LmRaptorWhy are the Air Force getting AIM-120Ds now if the F-22 can’t handle them until 2017?
Is there a vibration problem with the AIM-120C on the F-22?
Wouldn’t the F-22 be the perfect aircraft to patrol the no-fly zone over Libya?
Because the F-22s don’t need D now – putting D on F-15 and F-16 now is more essential. Other upgrades are more urgent on the F-22. Additionally work on 9X and D will start well before 2017, but it takes sometime to fully integrate the new missile.
No the F-22 would be far to expensive to patrol the no fly zone over Libya. The least expensive AtA platform in Nato’s arsenal would tend to be too expensive (F-16/Gripen)?- especially if it is backed up by AWACs and other off board sensor systems.
LmRaptorParalay, do you have an english version of that excel spreadsheet?
LmRaptorI must say that is fairly disappointing. I thought the Rafales rear fuselage stations were recessed?
LmRaptorI’m surprised nobody has linked this yet: http://online.wsj.com/article/SB10001424052702303654804576350083016866022.html
They didn’t reveal who has stolen which information.
http://www.channelregister.co.uk/2011/05/27/lockheed_securid_hack_flap/
RSA has publicly explained how the attack might have taken place but not what was obtained. It did however warn that the breach may affect the level of protection offered by SecurID tokens, which are very widely used for two-factor authentication.
Potential hackers would still need a lot of information – including user account names and PINs – to break into corporate email or remote access systems protected by RSA SecurID. Our best guess is that Lockheed detected an attempt to access just this information and responded by suspending remote access and shutting down portions of its network as a precaution.
LmRaptorLM raptor, Look
If you build a fighter with radarrreflection shaping as the main requirement.
aerodynamic drag and turnefficiency will suffer, thats a fact.
If you build a belly with big crosssection there will be exponential more drag. even if you add som stores under the wings that dont add as much as adding a big storage box in the same crosssection as the mainbody.IF you can build a stealthfighter with materials only in the future that will give “back” the aerodynamic freedom that was lost. and that is probably the way it goes..
just look at F-117>F-22
Firstly Sign, I am not here to argue with you mate, as I know what I am talking about. Secondly lets get a few things straight. You say aerodynamic drag suffers and thats a fact. From a purely semantical point of view you are absolutely correct. Thats because aerodynamic drag is a force and its an absolute – rather than a ratio. So assuming you have actually read what I have written – then yes aero drag does increase for the cases I have mentioned. But that isn’t what we talk about as an aerodynamicist. Aerodynamicists are the last people in the design chain – we get a design built from the inside and we tailor the outside to match the requirements. That means things like reference area are not directly influenced by our decisions – the areas are influenced by other design decisions. What is influenced by our decisions is coefficient of forces (being drag or lift). These are the measures of how efficient or advanced the design is from an aero point of view.
So say jet A and jet B are being designed to have the same flight performance; but A has this RCS requirement that B doesn’t have – meaning A needs an internal bay. Now flight performance is a proper engineering requirement – as opposed to an absolute drag value at some arbitrary flight condition. Now effectively what you and Wilde are arguing is that B will always be better from an aerodynamic point of view. What I am saying is that you are wrong. That is because A can be scaled to such a degree – assuming the engine is scalable (the caveat I mentioned at the beginning) – where not only is the the area offset by the thrust – but the drag coefficient reduced due to the bay which as a result of its sufficiently scaled size – is able to prove less draggy per unit of area than jet B with its external stores. This is because it can be tailored to filter out large curvature, wave drag effects, interference effects, asymmetry etc… THAT YOU ALWAYS GET – no matter if you have a BOMB or a MISSILE hanging under the wing. Now this BASIC principle has always been the case since we started building weapons bays. The first bays were designed to increase the aerodynamic efficiency of the design and therefore improve the flight performance. It was more typical on Bombers as the negative aerodynamic effects of bombs are more of an issue than missiles which would be seen on fighters. Now the tradeoff here is both COST and COMPLEXITY – and no one disputes that – the cost of scaling a bomber and developing internal bays more often than not was WORTH the COST and COMPLEXITY – but in most cases for fighter aircraft and missiles – it was not WORTH the cost assuming you could scale the jet.
But the fact remains that you can achieve the same flight performance/aerodynamic EFFICIENCY – assuming you can effectively scale the design. The F-22 and the PAK-FA are cases where that does indeed prove to be true. NO they do not have bays because of flight performance requirements, they have them for RCS requirements. But that doesn’t mean that bays are not more efficient from an aerodynamics standpoint – because they are – if designed properly they will always lower the drag per unit area. Its just that to make a fighter with a bay – assuming the scalability principle can occur – generally offers MARGINAL performance benefits for HUGE/HIGH cost increases. So therefore they are not employed typically in fighter aircraft unless other requirements become the main driver – namely RCS.
