The future of rotorcraft?

[Dave_Jackson]

Large twist is good for hover, but bad for fast forward flight.
High rotor RPM is good for hover, but bad for fast forward flight.

Consider blades that are made of Extension-Twist Coupled Laminates (http://www.geocities.com/mschliesman/comp_intro.htm).

In addition, consider an intermeshing helicopter with a pusher prop. The pusher prop provides all the forward thrust. As the craft's horizontal velocity is increased, the rotational speed of the rotors will be decreased. This reduction of rotor RPM results in less centrifugal force and this, in turn, results in less blade twist, due to the Extension-Twist Coupled Laminates. :ok:

At the maximum forward speed, the rotor blades will have no twist. The rotors are only required to provide lift, so now these rotors will be operating with minimal engine driven torque, and the rotorcraft will be flying, at high speed :ooh:, in a semi-helicopter / semi-gyrocopter mode.

_____________________

For those who like to read themselves to sleep, here are 449 more pages on the subject (http://techreports.larc.nasa.gov/ltrs/PDF/phd-93-nixon.pdf ). http://www.unicopter.com/Sleep.gif

[the wizard of auz]

Or we could make it real easy and nail the wings down so they dont move and call it ................ Oh I dont know,,,,, maybe and airplane. a whole lot less complecated. ;) :) :D

[vorticey]

what about feathering the turbine fan to produce forward thrust instead of the extra propeller.
all royalties to voticey

[Shawn Coyle]

Dave:
Do you intend that the main rotor would provide any of the forward thrust, or would it all come from the prop? Reversing prop for hovering with tailwinds, or slowing down when transitioning to the hover?
Does it also have a tail rotor?
I'll look at the other pages too.

[donut king]

What about Sikorsky's S-72 and the X- wing concept?

Is that what some guys are referring to...i.e slowing/ stopping the rotor in cruise flight.

D.K

[Dave_Jackson]

vorticey,

Different thrust devices work better at different forward velocities. Under approximately 400 mph the propeller or ducted fan will be the most efficient. At higher velocities, your idea may well have merit.


Shawn,

I feel quite strongly that; lower rotor rpm, extremely rigid rotors, active blade twist, a separate horizontal thrust device, and the exclusion of the tail-rotor, are all mandatory features for the next (2nd) generation of rotorcraft.

It will be interesting to see what, if any, horizontal thrust is provided by the main rotor(s) of these new rotorcraft. Perhaps there is consideration for giving the rotor-blades a slight positive twist in fast forward flight, but I suspect that total autorotation is not the optimal arraignment.

With the UniCopter, the intent is that the rotors will provide some of the forward thrust. One reason is because there is not enough room to swing a sufficiently large diameter propeller. The constant speed propeller will be linked to the forward cyclic, with consideration for linking it to the aft and lateral cyclics. The tail rotor is 'verboten':ooh:.


donut king,

Yes, but I don't think that the S-72 was ever flown with its rigid rotor. Perhaps the reasons for this were; an insufficient number of blades for aerodynamic stability and/or the asymmetrical aerodynamics of a single rotor at high speeds.

Boeing's new Dragonfly (http://www.boeing.com/phantom/crw.html) is supposed to fly within the next few months.

[Shawn Coyle]

Dave:
I'm sure you've thought of it, but one of the inherent problems with gyrocopters (not that you are advocating a pure gyrocopter, but there are some relevant things about them) is that they have a minimum airspeed that is dictated by the very poor efficiency of the propeller at slow airspeeds. No autogyro can fly slower than about 40 KIAS because of this, and you may have solved this probelm partly by having a powered main rotor.
But there are a whole host of other concerns that are relevant. Without a tail rotor or some other device to provide side thrust, how do you intend to meet the requirement of being able to handle winds from the rear and side?
Deeply interested in this, but there are often reasons why 'new' concepts have not been tried by the big boys.

[Dave_Jackson]

Hi Shawn:

You're correct. The use of the word 'gyrocopter', while discussing the attributes required for future rotorcraft, is an oversimplification of a complex situation.

The world's two most advanced helicopters at the end of WWII did not use tail rotors and I suspect that the tail rotor will be a serious impediment to very fast forward flight in the future.

Boeing has stated " The Chinook was developed in the late 1950s, less than a decade after the B-52 bomber entered service. Since then, two follow-on bombers have been fielded, but no new heavy-lift helicopter. There are many reasons for why rotorcraft technology has not significantly advanced in the past 60 years, but I do believe that it is now on the threshold of a new generation. To put it flippantly, today's rotor-blade, which has the dynamics of a wet noodle, and the little fan at the back will never stand up to the rigors of future fast forward flight.

Just a not-so-humble opinion. :ooh:

[nucleus33]

I of course disagree with Dave Jackson, I think that the conventional helicopter layout has many advantages (mainly efficiency and yaw control) that will make it the configuration of choice for at least the next 30 years.

Dave, you wrote: "The world's two most advanced helicopters at the end of WWII did not use tail rotors and I suspect that the tail rotor will be a serious impediment to very fast forward flight in the future."

Dave, which helicopters are you refering to? I thought that the Sikorsky machines were the most advanced... Remember the german machines had serious metal fatigue problems that limited the life of many components to something on the order of 20 hours.

Also, I disagree that a tail rotor is an impediment to speed, it is a nice vertical stabilizer at speed.

What the helicopter really needs is a low cost powerplant...

Hans Conser

[Lu Zuckerman]

Check this out. Excuse to foul language:

http://www.verticalreference.com/VRForum/CGI/ikonboard.cgi?;act=ST;f=1;t=448

:rolleyes:

[NickLappos]

Dave's wish for new ways to do things, and new capability for VTOL, is wonderful, and the work of the cartercopter crew must continue. The reasons why the ideas he proposes have not been successful in the past are quite explicable:

1) physics - the concept of an efficient hovering machine that also goes 250+ mph usually grounds out on the rocks of lost payload. Don't lose sight of payload efficiency in the hover, that's what we do, any compromise to this forgets why we were invited to the party. From tilt rotors to jump jets, to stop rotors and reverse flow rotors, the loss in hover efficiency has never been countered by speed. In other words, the product of speed time payload is what we seek, with a safe, fully controlled hover at each end. Anyone can make a VTOL go 500 knots, but it takes a very wise engineer to make it carry something useful, and do it in normal environments (wind and such). Real figures as to hover, cruise performance, and cost are quite scarce, so far.

