Sikorsky-Boeing SB-1 Defiant

Helicopters and tilt-rotor aircraft
  • Author
  • Message
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post21 Oct 2020, 06:09

sferrin wrote:IMO The V-280 has it in the bag. Raider will win FARA.


That has been the expectation of a number of folks, including me, if for no other reasons that DoD probably wants to keep two helicopter manufacturers around, and Sikorsky needs to have something big for the future besides CH-53K.

Lately, though, some doubts are arising. Most people think that the smaller X2, S-97, has just been blazing along and is demonstrating and proving the feasibility of what's promised for Raider-X. But like the song say, "...it ain't necessarily so...". S-97's been been flying for over five years and has yet to achieve its promised sustained top speed, or demonstrate all the maneuverability claimed for it. There are rumors floating around that it will never be able to achieve that speed. Last August 19, Sikorsky finally allowed a guest pilot in the bird (for comparison, V-280 flew its first guest pilot two months after first flight). Verticalmag reported on it, and there are some curious aspects to the report. For one thing, most of the time was spent in the simulator. When the Army pilot got into the S-97 he had to sit left seat instead of right. Turns out they built the S-97 with only one collective, in the center. Sikorsky's own test pilot that accompanied him said, "I am not confident sitting in the left seat of that machine and letting somebody take it for a spin around the block, so unfortunately it fell to him to sit in the left seat.” That is not confidence-building. Plus, after the flight the Army pilot was not made available for any interviews or questions.

Sikorsky says not to worry, they'll put two collectives in Raider-X. Is it just me, or does that sound like what Microsoft used to say about Windows, "It's not a bug, and don't worry we'll fix it in the next release"?

My point is that Sikorsky seems to be going for a higher cost but higher performance with a more advanced technology for which they'll say they have demonstrated they've removed the risk. But have they?
Offline
User avatar

geforcerfx

Forum Veteran

Forum Veteran

  • Posts: 883
  • Joined: 10 Feb 2014, 02:46

Unread post01 Nov 2020, 20:36

sferrin wrote:IMO The V-280 has it in the bag. Raider will win FARA.


I think it's reversed. I think they will go SB-1 for the medium attack competition and the Invitus for the FARA and then bell also wins the heavy with a advanced tiltrotor design. The Invictus is a very simple and risk adverse design and I think that wins them the competition because is looks more and more like the army wants those in service fast. While Bell got the V-280 out sooner this program is actually pretty far ahead of schedule. The army expects to get FARA in service before they get the Medium/assault program into service, both companies have a long time to test and tweek there medium/assault design and that's where most of the money is gonna be from the FVL program. Also it's Lockheed and Boeing on one team vs Textron on the other. I honestly see those two winning the big money prize as long as they don't completely screw it up.
Offline

tank-top

Enthusiast

Enthusiast

  • Posts: 49
  • Joined: 06 Jul 2018, 02:28

Unread post02 Nov 2020, 04:01

Counter rotating props makes my brain hurt. Looks fantastic at face value but turbulence created by the first set of prop blades must be a nightmare for the second set of blades to deal with not to mention the Doppler effect on radar of counter rotation.

Please don’t bother responding, either your answer is too simple and wrong or I’m not smart enough to comprehend the answer. I know it’s been done but it’s not straightforward.
Offline

boilermaker

Active Member

Active Member

  • Posts: 112
  • Joined: 22 Jul 2015, 18:12

Unread post03 Nov 2020, 01:52

aaam wrote:
charlielima223 wrote:While the Sikorsky is behind the curve compared to Bell's submission, progress is being made.

https://breakingdefense.com/2020/06/fvl ... s-for-288/


235 mph is 205 knots, which is a more apples to apples number to use when comparing with Bell's submission (over 300 knots) which was able to fly over 15 months sooner.

On October 12 it was proudly announced that the SB>1 had reached 232 knots. However if you look closely at the event you'll find that was achieved in a descent. In level flight they've only gained six knots (to 211) in four months. Also part of the announcement was that it used "only" two-thirds prop torque and engine power to hit 211 knots. Apparently they used a bit under 50% to get to 205, so we can see the effects of drag here. People a lot smarter than me are starting to wonder if the SB>1 will actually get to the promised 250 knot sustained speed.

Some report that the Defiant has now flown 23 hours total. That's less than 1 1/4 hr a month, so progress has to be assessed as somewhat less than breathtaking.



Meanwhile the old Westland Lynx still holds the 1980s speed record of 216 knots...
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post03 Nov 2020, 02:28

boilermaker wrote:

Meanwhile the old Westland Lynx still holds the 1980s speed record of 216 knots...


Because the FAI won't accept compound helicopter records.
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post06 Nov 2020, 08:08

marauder2048 wrote:
boilermaker wrote:

Meanwhile the old Westland Lynx still holds the 1980s speed record of 216 knots...


Because the FAI won't accept compound helicopter records.


