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F-35 Cancelled, then what ?

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F-35 Cancelled, then what ?

Old 5th Mar 2018, 12:21
  #11161 (permalink)  
 
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Perhaps I could help throw some light on the issue of conformal fuel tanks.

All fast jet combat aircraft face a common challenge - making space within the aircraft for enough fuel to do all the required missions. This challenge arises due to the iron laws of physics, and the achievable values for specific fuel consumption and engine thrust to weight ratios. The main solutions usually available are:

1. Reduce the fuel load and accept a shorter range/endurance - which nobody likes
2. Add fuel internally to the aircraft inn places you normally wouldn't.
3. Add fuel to the aircraft externally, using extra tanks.

Option 2 above has been used occasionally in the past, and is a good indicator of how hard the struggle has been. If aircraft have fuel tanks in their fins, tailplanes, flaps, or even their undercarriage doors, they've had a problem with internal fuel volume during their initial design phase.

The third option is almost always adopted, and it's unusual to find a tactical combat jet that hasn't used drop tanks. However, these generate a lot of drag, and it's common for tanks to generate so much that most of the fuel they carry is used up hauling the tank around the sky. I don't have precise figures to hand, but I think that any 'productive drop tank fuel fraction' over 50% would be very good indeed. I do know that the large tanks on the F3 (2250l?) gave only about 10% 'productive fuel' in some sortie profiles.

So, conformal tanks have often been adopted as a way to add fuel with less drag. Actually, some were around before conventional tanks, examples being the Bf110, Seafire belly tank, Lancaster spine mounted tank, and the Supermarine Attacker. They've appeared on Soviet aircraft (Mig-21, etc.) and later on US aircraft (F-15, F-16 and now F-18). Now they're appearing on the Typhoon. Essentially, what you do is add a new bit of airframe on to the outside of the aircraft to hold fuel, picking up on a number of attachment points along the fuselage. Most conformal tanks aren't jettisonable - they are a semi-permanent addition.

So why put them on? I don't know the precise reasons for each decision by type, but here are my (hopefully) informed guesses:

1. In service weight increases - most aircraft get heavier as time goes on. Extra this, extra that. all lead to more weight, so more lift required, so more drag. (Darn those pesky physics). Eventually, you just need more fuel and you can't lose another pylon.
2. Extra drag - you build a nice clean aircraft and then start adding lumps and bumps all over it (EO turrets, extra antennae, RWR systems, etc.). Or bigger external stores. More fuel required for the same range/endurance.
3. Changes to requirements. Here's an example. Might be Typhoon, or not. You build an aircraft that's basically an out and out high altitude BVR death machine, pulling tons of G and firing off telegraph poles of death on JTIDS data at the dastardly foe coming at you over the North German plain. A few years later, you then get told that the primary role is to haul tons of draggy bombs around at medium level for hours on end, as your available bases are hundreds of miles from the action. You end up needing more fuel, and lots of it. Losing a few 'G' off the envelope is now not so important.

I have seen claims that adding conformal tanks reduces drag. With all due respect, I find those slightly unlikely. However, it might be true at the new sortie profiles now being demanded. More likely, what they are actually saying is that a set of conformal tanks generate less drag than the equivalent set of drop tanks. That would be very likely. Conformal tanks usually appear toward the end of an aircraft's service life. Perhaps driven by the 'in-service' factors I outlined above. Sometimes, they appear during development - the V-22's external fuselage fairings grew massively during development to house more fuel as they struggled with weight increases.

LO aircraft designs make the design challenge I outlined at the start of this post even tougher - you don't have the 'add drop tanks' option available to you for many of the expected missions, and the internal volume of the aircraft is also being taken up by many of the avionics bits and pieces often carried in pods outside the skin. (I'm not making excuses for the F-35 here, just stating the facts). It's even harder if you also stress the internal volume with big lumps of powered lift gear. In the case of the F-35 (all variants, note) the aft fuselage 'hump' got noticeably larger during the SDD phase, driven by the need for more fuel. They just avoided carrying fuel in the fins - the fins had been designed to carry fuel, but during the weight reduction phase it was found that this imposed too much of a weight penalty in extra fin structure, and the fuel volume was found elsewhere.

To wrap up - designing tactical combat aircraft is really hard. keeping them relevant throughout their service lives is just as hard. Conformal tanks are a useful way of solving some of those problems. But for my money, the better option has to be to get as much fuel into the aircraft as you can first time around. Trading off 'high end' performance might just be a price worth paying. But try telling single seat pilots that.

