Future rotorcraft control systems

[Graviman]

Having recently had a go at R22 flying, i realise that the biggest impediment to wider helicopter appeal is the cost :{ . The hardest skill to master is the hover, so why burn good cash trying to learn a skill that is (from an engineering perspective) a design defect. Some of you high hour folks will disagree, since it's so long since you hovered toddled that you just see it as part of the machine quirks - most will have progressed on to fully augmented machines anyway, so won't see the point of this thread.

I was always impressed with the story of the Lockheed CL475, where a fixed wing pilot jumped in and flew the heli with NO additional training! Although unable to find any e-refs on the mechanics system, i have found a write up on the AH56A which (after development of the 186) the CL475 led to:

http://www.internetage.com/cartercopters/pics9.htm

This is quite a read, but the basics are: The pilot flies the gyro, the gyro flies the heli. This is fundamentally different from the Bell system, in that the gyro has full control of the heli and the pilot is not fighting the gyro. It is similar in design to the Hiller system, but is fully mechanical, without aerodynamic interaction outside of the blades.

Although mechanically simple, the dynamics take more understanding. Basically the gyro is connected to the pitch links and physically flies the rotor cyclic input (ie conventional rotor dynamics apply). The pilot is connected to the gyro via a swash plate, but with a 90 degree lead due to gyro precession. Since the gyro wants to "stay put", any uncommanded input (eg gust) that moves heli results in a stabilising rotor cyclic input. The practical upshot is the gyro will stay in the same relative orientation in the helicopter (or otherway round). When the pilot puts in a commanded cyclic input, the gyro moves (precesses) in the way the pilot wants the heli to go, and the heli just follows the gyro.

The clever bit, which always confuses folks, is the system details. Since the gyro is always at the same relative position to the heli, there are springs in the control links. These do nothing more than allow a reasonable movement, for the desired rate of pitch or roll. The really subtle bit is the flap pitch couple in the blade, which allows the rotor system to aply force into the gyro. This just produces an effective rotor dihedral (similar to flapback), only in this case the entire heli will gently pitch/roll in opposition to any movement. This just means the pilot has to maintain stick displacement for a given longitudinal (or lateral) velocity - just like a fixed wing.


I read/skimmed with interest similar trends developing in RC helis:

http://www.w3mh.co.uk/articles/html/csm9-11.htm

The main benefit for full size machines would be hands-off stability, without ANY reduction in controlability. Basically it is bringing full flight control systems to private helis. This opens up even more applications to helis, and reduces accident rates - no reverting to basic reflexes due to say IMC disorientation.

So how 'bout it? Is it time for the Lockheed system to make a return, but this time to private helis?

Mart

[Lu Zuckerman]

To: Graviman

The reason a fixed wing pilot can with minimal helicopter skills fly a Lockheed helicopter is because the helicopter flies like a fixed wing aircraft. The pilot displaces the cyclic, which in turn applies a nutating force to the gyro (via springs) and the gyro responds 90-degrees later in the direction of rotation. When the gyro is displaced it applies a force via the pitch links to the blades causing them to respond albeit not at 90-degrees. This was a major design fault with the AH-56 and before the fix could be applied the program was cancelled. Once the blades had been displaced by the cyclic input the pilot would return the cyclic to its’ neutral position very much like a fixed wing aircraft. By returning the cyclic to the neutral position the nutating force was removed and the gyro would remain in the commanded position and the blades would follow. On a conventional helicopter the pilot has to maintain the cyclic in the commanded position in order to maintain the control input.

The couple between the rotorblades and the rotorhead was so strong that the cyclic could not be displaced when on the ground. Squat switches had to be unloaded which would remove the mechanical locks from the cyclic control system. Without the squat switches the helicopter could be tipped over with cyclic input.

:E :E

[Graviman]

Are you saying the Lockheed system deserves to see the light of day again, or should it be consigned to the history books? Most folks seem to feel that way about the Bell bars and Hiller paddles.

"On a conventional helicopter the pilot has to maintain the cyclic in the commanded position in order to maintain the control input."

I thought that the spanwise offset of the pitch horn from articulating hinge was to allow blade lift to cause a nutating "feedback" force to the gyro. This meant that the gyro would gently respond to a continued rotor input, from say forward flight. Unless the pilot provided a constant input the effect was like fixed wing longitudinal and lateral dihedral.

"The couple between the rotorblades and the rotorhead was so strong that the cyclic could not be displaced when on the ground."

Yeah this could be a problem, but the cyclic should be central on a conventioanl during run-up and shut-down anyway. Maybe a cyclic lock or limiter in place of the normal frictions. It does prove that the machine could "fly" hands off though...

Mart

[Lu Zuckerman]

To: Graviman

I thought that the spanwise offset of the pitch horn from articulating hinge was to allow blade lift to cause a nutating "feedback" force to the gyro. This meant that the gyro would gently respond to a continued rotor input, from say forward flight. Unless the pilot provided a constant input the effect was like fixed wing longitudinal and lateral dihedral.

There is no articulating hinge on the AH-56 rotorhead as the head is rigid. The blade is attached to the rotorhead by a series of hinges, which allow pitch change. It could be said that there is an apparent flapping hinge on the rigid rotorhead and this flapping point would change with aerodynamic loading. If the blade did in fact flap any movement of the blade in relation to the gyro would result in a pitch change which would provide a restoring force to the blade returning it to its’ commanded position.

The gyro being rigid in space would provide a resistance to movement caused by blade feedback and being rigid would cause the blade pitch to change and not cause the gyro to move as a result of any feedback.


:E :E

[Graviman]

"If the blade did in fact flap any movement of the blade in relation to the gyro would result in a pitch change which would provide a restoring force to the blade returning it to its’ commanded position."

Ah OK. Thanks for clearing me up on this, Lu. I had read the Speciality Press book on the AH56, but got this point wrong. So the rotor really did just do exactly what it was told and nothing more. Must admit, as i typed my original post i was wondering how much lateral cyclic that "feedback" would require for forward flight. :=

Was there any part of the system which provided for hands off speed stability? I'm also curious as to whether the system had any way of providing sideslip stability? Basically would the system also fly forwards and sideways hands-off?

Do you have any views about whether this system should be reconsidered? I am always astonished by the pure skill (and technical knowledge) of heli pilots, but equally alarmed when i read about accidents that this flight control system may have avoided...


BTW how are things with you at the moment?

Mart

[NickLappos]

graviman,
You started out so well on this thread, noting how RC aircraft are stabilized, and now you are sliding off into the never never land of blade flapping as some kind of stability solution. Heaven help us from the designers who think more and varied hinges and complex configurations will solve the helo's handling problems, when simple stabilizers can be bought on computer cards for a buck!

The only true solution to stability and control for future helicopters is in electronic systems that are cheap and powerful, not in screwy mechanisms that seem to be stable, but are really just complex.

