Why only 7G ?

[RansS9]

As far as I am aware (which isn't far) the JSF is designed to tolerate 7G.

Why only 7G in a jet fighter when the pilot can for short periods endure 9G ? Is manoeuvring left to the onboard UAV's (Aim9X, Amrams) ? If so why not design to 5G or Airliner 2-3G ?

Any info gratefully received...TIM

[Alber Ratman]

Lots of things on a B won't like 9G! :E

[NutLoose]

They got rid of the Harrier rather than the conventional Tornado, because the Harrier couldn't supposedly do things the Tornado could, then go for another Jumping bean that cannot do or carry the load of the conventional version... I could understand it if you were going to operate in the field, but the fact we are building two bloody great carriers for them it beggars belief.

[Harley Quinn]

Out of curiosity how often do you drivers take F 16's and similar to the limit?
A model has a built in gun so maybe a need for aggressive manoeuvring?
B has greater basic mass with similar structure to A (except big hole forward of CofG)
C has big wing and beefed up structure for carrier ops

It could be argued that the superior stealth characteristics of F35 preclude any need for high g tolerance as the opposition will never see it; I think F117 was limited to +6g-3g? Only one was shot down by defenders using unexpected tactics to locate the ac

[MATELO]

They were a bit strapped and couldn't afford the mods for the 9g upgrade.

[longer ron]

The B is tight on weight anyway and I do wonder how it will cope with the almost inevitable beefing up as it matures.
The nose leg looks a little flimsy for ski jumping at heavy weight also !

[kbrockman]

Eglin F-35 initial cadre starts transition training - The DEW Line (http://www.flightglobal.com/blogs/the-dewline/2012/05/eglin-f-35-initial-cadre-start.html)
The veteran F-16 operational tester and Weapons School grad shared some of his impressions the F-35. The jet is powerful, stable and easy to fly.

"One of the things this aircraft usually takes hit on is the handling because it's not an F-22," Kloos says. "An F-22 is unique in its ability to maneuver and we'll never be that."



But compared to other aircraft, a combat-configured F-35 probably edges out other existing designs carrying a similar load-out. "When I'm downrange in Badguyland that's the configuration I need to have confidence in maneuvering, and that's where I think the F-35 starts to edge out an aircraft like the F-16," Kloos says.



A combat-configured F-16 is encumbered with weapons, external fuel tanks, and electronic countermeasures pods that sap the jet's performance. "You put all that on, I'll take the F-35 as far as handling characteristic and performance, that's not to mention the tactical capabilities and advancements in stealth," he says. "It's of course way beyond what the F-16 has currently."



The F-35's acceleration is "very comparable" to a Block 50 F-16. "Again, if you cleaned off an F-16 and wanted to turn and maintain Gs and [turn] rates, then I think a clean F-16 would certainly outperform a loaded F-35," Kloos says. "But if you compared them at combat loadings, the F-35 I think would probably outperform it."



The F-16, Kloos says, is a very capable aircraft in a within visual range engagement--especially in the lightly loaded air-to-air configuration used during training sorties at home station. "It's really good at performing in that kind of configuration," Kloos says. "But that's not a configuration that I've ever--I've been in a lot of different deployments--and those are the configurations I've never been in with weapons onboard."

Not really anything specifically negative but I wouldn't call it an overwhelmingly positive assesment either.
He's comparing the most capable F35 (the A) vs a run of the mill F16 with ,what sounds like, a CAS load, in which case the F35 sort of outperforms the old F16, but it doesn't seem to be so impressive when loads are lighter (eg. like only A2A missiles for air supremacy tasks).

All this knowing that besides the, albeit very capable, F16 there are also fighters like the F15, the RAFALE and Eurofighter which are all much more capable and have a substantially higher T/W ratio (let alone lower wingloading) than said F16 and ,more worrying, the F35.

I wouldn't call this a ringing endorsement for the F35A from someone who certainly is in a position to know, let alone the much heavier B and C versions.

[RansS9]

I understand the argument about comparing performance between combat loaded aircraft rather than their airshow unloaded equivalents but isn't that what the jettison stores button is for.

