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New Bell product - Bell V280

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New Bell product - Bell V280

Old 11th Apr 2013, 19:51
  #21 (permalink)  
 
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We appear to be going in circles.

Nobody suggests a tiltrotor is more cost effective than an X2 at the particular size of S97. Thats precisely why sikorsky went and built that thing unsolicited; its at the max of the veritable X2 gross weight sweet spot.

For anything larger, especially FVL-M, the cost effectiveness of one over the other is entirely indeterminate (though we at least have data and a precedent of multiple tiltrotor machines), and thats assuming theres some magic blade recipe that can avoid tip interaction and self destruction at 60 foot diameters during manuever.

My sole argument is simply that a comparable size Raider will be more cost-effective than a Tilt-Rotor (and which I do not believe is a startling revelation)
I find that startling. My argument is that your assessment that an X2 coax is more cost effective at any given comparable size has no basis. Where do you derive that axiom? What makes a given ABC coax inherently less complex or expensive than a tiltrotor? I contend the complexity is entirely on par.

Last edited by SansAnhedral; 11th Apr 2013 at 19:58.
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Old 12th Apr 2013, 11:41
  #22 (permalink)  
 
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This is Bell's JMR/FVL medium concept. Sikorsky and Bell are the two most likely candidates for JMR flight demo contracts (a Sikorsky compound and a Bell tiltrotor). Sikorsky and Bell have the most experience with their respective configurations which gives them a big advantage over their JMR competition in terms of development risk.
I wonder if Eurocopter will compete. They are developing an advanced X6 medium helicopter and a militairy aimed similar sized helicopter using X3 technology.

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Old 12th Apr 2013, 23:50
  #23 (permalink)  
 
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...But the 'planform' of this contraption is considerably larger (and therefore in my view more vulnerable) than the Raider concept. Plus, with the tilt-rotor you have two unique heat signatures effectively giving your assailant unnecessary opportunity...
Savoia- For sure, reducing IR is much easier with a conventional helo. The Comanche was a great example of how effectively it can be done. With a tiltrotor having tilting engines the long length (3 or 4 feet) of an engine exhaust IR suppression device can create ground clearance issues.

FVL won't enter service for at least another decade, and the model specs for each of the (4?) variants are still very much a work in progress. However, the BAA issued for the JMR phase I TD aircraft has requirements for DGW of 30,000lb or less, and a speed of 230+kts. Sikorsky had to push hard to reach 250kts with their X2 demonstrator design, which was optimized for only going fast. Once compound helo designs like X2 or EC's X3 make the compromises needed to meet FVL program requirements for payload, range, cabin volume, etc., they will be hard-pressed to attain 250kt speeds. On the other hand, tiltrotors can easily achieve 250kt speeds.
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Old 13th Apr 2013, 21:13
  #24 (permalink)  
 
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It looks as if there could be larger X2 technology on offer.

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Old 16th Apr 2013, 01:38
  #25 (permalink)  
 
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Regarding Tilt-Rotor (TR) vs. ABC, there are a few things that need to be taken into consideration.

A TR is always going to have the penalty of the weight and area of the wing. Although you can have much more twist in the blades of a TR (because there is no need to design for the case where the blades are flying through the air sideways at higher speeds), the smaller the size of the air vehicle, the greater proportion taken up by the wing. On the other hand, once you stop hovering, you have the advantage of having the wing. Your propulsion source doesn't have to be your lift force as well, which gives you greater efficiency and performance. The ratio of hover to forward flight determines which is the most efficient. It's worth remembering that there were likely going to be two TR proposal for LHX until the Army reversed course and changed the specs so as to preclude a TR bid. From the information that leaked, it looked like the TR proposals would far outperform helos, even allowing for the hovering penalty.

A TR does offer lower risk. The XH-59 was pretty much a flop, and the X2, unquestionably an impressive achievement, was years late and has only demonstrated a few minutes at its design speed, whereas the XV-15 was routinely cruising at those speeds and above over 30 years ago.

