kilcoo316Yeah – real “cool” :rolleyes:
Nothing like a bit of bloodlust to brighten up a day huh? 🙁
kilcoo316NAVAIR pretty much put the kiss of death on any airplane with a landing speed greater than 130 knots. Heavy weight (ordnance bring back) and high landing speed exceeds the capability of the arresting systems and would cause an order of magnitude more landing accidents (not good especially if bring back ordnance is involved). I believe Su’s landing speed is ~150 knots.
Fair enough.
It makes the choice of wings pretty simple though… you’ve either:
– swing wings
– or –
– sh_t wings
:diablo:
kilcoo316If you guys are right (as you must be), I don’t know why a number of big names have bought into this technology (?) Maybe they have something, or maybe they figured out how to include the mesh error in their calculations..
A boundary element technique cannot account for turbulence properly, indeed, it would be completely useless at it. Thus, even for highly laminar flow (50+% over an aerofoil) it still wouldn’t be right as it doesn’t get the turbulent boundary layer wake correct.
For lift generating wings, induced drag forms the majority of the drag produced. Again, boundary element techiques cannot really approach this properly, apart from using Prandtl’s lifting line and making guesstimations as a result.
There is no such thing as a free lunch in CFD – but I do recommend you look at companies that are willing to use GPUs as accelerators for the operations (like the NASA SETI program does with some ATI cards). AMD have demonstrated 1 GFLOP performance from 2 opterons coupled up to 2 crossfire ATI/AMD cards that can act as accelerators. Thats around 10x the speed of current CPUs – and it would be real useful for CFD work.
kilcoo316Thank you djcross and Kilcoo316 for the tips. Taking the opportunity, I would like to ask you how probable you think it is to see some day soon the Super Hornet with conformal fuel tanks like those of latest f16 bloks and the ones tested over the Rafale recently? What about the aerodynamics if such a scenario gets implemented?
Thank you
Hmm, just thinking about that I’m wondering why they haven’t stuck conformals on the outside of the two engine nacelles, then with some nice design touches, it might not be necessary to splay the two inner pylons out to ensure weapons seperation.
Although, what is the Super Hornet’s T/W ratio like? Is it not pretty shocking at the moment? You don’t want to add more weight to an already handicapped airframe.
Also, ff it cannot get off the deck with conformal tanks and a decent loadout, it probably won’t get them.
kilcoo316Hey Flex, you’re the biggest ANSYS guru here I recon. Its a small Russian company called GDT Software Group. I must admit I’m in a bit of a fix as this company was not in my plate for the last 2 months but got dumped on me 12 hours ago and now I need a crash course in comparing gas dynamics software and 3D visualization software.
They have some big names as their clients, I’m wondering if they can compete against the big names in this sector like ANSYS, (particularly after ANSYS’s acquisition of Fluent).
Also, the key element for them is that its claimed to be 50 times faster than Fluent or the other competitors. How useful is that, practically for a typical user? I’d think it would be useful in analysing nuclear reactors on the fly but .. ? what else is there?
As flex says, there are 2 fundamentally different types of CFD solver, finite element (FEM) and finite volume (FVM).
Classic CFD [like fluent, CFX, star etc] use the finite volume technique, it takes longer, but produces results with less numerical error.
The FE methods will have more numerical error, but importantly, they can quantify discretisation (mesh) error, which a FVM solver won’t.
There are also boundary element methods, but these are used more for acoutics than for aerodynamics. They cannot consider turbulence interaction, so for detached flows [like an aircraft at high AoA] they are essentially rubbish.
However, if the flow is nearly all laminar, or the only turbulent section is the boundary layer, you may get quite accurate simulations. But you need to be careful.
What exactly are you looking from the software?
kilcoo316MCAir did fix deficiencies of the A&C fuselage with the exception of aft fuselage droop when the engine bay doors are open. Where the F-18 design fails is the straight wing to provide slow landing speed for CV operations. To reduce drag, the wing had to be thin and this caused aeroelastic problems. Despite all that, the straight wing is still super draggy.
Yeap, I’d pretty much agree with all that.
Thing is, a thin wing is usually pretty crap subsonically [certainly compared to a thicker section], so they shot themselves in the foot to a degree there too. There was a good reason for the Tomcat having a swing wing, and they thought they could get around it with the Hornet.
It does look like the Su-33 has got around those problems to an extent, a cat launched version of it probably would have comparable operational capabilities to the F-14.
kilcoo316Could it be possible that some short of a redesign over the airframe of the Super Hornet, would deliver a most capable aircraft, especially now that potential clients like HAF and Indian Airforce appear and companies like LM, EADS & Dassault contest too?
Thank U
It would be much better going from stratch, then you are able to fit your wingbox optimally, stress the components much better and make a lighter machine with more available internal volume and have better control of the centre of gravity.
