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Rockwell NR-356 Sea Control Ship (SCS) V/STOL fighter (XFV-12A)

KnightTemplar

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The Rockwell International XFV-12A, a thrust-augmented wing prototype supersonic fighter/attack aircraft, was designed to operate from small ships. The single engine, single seat prototype aircraft used parts from the A-4 and F-4; the fuselage was 44 ft long with a 28.5 ft wingspan and a 12 ft canard span. Operational vertical take-off weight was expected to be 19,500 lb, with a maximum speed of over Mach 2 anticipated by Rockwell.

In the fall of 1972, the US Navy issued a request for proposals of the next generation V/STOL aircraft. Unfortunately, the list of candidates did not include any further development of the Harrier. Instead, the Navy favored the North American Rockwell XFV-12A supersonic fighter design. The XFV-12A used a thrust augmentation scheme that diverted the total exhaust flow of the main engine and ejected it through a venetian blind arrangement in the wings to give vertical-lift capability. The concept was considered by many to be very risky when compared with the proven Harrier approach, but the Navy was prepared to fully fund the development of the aircraft and close out further development of the Harrier.

The results of the tests at Langley influenced the Navy’s decision to cancel the XFV-12A Program. Lift improvement testing and plans to modify the ejector/augmentor system were discontinued in 1981 due to cost overruns and waning Navy V/STOL interest.

The Rockwell XFV-12 was a prototype supersonic United States Navy fighter which combined the Mach 2 speed and AIM-7 Sparrow armament of the F-4 Phantom II in a VTOL fighter for the small Sea Control Ship which was under study at the time. On paper, it looked superior to the subsonic Hawker Siddeley Harrier attack fighter. It's augmented wing concept was somewhat like Lockheed's unsuccessful XV-4 Hummingbird. Such arrangement restricted weapons carriage to under the narrow fuselage and 2 conformal missile mounts. Its canards were extremely large, with almost 50% of the area of the wings, making it effectively a tandem biplane.

Over the course of six months, it was determined that the XFV-12A design suffered from major deficiencies with regard to vertical flight, especially a lack of sufficient vertical thrust. Lab tests showed that 55% thrust augmentation should be expected, however differences in the scaled-up system dropped augmentation levels to 19% for the wing and a mere 6% in the canard. While the augmenters did work as expected, the extensive ducting of the propulsion system degraded thrust. In the end the power-to-weight ratio was such that the engine was capable of vertically lifting only 75% of the weight of the aircraft.

After it's cancellation Aviation Week published an article with drawings of an even more ambitious proposal to fit a similar wing to the huge C-130 Hercules, but that plan never made it off the drawing board.

Do you think they should have stuck with it or do you think they did the right thing by abandoning the project? Does anyone think that the thrust-augmented wing concept can, will, or should be used on future combat aircraft?
 

elmayerle

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In this engineer's humble opinion, they were right to cancel this program. Like other thrust ejector augmentation approaches, this one failed due to duct loses in the scale-up from demonstrator rig to full-scale flight-worthy article. IMHO, given the dismal track record of ejector augmented lift programs (0 for 2 - XV-4A and XFV-12A), further such efforts should be foregone in the future unless there's some dramatic new developments that can be proven by full-scale rig testing.
 

Archibald

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Yeah, better option would have been its competitor, the General Dynamics 200. This one was really similar to the soviets Yak 36 /38 /41 in the sense that it had a tilting rear exhaust plus two lift jets behind its cockpit.
Despite its defaults (hot gases reingestion) this layout WORKS rather well.

I'm planing a model of the General Dynamics design using a Gripen as basis...

For more info on the GD 200A, browse the "US V/STOL projects" thread. 9 pages of oddball designs (I'm fond of the well-named NUTcrakers designs ;D)
 

stevoe

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KnightTemplar said:
...After it's cancellation Aviation Week published an article with drawings of an even more ambitious proposal to fit a similar wing to the huge C-130 Hercules, but that plan never made it off the drawing board...

Did you know more about this project? Did you have the drawing? Thank you!

