F-35 Derivative as Gen 5.5 OCA Stepping Stone

Variants for different customers or mission profiles
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by steve2267 » 24 Dec 2016, 22:03

Hypothesis: A canard-derivative of the F-35 JSF could serve as a lower-cost, supercruising OCA fighter to supplement the F-22 until a true 6th generation fighter can be fielded.

Rather than rushing development of a 6th generation fighter and pouring money into development, developing a derivative of the F-35 in the early/mid-20's for deployment around 2030 could be accomplished with a (relatively) minimal outlay of funds, permitting the gradual, and thus more economical, development of 6th generation technologies.

By moving to a canard configuration, the configuration originally designed / advocated by LM, and slimming the internal weapons bay, drag, especially wave drag, would be minimized. Combined with an F135 follow-on engine using ADVENT / AETD / AETP technologies, a modest-weight VLO fighter aircraft, optimized for air-to-air operations, could be created with Mach 1.2-1.5 supercruise over extended distances. This aircraft would leverage the F-35's existing 5th generation VLO and sensor-fused avionics technologies with a 6th generation engine, and possibly a new BVR missile, such that one could consider it a Generation 5.5 fighter.

If you have not read Dr. Paul Bevilaqua's AIAA paper, Genesis of the F-35 Joint Strike Fighter, I highly recommend it. I was surprise to learn that the original LM design originating from the DARPA Stealth Strike Fighter (SSF) contract was a canard aircraft:
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Although the aircraft in the initial sketch shown to DARPA res embled an F-117, highly swept wings produce anunstable pitch up, even at moderate angles of attack, and were quickly abandoned. The initial design of the STOVL Strike Fighter had a delta/canard planform, as shown in Fig. 13. The active canard was moved like a weather vane during subsonic cruise and maneuver, so that it provided no lift and little drag, but it was adjusted to provide lift for trimming the nose-down moments that were produced when the flaps were deflected and when the center of lift moved aft at supersonic speeds. The active canard has less trim drag than a horizontal tail [8]. The desired performance required an afterburning engine. Because the jet flap nozzles could not accommodate an afterburner, the jet flap was similarly abandoned. The aircraft carried two long-range AIM-120 missiles and two short-range AIM-9 missiles in internal weapons bays. Models of the aircraft were tested in the wind tunnel and on the radar range to verify the predictions of both the aerodynamic forces and the radar cross section.

Bevilaqua, Paul M., Genesis of the F-35 Joint Strike Fighter, AIAA Journal of Aircraft, Vol. 46, No. 6, Nov-Dec 2009, p. 1830


While I am not proposing that this notional F-35 derivative also be produced in STOVL variant, that would be possible. Dr. Bevilaqua pointed out that the combination of the canard and vertical lift fan easily accommodated either the lift fan, or extra fuel, and that both aircraft configurations retained identical mid-mission performance:
The conventional variant was quickly created by simply removing the lift fan and vectoring nozzle from the SSF and substituting a fuel tank and a more conventional cruise nozzle. This reduced the empty weight of the aircraft by about 15%, while improving its range and reducing its cost. The weight of the fuel tank and one-half of a tank of fuel turned out to be about the same as the weight of the lift fan. As a result, both variants had the same midmission maneuver performance. The canard was to be used for trim at other points in the mission, as the fuel was burned. These aircraft are shown in Fig. 14.

Bevilaqua, Paul M., Genesis of the F-35 Joint Strike Fighter, AIAA Journal of Aircraft, Vol. 46, No. 6, Nov-Dec 2009, p. 1831