2) money - The DARPA/NASA/Sikorsky X wing reached no fundamental engineering limits in its tests years ago, nor did the HLH. They ran aground when they ran out of money, and showed returns marginal enough to cause the moneybags to close the pocketbook. (Remember what caused the cancellation of the original Star Terk? ratings - money - the one monster Kirk could not defeat.)

3) mania - It takes a wise designer to keep preconceptions from screwing up his design. A campaign to rid a design of a feature (tail rotor, wiggly blade) must be undertaken because something better is found, not because these things are inherently ugly. Some of us seek metaphysical harmony, not engineering sense, and this can cloud judgement. Seeking tailrotorless symmetrical rotorcraft for their own sake is not the game. Making practical, monitarily justified machines that work in the real world is the game. The cathedral of Notre Dame has the marks of centuries of structural patches on its buttresses, evidence of the hodgepoge of fixes and claptrap that from day one been used to keep it standing. Those designers were not embarassed to try some screwball fix, they did what it took to keep the enormous space within dry and warm for its occupants. Remember the old adage - if its stupid but it works, it is not stupid.

[Dave_Jackson]

Hans,

What do you mean "I of course disagree with Dave Jackson, ..." :D

The following are a few specific responses to you concerns.

Efficiency:
All rotorcraft aerodynamists will say that current helicopters are extremely inefficient, in both hover and forward flight. A couple of reasons are;
The tail rotor consumes between 8 to 15% of the power, depending on whether a Western or Eastern (Kamov) spin is put on the information.
In fast forward flight, the root of the retreating blade and the tip of the advancing blade are imparting a downward (negative) thrust on the craft.
Elimination of the tail rotor is very, very easy. Developing Active Blade Twist will be very, very difficult. But, both WILL be done.

Yaw Control:
Yaw control can be achieved by;
Opposed cyclic, on twin rotor craft
Differential collective, on twin rotor craft
Lateral differential cyclic, on the propeller(s) of horizontal thrusters
Rudder or deflectors, if located in the airflow.
Early Advanced Helicopters
The two helicopters are the Flettner FL282 (http://www.germanvtol.com/flettnerfolder/fl282.html) and the Focke Achgelis Fa223 (http://www.germanvtol.com/fockeachgiles/fa223folder/fa223.html). Both were in production during WWII. At the end of the war, Germany was restricted from continue with the development of their aircraft.

Many, many moons ago Mr. Glidden Doman chaired a dinner meeting of the American Helicopter Society. Both Anton Flettner and Igor Sikorsky were present. After the dinner, an 8mm film of the Flettner FL282 was presented, which showed the technical details (http://www.unicopter.com/0474_2.html) of this craft. Mr. Doman told me directly that Igor was very obviously taken aback at the technological sophistication of FL282.

Flettner FL282 Transmission & Rotors (http://www.germanvtol.com/fl282rotorfolder/fl282rotor.html) shows a rediscovered and refurbished transmission & rotorhubs. For a 60 year old helicopter, it is quite something.

You mentioned "Remember the german machines had serious metal fatigue problems that limited the life of many components to something on the order of 20 hours.". The only reference to 20 hours that I can recall is from Prewitt's evaluation of the Fl282 after the war. The Maintenance section of the report says "It was interesting to note that during the twenty hours of flying this machine, no difficulties occurred in regard to maintaining the helicopter in flying condition."

_____________________

Nick,

Your points are all valid, but I think that advancements require both the dream of concept and the reality of detail.

At the risk of overselling one specific craft, Flettner and Hohenemser made a beautiful team. Flettner was the dreamer who kept on coming up with wild and wonderful ideas, whereas Hohenemser was the engineer who kept bringing Flettner back down to earth.


There must be a new future for rotorcraft, and I suspect that it will arise, in part, from the likes of Stepniewski's " Low Tip Speed Design Philosophy" and Sikorsky's "Reverse Velocity Rotorcraft Concept"

[NickLappos]

Dave,
Igor always commented on how the failure of many early helicopters was due to the designer seeking the perfection of balanced anti-torque through multiple rotor heads, either co-axial or otherwise. He said, "I believe in one God and one main rotor" only half in gest.

The wasted power hidden in carrying the friction, drag and weight of two transmission load paths, two full sets of rotor controls and/or the propulsive thruster is seldom given, but it is appreciable. The ABC cost 5% of the empty weight for the extra mechanism, and about 5% more drag. kamov has published similar numbers for their co-axials, with drag as probably 10% higher (due to the greater separation of their disks making a higher head mechanism.

In other words, all helos we envision "waste" at least 5% of their power, pick your poison.

I have said before, in the other dozen or so threads you have started on this same subject, that the persuit of symmetry as some mystical goal of perfection is not engineering.

[Dave_Jackson]

Nick,

Your points are well taken, but may be subject to a little fine-tuning.

Power Loss:

Dual rotor helicopters and 'single' rotor helicopters have two rotors each. In fact, the Chinook CH-47 has a similar load path to that of helicopters with tail rotors. The primary difference is a 50-50 power split between the rotors versus a 90-10 power split. In both cases, the total power train losses will be around 4-6%

Drag:

Aerodynamists say that drag increases as the rotor-hub is brought closer to the fuselage, due to the interaction between the two. It is also said that if the hub is brought very close to the fuselage, and the two are faired together, the drag will actually decrease.

As rotor rigidity has increased, the rotor-hubs have been brought closer to the fuselage. One of the theoretical advantages of the Absolutely Rigid Rotor is the ability to locate the rotor tight to the fuselage, and then fair them together.

Engineering

We have a difference, in that you are promoting existing products whereas I am promoting the research and development of new ones. Please don't underestimate the importance of overall conceptualization.

Conceptualization is normally done by those who know a little about many subjects. Detail engineering is done by those who know a lot about few subjects. In my company, I hired engineers to do the detail work.

[NickLappos]

So Dave, when you agree that the losses for various types of configurations is about 5%, you agree that the previous reference you made to an inefficient tail rotor is incorrect, right? All configurations lose about 5%, you now say. fair enough.