Best regards as ever to all those juggling with the iron laws of physics,

Engines

Last edited by Engines; 5th Mar 2018 at 17:39.
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Old 5th Mar 2018, 17:23
  #11162 (permalink)  
 
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Delploying on LHD

Looks like the first operational deployment of the B at sea is beginning. Several deploying aboard the USS WASP. Actual number unclear, but the usual deployment of the Harrier was around 6 aircraft, which were temporarily administratively assigned to a medium helo, now tilt-rotor squadron, (enhanced) for the deployment.


USMC prepares for F-35B maiden operational embarkation | Jane's 360
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Old 5th Mar 2018, 17:57
  #11163 (permalink)  
 
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I have seen claims that adding conformal tanks reduces drag. With all due respect, I find those slightly unlikely. However, it might be true at the new sortie profiles now being demanded. More likely, what they are actually saying is that a set of conformal tanks generate less drag than the equivalent set of drop tanks. That would be very likely. Conformal tanks usually appear toward the end of an aircraft's service life. Perhaps driven by the 'in-service' factors I outlined above. Sometimes, they appear during development - the V-22's external fuselage fairings grew massively during development to house more fuel as they struggled with weight increases.
Engines, according to those in the know (which I'm not), at least on the F-15 the conformal tanks resulted in no increase in airframe drag when subsonic, although transonic/supersonic was a different story (never heard anyone claim a reduction though). Looking at the installation, my aero engineer training says the claim is at least plausible as it gives the aircraft a more 'tear drop' profile.
I've not heard much about the F-18 conformal tank installation, but I'd expect similar results (especially since it's coming from the same people).
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Old 5th Mar 2018, 18:21
  #11164 (permalink)  
 
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Engines, your titbit on the large Tornado tanks is incorrect. The big jugs were quite slippy, the small tanks were the draggy ones. You could also take the big tanks to a higher speed and (on the GR version at least) achieve a higher cruise ceiling... or put another way, finding yourself descending when you jettison them in a misguided attempt to climb over a CB during a shooting war...
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Old 5th Mar 2018, 18:24
  #11165 (permalink)  
 
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tdracer,

Thanks for coming back.

Yes, I've seen these claims and, honestly, I am a bit sceptical. I don't know a single combat jet that didn't struggle with internal volume, and adding fairly large lumps on the outside (that definitely increase frontal area) without reducing drag seems unlikely. However, it's possible that the effects aren't as marked at subsonic speeds, as you mentioned. A change in desired sortie profiles can make big changes to both drag and fuel burn. It's also possible that the drag reduction claim includes the drag of external bombs - the F-15 combines conformal tanks with revised bomb carriage locations to reduce drag. (Interestingly, some of the F/A-18 proposals included a 'stealth' (probably also lower drag) weapons 'pod' on the centreline.

The other possibility, of course, is that the original airframe design wasn't worked as thoroughly as it might have been, and they found this extra volume later on, when the need drove them.

Incidentally, the Buccaneer belly tank on the S2B was originally designed as a solution to the excessive drag created when Blackburns looked at putting four more 1000lb bombs on the outside of the bomb bay door. They came up with the idea of adding a fairing on the outside of the door (which already had a fuel tank it, i believe) which would provide recesses for the bombs to lie in. The external bombs idea wasn't taken forward, but the belly tank provided a very efficient way of adding fuel.

Tough stuff, this pesky aerodynamics, ain't it?

Huge respect as always to those working the wind tunnels,

Engines
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Old 5th Mar 2018, 18:39
  #11166 (permalink)  
 
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JTO,

Very happy to be corrected on the F3 tanks. Very interesting how the aircraft could achieve a HIGHER cruise ceiling with all that additional frontal area and weight - there must have been some significant interactions between the tanks and the airframe.

By the way, the worst drop tanks ever (to my knowledge) were the original 'pinion' wing tanks on the Buccaneer, which (I was told) actually decreased the range. The fix was to add an angled fairing between the top of the tank and the wing leading edge.

Best regards as ever to all those who take the time to read my efforts here on PPRuNe...