Regards from Germany
Stephan
 

Deino

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stevoe said:
KnightTemplar said:
...After it's cancellation Aviation Week published an article with drawings of an even more ambitious proposal to fit a similar wing to the huge C-130 Hercules, but that plan never made it off the drawing board...

Did you know more about this project? Did you have the drawing? Thank you!

Regards from Germany
Stephan


Hi ... nice to meet You here ! :)

Here it is ... just look at reply no. 40 from Jemiba !

http://www.secretprojects.co.uk/forum/index.php/topic,219.msg16810.html#msg16810

Cheers, Deino
 

Archibald

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Thanks a lot for the NAR-382 drawings! This project is mentioned in Le Fana de l'aviation, april 2003 (article on the XFV-12 by A.Rocher). For four years I've tried to imagine this VTOL, F-100 Hercules... :D
 

stevoe

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Deino said:
Hi ... nice to meet You here ! :)

Here it is ... just look at reply no. 40 from Jemiba !

http://www.secretprojects.co.uk/forum/index.php/topic,219.msg16810.html#msg16810

Thank you, old Chinaman! ;) ;D

Regards
Stephan
 

Rafael

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Does anyone of you have a diagram with formers/cross-sections of this wonderful XFV-12?

Rafa
 

Rafael

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Thanks Orionblamblam!!!

I understand that one of the reasons behind this project being cancelled is the difference of "scale size air/gas flow" vs. "real size air/gas flow". Am I correct?

And is this configuration/architecture (if doable) less prone to suffer hot gas reingestion?

Rafa
 

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The theory behind it, as I remember it, was sort of a derivative of the jet flap theory. It's basically designed to increase efficiency, in the sense that the hot gas being ejected out of the augmenter/flaps would "entrain" the large mass of cool air on either side and cause a greater air mass flow then just what goes through the engine to be available for lift. So basically, they were trying to increase the mass flow of air available for lift without having to use a bigger engine. However, you lose so much thrust in duct losses from routing the mass flow to where it needs to be that it simply wasn't workable on a full scale aircraft.

It always seemed somewhat of a Rube Goldberg idea to me anyway. With all of the ducts and augmenters, do you really have enough room for fuel for it to be useful? Also, maintenance probably would have been a nightmare.
 

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For a fighter ejector-augmentors seem a bad idea even if they work, as the volume they take up is so great. Also lots of drag in transition and 'interesting' control issues, both of which I think 'did for' the GD E-7.

On the XFV-12 I heard that the engineer in charge of building it tried to cut corners by using crude details in the internal pipework, making pressure losses worse than they could have been.

Another of the engineers on the project later came up with the idea of the shaft driven lift fan, once he moved to Lockheed. He is a great proponent of ejector-augmentors still, and on the F-35B incorporated the idea, in a partial way - only half the lift actually comes from the vertical fan itself, the other half coming from the airflow around the fan inlet, which is how ejector-augmentors mostly work, by inducing additional airflow over favourably shaped bits of the airframe.
 

Archibald

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Glad to see you here! Aqui tienes un monton de projectos para tu modelos!
 

Sundog

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which had been been used by North American (later Rockwell) A-5 Vigilante...

And the F-104. Unfortunately, Jet flaps are much simpler and with less losses since they are just re-energizing the flow over the flap while it's moving, rather than trying to produce an entire augmented flow with a vehicle velocity of zero.
 

Archibald

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In fact it works for STOL, but not for VTOL... it's a bit like jet or props deflexion, which worked (and still works!) nicely on STOL cargoes (An-72, Br.941, C-17) but not on VTOL machine (think it was the VZ-14, this one never hovered correctly, it was too unstable...)

Blowned flaps have widely used, the Buccaneer also used this system if I remember well...
 

Weaver

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First UK aircraft with blown flaps was the Scimitar. The Buccaneer blew the whole of the wing leading edge as well, and the underside of the tailplane in order to give it enough control authority to balance the increased lift from the blown wing.