A TR of course offers higher speeds. In the case of the V-280, the power driver was the 6K 95F requirement. With the power to do that, the 280 knot speed came as a byproduct, not a driver. It also offers longer range, because of that wing, and lower fuel burn, since it can run at proportionately lower power settings while wingborne. Self deployment is relatively easy for a TR, as was demonstrated when V-22s were suddenly deployed from Afghanistan to the Libyan theater. Self- deployment is especially important for them, since it looks like it'll be a easier (if the height permits it) to stuff an ABC vehicle in a C-17 than a TR.

The control system on a TR can be argued to be simpler since there is no need for a separate system to provide thrust. An ABC can fit in a narrower LZ, but it looks like a TR can fit in a shorter one, and there's no need to worry about what the aft prop is doing relative to obstructions and personnel. I can't tell if the arc of the proprotors on the V-280 extend beyond the nose. If you watch Sikorsky's videos on ABC operations, they show the propeller not being brought on line until airborne. This can have an affect on operations and will have a big impact on civil use of the concept for EMS, since one of the big concerns in that arena is the tailrotor and people near it. One other thing: With a TR, at least in the attack version, conventional ejection seats could be provided for the flight crew, not practical with ABC.

Final cost will depend a lot on how the gov't specs out the final requirement, and how much they add on to the desired capabilities and what they stuff into the contract. I simply do not believe that Sikorsky (or anyone) could deliver the Raider for $15 million. Like a TR, the flyaway costs of an ABC are going to be more than that of a conventional rotorcraft. Like a TR, you mke it up in the back end and needing fewer vehicles o accomplish your missions. If all they want is a conventional helo can do (watch what they do with the speed and range requirements), then neither advanced concept a chance. If they back off to 150-175 knots and lower range requirements, both of these technologies will go away.

As to why Bell left the 609, I suspect part of that was that they needed to concentrate all their resources on the V-22 program and that they hired certain people at senoir level (and they definitely needed new blood at that level) who were known not to be fans of TR.

One other thing: door gunners. While in an attack bird, remotely operated turrets are the way to go, in the assault mission they can not react fast enough, don't have the versatility and are much more expensive and trouble prone than guys in the doors. Consider a situation where the vehicle has landed to infil/exfil. The turrets are pretty much out of the picture. Also, when low and slow for whatever reason, you can do a lot more with door gunners than with a turret, especially if there are bad guys on both sides. It's no accident that USMC as decided to give priority to getting UH-1Ys over AH-1Zs.

Last edited by Commando Cody; 16th Apr 2013 at 02:45.
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Old 16th Apr 2013, 13:10
  #26 (permalink)  
 
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Here's the B model




This is how they shoulda made it. The coat hanger design with the big prop (rotor) on top provides better auto capabilities. Point it forward and wheels retract and the struts supporting the gearbox become a lift producing airfoil.

Of course, I purport to know Evry Ting, he lives down the road.
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Old 16th Apr 2013, 16:35
  #27 (permalink)  
 
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Somewhere in Texas...

PR person: "Okay, so we've covered performance, range, technology and safety. Is there anything else we want to mention in the press release?"

Program manager: "No, I think that covers it. Let's go to press!"

PR person: "What about downwash. Do we want to mention downwash?"

Program manager: "Err...no. It's good as it stands, let's get it printed!"

PR person: "Are you sure? Isn't that something people will ask about?"

Program manager: "Well possibly, but it's not really something we want to draw attention to. The Valor's downwash is likely to be a bit greater than for other types. Let's just go with what we've got."

PR person: "Nah, I really think we should mention it. How about this..."