Regarding drag, the extra presented area of the two heads in your pet configuration will ALWAYS have more drag than a similar single rotor helicopter with one head. When you mix your magic (one config with two super-low heads, one without) you get screwy results. A synchropter will ALWAYS have more drag than a single rotor.

Regarding "promotion" of concepts, you are again confused. One "promotes" using PR, wild unsupported ideas about symmetry and balloons for the kids. One is not necessarily promoting when one sticks to the facts. As Lenin said, "Facts are stubborn things!"

[2rotors]

Nick and Dave,

I have been following your exchanges concerning helicopters for a long time and I appreciate the knowledge gained.

Nick, I also am interested in alternative helicopter designs. My motivation is ease of control. I have a friend with a R-22 and he has let me take the controls many times. I also have flown many fixed wing aircraft. Except for getting your descent and landing timing correct, the fixed wing aircraft are no more difficult to control than a car. The R-22 is unstable and difficult to control and it definately has my attention when I am trying to fly it. If anyone ever made a fixed wing aircraft with the stability of a R-22 they would never sell a single one. I know all helicopter pilots find the control of a helicopter as natural as driving a car, but that is a skill aquirred through many hours of carefull study. I feel if you could eliminate all the torque compensation issues that would be a step forward in the creation af an easy to fly helicopter. Therfore I am not very concerned about small differences in efficiency (5%) since a helicopter is already a very inefficient flying machine. Also concerning drag, if speed is limited by issues such as retreating blade stall or supersonic tips does it really matter if the second rotor has more drag than a smaller tail rotor?

So, Nick I would be interested in any insight you can provide into the potential for a tailrotorless design being easier to fly. Was the ABC easy to fly? Is a K-Max easy to fly? Also, can you comment on the pros and cons of servo flap control as on a K-Max or H-43? That is another area I am quite interested in as it seems to be an easy way to eliminate some critical highly loaded hardware in the rotor head.

If any of you reading this follow the Discovery Wings channel as I do you may have seen the recent Choppers episodes where they interview Charles Kaman. These episodes show early footage of synchropters flying around doing amazing things for their time. This was while the tailrotor design was in its infancy. The narrator specifically states that the intermeshing rotor helicopters performed extremely well. But then the intermeshing rotor helicopters just dissappear. There is no mention in the program as to why seemingly overnight the were replaced with helicopters that at that time had inferior capabilities. One guess I have is the reason was political since the best intermeshing designs were German. I would be interested in any comments anyone has as to why, other than Kaman's apparantly successfull designs intermeshing helicopters have disappeared.

I know I may sound biased in Dave's favor but I am really just looking for a helicopter design that approaches the design goals of the new Cirrus aircraft which are safe, easy to fly and accessible.

Thanks,
Rene

[NickLappos]

Rene,

The decision for the market to drop one design over another never occurs in one swoop, it takes bunch of individual decisions by a bunch of different buyers to end up dropping one design over another. Also the factors that make or break one idea over another are seldom easy to convey in a Discovery Channel show, even if the producers want to go there (which they don't, because lost causes sell deodorant). I tried once in a show to discuss the effects of disk loading and efficiency, it was all cut.

The idea that politics and some dirty work help to bury a carboretor that runs on water, or a Tucker car that gets 100 mpg or a synchropter that is better than a helicopter is pure bunk, the paranoid fumings of those with too much time and too little understanding. Believe it or not, syncropters have too many parts, too much drag and too little to offer the modern helicopter market. Dave doesn't believe it, but even Charlie Kaman does. He designed the very nice H-2 long after as a single rotor because it was the best for his customer, and he sold hundreds of them.

Flight stability and ease of handling is easy to get, these days, and it does not require us to perform the dubious trick of horsing around with the physical layout of the aircraft, like removing tail rotors or making two rotorheads.

Simple, capable flight stabilization systems using microprocessors and simple sensors are so mature that many RC helicopters use them, and the whole system costs a few hundred dollars. With a push from you folks, these systems will be adapted to the machines, and a cheap hands-off helicopter will be available, for a lot less than messing around with how the rotors are bolted on and where the anti-torque comes from.

Dave's arguments for symmetry are so seductive, you can start to believe that some wonderful balance of nature will make a hands-off flying machine.

Not true! The coaxials have the same need for autopilots and stability systems as the regular helos, mostly because rotors themselves are so darn unstable to begin with. Remember all those discussions about NOTAR being so stable that it was hands off? Notars need autopilots (in some of the models) because they are less stable than regular helos.

The world is not against development and change (quite the opposite), all configurations get a fair shake in the marketplace. I am certainly against the overblown promises of yet another scheme to make the all-singing-all dancing helicopter. I do believe that some of Dave's ideas are questionable, and are based not on engineering data, but on metaphysical arguments about purity and symmetry.

[Shawn Coyle]

Once again, Nick is right on the money.
Nearly every light helicopter could stand a stabilization system, and the first person to crack the cost problem for this would be real hero - if the pilots can be taught to accept it.
Far easier to design the stabilization system than to re-design the whole helicopter.
R&D, yes please, but something that has some possibility of working.

[Dave_Jackson]

Oh, Oh. Up against the top guns. :)

Nick,

"So Dave, when you agree that the losses for various types of configurations is about 5%, you agree that the previous reference you made to an inefficient tail rotor is incorrect, right? All configurations lose about 5%, you now say. fair enough."

Not exactly. We are talking of two different sources of loss.

Virtually all helicopters have two rotors. The mechanical losses, due to friction, in delivering power from the engine to the rotors will be ROUGHLY the same for all rotor configurations, and this value will be around 5%.

The other loss is that of lift. A helicopter with a tail rotor must apply approximately 10% of its remaining power at the little rotor, just to counteract the torque of the single main rotor. The dual rotor helicopter applies all its remaining power to lift, which is generated by the two counterrotating main rotors.


"A synchropter will ALWAYS have more drag than a single rotor"

I agreed that the drag will be slightly higher, BUT, the intermeshing configuration should be faster. :eek: This is because; its rotors are smaller, there is no tail rotor drag, and most importantly, the 10% saving in power [mentioned above] can be applied to forward thrust.

