Intermeshing Helicopters

[Graviman]

This post has been prompted by my interest in the helicopter concepts that Dave Jackson has put forwards:

http://synchrolite.com/SynchroLite.html

http://synchrolite.com/UniCopter.html

I first came across these ideas on the Eng-Tips forum, and freely admit to not immediately being convinced. Since then i have debated with Dave, and (not being content) have also read up a number of books on aerodynamics and helicopter design (Including Prouty). Allow me to put in my own words the advantages i perceive with the intermeshing concept (in particular Unicopter):

1. Both rotor downwashes will feed nicely into wake contraction, whereas single rotors suffer tip flow distorsion.

2. Symmetry of main rotors will allow reduced pilot workload/training.

3. Careful design could lead to commonised parts between LH and RH rotors.

4. Removal of tail rotor will reduce power requirement by at least 10% (includinh high speed stabiliser trim drag) - downwash rotation wastes at most 2%.

5. By ultimately designing a rigid rotor, retreating blade may be unloaded. This avoids tip stall drag and reverse flow region. Outboard advancing, may allow optimum blade AOA in all conditions.

6. By ensuring that effective wingspan is always across both rotors at high speeds (conventionals end up lifting in front and rear quadrants), more efficient cruise may be obtained.

7. Twin pusher props will allow efficient cruise, as well as effective yaw control in reduced g manouvres.


OK, this is a very brief summary of the conclusions i have come to. I thought to start this thread to pick the minds of the best helicopter experts out there - the guys that fly 'em. To some extent i will sit back, and see what points come out of this thread.

Thanks in advance for your thoughts. :ok:

Mart

[Dave_Jackson]

"i will sit back, and see what points come out of this thread." Hell Mart. You can sit back and see what 'pointy things' come your way. I'm going to do a Lu and duck for cover. :uhoh:

[slowrotor]

My opinion:
For a personal use helo the first consideration in configuration and rotor size is that it have good autorotation. Cruise is secondary.

Putting another rotor above the other only increases downflow and therefor is not as good for autorotation.

Coaxial has some advantages for easier to hover. But a large single rotor should be somewhat slow in reacting as well.

Just a friendly reminder, try searching this forum for extensive discussion on this topic.

regards
slowrotor

[Dave_Jackson]

Slowrotor,

The intermeshing Flettner FL 282's were the world's first helicopters to enter and exit autorotation. In addition, the FL 282 helicopters were equipped with rotor governors (http://www.unicopter.com/Governor.html).

Dave

[Graviman]

Thanks SlowRotor,

"Putting another rotor above the other only increases downflow and therefor is not as good for autorotation."

Intermeshing can be thought of as a "bunched up" side by side config. Retreating blade goes above other side, and is unloaded by feathering. This means autorotation performance is improved since advancing blade runs at optimum AOA rel TPP. I have suggested tip trim to Dave - this forces tip AOA to 0 in all flight conditions, so swash plate actuates only root (like BERP to some extent).


"Just a friendly reminder, try searching this forum for extensive discussion on this topic"

Quite right, i should have done an extensive search first. I really just wanted a concurrent view on this config, since i have only just finished studying chopper design...

Mart

[headsethair]

We've been flying one of these around the office. You should get one - the autos are c**p.
Go here and look for Bladerunner....http://www.dot2shop.com/detail.asp?s=58&id=18931

[slowrotor]

Dave,
Early helicopters all had low disc loading and probably autorotated well.

In my mind, two rotors are less efficient than one. Just like two wings are certainly (biplane) less efficient on an airplane.

If I could, I would go with one blade. The working part of the blade is near the tip. The inner part is mostly just there to support the outer part. A twin rotor configuration has a higher percentage of useless inner rotor.
In other words, one large rotor will lift more pounds per horsepower than two smaller ones.

Headsethair,
That Bladerunner sure is stable in a hover! The blades have too much pitch to auto unless you get the rotor to reverse rotation. Take the rotor off and drop it from the ceiling and it will spin in reverse.

[superiorheli]

You might want to take a good look at the Kaman Kmax design, which is a production version of the intermeshing, side-by-side rotor concept. There are other factors to take into account including aircraft weight, profile, etc., but to my knowledge the Kmax is the most efficient fuel burned/weight lifted and horsepower-to-lifted weight rotorcraft out there, due in large part to its efficient large chord, slow moving blade system. It is extremely quiet for its size and and the rotorwash is somewhat self canceling and minimal for an aircraft that will lift 3 tons. In short, it has many of the features you are looking at (although not the fast forward airspeed - it was built for lifting).

[Dave_Jackson]

slowrotor,

As you know, the subject of autorotation encompasses numerous things, such as; rate of rotor deceleration, cleanliness of entry into autorotation, rate of descent, and usable rotational inertia at landing. However, I think you will find that there is no significant relationship between autorotational efficiency and rotor configuration.

Each configuration will have its nuances. There is a pitch-torque coupling on intermeshing helicopters that causes the craft to pitch upon loss of engine power. Twin-rotor craft do not have to consume some of their autorotative power driving the tail-rotor and its power-train. As mentioned by superiorheli, the coaxial and intermeshing helicopters take advantage of 'swirl-recovery'

There probably is a relationship between the number of blades and the rate of descent. However, this has to do with the fact that helicopters with more blades normally have greater disk loadings.

It's anybody's guess whether a 4-blade coaxial or a comparable 4-blade single will have the slower descent rate, but I will bet on the coaxial. :ok:


superiorheli,

Interestingly, the initial market for Charles Kaman's helicopters was crop dusting.
Unfortunately, this created a belief that the intermeshing configuration is low disk loading and slow speed .


Dave

[slowrotor]

Dave,
"swirl recovery" and self canceling rotorwash, as mentioned by superiorheli above.
Can you elaborate on that?

I would think the downwash speed of the Kmax would be similar to other helos of similar disc load (maybe higher), is that not correct? The Kmax is efficient because of the large slow rotor more than or in spite of the intermeshing configuration. Maybe the customers (loggers) just didn't want to deal with tail rotor strikes.

Two coaxial props on an airplane regain some from swirl recovery, but still not as efficient as one large prop, I think. Coaxial props are used on very fast or over powered airplanes. Not used for efficient personal planes. I have not ever seen a coaxial or intermesher of full size or model fly.

But I am still interested.

[Dave_Jackson]

slowrotor,

As you have mentioned, swirl is a small component of the velocity in the rotor wake, induced by the spinning rotor. More on swirl. (http://www.unicopter.com/1302.html).