I/C

Last edited by Ian Corrigible; 16th Apr 2013 at 16:41. Reason: Script tweak
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Old 16th Apr 2013, 17:37
  #28 (permalink)  
 
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Well at the DGW of FVL-M from the BAA and the apparent rotor radius / solidity from the models, the downwash should be well south of a V22/CH53/HH47 at the very least.
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Old 16th Apr 2013, 18:03
  #29 (permalink)  
 
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One of the reasons, aside from smaller size/weight, the downwash should be less is that at this size they don't have to worry about required safety clearance between the rotor arc and the island of the Marines' air capable ships. On the V-22, the rotor disc is smaller than optimum for that reason and so that an Osprey can fold up within its own length and width of the empennage.

Regarding the HH-47, now there's downwash! The UK found as their Chinooks approached the LZ in troop insertion operations, the downwash would actually set off shallowly buried land mines.
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Old 16th Apr 2013, 19:01
  #30 (permalink)  
 
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Door Guns etc

CC, I'd guess that those readers who have ventured into unfriendly LZ's concur with your point re door gunners ( assuming that this aircraft is tasked with that type of mission ).

Two other points will sooner or later come up when considering a TR for this replacement program, points raised by V-22 experience and resultant constraints in their flight manual:

1. Can the JMR TR operational requirement accept a 40 kt/ -800ft/min envelope restriction?
2. Same question, but applied to the no closer than 250 ft separation between aircraft in the LZ?

Thanks,
John
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Old 16th Apr 2013, 20:09
  #31 (permalink)  
 
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John,

Those restrictions are part of the original procedures developed prior to fully investigating the Osprey's relationship with VRS. In the Osprey, if one rotor goes into VRS, you get massive roll. In a twin rotor like the CH-46, you go end over end. Since then, and with the flight envelope testing they should have done back then, it's been found that the V-22 is less prone to VRS than most conventional helos, and more importantly is easier to recover (you blip the nacelles a few degrees and the proprotors are in "clean" air and out of VRS). They've also put a VRS condition warning on there which the crews consider more of a distraction than an asset. My understanding is that when an actual tactical situation requires it they do exceed that limitation. V-22s also do put out a bit of rotor wash, which unlike a conventional helo in forward flight, goes aft, not down. This is why there is a limitation of 250 ft. cockpit to V-22 ahead or avoid a 30 degree bearing off the tail when flying at same or lower altitude when within 250 feet. That's why you rarely see them fly in trail. It's not dangerous, just different.

In any case, the two questions you pose are specific to the V-22, its size and its less than optimum disc area (imposed becuase of the shipboard requirement and other original JVX specifications when they tried to make it another F-111--all things to all people). They are not a function of Tilt-Rotor technology itself. JMR/FVL is for a smaller, and more agile vehicle, so it's not likley that those procedures would be required.
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Old 16th Apr 2013, 20:16
  #32 (permalink)  
 
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Are V22 flight envelope restrictions relevent to a completely different aircraft with purported lower downwash (and therefore disc loading)?

Bell claimed that lower disc loading on the BA609 incresed max RoD before VRS. Seems like they planned on a 800ft/min "normal operation limit" based on some sort of safety factor, since VRS occured 2000-5000ft/min. This is an old article, so I wonder if flight testing has since expanded the "normal" RoD limits.

Staying flexible - and safe

The issue of vortex ring state highlighted by the V-22 crash will be tackled mainly by training pilots to stay within the proper flight envelope, says Barbour, and by teaching them how to recognise and escape the condition. A form of rotary-wing stall, vortex ring state occurs when the aircraft catches up with the wake ejected by the rotor. "That will require a very high rate of descent in this aircraft because of our disc loading, and this is desirable for us," he says.

The normal rate of descent in the BA609 will be 300-500ft/min. At 800ft/min the pilot will receive an indication that descent rate has reached the limit of normal operations. This is well below the 2,000-5,000ft/min rate required to enter vortex ring state, says Barbour. And if the pilot does encounter vortex ring, escape will be a matter of tilting the nacelles down and applying power to accelerate out of the proprotor wake, he says.
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Old 16th Apr 2013, 21:45
  #33 (permalink)  
 
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History

CC, one interpretation of your note might be that the reasons cited at the time for the Marana and Eglin events were incorrect. Nonetheless, the accidents happened, and the descriptions of the flight situations involved in each weren't really out of the ordinary. As in, for instance, anyone ever get stacked up by the leader going into a hot LZ? Out of the 44K Vietnam pilots, there might be only 8-10 thousand in that category. Anyone ever get in the down wash of the ship in front while in formation? Same answer. Stuff happens and the JMR ought to be able to handle it. Is the argument that the JMR TR will be different, immune to V-22 proclivities? Bell will have to answer that query, and it will be interesting to see the response.