Stay with the electronic theme, it is the winner.

Also, the Lockheed Cheyenne was a loser from the start, but nobody remembers its flaws, they just remember the marketing hype that was spread about it when it was being sold. The program was cancelled for technical reasons that had no solution. That stabilizr bar did not work very well, in fact it needed a good old fashioned electronic stability system anyway. The stab bar went unstable at high speed, and caused at least two accidents, one that killed the crew. I'll bet you didn't see that on any marketing web site!

[drakkar]

Nick

Did you tell us that future helos will be designed and built unstabilized but pilotable because of the computer take over ??
If so, why electric command on helos are not the rule even on light ?

Jean

[NickLappos]

drakkar,
You ask the right question. The entre world has slipped past the use of mechanical controls, opting for simple mechanisms, and complex computer code to house the stability.
Examples:
The fuel injection of virtually every car is fly-by-wire, where the sensors know the rpm, temperature, altitude, exhaust, throttle setting (which has no mechanical connection to the fuel valve!) and others. The computations "know" when you back off throttle, when it rains, when you are in the mountains, and they give you ideal control and high economy.

Airport people-movers have entirely automatic controls to run the trains, open the doors, make the announcements, and even shut themselves down for maintenance. No people are involved with the routine operation while thousands of people use them for mass transport.

The latest Boeing and Airbus aircraft have all their handling made up inside their computers, the control surfaces are placed where they make the most sense structurally and drag-wise, and not where they lend the best natural stability.

The latest fighter configurations have no "natural" stability, they derive it all from their computers, and they are unflyable without the computers that quell their bad characteristics.

Those who chase good handling by adding hinges and mechanisms are like those villians in the Jules Verne novels, who use monsterous steam-powered blimps to destroy the world. This is thinking anachronistically (look that one up, its a doozey!)

BTW, light helicopters already use electronics instead of screwy mechanisms, if by "light" we mean a few ounces. Their electronics do all the stabilization, and do it very well. Expect someone soon to introduce this as the new means to control a light helo, it is coming. The investment right now is too big, but only because of certification. The electronic control system for a helicopter could cost 10% of the cost to machine the control rods of today's light helos, if the controls were made in large enough quantities. The controls for a modern computer-controlled elevator (one axis of the 6 axies a helo needs) cost about $10 to build.

Regarding what we can expect with computer controls, I wrote an article or two on the Comanche controls, I will try to dig them up and post them. A non-pilot could lift Comanche to a hover, move precisely in any direction, and land again without any training. It didn't just fly like an airplane, it flew like a dream.

[Graviman]

Hi Nick,

"...now you are sliding off into the never never land of blade flapping as some kind of stability solution."

Well not really, since i have accepted that my original "understanding" about flap pitch coupling was in error. The gyro just provided an attitude feedback reference.


"The only true solution to stability and control for future helicopters is in electronic systems that are cheap and powerful"

But rely on complicated power hydraulics to implement their control strategies. The biggest single problem area on our "simple" prototype truck is the hydraulics. I'll stick to well thought out mechanisms anyday - especially since a quick visual tells you if it is all there and working.


"Stay with the electronic theme, it is the winner."

As an electronics engineer i agree, as a mechanical engineer i disagree (i should stop studying sometime :ugh: ). For a smaller R22 type machine the only way would be to introduce (say) a electric power ram, along with associated power electronics and generator. Is it doable? Yes. Is it simple? No.


"Lockheed Cheyenne ... stabilizr bar did not work very well, in fact it needed a good old fashioned electronic stability system anyway."

Well, i'm really more interested in the CL475 light heli, but there is very little documented evidence of how this system worked or performed. It had no electrical or hydraulic complexities to worry about in FMECA design studies though.


"The (AH56) stab bar went unstable at high speed, and caused at least two accidents, one that killed the crew. I'll bet you didn't see that on any marketing web site!"

This is all well documented, but nothing like as well as being involved in that nature of project. I got the impression that McNamara's Defence Procurement Policy and the shortcuts it lead to were as much an issue. Lu could probably fill in the details of the nature of the actual failures, but i gather that disk loading beyond the concept specification was partly to blame. Loss of crew on any program is clearly unacceptable, however, and must be avoided at all cost.

Mart

[Matthew Parsons]

If you look at the evolution of FADEC, you'll see the future in helo flight controls. Hydromechanical monsters were simplified with electronics. Then electronics were used to do the pilots work on the manual controls, allowing the pilot to overide as required. Eventually the manual controls were dropped and the FADEC is the only thing that can control fuel systems.

I think the scenario that drakkar mentioned is really just limited by what level of over-ride the pilot is comfortable with. Once we believe that FBW is more reliable than mechanical (augmented or not) then the manufacturers will be able to offer unstable aircraft that the computer can fly.

I'm looking forward to that day.

Matthew.

[Dave_Jackson]

Graviman,

Nick is obviously correct. Forget the 'loosy goosy' things. Future rotorcraft control will be electric and electronic. However, the electron should not be used to mask aerodynamic problems. It should be used to effect aerodynamic solutions.

Why can't linear induction actuators be used in place of hydraulic ones? Double or triple redundancy will provide a very high safety factor. There are also the advancements being made in piezoelectrics.

Some predictions for the not to distant future; :8
~ Rotors will be powered by electric motors.
~ The use of an electric disk-motor will eliminate the need for gears.
~ Dual main-rotors will have a separate motor for each rotor and the inter-phasing of these rotors will be maintained electrically by encoders.

Heck, all of this could be done in an R/C today.

Then light-activated actuators for fly-by-light.


Dave

[Lu Zuckerman]

To: Graviman

What Nick stated about electronic stability control is correct. However what he stated about the gyro becoming unstable is not. It was the design of the blades that caused the problems. As a matter of history the US Army kept adding equipment to the AH-56 to the point that Lockheed wanted to extend the blades to increase lift. The Army would not allow any change to the planform of the AH-56 because it would impact the support and transportation of the helicopter.

Lockheed aerodynamics engineers (read Ray Prouty) decided to redesign the blades to increase the lift without changing blade length. They accomplished this by adapting a radical design approach where at each blade station the blade had a different shape and camber. Unlike a conventional design the aerodynamic centers and centers of pressure were different at each station making the blade unstable. This instability manifested itself in blade divergence. This blade divergence was unpredictable and varied with airspeed, disc loading, and other factors.

On two occasions the divergence manifested itself in such a way that the blade struck the cockpit while the helicopter was in flight killing the pilot. This particular helicopter was equipped with a downward firing ejection seat taken from a B-47 however it was mounted in the gunner’s position and the pilot was sitting in the rear seat. It is problematic if the pilot could have ejected as the divergence was so fast and the helicopter was flying close to the waters of the Pacific. The second case of blade divergence took place in a large wind tunnel at Ames Research Center causing severe damage to both the helicopter and the wind tunnel.