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Dr. Bevilaqua noted that when the DARPA SSF contract, circa 1988, morphed into the Common Affordable Lightweight Fighter (CALF) program in 1992 (regarded to be the start of the JSF program), the addition of ground attack / strike missions from the Air Force's Multi-Role Fighter (MRF) program de-emphasized the air-to-air nature of the SSF, resulting in a fighter with more emphasis on its strike role while retaining some air-to-air defensive capability:
The addition of four new ground-attack missions from the MRF program changed the design emphasis from a fighter with some strike capability to a strike aircraft with some air-to-air defensive capability. The development of stealth and long-range air-to-air missiles had changed the nature of air combat, and so the emphasis was on achieving a first-look, first-kill capability and reducing the need to dogfight at close range. For these reasons, the two AIM-9 missiles were removed and the aircraft was designed to carry two 2000 lb bombs in the internal weapons bays, in addition to the two AIM-120 missiles. This increased the aircraft’s frontal area and wave drag. The Air Force variant was derived, as before, by removing the lift fan and thrust-vectoring nozzles and substituting a fuel tank and conventional cruise nozzle. These aircraft are shown in Fig. 15.

Bevilaqua, Paul M., Genesis of the F-35 Joint Strike Fighter, AIAA Journal of Aircraft, Vol. 46, No. 6, Nov-Dec 2009, p. 1832

Image

So while the F-35 possesses excellent transonic performance, the requirement to carry two 2000lb bombs internally appears to be the reason that its supersonic performance suffers somewhat. My hypothetical F-35 derivative is not required to carry such a large bomb internally, but rather is sized to carry 4 (maybe 6) internal AA missiles, at least AIM-120 sized. The idea here is to minimize wave drag and maximize supersonic engine performance (via ADVENT/AETP 3-stream technologies), to enable an F-22 like supercruise capability. If the resulting aircraft was able to still carry, say, a pair of 1000lb JDAMs along with two AIM-120's, great. But that would not be a requirement. If two 1000lb JDAMs kill the wave drag reduction, then it seems reasonable that at least a pair of 500lb bombs (e.g. GBU-12) or four SDB-I/II's could be carried.

As an aside, the full scale wind tunnel / vertical lift fan test article that LM built to prove out the vertical lift fan technology was a canard platform:
When these tests were complete, the propulsion system was installed in a full-size airframe model made of fiberglass and steel. This model is shown in Fig. 16.

Bevilaqua, Paul M., Genesis of the F-35 Joint Strike Fighter, AIAA Journal of Aircraft, Vol. 46, No. 6, Nov-Dec 2009, p. 1832

Image

In 1993, the CALF program morphed into the Joint Advanced Strike Technologies (JAST) program. LM abandoned the canard platform to lessen the perceived risk since they were already proposing the radical lift fan:
Because the shaft-driven lift fan propulsion concept was new and therefore considered the riskiest of the alternative propulsion systems, it was decided to reduce the perceived risk of our aircraft design by replacing the canard with a more conventional aft tail. This was easily done, as one of the advantages of the lift fan concept was the ability to rebalance the aircraft with relatively small changes in the size and location of the fan.

Bevilaqua, Paul M., Genesis of the F-35 Joint Strike Fighter, AIAA Journal of Aircraft, Vol. 46, No. 6, Nov-Dec 2009, p. 1834


In summary, the original LM JSF design was a canard design. The addition of the requirements from the Air Force MRF program resulted in a larger internal weapons bay which increased frontal area and wave drag. By removing the requirement to carry such a large air-to-ground load, and returning to the canard layout, an F-35 derivative, with an advanced 6th generation engine (e.g. an F135 or F135 follow-on incorporating ADVENT/AETP 3-stream technologies) could provided a supercruise air-to-air capablity combining VLO (aka stealth) and advanced sensor-fused avionics. Leveraging existing production technologies developed for the F-35 along with re-use of existing F-35 avionics (and software) would keep costs down. In addition, existing F-35 structure would be retained as much as possible. (While a STOVL version of this concept is also doable, the lift-fan integration with a new powerplant would involve additional expense. Therefore, without any firm requirement by the USMC or any other operator of the F-35B for a supercruising air-to-air fighter, this idea would not incorporate the STOVL lift fan in order to keep costs down.)

