Igor. Why you do dat?

[Dave Jackson]

Why did you stick that little fan on your helicopter? Did the complexities of flying a rotor edgewise overwhelm you? Did you say to yourself "why compound this problem with two rotors. Let's try and get away with one."? I've heard that you were later astonished by the technological sophistication of Flettner's intermeshing helicopter, when you saw his film at the AHS meeting. Please say that you didn't contribute to Charley K. leaving the company, and then having to develop his intermeshing helicopter idea with insufficient funds.

You must agree that virtually every living creature, with mobility, has laterally symmetry. You must agree that most of mankind's progress is founded in nature. You must agree that this lateral symmetry is universally applied in man's vehicles. Do you not agree that optimal VTOL can only be achieved by adhering to nature's Darwinian logic?


Why oh why did you stick us with that dinky little fan. Sixty years is long enough. Let vertical flight resume its rightful place in air transportation.

Signed,

I. M. Perplexed

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

Lateral Symmetry is Functional Beauty :)

[Shawn Coyle]

Dave:
agreed that lateral symmetry is functional beauty, but simplicity of design is also a good principle.
Not much has touched the single main rotor / tail rotor for overall simplicity and functionality for small helicopters.
For larger ones, options like tandem and co-axial are viable, but there must be a good reason besides marketing why the overwhelming majority of small helicopters are fitted with tail rotors.
There has to be a reason for it, perhaps we just don't know all the tradeoffs.
Shawn

[Nick Lappos]

Poor Dave, like so many midevil clerics, he seeks metaphysical justification for physical situations. The Earth must be the center of the universe, because all things are balanced that way; the moon must be perfect, and can have no mountains, because it is an example of heavenly perfection. Symmetry is a measure of perfection, and so all things good come from it....

There is no system in the universe that has symmetry, none. The very rotation of the electrons within the atoms illustrates this. The creatures that Dave cites are not symmetrical in any real sense, and neither are the machines he mentions. Why not seek vertical symmetry, if symmetry is important? Why do all those vertical irregularities escape your gaze?

Seek practical answers to real problems, not theoretical "improvements" for machines that work! And try actually building the machines you advocate, not publishing the concepts in theoretical tomes.

I suggest, Dave, that you just build the machine that you love so passionately, and show its excellence. The world will beat a path to your door if it flies as well as you believe! You will recognize the path, it will look like the one that leads to every other helicopter plant in the world.

[Dave Jackson]

Shawn

I agree with what you say, but think that 'simplicity of function' may be more important than 'simplicity of design'.

Another major obstacle facing helicopter developers is lack of money. This was particularly true of the German companies after the Second World War. Their helicopters were unquestionably the most advanced, but monetary limitations and Allied imposed restrictions did them in.
_________________

Nick,

Your knowledge of the helicopter is vast and your sharing of that knowledge is much appreciated.

Why then must you resort to metaphysics and semantics to defend the tail rotor?


Dave J.:

[HOSS 1]

You must agree that virtually every living creature, with mobility, has laterally symmetry.


I'm not sure about that. One of my nipples is lower and smaller than the other.

I'm quite happy with my tail rotor.

HOSS

[Nick Lappos]

Poor Dave,

Even your arguments lack symmetry!

Let us know how well your symmetrical helo flies, when you build it, OK? Good luck!

Nick

[Kyrilian]

Dave,
As many have pointed out, symmetry is not always the answer. People aren't really symmetrical, neither are cars or planes. Only race cars put the driver in the center, and even then the guts of the car aren't symmetric. Sure, some twin engine planes have counter-rotating props/engines, but it's an unnecessary expense. Actually, a plane that I find fascinating is the Boomerang :) Apparently, it performs quite well.

Your helicopter idea sounds like fun, and asking for input is certainly a good first step in your case. However, I think you're kidding yourself with respect to the vast superiority of your design. It won't be cheap, it won't be significantly easier to fly, it won't be more efficient, etc...

Consider the cost of helicopters. Compare the Mini500 to the CH7. Both are single pilot, small, homebuilt helicopters of similar size and performance (I'm not entirely sure of this), but greatly differing quality and therefore cost. It seems as though your concept would fit in the same class as these designs. I know you have wild dreams of cost control through volume, but I don't have your optimism. It's gonna be expensive if it is designed and made well. Your advanced autopilot/governor ideas only make low cost more far-fetched.

Now, to the basis of your design. As I see it, the performance difference between conventional (main and tail rotor) and contrarotating designs is miniscule. Kaman designs are popular with the Russian navy because of their small size. The induced power losses losses due to a high disc loading of most cr designs are comparable to those of the tail rotor. The weight advantage of no tail rotor is offset (perhaps even more) by the addition of a stronger, heavier main rotor gearbox. The control systems aren't necessarily that different. One design has a complex rotor head, while the other puts stuff on the tail boom/tail rotor.

