New Rotorhub Invention

[Intermesher]

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. In addition, it will be very inexpensive to build.

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

Any criticism, comments or questions will be appreciated.

Thanks;
Dave J.

 

[PEW]

Hi Graviman,

You said:

"What I suspect happens is that the chopper continues forwards, until the centroid "pendulums" the chopper back to hover again. Likely it will swing a couple of times before settling back into a hover."

The pendulum effect doesn't work like it might seem due to aerodynamic effects on the rotor system with any sort of lateral airflow across it. There is really no such thing as an automatically "stable" hover with conventional flying controls; any displacement from the hover becomes divergent due to something called flapback. The rotor system (disc) progressively tilts away from the direction of the initial travel. The "pendulum" effect actually causes an "overswing" of the aircraft's fuselage, resulting in a larger travel in the opposite direction and the situation gets quickly worse. Present day helicopters often have an autopilot, using gyros as a trimmed attitude reference, to help the pilot out.

 

[Intermesher]

Graviman,

OK. I understand what your objective is.

A couple of related quotes;
"The ubiquitous nature of cross-coupling constitutes one of the chief reasons why piloting this type of aircraft [helicopter] requires such high skill levels developed through long training programmes" ~ Gareth D. Padfield - 1996

"In more distracting circumstances, however, he [the pilot] would benefit if the helicopter control system would make the aircraft quickly do what the pilot wants it to do, and nothing more." ~ R.W. Prouty


"The Lockheed system allowed the pilot to hover hands off."

A book called 'Whirlybirds ~ Americas first 50 years' talks about hands-off hover for the Cheyenne. In a separate chapter, it talked about hands-off for the Hiller with paddles. There was a picture of the Hiller hovering in ground effect and the only things in the pilot's seat were some bags of sand.

This is the stuff that I've pulled together on the subject.

http://www.synchrolite.com/B306.html

http://www.synchrolite.com/B326.html

http://www.synchrolite.com/B318.html

Dave

 

[GraviMan]

"The pendulum effect doesn't work like it might seem due to aerodynamic effects..."

Thanks PEW. That is a much better explanation of what i was getting at.

"Present day helicopters often have an autopilot, using gyros as a trimmed attitude reference, to help the pilot out."

What really impressed my about the original Lockheed system (as fitted to CL475) was that it was entirely mechanical. Electrohydraulics are fine, but not really in the budget of a recreational craft.

"...Hiller hovering in ground effect and the only things in the pilot's seat were some bags of sand."

Wow! I have never been sure how well the Hiller system worked in aerodynamic regimes other than hover. I imagine it's weakness was that the trim forces vary with helicopter velocity (in all 3 axes).

"This is the stuff that I've pulled together on the subject..."

A usual, very well researched. How do you use the equations of motion? In automotive the dynamics are checked out in a package called ADAMS. By having an explicit (in time) simulation of the modal behavior, it is possible to see (graphically) the vehicle dynamics at a very early stage. This has been helpful in the truck project i am on, in spotting potential ride/handling quirks.

Usually Nastran and ADAMS are used in combination to pick up dynamic/structural interaction. This is similar to aeroflexing used in fixed wing design. I imagine the licensing costs of these packages is prohibitive, but if you have a friendly university with research budget...

Mart

 

[GraviMan]

Been thinking a little about a gyro stabilised control system. Although it doesn't matter where the gyro goes, for packaging convenience lets say it is fitted to the base of the cyclic. This would require a very high rpm gyro, so may not be the best solution.

Basically the gyro is connected to swash plate through the normal controls. In this way, especially with a rigid rotor, the helicopter manouvres to keep level with the gyro (linear direction changes being ignored). The cyclic then connects to the gyro with a lead of 90 degrees. The input force into the gyro then processes it, resulting in helicopter roll/pitch rate being proportional to input force. For pilot feel, the cyclic connection to the gyro has inbuilt springs, thus giving the helicopter a linear roll/pitch rate for given cyclic movement.

In the Lockheed system the gyro was part of the rotor assy, since this avoided the need for seperate drive. some sort of geared system may be better suited. The Hiller system was also force controlled, but the force was generated through the aero trim tabs - this may have given awkward dynamics in air velocity vector fields other than hover.