Now, do I think such an aircraft will be built? Not a snowball's chance between he and double toothpicks. My question is: do you think these ideas have any merit? By slimming the weapons bays down to only carry four (maybe six) AIM-120s, going back to a canard planform, and incorporating an F135 follow-on engine, could such a supercruising fighter be produced? By keeping requirements for "new stuff" to an absolute minimum, if technically feasible, could this aircraft be produced "economically"? Let's say for a flyaway cost no greater than existing F-35s?
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.


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by botsing » 24 Dec 2016, 22:10

Why develop a new airframe when the F-35 is designed to be upgraded by the things you state?

It only makes things more complicated and costly.
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by steve2267 » 24 Dec 2016, 22:20

botsing wrote:Why develop a new airframe when the F-35 is designed to be upgraded by the things you state?

It only makes things more complicated and costly.

Two reasons:
  1. Current size of F-35 internal weapons bays are too large for the aircraft's length, adversely affecting it's fineness ratio and increasing it's wave drag.
  2. The proposal to return to a canard configuration is conceptually aimed at reducing the supersonic wave drag by ensuring the wingtips are aft of the Mach cone and by reducing the trim drag.
Since the internal weapons bays resulted in increased aircraft wave drag, their re-design / minimization would, by definition, require a new airframe.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.


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by wrightwing » 25 Dec 2016, 00:31

steve2267 wrote:
botsing wrote:Why develop a new airframe when the F-35 is designed to be upgraded by the things you state?

It only makes things more complicated and costly.

Two reasons:
  1. Current size of F-35 internal weapons bays are too large for the aircraft's length, adversely affecting it's fineness ratio and increasing it's wave drag.
  2. The proposal to return to a canard configuration is conceptually aimed at reducing the supersonic wave drag by ensuring the wingtips are aft of the Mach cone and by reducing the trim drag.
Since the internal weapons bays resulted in increased aircraft wave drag, their re-design / minimization would, by definition, require a new airframe.


Speed isn't an urgent requirement. Range and payload are higher priorities.


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by popcorn » 25 Dec 2016, 01:35

I'd say the F-35 weapons bay is one of it's most valuable features. Would have loved to have the Raptor accommodate 2000lb-class ordnance.
"When a fifth-generation fighter meets a fourth-generation fighter—the [latter] dies,”
CSAF Gen. Mark Welsh


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by quicksilver » 25 Dec 2016, 18:41

"Current size of F-35 internal weapons bays are too large for the aircraft's length, adversely affecting it's fineness ratio..."

Then the most economical option is to increase the length of the fuselage. What you have proposed is a whole new aircraft with all the programmatic pieces (think: 'time and expense') that accompany such a thing. And, as ww points out above, the performance improvements suggested by this hypothetical design aren't of critical importance right now.


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by hornetfinn » 27 Dec 2016, 08:05

popcorn wrote:I'd say the F-35 weapons bay is one of it's most valuable features. Would have loved to have the Raptor accommodate 2000lb-class ordnance.


I totally agree. Definition of OCA is the following:
The objective of offensive counterair (OCA) is to destroy, disrupt, or degrade enemy air capabilities by engaging them as close to their source as possible, ideally before they are launched against friendly forces.


Many people think that OCA is air-to-air combat only. In reality the most effective and efficient method for OCA is to blow the enemy aircraft on the ground. I'd say the role of air-to-air combat is "merely" to allow bombing the enemy or deny enemy doing the same. Air-to-air combat is great for movies but in real life ability to avoid it is much better.

I think if F-35 weapon bays were smaller, it would lose a lot of effectiveness in day 1 configuration and it would take a lot longer to achieve air dominance. It would not be able to carry JSOW, largest JDAMs, JSM and possibly not 8 SDBs but possibly 4 of them. I also don't think that speed is that important in comparison.

From Red Flag descriptions, it seems like F-35s are doing OCA in reverse order to what has historically been done with non-stealthy aircraft. They avoid detection altogether and bomb their targets and then take out the any defending fighters. This gives enemy no warning that they are about to be attacked and runs the enemy defences in to disarray as they don't know where the hell the enemy aircraft are. Speed is far less of an importance here while stealth and SA is most important.