It would be interesting to know which is the more quickly reconfigurable a conventional jet with hung stores /weapons or a stealh design with fuel and weapons integrated. Having said that you can still have them hung off the stealth design. What price stealth ?

Back to the 7G. Is the consensus that it is worth building jets to manoeuvre upto the restrictions imposed by the pilot or is this level of manoeuvrability not required tactically?

I thought i heard (not a pussy cat!) that USN F18 were restricted to 7G ?!?

TIM

[kbrockman]

Feel free to correct me if I'm wrong but I believe the classic Hornet was/is limited at 9G, at least the Swiss Hornet's are.
The newer Super Hornets are 7.5G, I think.

Also, just to show what a full loadout can do, a RAFALE with a full load is limited to 5.5G, mind you, a fully loaded RAFALE brings a hell of a lot of weapons and fuel to the fight.

[Feck]

Hornets are all 7.5g bar the Swiss ones.

F35A = F16 replacement = 9g
F35B = Harrier = 7g
F35C = F18 = 7.5g

The point of F35 is sensors and stealth...that there are jets out there that will outperform it shouldn't be a surprise.

[ICBM]

Available 'g' is vital in a dogfight; that's why dedicated air-to-air fighters are designed to pull a lot of g. At the inception of F-16 and Typhoon designs the philosophy was that a dogfight would be the end result against a worthy adversary and that manoeuvre potential would ultimately decide the winner; 9g being an uncomfortable yet tolerable limit for sustained fighting.

The philosophy behind F-22 and F-35 is that if they get into a merge something has gone wrong. Both will kill enemy fighters without them knowing what's going on and you don't need 9g to fire a missile. If you did find yourself in a turning fight one would hope that even if the advanced sensors didn't allow you to merge with advantage, modern missile capability would put the fight in your favour.

I would bet that in 99.9% of engagements JSF doesn't pull 7+ g at all.

[5 Forward 6 Back]

I'm not sure. While sensors and weapons have increased in capability to allow fighters to kill adversaries BVR better than ever before, I don't think you're ever likely to see suitably ROE to allow you to employ at that range.

I can see a lot of situations where a VID'll be required; and then he's a lot closer, even using an IRST system.

[sycamore]

Same question,but not answered..Who is `HE` gonna be...?

[davejb]

5F6B sounds (to me) like a sensible opinion - capabilities generally outperform the ROE restrictions, in which case you can argue that sensors trump all else (the better they are the sooner you can call the other guy a baddie and kill him) or manoeuverability wins out as everyone ends up in a visual range knife fight.

Here's a plan - shoot the politicians and let the airforce draft the ROE... problem solved?

[thebmer]

Out of curiosity how often do you drivers take F 16's and similar to the limit?
Used to depend on how old you were.

My expereince was I could do it just as often as I got older but not for as long. Kind of the reverse of life's other great pleasure.;)

[ICBM]

ROE is a fair argument however it depends on the conflict and the rules. The 5th Generation platforms have made huge advances in this regard. After all, sometimes you only have to know who NOT to shoot to distinguish friend from foe. Like I say, it's conflict dependant and won't always apply - so there are a few more tricks up the sleeve ;)

[henra]

If you did find yourself in a turning fight one would hope that even if the advanced sensors didn't allow you to merge with advantage, modern missile capability would put the fight in your favour.


That's at least what the LM marketing department suggests.
My problem with that is that (at least in a stealthy configuration with only internally carried weapons) F-35 can't employ AIM-9X and is consequently at the moment not planned (budget wise) to be equipped with them.
So once out of the inner AMRAAM envelope you'r in deep s**t vs a HOBS IR missile equipped opponent.

I'm not sure about ASRAAM for the UK version though.

[Courtney Mil]

If you can 100% guarantee to kill all the bad guys pre-merge, you only need enough g to position to shot them and turn round once they're all dead. If out-numbered, targeting isn't perfect or Pk/counterneasures leave survivors of the first fox-3s then you have a choice. Blow-through, run and at sometime come back to re-engage. Turn and run, neatly placing the bad guys behind you or stay and fight. Even with off-boresite weapons and versatile aiming, turning at 7g against a 9g+ opponent is a massive disadvantage and is likely to end in tears.

