You can't keep a good man down. A new design is born.

[Lu Zuckerman]

Look what I found on the internet

New Rotorhub Invention:

The link http://www.SynchroLite.com/1377.html is to a web page that describes a new style of rotorhub. This hub should offer significant flight-control and aerodynamic advantages over existing rotorhubs.

This invention has been placed in the Internet and is referred to on a number of forums so that it is the public domain. It can therefore be used by anyone and patented by none.

Any criticism, comments or questions will be appreciated. They should be directed to;- [email protected]




:E :E

[Cyclic Hotline]

I was actually wondering what happened to Dave, just the other day. Looked up his website even.

I was thinking about a whole lot of the old PPRuNe crowd, who had just disappeared.

Anyone else out there?

[Spaced]

Dave got sin binned for some political comments a while ago, and hasnt been allowed back since.
How about it mods? I reckon he learnt his lesson.

[Heliport]

Dave was only in the sin bin for a few days.
There was more to it than political comments, but he wasn't banned.

I don't know if anything happened in another forum at some point (Dave was a regular in Jetblast) but he's listed as having access to all forums.

Perhaps he's been busy working on his new design. :)


Heliport

[sprocket]

More power to the man, looks like a true designer at work. :ok: I gotta admit I have been quietly watching his work in his other forum.

[Dave_Jackson]

WOW!! The password works. :D

Now, where did things leave off? http://www.unicopter.com/devil.gif



http://www.unicopter.com/wink.gif

[sprocket]

:D Ban him Heliport, he's making threatening remarks again. :p

[Flingwing207]

OK Dave, Lu - I finally figured it out! Cool stuff, but...

Dave (or anyone), coupla Q's. It seems to me that only four blades will work on this hub (or two, but then what's the point of the double U-joint). For instance, if you have three blades, then when the blade at 90 deg was flapping up, both the other blades (at 210 and 330) would have to flap down - what am I missing?

Four would work because cyclic feathering would hold the blade angles constant on the 0 deg and 180 deg blades while the 90 and 270 blades were flapping (and so on).

I take it would you would rely on hefty, broad elastomeric bushings and wide contact areas to provide the couple between rotor hub and mast (to give that articulated/rigid airframe/control response).

What I wonder is given the number of bearings and pivot points, and the way the torque has to be transmitted, are you really going to gain much in simplicity, maintenance or weight savings vs a "traditional" fully-articulated rotorhub?

Just so you know, I just spent the last hour buinding a model of your d***d rotorhub out of an old yoghurt container and some Q-tips... :8

Hm, 'nother question. if you have the blades underslung in relation to the virtual pivot point, then when the 90 - 27 blades are flapping up and down, won't the 0 - 180 blades be traveling in an arc when view from directly behind the disk?

Not sure how to describe this - imagine you were standing nose-on with the blades perfectly aft-forward/side-side and someone pushed the right-side blade up. The blade-tip you were looking at would scribe an upward arc to the right. Am I making sense? :uhoh:

[Ascend Charlie]

How about some droop stops?

When the blades are at rest, what stops them from sagging down and contacting the neck of the bearing? The neck would need to be very strong, which adds thickness and weight to the system.

And, Dave, please go onto your web site and change the spelling to read "THAN" instead of "then" when making a comparison. Some people more pedantic then me mite make sum comment...

[Dave_Jackson]

Flingwing207,

This invention consists of two functions, which interface with each other.

The first function is a hub spring. A definition can be seen here (http://www.synchrolite.com/B329.html#Hub_Spring ). The heading of the definition is a link to a full page on the subject. This full page has excerpts by Nick and Lu from a thread on PPRuNe a couple of years ago.

The second function is the constant velocity joint. This is where 'the going gets tough and the tough get going'. Probably going to another thread. This rotor must be thought of as a teetering rotor; a rotor without individual flapping and lead/lag hinges on each blade.

