S97 Raider

[IFMU]

Congratulations to the Raider team! Very cool! The video looked great.
Bryan Cotton
Sikorsky/X2 Alumni

[whoknows idont]

Seems to me like they changed the layout on the flying prototype.
From the video above ("Sikorsky S-97 RAIDER Journey to First Flight"), 1:26:

[SansAnhedral]

On the videos, check out the stationary fastener pattern between the rotors. I think they solved that problem on RAIDER.

That is the same as the X2. It was the weathervane apparatus (of which they patented 3 implementations on their patent) which proved troublesome.

Congratulations to the Raider team! Very cool! The video looked great.
Bryan Cotton
Sikorsky/X2 Alumni

So you have seen the video! Hopefully they didnt make the same miscalculation with the control gains as the X2 maiden (I am sure you remember that having been so involved in the FBW). Bredenbeck had the thing dancing on him that afternoon.

edit

Here is the video, pretty stable this time

[IFMU]

Sans,
I watched the vid and I think SplineDrive is right on the sail fairing provisions. Not the same as X2. The X2 was a good aircraft but I think the workd will see that Sikorsky has stepped things up a notch or two for the Raider.

The initial gains did look a lot better! Or Bill is steadier.

Bryan

[SplineDrive]

Fairing provisions

30 seconds into the retrospective video http://youtu.be/j2CJP78WkGs you can see an entire composite skeleton above the lower rotor that isn't rotating. I bet the fairing bolts to that.

Nice video, too.

[NickLappos]

What a gas to watch the next generation of Sikorsky pilots take to the sky in a new design! Raider (and its big brother Defiant) are the new boys on the block, with a nice blend of low speed agility (akin to the BK-105) and high speed load factor and cruise payload efficiency (much better than helicopters, approaching that of Tilt Rotors, and much better than winged compounds.)

The Raider is a rapid prototype, but it is a practical aircraft, akin to a Y plane as a pre-production prototype. It has many prime components that can go straight to production, saving much time if a customer requires fast delivery.

The flight was terrific, all as expected. Here is some info on the aircraft:

Sikorsky S-97 RAIDER?

Sikorsky S-97 Raider - Concept Light / Attack Helicopter - History, Specs and Pictures - Military Aircraft

Sikorsky S-97 Raider Specification & Technical Data | Defence Aviation

For those with sharp eyes, like SplineDrive, the space between the heads has a standpipe that is stationary, allowing a nice fairing to be fitted to fill in that area, and dropping drag by quite a bit. The transmission design team in Ft. Worth thought that up, it could be worth an additional 5 to 10 knots.

[SansAnhedral]

the space between the heads has a standpipe that is stationary, allowing a nice fairing to be fitted to fill in that area

Does that imply its a fixed fairing and they dropped the weathervane design I read so much about?

One thing I am curious about is the expected efficiency of the Defiant in cruise. To date, all ABC ships have buried the QCA/transmission in the middle of the fuselage, keeping that massive drag out of the freestream - and simultaneously eating up almost the entirety of the cabin.

In order to regain useful payload space, that entire assembly has to be mounted on top of the pylon (to avoid what would otherwise be immense CG issues), which probably almost doubles frontal area.

What happens to Vcruise and efficiency in this case?

[exwessex]

Can anyone explain the pilots controls we can see in the picture above-it appears that each pilot has just an outboard side-stick.How is this used?

[SplineDrive]

Sans, yup, it looks like the lawyers made good money processing patents for fairing anti-drive units when the production solution is to mount the fairing to a stationary shaft. Sounds more robust to me.

As for Defiant, the public artwork shows the rotor to be a little higher from the cabin, proportionately, than on RAIDER, but the twin engine installation might also affect that. In any case, I see no evidence that the transmission needs to be completely on top of the cabin structure and it does not appear that is the layout. Looks like the passenger cabin is forward of the transmission bay. Also helpful is that larger helicopters typically have a higher cruise speed than their smaller relatives for a given aircraft layout. I have no doubt that Defiant will be fast and a significantly lower L/De than a conventional helo.

When it comes to balancing CG, few rotors in the world will have the moment generation cabailities of the Defiant main rotor ;-) If they want to fly level body I'm sure they can.

[NickLappos]

SansAnhedral,
The faring doesn't weathervane, that was decided to be impractical. The transmission standpipe runs up to keep the fairing in place.

I think you are under the misapprehension that something about the transmission is "massive" and a real problem to house and a real drag issue. The preconception fills your questions, as if we hadn't yet stopped beating our wives. That is not the case with the X2 transmission, and I believe it is not the case with the Kamov transmissions that I am familiar with.

Frankly, the transmission diameter of most helos is sized by the main "bull" gear diameter, which establishes the basic diameter of the box, and the coaxial transmissions with a double shaft tend to fit within that basic bull gear diameter without a problem. Fitting it within the fuselage is no big deal, frankly, and doesn't take up much internal space, as your question says. I found a shot on a public source that shows the Raider's cowing off, here it is: Sikorsky S-97 Raider - Concept Light / Attack Helicopter - History, Specs and Pictures - Military Aircraft


Anything orange in there is test instrumentation. Note that the transmission is "normal" in size and width, and that plenty of internal space is left to carry stuff, which is why we build these machines!

