Item 0828

OTHER: Aircraft - Gyro/Heli - Gyrocopter/Helicopter (w/ power split)

Gyro/Heli I

Unified Gyrocopter & Helicopter (compound in future?)

Overview:

A theoretical and preliminary design for a hybrid helicopter/gyrocopter, where a percentage of the engine power goes to the rotor and a percentage to the propeller. Handling of reaction to rotor torque not yet satisfactorily solved.

Drawings:

Overall Conceptual Outline: The rotor and the propeller are located together, between the pilot and the engine.

Varying the pitch of the propeller offsets the torque of the rotor.

The engine is direct-coupled to the sun gear of a planetary reducer (primary reduction). The planet gear holder drives the pinion and ring (secondary reduction), which, in turn, drives the rotor. The propeller blades are mounted on the outside circumference of the ring gear.

There is a "tube' through the center of the transmission which is used to structurally connect the front and rear of the fuselage.

Features:

Power Splitting: The pilot's throttle controls the total amount of power being delivered. The planetary reducer (epicyclic differential) automatically splits the power between the rotor and the propeller.

"In an automobile and other wheeled vehicles, the differential allows each of the driving wheels to rotate at different speeds, while supplying equal torque to each of them." "An epicyclic differential uses epicyclic gears to split torque asymmetrically between the front and rear axles."

Rotor Governor: A rotor governor automatically controls the rotor's collective pitch so as to maintain a constant 100% (operational) RRPM. Is this necessary? At low forward speed, such as before takeoff, the angle-of-attack of the propeller will be at its highest This means that the propeller will have greater drag and this will result in the rotor having a higher RPM.

Prop Feathering: The pitch of the propeller blades can be varied from reverse thrust to full forward thrust. Why? Lateral cyclic to counter torque from the main rotor? Vertical cyclic to counter bunt-over??

Power Splitting:

General Gyrocopter Data from Homebuilt Rotorcraft:

If ship's gross weight is 1000 lb then there must be 500 pounds of static thrust.

An efficient prop will develop around 5 pounds of thrust per horsepower.

It will take at least 100 HP to develop 500 pounds of thrust.

Torque Calculations for 50% of power to Rotor and 50% of power to Prop:

Rotor [Torque x RPM] = Prop [Torque x RPM]

Assume; operating Rotor RPM is 400 and operating Prop RPM is 2000. Ratio of 5:1.

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

Therefor Torque [Q] = (Horsepower [HP] * 5250) / RPM [RPM]

Rotor [Torque] [QR] = (Horsepower [HPR] * 5250) / RPM [RPMR] = (50 * 5250) / 400 = 656.25 lb-ft

Prop [Torque] [QP] = (Horsepower [HPP] * 5250) / RPM [RPMP] = (50 * 5250) / 2000 = 131.25 lb-ft

Reaction to Rotor Torque:

The torque of the rotor (profile and induced drag) must be offset by the propeller, or vertical fin(s), or tail rotor or twin lateral main rotors or (???).

What about a co-axial configuration, where the 2nd bevel gear is driven from the bottom of the bevel gear on the ring gear ?

Rotor Governor:

Maintain constant 100% (operational) RRPM by varying the collective blade pitch:

A mechanical rotor governor is located at the rotor hub and automatically controls the collective pitch of both blades. This mechanical governor consists of small weights that move outward by centrifugal force. The centrifugal force is created by the rotational speed of the rotor hub. The minimum allowable pitch is that which will be appropriate for autorotation. The maximum allowable pitch is that which is appropriate for maximum power. The movement of the weights on the governor is in the plane that is normal (at right angles) to the axis of the mast. This arraignment will eliminate changes in G-forces from effecting the governor. Springs hold the weights in and centrifugal force moves them out.

A dampener will be required to stop oscillations etc.

Semi - jump take-off:

Should the pilot wish to perform a more vertical takeoff, he can over ride the rotor governor and hold the blade pitch down at zero degrees until liftoff. This will cause the blades to have a higher RRPM, and more inertia, at the time of lift off.