On a 2-blade teetering rotor, when the tip-path-plane is not aligned with the mast-plane the rotor-mast assembly will experience a cyclical Coriolis effect and a Hooke's joint effect. The mathematics for the cyclical Coriolis and for the Hooke's joint are different, but they both come to the same answer. If the Hooke's joint is then replaced by a Constant Velocity Joint, the Hooke's joint effect and the Coriolis effect will both disappear.

Test question: Since Captain Hooke and Mistress Coriolis are one and the same, does this make them/it a transvestite?

If the rotor hub and its blades are tipped 10-degrees, there is no Coriolis effect. This is because the constant velocity joint causes the rotor hub to think that the mast has tilted 10-degrees as well.

To put it in different words; by putting a constant velocity joint between the rotorhead and the mast, the mast doesn't know if the rotorhead is tilted or not, and the rotorhead doesn't know if the mast is tilted or not. For all intent and purpose, the helicopter could be hovering and a hovering helicopter does not experience Coriolis effect.

The nut and bolt stuff is on. OTHER: Mechanical - Joint (http://www.synchrolite.com/B274.html)

Hope this is clear.

_______________

Ascend Charlie,

"How about some droop stops?"

Hopefully, droop stops will not be required. The blades do not independently flap. The whole three (or more) blade rotor 'teeters' as a unit. The function of the hub springs is to resist this teetering on the ground and to put a moment on the mast when the disk teeters during flight.

Dave J

[Flingwing207]

Hi Dave,

I understand how the CV joint works, and how the hub spring works. However, your drawing shows the blade grips to be underslung - the center of the feathering axis is lower than the teetering point of the hub (as in a conventional 2-bladed rotor). CV joint or no, this would mean that (if its a 4-bladed rotor) that the blades parallel to the flapping axis (the ones not flapping) would be moving through an arc when viewed end-on.

The second question also remains - three bladed system: if the blade at the 3:00 position is flapping up, both the other blades (at 7:00 and 11:00 position) would have to be flapping down - this would seem to be in contravention of how flapping works.

[Spaced]

Fling, i could be wrong, but I think that your thinking about it as a static system instead of a dynamic system.
When the blades are flapping they are essentially scribing a sine wave if you drew the tip path on a peice of paper.
So assuming that the helo is at constant speed, and no input forces are being applied to the blades each blade will hit the same point at the same position. This will change when there is an disturbance to the system as a whole, then it will flap to equality, balancing the system out.

[Flingwing207]

Sine wave, yep.

Let's track the red blade - say (for illustration only) at 90 degrees it is about to reach the top of its upflapping curve. That means that the rotorhub at the 270 degree position (where the other blade would be on a 2-bladed system) is reaching the bottom of its downflapping curve. It also means that ANYTHING attached to the hub more than 90 degrees away from that upflapping blade is also flapping down, so the yellow blade at 330 is flapping down and the blue blade at 210 is also flapping down. Remember that even though Dave's design is a CV joint, the hub is rigid in the flapping plane, therefore the blades are not free to flap independantly. Put another way, you are trying to impose split-phase dynamics on a three-phase system (or vice-versa).

Take a conventional fully-articulated 3-blade system. The red blade at 90 is reaching maximum upflap, the yellow blade at 330 is on the way down, the blue blade at 210 has passed maximum downflap (which occured at 270) and is on the way back up. The blades are free to operate independantly in the flapping plane.

Only a 2 or 4-bladed system will remain in proper "flapping phase", but the problem of the underslung configuration (required to reduce/eliminate the Coreolis effect) remains for the 4-bladed system.

(I am using the maximum flapping positions of 90/270 for convenience - I realize they occur at different places depending on where the air is coming from.)

[Dave_Jackson]

Flingwing207,

Thanks for pursuing the subject and stimulating the neurons. The following is my perception of the rotor. Criticism appreciated.

Re: Flapping

"The second question also remains - three bladed system: if the blade at the 3:00 position is flapping up, both the other blades (at 7:00 and 11:00 position) would have to be flapping down - this would seem to be in contravention of how flapping works."

You are saying that " at the 3:00 position is flapping up" not that 3:00 is location of greatest positive flap. Therefor the following assumes that the location of greatest positive flap is 12:00.

