In My Humble Opinion

[Dave_Jackson]

IMHO

IMHO, the improvements mentioned by Sikorsky in 1980 to its original ABC (http://www.unicopter.com/0891.html) represent the future of the helicopter. Newer additional improvements to the rotor must, and will, come about.

The only difference between big old Sikorsky and little old me is in regard to which configuration will be the most efficient for the various missions that these new craft must serve. I believe that the Coaxial, the Intermeshing, the Interleaving, plus the Side-by-side, are ALL potential candidates.

IMHO, the Intermeshing configuration will be the best one for small agile craft and the Interleaving configuration will be the best one for large transportation craft. However, this is just one person's assessment.

Before the industry, or one of its members, jumps on a specific horse and gallops off into the future, I believe that a serious evaluation of all four configurations should be conducted.

Then let the real battle begin;
ABC-rotors ~ vs. ~ Tilt-rotors
http://www.unicopter.com/Boxing.gif

[Graviman]

Clearly we are talking pusher/puller props for all of these configs, or the formula doesn't work (hub drag mostly).

My own thought is that Sikorsky are taking a sensibly cautious step into this world with X2. High effective hinge offset coaxial rotors represents a proven approach, particularly from the point of view of hub control systems. In sideward and rearward flight rigid rotor coaxial might offer most versatile configuration. The only possible disadvantage is blade clash, most likely from startup with wrong pedal held down. If tail rotor function becomes part of pusher prop, even this concern disappears. Lack of symmetry is not an issue since the FBW pitch/roll gyros & accels will take care of that: http://www.gyroscope.com/d.asp?product=PIEZO

I have a preference for intermesher, since this allows compact rigid rotor hubs to be developed with reduced bending moment at the shaft root to main thrust bearing. Wider shafts with spider controls allow even lower stress at the thrust bearings, which all helps to improve payload/MAUW ratio. I don't think pilot will notice significant differences in handling qualities over FBW coaxial. Lower (outboard) advancing may offer aerodynamic advantages by having rotor plane normal to wake contraction inflow. Upper (inboard) advancing will offer better sideslip/yaw and lateral dihedral characteristics. Again pitch/roll gyros & vert accels could correct any handling problems, so i don't think pilot would notice. Complex control systems like blade twist would package better in intermeshers too.

Regarding interleaver, i only see this as a contender where payload forces significant increase in gearbox mass. Two rotors mean that Nr can be kept higher so allowing two smaller gearboxes. The Chinook thread indicated to me just what a cost disadvantage complex powertrain is. Since aircraft length is more versatile than width i think some of the 4 rotor designs based on Chinook stand a better chance than side-by-side - but MIL26 has proven that large rotors are feasible. I think the required waste power on single gearbox cooling will always be more cost effective than multiple gearboxes. I also imagine two seperate 10 tonne MAUW helicopters work out cheaper than one Chinook - i could be wrong. Besides the retreating portion of the disk may raise aerodynamic disadvantages for interleavers at speed.


Thoughts on fly-by-wire:

I accept that the Lockheed system had it's time, which was never realised by Lockheeds decision not to enter the commercial sector with the 286. FBW is now proven technology, so the question is how to make it accessible to market. My own thought would be to base it around a mechanical system, using electric servos to isolate cyclic (and collective if required) from any swashplate forces. The stability could then be introduced by leverage mixing a second electric servo into the pilot controls (perhaps very weak cyclic springs). As sidesticks become more proven in the market place, maybe even this will become too conservative for the R22 end of the market.

Mart

[quadrirotor]

IMHO, i don't think there will be any moving parts above, let's say, Mach 0.6...

[IFMU]

IMHO, i don't think there will be any moving parts above, let's say, Mach 0.6...
http://www.rotaryforum.com/forum/attachment.php?attachmentid=27753&d=1162647749
So far the data for the CRW program seems to bear that out. In speeds of "slow forward flight" it crashes, at which point all moving parts stop.
http://www.aviationnow.com/avnow/news/channel_aerospacedaily_story.jsp?id=news/DRAG04216.xml
-- IFMU

[quadrirotor]

I don't know what you are looking for...I don't want to go very fast with a lot of power and a lot of money! I want something flying slowly (100 mph) with sustainable expenses! only for touring!... That's what i am dreaming of:


http://www.rotaryforum.com/forum/attachment.php?attachmentid=27522&d=1161853672

[Dave_Jackson]

Mart,

Your admiration for computers is understood. However, with little humility, I would mention that I have been deeply involved in computers since before Gates bought DOS. Sensors and actuators are only two small parts of a computerized control system.