Not an anti-V-22 rant. It is a very fine machine, whose efficiency doing certain tasks is excellent. Every different rotor propulsion system has its strong points and compromises, be it single MR, tandem, coax, stiff coax, TR. Mission requirements will shine a bright light on which strong points and compromises make the most sense.

Thanks,
John
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Old 16th Apr 2013, 23:24
  #34 (permalink)  
 
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John,

Point I was making is that a TR is not more difficult or more dangerous, but it is different, and the tactics are as well. You've got those big proprotors blowing aft in forward flight, and the vector of that changes during transition as well. That's why they normally don't fly directly behind each other. The wake, if you will, is bigger than a comparable conventional helo.

By the same token, though, normally one conventional helo (or ABC) is not going to formate directly under another at close range, whereas with a TR you could, in forward flight.

As has been reported elsewhere, a refueling package is under study for the V-22. It already can normally refuel from a KC-135, which no helo can do, but it also has the speed to act as a tanker for fixed wings, for example USMC's F/A18s and AV-8s. It's still going to have its wake, but that's jsut something that will have to be planned for, just like it is for a -135, -130 or other tnaker. Of course, tanking operations won't be taking place at 500-100 ft. either! Flight testing will find out.

Accidents do happen, but they happen to everything. One of the more famous, for example, was the H-60 crash on Mt. Hood during a rescue attempt. From the video, it looked like a classic case of VRS, but could have also been a tail rotor malfunction.

It's not a matter of a JMR being immune to V-22 proclivities, they are differently sized aircraft performing a different mission. A JMR is not a V-22. It's a smaller aircraft with an optimally sized proprotor. Bell has already said they're looking at ways to reduce downwash in the hover, and that should also benefit the wake. As with anything, you have to make some choices. Do the speed, range and other advantages outweigh other factors that may be more problematical?

An ABC is going to have to answer the same questions, and it's going to have issues of its own. We have very little data on ABC, but a lot on TR. One of the things that came out in V-22 development is our computer models aren't as good as we thoght. We still need to do real flying to get answers and this will be true of ABC as well.

This isn't an anti-ABC rant, BTW. I'm simply saying that TR won't be the only advanced technology for which questions will have to be answered. Frankly, TR and ABC look like the only things to be viable to meet the Army's desires.

Last edited by Commando Cody; 17th Apr 2013 at 00:02.
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Old 17th Apr 2013, 02:02
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Reagan?

CC, now really! The Mt Hood to-do an example of VRS! As the Great Communicator might say: " There you go again". Not meant personally, of course, but the amount of misinformation promulgated in the wake of a few of the V-22 ooops events as regarding basic helicopters all being subject to VRS at the 40 kt/-800fpm boundary was simply unbelievable. Notice that one never caught the Project Pilot, Tom McDonald speaking thusly.

Anyhow, the Mt. Hood fiasco was a case of the pilot running the engines against the T4.5 limiter, drooping Nr, hence drooping tail rotor Nr as well. Rotor lift being a V squared function, the result was a descending right yaw spiral into the snow as the video showed. No mystery there.

It looks as though you at least are convinced that Bell now understands the shortcomings of the present TR design and has the answers as to how and why the Marana and Eglin events will be designed out of the next version. Have to say they have been really quiet about that aspect of things. And it is not simply a downwash velocity question alone, necessarily. When a few empty moments are available, do a hand calculation of the Marana blade loading number ( Ct/sigma ), allowing a reasonable addition for the increase required for the deceleration.