When view from the perspective of the 'real' mast [mast plane] your statement is correct. Assuming a CCW direction of rotation, the high point of the disk is at 12:00 and the low point is at. 6:00. The blades are 'flapping' up on the advancing side and 'flapping' down on the retreating side. Or, in teetering-rotor related words, the rotor disk [tip path plane] is teetered back when view from the perspective of the 'real' mast [mast plane].

Because there is a CVJ in the rotorhub, the rotor disk is rotating at a constant velocity. We can therefore look at the activity from the perspective of the rotor disk [tip path plane], From this perspective, there is no flapping or teetering. In fact, because of the CVJ, we don't care if the 'real' mast is normal to the rotor disk, pointing down to the ground or pointing up to the stars.

Because there is no flapping there is no need for flapping hinges and because there are no flapping hinges, there is little need for lead/lag hinges.

Numerous activities cause lead/lag. An attempt to quantify them is given on OTHER: Flight Dynamics - General - Lead/Lag (http://www.synchrolite.com/1239.html) . The greatest cause is blade teetering (flapping) and, as mentioned above, the CVJ should significantly reduce this cause.


Re: Undersling (http://www.synchrolite.com/B329.html#Undersling ):

A pre-cone angle is included to reduce the loads on the feathering bearings and the blades etc. Of course, this cause the rotor's center of mass being further above the intersection point of the feathering axes and the mast's centerline.

The undersling was included on this 3-blade teetering rotor for basically the same reasons it is included on the 2-blade teetering rotor. It helps in keeping the rotor's centers of mass, inertia, lift and drag etc. as close to the centerline of the mast as possible during all flight maneuvers (except for inverted flight :)). With the CVJ causing the 'virtual mast to be normal to the tip-path-plane these justifications for undersling may be marginalised, then again, because the hub spring is resisting the teetering some undersling may be beneficial.

More thinking and prototype testing will be required to determine if undersling is needed, and if so, how much it should be. However, there does not appear a downside or difficulty to including it, at this point in time.


Dave.

[zeeoo]

hello everybody, its the sticky frenchie ! :} !
ok, i ll just keep quiet, following the debate... :rolleyes:
but some persons, here know HOW full of interrogations i am...:confused:
cheers
victor

[Flingwing207]

Just so you know, no debate on my end, I'm just trying to model the dynamics to see whether I have a valid point or not. I've been monkeying around with Excel and a lot of little arts & crafts projects to try and figure it.

[zeeoo]

flingwing,
i m like you on this forun ...
so, who s going to torture Dave first ?:p
you have begun in a such nice way, i let you go on :} c'm on ! make him talk !

cheers
victor

[Lu Zuckerman]

On a counter clockwise rotor system viewed from above with the rotor system having four blades (it’s easier to explain that way).

Over the nose is 12:00. Over the left lateral axis is 9:00. Over the tail is 6:00 and over the right lateral axis is 3:00.

With the helicopter flying forward the disc is tipped down over the nose and tipped up over the tail. The blade is at its’ lowest point of flap over the nose and the highest point of flap over the tail. As the blade passes over the tail it is transitioning to the 3:00 position and flapping downward in the process. When the blade reaches the 3:00 position it is at its’ lowest degree of pitch and due to (gyroscopic-Aerodynamic precession) will reach its’ lowest degree of flap at the 12:00 position. When the blade leaves the 12:00 position and transitions toward the 9:00 position it starts its’ upward flap and when it reaches the 9:00 position it is at its’ highest degree of pitch and due to precession will reach its’ highest point of flap over the 6:00 position.

To simplify Dave’s’ design get rid of the two hooks joints and use the hub spring as the constant velocity joint. In this way it will not be necessary to undersling the blades as the constant velocity joint/hub spring eliminates lead and lag. If the blades are not allowed to flap then I can forsee some aerodynamic instability in forward flight. Apply elastomeric spherical bearings and this instability will be eliminated because in the plane of rotation the blades can flap to equality due to gusting and be repositioned using some form of Delta hinge control linkage.

This is the system used on the V-22 Prop Rotor ™. On the V-22 the Delta hinge effect is electronic and it causes the servos to counter the flapping.