The problem of divergence was turned over to Parker Bertea the makers of the AH-56 hydraulic system. I do not know if they investigated the use of electronics but the decided to go with an Electro-mechanical feedback loop. The system consisted of flap detectors and the resultant signal was transmitted via mechanical linkage the ran through the mast and the resultant signal was fed to a black box that monitored blade movement in relation to the signal being supplied to the servo. If there was a variance between the detected signal and the servo input the black box would alter the servo input to compensate for the divergence. A system very similar to this design is used on the Lynx, which has a 15-degree rigging offset. When the pilot pushes cyclic the electronic detectors measure any difference between pilot input and blade response and a signal is sent to the servos to counter the effect of the offset.

The Parker Bertea design worked perfectly according to Lockheed and Army test pilots but it was rife with single point catastrophic failures. By this time the program was cancelled.


:E :E

[Jack Carson]

There are two elements to this discussion, controllability and stability. Entry level helicopters are generally very controllable and exhibit docile flying qualities while not being very stable in the classic sense. These machines use rotor inertia, stabilizer bars or a combination of the two to achieve the pleasant flying qualities we have grown accustom to. By contrast, larger more complex machines use electronic solutions for stability as Nick mentioned to achieve true stability. As an example the S-92 is inertially stabilized in a hover. It uses rate gyros, accelerometers or an inertial reference system to neutralize any tendency to drift that would be common to an un-augmented machine.

[Graviman]

Lu,

Thanks for the info - you really know your stuff on this. My understanding then is that the basic mechanical system is very reliable (Blade divergence is a potential problem on any project). Do you know much about the history of the CL475 or 186? Did the 186 progress to hydraulic or was this a Cheyenne feature?

----

Matthew,

"Once we believe that FBW is more reliable than mechanical (augmented or not) then the manufacturers will be able to offer unstable aircraft that the computer can fly."

I accept this, and even recently went for a job interview to a supplier for aerospace electrohydraulic and electromechanical systems (what's left of the auto industry has taken on e-steering in a big way). However, if there was a simple mechanical solution for light helis why overly complicate it? On large machines that require servo assistance i can see the point, but an R22?!?

BTW my car does not have power assist, and at 160'000 miles of hard driving i don't want it - more to go wrong...

----

"Why can't linear induction actuators be used in place of hydraulic ones?"

No reason at all. I even like some of the systems on offer. The point is for an R22 size machine why introduce the complexity of power assist? A gyro as part of the swash plate is simple and effective. Find me a fault with that system and i'll drop it...


"~ Rotors will be powered by electric motors."

Yes. I'm even working on a fuel cell concept that may offer that dream, but i'm first designing a diesel engine as a control and a fall back research option (got to know your stuff to get funding).

"~ The use of an electric disk-motor will eliminate the need for gears."

No. Electric motors have a maximum torque/mass figure driven by the 1 tesla flux in the mag circuit. Gears are good in that they allow the motor to spin at high RPM to maximise power/mass. Disc motors reduce mass/torque (less mag circuit iron) but would still benefit from high rpm.

"~ Dual main-rotors will have a separate motor for each rotor and the inter-phasing of these rotors will be maintained electrically by encoders."

Highly unlikely. For intermeshing/interleaving the potential modes of failure for this would be catastrophic, this would fast be rejected by any sane design team. The safest means of autorotative (which already implies one mode of failure) synchronisation is the humble gear. SBS tandem would fly with desynchronised rotors, but i can guess how Nick would feel about having to watch 2 NR guages while looking for a soft spot.

Still, solid state will come...

Mart

[edit:typos]

[Dave_Jackson]

Graviman,

If this is getting too far off topic, please say so.

Your knowledge of electricity is far above mine, so I get to question you. :ok:

Mass/Torque:

An electric motor that is extremely fast and small has an advantage. However, the helicopter rotor is a large disk with insignificant thrust comes from its center. Why could not a reasonably large diameter, linear induction disk motor be an integral part of a special rotor hub, which is shaped like a very large Frisbee? It might have thousands of poles (with 50% or 33% of them activate at one time) and air bearings to maintain the gap. The weight will be kept down by the preceding integration, composite construction and the elimination of the gearbox.

To double the motor's speed on coaxial helicopters, the motor could be located between the rotors, with the 'armature' connected to one rotor and the 'stator' to the other rotor.


Potential Intermeshing failure:

What if triple redundancy was applied to all facets of the drive. In other words, separate batteries, motors, and controls etc. Electrical systems are very reliable, but, if one system went down, the other two would probable still provide slow level flight.

The large electrical force and its large moment arm should be able to maintain rotor inter-phasing, considering that CNC milling machines can inter-phased multiple motors to within a 10th to 100th of a degree.


Just a demented idea.

Dave

[Graviman]

Hi Dave,

Not worried about topic, as long as thread is constructive.

"Why could not a reasonably large diameter, linear induction disk motor be an integral part of a special rotor hub, which is shaped like a very large Frisbee?"

Why not, but aerospace motors and generators run at 80'000 rpm regardless of shape. Any less and you are just introducing unecessary weight.


"It might have thousands of poles (with 50% or 33% of them activate at one time) and air bearings to maintain the gap."

Why not. Sounds unecessarily complex to me though and doesnt get around the torque/mass limitation. You are just packing more copper into the 1 Tesla mag flux.


"The weight will be kept down by the preceding integration, composite construction and the elimination of the gearbox."

Nope. You still need an iron return circuit, which is the cause of the 1 Tesla limit. Careful design can just about get up to 2 Teslas. Nano carbon fibre promises room temp superconductivity, but you won't be able to buy 'em for quite a while.


"To double the motor's speed on coaxial helicopters, the motor could be located between the rotors, with the 'armature' connected to one rotor and the 'stator' to the other rotor."

Sounds draggy. Why not just use an epicyclic reduction gearset (lowest mass for given torque) and run the motor at 80'000 rpm, or whatever is centrifugally achievable? Why not use a gas turbine...

----

"What if triple redundancy was applied to all facets of the drive."

Then, as long as pilot (or more likely operator) has common sense to ground aircraft on single failure, the crew only crash and die during a triple failure. What if a +ve lightning strike over the north sea wipes out all of the redundancy?


"The large electrical force and its large moment arm should be able to maintain rotor inter-phasing..."

Agreed, but so should gears. My concern comes from the fact that the best motor will likely be a brushless DC requiring power electronics, unless you want all the wear and reliability problems of a brush. The power electronics, although reliable, do go wrong and never when you want them too. You are talking about aerospace motors which will have to run at high rpm and are going to be expensive. When was the last time you drove a hybrid car? I drive a diesel.

----

"Just a demented idea."

