Sikorsky X2 coaxial heli developments.
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes
on
0 Posts
IFMU,
Yes, he does mention the change that Sikorsky would make to the hinge angle of the rudder on a future ABC.
I would quote it, however, when reading the last sentence in the chapter my eye's watered up and the book had to be put down.
"The synchropter may be an idea whose time has come and gone. On the other hand, it may have been ahead of its time and just the right configuration for some future helicopter requirement."
Dave
Yes, he does mention the change that Sikorsky would make to the hinge angle of the rudder on a future ABC.
I would quote it, however, when reading the last sentence in the chapter my eye's watered up and the book had to be put down.
"The synchropter may be an idea whose time has come and gone. On the other hand, it may have been ahead of its time and just the right configuration for some future helicopter requirement."
Dave
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
Dave, synchropter has a compact gearbox and rotor configuration. The rotor mast shafts are short, so minimise flexure. Access of control links to swashplate is straight forwards. It also offers the performance advantages of coaxial.
The only possible disadvantage is head clearance...
The only possible disadvantage is head clearance...
Join Date: Apr 2003
Location: Vancouver, BC, Canada
Posts: 1,635
Likes: 0
Received 0 Likes
on
0 Posts
The Flettner FL282; Transmission plus Flight controls plus Rotor-hubs.
Graviman,
The only possible disadvantage is head clearance...
The Flettner FL282 had an angle of 24-deg between the two masts. Kellett wanted to go to 3-bladed rotors with greater rigidity, however lack of funding and his demise ended that endeavor.
Extremely rigid rotors result in a smaller angle between the two masts, plus no blade droop. The blade at 90-deg azimuth on the proposed wide stagger UniCopter actually has a positive angle of 1-deg.
Dave
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
That said, Sikorsky President Jeff Pino told Rotor & Wing his marching orders to the X2 team have been: "Fly when you’re ready."
I'm tempted to head back Houston way just to see this - probably a little short notice for flights etc.
Good luck Sky, and take your time. The X2 fans will patiently wait.
But we may revive the VDTR.
Dave
-- IFMU
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
CEFOSKEY,
Those are some pretty neat concepts. It would be great to see some of these take to the skies in the future.
Why would Variable Diameter Tiltrotor be of interest to Sikorsky?
Those are some pretty neat concepts. It would be great to see some of these take to the skies in the future.
Why would Variable Diameter Tiltrotor be of interest to Sikorsky?
Join Date: Feb 2006
Location: Sydney
Age: 74
Posts: 292
Likes: 0
Received 0 Likes
on
0 Posts
stiff as in hard
With that 6 bladed pusher & 4 times as many rotor MR blades as I'm used to, that machine must be all my fixed & rotary wing fanatasies rolled into one?
Boy when they stiff MRBs, they do mean stiff eh?
Boy when they stiff MRBs, they do mean stiff eh?
That is a bad ass looking machine.
-- IFMU
-- IFMU
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
CEFOSKEY, that is one seriously sexy looking ship. Even without all the fairings. 
Nick, i'm suprised you're not popping back to Sikorsky for some stick time with that good looking bird!
Good luck on the tether test flying. Although excited, your fans are still patient - this is a challenging project.
Nick, i'm suprised you're not popping back to Sikorsky for some stick time with that good looking bird!
Good luck on the tether test flying. Although excited, your fans are still patient - this is a challenging project.
Join Date: Jul 2004
Location: Huntsville AL
Age: 51
Posts: 139
Likes: 0
Received 0 Likes
on
0 Posts
Good looking machine for sure! At first glance it almost seems as if there is not enough vertical fin area. The cabin section ahead of the mast looks like it is a good bit larger than the back half. I'm sure it is fine as there are far smarter people than I putting it together. Maybe it will look different once the last cowlings are on over the oil cooler in the back. Nevertheless I can't wait to see this thing go!
Max
Max
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
That's an interesting point, maxtorque. The yaw control is entirely dependant on differential collective pitch of the main rotors. Excessive weathervane stability may have adverse affects yaw control. I have been trying to work out if the central rudder is steerable for autorotation.
