XB70 Valkyrie

[Marcus]

Un avion superbe même si son utilité était franchement douteuse.

Exactement comme Concorde finalement  :lol:

Par contre, le plus attristant, c'est que son accident mortel a pour origine la publicité!  >:(

L'USAF interdisait de faire des vols pour faire seulement des séances photos.

Le fabricant des moteurs du XB70, Westinghouse, a fait du lobbying pour réaliser un campagne publicitaire de rêve :  une formation avec tout les avions militaires équipés des moteurs Westinghouse qui encadrerait le XB70. Le tout pris en photos sur tout les angles...

C'est pour cela qu'il y avait cette formation curieuse : F4, F5, F104, T38 et XB70.

Ce n'est donc pas un vol d'accompagnement standard mais une formation serrée pour faire joli.

Il ne devait pas être facile de faire voler ensemble un tel mélange d'avions différents. Le F104 fut aspiré par les tourbillons d'ailes du XB70...

Tout cela pour de la pub  :'(

[Berkut]

En même temps il était tout à fait logique que cela soit le fait du Fallfighter de claquer la Valkyrie.

Par contre les moteurs c'est pas Westinghouse, mais General Electric ;)

[Marcus]

En même temps il était tout à fait logique que cela soit le fait du Fallfighter de claquer la Valkyrie.

Par contre les moteurs c'est pas Westinghouse, mais General Electric ;)

Oups mea culpa  :'(

Je ne connaissais pas le terme Fallfighter mais cela lui va bien  =)

[Berkut]

Le F104 a tout plein de petits noms "affectueux". Cet appareil était un vrai cercueil volant, on l'appelait aussi comme ça, entre autres choses, widowmaker aussi, c'est joli ça, widowmaker, enfin jusqu'à ce qu'on sache ce que ça signifie  :-[

Mais bon quand tu vois la tronche du coucou... un V2 avec un cockpit. Pas étonnant au final que sa parte en sucette.

[flanker]

m'empèche que je le trouve superbô. A cette époque là ils savaient dessiner les avions, même s'ils allaient tout droit, pas comme maintenant avec ces furtifs où l'on s'attendraient presque à trouver "made in taiwan" en regardant dessous  >:(

Vous imaginez un mirage mach 4? ça vaudrais tout les rafous du monde pour moi  :'(

EDIT : 500e message houaa, en a peine 5 ans  :lol:

[iborg]

Le B70 est un superbe oiseau et incarne en effet ce qui fut la "croisée des chemins" du développement aéronautique : continuer dans la voie "vite et haut" avec des bombardiers supersoniques (option B70) ou bien fabriquer des ICBM (pour la frappe stratégique) et des bombardiers subsoniques et "furtifs" (option finalement retenue, culminant avec le B2).

Les scénarios "what-if" font les choux gras des forums spécialisés sur l'internet (principalement aglo-saxon), et l'un des plus développés en la matière est "The Big One", sa particularité étant que les Etats-Unis y poursuivent la voie du bombardement nucléaire stratégique (la 2è GM y est terminée quand une flotte de B36 atomise le IIIè Reich, et la suite de la série poursuit sur cette lancée avec un Curtis LeMay Président des Etats-Unis et un SAC d'autant plus puissant).

Je le mentionne parce que l'auteur a apparemment une connaissance assez pointue du sujet "bombardement stratégique" d'après sa bio, et qu'il développe une argumentation en faveur de la voie B70 (dans la FAQ et d'autres fils de forum dont j'ai perdu l'adresse).

Je cite la section où il évoque le problème B70 contre SAM.

Why does the US buy B-70s which fly from 75,000 to 100,000 feet when the ceiling of the Nike-Hercules SAM is 150,000 feet? (Stuart)

Most reference sources on missiles give two pieces of data on range. One is maximum range, the other is maximum ceiling. The critical thing to remember is that these figures are mutually exclusive. Achieving one precludes the achievement of the other. If the maximum range of a missile is 100 miles and its ceiling is 150,000 feet, it's range (when measured as a horizontal distance from its launch point) when fired to 150,000 feet will be zero. It goes straight up and come straight back down.