Prop Pitch Control:

Prop pitch control is required to offset the yaw caused by rotor torque. (unless twin rotors are used)

The values in next two lines come from the Power Splitting segment above:

The prop thrust is (1/2 of 500) = 250 pounds of static thrust.

The rotor torque is 656.25 lb-ft.

At the start of ground roll, when taking off, the propeller is required to
  1. Offset the rotor torque of 656.25 lb-ft.
  2. Direct all of its thrust backward, to build up forward speed as quickly as possible.

Therefor the length of the moment arm of the propeller will be 656.25 / 250 = 2.625 feet. If the center of thrust on the propeller blade is at 80% of its radius, then the propeller must have a 6.56 ft. diameter. Having a movable rudder (or twin movable rudders) linked in with the propeller pitch yaw control can reduce this diameter to a reasonable size.

Overrunning Clutch:

A overrunning clutch will be required on the rotor mast to allow the rotors to continue turning in the event of a disabled drive. The rotor governor will automatically set the collective pitch of the rotors to the autorotative setting

Drag and Forward Velocity:

The drag (profile and parasite) will always be greater on the right hand side of the craft therefor in straight flight the right hand side of the prop will be set at a slightly greater pitch then the left side.

Method of Operation:

Takeoff:
  1. Lock wheels.
  2. Set propeller to 'counter-rotation' position for takeoff by movement of pedals.
  3. Increase to full power and wait for the rotor to come up to operational RRPM and the governor controlled cyclic to rise to maximum pitch.
  4. Release brakes and as speed builds start re-centering pedals.

Probable Advantages:

Miscellaneous:

Long tail boom for stability.

To decrease the rotor induced yaw, consider offsetting the mast a few inches to the left of the craft's centerline. Using hypoid gears in lieu of ring and pinion might do this.

HYPOID GEARS; A type of differential final drive using a spiral bevel gear on the drive shaft, allowing it to be located below the center of the ring gear on the axle. This makes possible a lower floor in the car. Ratio around 4:1

Consider partial flapping restrainer, located in teetering hub. (for use in conjunction with hypoid gear mast offset)

Consider anhedral at blade tips, to reduce flapping.

Start-up clutch not required because the prop can accept the rotation.

Option:

The propellers thrust must offset the thrust of the rotor. This thrust must be located approximatly 2-1/2 feet to the right of the centerline during hover and move toward the centerline as the forward speed increases. Therefore, consider 2 propellers, one on each side of the mast. The starboard propeller has a fixed pitch and the port propeller to have a variable pitch. This variable pitch would not move to a feathered position but to a flat-on position or a reverse thrust position during hover.

Idea re Yaw:

This craft will not have the same level of rotor induced yaw as a helicopter since only half of the engine's power is going to the rotor. Perhaps the vertical stabilizer could have a built in anti-yaw alignment. This way the thrust from the propeller will hold the craft in alignment. As well, since the thrusts from the rotor and propeller have a fixed relationship, as the rotor induced torque decreases so will the airstream from the propeller. This will be in effect during hover and forward flight.

 

More Miscellaneous:

Date: 14-Apr-01 18:00
Author: Dave Jackson (dave_jackson@ultranet.ca)
Subject: Toss accolades or rotten tomatoes

Premises (re gyrocopters):

  1. Drag in forward flight comes from both the fuselage and the rotor.
  2. The center of thrust should be located near to the center of drag.
  3. The drag from the rotor is significantly reduced when it is in an unloaded state.
  4. In this state, the thrust from the propeller is now well above the new center of drag.
  5. This can cause a push over, bunt (PPI, PPO PPS or whatever)
  6. This can result in a severe headache.

________ now from the _________

~ Department of Demented Designs ~

Where the lights never go out ~ cause the light never came on.

In the foot steps of Chuck Beaty, Craig Wall, Dick DeGraw, me and a few unmentionables.

The PPR *

* Partially Powered Rotor

It has previously been mentioned that a PPR will offer;

  1. A shorter takeoff roll.
  2. A maintaining of the RRPM during an unloading of the rotor.

But; has the following been mentioned or considered?