I must also admit to wondering whether the fly-by-wire is doing a lot more than just the normal pitch and roll stability and control augmentation. It may also extend to eliminating any tendancy for dutch roll, which is the norm in fixed wing now (non FBW favoured spiral divergence). The guy behind the Comanche control system has some pretty remarkable ideas for extending the fatigue life of all the main systems. I would not be suprised to see that implemented here too.
Also notice the small diameter of the main rotors. This is the necessary compromise of increasing disk loading in hover to push up the min power speed (Vy), which improves cruise efficiency. The added benefit is a higher natural frequency of the rotor blades, which pushes up the effective hinge offset for a snappier response.
That pusher prop also looks capable of sinking a lot of power at lower than cruise speeds (Ct/Sigma). I wonder whether the old Cheyenne trick of using the pusher prop for holding various pitch attitudes in hover is being saught.
If ever there was a machine which looked fast standing still this is it...
I must also admit to wondering whether the fly-by-wire is doing a lot more than just the normal pitch and roll stability and control augmentation. It may also extend to eliminating any tendancy for dutch roll, which is the norm in fixed wing now (non FBW favoured spiral divergence). The guy behind the Comanche control system has some pretty remarkable ideas for extending the fatigue life of all the main systems. I would not be suprised to see that implemented here too.
Also notice the small diameter of the main rotors. This is the necessary compromise of increasing disk loading in hover to push up the min power speed (Vy), which improves cruise efficiency. The added benefit is a higher natural frequency of the rotor blades, which pushes up the effective hinge offset for a snappier response.
That pusher prop also looks capable of sinking a lot of power at lower than cruise speeds (Ct/Sigma). I wonder whether the old Cheyenne trick of using the pusher prop for holding various pitch attitudes in hover is being saught.
If ever there was a machine which looked fast standing still this is it...
Last edited by Graviman; 23rd Feb 2008 at 14:59. Reason: Pusher prop windmill brake comment removed.
Join Date: Jul 2004
Location: Huntsville AL
Age: 51
Posts: 139
Likes: 0
Received 0 Likes
on
0 Posts
Graviman,
I agree...doing Mach 2 without moving in my eyes!
I wonder also if there is a gearbox at the end of the boom for the pusher prop or if it is a direct driveshaft from the main box. It looks as if the latter is the case and if so that would put the driveshaft running right OVER the engine. I guess it isn't a big deal but just out of the ordinary.
Speaking of disc loading, how is it figured for a coaxial aircraft? Do you figure the disc area for both rotors or just one since they are acting on the same stream tube?
Max
I agree...doing Mach 2 without moving in my eyes!
I wonder also if there is a gearbox at the end of the boom for the pusher prop or if it is a direct driveshaft from the main box. It looks as if the latter is the case and if so that would put the driveshaft running right OVER the engine. I guess it isn't a big deal but just out of the ordinary.
Speaking of disc loading, how is it figured for a coaxial aircraft? Do you figure the disc area for both rotors or just one since they are acting on the same stream tube?
Max
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
maxtorq, that's one for Dave Jackson and his magic spreadsheet.
In a nutshell you assume the same column of air is being induced by the blades in both rotors at the same time (ie on a single plane). There is a pedantic argument that the lower rotor sees a higher induced flow, but Nick would go to lengths to point out that only works in ideal hover conditions. At cruise the flow outwash contraction will be some way behind the machine before you need to overly worry about this. I would imagine the FBW uses a laser gyro to trim differential collective for precise yaw control. I'll give you a better answer though when i've read the Leishman paper on my desk.
The other feature to notice is the blade profile. The tips have a nice elliptical taper to produce large vortices with reduced local velocities. The inboard section uses an inverse taper so that the retreating portion in the reverse flow circle can be feathered. Again a compromise which sacrifices some hover performance for improved cruise efficiency.
I'm not sure about that rear structure being a reducer gearbox though. It looks more to me like a pusher prop collective pitch mechanism. Driveline failure is generally the result of joints failing. It can normally be contained by designing a surrounding structure which limits the radial movement of the broken driveline. In the worst case that the single LHTEC800 engine was damged, the main rotor and flight controls still allow an autorotation. FBW will be triplex or quadruplex.