Another point of contention is handling qualities. You argue that a more symmetric design would be vastly easier to fly than conventional designs. I argue that after 10 or 20 hours, most beginning pilots have that all out of the way. Sure, finesse and smooth flight all improve with more experience, but I don't think the 1000+ hours that are required to get a turbine job or even become insured in some aircraft has anything to do with symmetry or the difficulty of juggling the coupling caused by asymmetry. Heck, larger helicopters have mixing boxes that take care of a lot of this already. Now, on the other side of the argument is the control of a contrarotating helicopter. I have no experience with any, but my understanding that yaw control is not as direct/crisp, and that control in an autoration is also cause for concern. Pilots like to be in control, and giving them mushy response or requiring them to be moving fast enough to get some semblance of control out of a vertical fin is not what they want. I think they'd much rather deal with translating tendency, transverse flow effect, and all the coupling that accompanies a conventional helicopter. This can be be "band-aided" by mixing boxes and blade tip spoilers on a cr helicopter, but I thought we were going with simple, light and cheap!?

I'd personally like to know more about contrarotating rotorcraft, and think they have promise, but I don't think they are going to solve all the problems you predict. As an aside, I think you've probably reached everyone on this an other online forums that you will, and are starting to sound like a broken record. I don't mind, but it seems others are sick of it. If, as I presume you haven't done any helicopter flying, I'd strongly suggest you take a bit of dual in a small helicopter. Take at least enough so that you can hover, and you'll see why all the pilots who have responded don't care for your ideas vis-a-vis ease of control are concerned ;-)

Good luck

[Cyclic Hotline]

Here Dave.

This should keep you busy for a while! ;)

Mystery ship! (http://www.icon.fi/~jtki/vikipage.html)

[Flight Safety]

Dave, after 2 of the most knowledgable people in Rotorheads (Nick and Shawn), as well as others, have posted their opinions, I can only add the following:

Go ahead and build the helicopter and get it flying, then use the idea of "natural lateral symmetry" (complete with pictures) in marketing the helo. It would make an outstanding brochure.

[Dave Jackson]

Kyrilian,

Thanks for questioning this concept, from a technical perspective. The objections that you and others raise may prove to be its demise or, hopefully, they may highlight the obstacles, which can eventually be overcome.

Most will probably agree that, other than the turbine engine, there has not be any quantum leap in rotorcraft technology over the past sixty years. In addition, the vertical flight industry is currently in the doldrums. Some radical changes are necessary to pull it out, be it the tilt rotor, the intermeshing configuration, or what have you.


The following reply to your post is offered; at the risk of boring some [who have probably moved on to a more interesting thread by now], but with the hope of enticing additional constructive arguments from others:
__________________________________

The issue of symmetry is only in reference to aerodynamic lateral symmetry. The intermeshing Kaman Huskie was used to trail military pilots for a short period of time. It was then discarded because it was too easy to fly.

Consider the Boomerang, symmetry and the world's first vehicle. If the logs that were put under the Egyptian's stones, had their port diameters greater than the starboard diameters. There would be no pyramids, and those poor slaves would still be going in circles. ;)

Gareth D. Padfield said "The ubiquitous nature of cross-coupling constitutes one of the chief reasons why piloting this type of aircraft requires such high skill levels developed through long training programmes". The intent is to eliminate cross coupling by the use of absolute rigid rotors. It is interesting to note that Kellett attempted to raise one million dollars to produce his 3-bladed intermeshing rotors with high rigidity. Unfortunately, an earlier fatal accident brought down his company.

I have spent my life in the manufacturing industry. The advantages of volume production should not be underestimated.

For decades, western aerodynamic texts have mathematically shown that the tail rotor wastes 8 - 10% of the power. Recently, Kamov has explained to the west that the tail rotor wastes approximately 15% of the power. In addition, the latest aerodynamic text (year 2000), by Leishman (University of Maryland) concurs with Kamov's position. If a craft's gross weight to empty weight is 2:1, then the above constitutes a 30% difference in payload. That is significant!

Kamov and Kaman both produced twin rotor configurations. Kamov went with high disk loading, whereas Kaman elected to have low disk loading and high lift. I suspect that Kaman went to low disk loading because the much larger Sikorsky had the ear of the military and command of the 'conventional' market.

Perhaps Nick is right: Just shut up and build the damn thing.

___________________

Cyclic Hotline,

Another twin rotor admirer. :)

Thanks.


Dave J.

[helmet fire]

Dave,

Your discussions are always intresting, but I am beginning to want to join the "shut up and build the damn thing" camp.
;) ;) ;) :p

We have continually discussed your concepts, and it has be an enlightening journey. It is getting a wee bit reptetive now though! We have discussed your ridgid blade concept in much depth - and you remain unconcerned by the practicalities, let alone the physics of the thing. If you can make it work, you will revolutionise verticle flight - so get to it.