The Hornet’s main advantages are its avionics and radar. Both of these can be swapped out into something else comparitively easily. I see no reason to retain the hornet in any way shape or form.
kilcoo316But you should be careful which such broad statements. For example, the SH really has a (minor) range advantage over older bugs (“we outran them…”)
and it also can break the soundbarrier below 10000 feet, contrary to what some hardcore Tomcat people say.
While it may carry more fuel, it also has much higher drag rises, so its very concievable a smart C pilot will outrun an E.
What? In a vertical dive? :diablo:
kilcoo316E/F is a great airplane that is hamstrung by a wing design optimized for carrier-based operations. But it is now and will forever be what it was originally designed – a light attack airplane to replace the A-7.
Gotta disagree man, the airframe itself is a pile of s__t.
The original F/A-18 needed several fixes, that didn’t change for the E/F model.
That AESA radar and the cockpit avionics are great – but they are let down by a savagely bad airframe.
kilcoo316As for the old hat story of the Standard crew saying -“We out flew……ran them out of gas ” was just macho nonsense,probably bar room talk, the Classic hornet was/is notorious for its short legs & carries 4000lbs.less internal fuel than the SH., its never going to run it out of gas,
the above report is now 8 years old & the SH , now in block2 is a far different beast to the one they derided all those years ago. [ ****,where did those years go to]
Don’t be so quick to dismiss it – we know the SH bleeds energy at shocking rates, so it stands to reason the SH pilot has to sit on the afterburners for much more time to conserve energy. It would not be a surprise at all considering all the band-aid aerodynamics that combine to form the E/F – which of course means in real terms, the legacy Hornet has a better combat radius than the SH.
kilcoo316Navalize an aircraft is not as difficult as it seems
No way man!!!
1. Lower take off speed, need alot more pitch up authority for rotation
2. Lower take off speed, need much better CLs from wing in max lift config
3. Electronic, Airframe and engine exposed to salt – all need corrosion protection
4. Undercarriage takes massive thumps on landing
5. Loadpaths for undercarriage transmits massive thumps on landing
6. Catapult
7. Load path for catapult
8. Engines need to provide much more thrust at much slower ambient flight speeds
9. Pilot needs a view of the flight deck on final approach
10. Aircraft needs to have excellent stability a low and slow flight regime, aileron induced wing stall a possible problem
11. Aircraft has to be stored in a cramped area, large wingspan an issue
Doubtless there are more, these are just off the top of my head.
kilcoo316I said they were better for the flight envelope they were used at.
But they aren’t!
You can NEVER have too high a core pressure (obviously that includes the materials limits) – means better combustion, less fuel use for better power levels.
I thought the other 3 (especailly the MiG-31’s) OPRs would have made that clear.
kilcoo316J-93, J-58, and the engine in the Foxbat were all low pressure ratio engines.
They were low pressure ratio engines for other considerations, not because a low pressure ratio core is better.
The J58-P had an overall pressure ratio of 6 (from 9 compressor stages), while the J-79-GE-17 (as used in the F-4) had an OPR of 13.5 (from 17 compressor stages).
The J85-GE-5H in the T-38 has an OPR of 7 from 8 compressor stages.
So the compromise for the J-58 was fitting in the number of stages, you also have engine turning into a ramjet above Mach 2.2 ish, so they had alot of space considerations within the nacelle – no doubt forcing the low compressor stage count.
Contrast these pressure ratios with the F100-PW-229 (F-15) OPR = 23, the F101-GE-102 (B-1B), OPR = 26.8, the D-30F6 (MiG-31), OPR = 21.15.
All high speed machines, all with higher pressure ratios because the engineers could get it without compromising other things too much.
kilcoo316One of the factors that killed the F-14 was it was over specialized and basicly was only purchased due to the fact the US navy wanted their own fighter, The F-15 was better as a dogfighter and also had AIM-7, it could had been navalized, even carry AIM-54s but since the whole reason the F-14 remained a need was the AIM-54, once the AIM-54 became obsolete, the F-14 also became obsolete and unwanted
Hit the brakes there MiG.
OK, the Phoenix as it stands now is obsolete.
Now, imagine what kind of ramjet you could put into a missile that size 😉
You’ve all of a sudden probably got double the range of the meteor (makes sense since the AIM-54 had at least double the range of the AIM-7). While efficiencies have improved, you can always use the space to give it more fuel, a bigger engine, a bigger warhead etc etc etc.
Compare like with like, not a 1970s missile with one designed 35+ years later!
kilcoo316The type the Foxbat has is more like those on the B-70 ie. lower pressure ratio turbojets designed for high speed.
Don’t mean to **** on the parade, but no designer goes after a low pressure ratio in the core – its bad for a dozen different reasons.
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