What happened to RALS?

Rafael

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Yeah, Whatever happened to RALS?
I think it was a great "paper" concept, but, what were the reasons such advanced Remote Augmented Lift System dissapeared from the R&D programs?
 

elmayerle

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Well, it's only my informed opinion, but I'd hazard a guess that large-scale rig testing found either too high duct losses in getting to the remote augmentor or the fuel flow requirements for a full-scale aircraft were prohibitive. You can also add in the effect such a hot lifting thrust would have on 'most any umprepared surface.
 

sferrin

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I remember reading somewhere that the general concensus on RALS was that it would make a good post-hole digger.
 

Rafael

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Interesting. As is the case of the XFV-12, discussed in another thread, all those attempts to achieve vertical sustained lift "crashed" for duct loss.

Then, is direct lift, be it two, three or four-poster the only way to achieve vertical take off?

In your opinion, true, economical, practical VTOL is achievable?

I think STOVL, V/STOL, STOBAR and other variations that escape me at the moment are nice and have all their place, but are a substitute to real vertical envelope operations.

I remember something Mr. Sikorsky said about the helicopter never surpassing the airplane in terms of speed and performance, and the airplane never equaling the helicopter's hover capability.

Rafa
 

Archibald

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Seems that there's only 3 viable ways of making a viable V/STOL fighter... all use a tilting exhaust (so that you can use power of the horizontal engine in V/STOL mode)

But the tilting exhaust only lift the rear of your fighter... you need something else to lift the forward part of your fighter ;)
Interestingly, 3 countries (USA, GB and Russia) found 3 differents solutions to the problem...
GB' Harrier use cold air deflected from its Pegasus fan. Good thing is, no dead weight in conventional flight. Bad thing : you need a BIG compressor to do the job

US F-35 prefer having two compressors, one for its F-135 engine, other dedicated to V/STOL mode. Of course the latter become dead weight in conventional flight...

Russian Yak-41 had no fan at all, rather full jets engines (lift jets). Hot gases, more fuel consumption, but at least the system is viable...

Et voila!
 

TinWing

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Archibald said:
Seems that there's only 3 viable ways of making a viable V/STOL fighter... all use a tilting exhaust (so that you can use power of the horizontal engine in V/STOL mode)

But the tilting exhaust only lift the rear of your fighter... you need something else to lift the forward part of your fighter ;)

I guess you forgot about the X-32B.

Archibald said:
Interestingly, 3 countries (USA, GB and Russia) found 3 differents solutions to the problem...
GB' Harrier use cold air deflected from its Pegasus fan. Good thing is, no dead weight in conventional flight. Bad thing : you need a BIG compressor to do the job

Actually, opinion has always been highly divided as to V/STOL concepts. For instance, Rolls Royce continued to promote the lift engine concept - as used in the French Balzac and Mirage III-V, long after the Kestrel proved the 4-poster concept. Rolls Royce even produced its own scaled down 4-poster engine, which was meant to be combined with separate lift engines.

The most recent instance in the United State, the JAST/JSF competition witnessed a flyoff between two very different concepts that both were viable - to some extent.

Archibald said:
US F-35 prefer having two compressors, one for its F-135 engine, other dedicated to V/STOL mode. Of course the latter become dead weight in conventional flight...

To the contrary, the NG/MD JSF entry was rejected largely because of its separate lift engine.

The X-35B's arrangement is unique in being shaft driven from the main engine, which solves the exhaust gas ingestion issue.

Archibald said:
Russian Yak-41 had no fan at all, rather full jets engines (lift jets). Hot gases, more fuel consumption, but at least the system is viable...

It is not entirely clear that the Yak-41 was entirely viable. The ground errosion and gas ingestion issues apparently remained unsolved when the funding was cut.

The Yak-41 did have a very clever 90 degree vectored exhaust for it main engine, a feature that Yakovlev contributed to the JSF program, but beyond that the Yak-41 was just as flawed as any separate lift engine concept.

Of course, the Yak-41's predecessor, the Yak-38 was truly remarkable only for its automatic ejection seat! If the Yak-41 had ever made it into service, this feature would have been invaluable because a tremendously high attrition rate would have been inevitable.
 

Rafael

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I may be risking to be given a highly technical explanation, but, Is the shaft-driven fan like the one in the F-35 more efficient in terms of thrust/energy consumption than duct flow transfer?

Is the shaft length an issue?

And the force having to transit through gearboxes to move the fan are also a liability (in terms of energy loss)?

Thanks,
Rafa
 

Archibald

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Yups, I have too look again at my Italeri X-32. ;D
I thought this one had a tilting exhaust... ??? Is there two separate exhausts on each side of the fuselage, like the Harrier ? I stand corrected...

