Incremental Lift Flight Control System

Rather than incur the complexity of a goal-seeking blade (more or less lift with minimum drag), the risk of inadequate sensor analog to digital converter speed, or the possibility of a blade driving itself dynamically unstable under certain flight conditions, a set of blade configurations can be predefined such that each provides an increment of lift. The discontinuous linear increments are small enough to result in what appears to be smooth continuous flight. Then the Level Flight and Perturbation Computers need only specify a desired lift amount as an integer, and each Blade Computer need only sum the Level Flight and Perturbation Computer lift requirements, look-up the blade configuration that corresponds to the lift amount and command the flap and slat actuators to establish and maintain that configuration until the next lift requirements are received.

The following explores this approach with a few scenarios.

Definitions

AM= angle of mid-body relative to hub.
MAM = Maximum AM, e.g. 90 degrees.
DAM = +/- linear divisions of MAM for smooth flight, e.g. +/-90.
 
AS= angle of slat relative to mid-body.
MAS = Maximum AS, e.g. 30 degrees.
DAS = +/- linear divisions of MAS for smooth flight, e.g. +/-120.
 
AF = angle of flap relative to mid-body.
MAF = Maximum AF, e.g. 40 degrees.
DAF = +/- linear divisions of MAF for smooth flight, e.g. +/-160.
 
BV = mid-span blade velocity along the mid-body plane.
MBV = maximum BV.
DBV = linear divisions of MBV, e.g. 1000.
 
BL = blade lift.
MBL = maximum blade lift before stall.
DBL = +/- linear divisions of MBL for smooth flight, e.g. +/-1000.

At each DBV, predefine combinations of DAM, DAS and DAF to achieve a set of DBL (1000 DBL or less depending on the effective range available) at minimum drag. These can be empirically refined.

To achieve changes in AM without resorting to a mid-body actuator, the AF must be suddenly and dramatically increased to change the AM, and then the AF and AS must be quickly changed to maintain the new MBA. This sequence of events can be predefined for each DAM, so when one of the predefined combinations of DAM, DAS and DAF requires a DAM change, the configuration change must be preceded by the corresponding MB sequence.

Although a value for divisions of blade drag, DBD could be predetermined for each blade configuration, and used to somewhat compensate for the thrust lag of the engines and the velocity lag due to the hub-blade-engine-vane mass, the mass of the fuel and the additional drag of the hub and its payload for all possible attitudes and orientations cannot be predetermined, so DBV is used as the sole driver for engine thrust.

ET = engine thrust.
MET = maximum thrust.
DET = linear divisions of MET that correlate with each DBV, e.g. 1000.
 
AH = angle around hub where zero can be arbitrary, but for convenience is fixed on the axis perpendicular with the blade axle axes.
MAH = maximum angle, e.g. 180 degrees.
DAH = +/- linear divisions of MAH for smooth flight, e.g. +/-90.
 
CU = Controller Computer up command.
MCU = Maximum CU.
DCU = +/- linear divisions of MCU for smooth flight, e.g. 1000.
 
CF = Controller Computer forward command.
MCF = Maximum CF.
DCF = +/- linear divisions of MCF for smooth flight, e.g. 1000.
 
CL = Controller Computer left command.
MCL = Maximum CL.
DCL = +/- linear divisions of MCL for smooth flight, e.g. 1000.
 
CV = Controller Computer velocity command.
MCV = Maximum CV.
DCV = +/- linear divisions of MCV for smooth flight, e.g. 1000.
 
CC = Controller Computer clockwise command relative to forward.
MCC = Maximum CC.
DCC = +/- linear divisions of MCC for smooth payload rotation if a payload orientation device is available, e.g. +/- 90.
 
VV = vehicle velocity as measured at the center of the hub, using a sensor, inertial navigation, GPS, other means or a combination of means.
MVV = maximum vehicle velocity.
DVV = linear divisions of MVV, e.g. 1000.

At each DVV, predefine combinations of DAM, DAS and DAF to achieve a set of DBL (1000 DBL or less depending on the effective range available) at minimum drag. These can be empirically refined in a wind tunnel.

VA = vehicle altitude as measured at the center of the hub, using a sensor, inertial navigation, GPS, other means or a combination of means.
MVA = maximum vehicle velocity.
DVA = linear divisions of MVA, e.g. 10000.
 