A slow rotor is only more efficient than an identical fast rotor because the collective angle of attack must be increased (toward the optimum of roughly 8º) to maintain the same thrust. At some high pitch angle, this becomes unsafe, particularly during forward flight and maneuvering. You may find US patent 6,007,298 ~ Optimum Speed Rotor of interest.
"I would think the downwash speed of the Kmax would be similar to other helos of similar disc load (maybe higher), is that not correct?" Yes and no.
A 2-blade single rotor (1-blade rotor excluded) provides the best lift/power ratio, however, the necessary tail rotor consumes 5-15% of the engine's power. Therefore, the side-by-side configuration, with 2-blade rotors and a combined disk area equal to the previous single rotor, becomes the best. This configuration is a little 'unwieldy' so one can start bringing these two counterrotating rotors together. First comes the interleaving configuration, then the intermeshing, and finally the coaxial. Even thought the blade radius of all four rotor configurations is the same, the effective disk area gets smaller and smaller, and therefor the disk loading increases. What has happened is that the craft has morphed from a craft with two separate 2-blade rotors to what is basically a craft with one 4-blade rotor.
Each configuration has its pros and cons.

The following assumes what your desire is.
Your requirement for a slow forward speed and good thrust (to support stronger components) will be helped by blades that have a large (-12º) negative twist.
Your requirement for a slow autorotation speed will be helped by blades that have a small (+1º) positive twist.
The way to achieve both is by Active Blade Twist (http://www.unicopter.com/B372.html ), and the big boys are still trying to figure this one out.

Dave

[Graviman]

Wowsers, i kindof feel like a lamb to the slaughter!
Search "Intermesh":

http://www.pprune.com/forums/showthread.php?threadid=163983&highlight=intermesh

http://www.pprune.com/forums/showthread.php?threadid=163983&highlight=intermesh

http://www.pprune.com/forums/showthread.php?threadid=61588&highlight=intermesh

http://www.pprune.com/forums/showthread.php?threadid=18753&highlight=intermesh

http://www.pprune.com/forums/showthread.php?threadid=163538&highlight=intermesh


I have just had my second go in an R22. Ever had that amusing occurence when you pull collective to flare then wonder why you have turned to the right? :} I imagine switching from clockwise to anti-clockwise main rotor provokes similar experience. Soon figured my goof, and naturally thought of the lateral symmetry of the intermesher. Less likelyhood of stinging yourself too (no i didn't) - no tail rotor...


Thinking about some of the points raised in all the above threads:

Since there is no transfer shaft, i see desynching mains as unlikely - as long as gearbox is well designed/tested. Interleavers far more vaulnerable.

Don't believe synchropters would be any worse or better than a similar disk loading conventional. A twin 3-rotor would have similar performance to 6-rotor - ie higher profile drag, but very low vibration.

Since, ideally higher, retreating blade is unloaded there will be no "bi-plane" drag. Agree that active blade twist is required to optimise AOA across blade in all conditions. Still suggest tip flaps to force elliptical lift washout at tip (lowest tip losses). Convinced this offers superior highspeed performance potential to ABC - Nick?

Regards ease of piloting, now at least i have some experience of the problems of conventionals - will have a couple of more goes, but don't tell my bank :eek: . Pedal symmetry a definate plus! Rigid rotor would allow fast response to input - ie good pilot feedback. Dave you really must think about hand-off hover stability. I don't see how synchropter will be improved over conventional rigid. I honestly suggest a lockheed CL-475 style spring input gyro system - being mechanically simple, and so reliable.

Any thoughts, or is everyone quietly hoping Dave will jus' built it an' see? My offer of FEA/CAD still stands BTW...

Mart

[Chiplight]

My own experience with intermeshing helicopters has not been especially rewarding. :O
http://www.rotaryforum.com/forum/attachment.php?attachmentid=10372

[Dave_Jackson]

Mart,"Dave you really must think about hand-off hover stability."The Unicopter has Absolutely Rigid Rotors (http://www.unicopter.com/0815.html) and they rotate in opposite directions. They will provide the stability, due to the opposing gyroscopic precession.

Dave

[Graviman]

Chiplight:

Wow, they'se helichoppers is good an' intermeshed! They are radio control choppers? Had me pretty worried at first look...

Dave:

Really don't understand this point. If (say) a gust caused undemanded roll, i don't see how this would resist input. If anything counter-rotating systems are normally done to avoid gyroscopic coupling, thus reducing effective rotational inertia.

The two counter-rotating rotors will avoid cross coupling, simplifying pilot workload. He/she/it still can't take his/her/it's hands off the cyclic the way he/she/it could the collective or pedal, given enough height and forward velocity (naturally).

I am still a big fan of this project, and wouldn't raise these concerns if i didn't feel they were valid. OK y'aint gonna get as good as full fly-by-wire with laser gyros and ground hugging radar, but i'm trying to suggest a practical means of reducing required hours to solo - hence cost...

Mart

[Chiplight]

Graviman,
you are correct on several points;
those are r/c choppers in the "intermeshing" photo.

Counter rotating disks(such as coaxial props on a single shaft) nullify gyroscopic precession effects. You might expect twice the resistance to movement out of plane, but in fact it is near zero.

I fondly recall a discussion on a gyro forum with Chuck Beaty about this. It is one of the few times he's had to eat crow. He finally resorted to doing a hands-on experiment and was stunned to discover that the forces do indeed cancel as I'd learned from searching on the net.

[Graviman]

I sincerely hope Dave takes the criticism in the constructive way in which it is intended. :ok:

The Lockheed system, as fitted to CL475 (and initially to Cheyenne, before DOD spec increased disk loading to give dynamic problems) was exceptionally clever. I can only begin to describe it's subtlety:

Underneath the rotor, as part of the swash plate was a large gyroscope. Being rigid, the lead angle to plate was less than 90 degrees (~30 I seem to recall, since even "rigids" have flex and a floaty helicopter inertia). The cyclic was connected to this gyro via springs, with an additional lead angle of 90 degrees. The gyro tried to follow the horizon, and effectively flew the helicopter. Pilot cyclic input caused the control gyro to precess (in same way as teetering swash plate), by being 90 degrees lead. The springs were really just there to provide a sensible movement for a given input force.

If you think about it, the chopper will always try to fly in trim with the gyro. The pilot is thus directly controlling the pitch and roll rate of the gyro with stick position, hence directly controls heli pitch and roll rate. I just can't think of a more linear system, in all flight conditions. I was hoping Nick Lappos (ABC man) might like to comment on his thoughts about this system, but respect if he prefers to steer clear of this thread.

It would be easy to take a lead off the gearbox to drive a much higher speed gyro, thereby reducing required mass. The cyclic would go to the gyro, and the gyro to the two swash plates. Some additional mechanical complexity (which i appreciate is bad), but with FMECAs and design calcs/simulations a very easy bird to fly.

Mart

[Dave_Jackson]

Mart,

You're correct. My reply was very short and doesn't properly address the subject of stability. The web page UniCopter ~ Trim, Stability & Control (http://www.unicopter.com/UniCopter_TrimStabilityControl.html) is an attempt to address this subject in respect to the UniCopter.

