AeroVantage ~ Trim, Stability & Control - Stability

• Both:
• Vortex Ring State:
• 'It was argued that VRS could be initiated in one or both rotors simply by the effect of yaw rate or roll rate, even when the tilt-rotor aircraft was operating outside the steady state VRS boundary.' ~ Leishman, J.G.
• During hover and transition, will the short longitudinal and lateral moment arms result in the craft being very sensitive and unstable? Will the wings and HS act as dampers and reduce any lack of stability. Will the gyro control be sufficient to maintain stability.
• Idea: The V-22 limits were 800-fpm descent and 40 KTAS. This represents relatively low airflow velocities. It would appear that lightweight device(s) could be deployed while the craft is operating below these settings. This device(s) might be gas filled aerodynamic balloon with cables to each wing, additional retractable stabilizers, etc. In other words, anything to resist roll and yaw. The wings, which are subjected to very little downwash, so help resist a rapid descent; as long as their planform is horizontal. Alternatively, consider substituting a parasail for the 'balloon', which is automatically furled and stowed upon landing. None of the above devices are intended to slow the descent of the craft. They are intended to arrest any roll, and subsequent yaw, which may come about due to asymmetrical entry into a VRS.
• Also see; OTHER: Aerodynamics - General - Vortex Ring State (settling with power)
• V-22 HIGH RATE OF DESCENT (HROD) TEST PROCEDURES AND LONG RECORD ANALYSIS Have on E-drive
• 1x2
• Concern ~ Lateral Stability during Rapid Descent and in Ground Effect:
• The very short moment arms between the craft's longitudinal centerline and the location of mean thrust on the PropRotors may not be enough for lateral cyclic to provide sufficient control during hover.
• One perhaps small advantage is that the lift on one side will be assisted by the reduction of lift on the other side.
• The PropRotors are always working with axial flow. Therefore, perhaps the planform of the blades should be that of a propeller. This 'inverse taper' will result in a longer moment arm.
• If the vertical stabilize and its rudder was located directly behind the rear PropRotor and tilted with the PropRotor then it would always be in the streamtube when the Proprotor is in hover mode and in cruise mode. A small skid or wheel could be located in this rudder for landings in the hover configuration. Any thickness of this rudder might also serve as the exit tube for the motor's cooling air.
• Potential Solutions:
• Wing Dihedral.
• Small amount of flap at the blade roots; to increase the moment arm length between the craft's CG and the rotor's center of thrust.
• Rudder; to deflect some of the rear PropRotor's thrust
• Larger PropRotors; to increase the moment arm of the rotor's thrust.
• Note: August 9, 2009. Consider having the outer portion of the two wings attached by a longitudinal pivot, which is located on the fence and 1x2 - Extendable Tubes extension line. Raising the wings by a rotation of 135˚ after the PropRotors have achieved or ar near their hover position will result in a reduced value of rotational inertia about the fore-aft X-axis, and, it MAY reduce the ability of a gust from the side to roll the craft.
• The forward supports may swing out from under the fuselage to their landing position as the wings swing upward.

• Problem: The wings are too long and therefore they stick up too high.

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• Wing Anhedral
• Consider have the outer portions of both wings droop 5º to 15º when the craft is on the ground, hovering, and in very slow flight. This will result in a gust or wind from the side wanting to try and roll the craft into the wind. The drooped wings might be held in this down position by gravity.
• During the transition to forward flight, the lift on these two outer wings might cause them to lift to their normal flight position.
• Dampers may be required. Power actuation may be required (assisted by the above mentioned gravity and lift). Position locks may be required.
• Weird idea, but perhaps this action by the individual wings may be used as the means of providing roll.

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• Lateral tilting of complete Proprotor and motor.
• For roll and for yaw.
• This tilt axis should be as high as possible so as to maximize its effect.
• There will be a gyroscopic cross-coupling but it might be relatively insignificant due to the blades not requiring tip weights and perhaps reduced leading edge weights. In addition. the PropRotor's diameter is a little smaller than a conventional helicopter would have. Concern, the craft might require gyro stability coupled to very fast lateral-tilt actuators and this will increase the gyroscopic precession. Perhaps the gyroscopic precession of the rotating PropRotor might be over powered by servo if the rotational inertia of the Proprotor is very low. Note that tilting the 'Electrotor Assembly' will want to tilt the fuselage in the wrong direction, slightly,
• This lateral tilt will be faded out as the PropRotors translates into forward flight.
• See; See Roll Input on Web page 1712.html
• Wing dihedral.
• Lateral Cyclic Control.
• identical lateral thrust vector changes about the Z-axis of both rotors.
• Diagram shows the greater roll moment that may be produced by Absolutely Rigid Rotors

• The '43' is for a blade at 90º or 180º azimuth. In actuality the moment arm will be a lot, lot less.
• The ailerons on the wings are moved also, but this is useless for hover.
• Concern: For lateral stability, particularly during a perturbation, the means of achieving it must be improved.
• Consider having collective control but not cyclic control. Lateral control would be by so called weight-shift where the rotor-motor assembly (Electrotor Principal Assembly) would roll left and right on a knuckle joint. Note that there will be opposing gyroscopic precession between the 2 rotors.
• Lateral Control by Rudders.
• Idea. Locate a rudder on the leg of all 3 landing wheels. When the craft is in the hovering mode the bottom portion of the vertical rudders can be quickly swung to Port or Starboard.
• Opening up of Wings.
• Idea. Consider that the the wings be open to the flow of air when the rotors are in the hovering position and the landing gear is down. In other words all three activities are interlinked.
• Use the batteries in a Stabilization Gyroscope. ~ September 13, 2009
• Use the batteries as a stabilization gyroscope during these short periods of time.

• Could the swirl from the front rotor create a rolling moment about the wing's roots?
• Consider modifying the profile of the wing's roots.

• 2x4
• Concern ~ Lateral Stability During Hover:
• Consider having the 4 PropRotors angle inboard slightly as they transition to the hover position. This may give greater stability during hover. Will it really help?
• Concern ~ Lateral Stability During VRS:
• Lowering the craft's center of gravity during hover may improve it's stability an reduce the VRS concern. Having the rotor disks at a higher elevation in respect to the fuselage when in the hover position could do this.
• Could giving the rotor disks a slight lateral inward angle (dihedral) during hover be advantageous. This may result in reducing the interaction of the vortex rings of the rotors.

 Working Papers:

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