One should not think in terms of the slow Kaman Huskie. The intermeshing Flettner FL282 was faster than its contemporary, the Sikorsky R-4B.


"I do believe that some of Dave's ideas are questionable."

You're being very polite to use the word "some". :O I couldn't agree more with your comment. But; ideas create other ideas, and with enough synergy the occasional good one comes forth.


Shawn,

"Nearly every light helicopter could stand a stabilization system."


True, but Gareth Padfield mentions in his book "Helicopter Flight Dynamics: The Theory and Application of Flying Qualities and Simulation Modeling " that the helicopter should first have the ability to dynamically enact the desired actions in the most effective means possible. He also comments on the importance of this when components fail.

Stability Augmentation Systems cannot be used as a Band-Aid to cover over aerodynamic or dynamic inadequacies.

[NickLappos]

There we go again! You bash about the amount of loss to squeeze some hope from your arguments, Dave. The losses in this case are what they are, about the same for all configurations, no matter how you try to squeeze them.

I like your use of Gareth Padfield's book as a reference, since he and I worked together on several panels and papers. Gareth is one of the foremost authorities on how to use digital controls to improve the handling qualities of aircraft, in spite of the ideosynchrocies of their rotors. He would laugh at an argument that proposes developing a whole new rotor configuration purely to derive some improvement in handling.

I would also derive some eenjoyment at a guy who has, as his best arrow to shoot, a comparison between the Flettner and the R-4! Dave, you are as stubborn as Lu, and as likely to admit you are cornered!

[Dave_Jackson]

Nick,

You're strong support of the tail rotor configuration and objection to the lateral twin rotor configurations is understandable, and commendable. Your employer only manufactures this configuration.

Opposing this; I have never found a knowledgeable employee of a firm that manufactured laterally mounted twin rotors, who stated that his configuration was an inferior one. Have you?

Both sides of the argument are quite theoretical and speculative, until there is actual flying proof. Any ideas on how to relieve the V-22 project of a few million dollars, so that a modern lateral dual rotorcraft can be built? :ok:

[Shawn Coyle]

the only laterally mounted twin rotor helicopter that I know of is the Soviet Mi-12. It was not a success - but was this due to it's size, or something else.
The problem is handling and dynamic instability- the cheap and easy answer is a stabilization system. Having seen several of these, I can attest that even a simple rate damping system transforms the handling - underslung loads become a piece of cake, IFR flying is easily achieved, and so on.
The winner will be the person who develops a low cost, reasonable AFCS for light helicopters.

[Chiplight]

I can't help but notice how recent developments in the UAV arena are proving that much can be gained from moving away from traditional concepts.
For example the A160 Hummingbird , rather than slowing down its rotor at high speed (likethe CarterCopter and others), slows its rotor at LOW speeds.
They achieve a 50% payload increase and 50% reduction in fuel burn. Yet interestingly, the design keeps the tail rotor and single main rotor concept. No syncropters needed.
Here's a blurb:
******************
A contemporary helicopter features lightweight flexible rotors that are connected to the rotor hub through articulated joints. Such rotors are designed to provide smooth flight operation with little vibration and good control authority.

However, they can only do so within a limited range of speeds, normally at as high an RPM as possible before the wingtips break the sound barrier. The helicopter's rotor RPM is roughly constant while the aircraft is in flight. This is inefficient, particularly when the helicopter is flying below maximum speed or with an optimal load.

The A160's carbon-fiber composite rotor blades are tapered, and their cross-section varies from root to tip. They are light but stiff to avoid vibration, and their stiffness also varies from root to tip. The rotor system is rigid and hingeless, and features a larger diameter and lower disk loading than that of a conventional helicopter with the same lift capacity.

The A160 rotor can be operated from 140 to 350 RPM. Coupled with a fuel-efficient piston engine results in a helicopter that not only has unbelievable fuel efficiency, but good speed, unprecedented altitude capability, and is very silent.
********************************************

This aircraft is now flying, BTW,and a mpg movie can be seen here: http://www.darpa.mil/body/NewsItems/ucav/A1604blade5t%20flight2-10-03.mpg

and an article here:
http://www.globalsecurity.org/intell/systems/a160.htm

[NickLappos]

Dave,
You fall into the trap that catches many folks who are good with language and low on technical knowledge, you think this is a vote.

the only vote that counts is what the customer buys. If you read the papers published by Sergei Maheyev, you would see the same losses I report, and the same drag issues dioscussed, as well as reasonable assumptions of the weight penalties. It is rumored that he built a few coaxials. His latest helo is a single rotor, with fan.

Regarding this thread, it is not about change vs same. That is Dave's last refuge for his poor argument- that I must not want change if I don't think his symmetrical stuff is a good idea. Let the record show, I have flown more experimental helicopters, and more changes than ost other folks, change is the coin of an R&D pilot! I certainly advocate change, it is syncropters and symmetry that I describe as lost causes.

The Hummingbird has neither of those features, it is a single rotor helicopter with a tail rotor. Somehow, Chiplight, you would like to show me that the Hummingbird proves me incorrect, which is a mystery. Its variable rpm is a great idea, let it prosper!

For the record, I think change to introduce improvements is always good, change to introduce mystical properties of symmetry is almost never good.

[Chiplight]

Nick, I was supporting your point about the tail rotor not being the liability some would make it out to be.

Chiplight

[Dave_Jackson]

Shawn,

Yes, both the Germans and the Russians have built a number of side-by-side rotorcraft. The German Fa223 (http://www.germanvtol.com/fockeachgiles/fa223folder/fa223.html), actually saw limited service during the Second World War.

The downside to a totally new rotorcraft OR a computerized system is the cost, just as you and Nick said.

I understand that if a new rotorcraft was built today, the required pilots' seats will cost $25,000,00 each.

Nick can give a better answer, but I believe that the software for the Comanche involved hundreds of thousands of lines of code. This is not cheap. Microsoft can write off the cost of an operating system against 5,000,000 copies. Sikorsky must write off the cost against, say, 500 copies.

This high cost of writing off R&D expenses is also a partial answer to Hans Conser's earlier statement "What the helicopter really needs is a low cost powerplant...". As I recall, only 3,500 reciprocating aircraft engines are built each year. Lycoming or Continental has mentioned that this makes it impossible to develop a next generation reciprocating engine.


