Abc

[3top]

To Nick Lappos:

Nick, I just read somewhere on the net, that you actually flew the S-69.

I understand the ABC was studied to be able to "forget" about disymmetry of lift and retreading bladestall and so go faster.

On the S-69: Did they just ignore retreading bladestall or was there a way to actually reduce the angle of attack on the retreading blades to somewhere near zero (so there would be no stall or at least would not be of any concern - like on the cartercopter on the rotor at high forward speed, with the lift all on the wing....).
If there was a way to adjust the retreading blades:
a) How was it done (technically...)?
b) at what (forward) speed was this started?
c) at what relative angle (on the rotordisc) was it started?


I understand this would introduce fairly high bending loads on the mast, however at the speeds the s-69 was supposedly flown and the published rotorspeeds, there must have been a huge portion of the retreading blades in a stall already with a huge drag in tow!


Is there any research going on in ABC or died this with the S-69?

Thanks for your time!

3top :)

[Dave Jackson]

3top,

Nick did fly the S-69. He may be tied up (kinky :)), so here are some answers to your questions. Nick may wish to elaborate or correct them, later.
The angle of attack on the retreating bladeis reduced, just as you suggest. But, unlike the CarterCopter, the additional load is taken by the advancing blades, not by a pair of wings. The two rotors are counter-rotating and their hubs and blades are very stiff. This allows the advancing blades, on both sides of the craft, to accept the load with minimal flapping. The act of loading the advancing blades more than the retreating blades takes place at all forward speeds. This is the reason it is called the Advancing Blade Concept. The craft had two methods of adjusting the advancing/retreating loading ratio. One was opposed lateral cyclic and the other was in-flight changing of the phase angle [Gamma]. I think that Gamma was the only one that they used. At the initiation of forward flight, Gamma would have a very low value. As the speed increased, the phase angle was increased to assure that the blade tips of the two rotors did not get too close to each other.
The rotor was slowed down from 650 ft/sec in helicopter mode to 450 ft/sec in compound mode, to reduce compressibility on the advancing tips.

If you wish additional information, there is quite a bit of stuff at Sikorsky ~ S-69 (XH-59) ABC (http://www.unicopter.com/0891.html)

Nick's answer to you last question will be interesting, if corporate policy allows an answer about future projects.
___________

An apology to those who dislike the phrase 'phase angle', and have actually read this far. . :D

Dave

[3top]

Thanks Dave,

first thing I have to do, is to look up "phase angle" or "gamma"

As metioned somewhere else in Rotorhead, my academic understanding of all this is extremly limited, however I think I understand principle things about helicopters (as far as I need them for "daily" life as a helo-driver), however the ABC- idea is very intrigueing. I understand someone is working on that pricipal for an Ultralight machine, but with intermeshing rotors - kaman style. Check it out: http://www.synchrolite.com/UniCopter.html Both machines look interesting after longer study......

Personally and from a visual point, I would prefer a counterrotating system like the S-69.

What I am interested is how the setup was, to change "phase angle" so that the retreading blade has less or zero angle of attack! If possible in layman terms!!! If not, I take the academic answer and try the next half year to figure out what it means!!

Was this done at fix settings or was this somehow depending on [relative forward] speed, as I believe it would be of advantage to have the retreading blade produce lift, as long as it does get into the retreading blade stall region? Electronic, electric, hydraulic, mechanical, or.......?

To the future of tiltwings and rotors:

As long as they do not have helicopter-like autorotation capabilities I would rather stick with some slick ABC-machine.
Did they (Nick & Co.) actually autorotate the S-69? ...to the ground?

:) 3top

[3top]

Hi Dave J.,

oops, seems we were surfing the same site. The S-69 info you recommended, I found on the site I posted last.............

:D :D :D 3top

[Dave Jackson]

3top,
Personally and from a visual point, I would prefer a counterrotating system like the S-69.
:D Don't go to that site too much. You might end up preferring the intermeshing system. :D

Dave J

[Flight Safety]

Hey 3top, you actually know the guy who's working on the Unicopter.

Hint: look at the bottom of the webpage on your Unicopter link. ;)

[3top]

Yeah right!!!

Read the small print,....always!!

Dave, you are doing a great job NOT "pushing" your project on this site!!

I still have to get through everything on your site (that´s why I never got to the bottom of it!:D ), so maybe the answer for a question is there, but here it goes anyway:

Did you ever consider a counter rotating system alá S-69 or Kamov? If, why did you go for intermesh?

3top,:)

PS: My preference for the counter rotating system is purely from an visual point of view, my dream would be a 2- or 4-seater S-69 style, even with pusher engines. B.J. Schramm did in on his helicycle......

Engines: If had the time&cash for a well equipped machine shop, I would contact the guys from the Quasiturbine and get going making prototyps.......http://quasiturbine.promci.qc.ca/QTIndex.html (http://), see also their Ultralight-engine-prototyp.......http://quasiturbine.promci.qc.ca/QTAviation.html (http://),

...actually that engine could be a perfect fit for any of your concepts!

[Dave Jackson]

3top,

Dave, you are doing a great job NOT "pushing" your project on this site!! It gets pushed. :) Perhaps it doesn't appear so because its a concept not a product.



Did you ever consider a counter rotating system alá S-69 or Kamov? If, why did you go for intermesh? Yes. An attempt was made to evaluate all weird and wonderful concepts, and the intermeshing won out. From all that has been subsequently uncovered, my believe is even stronger that it is the best; for certain applications, of course. Hopefully, this belief comes from an objective perspective and not an acquired bias. :eek:



The Quasiturbine engine is intriguing, but for one person, just working on configuration related concerns give enough pleasure and pain.

Dave J

[3top]

Dave,

what are the main reasons to go with intermeshing rotors instead of coaxial?

3top,:cool:

[Dave Jackson]

Hi 3top,

No single design or configuration is optimal for all application. Each has its advantages and disadvantages. One advantage that the intermeshing (synchropter) has over the coaxial is that it gives greater thrust for the same power. it has also been stated that it is easier to fly.

For more information on the intermeshing helicopter you may wish to read; The Synchropter - Popular Rotorcraft Association Classroom (http://www.unicopter.com/B296.html)

For even more; Objections to the Intermeshing Configuration (http://www.unicopter.com/B280.html)

The Flettner FL-282 (http://www.unicopter.com/0474.html) was unquestionably the best helicopter at the end of World War II. Personally, I feel that Kellett and Kaman did it a disservice by taking advantage of its high lift, to the detriment of its other features.

We may be about to witness a metamorphosis of the intermeshing configuration. Kaman could be quitting helicopter production, and there is murmuring about its advantage for high-speed flight.