Actually, opinion has always been highly divided as to V/STOL concepts

you said it... its just like spaceplanes concepts, it's very hard knowing what is viable or not... :-[

The thruth is, that V/STOL fighters will always be compromised designs... range of the F-35B (V/STOL variant, its the -B, never remember!) is inferior to its siblings...

The X-35B's arrangement is unique in being shaft driven from the main engine, which solves the exhaust gas ingestion issue.

Yeah, the big fan produce a huge mass of cold air which blast away hot gases. Seems Lockheed made a film of a hovering X-35 with an IR camera, results are spectacular...

Of course you need a very solid gearbox to transmit engine power to the fan...
 

Jeb

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Archibald said:
the tilting exhaust only lift the rear of your fighter... you need something else to lift the forward part of your fighter ;)
Interestingly, 3 countries (USA, GB and Russia) found 3 differents solutions to the problem...
GB' Harrier use cold air deflected from its Pegasus fan. Good thing is, no dead weight in conventional flight. Bad thing : you need a BIG compressor to do the job

US F-35 prefer having two compressors, one for its F-135 engine, other dedicated to V/STOL mode. Of course the latter become dead weight in conventional flight...

Russian Yak-41 had no fan at all, rather full jets engines (lift jets). Hot gases, more fuel consumption, but at least the system is viable...

I think you've got some of your facts mixed up.

The Harriers, first off, do use tilting exhausts, but remember, there are four of them at midbody. The front two blow "cold" air and the rear two blow hot exhaust. But technically, all of the lifting force is at mid-body, not at the tail and up front.

The X-32 took that concept a step forward, retaining the forward set of cold-air lift nozzles (that tuck up into the body when not in use) but went to a traditional rear-exit exhaust that lifts the tail.

The X-35 has the shaft-driven lift fan up front. I'd wager that it has more dead weight when not in use than the X-32's system, but like others mentioned, the benefits of the massive amounts of cooler air that it pushes in the hover are pretty significant. Plus, without the fan, there's a nifty void behind the pilot that could hold more fuel, or could hold some sort of assembly that can make use of that shaft coming forward from the engine. Imagine all that power driving a generator...you'd have an awesome jamming platform or maybe even enough juice to power a laser.

In my mind, that has to have been part of the reason that the X-35 won. There is just so much potential there for advanced engineering.
 

elmayerle

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Rafael said:
I may be risking to be given a highly technical explanation, but, Is the shaft-driven fan like the one in the F-35 more efficient in terms of thrust/energy consumption than duct flow transfer?

Is the shaft length an issue?

And the force having to transit through gearboxes to move the fan are also a liability (in terms of energy loss)?

Yes, the problems with duct flow transfer were why the air-driven lift fan originally intended for the NG/MD JSF entry was scrapped and a separate lift engine adopted, automatically removing this entry from the competition because one of the rules was one engine for lift and cruise. Shaft length isn't an issue and while the gearbox loads are higher, due to the higher power levels involved, most of the technology for this has been dealt with over the years with the development of drive shafts for AMAD (Aircraft Mounted Accessory Drive) gearboxes instead of mounting all the accessories on the engine (does wonders for expediting engine changes). The engine gearbox is again based on this well-developed work while the lift fan gearbox is based on considerable operational experience (not military, but in a very competitive environment) with transmissions having to handle sudden inputs of a thousand horsepower and more (again, another case where JSF is dropping the NIH attitude and "looking outside the box" for solutions).

Oh, for the 3-/4-poster approach, Vought suggested a differnt way of dealing with the large airflow needed for vtol, the tandem fan concept (see their TF 120) but I surmise that it had its own mechanical and/or operational complexities that argued against adoption.
 

Jeb

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elmayerle said:
the lift fan gearbox is based on considerable operational experience (not military, but in a very competitive environment) with transmissions having to handle sudden inputs of a thousand horsepower and more (again, another case where JSF is dropping the NIH attitude and "looking outside the box" for solutions).

Let me guess...drag racing?
 

Rafael

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Thanks, Guys, this is getting very instructive.

Ay, Caramba! Evan!!, I forgot totally about the tandem Fan!!! That's another wonderful concept, but I wonder if a few extra compressor stages (I am over-simplifying here) in front of the mains would be as effective as the F-35 separate compressor arrangement?

