required, could be developed by another company.
• Design:
• The spine and tailboom may be horizontal and slightly higher if the ELECTROTOR ~ SloMo or the 3-blade CVJ w/ Hub Spring were implemented at some later date.
• The battery packs will be separate items that will be attached at the rotors.
• The in-flight mission equipment will be a separate module(s) that will attach to the spline.

• Lateral Static stability: Point the two disks slightly inward.
• Consider using weight shifting for flight control. See musings below.
• A ruddervator could be mechanically linked to the action of weight shifting.
• Consider locating a fixed azimuth hub spring to significantly reduce any chance of a blade striking the lateral X-tube at 270º azimuth.
• Consider adding ramp bars on the lateral X-tube so that a blade tip will actually have to climb the ramp, should a blade get excessively low at 270º azimuth.
• A higher lateral X-tube might be used to house a means of rotationally linking the two rotors, not that this is needed.

• Motor: A failure of torque to one rotor must be matched by an immediate matched by the removal of torque to the other rotor. .
• Control - Flight: The opposing torque of driving both rotors will increase the friction in the pitch and roll control bearings. This might result in high cyclical control forces.
• Vibration: The thrust (Collective) is by the rpm of the rotors. This means that the fuselage etc will have to be 'tuned' so that it does not have a frequency within the operational frequency of the rotors.
• Motor: Will the two motors be strong enough for any prolonged flying. They may require special cooling. Dry Ice :). What about spraying a fine mist into the motor and cool by evaporation????
• There is the possibility of an asymmetrical settling with power (vortex ring state) during an autorotation.

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