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Why RB24J?


2-niner

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I'm just wondering if anyone know why we can only carry the RB24's on the outer wing pylons and not the RB74?

 

As I have understood it - enabling the outer wing pylons for sidewinders was part of the 90's AJS upgrade, so why on earth did they then not enable support for the RB74 and just the RB24(J)?

 

The only reason I can think of is because of weight, since that would be a sensitive issue so far out on the wing, but the RB74 is actually only 10kg heavier than the RB24, which isn't a lot relatively speaking, so I'm guessing that's probably not it.

 

It's just super ironic that the 2 pylons which are dedicated for carrying sidewinders and where you pretty much always will carry them - is also the only 2 pylons which can't carry the much more modern variant! :huh:

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Interesting... I'll go read up on how the cooling for these things worked, thanks.

It was not missile cooling itself.

 

But rather the RB 74 Required a different Type of pylon to help cool its seeker.

 

Where as the RB24J could use a smaller / Simpler Launch rail system,

That could be more easily mounted on those outer Hardpoints.

 

Atleast that is my understanding of the situation,

Though is probable that there were also other considerations that played a part in the decision.

 

Somebody else (Like Renhanxue for example) can probably add more information.


Edited by mattebubben
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I'm unfortunately quite lost on this one! As far as I know though you're correct on the different pylon or mount or launcher or whatever you call it for the rb 74, so it does seem like a plausible explanation that they didn't want to spend too much money on adding those to the outer wing stations when the AJS 37 was hardly much of a fighter anyway, especially not when carrying heavy ordnance on the inner pylons.

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Well the outer wing pylons where seriously limited when it came to loading.

Even carrying Sidewinders there during normal flight seriously limited the airframe life of the Viggen.

It could be that the heavier cooling assembly fore the RB74 was simply too heavy.

Or it could have been too complicated to install.

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There is a story behind it in the book System 37 Viggen.

Originally the pylons were designed for the RB28 Falcon (AIM-4C) during aircraft development. This was at the time the standard IR missile for the J35 Draken. The missile had better performance than the early RB24 (AIM-9B). But it also had it's drawbacks especially since the missile become unusable after it had been used for aiming due to its battery being acivated.

This ment the airforce looked towards the sidewinder series again and managed to buy the RB24J (Modified AIM-9J).

The airforce asked SAAB several times if they could fit the RB24J on the outer pylons but the answer always became NO after the engineers had done thier calculations regarding fatigue in the wing. This due the RB24Js weight of 81kg vs RB28s weight at 61kg.

When it was time for the AJS upgrade the Airforce did a final push and asked again with a little rephrased question. "For how many flighthours can we carry the RB24J if we add it?"

The engineers at SAAB went back the thier calculations and came up with the answer of 100 hours. This settled the deal and the modification to finally carry the RB24J got implemented.

The RB74 is about 5 kgs heavier but with the extra launch rails it would have added weight further and given a more limiting flighttime. Also the priority was to use the RB74s on the fighter version primarily as the attackversion is only carrying its offensive weapons as a last resort of self defence.

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^Just to clarify - is the book specific on the following?

In a forum post (on soldf) there's talk of 100 hours lifetime for the Sidewinder, not the wing itself.

 

http://forum.soldf.com/topic/5168-saab-ja-37-viggen-aj-37-ajs-37-sk-37-sf-37-sh-37/page-23

Scroll down halfway to post 677.

 

-Och det enda som var påtänkt för AJ var RB28, men så blev det aldrig. Om det var för att det var en dålig självförsvarsrobot (det var det) eller för att de inte skulle hållit pga vibrationer (kommer jag ihåg rätt kom man fram till att en Sidewinder skulle kunna hänga där ca 100 flygtimmar innan den skulle kasseras) är jag inte riktigt klar över, men det var det senare som nämndes oftast.

 

-Vibrationer, jag vill minnas att det endast var ett krigsalternativ att hänga längst ut på vingen.


Edited by emg
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No the book was pretty clear that it was wing fatigue limiting the use of rb24js on the outer pylons.

The cutoff decision was to implement the missiles if they could be carried for more than 30 flight hours and since saab said 100 hours it was an easy descision.

The numbers doesn't seem much but when you consider the amont of time that they would actually carry a missile in that position not having any other stores available, it makes a bit more sense. The amont of missions requiring the full loadout for the remaining lifspan of the fleet was pretty limited.

I will try to get a picture of the text section when I get home mid next week.

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There is a story behind it in the book System 37 Viggen.

Originally the pylons were designed for the RB28 Falcon (AIM-4C) during aircraft development. This was at the time the standard IR missile for the J35 Draken. The missile had better performance than the early RB24 (AIM-9B). But it also had it's drawbacks especially since the missile become unusable after it had been used for aiming due to its battery being acivated.

This ment the airforce looked towards the sidewinder series again and managed to buy the RB24J (Modified AIM-9J).

The airforce asked SAAB several times if they could fit the RB24J on the outer pylons but the answer always became NO after the engineers had done thier calculations regarding fatigue in the wing. This due the RB24Js weight of 81kg vs RB28s weight at 61kg.

When it was time for the AJS upgrade the Airforce did a final push and asked again with a little rephrased question. "For how many flighthours can we carry the RB24J if we add it?"

The engineers at SAAB went back the thier calculations and came up with the answer of 100 hours. This settled the deal and the modification to finally carry the RB24J got implemented.

The RB74 is about 5 kgs heavier but with the extra launch rails it would have added weight further and given a more limiting flighttime. Also the priority was to use the RB74s on the fighter version primarily as the attackversion is only carrying its offensive weapons as a last resort of self defence.

 

 

This is very interesting. Do you know how extensive the required modification was? Was this something which could have been applied to the AJ 37 in wartime*? Was this something the Swedish Air Force planned to do?

 

 

*Leading up to the Falklands war, the RAF bolted Sidewinders to Nimrod maritime patrol aircraft in a matter of days.

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  • 3 months later...
This is very interesting. Do you know how extensive the required modification was? Was this something which could have been applied to the AJ 37 in wartime*? Was this something the Swedish Air Force planned to do?

 

 

*Leading up to the Falklands war, the RAF bolted Sidewinders to Nimrod maritime patrol aircraft in a matter of days.

 

A Sidewinder is extremely easy to install any maintenance crew can probably do it in a few hours as long as they have a pylon to work with !

Also for comparison the fighter version has been reinforced structurally and is actually heavier and that thing carried Rb-74's on the outer pylons all the time.

 

Something the air force could have done though is use the H7 pylons which was completely unused on the AJS series and only carried dispensers on the JA-37 after and upgrade late in its career.

Those pylons where rated to 500kg and could easilly have carried say Mk83 bombs if Sweden had used them at the time. That way the two pylons on either side of the drop tank could have used Sidewinders.

 

JA37_N2__bev_700.jpg

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