Your original statement was "Dave you really must think about hand-off hover stability. I don't see how synchropter will be improved over conventional rigid. " I suspect that you are correct. An intermeshing (synchropter) helicopter will probably not be any more stable than a single rotor helicopter; if they have identical rotor types. (Teetering v.s. teetering.) (Offset flapping v.s. offset flapping.)

The UniCopter should be a different story.
The two rotors are extremely rigid and they are rigidly mounted to the rest of the helicopter. Their rotational inertia will want to resist (hopefully not too much or not too little) the pitching and rolling of the helicopter. In addition, because their axii are close to being aligned and they are rotating in opposite directions, the gyroscopic precession of one will offset the gyroscopic precession of the other.A little elaboration. (http://www.unicopter.com/0940.html#Counterrotating_Gyroscopes) You are correct in that the above will only reduce the rate of pitch or roll. However, I believe that this will be an improvement over conventional rigid rotors. In addition, the UniCopter's absolutely rigid rotor will provide the pilot with a very fast cyclic response to correct the pitch or roll.


Concerns by you and others are desired, because they cause an assessment or reassessment of potential problems. If there is any disagreement with the above, please fight back.

Dave
______________

A not so little sales pitch. :cool:

slowrotor is very interested in safety.
Theoretically, the UniCopter should have trim, stability and control that is quite similar to that of an airplane. In fact, I think that the rotors could be fully stalled out, just like an airplane, and then the craft be put through a stall recovery.

[Chiplight]

Dave, from your website,
If we put two counterrotating gyroscopes on the same rigid axle and again apply an upward force on the West the opposing North and South force will cancel each other. The axle can freely yaw but there is resistance to pitch and to roll.



No, I think you are incorrect in the last sentence. See my previous post above.
The angular momentum of a spinning disk is represented by a vector pointing along the axis of spin.(right-hand rule?) Two disks spinning in opposite directions have vectors pointing in opposite directions, so they sum to zero. What remains is the inertial mass of the static masses, but no rotational momentum. Like I said, Chuck did the experiment and conceded this was correct.

If you put two gyroscopes on the same axle, spinning in opposed directions, you would have no way of knowing that you were holding a gyroscope by feel alone. There would be no resistance to movement, although intuitively we think there should be.

[Dave_Jackson]

Chiplight,

In other words, it appears that you are saying that the two precessional forces will self-cancel, leaving only the requirement for enough force to rotate a static mass. The following excerpts from two web sites may support your position.

Damn it! :{
__________________

http://www.accs.net/users/cefpearson/gyro.htm

"Sometimes precession is unwanted so two counter rotating gyros on the same axis are used. Also a gimbal can be used. Gyroscopes, when gimbaled, only resist a tilting change in their axis. The axis does move a certain amount with a given force."
__________________

http://www.halfbakery.com/idea/Enhanced_20gyroscopic_20force_20generator

"Of course, with two gyros in counter rotation, the center point of the shaft is rotated so that Laithwaite's demonstration is performed by two gyros together. However, this requires a steady place to turn from (Laithwaite had his feet on the ground, and used his body to twist the gyro around, with respect to the ground.). Laithwaite claimed a few percent decrease in the apparent weight of his two gyroscope system (not antigravity! - just force in the upwards direction). He also had big problems with the shafts breaking.
In space, this system could never work, since as the gyros were twisted one way, the spaceship would twist the other."

___________________________________

Mart,

Yes. A number of peolpe have given positive comments and information about the Lockheed system on this forum.

[Dave_Jackson]

Chiplight,

Chuck maybe able to 'upchuck' some of the crow he ate. :yuk:

The previously mentioned web page http://www.accs.net/users/cefpearson/gyro.htm (http://www.accs.net/users/cefpearson/gyro.htm) talks about the Gimballed Gyroscope. I believe, it is saying that a continually applied force is necessary to rotate a gyroscope about its gimbal bearings. This implies that this force is greater then the force that would be required to simply start a stationary mass rotating.

It appears, to me, that the above should also apply to the tipping of two counter gyroscopes, which are located on a common axis.

If this activity was transferred to a helicopter, which had two absolutely rigid rotors, the power-train and fuselage should represent the rim, which is shown in the sketch of the gimballed gyroscope.

If the above is true, then two, counterrotating, absolutely rigid rotors, should experience some amount of damping during pitch and roll. I.e. Dynamic stability.

Dave

Any thoughts?

[Chiplight]

Dave,

My primitive thoughts on the matter are this:
If the two spinning masses are on one shaft, then they cannot both be tilting in different directions. That's the point, really. Sure it takes force to tilt one gyroscope, but if if a second gyroscope acts to prevent that motion and there is therefore no total tilting motion, then no work has been done to change the orbit of either gyroscope.
If you do tilt the object as a whole, whatever resistance is offered by one gyro is always nullified by the other and only the static mass properties remain.
To take this to an extreme, think of billions of gyroscopes assembled into one structure. The spin of each gyro is random, so the total angular momentum is zero.
That pretty much describes ordinary matter, which is made of atoms, each of which is a little gyroscope.

By your reasoning, all matter should resist being moved about any axis because all the gyro forces of all the atoms somehow add together.
Chuck's experiment with a drill and some odds and ends confirmed it very nicely. Only then did he dine on crow...

[Graviman]

"If the above is true, then two, counterrotating, absolutely rigid rotors, should experience some amount of damping during pitch and roll. I.e. Dynamic stability."

Nope, sorry Dave it really doesn't work that way!

"If the two spinning masses are on one shaft, then they cannot both be tilting in different directions."

Yup, that's about the size of it!

Don't be too disheartened Dave, i really do think the Unicopter offers a number of major advantaged over the conventional - but additional hover stability ain't one of 'em. On the other hand, so what - with some repackaging of the gearbox you can fit in a simple Lockheed gyro stability system, and really get the most from your Absolutely Rigid Rotors.

I have the greatest admiration of the pioneering work of Eric Laithwaite in mag-lev technology. He really was just totally wrong about gyro-levitation (but i sympathise with the intention). The best explanation i ever heard was from a pal of mine who had retired from Rolls-Royce:

A gyroscope can be thought of as a series of point masses spinning about the axis. If the disk is additionally rotated about an axis on the plane, when seen along this new axis, each point is either travelling toward or away from the new rotation centre. By rotating about new axis, each point is subject to the good old coriolis force (frequently the subject of chopper discussions). When you think about the position of each point around the disk, and the direction of it's coriolis force, you realise that the torque along the orthogonal axis is inevitable.

That really is al there is to it! Gyroscopic precession is just a convenient engineering way of reversing the problem, so that the torque becomes the input and rotational velocity becomes the output. In actual fact the gyro will wobble/fidget on application of input torque until a new equibrium between torque and movement is established. There really is no mystery when you see it like this, and besides it makes understanding the teetering rotor 90 degree lead angle make so much more sense.