Chiplight,

The Hummingbird A160 is another attempt to push the frontiers of rotorcraft and that is good. I believe that their patent is US 6,007,298. It's not a new idea but since the craft is unmanned, in hover they can risk operating the main rotor closer to total stall.

For simple hover, unquestionably, NOTHING can beat two side-by-side rotors in close proximity.


Nick,

We have already discussed Kamov's calculations about tail-rotor losses verses the earlier western calculations. Leishman and other westerners have now move closer to the Russian's claim of higher losses. Whatever, I have never suggested that the coaxial is a better configuration.

I have only claimed that the intermeshing configuration is probably the best configuration for short small fuselages. Your guru, Stepniewski, concluded, in his last known report, a couple of years back, that the intermeshing configuration was even the best for large transportation craft. The latest issue of the AHS Journal arrived today. You will notice that the first article is 'Preliminary Design of Transport Helicopters' and in this article, Stepniewski is cited in 2 of the 8 references.

In addition, I have never talked about 'mysticism', only about 'nature' and about man's striving to technologically get closer to what it took hundred of millions of years for evolution to achieve.

"the only vote that counts is what the customer buys",

We all know the value of marketing. We also know of many, many instances where the best product was not the best seller.
_________________


Fact: In 1945, the best helicopters in the world were the two German lateral twin rotor helicopters.
Fact: Countries developing helicopters at this time, such as Germany, Italy, Russia, France and England all lost the war ~ financially. The exception was the US, which was predominantly single rotor oriented.
Fact: Since 1945, far, far more money has been spent on single rotorcraft development than has been spent on lateral twin rotorcraft development.
Assumption If the allocation of this money had been reversed, today's rotorcraft would be far ahead of what they currently are. :oh: :oh:


~ and the $hit just hit the fan ~

[3top]

hi all,



2rotors:

you mentioned the R-22 being unstable. By now I have about 600hrs in it (out of 6500).

Actually I think it is a VERY STABLE helicopter. Just flew it for 12 hrs in 2 days right into mountains with a bit turbulence.
On the way home I even got it to fly hands of for 30 sec. at a time (horsing around to cut bordome on the ferry...)
I think what you call unstable in the R-22 is rather light weight. Of course a little ****** like the R-22 will be thrown around in any little breeze there is, so would any other small helicopter.
However sofar I do not know of any like small helo that is so maneuverable and fast (relative . . . vne 102 kts and I did 90 on cruise)

Rotordisk distance to the hull:

I am definitely not any match to discuss this issue amongst you guys, but observe this on the R-44 (I know I like the R-product a lot, .....I fly it a lot - for Nick this is probably a couple of thousand pounds below his lower weight redline........). This machine has the rotorhead rather far away from the hull. The new Raven II does on regular cruisepower some easy 110 kts in ISA+15 deg conditions, versus 90 for the old model. Remeber this chopper has a max gross of 2400lbs (2500 the Raven II), so it is still a light weight chopper. And it still is extremly stable, not to mix this up with agile - you can do amazing things with it and you can do them fast (AGAIN relative - we have a simple underslung rotor and all its limits - no loops and rolls here, as far as I know)

Last 2 cents:

Everyone talking off making even the small choppers easier to fly. I do not know if this is so good. There is a reason why only seasoned pilots do certain work. I would not want to have a lot of folk up there to get in trouble because of the extended flightenvelope a helicopter gives them versus a fixed wing.

I personally apreciate the rather demanding training one has to go thrue to get a helicopter licence, and I am glad that all those who do not cut it, do not get themselves into trouble.

Artificial stability and control is all fine, until it fails (that one time out of a million...),keep these systems in the big machines and keep the smaller ones sensible, it sorts the ones that should from the ones that do not!!

3top:cool:

[Dave_Jackson]

______________________

The future of the rotorcraft industry is in dire straights. This is evident from the limited current projects, the proposed concepts, the lack of supporting funds, and the depressing industry articles. In essence, there are very few VTOL configurations currently contending for future high-speed/vertical aircraft, and all of them are flawed.

In my opinion, there is only one realistic future VTOL configuration. It is the unification of the Intermeshing Configuration and the Advancing Blade Concept. A configuration that appears to have no show-stopping flaw.
______________________

John K. Northrop (1895-1981) was a project designer at Lockheed's Skunk Works. His lifelong passion was to build a flying wing. Out of deep respect for this gentleman, Lockheed showed him the secret B-2 bomber, just before he passed away. It was done in appreciation and acknowledgment that his dream was finally becoming a reality.

The 80-year-old Charles Kaman, started his aerospace career in 1942 as an engineer with United Technologies, working as an aerodynamicist with Igor Sikorsky. When Kaman's ideas were rejected, he left, and with $2,000.00 started his own company, to produce an intermeshing helicopter. His decision to emphasize lift over forward speed may have been based on his inability to compete with the larger United Technologies.

Sikorsky has the most experience in the Advancing Blade Concept and Reverse Velocity Utilization. Therefor they have the advantage in developing this style of advanced rotorcraft.

Out of consideration for their former employee, might they invite Charles Kaman to come and see the potential of his intermeshing dream. :D

Perhaps it's a secret project, and they already have. :D :D

[Thomas coupling]

Hi Dave, all very interesting stuff, I'm sure. I never got round to asking you, but what do you do for a living?

regards,

TC

[Dave_Jackson]

Hi TC,

When not writing provocative postings, my 'life' is spent trying to develop, and disseminate information on, a better rotorcraft. :O :O

Dave
UniCopter (http://www.unicopter.com/UniCopter.html)

[46Driver]

It was said that there has been no heavy lift helicopter built since the CH-47 Chinook? What about the Sikorsky CH-53E?

As for other technology, the Navy is funding Piasecki's work on the Vectored Thrust Ducted Propellor modification to the H-60. Anyone have any comments or observations about it?

[Dave_Jackson]

46Driver:

A couple of notes on the Vectored Thrust Ducted Propeller, which were probably not mentioned in last year's thread, are;

Sikorsky's Reverse Velocity Rotorcraft (http://www.unicopter.com/1281.html)
A gentleman who was involved in researching and developing the VTDP concept dropped the project after coming to the conclusion that it could not be what it was hoped to be.