On the subject of the XFV-12, according to American Secret Projects - Fighters, NAVAIR's evaluation rated the XFV-12 worst of all the proposals, most of which were sensible(ish) lift+lift/cruise designs, on every count, and yet they decided to build it over all the rest anyway. This seems exceptionally perverse even for a military procurement decision, so I wonder if there was some politics going on here too. The aircraft being evaluated were for service on the Sea Control Ship, which many USN aviators saw as a threat to their beloved super-carriers, so it occurs to me that maybe the XFV-12 was chosen as way of indirectly sabotaging the SCS by making sure it never got a credible aircraft to operate.

Any thoughts, or better yet, any dirt to dish? ;)
 

Archibald

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One of the most interesting contenders was the Grumman entry (think it was type -201). I've build a 1/72 scale model of this machine last year (a Mirage 2000 / X-35 hybrid)
 

sferrin

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My favorite was the 200A. Like a Yak-141 but 20 years earlier.
 

Pyrrhic victory

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Weaver said:
Any thoughts, or better yet, any dirt to dish? ;)

According to George Spangenberg, Evaluation Division Director of NAVAIR, the push for the XFV-12 came from NAVMAT. Specifically from Rear Admiral Thomas Davies head of R&D at NAVMAT, who felt that the Navy's frigates and destroyers could not do the ASW mission, and small carriers with ASW helos could get the job done. Naturally, said carriers would need air defense if they were going to operate on their own, AEGIS being nearly a decade away, and in 1972, in an unprecendented move by NAVMAT, feelers were sent out to the aerospace industry for a VTOL long range senor aircraft and a high perfomance VTOL fighter. A wide variety of proposals from the industry came back, and NAVMAT had NAVAIR review them. The submissions were all over the place, ex C-130 variant, because the Sea Control Ship was so poorly defined. As you mentioned before a lot of squids were worried that a supplement such as the SCS would end up being shoehorned in as the main type of carriers due to budgetary concerns.

This was at the time in the OSD that prototyping was all the rage and the Navy would be allowed one prototype. The three final fighter designs considered were the McAir's AV-16, Rockwell's North American Columbus Division's FV-12 and General Dynamic's Convair Division 200. Using the lift+cruise VTOL method, the Convair 200 coming in first place because it could do the air-to-air well and possibly air-to-ground, the Harrier variant AV-16 placed second as it couldn't do the a2a mission being so slow, but had a2g capability and the thrust augmented wing FV-12 dead last since it would not be able to do either role effectively. NAVAIR gave a presentation to NAVMAT recommending that work on a lift engine be started before prototype of a fighter be ordered, and for the sensor aircraft a modified OV-10 with thrust augmentation system could be prototyped at minimal cost. Adm. Davies took the charts from the NAVAIR presentation then modified and cherry picked the data for his FV-12 sales pitch to Assistant Secretary of the Navy Frosch, who gave the green light. With NAR-Columbus promising Mach 2.0 speed and 55% lift augmentation, the project also had support from OpNAV's "high risk, high pay off" officers. The aircraft was chosen a the Navy's aircraft to prototype and funded.

Soon there after NAVAIR's reservations about the design reached Assistant Secretary Frosch, and he blew a gasket. Frosch called in representatives from NAVMAT, CNO, CNM and NAVAIR to talk the project over, stating he never wanted any project to be pitched to him again without both sides of the story being told. The next year, Dr. Frosch left the Navy for the UN Environmental Program and then NASA. Adm. Davies, the instigator of the program, retired from the navy to become Assistant Director of the United States Arms Control and Disarmament Agency which he held for 7 years. Ground testing of the engine began in 1974. NASA wind tunnel studies showed that the vertical lift figures were overly optimistic, yet the program still continued. *insert VTOL sabotage conspiracy theories here* In 1977, 5 years after go ahead, the first (and after the second was cancelled) and only prototype was rolled out, cobbled together from various A-4 and F-4 parts with a still uncertified engine originally meant for the F-14 (F401). In a 6 month period in 1978 during tethered test the XFV-12A was only able to achieve vertical flight under its own power a total of once, earning it the title of "ground hugger-1". The augmented lift wing only deliver 25% vertical thrust, only enough to lift 75% of the airframe's total weight, primarily due to loss of thrust through extensive ducting. It didn't help either that the airframe was overweight.