Engines
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Old 6th Mar 2018, 12:44
  #11167 (permalink)  
 
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Could it be that in some cases interference drag is reduced ? This might be true of the F-15 and F-18, but it doesn't look like it for F-16, Typhoon, etc. .......
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Old 6th Mar 2018, 18:25
  #11168 (permalink)  
 
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F-35 Finally Can Use All Its Weapons In Combat

On Aviation Week today:-
F-35 Finally Can Use All Its Weapons In Combat

Snip:-
The newest U.S. Air Force F-35s, both stateside at Hill AFB, Utah, and overseas in the Pacific, finally can employ the stealth fighter’s full suite of air-to-air and air-to-ground weapons in combat.
The F-35 Joint Program Office (JPO) has delivered the flight clearances, simulators, threat information, and logistics system required for the Air Force’s F-35As equipped with the latest software load to employ all of its weapons throughout the full flight envelope, according to the JPO, Lockheed Martin and Air Force officials.

This milestone gives the Block 3F-configured F-35As assigned to the 34th Fighter Squadron stationed at Hill and those forward-deployed to Kadena Air Base, Japan—on North Korea’s doorstep—some lethal capabilities. The aircraft now can fire Raytheon’s short-range AIM-9X Sidewinder missile, the GAU-22 25mm gun, and Boeing’s precision-guided Small Diameter Bomb, all while flying up to 9Gs at 1.6 Mach.
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Old 7th Mar 2018, 12:12
  #11169 (permalink)  
 
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Harry Hillaker (Mr F-16) once remarked that the natural evolution of a fighter was in terms of greater zero-fuel weight (payload and equipment), which meant more thrust and more fuel to maintain performance. Eventually, he added, you would run out of wing area and external stores capability, and if you ever saw anything above the wing you knew the limit had been reached.

The F-16 had two volume-adding mods in its lifetime: the conformal tanks (the first set had been designed in the 70s) and the originally-Israeli fat spine, which was intended to create a two-seater with similar internal fuel to the single-seater.

I don't think it would be a bad idea, in fact, to design conformals into a fighter from the outset. It would be a nice way to add flexibility and it might be possible (if difficult) to add them in a way that minimized LO issues.

I too tend to be skeptical about the idea of conformals reducing drag, except when qualified by "with the same fuel load" or even "loaded for equal range". However, ISTR being told in one case that the jet trimmed better at subsonic speed with the conformals in use.

Finally - looking at the F-35, I have no idea where you'd put conformal tankage, except maybe on the upper rear centerline. You could put a few gallons into the horrible wart that covers the Noggies' brake chute, even. And IMHO the A/B versions are already at their limit for wing loading.
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Old 7th Mar 2018, 13:10
  #11170 (permalink)  
 
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Originally Posted by Just This Once... View Post
Engines, your titbit on the large Tornado tanks is incorrect. The big jugs were quite slippy, the small tanks were the draggy ones. You could also take the big tanks to a higher speed and (on the GR version at least) achieve a higher cruise ceiling... or put another way, finding yourself descending when you jettison them in a misguided attempt to climb over a CB during a shooting war...
Can confirm this, they generated useful lift according to my mate ginger over a few swallies one night at the north pole gentleman's club...
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Old 7th Mar 2018, 14:38
  #11171 (permalink)  
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Jus5 bemused about the climbing over CBs bit.

IIRC when the tankers all went off to war they looked at the best fit for the F3s to reach Cyprus unsupported. On paper the best fit was the 4 tank ferry fit and filling up from one of the few tankers left near the Channel before heading south. The only problem was they wouldn’t be able to clear the Alps without using burner.

The next best fit was with 3 tanks, 2 big and 1 small - but no one had ever done the clearance trials....

Getting airborne with full tanks was of negatory value, the take-off and climb burned all the xtra fuel, if not more, and you still had the drag. The optimum was to get airborne with empty tanks and RV with the tanker at cruise altitude before proceeding to CAP/en-route which could double the time on task.

The plan, in war of course, was to fly on external fuel, topping up the tanks as required. The tanks would then be dropped when committing to combat, entering the fight with full internal fuel. If you are carrying the extra fuel internally or in conformal tanks then you carry the weight of the additional fuel and tanks into the fight with you*....

*Clever Jets have a fuel dump where you can select to dump down to a selected weight where it stops. Unlike a certain jet where you had to remember to switch it off before the fuel emergency caption lit up.....

Last edited by ORAC; 7th Mar 2018 at 18:06. Reason: Sp
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Old 7th Mar 2018, 17:38
  #11172 (permalink)  
 
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Glad,

Thank you for that response - what an interesting subject. Three quite different (?) responses on 2250 litre tanks on the F3. Perhaps, to square the circle, the big tanks generated some lift, probably depending on speed and angle of attack, possibly at lower speeds, but seem to have had a significant effect on available 'G' and also the (already not exactly stellar) SEP curves of the F3.

