1361

Item 1361

DESIGN: ElectrotorPlus ~ Rotor - Hub w/ Offset - General

Moment Rod w/ Incorporated Spring or Damper:

The initial idea was to incorporate a spring into the moment rod for the purpose of allowing the MRGA to teeter at a smaller angle then that of the rotorhub at each cyclic. The idea is no good because the purpose of the moment rod is to apply a moment to the MRGA when the rotorhub is teetering not after it has teetered.

Therefore, consider the use of a damper in lieu of the spring. The damper will only apply the force when the rotorhub is actually flapping; up and down

These dampers are to be located on the two Moment Rods at one damper per rod.

Each damper is designed to give a force equal to the torque at the amount of movement for a given degree of teeter of the rotorhub plus the accompanying teeter of the MRGA. This is so the force rods can apply the appropriate torque about the X-axis of the MRGA.

The use of a damper within the rods means that the two rods do not have to have equal center-to-center distances. This, in turn, means that a teetering ratio of other than one-to-one can be used between the offset angle of the rotor hub and the teetering angle of the MRGA.

Note that when the rotor-disk and the MRGA have different teeter angles from each other there will be a cyclical Corollas action between the two

Rotor Disk:

See Disk

Assembly:

To minimize the range of angular differences between the axis of the motor and the axis of the mast, consider giving the mast a forward tilt. The angle of the till should probably be midway between the hover angle and the cruise angle. The aft and forward longitudinal cyclic range can be set to suit the forgoing.

For a general arrangement see; OTHER: Flight Dynamics - Rotor Hub - Offset Teetering Rotor and particularly drawing 1127.dc

Hub:

The hub and its teetering hinge must be stronger than normal to take the offset and gyro forces.

Undersling: The undersling will be based upon one specific mean operating weight (say the GW of 550#) irrespective of the final helicopter's configuration of application. The undersling on MAKE: SynchroLite ~ Rotor - Hub - 2-blade Teetering - Assembly (w/ 15º Teeter Offset) is 1.2055".

Blade:

See SynchroLite - Rotor.

Miscellaneous Related Stuff:

Much of the following has been coded into Access database; ELECTROTOR - Gyro and Gyro Data forms.

Constants:

Centrifugal effect per blade [F] = 3,949 lb. For the calculations on the SynchroLite (2-blade) see; DESIGN: SynchroLite ~ Rotor ~ Initial Rough Calculations for Rotor Consider adding the SI units etc. on the linked page and just having the link here. IE one data location.

Rotorhub Speed: [ω_RH] = 600 RRPM = 62.857 rad/sec.

Teetering frequency [ν_β] = 10 cycles/sec.

Teetering hinge Offset: [e] = 2" = 0.0508 m

Undersling: [?] = 1.6" = 0.0991m

Precone angle: [β_p] = 4º = 0.0698 rad.

Weight of two blades and grip = 8.25 lb * 2 = 16.5 lb = 7.48 kg.

Radius to CG of blade = 3.9 ft = 1.189 m

Force arm radius: [?] = 3" = 0.0762 m

Variables:

Teetering angle: [β] [Beta] Between maximums of -15º to +15º, = -0.262 to +0.262 rad.

Angular Velocity of teeter [ω_X] [OmegaX] Calculated; based upon maximum teeter and Sector. A varying velocity, from the Rotorhub via the Force rods,

Moment of teeter [M_X] [LX] Calculated; based upon maximum teeter and Sector.

Torque is a variable, from 460.2 N m to 0.0 N m depending on the angle of teeter [β]. For Moment [M_X] and Torque [Q_X] see the above web page. 1 N = kilogram * meter / second².

Offset:

The moment will increase by the square of the offset length.

Moment: [M] & Torque [τ & Q ]

The objective is to have approximately half the torque from the teetering rotor go to the mast and the other half go to the gyro. The intention being that the both torques on the mast will be equal.

For sketch of rotor see OTHER: Flight Dynamics - Rotor Hub - Offset Teetering Rotor, Sketch 3.

Complete Rotor:

Polar moment of inertia [J_M] = m * r² = 7.48 kg * 1.189² m = 10.57 kg-m²

Angular momentum [L] = J_M * ω = 10.57 kg-m²* 62.857 rad/sec = 664.69 kgm²s^-1It looks like the gyro has about 15 time more angular momentum than the rotors. See Access form. Does this make sense?

Moment = Centripetal force of one blade * Moment arm

In U.S. Customary Units and SI Units;

Torque is the sum of moment of the two forces. In other words the torque is the sum of the moments generated by the 2 blades.

The algorithm for the table below is teeter Torque [Q_R] [M_R]of rotor = Centripetal force * 2 blades * sin (teetering angle) * Teetering hinge offset = F * 2 * sin(β) * e

y = A * sin(ωt)

where;

y = ??

A = amplitude (rotor disk tip ~ in degrees) = β

ω = radians per second. For rotorhub this is 62.832

t = time

Example for 7.5º; 17,566 N * 2 * 0.130526 * 0.0508 M = 233.0 N m.

The torque [Q_X] [QX] In the database [Gyro Data form is the total torque from the offset. A portion of it is applied to the mast the other portion is applied to the X-axis (input torque) to the gyro. I do not know what the ratio is.

~ From here go to ElectrotorPlus_Gyro.html - Calculations ~

Place database forms Gyro and Gyro Data on Web page and link to it.

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Last Revised: May 18, 2007