One major advantage of the system is that it tunes out ANY helicopter handling quirks. The rate of roll/pitch is directly proportional to cyclic position. This will result in a machine with very easy to learn characteristics. There may even be CAA FAA incentives for such an easy to fly machine - especially if light. Maybe an rpm controlled rotor, to avoid auto-rotation stalling, would also improved safety factors...

Any thoughts?

Mart

 

[Intermesher]

Graviman,

A few thoughts.


Lu Zuckerman on PPRuNe is very knowledgeable about the Lockheed gyro system. You may wish to search past threads on PPRuNe on this subject, or start a new one.


"There may even be CAA FAA incentives for such an easy to fly machine"

The reason for trying to get the SynchroLite under 254 lbs is to escape all mandatory FAA piloting restrictions. At the risk of being boring ~ In my opinion, the intermeshing configuration is the first step toward ease of piloting.


"Maybe an rpm controlled rotor, to avoid auto-rotation stalling, would also improved safety factors..."

The world's first production helicopter, the Flettner FL-282, had a rotor governor. Here is some information on rotor governors, which might be of interest.

http://www.synchrolite.com/Governor.html

Dave

 

[GraviMan]

"Lu Zuckerman on PPRuNe is very knowledgeable about the Lockheed gyro system."

Thanks for this - interesting read. From Lu's comments i gather that the (3 bladed) CL475 was a success, and that the system only really struggled when scaled up to meet the increasing weight demands of any program.

"The reason for trying to get the SynchroLite under 254 lbs is to escape all mandatory FAA piloting restrictions."

Neat. Not sure how that works with the CAA (uk). Hopefully not too different, but I'm not sure if there is a microlight rotorcraft class...

"...the intermeshing configuration is the first step toward ease of piloting."

Agreed, but it might still be worth getting a friendly university to simulate the dynamics. This is old hat in the auto world, then again the volumes are different. You would be suprised how many handling bugs you an pick up from an early stage. I realise rigids will not have the flapping problem, but I imagine that there will still be some "pendulum" tendancy. Even though the craft has lateral symmetry, there will still be characteristics that need to be learned.

I'm happy to put this in another thread if you feel there is threadjacking going on. Perhaps I should revive:

http://eng-tips.com/viewthread.cfm?qid=97039

I really like your hub design, and just wonder if it is worth goint a bit further. My thought processes find it hard to constrain themselves!

"Here is some information on rotor governors, which might be of interest."

Interesting, but I wasn't sure how these helped with low RRPM stalling. I presume the collective minimum is governed by RRPM and variometer (or vertical flow velocity), to not allow blades to stall. A hard landing is better than a crash...

Mart

 

[GraviMan]

"A little story for the heck of it...It now looks like this Concentric Double Universal Joint and Hub Spring should overcome the second of the above concerns and thereby make the SynchroLite a more viable craft."

I take it that your emphasis has now shifted back from Unicopter to Synchrolite? Why not design Synchrolite II? It could be built using tubular steel, to keep cost and weight down. Once up and running, the project would also then provide a testbed to try out concepts eventually destined for the Unicopter. At that stage you could look at composites. I would suggest the gyro control system as something that might be worth prototyping...

"Is there a smiley for 'fingers crossed?"

Not sure, but my fingers is crossed anyhow.

Mart

 

[Intermesher]

Graviman,

The SynchroLite and the Unicopter have a lot in common. They both are intermeshing and they both will have 3-blade rotors. One of the differences is that the UniCopter is to have the 'Absolutely' Rigid Rotors [

http://www.synchrolite.com/0815.html

], whereas the SynchroLite is to now have the Concentric Double Universal Joint partially rigid rotors [

http://www.synchrolite.com/1377.html

].

"I take it that your emphasis has now shifted back from Unicopter to SynchroLite?"

Yes. Both are being developed. The 'flip-flop' comes about when the current project hits a small snag or a neat idea comes about for the other one.


Your comments regarding the building and testing of the new concepts makes good sense.


" I really like your hub design, and just wonder if it is worth going a bit further. My thought processes find it hard to constrain themselves!"