Mercifly the program was terminated in 1981, ending nearly a decade of unadulterated failure on all levels.

SOURCES:

George Spangenberg's Oral History
http://www.georgespangenberg.com/history3.htm (XFV-12 is mentioned towards the end)

Supplemental Exhibits

Other sources:
 

Weaver

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Cheers Pyrrhic, that's very interesting.

I'll have a look at George Spangenberg's site when I get the chance: I noticed that it's quoted quite a lot in ASP - Fighters.
 

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Quite a rare photo I suppose. Enjoy.
 

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frank

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Exactly which version of the An-71 had the underwing engines? All pics & drawings I've ever seen had the overwing engines. Not that I've seen them all mind you, but I've never seen one with an underwing layout.
 

F-14D

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Weaver said:
First UK aircraft with blown flaps was the Scimitar. The Buccaneer blew the whole of the wing leading edge as well, and the underside of the tailplane in order to give it enough control authority to balance the increased lift from the blown wing.

On the subject of the XFV-12, according to American Secret Projects - Fighters, NAVAIR's evaluation rated the XFV-12 worst of all the proposals, most of which were sensible(ish) lift+lift/cruise designs, on every count, and yet they decided to build it over all the rest anyway. This seems exceptionally perverse even for a military procurement decision, so I wonder if there was some politics going on here too. The aircraft being evaluated were for service on the Sea Control Ship, which many USN aviators saw as a threat to their beloved super-carriers, so it occurs to me that maybe the XFV-12 was chosen as way of indirectly sabotaging the SCS by making sure it never got a credible aircraft to operate.

Any thoughts, or better yet, any dirt to dish? ;)


The SCS died when it became apparent that the technology for the aircraft it required to work simply wasn't there. It also died once it was realized that to deliver meaningful airpower the SCS concept was more vulnerable, less responsive and in fat more costly than supercarriers. I suspect the reason they went for the XFV-12 was a "roll the dice" maneuver. If it had worked, it might have offered a way for the technology of the day to provide a viable VTOL fighter, since none of the others would. If it didn't work, they were no worse off than they already were. Lift + lift cruise looks great on paper, but isn't viable in the real world. It wasn't until DARPA's pioneering work in fan technology advanced to the point where you could have a "virtual" lift engine (as in the F-35B) that this concept merited consideration.
 

Archibald

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If it had worked, it might have offered a way for the technology of the day to provide a viable VTOL fighter, since none of the others would.

Maybe the Grumman would ? the Yak-41 didn't worked too bad...
 

LowObservable

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Of course, it did not help that the goal for the V/STOL fighter was always the F-18's specified performance. Since the F-18 itself missed its specs by a mile, this was a tall order.
 

sferrin

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It seemed to work pretty good on the YC-14.
 

hs1216

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just out of curiosity, was the xfv-12 capable of preforming conventional takeoff
 

F-14D

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Archibald said:
If it had worked, it might have offered a way for the technology of the day to provide a viable VTOL fighter, since none of the others would.

Maybe the Grumman would ? the Yak-41 didn't worked too bad...

Actually, the YAK-41 didn't work all that well. For one thing, it had to use afterburner for takeoff or landing. Ashore, this resulted in it tearing up the surface underneath while throwing FOD around. At sea, the Gorshkov had to have a special system to mitigate the heat from the exhaust through water cooling

The bigger problem with the YAK and with lift + lift/cruise in general is that

1. You have to develop an unique lift engine.
2. Except for a few moments at takeoff and landing you have to haul around an enormous amount of dead weight for most of the flight (by contrast, on the AV-8B, the V/STOL unique portion of the powerplant is only a few hundred pounds).
3. The fuel supply system has to be fairly complex in order to supply the two different propulsion systems
4. The control system has to be fairly complex because you are using two independent systems to provide your powered lift.
5. There is a lot of "noise" right behind the cockpit.
6. You've got to protect the crew from the effects of blade separation, vibration and heat.
7. A lot of space that could be used for fuel or other things is lost.