My concern comes from the fact that the idea comes from a false premise (assuming you are trying to avoid driveshafts in SBS tandems). Tail rotors in themselves are not bad things, but counter-rotating rotors offer better potential for aircraft flexibility.

The main problem with ANY rotorcraft is the retreating portion of the rotor. In a conventional heli the retreating portion of the rotor limits top speed. In a counter-rotating heli the retreating portion can still introduce unecessary power loss, through distorted downwash distribution. Intermeshers will suffer vortex spill blade slap, and interleavers will still have to operate retreating tip at higher than ideal AOA. Either work at highest aerodynamic efficiency with outboard advancing.

Why not just accept the loss and just use root/tip control to perfectly feather the retreating blade? If you do this the Stepniewski rotation intermesher wins hands down, and ANY other configuration is just unecessary complexity.

Unicopter, with a tandem instructor seat, is a good design concept - why not just stick with it? :confused:

Mart

[Edit: typos]

[Lu Zuckerman]

To: Graviman

Do you know much about the history of the CL475 or 186? Did the 186 progress to hydraulic or was this a Cheyenne feature?

When I worked on the Cheyenne I walked through a door leading to a warehouse that was adjacent to our offices. Hanging from the rafters was a Lockheed CL-475. It differed from the version with the gyro bar (similar to the Bell stabilizer bar) in that the gyro was a circular ring that was mounted around the rotorhead. I do not know if this was a variant of the CL-475 or a modified version. In any case I couldn’t get any information on it because there were so few knowledgeable Lockheed types in our group.

I saw the 186 in several variants flying on test flights but I was unable to get close to them. One major point was that this helicopter was so stable and flew so well that the Lockheed designers decided to scale up the dynamic system in designing the Cheyenne. Needless to say this did not work


:E :E

[NickLappos]

Hydraulics are not necessary at all, graviman. The "power assist" could very well be electric, such electric jackscrew actuators are in normal use today on many aircraft, and they have the force to be used wherever pilot muscle power alone can be used to control an aircraft. these cost about $1500 apiece, so all four axies of control should be less than $10,000 cost including the computation. Simple inertial sensors are also quite cheap, when they are useful for stability only (Flight Quality vs Nav Quality Inertial Sensors). The entire cost for the auto fly could be 12000 today, at very low quantities, at high quantities, the cost could be down to $2000 or so.

Unmentioned by the stabilizer bar advocates is that the bar specifically ignores pilot input unless the input is held long enough. This means that mechanical stability systems almost always reduce plot controllability and control response as necessary costs of their use.
As I said before, I see no reason to make complex mechanical systems (stabilizer bars, dual rotors, specially designed flapping hinges, etc) to achieve ease of control and high stability.

[Dave_Jackson]

Nick,

All the point you make have validity, with one exception. At the risk of belaboring a point, I do not believe that a 'rotorcraft' can achieve significantly higher forward speeds without having some configuration of twin counterrotating main-rotors.

I think you will agree that high forward velocities necessitate a reduction in the rpm of the rotor(s) so that compression at the advancing tip does not become a problem. This high forward velocity combined with the slower turning rotor(s) puts a significant portion of the retreating side of the rotor into reverse velocity.

Mart suggests simply feathering the retreating blades, however, logic, and others, suggest that this reverse velocity should be utilized by putting the blades on the retreating side into a negative pitch.

Two years ago Sikorsky proposed that high forward velocities could be achieved with their single rotor Reverse Velocity Rotorcraft (http://www.unicopter.com/1281.html). However, the forgoing linked web page gives a strong and valid reason why I believe that the single rotor proposition is fatally flawed.

IMHO, Sikorsky's recent return to the twin-rotor configuration reaffirms the necessity for the lateral symmetry, which is provided by twin main-rotors through the complete range of forward speeds.

Dave

[Graviman]

Lu,

"... Lockheed CL-475 ... the gyro was a circular ring that was mounted around the rotorhead."

This is the system i am really interested in, since it was basically just a gyro augmenting a rigid rotor in a light helicopter. Mechanically very simple, with no need for power assist.

"... 186 ... was so stable and flew so well that the Lockheed designers decided to scale up the dynamic system ..."

Shows system works on a medium size machine. A modern implementation of this would clearly be electronic with laser gyros and electric linear actuators.

----

Nick,

"The "power assist" could very well be electric ... the cost could be down to $2000 ..."

Agreed for a medium heli, but why introduce more active systems on a light heli trainer?


"... stabilizer bar ... specifically ignores pilot input unless the input is held long enough. This means that mechanical stability systems almost always reduce plot controllability and control response as necessary costs of their use."

Ah, you're getting confused with the Bell system here. The Bell-bars were designed to supply attitude inertia into the teetering rotorhead, to "low pass" pilot input. IMHO it is a bad system and should not be considered. The Lockheed system did not affect rotor attitude inertia, but just put an attitude reference into the system - as Lu highlights, control was exceptional.


"As I said before, I see no reason to make complex mechanical systems (stabilizer bars, dual rotors, specially designed flapping hinges, etc) to achieve ease of control and high stability."

Agreed, but if we take (say) a Sikorsky/Schweizer 300, then i am just talking about a single gyro in (say) the swash plate mech. That $2000 would be overkill on this modification, and (provided a CL475 type mech) the control would be exceptional.

Due (only) to limited finances i have only had an introduction to the R22. Most of the flying was suprisingly similar to gliding, once you retrain your feet (no collective but there is an airbrake lever). Mastering the hover was clearly going to ingest to much cash for my tastes, hence this thread...

----

Dave,

"... feathering the retreating blades, however, logic, and others, suggest that this reverse velocity should be utilized by putting the blades on the retreating side into a negative pitch."

I'm not against this, but am convinced that you can never get close to the optimum downwash distribution using this technique. This goes for conventionals, coaxials, intermeshers and interleavers. For a start you will always get upwash (fountain effect) in the circle (rotor planform) of zero velocity. The alternative is the V22...

Just in case it is reverse velocity utilisation that has lead you to the tri-teetering hub, check out Widgeon's post (especially the links to the pics) in the thread:

http://www.pprune.org/forums/showthread.php?s=&postid=1923883#post1923883

Mart

[Edit:ammendments]

[IFMU]

Nick Said:
Hydraulics are not necessary at all, graviman. The "power assist" could very well be electric, such electric jackscrew actuators are in normal use today on many aircraft, and they have the force to be used wherever pilot muscle power alone can be used to control an aircraft.

Nick,

Let's not go planning the funeral for hydraulic systems just yet. Tough to beat hydraulic power for its combination of load generating capability AND bandwidth. For a given electric system, bandwidth goes down with load. As the load or bandwidth requirements go up, the electric servo gets bigger. Seems the tradeoff goes to electrics for smaller aircraft to me.

