CEFOSKEY:

http://www.unicopter.com/Temporary/Heart.jpg

_______________________


TRIVIA:

The XH-59A ABC was the forerunner of the X2.

Perhaps this was the forerunner of the XH-59A ABC.
"As a result of the NACA tests, Hiller initiated redesign of the X-2-235 to incorporate three-bladed coaxial rotors augmented by an aft-thrusting rear propeller. The reworked craft was obviously geared to flight at speeds substantially higher than those attained by existing helicopters."


Dave

Yep! High hinge offset coax, Hiller never flew it, it appears:

http://www.aviastar.org/foto/hiller_x-2-235.jpg

Any feedback on the ground testing?

Is the X2 behaving the way it's meant to?

That's great news! :ok:

My fingers are crossed that everything behaves itself.


BTW, looked at Ansys 10/11 recently: very capable analysis package. For my own part i'd prefer to use Hypermesh as preprocessor - still it's nice to crawl out from under Ideas 12NX. Transition going smoothly...

S-69 ABC Helicopter Limitations
 

Does anyone know what the top speed of the S-69 ABC helicopter was, in level flight without the two jets strapped to its side and what speed did (with and without the jets) would retreating blade stall and/or blade collision become a problem?

Also what is meant by rotor hinge offset?

Thanks
Obi

Obi,

Effective hinge offset is a measure of how stiff the blade is, and can be related to blade natural frequency over rotor rpm. As a flapping hinge moves outboard the centrifugal effect pushes up flapping frequency, hence the term "effective" hinge offset.

Actually i've been doing nothing but effective hinge and cyclic Lead angle calculations all week for my FEA invetsigations. I've even developed a nifty spreadsheet to calculate rotor lift and induced velocity. Alas not for rotors, but for high horse power cooling fans. I'm working closely with some ex-Rolls guys to really get to grips with turbine compressor design too - interesting field. ;)

---

Delta3, are you still out there? When time permits i'm going to have a go at the Leishman algoritm myself.

---

CEFOSKEY, how is the X2 doing? I've lost touch... :sad:


My busy work schedule leaves me less time now to check this forum, but the interest is still there...

If this post is crap, one of the experts please tell me and I'll delete it.

Obi - the way I think of hinge offset is this. Imagine you're doing gymnastics and you're hanging from a bar by one hand. Difficult to move sideways isn't it? You need a very strong wrist. Now change that to hanging from the same bar but with two hands, shoulder-width apart or wider. Total different experience. The difference between an R22 (or a 206) and a 105.

As I say, experts please pile in if required.

From rotor&wing:

I'm certainly no expert but:


Effective Hinge Offset: [(e/R)eff]
The ratio of the hinge offset divided by the radius of the rotor.

Dan:
Your formula is right for an articulated rotor - the problem comes with rigid rotors and bearingless rotors where there is no physical hinge.
For those rotors, the 'effective' hinge offset is a calculation of where it would be if there were a real flapping hinge.
For those rotors, you can say that the flapping hinge was replaced by a flapping hinge plus a spring.

The company deflected the real questions on the X2 status at Farnborough but I was told that they have had transmision development problems ,especially integrating the prop drive system ....anyone else heard that ?

Uh-oh, they better scrap this program while they're ahead.

Transmision
 

The earlier Sikorsky XH-59A ABC had two-speed rotors. The tip-speed was 650 ft/sec in helicopter mode (hover to medium forward speed) and 450 ft/sec in compound mode (high-speed cruise).

The Sikorsky-X2 ABC uses a rotor-propeller relationship that is yet to be made public; to my knowledge. One of the patents appears to imply that the rotors are to have variable speed. The tip-speed is 700 ft/sec in hover and 560 ft/sec during high-speed cruise.



The Stepniewski ABC has slow constant-speed rotors, with a proposed tip-speed of 513 ft/sec. This slow speed works in conjunction with wide chord blades.

_______________________________

There are a number of other interesting differences between Stepniewski's ABC and Sikorsky's ABC. Perhaps in the near future these differences will be placed on a separate thread, so those with a technical interest can evaluate and discuss them.


