kilcoo316Maybe true of the Focke Wulf Ta183 but not the Me163 – the use of swept wings was for increased stability, not to mitigate the effects of compressibility (sweeping the wings gives a similar effect to dihedral). In fact the Me163 had extremely poor high-Mach characteristics as do most swept wing, tailless designs. There was a supersonic wind tunnel in Germany during the Second World War, but the advantages of swept wings in high speed flight were discovered entirely accidentally.
Nope, your getting confused between the Me262 and the Me163.
The sweep on the 262 was for stability (although the designers were aware of the compressibility effects). The sweep on the 168 was for compressibility – which was very necessary considering it achieved speeds of up to Mach 0.8.
As for the benefits of sweep being discovered purely accidentally, that was simply not the case. The following is an extract from one of my own undergrad reports (feel free to use google if you have any doubts):
Adolf Busemann of the German Luftfahrtforchungsamt (aeronautical research establishment) had suggested that swept back wings would reduce the drag in the ‘transonic’ region of flight (where the plane is travelling subsonic, but local areas of supersonic flow may exist, from Mach 0.6 to Mach 0.9) as early as 1935 at the Volta Conference. He had been experimenting using supersonic wind tunnels at the Braunschweig research laboratory and based his ideas on the data gathered during these experiments. Although aerodynamicists from several other countries were present, they did not take his ideas on board, unlike Busemann’s fellow Germans.
—
The high speeds achievable by the Me 163 also showed up a dangerous condition, which became known as the “Mach tuck”. If the pilot exceeded Mach 0.85, a supersonic region would form on the upper surface of the wing, and a shock wave would form, causing a ‘shock stall’. This adversely affected the centre of pressure of the wing, moving it aft, thus inducing a nose-down pitching moment. As the pilot would pull back on the controls, and pull the elevons upward, this caused a shock wave to form on the underside of the wing at the elevon hinge line. Thus the elevons would shock stall and be unable to pull the nose of the aircraft up. The only solution was to let the aircraft dive to a lower altitude, where the speed of sound is higher, reducing the Mach number, then pulling out of the dive.
Alexander Lippisch was aware of the causes of Mach tuck, and tried to design the Me 163B to have as high a critical Mach number as possible. Thus the wings had very little washout (twisting the wing to have a lower angle of attack at the tip than at the root), this is very important for swept wings, as the wingtips stall more readily (tip-stall) which causes the wing to drop. The problem Lippisch faced was that the washout caused the wingtip to shock stall at high speeds, inducing Mach tuck. He then used fixed leading edge slots (called C-slots) to delay the stall of the wingtips (shown in fig 6). Due to its propulsion system, the Me 163 could sustain an angle of climb of 45o, unheard of in those days, at a climb rate of 16,000 ft per minute, which was around 10 times more than any other fighter of the day.
kilcoo316Truth is in 1946 no-one had sufficient experience with compressibility – Spitfire PRXI had made it to Mach 0.93, losing its prop and reduction gear into the bargain, Mustang not quite so good… (If this was sole factor, Supermarine 510 would have gone supersonic and Swift would have been the new Spitfire instead of a dead loss)
Correction, both the Me163 and the Ta183 were designed very much with compressibility effects in mind, and both were designed (the Me163 actually built and flown) during WW2.
kilcoo316Hmmm….
1. Ta183, while probably not technically ‘post WW2’, the MiG-15 which evolved directly from it was still a feared machine in Korea some 10 years later. So the aerodynamic platform was very advanced for the time.
2. MiG-25, put the fear of god into the US, and forced the F-15 and F-14 to become double the machines they would have been.
3. F-14, took the F-4 concept of BVR to a new level. Made the US CVBG the undisputed king of the seas and without the F-14 there would have been no thought of camping out in the Soviet backyard during WW3.
4. E-3, the success ratio of the USAF owes alot to its development of AWACs, and reducing the workload of the pilots to a minimum to maintain situational awareness.
5. F-15, the kill ratio says enough really.
6. MiG-31, still the best interceptor in the world. Who give a sh_t about supercruise if you can stick the burners on for a 1/2 hour?