[riff_raff]

...Frankly, the transmission diameter of most helos is sized by the main "bull" gear diameter, which establishes the basic diameter of the box....

I would agree with this point. A torque split configuration should help reduce the plan view profile of a (intermediate or final) bull gear stage. One major consideration when sizing a bull gear stage is the L/D limit of the bull pinions. A spur gear pinion is limited to an L/D of around 1.0 or less. If more pinions are used to drive the bull gear, each mesh will need to transfer proportionally less torque. This means the diameter of the pinions and bull gear can be reduced while maintaining an appropriate L/D and the required stage gear ratio. A coaxial counter-rotating MRGB configuration would have the same effect on plan view profile (vs. a single rotor config) since there is an additional torque split at the two output drives. The drawback with this configuration is that the vertical length grows due to the extra space required for the dual coaxial outputs.

I was not familiar with the term "standpipe" as used in NickLappos' posts. I had always heard such a device referred to as a "static mast". So out of curiosity I did a search of recent published US patent applications from Sikorsky using the term "standpipe", and sure enough I found a couple documents. Interesting stuff.

[SansAnhedral]

Nick, to be fair I never said the transmission itself alone was large, or of large diameter. Note I mentioned QCA, which as a Sikorksy alum I am sure you know the acronym.

You have deftly danced around the issue I was trying to get at; a not-insignificant increase in frontal area. As has been published through many whitepapers during G-LYNX days, XH-59 days and so forth, its well understood that a major contributor to profile drag has always been frontal area, specifically the rotor head. I have read it mentioned that approximately 40% of drag on an edgewise flight helicopter is driven by the head/mast.

So lets take the X2, XH59 and S97, all of which were designed to have negligible payload within the cabin. This allows for a very clean installation using the area below the top deck to be used to house the QCA attachment along with the single engine power pack. Now, if you must reclaim this area due to the payload and egress requirements of FVL-M, you have 2 options:

• Mount the QCA and twin engines above top deck in pylon
• Mount the QCA and twin engines fully aft of cabin below the top deck a la X2/XH59/S97

The latter of which would almost certainly cause extreme CG issues, as I mentioned before.

It would stand to reason that this was realized by the Sik-Boeing design team as it would appear from they have chosen the former (over time the main gear has migrated in concept art as well, likely due to cabin rearrangement for CG):



So, in addition to all of this new area in the freestream due to dynamic systems, we have a larger diameter rotor, which increases rotor spacing. From layouts of the SB>1, the overall height looks something near 20 feet.

For small GW tatical aircraft like the S97 where you can use the fuselage itself to fair the dynamic system, and keep the rotor spacing low, the ABC concept works well.

I have a hard time fathoming how installed power is going to overcome the apparent large increase in drag from both pylon mounted engines+QCA and increased rotor spacing in edgewise flight on a larger version. I think this is even well-understood by SAC, considering the amount of lobbying done on the FVL IDRR in an attempt to keep the speed requirement closer to 170kt than what was settled on for MPS @ 230kt.

[NickLappos]

Sans,
There is surely more drag due to the extra rotor head, but you went on about lost cabin area due to volume, so I answered that misimpression.
Your worldview of helicopter drag seems drawn from airplanes, where "presented area" and cross section drag are dominant. Rotorcraft are far different, and need a fresh way of examining their efficiencies. Mostly, you must look at the entire package, especially the power consumed by the rotors to produce the lift and thrust, and the hover performance lost when large wings lay within the rotor downwash field.
A twin rotor head design carries an inherent drag penalty, for sure, mostly driven by the extra head but also vastly compounded by the tall mast and space between the rotors. Mikheyev of Kamov published several papers that described his estimate at 10% extra for his designs, I have no reason to doubt that.
The fairing we were talking about on the X2 designs, and the much reduced X2 rotor separation (which drops the upper rotor height substantially) help limit the frontal area drag to very reasonable numbers relative to older coaxials. The head separation on a Kamov is about twice as much, because the low hinge offset rotors have to be kept apart (to prevent self-midair collisions). The very rigid ABC/X2 rotors have almost no flapping, so they can be kept closer together, and with the ensuing lesser drag.


The most important power loss/drag increaser at speed is not the frontal area, but the large power penalty of the retreating blade stall. The rotor alone consumes a vast amount of the power at higher speeds, You could reduce the presented area to a point in space and the rotor blades will consume 3/4 of the power anyway. Helicopters must have balanced lift on both sides of the disk, so the retreating blades, operating at very high angle of attack, and in some reversed flow, are famously inefficient. This is while the advancing blades are approaching Mach 1 and consuming power due to drag divergence. Can't slow them down, or the retreating side gets worse!


