0825

Item 0825

DESIGN: SynchroLite ~ Control - Flight - Governor - Rotor Type

Under Construction

Overview:

The conventional rotor governor appears to change the collective when the rotor speed changes. This would seem to result in a slow response to pilot inputs, since there will be a delay between the change of power and the change of speed with its resultant change in collective pitch.

The idea presented here is to change the collective when the torque changes since the torque will change before the rotor speed does.

The Drawing is of the conventional method where RRPM is measured and throttle changes are also read as a pre input to the electronic system.

Drawing: (Electronic Governor)

Basics:

Torque applied to the mast will cause the azimuth of the overrunning clutch (location of power into mast) and that of the hub (location of power out of mast) to differ. The greater the torque the greater the 'twist' in the mast. This relationship between torque and azimuths differential (i.e. mast twist) will be exponential not linear (see the sketch below). The collective is associated with this azimuth differential [ψd].

The rotor thrust is varied by the pilot's throttle control. This throttle could be in the cyclic grip as a twist, wrist rocker or for/aft thumb lever on the top.

A change of the drive-train's torque [Q] will change the collective pitch [θ₀] via a link to the collective mechanism in the mixer box. In other words; the throttle, not the collective lever, is the means by which the pilot controls the lift.

Consider reading the RRPM and using the throttle of torque reading to get a 'jump on the change to the pitch. October 20, 2000

Adjustment (Pre-flight settings?):

The minimum allowable collective pitch [θ_a] is that for ideal autorotation. It is at zero torque.

The maximum allowable collective pitch [θ_m] is that for ideal full power. May require more in "emergency" situations. It is at maximum torque. May require more in "emergency" situations.

This adjustment could be in the grip or thump control of the (infrequently used) collective.

Idea:

Have the mechanism adjustable so that it can be changed to suit the payload weight. In other words for a given torque we want a given angle of attack [ά] not given blade pitch [θ].

The ratio of change between torque and pitch is not linear but exponential. This way the pitch change is large at low torque level changes and small at high torque levels. [see sketch below]

The throttle control could be located on the cyclic. The collective lever will still exist but only be required for emergency situations. In other words, the only time that the pilot will have his hand on the collective is when the helicopter is in a 'near ground' situation.

Power/thrust change:

Horsepower [HP] * 5250 = Torque [Q] x RPM [RPM]

Power [P] = Torque [Q] x Rotational speed [Ω]

A change to the power setting [P] will change the torque [Q]. This change in the torque will immediately change the collective pitch [θ₀] (greatly at low torque levels & slightly at high torque levels. see sketch below.) and start changing the speed [Ω]. The change in the pitch [θ₀] and the associated change in induced drag [D_i], will partially oppose this change in speed [Ω]. The rotor speed [Ω] will then slowly adjust to the new power setting and the torque [Q] and collective pitch [θ₀] will slowly return part way toward the settings they were at before the change in power.

Autorotation:

There will need to be a mechanical collective lever that would only be used for the flare at auto-rotation.

The total loss of power will cause the collective pitch [θ₀] to drop to the autorotation setting [θ_a].

Flare and other requirements for dynamic energy stored in rotor disk:

Should the power from both engines stop then the collective lever will drop to the autorotation position [θ_a]. It is now up to the pilot to manually raise the collective for flare.

Sketch:

Exponential torque/pitch curve

Autorotation in the above sketch will be around Pitch = 1 deg. & Torque = -10 ft-lb

See [MDD p.112] for somewhat similar idea. Using Rotor Governor.

FORM: Auto-Collective:
Not yet scanned in.

Relevant Web Pages:

Snow Tech Magazine on CVT design

Possibly Relevant Info:

	Constant Rotor RPM	0786
	DESIGN: Control - Power Train - Synchropter- Hydraulic Schematic	0408

Varying the Rotor Operating Speed:

US Patent:

Number	Field	Date	Title
6,007,298	Rotor	2/19/99	Optimum Speed Rotor

Thoughts on the Subject:

Relevant Variables:

Input:

Rotor Speed [Ω]

Azimuth Differential [ψd].

Inflow Angle [ψ]

Collective pitch [θ₀]

Adjustment:

Collective pitch - Maximum [θ_m]

Collective pitch - Autorotation [θ_a]

Internal:

Angle of Attack [ά]

Coning Angle [a₀]

Induced Drag [D_i]

Power [P]

Torque [Q]

Constants [K₁] , [K₂] , [K₃]

Output:

Collective Blade Pitch [θ_c]

Relevant Algorithms:

[θ] = [ά] + [ψ]

[P] = [Q] * [Ω]

Torque [Q] = Horsepower [HP] * 5250 / RPM [RPM]

Perhaps the rotor speed is held to a constant or should it move slightly with the torque?