Anyhow, you never commented on blade tip flaps to force an elliptical lift distribution. The idea is that the swash plate thus only affects the blade root - assuming blade is torsionally soft (and not flutter divergent). I seriously believe this will reduce tip losses significantly in all flight conditions. This reduces bladeslap (handy for uncoordinated pilots :rolleyes: ) - and besides I was quite astonished at the poorness of the R22 autorotation "glide slope".

I figure you should be aiming for a minimum lift/drag of at least 10:1 at best cruise speed. This is why i am also keen on feathering retreating blade, to follow local airstream - avoids "bi-plane" effect. It is realistically the only way forwards for choppers.


Would it offend anyone if i discussed blade hub mount dynamics in this forum? I have been bouncing ideas around for a while and would like some thoughts. Dave favours something called CVJ+HS, while i favour lead/lag unimpeded rigid roots, with damping (and possibly corriolis correction for blade flex - i notice Sikorsky/Boeing have gone this route with the Comanche). Westlands are playing with servo-electric HHC (their name H.E.A.T. - can't remember the abreiviation), and i wonder if they are wearilly treading this path too...


Mart

[Dave_Jackson]

Mart,

Agreed. It is better to keep different subjects on different threads. Plus, a thread does not cost much. :) Go for it.


Chiplight & Mart,

I understand and agree 100% with your basic argument that the gyroscopic precession of one gyroscope will be canceled by the opposing gyroscopic precession of the other. This is why "He [Laithwaite] also had big problems with the shafts breaking."

However, the gyroscope does not appear to be that simple. It appears that "only the static mass properties remain" ain't quite true. If only the static mass properties remain then any TEMPORARY moment applied to the static mass will start it rotating and this rotation will continue. It can only be dampened by bearing friction, or aerodynamically in the case of a helicopter.

Again, please note that the web page http://www.accs.net/users/cefpearson/gyro.htm talks about the Gimballed Gyroscope. It says; " Gyroscopes, when gimbaled, only resist a tilting change in their axis. The axis does move a certain amount with a given force." These two statements imply the application of a CONSTANT force.

Reading the section "A more detailed explanation of how a gimbaled gyro functions" appears to logically support the necessity of a CONSTANT moment, if the rotation is to be maintained. This means that a (possibly small) dampening is constantly taking place.

Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros.

Chuck was probably unable to detect this constant damping. Reference the Questions and Answers near the end of this page.

Dave. :ok:

[NickLappos]

I sit amused by this thread, which is like those classical arguments about how many angels could sit on a pinhead.

The helo that Dave imagines is only that, imaginary. If someone knows how to build a successful rotor that is incredibly rigid (Dave says "Absolutely" which is also incredible), he is hiding that secret from the rest of the planet.

Dave can you defin "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be?

Dave, you pull this chestnut out about every 60 days! How about building the thing, already?

[Lu Zuckerman]

To: Graviman

The gyro control on the Cheyenne was mounted above the main rotor and was connected to the swashplate via control rods that ran through the hollow main rotor shaft. The swashplat, springs and the power control unit (servo) were mounted underneath the gearbox. The springs you mentioned were there to provide a force proportional to the movement of the servo piston rods.

Although the pilot would cause the gyro to displace inputting a control force to the respective rotor blades the pilot would return the cyclic stick to the neutral position and the gyro due to rigidity would maintain the position commanded by the pilot. The springs would return to their static position and the nutating force to the gyro would return to “0” This is similar to the control input to that of a fixed wing aircraft.

The original design of the Cheyenne incorporated a 90-degree lead angle on the position of the servo in relation to the swashplate. However this caused problems when the rotor blades were redesigned to compensate for a significant weight increase in the airframe. The Cheyenne had a serious problem with rotor blade divergence resulting in the fatal crash of one Cheyenne and another that flew apart in a wind tunnel.

Parker Bertea the designers of the Cheyenne hydraulic system were charged with finding a solution to the problem of divergence. It took well over a year and they came up with a system of push pull rods and electrical sensors running from the rotorhead down to the servo. The mechanical linkage would sense a divergence and signal the servo to modify the pilots input. (**) The system worked beautifully and provided a vibration free ride. However, there were so many single point failure modes that would cause loss of control and by that time the program was cancelled.

(**) The Lynx has a similar system but it is electronic. If this system were turned off in flight the helicopter would fly to the left with forward cyclic. Did someone say 18-degree offset. The Lynx has a 15-degree offset during the rigging procedure.

The gyro was mounted to the rotorhead using a constant velocity joint. This eliminated leading and lagging of the gyro arms.

:E :E

[Dave_Jackson]

Awe Nick, you're changing the subject from Gyroscope to Next Generation Helicopter. http://www.unicopter.com/LaughRolling.gif

I use (and have defined) the expression "Absolutely Rigid Rotor" in the context that 'absolute' is the optimal, albeit impossible, objective. When Sikorsky misused the expression 'Rigid Rotor' to describe a blade with the consistency of a wet noodle, it left very little wiggle room.

Since you asked; the blade for an Absolutely Rigid Rotor WITH Active Blade Twist is the current project; when not enjoying the pleasures of posting on PPRuNe.


Having left Sikorsky, you now have the ability to look objectively at ALL rotorcraft proposals. Please explain how in hell the proposed Sikorsky Reverse Velocity Rotorcraft (http://www.unicopter.com/1281.html) will be able to make a non-fatal transition into autorotation after a loss of power in forward flight. :rolleyes:

I say it can't, and, have provided the supporting explaination.

Dave

[Graviman]

Hey hey, this thread is getting pretty interesting...

"Envision the two counter-rotating gyros replacing the gimbaled gyro and I see no reason why this gimbal activity is not applicable to the two counter-rotating gyros."

Well ok using your CVJ+HS hub system, the compliance will allow some seperate gimballing. Hence there will be an initial increase in apparent rotational inertia in pitch or roll, until the hub spring reached equilibrium. Not sure whether the spring limited compliance would really damp the pitch/roll or just limit inertia increase to an initial resistance. For the sort of pitch/roll damping you are talking about you would normally design a damper into the gimble (ie torque/rot_velocity), so that gyro only providided part of restorative force required to resist input.

Don't forget this is all at the cost of reduced clearance between contra-rotating rotors, hence risking rotor clash - pilots are (rightly so) a hard bunch to convince about the safety of a machine. You really do need to build a test rig to understand this interaction properly, before moving on. At any rate this all provides resistance to gust loading, but does not adress my primary concern about pilot controlability - ideally cyclic position would directly control pitch/roll rate.


"If someone knows how to build a successful rotor that is incredibly rigid ... he is hiding that secret from the rest of the planet."