Not certain that I have read the JMR news correctly, but it appears that they want to have two competing prototypes, and I guess that means a fly-off. A very healthy and in the long run, a cost-effective way for the Army to know they have the right machine. The Army was quite thorough in the UTTAS fly-off, doing both an engineering and an operational comparison, using both their test pilots and a group of specially selected operational pilots ( including some with very little experience-on purpose ). Prior to the formal fly-off, there was a preliminary evaluation at Boeing and at Sikorsky, and that evaluation included power off landings ( not talking about power recoveries here ) for each of the three government pilots. Something else for the Bell TR folks to think about.

All of that in the future.

Thanks,
John
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Old 17th Apr 2013, 02:47
  #36 (permalink)  
 
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John,

I didn't say Mt. Hood was VRS, just that from the video it looked like it. Since I've never seen the accident report, I totally accept what you say...


Regarding a fly-off, I enthusiastically hope it is so. They always pay off in the long run, but because of the high upfront costs, they are now few and far between. In modern times we had UTTAS, AAH, A-X, ACF and then JSF (no I didn't forget ATF, that wasn't a flyoff-- 'nother story for a different time). I think we'd be well served by a flyoff between the two concepts, but I am not hopeful giving fiscal priorities.

There is an implication, I perceive, in your post that TRs can't autorotate to full landing. This is something that comes from the fact that the V-22 normally won't. That is true, because it wasn't required to. The requirement specified a survivable landing either through autorotation or through gliding to a short rolling landing. The V-22 team chose the latter. The larger the aircraft, the tougher an autorotation all the way gets to be to accomplish. A JetRanger does it nicely, the XV-15 was pretty good (although with only two they were not going to take it all the way), a CH-53, not so much. I suspect that if that is written in as a a pass/fail requirement, the V-680 will be able to do it, just like Sikorsky's JMR submission will.

I really hope we get a flyoff, but I'm not optimistic.
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Old 17th Apr 2013, 10:48
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Fly-Off

CC, your mention of the AAH fly off brought to mind some memories. You will recall that SA built the S-67 with company funds, and later, in 1971, equipped it with an external stores ( rockets and/or aux tanks ) and armament system. F-111 head up display with low light level TV, a 3-barrel 20 mm turret run off a helmet mounted display, ins driven dig-map etc, all pretty good stuff for that time.

By the time the AAH RFP came out, SA was in good position to compete, but was not selected for the fly-off. While the UH-60 started deliveries in 1978, the AH-64 didn't reach the Army until six years later. I was down at Ft Rucker shortly after that, and had a look at the AH-64 , which had adopted a flying stabilator. The way it is/was mounted, it was easy to look at the installation and the actuator. Guess what: the actuator part number started with 70xx.... It was a Sikorsky Blackhawk stabilator part. Nothing illegal, of course, as the design belonged to the government.

Water under the bridge, and I supposed that DOD did not want too many eggs in one basket, but I always believed that if SA had been selected for the AAH fly-off, the SA candidate would have won and certainly been in the hands of the Army pilots a lot earlier than 1984.

Thanks,
John
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Old 17th Apr 2013, 16:54
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Being a history buff the illustrations of the Valor reminded me of designs for tilt rotors produced by Raoul Hafner in the 1960s ,using the same basic engine/tilting gearbox design. Anyone else do similar?
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Old 17th Apr 2013, 17:15
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Can't say I have ever seen anything from Hafner that approached a tiltrotor. Everything I recall from memory resembled an autogyro. Do you have any links/images?
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Old 17th Apr 2013, 18:00
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Anyone else do similar?
Heli1: There were several tilt-rotor types subsequent to the 1955 Bell XV-3 including a number of 'tilt-wing' projects one of which was the 1964 NASA testbed the XC-142 which I always thought looked most interesting:



And if you wanted something where the just the rotors tilted then the ducted fan Doak VZ-4 was another interesting contraption:

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