Item 0831

DESIGN: SynchroLite ~ Control - Flight - Governor - Rotor type - Hydraulic


To have all the primary controls on one lever. A separate overriding collective lever is included, for use when desired. The intent is to have a helicopter that is easy and safe to fly, yet can still be flown in a conventional manner when desired

Outside Helicopter

Flettner FL- 282

The Prewitt Aircraft Co's. technical report ATI #20283 on the flight tests of the FL-282 states that the rotor governor was found to be very effective.

Information on governors: [Source ~ MDD p.111-115]. Sketch of 1940's rotor governor: [Source ~ MDD p.145]

It used a fly-ball rotor pitch governor. There was 10 % of RRPM adjustment. There is a specific report on it ~ Prewitt Aircraft Report N0. 5-130-2 (Do not have.)

"Helicopter Theory Interview with Dr. Kurt Hohenemser Concerning his recent Contributions: Air Technical Intelligence Review No. F-IR-133-RE. Report # 4. (Do not have.)




Control Logic:

There is not a direct correlation between the RRPM and the collective pitch. In other words, the actual value of the collective's pitch does not have a direct relationship with the actual value of the rotor's RPM. The difference between the actual and the desired RRPM determines the rate of change of the collective pitch. This change will be in the direction of bringing the actual RRPM up or down to the desired RRPM.



The pump is driven from the rotor mast, or in the case of the Unicopter and Dragonfly, from the X-over shaft. For the UniCopter and the Dragonfly, this pump might draw the oil from the central gearbox and then distribute the oil to all three gearboxes, for lubrication.

The volume/pressure of the oil has a direct relationship with the speed of the rotor. Pump is a non-positive displacement type? Have not found a miniature pump yet.


The cylinder is attached to the collective arm assembly, by way of a position matching and friction device.

Needle Valve A:

Located in cockpit. Used to set the rotor speed to the desired operating RRPM;

Note: the oil viscosity changes with the oil temperature. If this valve incorporates a device that varies the size of the orifice in accordance with oil temperature then manual adjustment of this valve can be reduced significantly. Perhaps this valve can be controlled by the pressure of a gas in a chamber. A heat exchanger would also be located in the chamber. As the oil changed temperature the gases pressure would change and, in turn, the size of the orifice would change. There must be a company that currently markets such an item.

Needle Valve B:

Controls the rate of movement (speed) of the cylinder's rod. Acts as a damper on rotor induced vibrations. Ambient heat changes may change the viscosity of the oil and thereby change the amount of dampening. Keep all hydraulic components away from engine and exhaust. Note: the oil viscosity changes with the oil temperature. If this valve incorporates a device that varies the size of the orifice in accordance with oil temperature then manual adjustment of this valve can be reduced significantly.

Open/Closed Valve C:

This Open/closed valve is used to activate or remove the governor from the collective system. When open, the cylinder can be moved independently in respect to the rest of the hydraulic system. Control of this valve should be located on the collective stick. If transmission oil is used, its viscosity will preclude the ability of passing tubes to the collective lever. This may necessitate an electrically controlled valve located on the exterior of the transmission housing or a light Bowden cable from the collective stick to a mechanical valve on the exterior of the transmission housing.

Throttle Tweak Control Valve (partial correlator): see Alternative below

Linked to the throttle. Turning the throttle grip, to increase engine power, will also slightly increase the restriction to the flow of oil. This will causes the collective pitch to increase slightly, while the additional engine power will maintain the RRPM against the increased thrust.

Accumulator A:

Uses compressed gas to exert a downward pressure on the cylinder. The larger the accumulator, the smaller the differential in pressures over the range of cylinder travel. See Bimba catalog for small accumulators.

Reservoir: (option)

A small reservoir for holding and cooling the oil.

Heat Exchanger: (option)??

Magnet metal Remover: ??

Filter: ??




Alternative Option:

Can the Accumulator and the needle valve B be replaced by a spring?

Manual Override & Warning Sensors:

Use transmission-cooling oil or separate oil system? See below Governor and Transmission Lubrication:



Could consider use of pitch-lag coupling, based on rotor torque, as a means of providing the instantaneous action (tweaking).

Related Web Sites:


Introduction to Fluid Power



Parker Hannifin

Handled locally by; Hyseco, 879-8851, Matt, 145 W 2nd


Clippard Products

For small hydraulic cylinders only.


Hypac Hydraulics






Lee's Micro Hydraulics Products

Very small valves


Governor and Transmission Lubrication:


Can one type of oil serve as hydraulic oil and lubricating oil? ~ January 3, 2003; Oil for use in gearboxes will have a higher viscosity than oil that is used in hydraulic systems. Automatic Transmission Fluid might serve both functions but not be optimum for either. The additives might have to be considered as well. ~ Perhaps the simple hydraulic control system can be designed to work with the thicker transmission oil, since the control system has is very little flow and the design of the system is based on the principle of 'bleading/leakage'.

Potential Answer:

The K-Max uses Dexron III, a mineral based ATF (automatic transmission fluid) made to General Motor's specifications. This information is from 'K-Max Intermeshing Rotor Drive System' 53rd Annual Forum Proc., AHH, 1997. I have hard copy



A collection of 'positives' for the hydraulic rotor governor.

Related Thoughtless Ideas:

DESIGN: SynchroLite ~ Control - Flight - Governor - Rotor Type - Electronic & General


OTHER: Miscellaneous - Thoughtless Ideas - Constant Speed Rotor


OTHER: Misc. - Thoughtless Ideas - Rotor Governor from Torque (elastomeric)


DESIGN: SynchroLite ` Control - Flight - Hydraulic Schematic


Some Additional Thoughts:



FORM: Auto-Collective Does this serve any purpose here?


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Last Revised: February 27, 2011