SchorschAnyone know if they will employ 787 technologies like carbon fibre on the i? As you can tell I’m no engineer!
As I learned the B747-8I is intended to bring maximum improvement over the B747-400 with minimum cost. The basic structure remains unchanged but gets a new profile (supercritical), new high lift devices (replacing the 1960s stuff) and new wing tips. Some strenghening of course due to higher take-off weight and heavier engines.
Add new engines and a slightly enlarged fuselage and you have the -8F/I. Although Boeing and its supporters sell us the B747-8 as huge step, it is a warmed over minimum cost solution. Accordingly cargo airlines are the prime customers. But don’t think that old means bad: the B747-8F practically killed the A380F as it was planned originally. Airbus will come back with a new A380F in a few years.
Schorsch“the F-4F… differs mainly in electronic equipment and systems, partly because the US devices are classified and not available for export and partly to meet the specialized needs of the Luftwaffe or German industry.”
– F-4 Phantom, by Bill Gunston, c 1977The “not available for export” line doesn’t make sense to me. Iran got the F-4E with Sparrow and the F-14A with Phoenix not much later. Japan got the F-4EJ with Sparrow.
I think the real reason was that Germany was looking for a cheap lightweight fighter. They were going to buy a bare bones version called the F-4EF, with one crewman, only the belly tank, reduced internal fuel, simplified radar, and no Sparrow. The F-4F that they finally went with is 3300lbs lighter than the F-4E because off all the stuff they left out of it. The F-4F was a better dogfighter, and it cost less. It was the F-16 before the F-16 was invented.
Also take into account that Germany was officially not responsible for security of the airspace over Germany. This very delicate job was responsibility of the Allied aircraft (actually, in Eastern Germany the local German air force participated in QRA).
And consider the cost of the Sparrow system: besides the radar illuminator (which wouldn’t make the big bill), add the missiles and the training. Every crew needs to launch life missiles from time to time. Sparrow also require maintenance.
In a war scenario (and remember: German army was by law excluded from exterritorial use) fights were supposed to take place in the low level mostly. In that arena the advantages of “BVR”-weapons shrink considerably.
Germany was never restricted from American technology I think. Hey, we’ve had aircraft designated to carry American nukes.
SchorschAviation is no linear affair most of the time!!!!!
It is often non-linear, and always a function of several variables!
SchorschMilitary transports are built for military operations but 90% of the time used as cargo haulers. With the A400M rapid deployment is possible, though some heavy pieces of equipment are excluded (what also challenges the army to procure more flexible equipment).
For missions like in Afghanistan (which is a quite difficult one: weak local infrastructure, some distance to Europe and hot&high conditions) a regional cargo hub makes sense, where cargo haulers like MRTT bring in palettes and these are lifted into more capable A400M/C-130.
SchorschOne of the key capabilities offered by the A400M is its steep descent rate into austere airstrips, which is seen as reducing vulnerability to AAA. This dictated the selection of props instead of fans, and was – along with Euro politics and some extraordinary claims for the A400M’s unit price – the reason why the C-17 was looked over. In retrospect the C-17 clearly offers far better value for money (payload/volume/range vs. cost).
The schedule projected for TP400 development program was pure fantasy from day 1, predicated on ‘equivalent’ timescales associated with civilian programs such as derivatives of the Trent. As with the overnight merging of two previously competing engine offerings from Snecma/Fiat and RRD, it provoked remarkably little comment at the time. EPI is to blame for proposing an unrealistic development program, but AMC is equally guilty of being so gullible as to believe it!
Look where most European air forces are today: a mixture of C-130 and two with Transalls. Some have even smaller aircraft. The A400M offers the best mixture of strategic airlift (twofold better than C-130) and exceptional field performance (better than C-17). It is not useful to supply large forces over long distances, like the USA is doing with its troops in Iraq.
A C-17 is most of the time absolute overkill. How often does it transport tanks? Just that is what it was designed for.
SchorschI’m sorry but your statement still doesn’t hold water. Misiions can be flown in a number of configurations of lo-hi depending on the circumstances. Then there is such things as toss-bombing (even the Vulcan used to do that).
The rigours of military life are much more extreme. You only have to look at the low engine life between servicings on mil a/c to understand that.
I think toss-bombing was abandoned on the B-47 and I think the B-52 will have its problems with it, too. The B-52 is basically a civil aircraft in its flight loads requirements. As such it is hardly representative for other military aircraft.