VH = vehicle height as measured at center of the hub, using a sensor, inertial navigation, GPS, other means or a combination of means.
MVH = maximum vehicle velocity.
DVH = inear divisions of MVH, e.g. 10000.
 
AV = angle of engine vane split flap relative to closed position.
MAV = Maximum AF, e.g. 60 degrees.
DAV = +/- linear divisions of MAV for smooth flight, e.g. +/-120.

A set of DBL and DAV are predetermined for optimum coordinated turn control during conventional flight.

If a human pilot is involved, moving the joystick forward or backward correlates with positive and negative DCF, respectively. The more the movement, the larger is the DCF value. Similarly, moving the joystick left or right correlates with positive and negative DCL, respectively. Lifting and depressing the joystick correlates with positive and negative DCU, respectively.

The more the movement, the larger is the return-to-zero (level hover) resistance to increasing the amount of joystick movement. This safety feature can be temporarily disabled by depressing a button on the joystick to maintain the current joystick position for the few seconds it takes to alter a setting (DVA, DVH, GPS destination, radio frequency, etc.).

Twisting the joystick clockwise or counterclockwise correlates with positive and negative DCC. The magnitude of the joystick twist increases the magnitude of DCC.

A roller switch is used to set the values of DVA or DVH depending on the position of a toggle switch. Any value of DCV other than zero overrides any value of DVA or DVH.

Scenario 1 - Hover with lift imbalance between the blades or a cross-wind while incurring an increase altitude command:

When the Level Flight Computer detects that it needs more lift at DAH +42 and less lift at DAH -47, it commands each Blade Computer as its blade sweeps through the 90-degree arch of which +42 is the mid-point to increase its positive lift one DBL for each of the 45 DAH in the first half of the arch and decrease its positive lift one DBL for each of the 45 DAH in the second half of the arc, and it commands each Blade Computer as its blade sweeps through the 90-degree arch of which -47 is the mid-point to increase its negative lift one DBL for each of the 45 DAH in the first half of the arch and decrease its negative lift one DBL for each of the 45 DAH in the second half of the arc. Multiples of one DBL can be requested of the Blade Computers as a function of the severity of the correction requirement.

When the Controller Computer issues a positive one DCU value, the Perturbed Flight Computer instructs the Blade Computers to increase lift one DBL throughout their rotation about the hub. Multiples of one DBL can be requested of the Blade Computers as a function of the value of DCU, i.e. the severity of the flight requirement. If the Controller Computer issues a DVA value in lieu of a DCU value, the Perturbation computer issues DBL requests of the Blade Computers as necessary to achieve and maintain a desired altitude (fixed altitude mode). If the Controller Computer issues a DVH value in lieu of a DCU value, the Perturbation computer issues DBL requests of the Blade Computers as necessary to achieve and maintain the desired height above the surface of the Earth (terrain-following mode).

The Blade Computers sum the lift requirements demanded by the Level Flight and Perturbed Flight Computers, and comply by altering their configuration, and informing the Engine Computers of the DBV needed by their new configuration.

The Engine Computers accordingly demand DETs from the engines to meet the worst-case blade velocity demand while balancing the thrust of the engines to minimize hub oscillation. To accommodate a performance difference between the engines or the failure of one engine, i.e. when at DBV cannot be accommodated by a corresponding DET from both engines, then the DET is doubled for the performing engine until a predetermined hub oscillation maximum is reached. Thenceforth additional DBV requests are rejected, which cause DBL requests to be rejected, which cause additional DCU requests to be rejected.

As the next DBV is achieved, the Blade Computers start using the set of DBL appropriate for the new DBV.

As MBV is approached at MET, a stall warning is issued to the Perturbed Flight Computer, which relays the warning to the Controller Computer, which enables appropriate audio, visual and tactile (shake and preclude further joystick advance) alarms if a human pilot is involved.