7. Gripen, cheap, good… no, a great avionics pack, and proof that a competent fighter need not cost sqillions to develop.
8. Su-30, in my opinion the single seat flanker imposes too much workload on the pilot, with the -30, particularly the MKI version, the flight crew can concentrate on their jobs more effectively, namely getting the best out of an undisputably brilliant machine.
9. Tu-22M Backfire, the opponent of the F-14… it had to be good to have a chance of beating the Tomcat, and could well have been – luckily we never had to find out.
10. F-117, signalled a new dawn in air operations.
Notable exclusions and reasons why:
F-22: I don’t consider its rivals to have made their appearance yet. [The EF and Rafale are 4+, not 5th gen IMO].
B-52: A big, fat, slow target on its prime mission of invading Soviet airspace IMO – without fighter cover it would have been a sitting duck.
SR-71: Undoubtedly a top machine, but its influence on the world is relatively small. I would consider the XB-70 more of an influence on the MiG-25s development.
kilcoo316Had Grumman developed and pitched to the U.S.N over the years it might be sitting in better shape, but, it didn’t.
You might be interested in reading this:
http://www.aerospaceweb.org/question/planes/q0132.shtml
Schorsch – ok, transonic drag rises do rule out part of my theory – however, a swing wing will reduce the transonic envelope, and you’ll have the benefits of reduced drag coefficient above Mach 1.5 ish.
Its pretty crucial for a carrier wing to get to defensive intercept positions quickly no?
Don’t forget, that we are comparing what was a pretty basic design of wing with some much more complex ones – with current CFD capabilities, one could expect to improve significantly on the design. Did the F-14’s wing even incorporate LE slats?
edit:typo
kilcoo316This is stolen from elsewhere, but I want to chuck it in here to see if it actually happened – can any verify it as true or false? :confused:
I was paging through my old AFMs when I saw this in an article in the August 1990 issue of AFM on the F-14 written by Squadron Leader Stu Black (RAF):”It was during one of these detachments to Key West that we were able to stage a predominantly RAF battle between F-14s and F-15s. The event took place shortly before my return to the UK and we were in the process of converting a replacement RAF crew who had recently arrived at VF-101. By chance, another RAF exchange officer, F/L Mac Macready was also at Key West with an F-15 squadron from Tyndall. With some reluctance our skipper agreed to a British led four v four Eagles. It was one of the toughest fights I’ve ever been involved in! I had better not go into precise details of the outcome, but I can tell you that we drew Eagles hanging from the gallows in the debrief.”
kilcoo316Blair will be gone by then hopefully :diablo:
Although I don’t think any of the possible replacement candidates are much use 🙁
kilcoo316My understanding is that F-18 and Su-27 (as well aus MiG-29) have less shielded fins. First, the fins still get some air through the gap between wing and tail.
Yeap, unfortunately the F-14’s VG arrangement largely sheilds the fins no matter what the wing position is. It also has to do with the fin placement, on the F-14 it is centrally on top of the engine, on the flanker its outside the engine. Not a big deal to re-engineer in my opinion.
Second, the vortex extending from the LEX increases dynamic pressure on the fin. This effect was so violent on the F-18 that is has small vertical fences on the inlet channel to reduce the load on the fin. There are some downloadable videos on the NASA homepage, just look for HIRV (??) (High Incidence Research Vehicle).
Yeah – incidentally, the F-22 had a similar problem to the F-18, flutter on the vertical stabilisers, LM/NASA looked at it, and have strengthened a few things.
kilcoo316I would be pleased if you can elaborate on that point.
OK.
A basic unswept aircaft has thickness to chord ratio (t/c)0, cruises at M0 and has a lift coefficient of CL0
Thus for a swept wing aircraft (wing sweep is $) assume (its approx right):
t/c = (t/c)0 cos($)
M = M0/cos($)
CL = CL0 cos($)
If you assume the wing area [we’ll call it S] stays constant (it probably won’t quite since a little bit dissapears into the fuselage) then:
wingspan = b = b0 cos($)
Aspect ratio = Ar = (b^2)/S = {[b0 cos($)]^2}/S = Ar0 [cos($)]^2
So after already assuming the wing area stays constant, you can assume the wing loading stays constant.