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by blindpilot » 27 Dec 2016, 09:19

hornetfinn wrote:
popcorn wrote:I'd say the F-35 weapons bay is one of it's most valuable features. Would have loved to have the Raptor accommodate 2000lb-class ordnance.


I totally agree. Definition of OCA is the following:
The objective of offensive counterair (OCA) is to destroy, disrupt, or degrade enemy air capabilities by engaging them as close to their source as possible, ideally before they are launched against friendly forces.


Many people think that OCA is air-to-air combat only. In reality the most effective and efficient method for OCA is to blow the enemy aircraft on the ground....etc. .. I also don't think that speed is that important in comparison.

From Red Flag descriptions,.... Speed is far less of an importance here while stealth and SA is most important.


Things can get confusing when paradigms change. For example my old Samsung Intensity II had the size of the smallest flip phone and a < 2inch screen. The battery lasted a couple days in normal use. The first iPhone jumped to 4 inch screen, and everyone said we don`t want bigger screens.That`s backwords! It`s like going back to carrying bricks, and the battery life is too short "for a phone". Now it`s do we want 5 inch,or 5.5 or would you like a "plus?"

Today ... well we don`t have 2 inch screens, and it has little to do with what a phone needs. We don`t use phones any more. Well other than I can stay in touch with my family all over the world in an instant, with pictures, or video clips, and ....

In other words we don`t use "fighters" any more ... although we haven`t yet decided whether a 5 or 6 inch screen is better etc. etc. It definitely isn`t a flip phone .. maybe a watch? or glasses .. or ? But just like I can make a phone call ... the 5th Gen fighters can do "fighters" if that`s what you want ... we just haven`t sorted out, that that`s not exactly what we want now ...

We`re not in Kansas anymore Toto!

MHO
BP


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by hornetfinn » 27 Dec 2016, 12:57

blindpilot wrote:Things can get confusing when paradigms change.


Totally agree. I think a lot of people are still clinging to some rather old ideas about aerial combat. 5th generation changes everything and I've said a long time that going from 4th to 5th generation is possible the largest change ever in how aerial warfare is done. As you said, 5th gen systems are something far more than mere fighters. They change so many things totally that it's very difficult to understand for anybody. I think the way they are used will evolve a lot during the next several decades as they continue to evolve themselves, especially the F-35.


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by mixelflick » 27 Dec 2016, 17:31

Interesting concept.

I'm of the opinion the $ goes into 6th gen though, hopefully getting it here sooner vs. later. Range and payload are needed for the South China sea. Going to be a big bird..


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by vilters » 27 Dec 2016, 22:50

mixelflick wrote:Interesting concept.

I'm of the opinion the $ goes into 6th gen though, hopefully getting it here sooner vs. later. Range and payload are needed for the South China sea. Going to be a big bird..


Not exactly.
Remove cockpit, pilot and seat and you gain room for about 2.000 - 3.000 lbs of fuel.
Who says that for Gen6, the pilot "has" to be inside the A/C?

The pilot can be on the other side of the world, playing golf with his wingman while their A/C are patrolling a coastline.
The A/C will call their pilots on their cellphones when some sort of action is required.

The pilots put a checkmark next to :"Valid target" or : "Not a valid target", the A/C take a "Yes" or a "NO" action by choosing the best weapon for the Job, and the mission goes on.

Low on fuel they go find a tanker, and continue.
Out of weapons they return to base for rearming.

All the pilots have to do is tell the A/C when they go to bed, so the A/C know they have to call another crew when something comes up.

THAT's gonna be Gen 6 for you.


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by steve2267 » 28 Dec 2016, 03:05

mixelflick wrote:Interesting concept.

I'm of the opinion the $ goes into 6th gen though, hopefully getting it here sooner vs. later. Range and payload are needed for the South China sea. Going to be a big bird..


I am of the opinion that when you try to develop a "new generation" of something, but the underlying technologies are not yet mature, you will end up pouring a LOT of money into the "new generation of something" and you may not end up with "new generation" of something. Oh, you'll get something, you just may not get the new generation of that something.