As long as you can keep the major ratios the same – then the performance will be the same – and the aerodynamic tailoring will be as advanced if not more so for the scaled up aircraft. Generally speaking performance actually improves as the drag and mass of the aircraft don’t scale linearly. So to maintain the same TWR ratio between Jet A (F-22/PAK-FA) and Jet B (Typhoon) you get an improvement for A in (T-D)/W ratio.
I’d also like to point out that adding a bay doesn’t exponentially increase drag – I wonder do you know what exponentially means? Also I have no idea what you mean by F-117>F-22??
Wouldn’t a large a/c like that be better off shaped like flying delta wing,
also how fast is it intended to be, straight wings will suffer wave drag.
Anyway perhaps the struts can be shaped to create some additional lift,
almost like WW1 revisited.
Yeah aerodynamicists are looking at making the struts add to the lift. The point of the strut is to alleviate bending moment and as a result reduces internal wing weight needed to stiffen the wing. This drops wing weight – which drops lift requirement – which drops wing area – making the wing smaller. So much so that for typical airline cruise speeds of Mach 0.85 we can reduce the t/c (look at how tiny that wing box is compared to a modern airliner) so much that the sweep becomes less relevant. Lower sweep = less wing weight = less area etc.
A winglet only serves two purposes. It moves the outer wing vortex away from the wing. This is needed to make use of the whole wing creating lift. And it tries to reduce the size of the outer wing vortexes, because multiple small vortexes are better than one huge one.
I agree with Sign. You can tailor an omnibus all you want but it wont become a Ferrari. The difference with/without bay might not be that big. But it will always be there and it will always inflict consequences. They are not doing it for aerodynamical performance, but for stealth. It’s a compromise of forsaking aerodynamical performance to gain survivability due to radar avoidance.
Which in effect increases the efficiency factor k = 1/e in the Cdi equation – lowering induced drag and creating a more elliptical lift profile.
Firstly Wilde – your analogy is incorrect – as a car cannot be scaled sufficiently – it is restricted to the Road which is of fixed size. These issues become less relevant in aviation.
Secondly, yes, they are not doing it for aerodynamics – sure – but that doesn’t mean, if done well like in the case of the F-22 and the PAK-FA, that it is aerodynamically less efficient or compromised at all… this is what you guys need to get in your head. They have scaled the jets in the other relevant areas to turn what would be an aerodynamic compromise that you get on JSF into a cost and complexity compromise only.
LmRaptor
This is the idea. Strut in tension against lift during flight, dramatically lowers root bending moment – meaning less internal wing mass needed to stiffen wing against lift. Resulting in a long span for a given application – since strut carries a lot of the load more efficiently than the cantilever wings on typical airliners – resulting in lower drag – smaller wing and so on and so forth – till you iterate down to a much lighter wing which has more area along the span. The higher AR means designers are looking at L/Ds of 30 + while today most state of the art airliners are flying around 20. Other than L/D benefits – the wing itself has dramatically lower wave drag and a much higher critical Mach. Problems are that strut wing brace of course and also when the jet is idle and on the tarmac – the root has to take all the load – unless the strut is cleverly designed.
LmRaptoryou can stroll around F-16.net and find out what they really are for.
as to winglets,
Think about it this way, what’s the best dihedral angle for winglet?
flat and become part of the wing of course!a bigger aspect ratio would always, always, always get you better L/D.
so why doesn’t airliners etc have flat winglets?
ah, it turns out a bigger aspect ratio wing would increase your wing root bending moment… key indicator of structure fatique and loads.
increase loads = increase structure = increase mass.by having mass in outer span, the total load on the wing is the same… the wing would still carry the same weight, but the wing root bending moment is smaller now.
so there is always a trade. 😉
( btw, a true loads/structure experts can correct me, I do not pretend to know all about this stuff )
Haha, what you say is generally true i.e. A flat winglet however is effectively an extension of the wing which does help with L/D as you rightly point out by increasing AR. The major issue here from an airliners point of view isn’t actually structural – its regulatory – from a structural point of view we could be building high aspect ratio airliner wings with AR > 12 quite feasibly. The big issue with this is of course the span which breaks airport compatibility limits. IIRC looking at the Dreamliner with its winglets – I think it barely manages ICAO Code ‘D’. So winglets help cheat span issues – not just structural but also and mainly – regulatory.
Or if we are brave and perhaps clever as designers – to truly alleviate huge root bending moments and radically increase AR at the same time – we should look to my favourite idea – which is a strut braced wing. Similar to a Cessna but taking it into the world of transonic drag – which is the major issue. The acute angle between strut and wing produces a choking effect and lowers aircraft crit mach significantly – although work is currently underway at a few institutions – including mine to work around this.