The drag coefficient is given by:
Cd = Cdf + [K/(pi*Ar)]* CL^2
The above is basically the drag polar with the lift dependant drag factor seperated out a bit. Cdf and K are independant of sweep $ and Mach no. M
It can be said that lift/drag max is given by (equality of friction and vortex drag):
1/2 ({[(pi*Ar)/K]/Cdf}^0.5) = (L/D)max
If you assume cruise L/D to be a function of (L/D)max, i.e.
(L/D)cruise = n(L/D)max
n is usually 0.95 or so, but importantly at cruise the L/D is proportional to the square root of the aspect ratio i.e.
(L/D)cruise = n/2({[(pi*Ar)/K]/Cdf}^0.5)
-so dropping out the constants [Cdf and k are independant of M and $]-
(L/D) = (L/D)0 *[(Ar/Ar0)^0.5] = (L/D)0 cos($) (L/D)
Not forgetting that cos($) = M0/M
(L/D) = (L/D)0 (M0/M)
-or-
ML/D = (ML/D)0 = constant
Since L is a constant (with weight obviously)
M/D = (M0/D0)
or
D = (M*D0)/M0
So drag for a VG aircraft increases linearly with M, whereas for a fixed sweep aircraft, it increases with the square of Mach number (rearrange the equation for drag coefficient subbing in rho = (gamma*P)/(gamma*R*T) = (gamma*P)/a^2
a is the speed of sound… v^2 over a^2 is M^2
kilcoo316Can anybody give me a robust figure for the Tomcat’s range or operational radius?
Deck launched intercept F-14A – 915 nautical miles radius with two 280-gallon drop tanks jettisoned when empty
Deck launched intercept F-14D – 656 nautical miles radius combat range with two 280-gallon drop tanks
F-14D – With two 280-gallon drop tanks retained, 1,591 nautical miles ferry range
Best I can come up with.
Probably more in magazines I have at home, but no access to them at the moment – sorry.
kilcoo316Swing Wings
I tend to disagree.
Your story about drag has wet feet: Drag increases basically squared with speed, but only for subsonic speeds. When the airflow becomes transonic, things get funny. Right is that aircraft with high wing sweep experience less transonic drag rise between 0.9 and 1.2 (which is a reason the Hornet has a little drag problem in this region)
I can post up the maths of it if you want?
but there are better ways:
- A delta with moderate sweep and good high lift (blown flaps) gives nearly equal results.
- Accept higher AoA at carrier approach.
- Reduce weight!!!!! Don’t have a 19ton empty weight supersonic fighter on your deck!
The big drawback of variable sweep is weight, limited structural strength, complexity and limited number of pylons. That does not offset the advantages any more. Just look for the last proposal with swing wings.
A delta does not work in the same way as a VG wing to optimise your wing speed for the flight speed – indeed, it doesn’t come close. No amount of tricks and cfd can overcome basic rules. Don’t forget, what if cfd, blown flaps etc was applied to the Tomcat’s wing? You would expect to see increases in efficiency
Funnily the Tomcat wasn’t particularly good in aerodynamics. The lateral stability must be considered poor in some flight regimes (OK for 1970, but not OK for 2005).
Your “supersonic manouvering” is limited on the Tomcat mostly by the G-limit and the available thrust, I don’t think that control authority is an issue.
It is my understanding that the static margin in supersonic flight was not in the sweet spot.
Yes, I do agree that the lateral stability was poor, a result of sheilding alot of the vertical fins at AoA.
Of course, new engines (with unrestricted intakes) would dramatically improve thrust throughout the flight regime.
Again: How many tri-plane configs have entered service? Additional surface = additional drag and weight. Not the best way to lose something of the 19 tons.
How many prototypes of triplane configurations have there been? 2? 3? the F-15 Active and the Su-35 are the only two that spring to mind.