The breakthrough achieved by DARPA and Lockheed with the lift fan avoided problems 1-6 and minimized the impact of 7.

To my mind lift = lift/cruise is sort of like tailsitters: An engineering exercise that looks good on paper, but is not practical in the real world.
 

flateric

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GTX said:
Not to mention the An-72/74 series.

While being quite right for -72, not so right for -74 with its new wing, that almost lost Coanda effect magic. We've already discussed this subject somewhere.
 

AeroFranz

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I was told by someone who was working at Rockwell at the time that the results of wind tunnel tests would leave that section with certain values, then go through management and come out with different (much improved) ones. The poor results achieved by the ejectors were no surprise. In VTOL design, the key to succes is to not torture the gas paths with bends and small diameter pipes (see Harrier, F-35...). The ejector idea might have had half a prayer if they had a long aspect ratio ejector "trench", which the XFV-12 did not have in either canard or wing.
 

Artie Bob

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I worked with a former NA Rockwell test engineer who had participated in this project at Columbus. He told me that the management of the project, particularly from the technical side (something about Phds descending from their ivory towers to the dismal reality of the full size hardware), was pretty bad. He also indicated that the concept did not work well and most changes made just made things worse. All second hand and many years ago, but it seems to fit with the previous post.

Best Regards,

Artie Bob
 

LowObservable

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USB = scrubbing drag = eats lunch.

At least, that's what I told the Allison guys when I saw the first EMB 145 design. I assume somebody at Embraer figured that out too. Otherwise I left a small mark on the business.
 

LowObservable

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LPLC versus The Shaft -

1. You have to develop an unique lift engine.
The installation (inlet and nozzle) is the same whether the fan's powered by a shaft and clutch, or a gas generator. Essentially, in development terms, you get rid of the HP section and LP turbine, but have to design, build and test the drive mechanism.
2. Except for a few moments at takeoff and landing you have to haul around an enormous amount of dead weight for most of the flight (by contrast, on the AV-8B, the V/STOL unique portion of the powerplant is only a few hundred pounds).
I'd be interested to see the real-world comparision between a lift engine installation and the shaft-driven solution, but would bet the difference would not be that large. XJ99 had a 20:1 T/W ratio in the 1960s.
3. The fuel supply system has to be fairly complex in order to supply the two different propulsion systems
You do get a savings there.
4. The control system has to be fairly complex because you are using two independent systems to provide your powered lift.
An extra FADEC box or two.
5. There is a lot of "noise" right behind the cockpit.
6. You've got to protect the crew from the effects of blade separation, vibration and heat.
Same for LPLC and SDLF.
7. A lot of space that could be used for fuel or other things is lost.
I'd guess that the LPLC would be more compact because of the volume occupied by the shaft.

And, as we're seeing now, SDLF makes the design of the main engine's LP turbine difficult.
However, there was a huge degree of prejudice against LPLC in the JSF process up to 1996. It was indicated early on that the Marines' logistics people did not want a second engine. Also, the SDLF looked good because of its potential for eliminating puffers - the shaft gives very rapid front-to-rear thrust transfer. We'll see whether it was the right thing to do.
 

hesham

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Hi,

in old magazine,I remember that I saw an artist drawing to a project
developed from XFV-12,but with inverted wing position,the canard
wing was high and the rear one was low.
 

AeroFranz

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Frank,

The model with underslung engines is the An-74 TK-300 (I think). The mods are limited to the engine (fuselage is the same, wing too). I guess they seem to think the USB scrub drag was too penalising.

Regarding the An-71 'Madcap', plenty of goodies here:
http://www.airwar.ru/other/draw/an71.html

I am not sure, but the third engine might be used as an auxilary propulsive unit (for takeoff)/oversize APU for the sensors.
I think some other US AEW concept had explored the possibility of putting the rotodome on top of the vertical..anybody know what i'm referring to?

regards,
Francesco
 
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