For my part, they looked like ferry tanks, and would probably have had a serious effect in a fight. I have to observe that (just my opinion) the Tornado was slightly more optimised as a bomber than it was as a fighter, and the use of a tank as big as the 2250 litre seems to confirm that it had some challenges meeting the fighter sortie profile requirements.

None of which, of course, takes anything away from the professionalism and dedication of the crews flying and supporting them.

Best regards as ever to those doing the fuel calculations,

Engines

PS: beaten to the punch by ORAC - I have to say that when you have a fighter that can't get over the Alps in dry thrust, you have unusual thrust/weight and SEP values. For a fighter. I'd love to know how many of the tanks were provisioned if the plan was to bang them off in combat.

Last edited by Engines; 7th Mar 2018 at 17:42. Reason: Update
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Old 7th Mar 2018, 18:16
  #11173 (permalink)  
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I’m not sure about those procured for the F3, but at LU during the F4 day’s the airfield was literally crammed, all around the perimeter track and elsewhere, with rotting wooden crates full of underwing fuel tanks.

When visitors asked what they were I used to explain, with as straight a face as possible, that if the runway was cratered in wartime it would be flooded and they were pontoons to fit over the wheels on the undercarriage to allow water take-offs and landings....
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Old 7th Mar 2018, 18:20
  #11174 (permalink)  
 
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Originally Posted by Engines View Post
Glad,

Thank you for that response - what an interesting subject. Three quite different (?) responses on 2250 litre tanks on the F3. Perhaps, to square the circle, the big tanks generated some lift, probably depending on speed and angle of attack, possibly at lower speeds, but seem to have had a significant effect on available 'G' and also the (already not exactly stellar) SEP curves of the F3.

For my part, they looked like ferry tanks, and would probably have had a serious effect in a fight. I have to observe that (just my opinion) the Tornado was slightly more optimised as a bomber than it was as a fighter, and the use of a tank as big as the 2250 litre seems to confirm that it had some challenges meeting the fighter sortie profile requirements.

None of which, of course, takes anything away from the professionalism and dedication of the crews flying and supporting them.

Best regards as ever to those doing the fuel calculations,

Engines

PS: beaten to the punch by ORAC - I have to say that when you have a fighter that can't get over the Alps in dry thrust, you have unusual thrust/weight and SEP values. For a fighter. I'd love to know how many of the tanks were provisioned if the plan was to bang them off in combat.
The F3 wasn't a fighter. It was a missile carrying interceptor optimised by original (short arsed) design for low level.
If we wanted a fighter we should have bought Eagles instead. And retrofitted speys to **** it up just like the last time...
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Old 7th Mar 2018, 20:30
  #11175 (permalink)  
 
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Glad,

At the risk of pulling at an open sore, I was under the impression that 'F' stood for 'fighter'.

I lost count of how many light blue wearers told me that the Tornado F3 was handicapped by the compromises required for the low level role. About as many light blue wearers that told me the GR was handicapped by the compromises required for the high level role.

My opinion here, the original design idea seemed to be that adopting a swing wing design would allow the two very different sets of requirements to be met. (not too different, albeit on a smaller aircraft, than the F-111A/B idea).

Again my view, but the structural and layout penalties that came with swing wings (before the days of full authority fly by wire) handicapped both the F and the GR to a significant extent.

But, let me add again, commenting on the suitability of a design takes absolutely nothing away from the people who flew, and fought so bravely, in them. And this who still do it to this day. Respect.

Best regards as all those who do it for real,

Engines
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Old 7th Mar 2018, 20:36
  #11176 (permalink)  
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Not so much a “modest proposal”, as the way the USN has already gone over the last few years. Posted because of the relevance of the F-18G slides to the discussion on the use and relevance of conformal tanks vs underwing....

SNAFU!: Evolution of the Super Hornet & A Modest Proposal!
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Old 7th Mar 2018, 23:39
  #11177 (permalink)  
 
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I think I will wait till Air Power Australia gives their opinion. After all, they are the experts on the Super Hornet and the F-35. I've often seen SANFU bow to their greater knowledge.
ausairpower.net/bug.html

It's just that if they wake up to themselves and cancel it, it had better happen soon. There is a commitment order for 1,000 F-35 by 2022 and Australia will have all their 72 delivered by 2023. Eight of which are being delivered this year. If they don't hurry up. Australia will be the first country with a complete f-35 fleet and be stuck with them, when everyone else cancels theirs.