Any or all of your wild or wonderful thoughts will be appreciated.


" rotor governors" & "low RRPM stalling"

A rotor governor controls collective blade pitch and thereby controls the inertia being removed from the rotor disk.

If you're interested in a very different rotor governor idea, look at this one.

http://www.synchrolite.com/0575.html

Dave

 

[GraviMan]

"The SynchroLite and the Unicopter have a lot in common..."

Hence the shift back to Synchrolite. I take it that an ARR has more potential aeroflexure problems to overcome/investigate? I like the idea of a rigid mast, and thrust bearings - sensible approach. I never liked the idea of rotating shafts taking bending moments - to much fatigue risk at (accidental) high loads...

"...'flip-flop' comes about when the current project hits a small snag or a neat idea comes about for the other one."

Probably the best way. So the emphasis is always:
Synchrolite - affordable microlight (intermeshing) rotorcraft;
Unicopter - High speed, high performance (intermeshing) rotorcraft.

"Your comments regarding the building and testing ... wild or wonderful thoughts will be appreciated."

Well i may not be aerospace (yet), but I'm used to juggling prototype requirements during a program. I'm the ideas man on my current project (you'd be suprised how technically clever an off-road truck can be), although i usually state durability, dynamics & design. I get involved in pretty much everything!

"A rotor governor controls collective blade pitch"

Yes, I definately appreciate the concept of cone/pitch coupling. This makes sense in removing uncommanded responses to lift/sink.

I didn't know if there was a design to limit maximum collective to just below blade stall. It could be done with either a combination of vertical velocity and RRPM, or a blade aoa (rel airflow) servo in rotor assy. Might stop some of those nasty falling from the sky type of incidents, by overiding a panicky pilot (me for example )...

"If you're interested in a very different rotor governor idea..."

Hmmm, i can see the point. Don't know if a machine with no direct vertical control is wise though. OK fixed wing pilots get used to having to manage the glide slope, but it would mean a change of flight procedure in rotorcraft engine failure. Might push workload that little bit too high...

I have often wondered if a simple one-way clutch between engine and flywheel would provide spare inertia to flare the blades. The collective could have a stiff spring, normally retracted with engine running, that would give a pilot a the feel that he was pulling the rotor into a potentially dangerous state. Rotor would detent to autorotate position, and pilot would have to "fight" collective to flare. Gives a safe landing, but also communicates the flight characteristics to the pilot.

Actually I think that the feel of controls is sometimes overlooked in aircraft. The dynamics guru at Peugeot used to reckon that you had a general idea of what your car was doing from the inner ear. The sensation of skidding (particularly at the back) came through the driver's backside. The most direct way to communicate the level of grip, though, came from the torque in the steering wheel. Only the mark I, fully gimballing, eyeball would override that input...

Mart

 

[Intermesher]

Graviman,

"I didn't know if there was a design to limit maximum collective to just below blade stall. It could be done with either a combination of vertical velocity and RRPM, or a blade aoa (rel airflow) servo in rotor assy. Might stop some of those nasty falling from the sky type of incidents, by overiding a panicky pilot (me for example "

At the bottom of an autorotative landing you may want to pull full collective to use up the rotor's inertia.

With a conventional rotor and loss of power, the pilot must take action to lower the collective. With a rotor governor, the pilot must take no action to lower the rotor. The 'theory' is that of letting the craft put itself into the authoritative state.
_________________

" Don't know if a machine with no direct vertical control is wise though.'

The collective pitch (lift) is determined from the engine's torque. Increasing the engine's torque immediately increases the lift. Then the engine slowly picks up the rotor's RPM.

Dave

 

[GraviMan]

"Increasing the engine's torque immediately increases the lift."

Works fine as long as engine is producing torque. I was thinking along the lines of chopper puts itself into autorotative state (ie no height velocity curve, using same governing mech), but still allows pilot to pull RRPM off to stall aircraft into ground. By having a (normally retracted) spring there, pilot feels when he is asking rotor to stall. Avoids pilot trying to stretch the glide, when he/she/it realises that chopper won't make the chosen landing spot...

Mart