The one active triplane configuration I know of is the Su-33… funnily enough a naval aircraft.
And it wouldn’t help too much. Look how F-18 and Su-27 achieve superior lateral stability. The F-14’s vertical fins are shadowed for higher AoAs. However, with modern control techniques and high authority FBW you could help out, but this would again need considerable investment.
The F-18 does it through having a different wing postion, the Su-27 is similar, although it uses ventral fins as well – which can be more aggressive as it doesn’t take off from carriers.
Hmm – about using FBW to get over it, stability and control people have fits if the airframe is unstable in both directions through the flight regime. But 3D TVC would solve all that.
I don’t consider the USN as extremely wise, especially is it always between needs, lobbies and congress (like basically every western military organisation). But I think they had their reasons for trading speed against stealth. Flying supersonic close to ground is luxury no fighter can afford for more than 2-3 minutes. For max speed dry at SL you will see Tomcat and Hornet within a range of maximum Mach 0.05.
You can never have too much speed when you need to avoid something.
I agree with your comment on the USN not being particuarly wise though 😀
Actually, I didn’t really consider it. But I don’t see why a mobile force like the US Navy should put the focus on range. For a force that is mostly limited by the number of aircraft available, the focus is on high availability, easy maintenance, similar stocks of weapons and spares, and multi-mission capability.
Surely the experiences of Afghanistan are evidence enough.
It is limited to M1.88 for most times and will not sustain anything beyond that speed much long, either.
Already answered above by Rocky.
The aircraft you propose would have its advantages, but it would not save much costs, would still carry the inherent weaknesses of the Tomcat (weight!) and would look best in a photoshop fan-work. Actually, that is all that I have ever seen of the Tomcat 21.
You would expect what is effectively a new aircraft, with new systems to be much more reliable than a 1960s design – look how far cars have come since then for instance!
True, some of the weaknesses would remain, but I think the Tomcat is ideal for a naval aircraft, big, heavy, long ranged, carrys alot, does it fast, big radar etc.
Basically, I don’t believe a carrier group needs little delicate fighters that can dance around… but cannot do it for long, with little in the way of stores on board, and cannot do it far enough away to keep the carrier from getting into harms way.
kilcoo316FECK SAKE!!!
I made another reply to this last night… that must have been ate by something too :rolleyes: 😡
kilcoo316Better at what?
Flipping the trust sideways in 1% of the flight time is better than hiding the nozzle IR emissions in 100% of the flight time?:confused: I don’t think so.The Mig-29 nozzle way of vectoring the trust is not the most efficient way devised. There is active flow control in the X-36:cool:
– The F-22 nozzles do not even try to hide the IR signature.
– Fluidic thrust vectoring is not anywhere near as efficient as mechanical thrust vectoring – and indeed, its doubtful whether it ever will be.
kilcoo316If something goes wrong it often helps to use the “browse back” of your Inet browser. Otherwise mark the whole text from time to time and press CTRL+C, that makes a copy in the Windows workspace. Arkvaard, but effective.
Unfortunately, there was a flicker in power – lights flickered… computer died 🙁 Even opera can’t recover that!
Swing-wings are outdated, a fashion of the 60s and 70s. Some newer designs proved that effective high lift and increased power, as well as some compromises on the upper right of the flight envelope will delete the necessity of swing wings. Swing wings and highly manouverable is contradicting: the structural problems coming with hinging the whole wing are enormuous. With the swing wing also comes a fixed scrapyard date, and the Navy can be happy they achieved it.
Swing wings enable much more efficient loading of the wing through different flight regimes – for a variable sweep aircraft drag increases linearly with Mach number – whereas for a fixed wing aircraft it increases proportional to Mach number squared. No amount of tricks are going to overcome that.
You can use a thin aerofoil section, like the F-18 has, to try and get away with not having the wing sweep – but we all know the problems associated with thin low swept wings (rather, I’m assuming you do).