In fairness to the FAI, there are some considerations. Clearly, a compound helicopter would have to be a separate category from regular helicopters if for no other reason than the propulsion system. So far, no one's asked for such a category. Also, there are specific procedures and measurements that must be followed for the FAI to recognize a record. So far, AFAIK no compound has attempted this or even asked FAI to certify their performance. If such an attempt had been made, the record would belong to the Airbus X3.

Interestingly, the Lynx's 216 knot speed still beats the level flight speeds achieved by most compound helicopters. The XH-59 with two turbojets attached beat it, but its range went to virtually nothing and it couldn't hover OGE and so operated STOL instead of VTOL. The X2 demonstrator went faster for a brief period of time, although there's some question whether it would be able to fly the FAI's required speed course. The Airbus X3 which could fly it easily is the fastest. Those are the only three to come to my mind. They'll need to crank another six knots out of the SB>1 in sustained level flight to beat what the Lynx did 34 years ago.
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post07 Nov 2020, 06:08

aaam wrote:
Interestingly, the Lynx's 216 knot speed still beats the level flight speeds achieved by most compound helicopters. The XH-59 with two turbojets attached beat it, but its range went to virtually nothing and it couldn't hover OGE and so operated STOL instead of VTOL.


Like the 216 is caveat free: water methanol injection and a record that could only be set at night so as not to melt the gearbox and to ensure that the maximum available excess energy could be routed to the modified exhaust system.

I find all of these one-off efforts a bit silly. Hopefully, this compound coax goes into serial production and
it sets records on that basis.
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post07 Nov 2020, 07:13

marauder2048 wrote:
aaam wrote:
Interestingly, the Lynx's 216 knot speed still beats the level flight speeds achieved by most compound helicopters. The XH-59 with two turbojets attached beat it, but its range went to virtually nothing and it couldn't hover OGE and so operated STOL instead of VTOL.


Like the 216 is caveat free: water methanol injection and a record that could only be set at night so as not to melt the gearbox and to ensure that the maximum available excess energy could be routed to the modified exhaust system.

I find all of these one-off efforts a bit silly. Hopefully, this compound coax goes into serial production and
it sets records on that basis.


Never said it was caveat free, just that the 216 knots beats the speed of most compounds that have flown so far. Note that the XH-59A, which had two 3,000 lb. thrust jets hanging on the side only beat its speed by 22 knots. Also, the rotor was the most significant advance of that Lynx. It was what permitted it to reach that speed, delaying the effects on rotors that limit all regular rotorcraft's top speed. You could put all the power you want on a conventional helo, it's not going to go much faster than that Lynx.

It would be great if X2 technology proved itself; maybe it will, but so far its progress has been disappointing.
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post07 Nov 2020, 09:35

aaam wrote: Also, the rotor was the most significant advance of that Lynx. It was what permitted it to reach that speed, delaying the effects on rotors that limit all regular rotorcraft's top speed. You could put all the power you want on a conventional helo, it's not going to go much faster than that Lynx.


Rather unconvincing given the massive uprating in installed power coupled to a new transmission and exhaust set
that could only work in cool conditions.

It's a one-off and a technological dead end.
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post08 Nov 2020, 06:52

marauder2048 wrote:
aaam wrote: Also, the rotor was the most significant advance of that Lynx. It was what permitted it to reach that speed, delaying the effects on rotors that limit all regular rotorcraft's top speed. You could put all the power you want on a conventional helo, it's not going to go much faster than that Lynx.


Rather unconvincing given the massive uprating in installed power coupled to a new transmission and exhaust set
that could only work in cool conditions.

It's a one-off and a technological dead end.


[Sigh]

Of course that particular Lynx was modified. The standard Lynx was never intended to reach that speed, just like the standard F-15 was never intended to have the performance of the Streak Eagle. Westland, to prove the capabilities of the BERP rotor and their own design expertise to investors and the Government, decided to take the helicopter world speed record with a modified Lynx, an available helicopter.



In addition to drag reductions, RR Gem 60s boosted by water methanol injection were fitted. Clearance was obtained to operate the transmission at One Engine Inoperative contingency power with both engines running. Smaller exhaust pipes were used to capture excess thermodynamic energy that the gearbox couldn't handle. All of this was needed to boost the power available to this special aircraft to get up to speeds above its normal envelope to demonstrate what BERP could do. .

But the ability to use that power for speed and the point of the whole exercise was to demonstrate the BERP blade, which offered increased efficiency and the ability to delay the effects on conventional rotor aerodynamics that eventually put an upper limit on how fast a conventional rotor can go. You should look them up. They include asymmetric lift, compressibility, retreating blade stall (something BERP was particularly intended to delay) and rotor tip speed, among others. The only way around this in a conventional rotor, once you've done things like BERP, is to slow the rotor, either by having an auxiliary propulsion system take over the job over propelling the craft so the rotor only has to provide lift, or offloading the rotor by having an auxiliary lifting surface such as a wing take over some of the job. This permits the rotorcraft to go faster before the effects I mentioned become prohibitive.

One thing: That "technological dead end" is in use on later Lynx 'copters, all Wildcats, all AW101s worldwide and the MH139 of the USAF. it can also be retrofitted to other helos, but unless you're willing to make other changes to the vehicles to take advantage of what BERP gives, the cost/benefit on older designs may not work out.