:E :E

[zeeoo]

hello dave, lu

dave, help

i must give out and admit i dont get it,
explain it to me please in simple words....

double join as teetering device, undersling or not, ok

what i really dont understand, is why no need for lag, flap
specially in fw flight, i may be poor understanding it, but, the drag forces on the blades are not symetrical ?,

lets take 4 blades, in a 12 - 6 hrs config the advancing blade generates more drag than the retreating one, do you think in the d3 angle to reduce it ?

that would mean that (according to your design) if i imagine a simple spherical bearing as rotor hub (admitting it's magically powered) i just can mount rigid blades without flap lag articulations, all we should need is a conical, or symetrical damping.... right ? :uhoh:

if so, you know what i have in mind ;)

mayday dave, lu

thank you

[delta3]

If the assembly is ridgid and even assuming a good average pre-coning there still will be a lot af stress at the blade roots. My simulations show that at higher speeds the higher harmonics (for instance second) are getting more important. Will the assembly be strong enough to support this or will max speed (or relative speed mu=forward/tip) be limited


Delta3

[Flingwing207]

On a counter clockwise rotor system viewed from above with the rotor system having four blades (it’s easier to explain that way).

Hi Lu,

First, thanks! Yeah I was using the "O'clocks" in a purely abstract fashion (or perhaps I was hovering sideways?).

Now then, the rigid hub works for a four blade system, as the blades are happy going through their flapping phases at 180/90 degrees opposition. But what happens with three or five or six blades?

Now on to the dreamy stuff...

The idea of a giant elastomeric bearing substituting for a rotor hub is interesting. Terrifying, but interesting! Perhaps we could combine that with a digitally controlled, pezioelectric-driven servo-flap rotor - eliminate the swash plate and all moving parts beyond the main rotor driveshaft (but don't fly too near those high-KV powerlines...).:ooh:

[Dave_Jackson]

Lu,

" To simplify Dave’s’ design get rid of the two hooks joints and use the hub spring as the constant velocity joint.
"

Your ideas are right on the money. However, the problem is that of implementing the idea. The hub's joint must allow tipping about the two horizontal axes while rigidly transmitting torque about the vertical axis. In addition, there can be no linear motion along any of the three axes. Sikorsky has a patent that attempts to achieve the above. It is 'Elastomeric high torque, constant velocity joint' 4,714,450 and it can be viewed at; US Patent Full-Text and Full-Page Image Databases (http://www.uspto.gov/patft/index.html)

The Sikorsky patent requires that the special elastomeric bearing compress in certain locations. Unfortunately, compression is a no-no for elastomeric bearings. I have tried to develop a CVJ elastomer bearing design (http://www.synchrolite.com/1301.html) that overcomes this problem, but no luck, also.

An interesting and related hub is the one that was used on the Doman LZ-1A. It consisted of a CVJ located inside a Hooke's joint. It appears that the CVJ delivered the torque and perhaps handled the horizontal loads, while the Hooke's joint handled the thrust load.

So far, it appears that only a Concentric Double Universal (Hookes) Joint can meet the requirements. The addition of the hub spring does two things. It becomes the mechanisms for locating the angle of the CDUJ's central components and it provides more control authority over the rotor disk.


delta3,

Your comments are of interest. I agree that even if the lead/lag coming from the Hooke's Joint Effect (cyclical Corollas Effect) is eliminated, by the implementation of a CVJ, there are other contributors to lead/lag. Would you elaborate a little more about your concerns?

Thanks,
Dave

[deeper]

Flingwing207,

The blue blade in your post has not passed its max flapped down position at 270, that was where it was at its max rate of flapping down. It still flaps down (but at a decreasing rate) until it is at the rear of the disc.

[Lu Zuckerman]

To: deeper & Flingwing207

The blue blade in your post has not passed its max flapped down position at 270, that was where it was at its max rate of flapping down. It still flaps down (but at a decreasing rate) until it is at the rear of the disc.

If the blade flaps down at the rear of the disc you are flying backwards.

:E :E