The following is from Access and is based on 600 RRPM, 9 ft radius, NACA 0012 blade, no twist

Collective pitch:	Thrust:	Horsepower:	RPM:	Torque:
7	768	66.6	600	582.7
6.5	697.7	60.0	600	525
6	628	52.6	600	460.2
5	493.6	41.6	600	364
4	364.9	32.4	600	283.5
3	244	25.2	600	220.5
2	135.6	20.2	600	176.7
1	46.2	17.6	600	154
0	0	17.1	600	149.6

Algorithm that give a close approximation to the above table:~ Q = 150 + (θ₀ + (1.3 - (θ₀ * 0.1)))^3

The above plots well to the sketch.

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There is a relationship between: Torque [Q] and Azimuth Differential [ψd].

Torsion: see FORM: PT-Mast Azimuth Differential [ψd].

___________________

There is a relationship between: Collective pitch [θ₀] and Azimuth Differential [ψd].

[θ₀] ≡ [ψd].

___________________

There is a relationship between: Rotor Speed [Ω], Torque [Q], Induced Drag [D_i]

[Ω] ≡ [Q] ? [D_i]; Rotor speed will change until [Q] = [D_i]

___________________

There is a relationship between: Torque [Q] and Induced Drag [D_i]. one to one ???

[D_i] = [Q] After change in speed stops.

___________________

There is a relationship between: Torque [Q], Collective pitch [θ₀], Rotor Speed [Ω] ??????

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[Collective pitch] = [Collective pitch - Autorotation] + ( K * ([Collective pitch - Maximum] - [Collective pitch - Autorotation]))

[θ₀] = [θ_a] + ([K₂] * ([θ_m] - [θ_a]))

More thought:

If the governor is located on the engine output then the rpm will be much higher and the governor can be much lighter. Consider using the engine with the long output.

The governor does not change the relationship between the collective lever and the collective pitch (ie. zero pitch = 5 degree lever angle). The collective attempts to influence a change in both.

Consider having a governor on both engines. The output is the sum of the output of the two governors. High rpm will try to push the collective up. If one engine goes down (ie. zero rpm) then the summed output will lower by half. A broken belt and the speeding up of the engine will cause the governor to increase the rpm, by half. Out-of-gas may cause a faster drop in the collective then if the governor was reading the rotor rpm.

Consider using low friction boden cables from the two governors to the mixer box.

Notes:

Before take-off a device is set to the current take-off weight of the helicopter. Fuel consumption during flight will only result in a (30/550) 5.5% change in weight during the flight.

Possible Problem: April 20, 1999

A problem could be caused by changes in loading on the craft while in flight, caused by the loading on the craft during changes in attitude, such as sharp turns, flares, air pockets (rough air) etc. I think the following is correct. The inflow angle [ψ] will decrease, the blade pitch [θ] will remain the same, therefor the angle of attack [ά] will increase, therefor torque [Q] will increase, therefor collective pitch [θ₀] will increase, therefor rotor speed [Ω] will slow down

Possible Solution:

The problem would appear to be the torque caused by aerodynamic loading, not the torque caused by the engine. Could a mechanical accelerometer device, measuring vertical loads only, be used to eliminate the aerodynamic torque being applied. Could the rotor speed be read also and the output (collective pitch change) be the result of the two inputs, also, could or should the throttle be linked to an output.

What about using a type of damper to give slower reaction time?

Rough Notes: The following is a collection of notes as rough draft only

Primary power settings

Max. Climb (maximum power)

Autorotation (minimum rate of descent)

Design consideration

Should the automatic setting be linked to angle of attack [ά] and not pitch angle [θ]? Some means of reading v1 will be required. Could this be a small flap on a cross bar, similar to the Hiller?

Pitch Angle [θ] vs. Angle of Attack [ά]

Should the helicopter be able to read "V" so that it will know the rate of descent or ascent and there by set the angle of attack to the thrust, not the pitch to the thrust?

COLLECTIVE

Consider linking the auto-collective to the angle of attack [ά] not to the blade pitch [θ]. This will require some means of reading the angle of relative airflow.

Oscillations - Possible problem

Could the pitch angle "bounce" back and forth about the given setting. It may need some form of dampening. Particularly if the blade is asymmetrical and could be unstable.

Could the firing of the engines cause an oscillating torque reading?

Thoughts - July 7, 1998

Air turbulence and wake interference will play with the torque value. We do not want resistance to the blade to cause an increase in the angle of attack (just the opposite - if it could be done instantaneously). We will there for need:

a) A "shock absorber type" damper to stop Alpha from change because of short duration torque increases or

b) Could a centrifugal weight be used (like the weights on the arms on a Bell helicopter)? There would be a torque sensor between the drive shaft and the centrifugal weight device and another between this devise and the rotor hub. Because the centrifugal device has virtually no resistance to rotation, it would be in azimuth synchronization with the rotor.

Calculation of Auto-collective

Maximum Climb

Select the maximum allowable rpm and torque that engine will be allowed to deliver.

Select the angle for the maximum collective pitch. [13 deg.?]

Computer to calculate total horsepower and hub horsepower???

Using Combined calculations get hub RPM at this horsepower.

Computer to calculate ratio? (Which will be same for all settings)

Computer to calculate hub torque for this hp and rpm?
Autorotation

Adjustments are settings that are made when not in flight

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Last Revised: March 8, 2002