Rafa
 

overscan (PaulMM)

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As far as I recall, the main difference is the front compressor is horizontally mounted rather than vertically, and that it is driven directly from the main engine shaft without a gear box. I imagine vertical thrust would therefore be less, with losses incurred in turning the exhaust gases downwards (plus the fan diameter is restricted). On the plus side, the compressor would contribute to forward thrust in non-vertical-flight mode by adding extra compression stages to the core engine.
 

elmayerle

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Jeb said:
elmayerle said:
the lift fan gearbox is based on considerable operational experience (not military, but in a very competitive environment) with transmissions having to handle sudden inputs of a thousand horsepower and more (again, another case where JSF is dropping the NIH attitude and "looking outside the box" for solutions).

Let me guess...drag racing?

You got it!! Though there's technology feed in from other areas, such as high-performance aircraft brakes for some of the details.
 

elmayerle

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Jeb said:
The X-35 has the shaft-driven lift fan up front. I'd wager that it has more dead weight when not in use than the X-32's system, but like others mentioned, the benefits of the massive amounts of cooler air that it pushes in the hover are pretty significant. Plus, without the fan, there's a nifty void behind the pilot that could hold more fuel, or could hold some sort of assembly that can make use of that shaft coming forward from the engine. Imagine all that power driving a generator...you'd have an awesome jamming platform or maybe even enough juice to power a laser.

The area where the lift fan is in the F-35B is occupied by a fuel tank in the F-35A and F-35C.
 

Archibald

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Yes it very instructive Rafa!
In fact we can consider that the Vought TF-120 concept, the Harrier, and
F-35 all use a compressor for lift, but in three different ways... on the Harrier, air is taken on the Pegasus compressor and ejected by tilting ducts, on the Vought and F-35 there's a compressor "dedicated" to V/STOL. Difference between the two as be explained before by Overscan...

That's truly fascinating!
 

Rafael

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Fascinating indeed!!!
I find the form/function factor a curious way of implementing "variations of the same theme", be it from the use of extra stages, a big Fan, or dedicated compressors/jets.

The way labs tests fail in real-scale prototypes is somewhat dissappointing, but gravity is a reality we must face every second.

One question: In the F-35B the space behind the cockpit is used by the Fan. In the CV and CTOL variants there's fuel there. Is there an aerodynamic difference purposely built in these later two to counter differences in weight/CG (if any)?

Rafa
 

Archibald

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I find the form/function factor a curious way of implementing "variations of the same theme", be it from the use of extra stages, a big Fan, or dedicated compressors/jets.

Yeah, I wanted to say something like that, but my english is not strong enough :D
"Variations on the same theme", that's the expression...
 

Jeb

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elmayerle said:
Jeb said:
The X-35 has the shaft-driven lift fan up front. I'd wager that it has more dead weight when not in use than the X-32's system, but like others mentioned, the benefits of the massive amounts of cooler air that it pushes in the hover are pretty significant. Plus, without the fan, there's a nifty void behind the pilot that could hold more fuel, or could hold some sort of assembly that can make use of that shaft coming forward from the engine. Imagine all that power driving a generator...you'd have an awesome jamming platform or maybe even enough juice to power a laser.

The area where the lift fan is in the F-35B is occupied by a fuel tank in the F-35A and F-35C.

True, but the shaft-driven generator and the potential for devices to be powered by it has been getting a lot of attention. My sources ( ;) ) tell me, for example, that LockMart has been testing an F-16 flight sim with a laser weapon, just seeing what they can do with it. And we know that the USAF currently has a glaring lack of tactical EW capability, but the only jamming solutions available right now to tacjets have propellor-driven generators on external pods. An aircraft with as much available internal volume as an F-35 could generate its own power and internalize its own jammer hardware. And so it goes.
 

elmayerle

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Rafael said:
Fascinating indeed!!!
I find the form/function factor a curious way of implementing "variations of the same theme", be it from the use of extra stages, a big Fan, or dedicated compressors/jets.

The way labs tests fail in real-scale prototypes is somewhat dissappointing, but gravity is a reality we must face every second.

One question: In the F-35B the space behind the cockpit is used by the Fan. In the CV and CTOL variants there's fuel there. Is there an aerodynamic difference purposely built in these later two to counter differences in weight/CG (if any)?

The main aerodynamic differences are more to accomodate the fan and its associated doors et al. than anything else, to the best of my knowledge. By the time you get it faired in properly behind the cockpit, there's less drag to extend the fairing aft and gain some tankage.

I'd be surprised if our AD or PD folk haven't looked at other uses for the volume used in the F-35B by the lift fan. However, they are quite a closed-mouth bunch and, really, unless we get a contract, design or study, for it, I don't honestly have a "need to know".
 

