This problem is similar to my concern about OTHER: Helicopter - Outside - Single (large) - Sikorsky's Reverse Velocity Rotorcraft Proposal

George Vranek's patent might work if there is a pusher propeller so that the disk can be level during vertical lift and tilted back (like a gyrocopter) during forward flight. There is a pusher http://www.vranek.ch/diskrotor.htm http://www.vranek.ch/images/diskrotor/Diskrotor-1-3.pdf

Another concern is the downwash from slow turning large chord blades of the upper rotor onto the large chord blades of the lower rotor on the coaxial configuration. Perhaps Sikorsky's X2 will have to address this potential problem.

• To consider an advanced electric UAV that is a coaxial rotorcraft during hover and a biplane during cruise. This will provide for VTOL operation and extend the time of flight.

• Quarter scale of electric UniCopter. The same scale as the Interleaving and the Intermeshing electric UAV proposals.

• Two coaxial rotors with two blades per rotor.
• 'Absolutely' Rigid Rotors.
• Reverse Velocity Utilization).
• The blades MAY have active twist (active wing warp) at 1/rev so that the retreating side will provide some lift as the rotors slow to stop. (I.e. as the advance ratio move to infinity.)
• The rotors will both stop when their blades are pointing to 90º and 270º azimuth.
• The blades will cross at 90º, 180º, 270º and 360º azimuths. It may be better if the cross at 45º, 135º, 225º and 315º. This will result in blades being at 90º and 270º when the other rotor's blades are pointing fore and aft.

• Option: Locate the propeller at the back [Pusher prop]. Probably a folding propeller. See info on Intermeshing - Electric - UAV

• Hover: The propeller drive shaft and the two rotor disks will be basically parallel.
• Transition: The RPM of the two rotors will slow down and the RPM of the propeller will increase. This will cause the rotors to change from helicopter mode to gyrocopter mode. Eventually, the two rotors will be stopped. At the same time the two rotor disks will be tilted back from the previous plane.
• Cruise: The two rotor disks (wings) and the fuselage will be pitched up to about 8º, whereas the propeller shaft will be tilted down so that it remains parallel to the horizon.
• The length and width of the bottom of the fuselage are increased to give a lifting body effect during cruise. This enlarges fuselage bottom should not be detrimental to hover.`

• Probably incorporate OTHER: Rotor Concept - Independent Root & Tip - Floating Root Method
• Alternatively: If the transition from mu > 0.5 & < 1 to mu > 1 is of a very short duration and there is no intention of flying in this speed range then consider excluding the independent Root & tip control and just employ a faster than 1/rev single flight control. In other words, the reduced lift during this short interval may not represent a problem.

• Plettenberg: http://www.plettenberg-motoren.com/UK/index.htm
• HP 370/40 Heli: http://www.plettenberg-motoren.com/UK/Motoren/Brushless/370_40h/Motor.htm
• Astro Motors: http://www.astroflight.com/e/env/0001QRb9JcOyK14XdU9d9k8/index.html?link=/index.html
• Astro 120 motor: http://www.astroflight.com/e/env/0001rSnsBqWgeRc5X05k3z2/store/store-Brushless.html?link=/store/store-type-tem.html&item=products:af-8120
• Hacker Motors: May not be big enough. http://www.hackerbrushless.com/motors.shtml

• The rotation of the motor's rotor drives the rotors. The counter-rotation of the motor's stator (frame) drives propeller.
• This results in a 2:1 speed reduction without the use of gears etc., when powering both the propeller and the rotors.
• The counter-rotation of the motor's two main components should eliminate the high-speed motor from creating gyroscopic precession. Of course, the bearings must be robust.
• Six gears (1 pinion and 1 crown) plus 4 spider gears in one housing. Operationally similar to a car's differential.
• The three 'brakes' in the above sketch might not be actual friction brakes. They might be motor/generators and be used to vary the power distribution between the three aerodynamic thrusters.
• The Inrunner+Outrunner motor can also be used for Intermeshing, Interleaving and Side-by-side configurations. On these configurations there will not be a need for the 'differential gears nor the third 'brake'.

• For speed controller between rotor & propeller see; DESIGN: UniCopter ~ Pusher Prop - Variable Speed Rotors and Prop - Speed Controller

• Battery:
• Lithium polymer batteries can be shaped to suit the aerodynamics of the fuselage.
• Information on Lithium ion and plolymer; by local person. http://www.batteryuniversity.com/partone-5.htm
• Capacitor:

• The blades of both rotors are pointed fore and aft. The propeller could fold aft when not operational. The tail assemble could be removable..
• The collapsed size of the craft should be; 5 feet long * 1 foot wide * 10" high.
• The weight of the craft should be 21 lbs.

• Consider having only one 2-blade ARR rotor. It will be the upper one and it must be slightly larger then if it was one of two rotors. The propeller might be pivoted so that it serves as a tail rotor during hover and thereby offset the torque of the single rotor.

• The onboard mission equipment will probably require 'look down' capability. Perhaps the bearing of the lower rotor could have a very large diameter (lazy Susan) and the equipment be within this diameter.

• The reduction between the motor & prop and the reduction between the motor & rotors will probably have to be reduced further. Consider conventionally mounting the rotor and driving the sun gear of a planetary gear set from the motor's shaft. The planet holder could direct drive the propeller and the ring gear could drive the pinion of the spiral bevel gear set.
• Gap between crown gears must be increased for pivoting shaft to prop. Not if only the propeller tips and not the drive shaft.
• Will the rotation of the lower rotor during hover detrimentally affect the camera or other mission equipment? Consider locating the sensors ahead (or behind) the rotors, perhaps under the canard.
• Serious concern: The lift of both rotors will be significantly reduced when they are turning very slowly and are located at 180º and 360º azimuth. Note that when one rotor is a 180º and 360º the other is at 90º and 270º, so this is not to bad.
• At this slow speed (low frequency) can the canard and HS have their pitch increased as a spike at 2/rev?
• Having the propeller directly in front of the canard, and to a much lessor degree the horizontal stabilizer may improve this temporary lift. C
• Consider stopping one rotor (wing) and then the other. In actuality, one rotor has to stop before the other and the only question is how many rotations sooner.
• Use blades/wings with camber so that the camber may help capture the 'lift' when the blades are at 180º and 360º azimuth, and turning very slowly during the transition.
• The airfoils are not optimized for rotor blade or for wing. This refers to overall profile and more importantly to the leading and trailing edges, which are subject to forward and reverse velocity. Basically put trailing edge profiles on both edges. This will result in a profile that is similar to a very high speed blade.

• Boeing stopped rotor: http://www.eyepod.org/Weapons-Boeing-Canard.html
• Somewhat related patent; http://patft.uspto.gov/netacgi/nph-Parser?Sect1=PTO2&Sect2=HITOFF&u=%2Fnetahtml%2FPTO%2Fsearch-adv.htm&r=18&f=G&l=50&d=PTXT&p=1&p=1&S1=(%22lifting+body%22+AND+helicopter)&OS="lifting+body"+AND+helicopter&RS=("lifting+body"+AND+helicopter)
• Google search [Sikorsky UAV coaxial Cypher]

• A COMPARATIVE ASSESSMENT OF HIGHSPEED ROTORCRAFT CONCEPTS (HSRC): Reaction Driven Stopped Rotor/Wing And Variable Diameter Tiltrotor

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