Agreed, and is why i suggest either coriolis correction or damped lead/lag movement. Prouty makes the point very strongly that even a "rigid" blade can be given an effective offset hinge dimension. Dave's proposed CVJ+HS is a half way house design, which aims to keep hub rigidity below rotor without altering pitch horn lead angle. I don't suppose the design will stop with that, but it is a good start - certainly until the dynamics are understood better.

"How about building the thing, already?"

Must admit some practical ground test rigs would be nice. As an engineer i appreciate how much time (and money) this sort of engineering endeavour costs, this is why i have offered any cad/FEA help i can. It is all too easy to start on the wrong path, and run out of cash...


Lu, thanks for the fascinating insight into the Cheyenne system - i have been an admirer for some time. You would be suprised how much of a headache the hydraulics can cause on even a prototype articulated mining truck! Would you say that the Lynx system is the way to go for a private helicopter? I have been thinking along the lines of cost and reliability, hence the idea of a fully mechanical system over an electronically controlled servo-hydraulic system - the CL475 (once the three bladed rotor was fitted) seemed to prove this point. Westland are considering elec-servo to replace the hydraulics, which is a good route but one that must be safety proven (as it has already been in fixed wing) - I would be concerned about development costs.

"The springs would return to their static position ... This is similar to the control input to that of a fixed wing aircraft."

This is very much my reasoning behind incorperating it into the Unicopter development program. Must admit i still find flying the R22 in a turn an interesting experience compared to (say) a K8 glider - admitedly my pedal reflexes are still a little incorrect. I think a complete avinitio would really struggle though.


Dave, I appreciate that the full helicopter design is still to soon. I have admired your packaging bucks, and would like to suggest that maybe it is time for a dynamic test rig. I'm not proposing anything too fancy, but it strikes me that there is a lot of debate speculating about the interaction of the twin rotor hubs, the fuselage, and the control system. Even a simple gyro mass test bed is a good start, and would allow a natual progression to the blade development. Do you prefer to discuss technical issues in detail on this forum, or is there another venue? I'm keen not to outstay my welcome on this forum...

Is there a development grant in Canada that would help you get started? I think you could put forward a good case.

Mart

[Dave_Jackson]

Your right ~ I'm wrong. :ouch:

A few years ago, it was stated that counterrotating gyros are used in space to hold orientation. I erred by assumed that the gyros were physically holding the orientation, and were not simply the sensors.

Thanks guys.
Tonight's entree is looking a lot like crow.

[Chiplight]

Isn't it delicious? :

Seriously, Dave, your humility is appreciated. If only Lu could be so open to suggestion regarding phase offset we could eliminate about a gigabyte of discussion on this forum. :}

[Graviman]

"Tonight's entree is looking a lot like crow."

Aw shuks, no need to get to disheartened about it. :ok: As i read through Prouty, i frequently thought about the various aerodynamic arguements put forward for Unicopter. It is still a very viable concept, but like ANY engineering concept will need some development - Synchrolite is the perfect stepping stone.

The Lockheed stability system is seriously worth considering, especially as it has inherent mechanical reliability. For a start if you could guarantee hands off stability, clouds suddenly look less daunting. Basically the chopper has to remain at a fixed attitude when flying hands off, which the stability system ensures, any lateral velocity caused by non-level flight then has to stabilise heli attitude by conventional aerodynamic means - longitudinal and lateral dihedral. You need both for it to work.

This would then open up new markets in temperate zones, where weather put-downs are often a fact of life (like Britain ;) ). As an example, this allows emergency services to consider cheaper helis for more roles - never a bad thing. Other markets in the private sector will also open up....

"A few years ago, it was stated that counterrotating gyros are used in space to hold orientation."

I'm not up on latest techniques, but i imagine laser gyros monitor attitude in 3D, while flywheels are used to adjust attitude trim (conservation of angular momentum). I know that ion plasma drives offer the best (existing) way to reduce propelant mass usage - always the main driver for space stuff.


I think the next thing to consider is definately the hub/blade dynamics for a rigid intermesher. Nick Lappos has a very good point about practically attainable rigidity levels. The trick is going to be allowing the best reduced-g controlability, without introducing unecessary vibration. I favour lead/lag compliance, you favour the CVJ+HS - so there is plenty to evaluate. Retreating blade root feathering, and tip feathering, (or IRAT if you like) is still another avenue of development.

Mart

[Lu Zuckerman]

To: Chiplight


If only Lu could be so open to suggestion regarding phase offset we could eliminate about a gigabyte of discussion on this forum.

I have been told so many times by so many people that I am wrong about my premise regarding the 18-degree offset that I almost believe it. Having said that I ask you the following question: How much of an aerodynamic genius would it take to design a rotorhead that was entirely different from all other rotorheads in that it had flapping hinges but no capability of leading and lagging. This rotorhead was married to a flight control system similar to that of a Bell and because of this disparity the rotor had to be offset 18-degrees in order to rig the helicopter.

Then this aerodynamic genius had to design a rotorblade that had a 72-degree phase angle.

The Lynx has a 15-degree offset during the rigging process and when forward cyclic is introduced the helicopter would fly to the left. Why couldn’t Westland design a blade that had a 75-degree phase angle so that it would fly like the Robinson which has an 18-degree offset and which according to what I have been told flies straight ahead with the introduction of forward cyclic.

:E :E

[NickLappos]

Dave,

I love the way you propose mythical helicopers, and use past mythical helicopters as rationale.

For the record, this isn't a debate, and I continue to have objectivity before, during and after my tenure at Sikorsky. You continue to base your speculations on myths and not on engineering. And you confuse the objections I raise as opinion, when all I ask is that you use some facts!

[slowrotor]

Dave,
As a follow on to Nicks comment about past failures (real or mythical).

In the book "Whirlibirds" by Jay P. Spenser, is a photo of the Hiller X-2-235s that had "super-rigid rotors" (coaxial configuration). The photo shows two people standing on the blades, at the tips, with little deflection. I don't know if the machine ever flew, there is mention of vibration problems. Of course, we know that Hiller went with single rotor after his experiments with coaxial. And that seems to be the case with countless pioneers. (such as Sikorsky)

The book is quite interesting for a helo designer.

[Chiplight]

Lu,

this is a thread about intermeshing helicopters, so I'll promise to make this my only reply on the topic of R22 swashplate phasing.

You always compare a bell system to a Robinson and state that the bell is rigged so that forward cyclic causes forward swashplate tilt, but not so on the R22/44.

I could turn the tables and ask you to again look at both systems,
but this time, watch what happens when you manually raise a blade to simulate flapping.
On the bell rotor, the flapping has no affect on blade pitch, but on the R22/44, it will cause a pitch change.

Now, keeping this in mind, doesn't it make sense that the two rotor systems are rigged with different phase offset ?
Both helicopters will fly forward with forward stick, as has been attested to by many pilots.
When a forward stick input is made on the R22, this affects a cyclic pitch change, which in turn causes rotor flapping, which in turn pulls out pitch...
--an interaction that must be compensated for in the swashplate phasing in the R22, but not in the Bell.