Scenario 2 &endash; Vertical flight forward movement command:

When the Controller Computer issues a positive delta DCF value (forward command), the Perturbed Flight Computer determines that it needs an attitude change for a lateral acceleration that will properly alter the flight path of the vehicle and achieve the velocity associated with the DCF value. It either tricks the Level Flight Computer into thinking level flight has been violated by changing the horizon of the attitude sensor or other method, or it issues lift requirements to the Blade Computers as if it were the Level Flight Computer as in scenario 1. The magnitude of the DBL requested during blade rotation is a function of the magnitude of DCF.

When the Controller Computer stabilizes at a DCF value, the Perturbed Flight Computer determines that it no longer needs a lateral acceleration, so it reduces the magnitude of the DBL requested of the Blade Computers to maintain the current DVV (constant horizontal velocity at the current direction and altitude, or the altitude that correlates with the value of DVA, or the altitude that correlates with the value of DVH.

The Blade Computers correspondingly notify the Engine Computers of their DBV requirements, which the Engine Computers attempt to satisfy with corresponding DET.

Reverse, left and right movements are similar.

If the positive delta DCF value continues long enough, the Blade Flyer eventually accelerates to a VV at which more BL is derived from VV than BV, and the AM of both blades has increased to the point that the blades are pointing into the flight direction rather than the rotation direction, slowing the rotation to zero. When this occurs (VV > BV empirically derived?), Level Flight Computer and Perturbation Computer demands for more BL are satisfied with the set of DBL associated with each DVV rather than each DBV.

At this point one blade is still oriented relative to the hub as it was before the transition to horizontal flight, but the other blade is not. The Blade Computers query a sensor to determine the orientation of the blade relative to the hub. The inverted Blade Computer accordingly inverts the DBL it (multiplies by &endash;1) receives to function properly when using the DVV set of DBL during conventional flight.

During conventional flight, the Engine Computers no longer seek to balance engine thrust, and roll control is the same regardless of configuration, but pitch and roll control differ according to the vehicle configuration. With the two-blade configuration pitch control is achieved by altering the mid-body angle of attack with flap movements, and yaw control is achieved with engine vane split flap extensions. With the four-blade or two-blade with extended hub configurations, pitch control is achieved with a canard and yaw control is achieved with a rudder. The following scenarios are for the two-blade configuration.

Scenario 3 &endash; Conventional flight with lift imbalance between the blades or a cross-wind, and incur an increase altitude command:

When the Level Flight Computer detects that it needs more lift at DAH +42 and less lift at DAH -47, it commands each Blade Computer as before. Although the blades are not rotating, the DBL demands still result in the desired roll correction with asymmetric blade lift. Pitch is not an issue, because the hub and its payload are free to pivot to level in that axis.

When the Controller Computer issues a positive one DCU value, the Perturbed Flight Computer instructs the Blade Computers to increase lift one DBL as in Scenario 1. That the blades are not rotating is immaterial.

The Blade Computers sum the lift requirements demanded by the Level Flight and Perturbed Flight Computers, and comply by altering their configuration, and informing the Engine Computers of the DBV needed by their new configuration. When using the DVV set of DBL, this translates into less camber and more blade mid-body angle of attack and engine thrust.

Scenario 4 &endash; Conventional flight forward movement command

When the Controller Computer issues a positive delta DCF value (forward command), the Perturbed Flight Computer determines that it needs more engine thrust than an attitude change for a lateral acceleration. When using the DVV set of DBL, this translates into less camber and more engine thrust.

A less positive delta DCF results in less engine thrust and more camber. A negative DCF results in a pitch up to near stall maneuver in additional to less engine thrust.

Scenario 5 &endash; Conventional flight left movement command

When the Controller Computer issues a positive DCL value (left command), the Perturbed Flight Computer determines that it needs an attitude change as in scenario 2 by requesting positive DBL by the blade at AH +45 and negative DBL by the blade at AH &endash;45. The left Blade Computer accordingly issues a DAV increase to its engine vane according to the predetermined DBL-DAV set. The Blade Computers may also request more DBV (right blade) or less DBV (left blade) from the Engine Computers, facilitating the turn. The magnitude of the DCL value determines the magnitude of the DBL value, and, hence the magnitude of the DAV and DBV values.

A right movement results in a similar scenario.

Contents

William Terry (Bill) Holmes
756 SE Linn Street, Portland, Oregon 97202, 503-432-8577 (home), 760-917-2498, wtholmes.com,
william@wtholmes.com