Consider for a moment; Nick has mentioned that the software for the Comanche required half a million line of code.
Consider for a moment; Sikorsky's coding was amortized over two helicopters, whereas Microsoft's coding is amortized over hundreds of millions of computers.

Consider for a moment this excerpt from the current issue of 'Journal of the AHS'; "The Airbus 380 fixed wing transport program has scheduled a mere 1,000 flight test hours between birth and deliveries. The Comanche helicopter was still not matured after 15 years and billions of dollars expended, exceeding the development costs of the 380. The V-22 has well over 10,000 flight hours at the time of this writing and was just entering OPEVAL! Our tools are still in their infancy."


Dave

[Graviman]

Flying an R22 has rekindled my interest in helicopter design. Serious thanks Andy - looking forwards to next w/end :ok: . Lots of "sofa flying" already planned to get that coordination sorted...


Dave,

Please bear in mind that i have to fit in PPRUNE postings between other time consuming activities, this often leads to revision "B" and "C" releases of my postings. Also i often have to reiterate technical points, since i am not convinced they have been properly understood. However, i will endeavor to moderate my enthusiasm :)


Consider that i do not believe a computer to be necessary to implement a "FBW" control system. This is particularly true if it is based on a mechanical primary system. Also consider that if you spin on a rotating office chair with your eyes shut you will soon lose all sense of rotational velocity - this is also true of flying in cloud, indicating the limit of the human balance system. A gyro system can be designed using analogue feedback, rather like a HiFi amplifier, to give pilot direct control over aircraft roll and pitch rotational velocities with cyclic position correction for airspeed (ie longitudinal and lateral dihedral). Since i have tried and failed to suggest the mechanical means of achieving this (Lockheed system), then the electronic means is by electric servos with the control/gyro difference signal actuating a mechanical mixer. This is all just 2nd year degree stuff, and i remember Nick commenting that such a system would cost between $2000 to $10000 per aircraft. The only reason to go digital is when the control laws became too complicated for a simple feedback model.

You have persuaded me that it is possible to significantly improve the flying qualities of a helicopter by aerodynamic only means. You have not persuaded me that this can be accomplished in a cost effective design, since two rotor heads and additional driveshafts will increase cost to achieve the same reliability. The best compromise is a Flettner rotation rigid rotor intermesher, although aerodynamic efficiency will be marginally compromised. Even this system will not offer dihedral stability, so does not achieve the holy grail of hands free hover.

What i propose is a compromise, like so much of engineering, taking the best features of all solutions. For example: A Flettner rotation intermesher could have the stability augmented by a reasonably simple 21st century modification to the control system. There is nothing to stop this system affecting a conventional helicopter, but i too am interested in designs that increase the operational capability of the rotorcraft (retreating blade stall). This generic approach is already being implemented by Sikorsky in the X2, which is why i believe it will be a very versatile basis for future helicopters.

Mart

[Dave_Jackson]

Mart,

As you probably know, the closing comment in my previous posting was removed.
The comment was nothing more than a reiteration of previous private e-mails on the very same subject.

Your comment; "i have to fit in PPRUNE postings between other time consuming activities.": is understandable. It probably applies to everyone on this forum.

By the same token, you will therefor appreciate the following two points;

In this thread, posting #2 was yours. Then posting #3 was yours, Then you removed posting #3. In addition, you have edited every one of your existing postings. It is very 'time consuming' to formulate responses when the subject matter keeps changing.

When the subject(s) of a thread expand in an exponential manner, it is very 'time consuming' to formulate responses to all the diversified subjects.

I love discussing specific technical aspects of rotorcraft; particularly when there are a number of participants giving and taking. There is intent at times to be provocative, but never to be mean.

_____________

Should a moderator feel that this posting is also inappropriate or insensitive ~ Please, pull it.
Should a member feel that this or another of my postings is unacceptable ~ Please, tell me directly, in front of all.

Dave J

[Graviman]

Dave,

Understood. No offense taken, no offense meant. I often PPrune to take my mind off what can be a very demanding/stressful job.

In this thread, posting #2 was yours. Then posting #3 was yours, Then you removed posting #3. In addition, you have edited every one of your existing postings. It is very 'time consuming' to formulate responses when the subject matter keeps changing.

Posts #2 and #3 were combined, but the technical content has not altered nor has this post altered since the combination. I deleted some of the more jovial responses, when it felt that the thread tone had altered.

Post #7 sat outlined on my desktop for a few days. Apart from one oversight it has not been altered.

Some of the large assy drawings i release now sit at "rev H", and no engineer would expect to capture all the facts in one sitting. Ammending ideas is just a fact of life, struggling to absorb the facts is just a fact of life - having a degree in engineering, and another in physics tells me i'll never know it all... :ugh:

Mart