[deeper]

DJ,

You stated or attributed a statement in an earlier post that helicopters are inefficient.

I am sure as a customer looking for a machine that I would look for alternatives to helicopters if this was the case. It is not.

Todays helicopters are as efficient as they can be as the state of the art develops.

You argue that nobody wants change yet millions are spent trying to get that little bit more out of the machine by the manufacturers to make the customer buy their product.

I have yet to fly a helicopter that has been inefficent at what I have asked it to do.

My many clients must think as I do.

Some of your theory needs a bit of brushing up also. (too much to go into here).

:bored: :bored:

[Dave_Jackson]

deeper,

'Efficiency' is a comparative characteristic.

I humbly submit that no one would claim the helicopter to be more aerodynamically efficient than its brethren, the airplane. It might also be stated that with a ratio of one helicopter for every half million people, it is obviously not a cost efficient form of transportation. What it does do is fill a niche market. A market that would be bigger, if helicopters were more efficient.

Unlike biotechnology or artificial intelligence, transportation is a mature industry. Yet, I believe that there is room for a significant increase in the efficiency of rotorcraft. Not by 'tweaking' improvements out of existing products, but by developing a new one. This appears to be possible by unifying the old ideas of the Intermeshing Configuration and Advancing Blade Concept with new ideas such as Active Blade Twist and Absolutely Rigid Rotors.


You are definitely correct in saying that "Some of your theory needs a bit of brushing up also.', but, I would argue that it is better to submit theories for critique then to resign oneself to the status quo.

For example;

The Sikorsky XH-59A ABC was a remarkable craft. It showed the promise of VTOL ~ with fast-forward. Unfortunately, vibration, resulting from an oscillating lateral dissymitry of lift, limited the craft to 230 knots. I theorize ;) that the craft could have gone much faster if 4-blade rotors had been used, instead of the 3-blade rotors.

The http://www.unicopter.com/Sleep.gif stuff;
Vibration - Rotor Induced - Analysis of Sikorsky ABC ~ Coaxial (http://www.unicopter.com/0893.html )
Rotor - Disk - Lateral Dissymmetry of Lift - 3-blade Rotors (http://www.unicopter.com/0871.html)
Rotor - Disk - Lateral Dissymmetry of Lift - 4-blade Rotors (http://www.unicopter.com/1218.html)

[RobboRider]

Deeper

As much as I love my spiralling bladed flying machine it is not efficient, in the proper sense of the word.

Scientifically speaking efficieny is the ratio of input to output the bang for the buck principle.
When I hear about the input output raios for my friends fixed wings I can only feel envious. Same engine as mine drives their machines at nearly 200 knots (Long Eze) at a fuel burn of about 22 litres an hour or for the same engine and fuel burn as me carries four fat blokes, their bags and plankers nav bag (Piper warrior) while I have to sweat about whether I take my lunch with me!

But................ I go and land on a beach, go for a swim, go fishing camping and stuff. Land in my mates backyard and fly him to the airport so he can get in his fixed wing etc etc

Its is as efficient as it can be, in the current state of the art but it fills niche (that can't be filled by any other known flying machine) and does that very well, but at poor efficiency.


Dave Jackson

I think even synchromeshes and all other bladed spinning things are still just tweaking round the edges. They are all just variations on a theme. The quantum leap is only going to come when someone discovers some completely unheard of anti-gravity system (God knows what it will be or when it will be - maybe only in a galaxy far, far away):p

[Dave_Jackson]

From an 'American Helicopter Society' email. ~ dated January 28, 2005

" As of today we don't have anyone nominated for the Gruppo Agusta International Helicopter Fellowship Award. Ditto for the Grover E. Bell Award. How about candidates for the Captain William J. Kossler Award which is given for the greatest achievement in practical application or operation of rotary wing aircraft? We know that there are individuals and teams out there that should be nominated for these prestigious awards. We are giving you one last chance to get your nominations in to the Society. We have decided to extend the deadline for receipt of the award nominations until Monday, February 7th.

Can it be that one of the university Rotorcraft Centers of Excellence don't have any qualified candidates for the Vertical Flight Foundation scholarships? As of today, we haven't received any applications from this institution. In order to make sure that we get in as many applications as we can, we are also extending this deadline until Monday, February 7th. We encourage all students interested in pursuing careers in vertical flight to apply for these scholarships."

How depressing. :(

Does this imply that there are few, if any, significant developments left in rotorcraft technology? Or, does this imply that there are few, if any, American manufacturers and institutions that have the ability or the motivation to 'think outside the box'?

[zeeoo]

Maybe it's time for the mass to get the benefits of all those wonderfull things achieved ?
or maybe the helicopter, in it's actual definition is simply prone to disapear... dinosaurs left the place to smart and small creatures .

[Jack Carson]

It sounds as if you are discussing a 2nd generation XH-59. The XH-59A aircraft had very rigid coaxial rotors that gave it very reasonable forward speed capability with thrust augmentation and more importantly good rotor performance at higher altitudes. It is a shame that this concept was retired so early in its developmental cycle.

[zeeoo]

Jack,
when you say "rigid", you're talking about something like the BO105 i suppose ?
thanks

[Dave_Jackson]

The article 'Looking for Lift' in the 3-9, May, 2005 issue of Flight International is about the future of rotorcraft research & development in the US; for those that are interested.

Dave J

[Ian Corrigible]

Dave,

Don't give up on the industry just yet ! There are still a few projects being worked on both sides of the Atlantic that represent significant developments. :ok:

As a follow-up to the Flight article, those with broadband (or dial-up connections and the patience of a newly-beautified saint) may also want to browse the helicopter section of the report to Congress recently submitted by the National Institute of Aerospace: NIA Aviation plan (http://www.nianet.org/nianews/AviationPlan.php).

I/C

[Graviman]

Interesting thread. I'll scribble some comments to points raised:


Intermeshers are less aerodynamically efficient:

Realistically, you have to develope the whole package to gain the full benefit. I am astonished at how quickly the fuel in an R22 just dissappears. Even a transition from 10% loss to 5% loss is beneficial. Intermeshers are mechanically complicated, and have to justify this with better efficiency.