LmRaptorThat french blog looks laughable
LmRaptor“while the Typhoon is at least 5 years behind in overall capabilities in every Ops you can think of , including the AtoA warfare .”
This is a nonsense statement.
LmRaptorMost modern early warning radar can detect VLO or LO even if they can’t guide a missile to destroy them. But a interceptor with a good radar (AESA) can investigate and do the job.
Hopefully they don’t die trying 😉
LmRaptorI.e. I would speculate that the main reason the F-16 carries AMRAAM on its wingtips is that it reduces spanwise flow and as a result reduces vortex induced drag (drag due to lift) – in a similar manner to a winglet on an airliner.
LmRaptorLook Wilde. If you read what ive said, you will notice im not advocating LMs products by following their PR chat. I used words like tailored and i mentioned specific cases where i believe an internal bay is properly designed i.e. F-22 and PAK-FA and cases like F-35 which due to other engineering constraints is not a good tradeoff aerodynamically. Nothing that i have said contradicts aerodynamic laws and i would know considering ive been fortunate enough to spend 4 years learning about aerodynamics. Reread that i was saying a well designed internal bay – aero optimised should be able to outperform an aircraft with external weapons given caveats ive mentioned. The reality is not all jets are designed so.
LmRaptorWhy? Internal bays increase drag-area much more than externally carried weapons. Yet external carriages, especially A2A missiles don’t exactly have a horrible drag coefficient either. Bays also increase weight and force compromises in fuselage design. How exactly do you reckon a bay improves aerodynamical performance?
Why? Firstly the stipulation of a sufficient engine by definition here means it needs to be scalable. Therefore as you scale aircraft size/volume – the related mass increase needs to be offset by a similar thrust increase to keep the TWR the same. Once that is achieved for that given increase in reference area, to fit the bay of sufficient size; an internal bay should then result in a lower drag coefficient in every condition as it has been sized sufficiently. Since it is sized sufficiently it can be tailored to taper in such a way to reduce curvature in normal flight. This becomes a big thing the lower you fly generally – especially if you want to increase your critical Mach. It also becomes essential at high speeds… weapons configurations are terrible at high Mach, even very well designed configurations seen on jets like Typhoon. The reference area on such a jet is – correct – less, but at these high speeds even conformal configurations balloon in drag coefficient at high speeds. This is due to the lack of tapering, the interference and the curvature. The other issue is also the lack of room for the conformal weapons. Usually pylons are then employed in a much less efficient state. Weapons bays also reduce asymmetry after weapons release and offset any trim drag issues as a result.
As a result, a well designed weapons bay for a given weapon configuration, should generally drop the drag coefficient in all conditions by a significant amount. The reference area generally does increase – but not always – and generally the effect of the decreased drag coefficient is greater – relative increased thrust levels of the scalable engine – than the effect of of the increased reference area. As a result all things do not remain equal. The externally configured jet with X thrust, Y reference area and Z drag coefficient – should be transformed into an internally configured jet with X + 10%, Y + 10% and Z -5% for example.
What happened in the F-22s case – a case where the internal bay is effective – is that for all things to remain equal – i.e. TWR, L/D etc we get to a point where the jet has very high excess thrust – reference drag area… A Typhoon would need the F-22 to be approximately twice as draggy to keep with it in an acceleration race. It isn’t close to twice as large from any reference area you choose – which is further exacerbated with the carriage of external stores.
nah even for top of the line jets where they can splurg they didn’t have much internal carriage (mig-25/F-4/F-15/Su-27)
typically given the same compression ratio and turbine inlet temp your engine’s sfc is about where it is. which means for bigger thrust requires a bigger engine that burned more fuel.
so unless you are building a manned rocket… the bigger body / bigger wetted area necessarily requires a bigger engine. given the speed constraints.
range then suffers.they had multiple requirements back then. turns out droppabe fuel tanks and stores get you more.
Of course – you need a bigger engine – as I said, it needs to be scalable. Range doesn’t suffer if L/D, Fuel fraction etc are kept constant – the greater engine power and volume allows for more fuel and as long as that fraction is the same then you get the same range.
Then with that all in mind – it comes down to cost/complexity as all those design issues can be transformed from technical issues that would effect the spec sheet into a cost issue.
LmRaptorIt wasn’t drag or engine size or anything else. It was simply mass which is relatively proportional to cost. When mass/size/cost do not matter, a tailored internal carriage jet paired with a sufficient engine can aerodynamically outperform a jet which carries the same weapons load externally with a sufficient engine. The real issue is cost and complexity. Efficient examples of this are the F-22 and the PAK-FA whereas the F-35 is not an efficient example due to other design constraints including – mass/size/cost.
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