But, I do agree the future is electric. Whether it is electric-hydraulic or just electric, time will tell.



-- IFMU:8

[Dave_Jackson]

Graviman,For a start you will always get upwash (fountain effect) in the circle (rotor planform) of zero velocity Where did this statement come from?

Just in case it is reverse velocity utilization that has lead you to the tri-teetering hub ... The tri-teetering hub is an attempt to give greater control authority to very light rotorcraft. It is not intended for high-speed flight.


This Lockheed article from the first Issue of Stu Field's new magazine Experimental Helo (http://www.experimentalhelo.com/eh_experInfo.htm) might be of interest.


Dave

[Graviman]

Dave,

"Where did this statement come from?"

I made it up! :O Seriously though it is common sense. Stepniewski describes potential theory in his "Rotary-Wing Aerodynamics", which is the origin of CFD. With CFD, as with so many C.A.E. activities, common sense goes a long way to getting the right answer. The computer just tells you if you were right. :p

If you think about a rotor operating in forward velocity, the ideal is to have a positive pressure across the entire underside of the disk. Around the perimeter of the circular reverse velocity region there will be no flow across the aerofoil. There is therefore no way that the aerofoil can generate downwash, or the pressure gradient associated with it. The practical upshot is that the air will leak from below to above. If you consider his chapter on vortex theory you see that this means that two opposed vortices will spill off either side of the zero velocity region. Ergo you will get an effect similar to the fountain effect that Prouty nicely describes in one of his books (Heli aerodynamics, i think) - where the air leakage at the hub actually forms a miniature tornado from the airflow towards top (beanies help).

Perhaps, though, i should have been more specific with that statement. The conventional will suffer the worst, but any twin rotor will lessen the effect. Either coaxial or intermeshing have a gap between opposing rotors, so will allow the effect to occur with reverse velocity utilisation (leading to further blade slap). An interleaver will suffer less, and indeed i did wonder if this was the reason behind your recent migration to interleavers. My reason against use of RVU with interleavers is that you still need a large blade AOA in forward flight to keep a good downwash, at both root and tip, which will be away from optimum. There will be forward speed where the zero aerofoil velocity regions will coincide, but this is over the fuselage so no big deal.

Basically if twin rotor hubs are rigid, feather the reatreating blade and design the hub for the rotor lift inbalance. As i say intermeshing looks good here. Your project, your choice...

----

"...tri-teetering hub is an attempt to give greater control authority to very light rotorcraft."

Right, i wasn't sure though. Must admit to still wondering what advantages this head would give over say the Sikorsky/Schweizer 300 articulating lead (rigid with lead-lag). This is generally percieved as having superior flight characteristics to the R22. The tri-teetering is a sort of half-way design.

Gyro stabilised Schweizer 300 - mmmmmmmmmmmmmmm... :}

----

From the (rather interesting) site:

"Prouty further states, the "hinge-less" design suffers from the characterization that "they all shook". Lockheed added a fourth blade and controlled the shaking to a more pilot acceptable level."

I don't recall any provision being made for lead-lag on the 186/XH51 rotor heads. This would go some way to explaining the vibration. Indeed the original CL475 had a 2-blade rigid rotor! :oh:

Mart

[Edit:typos]

[Dave_Jackson]

Mart,

Vortex theory is really neat and interesting, but it is too complex a theory to use at this level of evaluation, particularly when trying to apply it to twin main-rotors. Blade element theory and common logic will do.
the reason behind your recent migration to interleavers. I strongly believe, until proven wrong, that the Intermeshing configuration is the best configuration for small rotorcraft, where speed and agility are important.
I think, until proven wrong, that the Interleaving configuration may be the best for large transport rotorcraft, where lift and speed are important but high maneuverability is not.
Must admit to still wondering what advantages this head would give over say the Sikorsky/Schweizer 300 articulating lead (rigid with lead-lag). It might offer two advantages. One, that its undersling (http://www.unicopter.com/B329.html#Undersling) may eliminated the need for lead/lag hinges. And two, that its large flapping hinge offset will allow for a smaller obliquity (http://www.unicopter.com/B329.html#Obliquity) when used in an Intermeshing configuration.



Reguarding the 3-blade and 4-blade Lockheed, the Sikorsky S-69 (XH-59) ABC coaxial had quite rigid 3-blade rotors. It was intended to fly at 250 kts, however it only got up to 220 kts due to the high vibrations. This would appear to be the reason that the sketch of their new X2 coaxial series shows 4-blade rotors.

Dave

[Graviman]

Hi Dave,

"Blade element theory and common logic will do."

Agreed. These days you would go straight from blade element calcs to CFD. Building a ground rig will be a good way to avoid some of those ScArY licencing costs though. :ooh:


"I strongly believe ... that the Intermeshing configuration is the best configuration for small rotorcraft..."

I strongly believe that you are right! :ok:

"...the Interleaving configuration may be the best for large transport rotorcraft ..."

Agreed. The additional payload justifies the additional drivetrain complexity. I get puzzled sometimes since the questions are not in the context of a specific project, so i am not always sure where the discussion is going. :uhoh:

"(Tri-teetering hub) ... undersling may eliminated the need for lead/lag hinges."

OK. Need to be proven/optimised on a ground rig, for perfect blade hub stiffness match.

"...large flapping hinge offset will allow for a smaller obliquity ..."

This is heading towards a rigid hub though. I can't help but wonder if a hysteric elastomer lead-lag bush would work as well. Again, though, it just needs proving out on a ground rig.


"... S-69 (XH-59) ABC coaxial had quite rigid 3-blade rotors ... high vibrations. ... X2 coaxial series shows 4-blade rotors."

Again, i wonder about the use of elastomeric lead-lag bushes to avoid coriolis induced vibration. Don't forget 4 bladed rotor will introduce (potentially avoidable) profile drag, over 3 bladed rotors.

Mart

[Edit: Ammendment]

[Graviman]

The theme of this thread is: to design a cost effective control system for a light helicopter, reducing pilot workload, and thus time required to master that machine. The contention is that a system based on the Lockheed CL475 stability gyro, being entirely mechanical with no active components, is well suited to the task. For helicopters already requiring power assist, an electic servo system with gyro control is well suited (along with the additional cost/complexity involved).

On area not yet covered is collective control for auto-rotation. The only method i can think of is the addition of an electric servo to correct collective position for RRPM errors. Since engine normally supplies required power, and is auto throttled in an R22, this system would normally not detect a need for collective correction. If activated the pilot would easilly be able to overpower the servo, in the same way that he can overpower the throttle. Light and horn could be part of the same system. The pilot would detect a mild resistance to flaring, which would only serve to remind him/her that the RRPM was reducing.

Does anyone feel that these conclusions would result in a machine that was easier to fly, and therefore less likely to suffer incident?