SchorschI don’t agree with your contention that 15,000 hrs makes them under engineered. The flying regime for military a/c is far more demanding than civil airliners. These a/c are thrown around the sky more, that pushes up the FI usage per flying hour somewhat.
I agree that miliary aircraft are hardly comparable to civil aircraft in that matter. But in this particular case I would ask for an exception. The B-52 bascially flew the profile of a civil airliner, at least it was designed for it. The majority of flight time was spent at cruise speed and high altitudes.
Of course, the whole issue changed when B-52s started to fly low level missions at max VMO. That would tear apart any Airbus or Boeing after a short time, too.
Please understand my statement “underengineered” as a statement of 2007. For 195x it was state-of-the-art. First civil aircraft with comparable weights appeared over 15 years later (the B747 was the first civil aircraft to exceed the MTOW of the B-52).
SchorschNot to reheat the discussion, but for the sake of clarity:
The turn chart, “MiG-23MLD” is sticking to, shows what happens if the pilot fully applies the control stick to the limit allowed by the max. elevator deflection and by the SOUA stick stop device during the complete turn. At 5000m and 900km/h (IAS) the max available g-load is 7g, in this case limited by the max. elevator deflection (Please have a look at page 221 of the MiG-23ML manual you mentioned.). Which is not sustainable and bleeding energy/speed. If the pilot would start with about 4.5g the MiG-23ML could sustain the turn not loosing speed. For sustainable g-loads have look at page 240 of the ML’s manual.
For the F-4E the sustainable g-load is about the same, refering to the numbers of the F-4E manual (http://forums.airforce.ru/attachment.php?attachmentid=7569&d=1183809027).
Don’t know if the F-4F provides better numbers.
The max. 8.5 g-load doesn’t help the MiG-23ML at height 5000m. The is probably different at 1000m the Mig-23ML having the theoretically advantage pulling more instantaneous g compared to the F-4E. But the the speed is bleeding again.
Comparing the F-4E and MiG-23ML sustained turn performance they seem to be quite comparable, probably with a slight advantage for the MiG.
But I’m not an aerodynamic expert and this is oviously the wrong thread to discuss this. 🙂
Hi crossi,
thanks for the info. Limitations by elevator authority are often ignored as they are hard to assess. Thanks for the info and the reference to the according pages. I can’t read the text and I have to rely to guessing and interpretation of the numbers to figure out the meaning. Your input is always welcome.
The F-4E pages you posted show a bit worse performance than the F-4F, but that is most likely due to the load of 4 AIM-7 Sparrow that add ~1.2 tons of weight (aerodynamics don’t make a difference here actually).
Maybe I can deliver something more visible the next days, I guess not in this thread.
BTW: very interesting to note that the MiG is pitch authority limited in this case. So structural limitations don’t limit the instantaneous turn rate here. The swing wing after all adds another degree of freedom.
Regards
SchorschThat had to do with the intended role in Central Europe and not the denial to purchase that. The options were the F-4F, Mirage F1, Lockheed Lancer and Northrop Cobra, which later becomes the F-18.
At that time the GAF want to have the EFA (later Typhoon) and nothing close to that. The F-4F was bought as an interim fighter and was available in short notice. In 1971 non did thought, that the F-4F will be still flying in 2007!
I think the immediate availability of the aircraft was decisive, and its competitive price and potential role as fighter bomber. Some savings were achieved by having the J79 engine (same as Starfighter). The Luftwaffe already operated Phantoms in the reconnaissance role (RF-4E). Lockheed Lancer and Cobra were basically concepts, the Mirage F1 possibly a useful alternative. But I think the Luftwaffe was very US-happy at that time and was focused on twin engine designs. The USA spent billions in Germany during that time for troop deployment and some money was supposed to come back. So politics again.
SchorschFrom Boeing.com:
Does anyone think this is what airlines have been waiting for before placing an order for the type?
There are surely airlines (probably existing 747 operators) that don’t require the capacity of the A380 but would still like to invest in a 747-400 replacement.
An aircraft starts as rubber aircraft. You can form it a bit. Early customers make the rubber design a more and more solid design. In the end (~2 years before first flight) the design is solid so that production can start.
As airline you like to jump on board as soon as possible to form the rubber into a solid design most appropriate to your needs.