  1. The drag of the rotor will be less. This will allow the center of propeller's thrust to be located lower, closer to the center of the fuselage's drag and further from the center of rotor's drag.

In other word, with a reasonable amount of power going to the rotor, any unloading of the rotor will have very little change on the 'drag - thrust' moment arm.

The best thing since sliced bread, or is it chopped liver?

Dave J

Author: Michael Guard (rotors1@home.com)
Subject: newby understanding

Dave,
I'm not the expert here, but it seems to me the center of thrust can be located on the center of fuselage drag with or without the rotor being powered. Usually the prop length is what determines the location of the center of thrust, and the center of gravity and fuselage drag need to be adjusted accordingly by the location of the pilot/cabin. I realize you're speaking of the center of drag of fuselage and rotor combined, but look at the Dominator with center of thrust slightly below center of gravity (I'm not sure about the center of drag).
Come to think of it, if the rotor is powered and continues to produce thrust even when "unloaded" (stick forward), rotor thrust would be more likely to cause a bunt on an otherwise nuetral machine?
MG

Author: Dave Jackson (dave_jackson@ultranet.ca)
Subject: to newbie too from newbie two

Michael,

The plane of a gyrocopter's rotor disk is tilted back from the horizontal by approximately 9-degrees. Its thrust vector is normal (90º) to the plane of the disk. This means that the thrust vector can be broken down into a vertical component and a horizontal component. The vertical component is resisting gravity and the horizontal component is resisting the push of propeller etc.

When the rotor blades are suddenly unloaded, because of a downward gust, there is no more rotor thrust. This means that there is no more horizontal component and the opposing horizontal moment, from the propeller etc., suddenly bunts the gyro over.

The rotor disk it tipped back at 9-degrees so that it can be driven by the flow of air passing through its 'driven' region. If some of this power to drive the rotor were to come from a mechanical source (full time pre-rotor) then less power need come from the air. Therefore the plane of the rotor disk can be closer to the horizontal. see Note below

The closer the rotor disk is to the horizontal the smaller the horizontal component of the thrust vector is. The smaller the horizontal force is then the less likely hood of a bunt-over when this horizontal force is lost.

Note;- The rotor blades must be given a slight increase in their pitch. Also note; - if the mechanical power input is quite large, then the pitch change will be quite large and this will necessitate the inclusion of a simple rotor pitch control. Also, also note; - that Larry Goodhind's earlier comments about a governor and gyrocopter are valid in this context, because we are now starting to talk about a hybrid gyro/helicopter.

I think.

Dave J

Author: Michael Guard (rotors1@home.com)
Subject: bunt etc.

Hi Dave,
I think we may be thinking of different type machines; I'm thinking more of the Dominator type with thrust at or below the CG, it seems your'e thinking more of the RAF style with center of thrust above CG.
I'll go with the RAF style; the way I understand it, when airborne the prop thrust tries to rotate the craft forward, it does so until the rotor thrust vector is far enough ahead of the CG to have enough moment to stop the rotation. Assuming we're talking about the rotor producing the same amount of thrust whether powered or unpowered, it seems the disk will need to be at the same angle, all else being equal?
Michael G

Author: Michael Guard (rotors1@home.com)
Subject: another thought

Hi again Dave,
Another thought, say the rotor is producing more thrust when powered and therefore the horizontal component is smaller, it's still what is keeping the craft from bunting, remove it and it will bunt?
Since we are talking about a safer rotorcraft, shouldn't we make the first logical step and assume we are starting with a machine with center thrust and proper HS, since that's the most stable design? Then the tendency to bunt is already removed.
MG

Author: Dave Jackson (dave_jackson@ultranet.ca)
Subject: trying to think

Michael,

Yes, I was thinking mainly of the low profile gyro. It is my understanding that the Dominator with its high profile and horizontal stabilizer is a very safe gyrocopter.

This raises the question ~ Why isn't everyone buying Dominators?