Modern stealth was discovered by Denys Overholser in early 1975 at the Lockheed Martin Skunk Works. Ben Rich had to argue to get the Skunk Works included on the DARPA Have Blue project, which they won. Have Blue led to the F-117 which first flew in 1981. The ATF program began in 1981, with prototype teams chosen in 1986, and LM winning the F-22 contract in 1991. My point is that modern stealth or VLO was discovered in 1975, proven in Have Blue, and ATF / F-22 didn't start until after VLO had been proven. In other words, ATF / F-22 was not a development program of stealth. Stealth did not become a requirement until after it had been "proven."

In other threads on this board, people have not been able to come to a consensus on what will define a 6th gen fighter. Some say it will have to have beam or directed energy weapons. Others say it will be optionally manned. Others that it must supercruise. Others say it will be hypersonic. Yada yada yada.

As the OP, I started this thread to try to answer the question: With a next generation engine (e.g. ADVENT/AETP 3-stream turbofan), slimmed down the weapons bays to minimize wave drag, and moving to a canard configuration to minimize trim drag (and ensure the wing tips are aft of the Mach or shock cone), could such an F-35 derivative aircraft supercruise between M1.2 and M1.5 and supplement the F-22 as a dedicated air-to-air dominance fighter.

Yeah, I threw the OCA term out there. Yes, I agree, blowing the enema aircraft up on the ground before they have a chance to take to the air is best. But most people would seem to agree that 187 F-22's was not nearly enough. So my idea here is how to produce an F-22 lite, if you will, since the Air Force has pretty definitively stated the F-22 production will NOT be restarted. My thought was that by leveraging F-35 avionics, F-35 production technologies, and as much F-35 structure as possible -- though maybe re-using structure is not possible -- that such an aircraft could be produced relatively cheaply.

NO, I am NOT suggesting that this "derivative" aircraft replace or in any way reduce the number of F-35's planned for purchase. I see a number of comments about the greatest thing about the F-35 is the size of its weapons bays. No argument here. But again, I am not suggesting this derivative aircraft replace the F-35, rather it would supplement / bolster the F-22 in air-to-air operations until the technologies for the next generation of aircraft have matured.

So, if you want to debate 6th generation fighters, please go debate that in one of the existing 6th gen threads, or create your own thread.

Here I was curious if anyone thought my "idea" had technical merit -- could it be done? Would it supercruise as I suspect it would?

Now, whether it could be done "economically"... that is a big question. And I have no idea. I'm going to hazard a guess that an outfit like the Skunk Works could pull it off, but if it has to go through the "normal" military tactical aircraft procurement / contracting process, it will be too expensive.
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.


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by popcorn » 28 Dec 2016, 04:13

In other threads on this board, people have not been able to come to a consensus on what will define a 6th gen fighter.

That would be truly amazing as the DoD and AF haven't either.
"When a fifth-generation fighter meets a fourth-generation fighter—the [latter] dies,”
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by steve2267 » 28 Dec 2016, 04:20

popcorn wrote:In other threads on this board, people have not been able to come to a consensus on what will define a 6th gen fighter.

That would be truly amazing as the DoD and AF haven't either.


Yeah, well, I was trying to head this thread off at the pass and (hopefully) prevent it from turning into YA6GT.

Since people bemoan the fact we are short F-22's... I got the hair brained idea that returning to LM's original SSF / CALF canard design with four internal AAM's but with a new motor would get you a helluva lot of air-to-air bang for little buck.

But then again, US, tactical aircraft, and either inexpensive or affordable never work in the same sentence. :mrgreen:
Take an F-16, stir in A-7, dollop of F-117, gob of F-22, dash of F/A-18, sprinkle with AV-8B, stir well + bake. Whaddya get? F-35.


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by madrat » 28 Dec 2016, 04:28

Why build an F-35A equivalent of it's just going to cost the same to develop for less capabilities?

I could understand an F-16 equivalent that is stealth if it was less expensive, because the expectations would scale accordingly. But it it proved cheaper to buy F-35 for relative capability then stick to F-35.


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