F-15 and F-22 air-to-air pilots are trained to fight at maximum g at corner velocity. Any less and you lose. :eek:

Even LM can't change all the laws of physics.


Just This Once... indeed. Take those bulky red things out and there'd be space for more real weapons. :ok:

Courtney

[Lonewolf_50]

FWIW: The G requirement and limit doesn't just apply to the dog fight, it also establishes the boundaries of defensive maneuvers you can apply when defeating SAMS and Air to Air missiles via defensive maneuvering ... breaking lock and such.

No further comment.

[ICBM]

FWIW: The G requirement and limit doesn't just apply to the dog fight, it also establishes the boundaries of defensive maneuvers you can apply when defeating SAMS and Air to Air missiles via defensive maneuvering ... breaking lock and such.

Chuckle :rolleyes:

Courtney, LM aren't trying to change the laws of physics and aren't pulling the wool over the eyes of the misinformed either. F-22 is an 'Air Supremacy' fighter; so was the F-15C back in the day and it is no coincidence that the former is its equivalent in 5th Gen terms. Does F-22A require 9g capability? I'd argue not as much which is why she's introduced the ability to point her nose pretty much anywhere so that the HOB mxs can do the rest. JSF is a STRIKE fighter and was not designed as an Air Supremacy fighter at all. The prime design has traded a lot to result in the 3 variants we see today; you want all 3 to be 9g capable? thanks, that'll be $$$$$. You want 8 internal AMRAAM/METEOR per weapon bay? $$$$$ again and you've just increased the size/weight of everything.

So, a few F-22As with a few F-35s are a very good mix for a strike package for a multitude of reasons. You have a predominant AA platform that can do some AG as well as a predominant AG platform that can do AA. SA-wise? Mindblowing!

On balance I believe they've got F-35 mostly right in capability terms. Cost and schedule runaways aside of course but for that you can blame politics at all levels.

[GreenKnight121]

Which is why those F-35 customers which will be using it as their primary fighter are buying the 9G F-35A... which IS a pretty good A-A fighter!

[sevenstrokeroll]

I remember that the p51 H had a lower G rating, lower overall weight and higher airspeed than the other p51's.

I would like to think that the amazing advantage of stovl outweighs the improved g of standard takeoff/landing

also, I recall that the F8F Bearcat had a lower g loading than the other navy fighters and had other special qualities.

so, I'm sure , like all planes, there are tradeoffs.

now, me, I'd like to see an F106 SUPER

[ICBM]

Sevenstrokeroll,

Trade offs was my point. Keeping the cost down while preserving customers' Key Performance Parameters is why we have the variants we see now. The slight exception is STOVL as the weight reduction changes in 2005 did alter the design. USAF demanded the A have an internal gun and be 9g capable. Big deck USN was range and approach speed (driving wing size and a need for ailerons at slow speed). UK and USMC was bring-back, hence the crash diet in '05 that made the weapon bay shorter (1000lb vs 2000lb stores)

In response to JTO, UK doesn't want or need F-35 as its primary fighter yet. When it does the requirements to replace Typhoon will be created and IF F-35A meets them it MAY be chosen. It may not. We may be looking at a 6th Gen UCAV fighter that can manoeuvre up to 25g should it's 50 internal BVRAAM fail to do their job.

From our perspective these are separate issues to address.

[henra]

Which is why those F-35 customers which will be using it as their primary fighter are buying the 9G F-35A... which IS a pretty good A-A fighter!

Are you really sure about this?
agreed it will be a much much better A2A machine than the B.
Still I'm not terribly convinced it will be the best A2A machine out there.
Even the (usually rather diplomatic) comments from test pilots indicate to me a step back rather than forward wrt kinematic performance compared to what is lovingly called 'legacy' fighters, including the kinematically formidable Typhoon and Rafale.
Just hope no one finds a way to defeat stealth for the next 40 years...

[Courtney Mil]

the HOB mxs can do the rest.

Back to the laws of physics, kinematics in this case, the further away from the ideal firing solution an AAM is launched, the more work it has to do to perform an intercept. That work comes at a HUGE cost in that it bleeds energy at an alarming rate - massively reduced range and end-game manoeuvre. Easier to defeat and very much reduced Pk.