[Lu Zuckerman]

To: Chiplight

You always compare a bell system to a Robinson and state that the bell is rigged so that forward cyclic causes forward swashplate tilt, but not so on the R22/44.

The Bell swashplate tips forward with forward cyclic. Since the Bell has a 90-degree lead on the pitch horn the blades are laterally disposed when rigging for forward cyclic. Conversely the blades are aligned with the longitudinal axis when rigging for lateral cyclic.

The Robinson swashplate operates identical to that of a Bell in that with forward cyclic the swashplate tips the same way. However the Robinson pitch horn leads the blade by 72-degrees so that in order to rig for forward or aft cyclic the advancing blade is offset 18-degrees in order to place the pitch horn directly over the forward tilted swashplate. The same offset would apply to the lateral setting.

On the bell rotor, the flapping has no affect on blade pitch, but on the R22/44, it will cause a pitch change.

When the Bell blades are static and the blade is moved it will not change pitch because in the static condition the pitch horn is aligned with the teeter hinge so there is no pitch flap coupling.

On the Robinson blade there is pitch flap coupling when the blade is moved about the teeter hinge because the pitch horn is not aligned with the teeter hinge resulting in a Delta hinge effect.

The is no pitch flap coupling if in the static position the blade is moved about the cone hinge. However with the input of collective pitch the two points are no longer in alignment and pitch flap coupling will occur.

However if you read the POH and the maintenance manual there is a warning not to try to move the blades when they are at rest.



:E :E :E

[Graviman]

Gosh, i'm gonna stand back and let Lu and Chiplight sort this one out for themselves! :ok: Remember folks, this thread is intended to be an engineering discusion, so don't get too personal :ouch:

"...the book "Whirlibirds" by Jay P. Spenser ... is quite interesting for a helo designer."

Gonna have a look, once i've finished reading up on engin' design.


Regarding Nick's comment:

"And you confuse the objections I raise as opinion, when all I ask is that you use some facts!"

I suspect that a ground test rig (a budget whirl tower if you like), with carefully recorded data, would go a long long way towards satisfying his concerns - you'd be suprised how cheap good instrumentation can be. A static rig would get the inertia dynamics right, and i really liked your pick-up rig idea for the aerodynamics... :8

Mart

[Dave_Jackson]

Mart,

The Constant Velocity Joint + Hub Spring rotor is a theoretically viable concept and it may be of interest to other developers of very-light rotorcraft. However, in my mind, it is only a progressive step in the movement toward an 'absolutely rigid rotor'.

Since there is no desire nor need for government funding or outside investors, I am afforded the liberty of striving for the whole enchilada. The risks are greater but the challenge is more exciting.

____________________________


Nick

Your postings and critiques are truly appreciated. However, your last one is disturbing.I love the way you ....use past mythical helicopters as rationale. The Flettner Fl-282 (http://www.unicopter.com/0474.html), the Focke Fw-61 (http://avia.russian.ee/vertigo/fw-61-r.html) , the Kellett ~ XR-8, XR-10 (http://www.unicopter.com/0896.html) , and the Sikorsky ABC (http://www.unicopter.com/0891.html ) were not "past mythical helicopters". The only mythical helicopter is the Stepniewski (concept) (http://www.unicopter.com/1093.html ) and you have said in the past that Stepniewski was the aerodynamicist who you admired the most.And you confuse the objections I raise as opinion, when all I ask is that you use some facts!

Dave can you define "absolutely rigid" and also describe the stresses in that rotor? Can you tell us what the vibration would be? I defined Absolutely Rigid Rotor (http://www.unicopter.com/B329.html#ARR) for you. In regard to 'stress' and 'vibration', there is limited time available to deeply consider lower level details, at this stage of development. New concepts come from a top-down approach. A bottom-up approach can do no more than 'tweak' the existing.

While we are talking about mythical helicopters and facts; I have stated and provided a supporting argument on a valid concern about Sikorsky's latest concept, on my web page Sikorsky's Reverse Velocity Rotorcraft Proposal (http://www.unicopter.com/1281.html). Your "factual" response will certainly add to the knowledge of the participants on this thread.

_______________________

slowrotor,

A few years ago Nick mentioned that the extremely high vibration of the Hiller X-2-235 (http://avia.russian.ee/vertigo/hiller_x-2-235-r.html) had even done damage to a wind tunnel.

The question then becomes; Why?
The answer is the 2/rev lateral dysimitry of lift during forward flight.

This craft has two blades per rotor, which ain't no big deal. However, these rotors are 'absolutly' rigid, and this is a big deal. The blades will be crossing each other at azimuths of 45º, 135º, 225º and 315º. In addition, because the blades are rigid they will be producing more thrust at the back of the craft then at the front. At one moment, two blades are providing high thrust in the left-rear quadrant, then a fraction of a second later two blades are providing high thrust in the right-rear quadrant. = 2/rev lateral shake rattle and roll :)

Please note that if the blades cross at azimuths of 0º, 90º, 180º and 270º the vibration will be longitudinal instead of lateral.

Even the three blade 'fairly absolutely rigid rotors' ;) on the Sikorsky ABC (http://www.unicopter.com/0891.html) created an unacceptable lateral vibration (http://www.unicopter.com/0893.html) around 225 knots. IMHO, a four blade rotor (http://www.unicopter.com/1218.html) should eliminate this lateral vibration.


Dave

[Graviman]

OK folks, just another gentle reminder to everyone involved in this thread: This is an engineering discussion, the pupose of which is to tease out the best design of intermeshing helicopter. I would really hate for it to all fall apart due to differences of opinion/experience. I appreciate that experts are always passionate about their beliefs, but have been in enough projects to understand that it is critical that all agree to some level of compromise.

--------------------------------------------------------------------------------

Dave,

"The Constant Velocity Joint + Hub Spring rotor ... is only a progressive step ... toward an 'absolutely rigid rotor'. "

Agreed. Your rationale makes complete sense, and i accept that my interest in lead/lag compliance is only one possible long term solution - it may not even be the right one! I have eaten plenty of crow myself over the years... :rolleyes:

"...no desire nor need for government funding or outside investors..."

Wow, i wish i was in that position! :(

"The risks are greater but the challenge is more exciting."

Remember there are those of us who are willing to help you share the workload ;) (if not cost :{ ).

Mart

[Dave_Jackson]

Out of respect for Nick's question about vibration, the following is added

Nick,

If your concern is about the vibration within an absolutely rigid rotor blade, then I would suggest that the attempted solutions should be addressed at a lower level in the development hierarchy. If your concern has to do with the craft, as a whole, then it is an uppermost concern.