Some airlines participate in such definition things, Lufthansa is one example. Some don’t. In case of the B747-8I is doesn’t mean too much good: one firm customer at design final freeze means the design is suited only one customer. Emirates repeatedly said they would like to see the B747-8I walk a slightly different direction. However, design choices on the B747-8I are limited at best, considering the boundary conditions. It is limited cost approach to get a market share which would otherwise be lost. Boeing knows that.
SchorschThat runs counter to a number of accounts of the B-52 being structurally over-engineered. Loads for low level flying were not accounted for and thus structural modifications were made for that role in the H version, but they were not used much for low level flying. And unlike fighters, thry never turned and burned. That’s why they have excess structural life.
OK, when you look from that perspective. With today’s experience they would have completely fallen apart after their design service life, but they only fell apart in some areas. :diablo:
The B-52 have flown ~20000 to 25000 hours with low cycle count, so from todays perspective (considering they are practically similar to civil aircraft in some respects) they are underengineered. For the original service goal (something like 15000 FH if I remember right) they were truly overengineered in most areas (still structural failures happened before achievement of design service life).
SchorschThe three profiles that I posted at the end of the first page of this thread show the twin-seater single engine, the single-seater single engine, and the twin-seater twin engined profiles.
Once more they were sent to me by a friend so I do not know how accurate they are or whether the artist had official “hints”. My friend said that he has an identical profile to the first one he sent me, only that it has a variety of weapond that were in development beneath it. He will send it to me.
Interestingly, on the SAAF site, the one gentleman who saw some of the windtunnel models states that the photo of the model seen posted here (post32) has basically the correct design features as the models he saw.
I guess there never was an “official” version. The huge differences in wing and intake form indicate a very preliminary design stage. Looks like a Mirage III or 5 derivative.
SchorschSo you’re telling me that you need an advanced degree to understand that if you exceed the airframe’s design limitations re. hours something bad might happen? Funny, I’d think a five year old could understand the concept. Sure, you need the brains to figure out life cycles given a set of conditions but then we’re not talking about specifics now are we? Again (and more to the point) one can’t broad brush it and say that since the B-52 has been used for fifty years that ALL aircraft can be.
No, apparently one need an advanced degree to understand that you can exceed the original life time limit as it has a very arbitrary character. Guess why the F-16A incorporated basic structural health monitoring systems.
The B-52 was over-engineered, that’s why it could last this long. The F-15 won’t. Simple as that. Using the B-52 as an example of what to do with the F-15 isn’t wise.
According to sferrin the overall concept is dead easy and so I can use anything for reference, or not?
The B-52 was underengineered: to have acceptable structural weight it was build very light and flexible. Like many aircraft of that time it possesses huge reserves in some areas and none in other. The methods for large flexible aircraft were not established at that time. Additionally, the loads due to low level flying weren’t incorporated when designed. Other comparable aircraft run in similar or sometimes even more serious problems.
I also recommend further reading on aircraft types like C-5A, C-133 and Vickers Valiant.
SchorschBoiled down it’s pretty simple. If you’re flying more hours than anticipated when the thing was designed you’re going to use up the airframe hours sooner. If you’re flying the aircraft harder than anticipated at design then your 8000 hour life might turn into 6000 hours. For something like a B-52 that’s flying a relatively benign flight profile a noticable “hey we might want to fix that” is less likely to turn into a “whoops, the wing came off”. Yeah, there are a lot of details but the overall concept ain’t rocket science.
Hmm, it isn’t rocket science. I guess the 100+ people concerned with that issue at Airbus and Boeing will have different opinions. And they don’t build fighter aircraft.
The B-52 changed its flight profile in the 1960s. Additionally, it was the first large flexible wing jet-powered aircraft. Many design assumptions were unknown at that time.
One single 9g event can have more influence than 1000 5g events.
Fighter aircraft are normally cleared for a garantueed period, and then often cleared for more hours.
SchorschYou’ve shown an averaged turn rate for the MiG-23 ML… not the max instantaneous turn rate (which is specific to one airspeed/altitude – not a range).
I calculated the inst. rate for the first ~5 seconds. I know that such data is variable with speed/altitude/weight/external loads/engine settings. Anyways, you are welcome if you have anything better or more precise.
The data is at hand, why don’t enlighten me?
pride is only a sign of lack of confidence.
I am pretty confident on this specific issue.
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