Mart

[maxtork]

Graviman,

I have been following this post for awhile now and I am very excited to hear some of this stuff from engineering folks like you. I'm not an engineer by any means but I have had some ideas in my head for some time that are very similar to yours. This being the case I"ll share my ideas and let everyone fire away.

I have often wondered why we connect the collective directly to the rotor control system and then have to engineer a way to make the engine maintain RRPM. My idea, however crazy it may be, is to connect the collective to the engine power control only and use a flyweight driven governor in the rotor system to automatically maintain RRPM. The flyweights would be allowed to swing outward with increased RRPM and when they do they would be linked to the pitch horns and could increase blade pitch. With this system if you lost engine power the collective would automatically be lowered due to the flyweights retracting (under action of a spring) from reduced RPM. This could be a handy feature in a non forgiving aircraft like the R22 where the reaction time needed is very fast. The problem with this design would be in autorotation where we are expecting the RRPM to decay but we still want to raise the pitch in the blades. This could be remedied by a simple magnetic brake assy. which would lock the collective to the pitch change mechanism. I have this all worked out in my pee brain but explaining it in text is a bit tough.

Now that we have a set of flyweights near the head controlling the RRPM we could possibly incorporate your gyro stabilization set up. If the weights are there and already connected to the pitch horns for rotor control you are halfyway there.

This whole thing is similar to the governors in fuel control units on turbine engines. You can even anticipate a droop in RPM by changing the tension of the spring in the system which we could also do in our new rotor system. I think this set up would have some good qualities in that it would almost be impossible to get behind the power curve as the pitch of the blades would only increase as fast as the engine power. Lowering pitch in case of an engine failure would be an automatic event and not one the pilot needs to perform conciously. Couple all this with Gravimans gyro cyclic control and you could have a pretty safe small helicopter. I agree that once the aircraft grows in size that electric stabilization equipment may be better suited as you would need some type of power assist anyway be it electric pneumatic hydraulic or whatever.

Ok so now is your chance to tell the grease ball mechanic to go back to his tools and leave the engineering to the pros! Hope I didn't get too far off topic. I just thought it was interesting that smart folks were coming up with ideas not far from my hair brained schemes!

Max

[Dave_Jackson]

Graviman & maxtork;

It sounds like you guys are talking about a Rotor Governor.
The following may be informative; A search on this subject will reveal one or more previous PPRuNe threads. The web page Control - Flight - Governor (http://www.unicopter.com/Governor.html) Dave

[Graviman]

MaxTork,

I've been thinking about your system, and i think it may have merit. It might be worth sketching out some of your ideas, so Dave can post them on his site. It would struggle with some of the inverted flight threads on this forum, but we are only talking R22. It would need careful packaging, but may well be possible to incorperate it into the gyro system i am proposing.


"The flyweights would be allowed to swing outward with increased RRPM and when they do they would be linked to the pitch horns and could increase blade pitch."

The system "gain factor" needs to be very high. Since RRPM is constant in theory flyweights would be at same swing. This means that autorotation may still be lower than nominal RRPM, albeit marginal. Ideally you want the RRPM to be controlled by error correction, which implies active.

"With this system if you lost engine power the collective would automatically be lowered due to the flyweights retracting (under action of a spring) from reduced RPM."

True enough. I think you need a robust mechanism for flaring though, which must feel natural to a pilot already potentially stressed. I can see problems triggering the magnetic clutch.

I suspect in the real world this system may be an ideal candidate for electric control though (like throttle already is). Probably the pilot needs direct control over collective, with a system to assist the pilot make the right choices. Gas turbine power curve lagging could be cured with the system i'm proposing resisting pilot input (although he can over power it). The pilot would soon learn to anticipate the response, but would not feel he was only taking a vote in collective control.

Actually gas turbine lag is a good justification for a hybrid helicopter, using electric motors as suggested by Dave J. Motors would be directly coupled to gearbox, and would make up RRPM errors left by turbine response. If powerful enough variable RRPM strategies allow much higher figure of merit across rotor required thrust range.

Mart

[Edit: speelin]

[maxtork]

Graviman,

Glad to hear that I wasn't totally out in left field. I agree that packaging would be a bit of a chore but I think it could be done.

As for the gain factor I think this could be overcome much as we do in an engine governor. By anticipating the droop in rpm we can compensate for static droop conditions. By simply changing the spring tension which is balancing the centrifugal force acting on the weightsyou can change the rpm. This same mechanism could be made part of the mag brake for autorotations. Lock the spring in it's place and now you are acting directly on the pitch change mechanism for the flare.

I don't think the pilot workload would be a problem either. Pilots already need to react quickly to lower the collective during an engine failure. If we take this action out of the loop he can simply enter his auto and set up for the landing and on the way down after he is set he can energize the brake. On the way down seems a less stressful time to have to react then imediately after an engine failure...although I stand by to be corrected from our pilot types who may be reading.

I will take your advice and make some sketches of what I have in mind. I'd be happy to send it to Mr Jackson if he is at all interested. Although I believe he already has this idea in his head as well considering his page on "rotor governors" which is precisely what I am talking about.

Max

[Graviman]

Max,

Howabout positioning the brake trigger so that it trips once the collective has been lowered to the autorotation position? Heli will fly normally, other than turbine lag limiting. At engine failure collective becomes ineffective, while blades set pitch for auto, until pilot lowers it to begin auto descent. Flare is as normal, but no need for any additional check (which may well be forgotten in the heat of the moment). This basically gives a machine with a virtually non-existant H-V curve for safe flight (although pilot must still flare).

I would have to see sketches of the mag brake overide to comment further, but see what you are getting at. If it could be packaged with the Lockheed gyro, then this would be a neat intallation. Horn and light would still trigger when engine response fell below limits, but maybe horn can go out when collective lowered.

Out of interest do multi-spool turbine engines suffer from lag as badly as single spool? In auto engines the smaller twin turbo is effectively an intermediate pressure turbine, designed to respond to transients until larger (low pressure) turbo can spool up/down.

Mart


Note: I was planning to discuss tail rotor control strategies next(or general yaw control for counter-rotating helis). My accidental threadjacking of the thread below shows me what potential problems exist for such a system...

http://www.pprune.org/forums/showthread.php?s=&threadid=177812&perpage=15&pagenumber=2

[maxtork]

Graviman,

Well I finnaly got around to doing some drawings. Although very crued they do give an example of what I am talking about. Unfortunately I don't know how to post a power point slide nor do I have a place to host it. If you are interested I would be happy to email it to you. After seeing it on paper I got excited again and started thinking about making a small spinning model to see how it works in 3D.

As for your question about twin spool engines I would imagine that two spools would be better but it would also add considerable complexity and therefore cost to the engine. In a small helicopter engine I don't think it would be warranted as modern turbines can accelerate from min to max power in about 1 second if you didn't have to worry about the torque limitations on the drivetrain. I believe with a rotor governor you could simply pull collective as you wish while watching the torque gauge and the RRPM will be maintained all by it's self. But again I'm just a grease monkey so I stand to be corrected.