Sure, there are some efficiency gains due to new technology. But the investment is considerable. The more gains you want, the more investment you have to take. Starting with the simple task of designing a better Tomcat, you would subsequently change the swing-wing (see above), the inlet, the tail config (more lateral stability), add LEX, better cockpit view, change weapon storage …
I wouldn’t change the swing wing (for the reason mentioned above). To a large extent the aerodynamics would stay similar – perhaps a triplane configuration would be incorporated to improve supersonic manouvering. However, since the original Tomcat had a wing-glove, that shouldn’t be a large problem.
Increasing the size of the vertical stabilisers is not a large issue either (not on an aircraft with the structures for an arrestor hook close to the two fins).
I wouldn’t bother too much with stealth features, on a VG aircraft with external stores, your never gonna get great RCS figures anyway.
How hard is it to change the front windscreen of the cockpit… now really? Apart from that its ok – 2 pairs of eyeballs are always better than 1.
Finally you have a new aircraft for a role nobody needs any more: long range fleet defence against bombers. And by the way: you still lack the adequate weapon system. So, go to congress and ask for anoth billion to develop a long range AAM weapon system, which actually nobody needs.
Pardon?
A long ranged fighter-bomber? One which would be much more efficient than any Hornet for the Navy’s current needs…
I don’t think you considered that paragraph before posting it. 😮
As for the long ranged AAM – buy the rights to build the KS-172 🙂 {might be tough for some on here to stomach, but it makes sense}
AIM-120 can. Newer weapons systems have eliminated the need for “super manouverability” to some extend. Flying supersonic at sea level sure is a nice demonstration, but with the according fuel flow of ~20 tons/hour just a demonstration thing. I learned that quite a lot of “drag” comes from the inlets, which obviously underperform due to priority on stealth.
Flying faster at low level is an excellent way of getting into topology cover (i.e. get a mountain between you and the missile launcher) increasing your chances of avoiding the missile. No-one ever had too much speed in a warplane.
edit: Alot of the drag comes from the two inside pylons, which have to be canted out for weapons separation issues [great design huh? 😎 ]
Honestly, you have no performance figure available, but only the filtered and retold story by a flight magazine.
Whatever. The Tomcat can do Mach 1.2 at sea-level – and Mach 2.34 at altitude. Northrop Grumman
The ‘Super Hornet’ has a max speed (at altitude) of Mach 1.6. Boeing *warning PDF*
Unsurprisingly, neither Boeing nor the USN want to make the ‘Super’ Hornets abilities at sea-level public – and not because its good.
Great, why not add another ton of weight for a purpose which will hardly be used ever.?
I guess you better get that information to Lockheed Martin, MiG and Sukhoi before they get too many F-22s, MiG-29/35/OVTs and Su-27/30MKI/35 with TVC built!
Oh, and you might as well tell the EF team not to bother with it on the tranche 3 aircraft as well. 😉
kilcoo316And who cares?
The F-14 is outdated in airframe life and concept. Any “new Tomcat” would basically call for complete redesign. Then you can ask: do we need swing wings, do we need Phoenix (actually, they are gone). Update aerodynamics, new engine, more stealth. Finally you are where you are with the F-18E, or at least close. With higher costs, later IOC.
And finally: how can provide reliable data on how much better is F-14s acceleration? Or did you read that on another forum?
[Damn computer just ate a reply 😡 ]
Airframe life? That will be solved with new airframes 😉
The concept of the F-14 is a long ranged BVR killer… the concept for the F-22 is…. a long ranged BVR killer.
Do we need swing wings? They give the F-14 its long range, top speed, acceleration and payload capability off a carrier deck, so yeah, I’d say we need them.
We do not need Phoneix per se – but, with the room/weight available, you can build a missile that far outranges the 120D – something akin to a KS-172.
If you update the F-14 you are not where you are with the F-18 E/F – not even close. For a start, you’ll lighten the existing airframe through better materials, you’ll lighten the engine, whilst also providing more thrust and greater fuel efficiency – all that translates into is an even better range, with more load lugging capability – moving the F-14 even further ahead of the F-18s in this regard.
The F-18 E/F program was a mistake, that money would have been better spent on the Tomcat airframe, not the Hornet. That mistake cannot now be rectified (unless the Navy are willing to stick up the same amount of money again).
