What goes around ... comes around

[Rotor Rooter]

Two rotorcraft that fly at very different forward speeds.



Wilford WRK Gyroplane ~ 1931 [ maximum speed - 103 kts ]



Sikorsky X2 Advancing Blade Concept ~ 2008 [ maximum speed - 250 kts]



It is interesting to see two rotary-wing craft, which operate as gyrocopters in forward flight, have identical blades in Planform but have very different maximum speeds.


Dave

[kolibri282]

Very interesting indeed, Dave, thanks for posting! On the other hand the remaining variables in the game, especially distribution of twist and profile along the blades, could render them completely different in their characteristics. Would be great if a university could make such a comparison a project.

[Rotor Rooter]

Originally Posted by kolibri282

Very interesting indeed, Dave, thanks for posting! On the other hand the remaining variables in the game, especially distribution of twist and profile along the blades, could render them completely different in their characteristics. Would be great if a university could make such a comparison a project.

That true, there will be different characteristics, especially rigidity.

However, on the subject of twist;

• Neither 'Aerodynamic analysis of the gyroplane rotating-wing system' by Wheatly or Wind-tunnel tests of a 10-foot-diameter gyroplane rotor by Wheatly refer to twist.

[your forum has much value ]

• The first Sikorsky ABC, the XH-59A, had a number of recommendation, one being "the Reduced rotor twist; from -10º to -4º". The new X2 ABC basically removed the problem at the root by creating a very large root cutout. There is a small amount of + & - twisting in the its spar but it appears to be negligible.

Dave

[kolibri282]

There is another report that investigates rotors of different planforms by almost the same title as #536 that might be of interest in the context.

naca.central.cranfield.ac.uk/reports/1937/naca-report-552.pdf

I think they omitted twist and profile distribution from their research because at that time they were trying to verify the basic assumptions. Changing the profile along the blade by the way is equivalent to building in twist if the profiles used are not symmetric.

PS: perhaps you could add the above report to the thread where you posted the first one, it seems to me the two are a perfect match, aren't they?

[Rotor Rooter]

Juergen,

Opps, I had forgotten to put in the link. Thanks.
Your report has been added as requested.
Yes they do have a commonality.

Dave

[gyronutjoe]

Those reports are from 1935. Have there been any tests done on current designs?

[Vance]

Originally Posted by Rotor Rooter

Two rotorcraft that fly at very different forward speeds.



Wilford WRK Gyroplane ~ 1931 [ maximum speed - 103 kts ]



Sikorsky X2 Advancing Blade Concept ~ 2008 [ maximum speed - 250 kts]



It is interesting to see two rotary-wing craft, which operate as gyrocopters in forward flight, have identical blades in Planform but have very different maximum speeds.


Dave

I feel the available power may have something to do with the difference in speed as well as the power to the rotor on the Sikorsky X2.

In other words you appear to me to be comparing vastly dissimilar aircraft and wondering why their performance is dissimilar.

Please help me understand you point Dave.

Thank you, Vance

[Rotor Rooter]

Originally Posted by Vance

I feel the available power may have something to do with the difference in speed as well as the power to the rotor on the Sikorsky X2.

In other words you appear to me to be comparing vastly dissimilar aircraft and wondering why their performance is dissimilar.

Please help me understand you point Dave.

Thank you, Vance

Vance,

The point, or actually 'the surprise', is that two vastly dissimilar aircraft, with performance dissimilarities, find that the same non-conventional blade profile is optimal for their requirements.

Perhaps it may be saying something for future rotorcraft.

Dave

[kolibri282]

As I have tried to point out the similarity in blade planform does not say a single thing about the behaviour of the two designs. The S-X2 blade is the result of the combined effort of dozens of engineers using more computational power than a billion times the number of humans on the planet at Wilford's time could have mustered. The two designs have as much in common as a coal lifting dock crane and the curiosity mars lander. Real advance in rotary wing flight has been brought about by well trained engineers like de La Cierva, Flettner, Young and all the others on whose work we build today. Trying to advance rotary flight without proper analytical/numerical models is like entering a single cell amoeba into a Rubics cube solving contest....;-)

[Rotor Rooter]

Juergen thank you for your posting but it presents a conundrum. It is so easy to attack but so difficult to know where to start.


IMHO, de La Cierva, Flettner, Young excelled because they were good at Conceptualising.

Conceptualists know a little about a lot. (the associaters) ~ ~ Engineers know a lot about a little. (the practitioners)

To get really serious for a moment, the rotor blade is the essence of rotorcraft. These two blades have very different planforms. The top blade is the Sikorsky XH-59A ABC and the second blade is the later Sikorsky X2TD ABC.

I was unable to conceive a viable solution to the aerodynamic problem of the Advancing Blade Concept when in the reverse velocity region. There were many discussions on PPRuNe. Then Sikorsky anounced their intention to build the X2.

IMO, the Sikorsky X2 blade has not solved the problem either.


Dave

[kolibri282]

Dave, I am glad you didn't take my last post (which is indeed a trifle gross) all that serious. Of course you are right in that these engineers were also very creative. What I tried to point out is that even in this early stage of development of rotary wing aircraft a strong background in engineering made the difference between those who had lots of ideas and those who made ideas work (oh and I forgot Bensen). Today we find that very sophisticated tools for further development exist and on the other hand very many concepts have already been tried and investigated so that it is hard to come up with a visionary idea. So my impression is that today success for a gyro or helo comes with using the available tools to stay ahead of the competition rather than with brand new ideas.

Juergen

[kolibri282]

Those reports are from 1935. Have there been any tests done on current designs?

For gyros there is nothing comparable to those old reports as far as I know, Joe. There are some data on gyros but no measurements of standalone rotors. All research has shifted to helicopters:
http://www.rotaryforum.com/forum/sho...316#post496316

On the other hand one of the most widely used profiles for autogyros, the 8H-12, has been published in 1946 so "today's" designs aren't that new either and the old measurements tell you quite a lot about today's rotor systems

[Rotor Rooter]

So my impression is that today success for a gyro or helo comes with using the available tools to stay ahead of the competition rather than with brand new ideas.

Juergen,
I take the opposite approach, but hey, both lead to improvements, hopefully.

Dave

[kolibri282]

To me brand new ideas would be something that can not be described using existing theory, taken the power of today's CFD/FEM and other programs that will be hard. I do hope you come up with an idea that makes you very rich (I take it you're already happy and have fun doing what you do.....;-)
I will surely continue to read the very interesting threads you bring to the forum Dave.

Good Luck!

Juergen

[gyronutjoe]

Since everyone is talking about rotor blades. How about this design, a quiet blade. Here is a picture and a web address:
http://www.wired.com/autopia/2010/02...-whisper-mode/