The ideal intermesher has to aim for:
Outboard/lower advancing - for most efficient downwash.
Feathered retreating (or ABC) - to avoid interference and tip stall.
Faired hubs - to minimise drag (coaxials cannot achieve this).
Variable blade twist - to optimise for flight condition.
Pusher prop - to keep both hubs at minimum streamline profile.
Variable RRPM - even though compressibility will eventually limit speed.

Any less, or any program not aiming to achieve all this, will not offer sufficient commercial advantage over a conventional. The above can be done in stages, since this program would be a serious undertaking. Ideally a development intermesher would sort out the handling issues of outboard advancing and gyro-aug contol system. Then the long-term project then develops pusher prop and aerodynamics (including v-RRPM).


Intermeshers require less pilot workload:

Not convinced. I can believe that the Husky and F-282 are easy to fly, but neither can hover close to ground hands off. Breastsroke rotation explains the ease of flight, As explained in my 9th May post in thread
http://www.pprune.org/forums/showthread.php?s=&threadid=172358&perpage=15&pagenumber=4
Hands-off hover is a must for the above program, as is lower advancing, and can only be achieved reliably/safely and cost effectively using the Lockheed Gyro mechanical augmentation system. With this an unstable helicopter (ie all of them in the engineering sense, since you always need the pilot) can be made neutrally stable. By neutral stability i means hands-off hover (ie stays at attitude it is put), not stable oscillation. Fixed wing positive stability can only be achieved with aerodynamic effects, and is ideally designed in after/with gyro-augmentation using (say) a T-tail.


The practical upshot is that initially investigating blades, then hub design is paramount. The next stage has to be gyro control system. Then intermeshing, since you already have component designs that would improve conventional helis.

Dave, i seriously suggest you look at the Schweizer/Hughes 300C hub - these are generally regarded as easier to fly than the R22. Also, The reason i suspect you will succeed in developing a carbon fiber rigid rotor may be found by clicking 2.3MW in the link:

http://www.bonus.dk/uk/produkter/index.html


Finally:

"They are all just variations on a theme. The quantum leap is only going to come when someone discovers some completely unheard of anti-gravity system..."

An interesting thought, RobboRider. This is neither the place nor the time, but i admit to having my reasons for wishing to understand the limits of helicopter technology...

Mart

[Dave_Jackson]

I/CThere are still a few projects being worked on both sides of the Atlantic that represent significant developments. Good. :ok:. However, if these projects include; Sikorsky's Reverse Velocity Rotorcraft, Piasecki's compound helicopter, Boeing's Canard Rotor/Wing or Carter's Gyro Transport, I would love to technically discuss any of them, particularly with the guy who developed the concept.

My concepts are open to public scrutiny, let them do the same.


Thanks for the reference to the NIA Aviation plan.

Unfortunately, it is only a request for funding. The rotorcraft portion of this proposal was developed by the four major US rotorcraft manufacturers and the three primary US rotorcraft universities. They are seeking funding from NASA. These seven entities just lost funding when NASA quit supporting rotorcraft.

Much of the American rotorcraft industry appears to be unwilling to pursue new viable configurations. Perhaps this is symptomatic of current US capitalism. Even the US Army is looking outside this 'cartel' seeking any wild and wonderful ideas that will give them second-generation VTOL craft.

The European rotorcraft industry appears to be more R&D oriented. No doubt, the Orient will be even more oriented.


Graviman;

There are 'ideas' looking for 'needs' to be satisfied, and there are 'needs' looking for 'ideas' to provide satisfaction.

If the only 'need' is stable hover then perhaps nothing can improve on the hot air balloon.

If the 'need' is a montage of; fast forward speed, high L/D ratio, stability, controllability, reliability, and cheapability, then the ultimate solution might be teleportation. :D


Dave J.

[Graviman]

"There are 'ideas' looking for 'needs' to be satisfied, and there are 'needs' looking for 'ideas' to provide satisfaction."

Dave, I think you misunderstand the point of my last post. I am saying that the next gen rotorcraft needs to address all of the aerodynamic design points, to be commercially competetive. Ease of hover will then require augmented stability. I am suggesting practical and reliable ways to go about both.

"My concepts are open to public scrutiny, let them do the same."

The comments i often raise should be seen as constructive criticism. Rather than simply dismiss your ideas, i try to highlight what i see as good points while explaining my concerns with areas i see as bad points - hopefully to provide realistic engineering feedback. :ok:

Mart

[Dave_Jackson]

Mono Tilt Rotor ~ Developed by Baldwin Technology

US Army could set up to $5 million aside to study unusual heavylift rotorcraft design.

http://www.UniCopter.com/Temporary/MonoTiltRotor.gif

________________________________

Graviman,

Perhaps augmented stability should be provided electronically. In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented.


Dave J.

[Graviman]

"Perhaps augmented stability should be provided electronically."

Perhaps, but i am suggesting a method that is mechanically simple and has already been proven in the Lockheed CL475, 186 and Cheyenne. An aerodynamic variation was developed at Hiller, and all electro-hydraulic systems are based on the same idea of gyro feedback for attitude control.

"In addition, perhaps it should only be considered after all viable aerodynamic methods had been implemented."

Again perhaps, but i have not seen anything so far that leads me to believe that hands off hover can be achieved purely aerodynamically. The original De Bothezat heli had four rotors, with dihedral, and even this was unstable. I'm actually puzzled why you are so resistant to gyro-aug, when you were argueing for the gyro stability of intermeshers. I'm suggesting a simple way to achive one of your objectives, allowing greater freedom of design for aerodynamic efficiency.

Mart

[Dave_Jackson]

Mart,
I'm actually puzzled why you are so resistant to gyro-aug, when you were arguing for the gyro stability of intermeshers. The Lockheed gyro system may be an excellent one. However, I have a phobia about adding 'gizmos' to any machine solely for the purpose of rectify a problem that the basic machine didn't, or couldn't. My wish that the two intermeshing rotors could provide gyro stability was an attempt to get a free benefit from the rotors without having to add gismos. :O

gismo ~ A device that adds weight, complexity and cost. :E

Dave

[steamchicken]

This discussion points up, IMHO, the sheer engineering elegance of the Pegasus engine and the genius of Sydney Camm and the Bristol-Siddeley engine team...what is needed is a vectored thrust solution with enough robustness to permit a vertical landing with one engine out...