Regarding the second; The Prewitt evaluation of the Flettner Fl-282 was extremely flattering, however, it did express a concern about the high level of vibration. It appears that this vibration is mainly the result of a rotor to rotor aerodynamic interaction.

The following are the approaches that are been taken to minimize this problem; The blade count has been increased from 4 to 6. This increases the blade-to-blade passages per revolution from 4 to 9. This in turn, reduces the amplitude of the vibration and takes its frequency above that which is uncomfortable for occupants.
The craft is to have a pusher propeller and one of the advantages of this is a reduction in the thrust of the rotors during forward flight.
Independent Root and Pitch Control plus 2P Higher Harmonic Control on the root will provide a better distribution of thrust.
Future improvements to rotor induced vibration should be more meaningful to the intermeshing and the interleaving configurations than the single rotor configuration.
For the perverse and the bored their is more on UniCopter ~ Vibration (http://www.unicopter.com/UniCopter_Vibration.html )
Whew!


Dave

[IFMU]

Dave Jackson Said:
While we are talking about mythical helicopters and facts; I have stated and provided a supporting argument on a valid concern about Sikorsky's latest concept, on my web page Sikorsky's Reverse Velocity Rotorcraft Proposal. Your "factual" response will certainly add to the knowledge of the participants on this thread.


Maybe they have a department that makes pictures of mythical helicopters there. They haven't built it, have they?

-- IFMU

[NickLappos]

IFMU,

That's right, they haven't built it (reverse velocity rotor). The problems with speculating on these improvements is that they are improving on a problem that doesn't exist anymore, where symmetry is a perfection that must be chased, like unicorns and rainbow's ends.

Dave seeks a "balanced, symetrical" rotor as solution to handling issues that have been solved years ago without doing mechanical backflips - by installing a fly-by-wire control system. Chasing the ease of handling by adding whole rotors and mythical super-rigid rotors is a way to convert money into piles of scrap experimental helicopters. There is no designer on earth who would seek better handling by adding rotors and blades, not when good, cheap and powerful computers are available to solve that problem.

Following this logic, our cars should never have had anti-lock brakes (a fly-by-wire system) nor should we have had electronic fuel injection (another fly-by-wire system) we should have had mechanical systems with a boot full of critical parts instead.

[Graviman]

"Dave seeks a "balanced, symetrical" rotor as solution to handling issues that have been solved years ago without doing mechanical backflips - by installing a fly-by-wire control system."

Just my two cents worth - feel free to refute (i certainly value the opinion of the ABC T.P. very highly). I see the advantage of intermeshing as primarily being aerodynamic, by avoiding the retreating blade tip stall and reverse flow area. If blade divergence at u>0.5 can be avoided it would be possible to build a helicopter capable of hover, then safe transition into flight up to the limits of either compresibility or at least engine power. The synchropter, if well designed, just has the advantage of reduced drag/power in all flight conditions.

Agreed that fly-by-wire, or even a mechanical gyroscopic derivative cures all the handling quirks on a conventional. Other handling advantages come out of the symmetry, but are not driven by it. As i have freely admitted to Dave, my own interest really comes out my wish to understand the limits of helicopter technology, plus how easily implementable the techniques are in practice. (I tried for a job at Westlands, just as they were about to lay people off :ugh: - bad times in the UK)

Mart

[Dave_Jackson]

Nick,

Thanks for the response and the pleasure of a lively discussion. :ok:


You appear to be implying that current helicopters are aerodynamically OK. However, it is common knowledge that governments and commercial interests want higher speeds from VTOL craft.

The computer alone is not going to provide these higher speeds. The increase in speed is an aerodynamic problem.

I think that you will agree that tiltrotors and Boeing's Canard Rotor Wing (http://www.boeing.com/companyoffices/gallery/images/military/unmanned/dvd-128-01.html) (with its Absolutely Rigid Rotor :O ) are not satisfactory solutions; even though both are latterly symmetrical :O, in forward flight.

What configuration do you think is the most promising for the future?


Dave

[Graviman]

I would also like to touch on yaw control in this thread, since i see this as the biggest single weakness in intermeshing rotorcraft. Most do it by differential yaw control, either by torque biasing or differential cyclic.

The Unicopter concept has twin rear pusher props, which will allow a very natural and responsive pilot yaw control in all flight conditions. My thoughts on this post are really for the Synchrolite concept, which has just the twin main rotors, since this may suffer reduced yaw response in conditions of slow speed reduced loading (not sure if there was a controlled rudder) - a climbing pushover for instance. Remember that i see the main advantage of the intermesher as being performance (especially if gyro stability augmented).

Apologies Dave, it must really seem that i am joining the "throwing sharp pointy things" brigade! :uhoh: I am honestly just trying to get to the bottom of what i believe to be a good concept, that just needs a little grounding in engineering common sense. I am just this bad as a professional truck designer - but the product really does benefit. :ok:

Mart

[Dave_Jackson]

Mart,

Criticism and concerns are genuinely wanted. It's a lot better to discover the problems on the drafting table then later, on the assembly table.

All helicopters have pros and cons. There are numerous concerns about the intermeshing configuration (http://www.unicopter.com/B280.html) . IMO, the primary one is rotor-to-rotor vibration and next one is yaw control.

The means of reducing rotor-induced vibration was covered in a previous post in this thread. Here is some additional information on this subject (http://www.unicopter.com/1086.html)

Yaw control should only be a concern when considering autorotation. This concern is applicable to the intermeshing and the coaxial configurations. Here are a couple of pages on yaw control, as it related to the SynchroLite; DESIGN: SynchroLite ~ Control - Flight - Directional (http://www.unicopter.com/B257.html) & DESIGN: SynchroLite ~ Rotor - Disk - Opposed (Differential) Lateral Cyclic (http://www.unicopter.com/0717.html)
______________

When considering the pros and cons of different rotor configurations, you might look into the interleaving (http://www.unicopter.com/1368.html). If there is any desire for a discussion about the interleaving configuration, it should probably be done on its own thread.


Dave

[Graviman]

"...discover the problems on the drafting table..."

My thinking exactly. BTW i seriously suggest you invest in a low cost 3D cad system. On my current project we (collectively) moved from 2D to 3D (Ideas NX). You will find it bottoms out your concepts much better, since your 2D drawings are not linked to each other. When you come to drawing, the 3D model is the template, so it is much easier to assemble.

Maybe SolidWorks would be well suited to you. Whatever stage you feel the project is at, believe me it will benefit greatly from a move to 3D. For a start it is much quicker and easier than your blue styrofoam mockups... ;)


"... rotor-to-rotor vibration ... yaw control."

Agreed about 3 blade rotors, but 4 blade rotor Unicopter is definately complexity overkill. You would be much better getting into retreating blade feathering (or ABC) by this stage - the ultimate way to avoid downwash interference vibration.