This is an experimental machine, so Sikorsky are naturally being gradual about performance expansion. With 17 engine failures under his belt i'm sure Nick, or indeed any TP, would heartily agree that this is a wise philosophy.
In a nutshell you assume the same column of air is being induced by the blades in both rotors at the same time (ie on a single plane). There is a pedantic argument that the lower rotor sees a higher induced flow, but Nick would go to lengths to point out that only works in ideal hover conditions. At cruise the flow outwash contraction will be some way behind the machine before you need to overly worry about this. I would imagine the FBW uses a laser gyro to trim differential collective for precise yaw control. I'll give you a better answer though when i've read the Leishman paper on my desk.
The other feature to notice is the blade profile. The tips have a nice elliptical taper to produce large vortices with reduced local velocities. The inboard section uses an inverse taper so that the retreating portion in the reverse flow circle can be feathered. Again a compromise which sacrifices some hover performance for improved cruise efficiency.
I'm not sure about that rear structure being a reducer gearbox though. It looks more to me like a pusher prop collective pitch mechanism. Driveline failure is generally the result of joints failing. It can normally be contained by designing a surrounding structure which limits the radial movement of the broken driveline. In the worst case that the single LHTEC800 engine was damged, the main rotor and flight controls still allow an autorotation. FBW will be triplex or quadruplex.
This is an experimental machine, so Sikorsky are naturally being gradual about performance expansion. With 17 engine failures under his belt i'm sure Nick, or indeed any TP, would heartily agree that this is a wise philosophy.
Last edited by Graviman; 20th Feb 2008 at 21:13.
Originally Posted by Graviman
This will also benefit autorotation, by providing an additional source of windmill brake power.
Originally Posted by Graviman
Good luck on the tether test flying.
Originally Posted by Graviman
Any word on who the lucky TPs are going to be, or is it bad form to ask such a thing?
-- IFMU
Join Date: Nov 2004
Location: Cambridgeshire, UK
Posts: 1,334
Likes: 0
Received 0 Likes
on
0 Posts
IFMU, that pusher prop windmill brake power comment has been removed since i realise it was probably in error. [edit 23Feb08]
However, a potential advantage is that the pusher prop could be used to pull energy out of the airstream. The immediate advantage would be a lack of need to drop collective and flare in autorotation from cruise. This would also means that the main rotor would not have to be at flat pitch during autorotation, with forward cyclic, to allow good yaw authority. Coaxials can suffer reduced yaw control in autorotation, as the differential collective pitch does not transfer torque as when in level flight.
I imagine the pusher prop has an additional twist grip on the collective. Alternately the system may automatically trim the prop for all flight conditions. The system has good potential.
Once the machine has been tether tested, and the flight testing gently expands the envelope, i'm sure the TPs will have all sorts of interesting information. I for one will be very keen to learn and understand the TP feedback.
CEFOSKEY, I imagine all the engineers are mildly frustrated at the moment not having access to the X2. Prototype access is always a balance between the marketing department and development. Still at least the design breif of "take your time" means the X2 design can progress in a sensible manner - it is not always so.
However, a potential advantage is that the pusher prop could be used to pull energy out of the airstream. The immediate advantage would be a lack of need to drop collective and flare in autorotation from cruise. This would also means that the main rotor would not have to be at flat pitch during autorotation, with forward cyclic, to allow good yaw authority. Coaxials can suffer reduced yaw control in autorotation, as the differential collective pitch does not transfer torque as when in level flight.
I imagine the pusher prop has an additional twist grip on the collective. Alternately the system may automatically trim the prop for all flight conditions. The system has good potential.
Once the machine has been tether tested, and the flight testing gently expands the envelope, i'm sure the TPs will have all sorts of interesting information. I for one will be very keen to learn and understand the TP feedback.
CEFOSKEY, I imagine all the engineers are mildly frustrated at the moment not having access to the X2. Prototype access is always a balance between the marketing department and development. Still at least the design breif of "take your time" means the X2 design can progress in a sensible manner - it is not always so.
Last edited by Graviman; 23rd Feb 2008 at 15:04. Reason: Removal of speculation that pusher prop used in autorotation.