I am not convinced that all technologies can become due for a revolution as you seem to suggest: the wheel still works pretty good. Maybe the single main and tail concept works alright for the time being.

I await the gloosy brochures and the video tape of your first test flight.

:)

[vorticey]

you said > For decades, western aerodynamic texts have mathematically shown that the tail rotor wastes 8 - 10% of the power. Recently, Kamov has explained to the west that the tail rotor wastes approximately 15% of the power. In addition, the latest aerodynamic text (year 2000), by Leishman (University of Maryland) concurs with Kamov's position. If a craft's gross weight to empty weight is 2:1, then the above constitutes a 30% difference in payload. That is significant!


if the tail rotor uses 30% of the total power, im sure a extra main rotor blade is going to use an awful lot more. double the drag, double the MR weight and double the power to turn them, double gearbox and rigging complexity and weight.
doesnt sound like a power saving to me
:rolleyes:

[Nick Lappos]

Beware of raw data without the necessary caviots.

Measured S-76B data that I once published shows that the tail rotor for that aircraft consumes about 100 HP total in OGE hover, with a total aircraft power of about 1170 HP. That is 8.5% of the power that the tail rotor consumes, probably less in IGE hover, and about 25 HP in cruise.

Published papers by Sergei Mikheyev show that the drag of a coax is about 10% higher than a single rotor helo, so that the fuel burn is 10% higher. This infers a 10% shorter range (or a 10% higher fuel load) for a coax.

With the usual disk loading compromises due to smaller rotor disks on coax's (coax's need shorter blades so they don't self-midair!), there is almost no practical difference between single rotor helos and coaxes in terms of raw efficiency.

The Dave Jackson synchropter is perhaps midway between coax's and singles, with a more tightly packaged head (5% drag increase?), and no real tip clearance hazard.

IMHO the play on symmetry is nice but never has been a driver on rotor designs, especially now where electronics can smooth out responses. For training and transport missions, it is insignificant, for high bandwidth air combat weapons pointing, it might have some merit.

[Flight Safety]

Dave, I looked at the Kaman K-Max, very interesting helo.

Two intermeshing rotors, each 2 bladed with apparently solid rotor hubs (fixed to mast, no teetering hinge), and drag hinges.

http://www.helis.com/howflies/servo.jpg

Flight control is all done by servo tabs. Yaw in the hover is accomplished with differential torque through differential pitch at the rotors affected by the pedals. Forward/aft cyclic is accomplished by pitching both rotors foward/aft. Lateral cyclic is accomplished by affecting one rotor only, cyclic left causes the left rotor to tilt. etc. The pronounced airframe pitch caused by collective pitch changes (apparently common in intermesh designs) is compensated by the horizontal stab.

It has a total payload of close to 140% of empty weight. It has a HOGE of 26,300 feet (at what weight I'm not sure), wow. Rotor disk loading is low, so weight lift is high, and noise is low.

Have you thought about servo tabs? It's simple, light, and not too complex. Requires flexible rotor blades though. Also, your website shows 2 possible ways to control yaw. How about differential for/aft rotor pitch controlled by the pedals? Might not be too effecient in forward flight, but could transition to a rudder on the vertical stab for that. Could also roll the airframe to the wrong side in forward flight, so not so coordinated in the turn.

[Dave Jackson]

Flight Safety

Thanks for passing on the exploded view, information and suggestions.

With absolutly no intent to market some weird hypothetical idea :eek: , the following couple of points might be of additional interest.

It's hard to see, but the Kaman rotors do teeter. In addition, they have delta-3, just like the Robinsons. It is used for the same reason that Robinson uses it and in addition, Kaman uses it to handle some of the lead-lag between the two rotors.

The following supports you comment on payload. It is from a pilot with very high hours in many single-rotor craft, plus both Kamans and a Kamov. "The U.S. Forest Service pays more money for a K-max than they pay for a SK61 ..... Why? ..... because at altitude, 5000 ASL and above the little K-max out lifts the bigger 61. As for the Kamov ? In the states U.S. operators are doing what they can to make sure it can't end up in their back yard.":

[DeltaFree]

Making comparisons between K-Max and S-61's relative lifting abilities is surely a little irrelevant here, indeed between most helicopters. Each is designed for a purpose and while most can do most things they do them to varying degrees.
K-Max lifts, its lift capacity-basic weight ratio is very good and should be it was designed that way. A Lama has a very good ratio too but is much older! An S61 takes 23 pax in comfort, oh yeh and it lifts but the ratio is not so good.
If we are going to make comparisons it should be to prove a principle not a point.