BTW i'm confused on rotor rotation direction of Synchrolite --> Unicopter. If Unicopter is a development of Synchrolite (which is by far the best engineering approach) then i really would settle on one rotation direction - ideally outboard advancing so inboard can (eventually) be feathered. Don't get hung up on roll/yaw coupling, since you will otherwise need to develope 2 stabilty scenarios - bad idea (unecessary development), besides vert stabilisers and aumentation will help. You may even be able to hand over componentry and tooling...


"Yaw control should only be a concern when considering autorotation...."

Hmm, longitudinal differential cyclic: bad idea on helicopter where rotor clearance reduction is an objective - seriously risking an extreme manouvre clash accident. Electric motor idea interesting, but complexity again. Considering differential collective ineffectiveness/reversal in autorotation, i really don't understand why the controls would be reversed as long as rotor loading was >0g - the concern comes when in a reduced g situation, such as pushover.

Are you really against cable operated tip (or even hub) spoilers? The linkage could be arranged so that spoiler only comes in when rudder and differential collectice ineffective (ie large pedal movements required), at the risk of unecessary complexity. Maybe it's my turn to eat crow...


"...look into the interleaving."

No, i'm convinced intermeshing is the best solution (thanks for helping me see this). Too much risk of interleaver shaft failure, and besides you go back to all the retreating blade problems. Ideal rotorcraft is feathered retreating blade synchropter - let Vertol play with SBS tandems...

Mart

PS: check out www.midwestcontrol.co.uk for control linkages.

[Dave_Jackson]

Chiplight"Counter rotating disks(such as coaxial props on a single shaft) nullify gyroscopic precession effects. You might expect twice the resistance to movement out of plane, but in fact it is near zero." You mention "near zero". Can you shed anymore light on this? I did the Beaty two counter-rotating bicycle wheel thing and the gyroscopic precession was gone. However, there did seem to be a little more resistance to movement when the wheels were rotating, as compared to when they were non-rotating. Maybe it was just wishfull thinking. I'll try to get the wheels to rotate faster and see if that changes anything (besides busting the axle :))


"If you mount two gyroscopes with their axles at right angles to one another on a platform, and place the platform inside a set of gimbals, the platform will remain completely rigid as the gimbals rotate in any way they please. This is this basis of inertial navigation systems (INS)."

This statement, from the Internet, may mean that the two counterrotating rotors would slightly contribute to the stability of a rigid intermeshing configuration. This is because the masts on the intermeshing UniCopter are at 18º to each other. Do you have any thoughts?



Graviman,"BTW i'm confused on rotor rotation direction of Synchrolite --> Unicopter. If Unicopter is a development of Synchrolite (which is by far the best engineering approach) then i really would settle on one rotation direction - ideally outboard advancing so inboard can (eventually) be feathered." The rotors on the SynchroLite turn inside forward (breaststroke). This appears to be typical of all previous intermeshing rotorcraft. Either Flettner or Kaman tried the opposite direction and then went back to breaststroke.

The rotors on the Unicopter turn outside forward. this was done to take advantage of the 'wanted' lateral dissymitry of lift. Stepniewski's concept (http://www.unicopter.com/1093.html) is also outside forward."Considering differential collective ineffectiveness/reversal in autorotation, i really don't understand why the controls would be reversed as long as rotor loading was >0g" There is an earlier thread that discusses this. Basically, in powered flight the rotors are driving the air where as in autorotation the air is driving the rotors.


Dave

[Graviman]

"...counter-rotating bicycle ... gyroscopic precession was gone... little more resistance ... when the wheels were rotating..."

Hmm, well the physics is pretty well established. I imagine that the wheels were not counter-rotating at the same speed...

"... masts on the intermeshing UniCopter are at 18º to each other."

The vertical axis components will cancel, but yes there will be some residual horizontal component. This would give some roll/yaw stability, and accounts for the Flettner direction of rotation - breaststroke is thus equivalent to single gyro going top forwards, bottom backwards. In sideslip the vertical tailplane would input yaw torque, to cause gyro precession roll as if dihedral. Same sideslip causes downwind rotor to produce more lift, so precession causes yaw towards sideslip (like a tailplane). Don't forget sideslip "dihedral" is being countered, to some extent, by incorrect lift balance of rotors. There is also the yaw effect caused by torque imbalance of downwind rotor seeing more lift, breaststroke rotation causing yaw into wind.

However, non of this will really reduce pilot workload in hover, however , unless you have accounts of F282 hovering hands-off - this has to be one aim of your project...

"...Unicopter turn outside forward ... 'wanted' lateral dissymitry of lift."

I do see this, but my concern is that you will not be using synchrolite to learn how to stabilise an intermeshing heli with rotors turning the "wrong way" (ie outside forwards). To my mind the whole point of intermeshing is to improve aerodynamic efficiency, otherwise just fit the lockheed gyro system to an R22 - far simpler. Basically i believe that a large tailplane, above heli centroid, would overcome the adverse stability of the effective gyro going top rearwards - and the resulting T-tail is perfect for high speed flight without downwash affecting trim. Alternately fit a gyro running top forwards (engine flywheel?) to counter rotor precession ;) . Either way, you have to admit, Synchrolite is the perfect test bed...

"... in powered flight the rotors are driving the air where as in autorotation the air is driving the rotors. "

Not completely with you, since in either case increasing blade pitch will result in opposition torque!?! I can see that there would be loss of this torque strength with autorotation, becoming noticeable below powered descent (approx zero pitch). The real danger comes from reduced g manouvreing, where there will be pedal ineffectiveness. I'm willing to eat crow, but have thought this through :confused: . Maybe this is not worth dwelling on, since the Unicopter twin pusher arrangement solves the problem...

BTW do you still prefer unducted over ducted pusher props? Bearing in mind various pros/cons.

Mart

[Dave_Jackson]

Who's the mole? :uhoh:

I was playing with the following two-rotor, 90-degree gyro device outside my place today.

http://www.unicopter.com/Temporary/Gyro-90-deg.jpg

A guy on a bike stops and gives me his business card. It says that he is drywall contractor and his name is George Zachystal. He starts to talk about his gyro inventions. He then says that he had to get out of it. The people around him were being killed by government personnel, because he was onto gyro propulsion. On the back of the card he says go to Yahoo.com and type in ZACHYSTAL and the US patent number 4884465. The conversation was a little difficult because of his heavy accent, so we finished talking and he biked off.

He was obviously a fruit-cake but for the heck of it I punched his name and patent number into Yahoo. Holy ****! There is a patent in his name. :oh:

Now I'm really scared. This is more than a coincidence.

[Graviman]

He probably did have a mad gyro-levitation idea (lots of loons have), and saw you playing with gyros and helis. If anything it just proves how pathetic the Patent service now is, in that it will grant almost anything without investigating the claims or even requiring proof! I take it he had seen area 51...

Mart