So, the critical point is not what a missile's maximum range or altitude is, but what its range is when fired at a target at a specific altitude. These figures are mostly strictly classified. However, it takes a lot more energy to climb than it does to fly level so it is reasonable to assume that range decreases sharply as altitude goes up. A measure of how sharply can be determined by dividing the missile's horizontal range by its vertical range; this gives a rought indication of the ratio it takes to make a missile go up as compared to along. For most missiles, this energy ratio varies between 8:1 to 3:1.

The key here is the launch kinetics of the missile. A very energetic missile will burn its fuel fast, giving it a low energy use ratio that allows it to climb fast and have a larger range at high altitude. But, by burning its fuel fast, it loses horizontal range. A less energetic missile will burn its fuel more slowly giving it a greater horizontal range but it will have an unfavorable energy ratio and thus will have a limited range at higher altitudes.

Now, add into that manoeuverability. Missiles that depend on fins for manoeuvering (pretty much all off them until very recently) have a problem in that their small control surfaces are ineffective in the thin air at high altitudes. What may be a very agile missile in the thick air low down, are barely capable of manoeuver high up. Aircraft with their much larger control surfaces are effected to a lesser extent.

The effect of all these considerations is that each type of missile has an effectiveness graph of range against altitude that isn't a simple cylinder, its shaped like a lemon standing on one end. It has a narrow base (determined by radar horizons), swells out quickly as altitude increases then tapers off to a long thin spike at the top. If the altitude of the bomber is plotted across that lemon, it gives a cross-section of a circle, the radius of which is the range of the missile at that altitude. In order to score a hit, the missile crew must fire their missile so the target is within that circle at the time the missile reaches that altitude. In order not to be hit, the bomber shouldn't be in that circle. The smaller the circle, the easier it is for the bomber to change course and not be there. Also, the faster the bomber is, the less time it takes to cross that circle and thus the narrower the time window for the missile to be in the right place at the right time.

Even if the bomber is within the circle, it still is far from certain it'll get hit; that depends on the agility of the bomber versus the missile, the destructive radius of the missile warhead and the capability of the electronic warfare equipment on the bomber. This probability of a kill is called PK and missile producers like to claim PKs of anywhere from 80 to 100 percent. In the real world, 20 percent is doing very, very well and few missiles get that high. One gets around that by firing a lot of them........

Applying this to the B-70, even against missiles theoretically capable of reaching 150,000 feet, the missile range at 77,500 is so much smaller that the bomber has an excellent chance of being able to not be within that radius. At Mach 3.4 (37.3 miles per minute) even if it is within that radius, its vulnerability window is very small, a matter of a few seconds. Even if the missile is capable of getting to the B-70 in that time window, its chance of scoring a hit is pretty low.

By the way, the fastest anti-aircraft missile in the world today is capable of a tiny hair over Mach 6. That means it has a speed advantage over a B-70 of around 1.75. To have a marginal capability against a target, a missile is required to have a speed advantage of 2.0. This implies that the best anti-aircraft missiles in the world today have onlya very marginal capability against a B-70 type target.

Compare this with OTL; in OTL there has never been a successful attempt to intercept an SR-71 Blackbird (claims to have done so are either fictitious or wishful thinking). The B-70 flies higher than an SR-71, its significantly faster, is much more agile and has much better EW capabilities. And the B-70 shoots back.

In terms of numbers, the defense needs the following:

2.0 Speed Advantage and 1.0 Altitude Advantage for 25% pK

3.0 Speed Advantage and 2.0 Altitude Advantage for 50% pK

4.0 Speed Advantage and 3.0 Altitude Advantage for 75% pK

5.0 Speed Advantage and 4.0 Altitude Advantage for 90+ pK

So this means that when the SA-2 or it's equivalents come out in 1957, having a mach 2.0 (1,320 MPH) capability, this puts at severe risk the B-36J, having a 50% pK against it, due to having a 3.21 speed advantage over it, but against the B-52D, which flies 200 MPH faster, the SA-2's pK falls to 25%, since it only has a 2.08 speed advantage.

Against the B-70, the SA-2 doesn't even have a chance, it's advantage ranges from 0.67 to 0.59 depending on whether the Valkyrie is at Mach 3 cruise or Mach 3.4 combat speed.

When the SA-5 (S-200) enters the picture in 1967, it's Mach 4.5 (3,000 MPH) speed allows it to gain a 50% pK on the B-52D, but still can't begin coming close to killing the Valkyrie, as it's advantage is only 1.51 to 1.34.