Rafael

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Maybe this has been covered somewhere else, but it seems to me that the F-35B, even though lacking the total fuel capacity of the other versions is a longer-ranged airplane than the Harrier?

Rafa
 

LowObservable

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Jet velocity/temperature killed RALS. As far as I know, too, it was realized by the late 1980s that any solution employing afterburning in VL mode was a non-starter for land-based operations, although there were ways of handling it in terms of ship design. IIRC the Yak-141 hovered, but did not land vertically, at Farnborough in 1992.
There are several basic challenges.
1. Provide an adequate thrust/weight ratio for VL (permitting a practical aircraft with payload) with an acceptable exhaust velocity
2. Point said thrust vector through the CG
3. Manage issues of flight control through transition, hot gas ingestion
4. Avoid flight-safety or ineffiency snags
At that point it really depends on what your other mission requirements are. Frankly, a Marine-type CAS/limited air defense mission could be done very nicely thank you with a modernized Harrier solution or a variant of the X-32 layout.
For more demanding requirements - where stealth and internal weapon bays add weight and restrict inlet designs - then lift plus lift-cruise is attractive, but LPLC was ruled out in JSF from the logistics viewpoint. The shaft, transmission and clutch will probably always need more maintenance than a lift engine, but there you go.
 

Rafael

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Thanks LO!
Now I start to see it more clearly.

So a question arises, and half-answers itself: What if there were RALS concepts using more than one engine, to alleviate erosion and temp?


Rafa
 

LowObservable

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Not sure it would make a difference - the jet velocity and temp would be the same. Temperature softens surfaces, and velocity causes a pressure drop. Hence the flying manhole-covers in the early P1127 tests.
 

Mike Pryce

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So a question arises, and half-answers itself: What if there were RALS concepts ....... to alleviate erosion and temp?

There was an idea to use a system called RULS - Remote unaugmented lift system - from GE IIRC, early 1990s, which was just RALS with the front burner removed. This came about at the same time that Rolls Royce (with P&W) evolved the RB.571 Mixed Flow Vectored Thrust engine. Both were a response to the apparent failings of RALS, advanced vectored thrust and tandem fan. The RB.571 incorporated aspects of both RALS and TF, as well as the Pegasus.

The basic problem is that supersonic speed, agility etc. need hot jets, and jet-borne flight is easier on the environment and aircraft engine/structure (gas ingestion, erosion, noise) with cool jets. The attempts to find a practical compromise between these contradictory aspects is central to the almost endless struggle for a workable supersonic V/STOL aircraft. RULS would have needed a bigger basic engine than RALS for the same vertical thrust (or the forward flow ducted from the mixed flow of the fan and core, which would have needed thermally lagged ducts). The RB.571 got round this by boosting fan flow in vertical lift through using larger rear nozzles, allowing the back pressure on the turbines to be reduced and work increased, which is how the F-35B powers its lift fan.

Pics below show cool (blue), hot (red), bl*ody hot (yellow) flows. Note that the RB.571 looks like the X-32 propulsion concept plus a forward cool flow, and that if you turn the front fan of the tandem fan through 90 degrees you almost have the X-35 system. The same problems can lead to similar solutions, but with STOVL the devil is always in the detail, so it is hard to say what would have worked until flown (or not e.g. XFV-12).


Personally I agree that
a Marine-type CAS/limited air defense mission could be done very nicely thank you with a modernized Harrier solution or a variant of the X-32 layout
and don't really see the point of STOVL in other missions.

Finally, on RALS, I think it was workable in vertical lift, as long as the front burner was at moderate temperatures, and promised better 'up and away' performance than, say, vectored thrust/PCB. However, transition would have been an issue with various valves opening and closing and limited front nozzle vectoring, while the extra volume is not good in a fighter and duct losses could have been an issue. In the absence of any major tests (I think GE bench tested a burner) it would have been asking a lot to launch a programme on the back of it.
 

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Jeb

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elmayerle said:
I'd be surprised if our AD or PD folk haven't looked at other uses for the volume used in the F-35B by the lift fan. However, they are quite a closed-mouth bunch and, really, unless we get a contract, design or study, for it, I don't honestly have a "need to know".

I learned an interesting thing from *ahem* a senior editor at a publication that covers military aviation. S/He said "You'd be surprised at how much you can learn from spinning the questions the right way." In fact, that editor got a lead from me once off of a conversation with a crewman I had at an airshow, and ran it in print a couple of months later. The point is, the idea of using the fan space for a power generator isn't new, but when company men start talking about what kind of things they could do if they had enough power, it's just a matter of connecting dots.
 

elmayerle

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Jeb said:
elmayerle said:
I'd be surprised if our AD or PD folk haven't looked at other uses for the volume used in the F-35B by the lift fan. However, they are quite a closed-mouth bunch and, really, unless we get a contract, design or study, for it, I don't honestly have a "need to know".