Last edited by golder; 8th Mar 2018 at 05:18.
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Old 8th Mar 2018, 08:29
  #11178 (permalink)  
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The point here is that the USN hasn’t been ordering the F-35C. Each time the budget has come around they’ve ordered more Super Hornets...

Returning to my point that their Super Hornet orders have reached the point that they can retire the last of the F-18A/B/C/Ds that the F-35C was supposed to replace - and hence the fate of the 4 remaining legacy USN F-18 Sqns. It would seem it was indeed not a coincidence....

The future of the handful of USMC F-18 Sqns also supposed to require with with the F-35C as opposed to F-35B remains in the balance.. though the USN hand-me-downs will allow them to soldier on for a few more, expensive, years....

US Navy to scrap scores of fighter jets from its inventory

WASHINGTON ― The U.S. Navy is moving to scrap almost 140 older Hornet fighters from its inventory and accelerate the transition to newer Super Hornet models in a bid to cut the costs of maintaining old aircraft that have seen hard use over two decades of continuous combat operations. The Navy projects it will recoup the better part of a billion dollars over the next five years, money used to fund other readiness initiatives both in the beleaguered Naval Aviation Enterprise and elsewhere.

The plan, hashed out in June, is to strike F/A-18 “A” through “D” models for a total of 136 Hornets, 66 of which will be gone by the end of 2020.

Two strike board reviews with Fleet, CNO, and NAVAIR personnel determined that 136 aircraft could be authorized for strike because their effective life was consumed and would require significant repair,” said Lt. Lauren Chatmas, a Navy spokeswoman. “The Navy will strike these aircraft over the course of fiscal years 2017 and 2020”.

The Navy thinks this is an opportunity to get some usable spare parts for the in-service jets and help the Marine Corps by sending it the best of the remaining aircraft. “The decision was based upon readiness risk of existing F/A-18 A-D inventory, long term operational costs versus gain in capability, and the potential to improve USMC readiness by transferring best of breed aircraft to the USMC,” Chatmas said.

The plan recoups about $124 million in 2019 and $852 million across the five-year budget projection, Chatmas said. Four squadrons flying legacy Hornets will transition to the newer versions between now and the end of 2019, she said.

The Navy has been buying batches of Hornets in recent years to replace the ones that are at the end of their service lives. The service has been slow to buy its F-35C, citing development issues.

The Navy’s flight demonstration team, the Blue Angels, will have to sit tight with its legacy Hornets until there are enough “E” or “F” versions available to spare, Chatmas said.
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Old 8th Mar 2018, 10:27
  #11179 (permalink)  
 
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Navy cans knackered classic bugs on logistics grounds - shock horror! Must inevitably mean F35C is dead says well respected and not at all sensational blogsite.

Or you could try what the USN is actually saying

http://navylive.dodlive.mil/2017/08/...nto-the-fleet/

Which includes the following tidbits - albeit sprinkled with defspeak nonsense.

"Recognizing Naval Aviation’s capability of today and the need for increased capability tomorrow, the Navy remains committed to pursuing the right procurement ramp for F-35C to balance inventory management, affordability and force modernization. A detailed asset allocation study determined that the most efficient and effective composition of strike fighters for the future CVW is two squadrons of F-35C and two of F/A-18E/F. With 10 CVWs , the Navy’s objective is to attain 20 F-35C squadrons, two per CVW by the early-2030s. This strategy calls for the continued procurement of low rate initial production aircraft and the enhanced capabilities of Block 3F software, and eventually Block 4’s advanced capabilities. The Navy’s plan for full rate production optimizes the force for the introduction of next generation capabilities to the Navy in the near term, while allowing the fleet to build the community and work integration solutions."

That doesn't sound like "bin it". Nor does ;

"The F-35C’s stealth characteristics, long-range combat identification and ability to penetrate threat envelopes, while fusing multiple information sources into a coherent picture, will enhance the role that the CSG and numbered fleets must play in support of our national interests. Ultimately, with the F-35C integrated and interoperable with the CVW, the CSG of the future will continue to be lethal, survivable and able to accomplish the entire spectrum of mission sets to include day one response to high end threats."
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Old 8th Mar 2018, 11:55
  #11180 (permalink)  
 
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There would seem to be a logical case for the USMC to put the first F35C squadron on a carrier.

If the USN is happy with the F/A-18E/F in the near future and the legacy Hornets are getting too expensive to maintain, financially it makes some sense and builds on the USMC's knowledge base from operating the F35B.

Then when the USN is comfortable with the performance and integration into the CVW of the F35C, squadrons can be generated or transferred over to the F35C, which by then may have reduced in price.
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