When the SA-10 (S-300P) comes around in 1978 with its 3,800 MPH (Mach 5.75) speed, it's advantage rises to 1.92 to 1.69; it's still not really enough to gain a 25% PK on the Valkyrie.

Finally, when the SA-20 (S-300PMU-1) hits the market in 1992 with a 4,690 MPH speed (Mach 7.02), it can achieve an advantage of 2.37 to 2.09 against the Valkyrie, marking the first time a 25% PK is achieved against the B-70.

Of course, this is with historical missile development, e.g. trying to retain some sense of sanity in regards to dimensions. The enemy could simply say "screw this, I want a missile that can hit Mach 7 now" in the 1970s if he's willing to accept a massive increase in missile size, which decreases the amount actually available to the defense at any site, imposing virtual attrition. If you have to go from 4 SAMs on a TEL to just 2 in order to get a reasonable advantage over the B-70, the Valkyrie has killed half your missiles before he even shows up through said virtual attrition.

There are two additional factors that have to be included. One is electronic warfare; once an aircraft is in the engagement envelope of a surface-to-air missile, it depends on its electronic warfare capability to reduce the missile's PK. In this environment, bombers have a significant advantage because they have the power and internal capacity to carry fairly comprehensive EW systems.

The other is systems behavior. The SAM's (along with the fighters and everything else) fit into an air defense environment which has a built-in reaction time due to the delays inherent in its configuration. If the threat to that system develops faster than the system can respond to those threats, then the threat gets inside the reaction time of the system and said system falls steadily behind what is actually happening.

Missiles have the plus that they come in very, very fast so the defense system has a limited time to react. However, the problem with missiles is that they have no means of changing or developing their threat. They're coming in on a known ballistic arc and their position on that arc at any given time is predictable. That means the defense system doesn't have to react to them; it can predict what and where the threat will be at any specific time and then reacts to that predicted threat. In other words, it's inherent within the nature of the operational scenario that the defense system is far ahead of the threat. Since missiles don't - and can't - have defensive EW systems of their own, that makes them very, very vulnerable. The only problem is exploiting that vulnerability.

With manned, Mach 3.4 bombers, no such predictions can be made; the flight path of a manned aircraft is, by definition, not predictable. It can turn, climb or dive plus it can use its built-in electronic warfare capability to ensure (hopefully) that the defense system is receiving false data. So the bomber is ahead of the defense system. This was something that took us a lot of hard work to convince people of when we were consulting on the design of air defense systems; the performance of the system as a whole is much more significant than the performance of any one component of the system. Improving one (for example buying F-16 interceptors to replace F-5Es) makes onlya limited difference to the performance of the system as a whole. If, using that example, the improved performance of the interceptor is to be exploited, the whole system has to be upgraded with faster communications links, better operational display systems, better surveillance and target acquisition systems etc. If all those good things aren't done, the air defense system effectively has F-16s performing to F-5E levels. (It works the other way as well of course; if the interceptors cannot match the performance of the ground-based environment, then the added performance of that environment is wasted. So, a ground based environment that can exploit F-16 performance but only has F-86L interceptors doesn't have any advantage over an environment designed around the F-86L.)

L'un des arguments dont je me souviens par ailleurs, c'est que si le programme B70 n'avait pas été abandonné, avec la perte en conséquence des compétences relatives au vol haut-supersonique, la voie des avions-fusées à capacité orbitale aurait été ouverte beaucoup plus tôt... genre à la fin du XXè siècle.

[FAFA]

Quelques images d'un avion hors norme:

Pour commencer, une animation intéressante qui montre ( à 5 minutes ) que les ailes peuvent se "plier" vers le bas pour diminuer l'onde de choc. A partir de 5 minutes 30, explication du déroulement du vol photo qui a conduit à la perte d'un prototype. A 9 minutes il y a une explication sur le fonctionnement de la capsule d'éjection qui a été utilisé durant l'accident.

Ci-dessous: rien que pour les première images montrant les 6 moteurs de l'avion, cette vidéo mérite d'être visionnée. A partir de 6 minutes 15, impressionnant atterrissage d'urgence du monstre durant lequel son train d'atterrissage prend feu. 

 

 

[castle68]

Il n'y a pas à dire, à l'époque les ricains savaient faire des avions qui avaient de la gueule !