I learned an interesting thing from *ahem* a senior editor at a publication that covers military aviation. S/He said "You'd be surprised at how much you can learn from spinning the questions the right way." In fact, that editor got a lead from me once off of a conversation with a crewman I had at an airshow, and ran it in print a couple of months later. The point is, the idea of using the fan space for a power generator isn't new, but when company men start talking about what kind of things they could do if they had enough power, it's just a matter of connecting dots.

Oh, admittedly. And sometimes sheer informed speculation can lead you to certain understandings by what people don't say or don't want to talk about (ran into this one place I worked earlier). In this case, I'd not be able to say, no matter what.
 

Archibald

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any solution employing afterburning in VL mode was a non-starter for land-based operations, although there were ways of handling it in terms of ship design. IIRC the Yak-141 hovered, but did not land vertically, at Farnborough in 1992.

Hell, thought about this two days ago... I'm actually building a model of the General Dynamics 200 (Rockwell XFV-12 competitor for the SCS supersonic V/STOL interceptor).
I imagined exactly what you mention, Ie CTOL or STOL landing when land-based...

I suposed that lift-jets are "viable" on ships because
- no ground erosion possible (but you need a robust flight deck)
- hot gases reingestion are diminished by a 30 knot wind blowing on the deck
- a STOL take-off also reduce these problems...

Well, I suppose that both Convair and Yak fighters can make CTOL by not using their lift engine, and putting their exhaust in the horizontal mode...

THIS
Note that the RB.571 looks like the X-32 propulsion concept plus a forward cool flow, and that if you turn the front fan of the tandem fan through 90 degrees you almost have the X-35 system. The same problems can lead to similar solutions

is truly fascinating... starting from the same idea (lift jets are too hot, so why not using a cold-air fan instead ?) we actually have no less than FIVE different results!

- The Harrier / X-32 system
- the Vought TF-120 "tandem-fan" concept
- F-35 variant
- RALS
- RULS

All having their pros and cons...
 

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Hehehehe!!!

But then, this "cold RALS" would have ended needing a bulkier engine and bigger flow ducts to compensate the loss of energy of the missing front burner.

I didn't notice, but the MFVT sans ducts is the principle of the X-32 engine, something I asked about in the current X-32 Thread by Archi. Am I correct?

Rafa
How entertaning and instructive is this discussion, Thanks everybody.
 

Mike Pryce

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is truly fascinating... starting from the same idea (lift jets are too hot, so why not using a cold-air fan instead ?) we actually have no less than FIVE different results!

- The Harrier / X-32 system
- the Vought TF-120 "tandem-fan" concept
- F-35 variant
- RALS
- RULS

RALS was considered too hot, hence RULS, so that whittles things down. However RULS was a term used to cover other concepts such as REx (Remote Exhaust), which was the same as what MDC/P&W called MFVT, which itself differed from RR MFVT in using just the mixed core and fan flows, not separate fan/core flows, ducted forward to a pair of nozzles - essentially the X-32 system but with the engine further aft. Confusing?! There are so many ways to skin the STOVL cat, which is its source of fascination, as well as much frustration!

I would also say that the Harrier and X-32 are different concepts - the mixed flows from fan and core on the X-32 were not very cool - similar to moderate PCB temperature values, IIRC, as the core is very hot. And I recall seeing a documentary that showed how this gas could cause pop surges when re-ingested in VL as it was not at all cool.

Essentially the issue is whether you want to augment the basic engine for vertical flight, and if so do you want to do it through additional burning (PCB, RALS) or in some other way, such as lift jets, shaft driven fan, ejectors etc. I think Boeing failed with the X-32 because they did not augment the engine for vertical flight, leaving them with no margin for payload, hot/high conditions etc. A supersonic aircraft will always be heavier than a subsonic one for the same mission radius/payload etc., so you need to augment the engine thrust in some way for vertical flight. Similarly, there is little need to augment the engine of a subsonic aircraft, despite efforts in this direction in the 1960s (e.g. VAK191).
 

hesham

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Hi,


I am confuse with start a new topic or continue with this old topic,here is the General Dynamics configurations 101,201,300,400 & 500 V/STOL fighters,used RALS.


 

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hesham

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hesham

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Hi,


here is a two designs for RALS,maybe from McDonnell-Douglas,but the lower one is
new.




http://www.dtic.mil/dtic/tr/fulltext/u2/a053417.pdf
 

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hesham

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