You want 8 internal AMRAAM/METEOR per weapon bay?

No, unless the aircraft is on a purely air-to-air mission, which we may want it to do if it's the only FJ asset we have on our carrier. My remark was slightly toungue in cheek anyway.

Also remember that all that stealth technology becomes far less effective as your main self-protection method once you start transmitting radar and datalink - especially if you have to keep the target illuminated until A pol. All that time, you're closing on the bad guys (even with a signifiacnt crank manoeuvre).

So, a few F-22As with a few F-35s are a very good mix for a strike package for a multitude of reasons.

As we're not buying F-22, we may need F-35 to be a very capable air-to-air machine in its own right.

You can give avionics and stella SA to any platform at any stage of its life. What you cannot do is give it better aerodynamics, better energy management, supercruise or an increase in either corner speed or max G. The F-35 is what it is and I am not convinced that at IOC plus 7 years that anyone will hold it in high regard.

Absolutely correct. If you shoose to put all your eggs in one basket, it had better be a very capable basket. The figures we're looking at here, don't suggest that it is.

I would like to think that the amazing advantage of stovl outweighs the improved g of standard takeoff/landing

What amazing advantage? Being able to land and take off without cats and traps is not really an issue - just fit cats and traps. The trade-offs for this dubious capability are just too great in terms of range, loiter, cambat load, bring back and, most importantly, combat effectiveness. What's the point of having another jumping bean if it's out-perfomed by the bad guys' fighters?

Still I'm not terribly convinced it will be the best A2A machine out there.

Nor me.

I'd like to see an F106 SUPER

Now there's a thought!

[LowObservable]

ICBM

On balance I believe they've got F-35 mostly right in capability terms.

Possibly.... For a USAF/USN strike fighter, sort of an F-117 plus SA and self-defense, adverse weather and moving targets, with pylons for Day Two, - with other fighters leading against the adversary fighters.

For others, as the F-16/F-18-type fighter for strike, CAS, DCA, OCA, air defense, air policing, maritime, show of force, NTISR, making coffee and bringing in the coal... Not so sure.

Cost and schedule runaways aside of course but for that you can blame politics at all levels.

I don't. Neither does RAND.

Root Cause Analyses of Nunn-McCurdy Breaches, Volume 1: <em>Zumwalt</em>-Class Destroyer, Joint Strike Fighter, Longbow Apache, and Wideband Global Satellite | RAND (http://www.rand.org/pubs/monographs/MG1171z1.html)

Long read, but worthwhile. This program has been fully funded at all times.

[ICBM]

Just this once we seem to be in agreement.

12 years ago we set out on a requirements path for a STOVL carrier aircraft to fulfil our means and replace the venerable sea jet and GR9. It beggars belief that the requirement suddenly changed 2 years ago when some over-zealous senior officers sought their own nirvana of a British CVN-style CAG. They were fed incorrect cost and schedule data for conversion of CVF by sources close to the carrier programme and, unfortunately, somehow bent the ear of a fresh, new government that actually heeded this tripe. A poor move indeed. That has resulted in an embarrassing u-turn by the coalition politicians and red faces by those that said this could work - those individuals have IMHO made things worse than staying with the original plan. However, when you are a former Navy that once had eyes on 2/3rds of the globe it's hard not to resist a last minute upgrade to its current small fleet is it?!

All in all a bit of buffoonery

[ICBM]

LO

The Programme has always been funded; don't disagree there. How about LM politics of not being transparent with what was achievable in time and cost? How about those in the Pentagon who would not let a bad word be said on F-35 or let bad news out to those above? How about the politics of 8 partner international nations and not losing face; being seen to be out of control of issues?

They only came to light because they were impossible to hide or explain any more.

[Engines]

ICBM and Others,

I absolutely agree that the SDSR decision and the subsequent U-turn is a major cock-up. Although, perhaps, Hammond may deserve some credit for changing course when all the best evidence told him he had to. In 'Yes Minister' terms, it was certainly a 'brave' decision.

I don't know all the insider details, but trying to pin it on 'Over-zealous senior officers' in a 'Former Navy' who were pursuing a 'Nirvana' seems simplistic at best. I have heard, from reliable quarters, that by SDSR 2010 there were plenty of scientists and Service officers (including RAF and RN) who were briefing hard against the F-35B. My take, for what it's worth, is that is plenty of blame to go around.