This is really out of my league. Others are qualified to give better answers, but my impressions are;

          1. Like the plane and the helicopter, it is extremely preferable to have the center of gravity ahead of the wing's or rotor's thrust vector.
          2. Applying partial mechanical power to the rotor allows its thrust vector to be closer to the vertical.
          3. This makes it easier to have the GofG ahead of the rotor thrust vector.
          4. This means that the total center of drag is lower and that the center of thrust can be lowered.
          5. If all the rotor thrust was by mechanical means but the prop was still providing all the forward thrust then (excluding the H-force) the rotor thrust would be vertical and the prop thrust could be directly inline with the only source of drag, the parasite drag of the fuselage.

Dave J

Author: Douglas Riley (driley@lisman.com)
Subject: powered rotors/buntover

Dave, there are certainly advantages to have some power fed to a gyro's rotor: As pointed out in other threads, it wastes less power than our pure autogyros' "pneumatic drive" and it can lessen the likelihood of a loss of RPM in a sustained low-G maneuver. Disadvantages include weight, complexity and cost. Dick DeGraw uses helicopter-style articulated rotorheads on his machines: a far cry from the U-joint-and-a-bearing that the rest of us use quite successfully.

Your suggestion that a more nearly level disk is easier to arrange into a stable configuration is a red herring, I think. Any aircraft in level unaccelerated flight will orient itself so that the various forces on it are in balance. If there's a pushover tendency caused by the engine or by a low center of (fuselage) drag, then either (1)a horizontal stab will generate the balancing force by assuming a negative angle of attack, or (2)(if there's no HS) the frame will rotate nose-down until the rotor thrust is ahead of CG. The angle of attack at which the rotor must fly to lift the craft really has nothing to do with this process, only with the best placement of the rotor along the fore-and-aft axis so that the frame rides fairly level. (Going back to the old Air Commands, they rode very nose-down at higher speeds, almost like a helo, because the rotor position was based on Bensen's design but they had a big PPO moment to overcome. The factory HS fixed this pretty well.)

The important point with either a partly-powered or an unpowered rotor is to have the various pitching moments that act on the fuselage (EXCLUSING the rotor's thrust) add up to either zero or to a small nose-up moment. That way, when the rotor's thrust is added, this thrust will be either right through the CG or behind it (to neutralize the nose-up moment). More critically, when the rotor's thrust is taken AWAY (in a low/zero G situation), the frame won't pitch over, but will fly level or nose up a bit.

Author: Dave Jackson (dave_jackson@ultranet.ca)
Subject: re: powered rotor

Doug, thanks for the excellent points you brought up. I have started to read some of the articles by Greg Gremminger and Jean Fourcade. The complexities certainly make it interesting.

It still appears that a horizontal rotor disk has advantages in regard to static stability. This is because the rotor's force vector does not have a longitudinal component and therefore, since the system is in balance, there is no opposing longitudinal force. If the rotor is unloaded there is no force to cause a bunt-over.

The bottom line of this thinking is that if "bad' forces can be minimized then the means necessary to overcome these 'bad' forces can be reduced.

The problems in delivering enough power to the rotor to have it operate horizontally is another story. Next

Author: Doug Riley (driley@lisman.com)
Subject: horizontal component

Dave, the horizontal component of rotor thrust does not have to be bothersome. Just lay out the airframe so that, without considering the rotor, there is no net pitching moment about the CG. Then place the rotor so that, in cruise, its thrust line passes through the CG. That way, if the rotor's G load changes, there is no pitching effect. The easiest way to pull off this arrangement is to use centerline thrust and also place the center of fuselage drag on the CG. The same effect can be had with the thrustline and/or center of drag not on the CG by using a horizontal stab with the right amount of incidence, but it's trickier. (This "pitch-neutral" setup is also not optimum because stability won't really be quite neutral; the rotor is unstable w/r/t angle of attack and it passes this instability along to the airframe. Putting the rotor thrust line behind the CG cures this problem.)

Even a fully-powered gyrodyne rotor will experience some changes in the angle of its thrustline as airspeed varies. And it has the same instability w/r/t AOA that the autorotating rotor has.

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Last Revised: September 30, 2008