As for the F-14/F-18 acceleration.
The F-18 is a draggy airframe, it cannot even break Mach 1 at sea level.
Here is some extracts from a flight journal article:
The pronouncement appeared along with a spate of triumphal announcements that celebrated the “successful” completion of the Super Hornet’s first operational evaluation (OPEVAL). In a publication called “Inside Washington,” the Navy’s director of operational testing is quoted as saying that the Super Hornet was superior to its earlier models “… in every category but three: acceleration, maximum speed and sustained turning performance.” This pronouncement boggled our minds because these are the very performance capabilities that determine a tactical airplane’s survival.
The F-14D will be replaced by the F/A-18E Super Hornet, which attempts deep-interdiction missions. Though it’s a whizzy little airshow performer with a nice, modern cockpit, it has only 36 percent of the F-14D’s payload/range capability. The F/A-18E Super Hornet has been improved but still has, at best, 50 percent of the F-14D’s capability to deliver a fixed number of bombs (in pounds) on target. This naturally means that the carrier radius of influence drops to 50 percent of what it would have been with the same number of F-14Ds. As a result, the area ot influence (not radius) drops to 23 percent! No wonder the USN is working on “buddy tanker” versions of the Super Hornet.
Owing to its high drag and weight (and probably other factors), the F/A-18E is significantly poorer in acceleration than the F/A-18A. Also, its combat ceiling is substantially lower, and its transonic drag rise is very high. We have stayed in touch with some pilots at the Navy’s test center and have gathered some mind-boggling anecdotal information. Here are some examples:
* An F/A-18A was used to “chase” an F-14D test flight. The F-14D was carrying four 2,000-pound bombs, two 280-gallon drop tanks, two Phoenix missiles and two Sidewinder air-to-air missiles. The chase airplane was in a relatively “clean” configuration with only a centerline fuel tank. At the end of each test flight, the chase airplane was several miles behind the test airplane when the chase airplane reached “bingo” fuel and had to return to base.
* An F/A-18E Super Hornet is tested using the same chase airplane, an earlier model Hornet, in the same configuration. The chase airplane does not need full thrust to stay with the test airplane.
* An F/A-18E/F in maximum afterburner thrust cannot exceed Mach 1.0 in level flight below 10,000 feet even when it is in the clean configuration (no external stores). At 10,000 feet, the F-14D can exceed Mach 1.6.
Another aspect I had not considered – with the wide spacing of the two engines, the F-14 is ideal for using TVC to augment roll (as well as pitch) control, thus reducing somewhat the manouverability difference between the F-14 and F-18.
kilcoo316The fact we are all even having this discussion is enough to highlight the subpar performance of the ‘Super’ Hornet.
Anyone argue for F-15s being better than F-22s? Not a chance.
Anyone argue that F-16s are better than F-35s? Again, no way.
Yet… F-14 and F-18… many view the airframe as a step backwards, and I agree with them.
An F-14 with JHMCS and Aim-9X will for all intentions and purposes, be approximately equal in kill ratios to the F-18 E/F in WVR combat – thats just the way WVR combat works [if the Aim-9X works as advertised].
Extend the fight to BVR, and there is only one winner. The Tomcat, is larger, can carry more weapons, can fit a larger radar, can go faster, can accelerate faster, can go further – infact, in every facet of BVR combat, the old F-14 is a better airframe than the F-18 E/F.
The F-18 supports yammer on about AESA radar and avionics integration – as if such things could not be done better on the F-14 [larger airframe means more room to put more stuff into]. So, you’ve a stronger radar, with better processing capacity to reduce workload for the pilot, you’ve also got a backseater to share the workload etc etc etc. It all stacks up in one direction.
The 2nd argument is maintenance. Consider that many of the components on the F-14 were designed in the 60s – and consider how far design has come in the last 40 odd years. Its another non-argument, a fresh design F-14, utilising both modern systems (for VG wings, FADEC etc) and avionics would simply **** all over the ‘Super’ Hornet from a great height.
The US Navy screwed up – badly.
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