Max

[Graviman]

By all means send me drawings, Max. It would be useful to keep discussion in this thread though. I prefer CAD to models, but it is my approach to getting stuff done.

What is the cause of torque delay in a turbine? I presume it is mostly to do with stators reacting to pilot input. Does falling behind the power curve present real problems to novice pilots? Is this the reason behind your concept, or are you most concerned about safe autorotation entry?

Mart

[maxtork]

Graviman,

I emailed you the simple drawing I made. Anyone else who may be interested feel free to ask as I would be happy to share it.

I would love to make a CAD model in 3D as I agree that would be the easiest way to see how things work but I work with CAD programs about as well as I sing and I can't carry a note in a bucket!

Now on to something I know at least a little about. To answer your question about turbine torque lag. There are actually two types of turbines used in helicopters today. The free shaft turbine and the direct shaft turbine. Most current types use the free shaft variety. This type can be described as a jet engine blowing on a pinwheel. We have basically a jet engine with a second turbine mounted close behind. This second turbine is not attached in anyway rotatonally to the jet engine rotating assembly but only to the out put shaft of the engine. When the pilot increases load on the rotor system by pulling up on the collective we automatically increase fuel flow to the engine which creates more hot gasses to impact the second (or free) turbine. A by product of this is that the jet engine (known as N1 or NG) which has no load on it other than that of the compressor drag increases in speed. Normally this happens very quickly and becomes almost transparent to the pilot. However we do have two limits to consider.

First is the fact that as we increase the load and subsequently fuel flow we create a great amount of hot gas to impact our free turbine which changes this energy to a twisting force we know as torque. If we arent careful the torque may be greater than the loads the rest of the drivetrain can handle resulting in broken parts. So one cause for this "lag" is the simple fact that we need to avoid overtorquing the drivetrain. In real life the engine is quite happy to produce more torque than the drivetrain will handle and in a very short time. So, you could pull up hard on the collective and the engine would quickly adapt to the load and you would see the torque gauge run right past the redline without much lag at all.

The other limiting factor is compressor surge. During this power increase phase we need to meter our fuel carefully so as not to build the fire in the engine to fast. If we do the rate of compression becomes less than the rate of combustion and the fire starts to squirt out the front of the engine and not the rear. This is what is known as compressor surge. So we can say that if we had a ful flow of 10 gallons per hour and we wanted to increase to 50 gallons per hour we couldn't dump all that extra fuel in at one point or we could have a surge. We can increase the fuel flow over what we have and as the engine accellerates and we have more air being compressed we cna continually add more fuel. This situation does cause a slight lag in power output in a turbine engine however with the efficient new compressor designs this can be minimized to a point where it is almost a non issue.

My thoughts on the rotor governor are that it would help with the complexity of the fuel control system of the engine as now it would not need to have a governor system built in. It would help with entry into autorotation as the reaction time needed would be relaxed greatly. There may be a slight decrease in pilot workload when considering "getting behind the power curve" but this is usually an issue with piston engine helicopters more than turbines. So for your R22 example with the old Lycoming mill I would say it would be great as you have no torque limit to concern yourself with. The pilot could pull all the collective he/she wanted without fear of getting ahead of the engine. In a turbine ship the bennefits are much less since you would always need to fly the torque gauge as the engine could overpower the drivetrain.

Once again my diarreah of the mouth has spread to my typing fingers. I hope my explanations helped at least someone and I didn't teach everyone stuff they already knew. Now on to find Mr Jackson!

Max

[Graviman]

Max,

I owes you an apology. I forwarded the .ppt file to my works address, since i don't have powerpoint, but was so engrossed in the problem i am investigating i totally forgot. Dumb engineers, eh! :rolleyes: Can you send a jpeg or similar?

"Most current types (turbine helis) use the free shaft variety."

Of course - i'm thinking direct shaft :} . I even have a nice sample of an A250 spool up with rotor turbine in tow as my computer startup, so should have realised.

"I hope my explanations helped at least someone and I didn't teach everyone stuff they already knew."

Nice write-up, Max. Don't mind relearning stuff in context, since it helps me make connections about design techniques. Now i realise we are primarily talking free power turbines i'm right with you.

When piston helis get below the power curve, are we talking naturally aspirated or turbo? I can see problems with torque converters, EGR, and turbos (in fact frequently do ;) ), but don't see why (say) an R22 would suffer lag - seemed quick enough for my poor piloting anyhow :} .

Mart

[Edit: spialeeng]

[maxtork]

OK I think I figured this picture posting stuff out so here goes!

http://i7.photobucket.com/albums/y275/maxtork/Slide1.jpg

Max


Edit: Wow I'm not as think as I dumb I are! it worked

[Graviman]

MaxTork,

Must admit it took me a while to see the subtlety of this, but i see what you are getting at. Basically you are fitting in additional weights into the Lockheed gyros to force RRPM control. Very neat, since this obviates the need to find methods of getting collective input into the rotor head.

I was thinking along the lines of a govenenor fitted as part of the collective control. This would clearly still need mixers in the pitch links so that collective and cyclic would have authority over the blade pitch. I think i like your system better...

You mentioned about varying the mast head spring to keep RRPM exactly constant with varying collective pitch, how would this work? Also, how does the pilot override the mechanism for collective flare? I still think that putting the collective down should trigger this, maybe with the servo i mentioned for continued hands off collective control.

A model is the best way to test the dynamics of this system. I just suggest the cad as a good (but not necessary) way to get there. Definately this concept would need a ground rig to prove it out, maybe based on the Sikorsky/Schweizer S300 head. Machined wood is ideal for this...


BTW anyone else getting the feeling that the Lockheed gyro system deserves a reappearance in light private helis - best wishes and Godspeed Lu...

Mart

[Edit: 'cos i types faster than i thinks :rolleyes: ]

[maxtork]

Graviman,

I think there are a number of ways to make this set up work. We could use the swashplate as usual for cyclic and collective pitch control. Or we could use the swashplate and pitch links for cyclic control only and use the hub spring tension for collective. I'm not sure at this point which would be easier. Either way the weight assembly that is controlling the pitch is balanced between the two sets of springs, so if we change either one we upset the balance and get the required pitch response.

If we think of the hub springs as being pinched between the gyroscopic weight assembly on one side and a floating plate within the mast on the other side. If we move the plate up and down we can change the tension of the spring and therefore the balance which sets the pitch. So in the flare we can lower the floating plate and lower the tension of the springs which would allow high pitch anlges with low rotor RPM.

I hope my ramblings make a bit of sense. I can maybe try to work out some animations of some sort to explain it all better. I really think this whole thing could work and be a bennefit.

