1364

Item 1364

DESIGN: UniCopter ~ Control - Flight - Independent Root & Tip - Blade Root

Rotor Root Control:

Inputs to the Root Mixer: The algorithm for this mixer is in the form function root_mixer().

Collective lever. (elevating the lever raises the swashplate)

Rotor governor. (dropping RRPM attempts to lower the Collective)

Forward velocity. (increasing velocity lowers the swashplate)

Root Mixer to Root Swashplate:

There is one actuator [perhaps two] to the swashplate, (not the usual three). The single hinge is located at 180º azimuth. The movement is driven by mechanical linkage and hydraulic actuator, because of the large forces required.

Option: The root swashplate could have;

1 actuator and a single axis pivot.

2 actuators and a single ball pivot.

2 actuators and 2 scissors

3 actuators and conventional scissors.

1 actuator and 2 unequal scissors

The control input changes to the swashplate will be at a rate far below 1P, since they only vary with changes in collective and forward velocity.

Root Swashplate:

This activity might be in the Root Swashplate or it might be in the Root Mixer Box.

Forward <------------- Craft --------------> Aft

Thought: I suspect that one actuator can move the Swishring. There will be a ratio of movement between the 0ºψ and the 180ºψ ends; say 18/11. The slight deviation from the above should only have an insignificant effect.

Current Arm Lengths: The values below were copied from FORM: Flight Controls for UniCopter and may not be current.

Dim FwdVelocityArm As Single: FwdVelocityArm = 12

Dim CollectiveArm As Single: CollectiveArm = 4

Dim SwashplateArm As Single: SwashplateArm = 12

Dim SwashplateRadius As Single: SwashplateRadius = 4

Root Swashplate to Blades:

Conventional pitch links and pitch horns.
The blade roots will change pitch at 1P.
For pitches at various flight conditions and azimuths, see the following table.

Sketch of Reverse Velocity:

Sketch Notes:

The blue line is the location of zero airflow (rψ_0V) on the retreating blade at 150 Knots and a 478-ft/sec tip speed.

The red line is the location of zero pitch (rψ_0θ) on the retreating blade at 150 Knots and a 478-ft/sec tip speed.

The angle of attack (rψ_0α) is not plotted, but it will be zero also at the locations where the above two lines intersect. *

The objective is to have the two lines (and thereby the third line) as close to each other as possible.

*This will depend on how the induced velocity is determined, from momentum theory or from blade element.

The line of zero pitch will be modified in the FORM Flight Controls for UniCopter and then the resulting tables on the web page etc etc, which show the root and tip pitches various during various flight conditions, will then be modified as well.

If R < r > 0 then for the location of zero pitch to co-exist with the location of zero airflow, the following must be true.

Tip pitch (θ_T) = - Root pitch (θ_R) * (r / (1-r))

Root pitch (θ_R) = - Tip pitch (θ_T) * ((1-r) / r)

The following is based on the above 150 Knots and a 478-ft/sec tip speed. It is the pitch not the angle of attack (yet) and it does not include longitudinal dissymitry of pitch due to forward cyclic stick.

".. it is found that the effects of the reverse flow region are negligible up to an advance ratio of about mu = 0.5" ~ [Source ~ HT p.152]. It might be noted that the UniCopter is mu = 0.53.

I think that all of the greater cyclic pitch at the rear will be offset by the greater inflow angle at the rear. This might mean that the angle of attack is longitudinally similar.

Azimuth:	Tip Pitch:	Radius of Zero airspeed: (r)	Root Pitch:
º
90º	+2.0⁽²⁾		+4.00⁽²⁾
112.5º	+2.5⁽²⁾		+2.75⁽²⁾
135º	+3.0⁽²⁾		+1.50⁽²⁾
157.5 º	+3.5⁽²⁾		+0.25⁽²⁾
180º	+0º	0.00R	-1.00 ⁽¹⁾
202.5º	+9.0º	0.20R	-2.25º
225º	+5.96º	0.37R	-3.50º
247.5º	+4.94º	0.49R	-4.75º
270º	+5.32º	0.53R	-6.0º ⁽³⁾

(1)

(2) Guesses

(3) A very large negative pitch here will provide drag to help rotate the rotor. How would this efficiency/inefficiency compare to the efficiency of the required pusher propeller?

The use of the 2/P Swishring: at the root control might result in the line of zero angle of attack matching the line of zero flow better.

Related Pages at This Site:

OTHER: Rotor Concept - Reverse Velocity Utilization

Introduction Page | SynchroLite Home Page | UniCopter Home Page | Nemesis Home Page

Last Revised: 8/24/2007