The X2/ABC basically tilts its swash plates to dump the angle of the retreating blades, and making sure the advancing blades tote the lift needed while the retreating blades reduce their angles and loaf along. As Mach 1 is being reached, the rotors are slowed down as well, which keeps the high speed drag under control.


What this means, SansAnhedral, is that the X2/ABC design has much lower drag at high speed than helicopters. Its L/D is very attractive, especially when you compare its hover efficiency. Added benefits over other high speed configurations include: efficient helicopter rotors for good payload and good altitude hover performance, fantastic handling with low inertias and nimble pitch, roll and yaw handling, compact design so it fits into small areas.


This was all examined when the FVL was being considered by the Army, and speed, range and altitude performance were all part of the new way of doing business. Need independent proof of these comparisons? Boeing took months to examine tilt rotors, compounds and X2s, and came to Sikorsky to join the team, even though they have a great deal invested in tilt rotors, and know them very well. Defiant is very much a 50-50 partnership with a company that makes 50% of the V22, and chose to spend their effort and money on the X2/ABC configuration.


BTW, another misimpression is the mistaken belief that Sikorsky tried to hold back the speed goals of JMR/FVL. I have no idea who told you that, my suggestion is that if they tell you it is 2 o'clock and your watch agrees, throw your watch away! Sikorsky and Boeing are spending a ton building a machine (Defiant) that will be far, far faster!

[SansAnhedral]

All very good talking points that we have heard about ABC since circa 2005-6 (when Sikorsky was still showing what they considered a feasible 737-fuselaged ABC!). Since there is no precedent at this size, the proof is in the pudding, and I think it will be very difficult for a > 30,000lb GW ABC coax to achieve much more than 200kt. If an SB>1 actually gets built by late 2017, which I still have my doubts based on things I have heard from various industry suppliers on the program, I will be surprised.

Need independent proof of these comparisons? Boeing took months to examine tilt rotors, compounds and X2s, and came to Sikorsky to join the team, even though they have a great deal invested in tilt rotors, and know them very well. Defiant is very much a 50-50 partnership with a company that makes 50% of the V22, and chose to spend their effort and money on the X2/ABC configuration.

Agree to disagree on this point. From the grapevine, the real story is that Boeing intended to partner with Bell on FVL, but it seems Bell had learned the lesson that the 50/50 split on the V22 was far from their best interest to repeat, especially with the specifics of the requested FVL work split.

I still maintain that both Sikorsky and Boeing want nothing more than for FVL-M to go away, hence the teaming. Sikorsky wants to sell S97 as FVL-L or as something "off the shelf, ready to go" to replace Kiowa and AAS. They both subsequently convince Uncle Sam that the capability in the medium class can better be accomplished (read: cheaper) with next gen UH-60X and AH-64X to keep those revenue streams alive.

[IFMU]

Originally Posted by SansAnhedral

• Mount the QCA and twin engines above top deck in pylon
• Mount the QCA and twin engines fully aft of cabin below the top deck a la X2/XH59/S97

The latter of which would almost certainly cause extreme CG issues, as I mentioned before.

But, it was not a problem on X2. CG was good. Though what SpineDrive says is correct, you still need a forward enough CG for stability. This is a basic aircraft fact that is true for both helicopters and fixed wing.

On Raider, as you load up the cabin, the CG moves forward.

[NickLappos]

SansAnhedral,
Your beliefs are interesting, and many seem to be based on zero facts! Also, the more than a little conspiracy theory nature of those beliefs makes you suspect as a pilot flying passengers. Those who think we have money to burn spending millions on vehicles that we don't think will work are way past crazy.

[SansAnhedral]

It was not a problem because there was no payload on X2, and little on S97. The issue is exacerbated on a 30,000lb utility version.

From the layouts of SB>1, with empty payload, it looks to have little to counteract an aft CG condition if it is trimmed for a nominal payload way out in front as shown.

[NickLappos]

I guess you didn't read the info that I posted about the payload range and speed of the Raider.

[SansAnhedral]

SansAnhedral,
Your beliefs are interesting, and many seem to be based on zero facts! Also, the more than a little conspiracy theory nature of those beliefs makes you suspect as a pilot flying passengers. Those who think we have money to burn spending millions on vehicles that we don't think will work are way past crazy.

Fear not, as flying passengers (unless you count the odd bug-smattered windscreen) is not my meal ticket

But I digress. Nobody claimed that the aircraft "wouldnt work", but we all know that the program we are referring to is intended to "drive requirements" for a future program of record. To present an aircraft that is deficient in a category like cruise speed hardly qualifies as a reason not to try and influence your customer that his requirements are out of bed, and your product is still best for the job.

Having been a part of as much of the S-92 program as you were, surely you can attest to the politics involved in these sorts of things.

[The Sultan]

Nick

Your partisan attacks which denigrated the V-22's speed, range, and payload which have been shown by V-22 operations to be false makes you a poor source of aircraft performance numbers.

The Sultan