[NickLappos]

The inexerable loss of power from vectored thrust will be a hurdle for decades to come for them. To vector thrust like a Harrier requires about 1000 times more horsepower to lift a pound of payload. This penalty is fine when you need a military aircraft to bomb the end of its own runway, but it is almost laughable for any vehicle that must earn its way. It is elegant, in its way, but of no practicality in the real commercial world.

Those who don't understand disk loading are doomed to chase the sexiest idea, in spite of its impracticality. Those who think there is an inventor who will break Newton's laws in his garage next year are ripe pickings for the Mollers and Tilt Rotor advocates.

[Graviman]

"My wish that the two intermeshing rotors could provide gyro stability was an attempt to get a free benefit from the rotors without having to add gismos."

Believe me i really do understand this. My understanding of the problem is that no helicopter could be designed for hands off hover, unless it became aerodynamically impractical. The various four rotor aero-jeeps of the '60s came closest, but you are only considering two - this always leaves one unstable degree of freedom. An absolutely rigid rotor with seriously impractical cone angle may do the trick, but at a cost of weight and hub complexity (or needs a tip tension ring :uhoh: ).

It is your project, but trust me hover control is the greatest impediment to wider rotorcraft appeal - try it if you don't believe me! The gyro system can be easilly designed into the swash plate of a single rotor design, and i honestly don't understand why it has not become a standard light heli feature - but then neither have rigids/articulated. A twin rotor could either use a common gyro, or one on each hub.

For high speed work, i am convinced that the intermesher config is (theoretically) unbeatable for a given engine power. But this has to be outboard advancing and feathered retreating, ideally with pusher prop to keep constant trim, for serious aerodynamic gains. Less than high speed sees fewer, if any, advantage for intermeshing (especially when comparing gyro-aug machines) - i'm with Nick on that one. If you are serious about IRAT control, i don't understand why a proven gyro stabiliser ups the stakes so much. The control system needs development, so you start with a lower spec intermeshing project...

Mart

[slowrotor]

graviman,
Consider this. Your interest in a gyro stabilizer may not apply after you learn to hover.
The Hiller rotormatic and the Bell stabilizer system went away. The Hiller FH1100 has some other system and Jet Rangers have no flybar.
It takes more than just the ability to hover to be a pilot and pilots like control more than stability.
A bicycle is hard until learned. No need for stabilizing training wheels after the first lessons.
A little slower reacting rotor wouldn't hurt, but try not to add extra parts. Just my view on the subject.

[Graviman]

Hi SlowRotor,

"...interest in a gyro stabilizer ... learn to hover."

True, but my point is that a good machine eases the pilot workload. Especially if he/she is preoccupied, possibly in an emergency. It also reduces the likelyhood of accidents.

"The Hiller rotormatic and the Bell stabilizer system went away."

Both systems are fundamentally flawed, the primary reason being that they affect teetering rotors not rigid/articulated rotors (less pitch/roll control). Hiller also relied on aerodynamics, which at the hub are not steady. The Bell system only increases rotor apparent inertia, and does absolutely nothing for heli control.

"It takes more than just the ability to hover to be a pilot and pilots like control more than stability."

True, but i suspect pilots doing the three Ds would be greatful for a machine that "flew itself". If it was purely mechanical, then it could be relied on to a greater extent.

"A little slower reacting rotor ..."

The Lockhheed system has absolutely no effect on rotor response time. It just provides attitude feedback, so that into cyclic controls pitch/roll rate directly (like a fixed wing) - in simple terms: the pilot flys the gyro, the gyro flies the heli. It is the basis of all articulated rotor gyro electro-hydraulic systems (and future FBW systems). It that respect it was widely adopted, but not in it's original mechanical form.

Mart

[Dave_Jackson]

Mart,for hands off hover .... An absolutely rigid rotor with seriously impractical cone angle may do the trick. I agree with all that you say, except for the use of the word "impractical". :O
Hopefully, a large fixed coning angle of 4º or 5º will be practical for stability during hover and also for stability during forward flight.

During fast forward flight, an Absolutely Rigid Rotor will not provide any flap-back (http://www.unicopter.com/B267.html#Flapback) to give speed stability. This is where the higher than normal coning angle should be an advantage. This large pre-cone angle (http://www.unicopter.com/1216.html) should assist with speed stability by offsetting the nose down drag, which is caused by the fuselage.

Dave

[Graviman]

OK. Maybe it's my turn to eat crow then. :}

By balancing the stiffness of the tri-teetering hub and cone angle, it should be possible to have horizontal velocity in any direction cause corresponding dihedral (longitudinal and/or lateral) response of heli without any cross coupling - by tuning lead angle to coning/advancing rotor flap response. This means that heli left to it's own devices should want to hover right side up. This definately needs proving out on a ground-rig though, my main concern being how well the total system is damped (ideally critically at all speeds including hover) - worse case the system could hover/fly in a stable circle :yuk: .

The Lockheed system is a lot to live up to - i gave it some thought today. In this case the gyro provided both longitudinal/lateral damping and stability. The dihedral was affected by the blade flap being able to affect gyro reference position (so heli pitched/rolled to oppose motion) - it was actually too much feedback that caused the blade strike when disk load was pushed up on the original system. Attitude was still corrected by gyro, which had so much control power that the correction time constant was pushed well below the dihedral time constant. The effect was that the gyro damped the system.

I am still not entirely certain as to whether the low speed intermesher offers advantages over a conventional, from the aerodynamics standpoint, once you you move away from hover. The advantage of no tail rotor losses may well become offset by two hubs operating at an angle to inflow - as Nick suggests. I do appreciate that the inflow velocity flapping, with anything other than an absolute rigid rotor, will require intermeshing to avoid effective dihedral precession. For high speed, where retreating tip stall reigns, intermeshing (with pushers) is definately the way forwards - ideally outboard advancing, with large vert stabiliser. A low speed (non-pusher) intermesher as a step towards this makes sense, but i couldn't say for sure that it would improve fuel consumption over a conventional. :confused:

Again, don't feel i'm poking your project for the sake of it, Dave. I'm just trying to provide engineering feedback...

Mart

[Edited, since i felt my original post too critical of intermeshers :\ ]