By the way, in defense of X2, it is not a simple coax, which is just two conventional rotors mounted above each other. Look at Kamov if you want to see that. X2 is a much more advanced concept to get by some of the limitations of regular rotors for more speed and range. The concern is whether it will achieve its promises.
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post08 Nov 2020, 08:52

Hey, one other thing I came across...


Apparently the FAI told Sikorsky they would count the X2 demonstrator as a helicopter on the grounds that it didn't have a wing.

If under observation they would fly the standard course required for a record run (sustained speed for a certain specified distance followed by a turn and doing it again in the opposite direction to correct for wind) they would count it towards the world helicopter speed record over a closed course.

Reportedly, Sikorsky declined.
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post08 Nov 2020, 23:58

In addition to drag reductions, RR Gem 60s boosted by water methanol injection were fitted.



Discursive and pointless per your MO. I've read the same sources you have and we don't need them
to be regurgitated and reinterpreted.

The Lynx mods were extensive and never-seen-again modifications. How much improved thrust was contributing
to improved forward flight perf was never seriously analyzed but should have been. It's a confound.
But this combined approach was a dead-end; no one has pursued it in the intervening four decades.

There have been a number of blade mods over the years to deal with the well understood phenomena.
You see them on many other commercial helicopter types. No one has cobbled those together with
invasive mods to hit speed records. They typically let the improved efficiency speak for itself.
Offline

aaam

Forum Veteran

Forum Veteran

  • Posts: 949
  • Joined: 21 Aug 2010, 22:52

Unread post09 Nov 2020, 03:50

My, you certainly seem touchy. You seem to be upset regarding a contention I never made.

Let me try this once more. The Lynx was available. It was openly extensively modified as a one off to get that helicopter to the speeds that would take the record primarily to demonstrate that the BERP blade could help a helicopter function normally and efficiently at those higher (for a helicopter) speeds. There was never any consideration of repeating those unique mods into a production aircraft, there would be no point; they were simply to get that particular airframe to the desired speed to demonstrate what they wanted to demonstrate. Thrust can increase speed to a point, but dynamics of a conventional rotor are going to limit how fast you can practically go. That's why the record has lasted so long. Russia claims their Mi PSV has gone faster, although not a lot faster, but they haven't yet demonstrated this for international certification.

There have indeed been various rotor mods to squeeze out more efficiency and to delay the onset of the effects of speeds over 200 knots on a conventional rotor, but they aren't promising or delivering major increases. There's a reason the Lynx's record still stands and lack of thrust isn't the reason. Lots of helos today have much more powerful engines than what was on that Lynx and they don't go any faster. There's a reason no one proposed a conventional helicopter for FLRAA. Even AVX's design unloaded the rotor. It's the reason Sikorsky is pushing X2 for SB>1.

I'm not exactly sure how we got here. All I originally said was backing up boilermaker's statement regarding the Lynx still holding the record by noting that record still beats what most compounds have demonstrated. Doesn't really matter that that Lynx was an admitted one-off. Not a lot of compounds have as yet gone faster, and it's not that FAI won't recognize compounds, it's that compounds haven't applied for certification, even the one with two turbojets blasting away (which actually wasn't even the fastest compound).

The subject of this topic is SB>1, not the minute history of a particular helicopter flight from decades ago. Maybe we should return to that...
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post09 Nov 2020, 18:23

aaam wrote:My, you certainly seem touchy. You seem to be upset regarding a contention I never made.


You certainly seem excessively pedantic, discursive, unable to express views concisely or understand
that turboshaft exhaust, from the Lynx's grenade engine does contribute to next thrust in level heli flight.
That's a major confound. Especially given the extensive modifications including weight reductions.
Last I checked, thrust-to-weight ratio matters a lot.

At the end, what Lynx demonstrated was *sprint* speed at combat irrelevant conditions which is not a
strong driver for the Army's baseline perf reqs.

That no helicopter has emulated the Lynx approach in toto speak volumes.

aaam wrote:I'm not exactly sure how we got here.


A pathological inability to write concisely and clearly along with a propensity for tangents and
verbal effluvia.

aaam wrote:The subject of this topic is SB>1, not the minute history of a particular helicopter flight from decades ago. Maybe we should return to that...


Try to keep that in mind when you post meandering, rambling dissertations that provide background
nobody wants for foreground that's irrelevant.
Offline

marauder2048

Elite 1K

Elite 1K

  • Posts: 1453
  • Joined: 14 Mar 2012, 06:46

Unread post09 Nov 2020, 20:55

Can you make a cogent technical point that addresses the issues I brought up
in under, say, 1000 words?

You've just regurgitated what it's in the easily accessible sources which adds nothing.

If there's a scholarly source, where succinct technical prose is valued, you wish
to bring to my attention, by all means, please do so.

But you've shown an allergy to primary sources.
PreviousNext

Return to Rotary Wing Aircraft

Who is online

Users browsing this forum: No registered users and 3 guests