It's fair to criticise the programme, and also right. It's had plenty of problems and will have more. There are decent books to be written about the reasons, I'm sure, at some time in the future. But there has been plenty of independent, published reporting and analysis (GAO, Congressional Research Service and the US DoD to name three) throughout the project. You could, fairly, look at the lack of visibility on some UK and European projects, and wonder what PPrune would have been saying had they been subject to this level of scrutiny. As I said, I think this scrutiny is all good. But it needs to be rational.

My take is that the F-35 is a fairly typical US programme - they aimed very high, and are pushing the bounds of what is achievable. They are fired and fuelled by optimism, a 'can-do' approach, and of course, very large budgets. For my part, I like to focus on what they are getting right as well as their problems. Especially the stuff that our UK engineers and pilots are getting right.

Best regards as ever to those doing the job,

Engines

[Courtney Mil]

Totally agree, Engines.

In view of the words of wisdom elsewhere here, I wonder what the F in JSF stands for.

Answers on a postcard.

[glad rag]

And to the |OP| you may ask why only 9g when you are paying how many hundreds of millions per airframe?

Still I suppose it saves a bit on the Combat Edge apparel...

[Courtney Mil]

Good point, Glad Rag.

[LowObservable]

ICBM - Thanks for the clear-up.... I see you're not among the "Congress made us do it" or the "we'd be fine if it wasn't for the testing mafia" group.

It was unfortunate, I think, that the program coincided with the Iraq/Afghan wars - so that Congress and the media were looking the other way as it went off the rails.

[Engines]

LO and others,

I freely admit to being in the F-35 supporter camp - but as I've posted before, criticism is always a good thing.

I do, however, have to offer a view that this programme has not had any sort of honeymoon from the media or the politicians. There has been a steady stream of reports since it started, offering a wide range of views, analysis and opinions. Some of it is inaccurate, but many of the most critical reports (GAO are a good example) are stuffed with really very accurate detail. Go and take a look.

I also have to offer the opinion that the F-35 is not 'off the rails'. Problems? Yes, sure. Being tackled? Yes, that's what programmes like the F-35 are about. Nimrod MRA4 was 'off the rails' for years and no-one noticed. And it was REALLY off the rails. Typhoon had a very sticky couple of years and nobody leapt about, mainly due (in my view, anyway) to the low standard of UK defence reporting, as well as our natural secrecy.

To answer the question posed by the thread - why only 7g? Quoting my old aircraft design prof at Cranfield, you can imagine an aircraft's design space as a large balloon. The overall size of the balloon is driven by aerodynamics, physics and chemistry. Pull one bit out or push it in, and you will get a compensating push or pull somewhere else. For F-35B, the driver was weight, and taking 1.5 g's worth of metal off the airframe was, in the view of the designers and the customer, the right trade to do.

F-35, whatever variant, is not a light weight air superiority fighter, which is where the F-16 started out. Nor is it an Air Dominance fighter like F-22. Different requirements generate different designs, and comparing one bit of the performance envelope of two different aircraft is always going to be a bit of an academic exercise. The F-35 team, in my view, made a conscious decision to trade a high G capability for more internal volume for weapons, avionics and fuel. More internal volume means more structure, which in turn means that getting to 9g adds literally tons of metal.

Hope this helps a little

Engines

[GreenKnight121]

Quote:
Originally Posted by GreenKnight121 http://images.ibsrv.net/ibsrv/res/src:www.pprune.org/get/images/buttons/viewpost.gif (http://www.pprune.org/military-aircrew/486291-why-only-7g-post7212044.html#post7212044)
Which is why those F-35 customers which will be using it as their primary fighter are buying the 9G F-35A... which IS a pretty good A-A fighter!

Are you really sure about this?
agreed it will be a much much better A2A machine than the B.
Still I'm not terribly convinced it will be the best A2A machine out there.
Even the (usually rather diplomatic) comments from test pilots indicate to me a step back rather than forward wrt kinematic performance compared to what is lovingly called 'legacy' fighters, including the kinematically formidable Typhoon and Rafale.
Just hope no one finds a way to defeat stealth for the next 40 years... Note the two red-colored parts?