Max

[Graviman]

"...ramblings make a bit of sense ... this whole thing could work and be a bennefit."

Right with you MaxTorq, but some concerns to be addressed still.

A better approach would be to cone the existing Lockheed gyro, with one set of weights (or offset pivot). RRPM would be slightly dependant on heli g loading, even though counter spring will be stong. This can be solved by a shaft centre counter weight, being careful not to upset the original gyro aumentation. Also the spring will need to be soft, and pre-stretched, to give the required sensitivity. Even so high pitch will require slightly higher RRPM, or worse autorotation requires slightly lower RRPM.

This last problem really bothers me. The ideal is a mechanism that keeps govenor in exactly the same position (ie fixed RRPM), over a very large range of pitch angles. In steam engines the govenor didn't need to move very much. I can't see any obvious way of solving this without an electric motor, which could well be part of the original "pilot assist" system i was considering (since it would also gently fight too fast collective input for turbines).

A purely mechanical system is always preferable, for safety and reliability reasons. I am willing to accept a hybrid approach for collective, but am not yet convinced that a complex sensor-electric system can outperform simple gyro augmentation of cyclic - Lu's account was very positive, before blade divergence. If pilot over-ride is really required (should the pilot actually be there?) then a motor could "trim" the collective input - probably better to let pilot have direct control, but let system "suggest" corrections...

Another thought is pilot induced oscillation. In hover if a pilot pulled more collective, to correct mild sink, an over-ride system might inadvertantly encourage more input to overcome "that wretched control system" :uhoh: . A correcting force in the collective would simply encourage the pilot to "slow down" his/her responses. A pilot in a panick is likely to fight the control system more, which may make matters much worse - worse case a failing engine with reduced power near to ground...

Mart

[IFMU]

> A purely mechanical system is always preferable, for safety and > reliability reasons

Whoops! I should go yank out my fuel injection and electronic ignition out of my car, slap in a carb and distributor. I've been following the system, and I have to wonder if 1) we are fixing a problem that really exists and 2) if you really want an easy to fly helicopter, why not fly by wire?

I've been following this thread with interest, but I think the challenges of implementing it, much less certifying it would overcome the advantages of a 'purely mechanical system.'

Good luck!

-IFMU

[maxtork]

IFMU,

I would actually like to have my old carburetor and distributor back! but that may be just me. I agree that fly by wire could do the job quite well but I have one real issue with the whole electronics method. You just can't see when it's broke! I work with fly by wire systems everyday and even with the self diagnostics built in, troubleshooting can be a real nightmare. In more complex and expensive helicopters fly by wire could work and does today. When you are going to trust the control of an aircraft to something we must periodically inspect it to see that it is in working order. With a mechanical system you can normally see any anomalies that could cause you harm on the next flight but it is very difficult to see a short in a wire bundle or a bad contact somewhere in a cannon plug. So to be sure the system is ok we build in self tests and parameters that will warn us of what we can't see. Now we have just added another expense to the whole shebang and more complexity. Our simple off the shelf solid state fly by wire system is now a full blown computer control system that cost much more money and I'd be willing to bet much more difficult to certify. So again for the big expensive aircraft this is justified but for the R22 or comparable small aircraft it becomes costly ...maybe too costly. So back to square one. If we can get the same job done with a relatively simple spider with some weights and a couple springs mounted to the rotor head then why not. I suppose Graviman is right...one step at a time as there are still some things to work out. But even if it never comes to be it is still good exercise for the brain!

Max

[Graviman]

"Whoops! I should go yank out my fuel injection and electronic ignition out of my car, slap in a carb and distributor."

Hehehe, i drive a mechanical injection pump diesel - what's electronic ignition? :}

Seriously though you have a point - I am an oddball in that i have degree quals in mechanical and electronics. I just believe that you only turn to electronics (with potentially complex modes of failure) when you can't get there mechanically. Carbs are actually a good example due to emissions, but you should see the hassle AMTL are going through to convice the world about steer-by-wire (No, i wasn't totally convinced either). Ask Nick how much the FBW program is costing Sikorsky sometime...

"I suppose Graviman is right...one step at a time as there are still some things to work out. But even if it never comes to be it is still good exercise for the brain!"

I've learnt some good stuff - it's good to explore new concepts. I think my final conclusion has to be that the best control system for a light heli is:

1. Lockheed gyro augmentation of rigid (or do i mean articulated :ugh: ) rotor system cyclic pitch.
2. Motor feedback to collective pitch, as part of (R22) auto throttle to assist the pilot make fast but safe decisions.
3. Non-augmented pedal system, primarily to keep the tail rotor forces sensible (use top rearward rotation to stop occasional R22 tail rotor vortex ring).

These ground rules would be applicable to any light heli, regardless of config. The whole point is to enable the design of a light heli that really is easy to fly - sort of a 21st century S300 if you like. The whole thing comes from my frustration at realising how much it would cost to make me a proficient heli pilot :{ - in the mean time i'm going back to gliders! :ok:

Mart

[Edit: it's a plank driver thing, typing and thinking at the same time... :confused: ]

[rjsquirrel]

Graviman,

We must hand it to you! You settled on the failed gyro system from an experimental helicopter that killed its crew, added an unbuilt and unproven system to bottom the collective and create a hazard all of its own, and finished with a direction of spin for the tail rotor that COSTS rotor control!

Not too shabby, what comes next, nuclear power as a lunch-time hobby?

[Graviman]

RJSquirrel,

"...the failed gyro system from an experimental helicopter that killed its crew"

The gyro system was extremely well proven on CL475 and 186 before AH56. The AH56 problems came when DOD insisted on spec that pushed disk loading to the point of cambered aerofoil divergence (thanks Lu). As far as i know both 186s and CL475 were finally destroyed in a hanger fire, but had no serious flight incidents. Please correct if wrong.

Don't forget light helis don't currently have ANY cyclic augmentation. I have only ever hovered a teetering machine, so couldn't say how much easier an articulated head is (open to offers ;) ), but I'll bet the S300 still won't hover hands off like the CL475 did (even with an offset CG!).


"added an unbuilt and unproven system to bottom the collective and create a hazard all of its own"

Well that's engineering, and is why we do system FMECAs. The proposed system does strike me as the most fail safe method to reduce autorotation incidents, but would naturally take development. As a final say the pilot (or instructor) can just switch it off, like the auto-throttle.


"and finished with a direction of spin for the tail rotor that COSTS rotor control!"

The XH-40 (prototype UH-1) and the AH56 (amongst many others) had the prototype tail rotor rotating top forwards, but later changed to top rearwards for improved controlability. As i understand it the rotor is always countering main rotor wake, so suffers less from vortex ring state. I'll eat crow if i need to here.

Out of interest which way does it turn on AS350?

Mart