Dave

Another X2 article. Seems like the media reports one thing, then another.

http://sikorsky-x2-first-flight-could-slip-to-2009.html

-- IFMU

If the program slips by a year, this is a reflection of how difficult the concept is to achieve. Nothing more.

While it is frustrating for us fans, i am far happier with the "slippage" of an internally funded project than the idea that all development has stopped.

The point is that the concept of a low disk loading VTOL with a narrow ground profile is a worthy pursuit. When all the technical issues, associated with any new engineering project, have been resolved we will all be singing X2's praises...

CEFOSKEY, that LUH is a good looking ship - definately a vision of things to come.

Some aerodynamical theorizing while waiting for the next announcement.
 

CEFOSKEY, Thanks for the clarification on the variable rotor-speed.

GRAVIMAN, Stepniewski is not going to be building a rotorcraft and Sikorsky is, therefore this subject may be better on this thread,
_______________________________

Aerodynamic comparison: Sikorsky-ABC v.s. Stepniewski-ABC

The Sikorsky-ABC pictures appear to show that the thrust-line of the rotor is perpendicular to the thrust-line of the propeller and fuselage. If the rotor is to operate in autorotative mode during cruise then the rotor, fuselage and propeller will have a nose-up attitude.

The Stepniewski-ABC evaluation work takes into account that the forward propulsion from a rotor is more efficient that that of a propeller, up to an angle of incidence of about 9-degrees. It therefore would appear that having the angle between the thrust line of the rotor and that of the propeller less than 90-degrees will offer a meaningful increase in the efficiency during cruise with no detriment during hover.

If there is any interest in debating the subject, http://www.unicopter.com/Group.gif
Stepniewski's calculations and an elaboration on the above are available here; Angle of Incidence - Rotor & Propeller

Dave :8

Dave,

Why do you conclude that X2 will operate in autorotation during cruise? I would have though the objective was in trim cruise. It just has full autorotational capability from this flight condition. It will be a compromise, but i would have thought the design optimised to suit 250ktas.

Any details on how variable Nr is achieved?

BTW, i've been thinking about puller vs pusher while generating a vortex panel model of a fan aerofoil. You could think of the puller as an additional vortex line generator (like the HIGE rotor image) so that the main rotor is operating in more favourable inflow over a pusher application. In a nutshell the puller wins out because a larger total area is ingesting air. Then again if the rotor is sized sufficiently this is less of an issue.

Graviman, No conclusion. The reason for the preceding post was to invoke technical consideration and speculation. The subject of integrating the rotors, propeller, transmission, motor, and flight controls, in an optimal aerodynamic package, and mechanical package, is challenging.

Stepniewski and Sikorsky present a number of different potential solutions for consideration. On the subject of the rotors being in autorotation during cruise, this additional information has be added to the notes on the previously referenced web page. It is discussing Sikorsky's earlier XH 59A - Coaxial-ABC.

"In the auxiliary propulsion mode, the ABC rotor power requirements are reduced with increasing airspeed with maximum rotor L/D being achieved at or near autorotation."

"However, with the rotor flying at close to autorotation at high speed, differential collective pitch has little impact on yawing moment ....."

ABC aircraft could be considered as a unification of gyrocopter and helicopter. A similar subject has recently been discussed on a gyrocopter forum, where they were considering the pros and cons of a partially powered rotor.


CEFOSKEY may be the first PPRuNers to look under the hood (bonnet).


Re Pusher v.s. Tractor propeller aerodynamic:
I think that the Intermeshing-ABC will work better than the Coaxial-ABC when considering the subject of the propeller. This is because the stream-tubes of the Intermeshing rotors are a little more out the sides and away from the streamtube of the propeller.

I've got to be a little carefully using the word 'Intermeshing' since the boss may get mad. :)

Dave

Nick, my confusion comes from the fact that XH-59 had two rotor speeds while X-2 has apparently a variable rotor speed. Being honest i'm not sure how this is accomplished with such a high natural frequency blade - i just imagine Campbell plots with lots of red accel contours where each Nr order crosses the spin stiffened frequency...