I never said the F-35A "will be the best A2A machine out there", that is your distortion of my statement.

I said the F-35A is "a pretty good A-A fighter"... which is a very different thing.

All the USAF brief for F-35A said was "exceed agility and maneuverability of F-16".. nothing was said about Typhoon/Rafale/etc. So naturally, it compares favorably to F-16, but not so well against Typhoon or Rafale.


F-16s never could beat MiG-29s or Su-27s, but they could hold their own... which is all F-35A has to do against the various MiG-35/Su-33/J10, etc models... and to put up a credible defense against T-50s & J-20s.

Does this mean combat losses? Yes... but not overwhelming losses, and there won't be all that many T-50/J-20s (or MiG-35/Su-33/J-10s) to defeat... since Russia is having to keep a much smaller air force (as is China) than the huge numbers they fielded in the 1970s-80s-early 90s.

[John Farley]

Why only 7G in a jet fighter when the pilot can for short periods endure 9G

Because aircraft design is about compromise. To ask for 9G instead of 7G will make the aircrat heavier (which reduces its lower speed manoeuvrabilty) will make it cost more and reduce a whole lot of other performance parameters.

[henra]

Note the two red-colored parts?

I never said the F-35A "will be the best A2A machine out there", that is your distortion of my statement.

I said the F-35A is "a pretty good A-A fighter"... which is a very different thing.


Maybe I was a bit too polite towards the F-35.
I'm worried that if the best version is considered 'pretty good' compared to 70's designs where does that put the lesser versions in 20 years from now?


All the USAF brief for F-35A said was "exceed agility and maneuverability of F-16"..


If the statements were like that referring to a clean configuration I would be a little less worried.
However, I saw this statement always followed by 'in a normal combat load configuration', i.e. compared to F-16 with drop tanks and lots of ordnance.

Could you point me to a statement from a test pilot where he compares F-35 against F-16 clean A2A with maybe 2 heaters and 2 AMRAAM and 50% internal fuel?


F-16s never could beat MiG-29s or Su-27s, but they could hold their own... which is all F-35A has to do against the various MiG-35/Su-33/J10, etc models... and to put up a credible defense against T-50s & J-20s.


Which is exactly where I'm a bit worried. Although I don't buy into that Carlo Kopp paranoia stuff where even a SU-35 will have an even chance against an F-22 I see an alarming expectected kinematic difference between a T50 and an F-35. If they don't mess up completely (which they didn't with the predecessors) I expect that thing to have similar speed and acceleration performance in max mil as the F-35 in full AB.
not mentioning wing loading and thus turn rates.

And we are still talking the 9g variant. I wouldn't want to sit in a B against such a thing. The C Version should have at least very good low speed turn rates (ITR+STR) with that big wing area and low sweep even at 7,5g.


Does this mean combat losses? Yes... but not overwhelming losses, and there won't be all that many T-50/J-20s (or MiG-35/Su-33/J-10s) to defeat... since Russia is having to keep a much smaller air force (as is China) than the huge numbers they fielded in the 1970s-80s-early 90s.

I tend to agree to that assumption (at least for Russia).

[Lonewolf_50]

Chuckle :rolleyes:
Laugh all you like.

FBW designed in limitations to performance are all the rage in design these days.
(That said, maneuver isn't the only way to deal with SAMS, but it's part of the tool kit).


EDIT: From the Rand piece.
Unrealistic Baseline Estimates for Schedule and Cost.
The requirement to replace aging fighters, the need for affordability, and the belief that significant cost savings would be realized from implementation of acquisition reform practices all contributed
to an overly optimistic schedule and cost estimate.
Snow job, not that unusual in acquisition.

The JSF Schedule Was More Aggressive Than the F-22 Schedule. Although the JSF baseline program schedule allowed more time than most aircraft between contract award and first flight, and between contract award and IOC (March 2012), these time periods were less than those for the F-22. The original schedule for STOVL from contract award to IOC was tighter than for both F/A-18E/F and F-22.

Wonder how the OBOGS/Oxygen system is doing. :p