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Can´t get afterburner to max zone 3


illern

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When I use the afterburner I can´t get it the nossle to fully open.

See attached image.

I have the throttle at 100%. Checked both with the controller indikator in the overlay(see pic) and in Axis tune.

But the nossle indicator is only at 1/3 of zone 3.

 

/illern

843764695_Viggenebkzon3.thumb.jpg.3d76129122a6d270ed2effb6393cea1b.jpg

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I´m going to further explain why I think its wrong.

In the manual of the real Viggen it explains how the afterburner works.

In Chapter 1, section 9 point 3.2 it says:

"The thrust changes linearly through each zone in succession as the thrust lever is moved, but there is a slight stepwise change as each zone cuts in or out."

 

It also says somewhere that the 3:rd stage is longer. But that is also visible on the indicator.

 

As the function is implemented now it looks like it is 3 digital stages only. The needle jumps between stage 1,2,3 to fixed positions instead of analog positions as stated in the manual..

 

/illern

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I was thinking you were mistaken and that the nozzle position indicator was supposed to be just a 1/2/3 thing, but I've checked the SFI again and changed my mind - I think you're right. It's supposed to indicate the total area of the engine exhaust nozzle, and that should change with the thrust setting within each zone. See SFI fpl AJS37 del 1, kap 1, flik 9, sida 19, punkt 3.2.9.2 (page 143 in my PDF).

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  • 4 years later...

Just tested this and it's still bugged. It's not just the indication for zone 3 that is wrong, but all the zones. The nozzle indicator just points at a single fixed position in each zone instead of moving within the zones.

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On further thought, I'm actually not quite sure if the nozzle indicator is actually supposed to move within the respective zones.

 

The real Viggen manual says this:

 

AB_stages.png

 

English translation:

Quote

The nozzle position indicator indicates the open and closed position of the engine outlet nozzle and indicates which EBK zones are in operation. The indicator is an electric instrument which is controlled by an electric sensor which is mechanically connected to a line pulley in the outlet nozzle's return system.

That it doesn't really say much about how the needle is supposed to move depending on the AB stage the aircraft is on...

 

Any SME who can shed some light on this? @Holton181 maybe? :smile:


Edited by QuiGon

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33 minutes ago, QuiGon said:

On further thought, I'm actually not quite sure if the nozzle indicator is actually supposed to move within the respective zones.

 

The real Viggen manual says this:

 

AB_stages.png

 

 

It would make sense that it should move around inside the zones. If it shouldn't do it, what would be the reason to have it graduated with the thick lines for each zone, when in that case you might as well just use a lamp for each zone. Like for the throttle position, just to keep it as simple as it needs to be.

MUnstycke.png


Edited by MYSE1234
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Given the way the SFI describes it, it must absolutely move within each zone. Elgon does not translate to just "electrical", it's a very specific technical term (now long out of use, though) that translates to "synchro", and specifically I think it refers to a synchro-transmitter. That's effectively a very simple analog angle sensor, and given that it's explicitly mentioned that the sensor is mechanically attached to the nozzle via a pulley, I'm quite certain this is a very analog instrument that just reads the rotation of the pulley directly and rotates the indicator needle to match. There's nothing in the text that indicates there's any form of quantization going on here. I don't know exactly how the nozzle moves within each zone, though.

 

e: well, as for that last question, it's right there in the manual. Page 141 in the PDF (flik 9 avsnitt 3.2.4.3). I'm not going to post or translate the whole thing but as far as I understand it, the area of the nozzle opening is continuously regulated by a hydromechanical calculator, so yes, it makes a great deal of sense that the indicator is an analog instrument. In fact it seems to me the same pulley system that drives this instrument is also used by the fuel regulation system. See also section 3.2.9.2 which goes into more detail - it's explicitly stated there that the nozzle opening varies with the throttle level within each afterburner zone. I also seem to have already pointed to this section in this thread almost exactly 4 years ago... time flies, huh?


Edited by renhanxue
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11 hours ago, renhanxue said:

I also seem to have already pointed to this section in this thread almost exactly 4 years ago... time flies, huh?

 

It does indeed! :thumbup:

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Any SME who can shed some light on this? @Holton181 maybe?

He he, I feel honored to be called an SME, especially for the Viggen. But however much I would love that to be true, I'm sorry to say that I'm pretty far from it...
I guess your memory just slipped a bit, happens to us all.

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34 minutes ago, Holton181 said:

He he, I feel honored to be called an SME, especially for the Viggen. But however much I would love that to be true, I'm sorry to say that I'm pretty far from it...
I guess your memory just slipped a bit, happens to us all. emoji2.png

 

Oh, alright then. I saw some posts of you in the Viggen forum, that sounded like you might know *a bit more* 🙂


Edited by QuiGon

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Oh, alright then. I saw some posts of you in the Viggen forum, that sounded like you might know *a bit more*
I don't know what that might be, but I really hope this doesn't make me look like a self proclaimed know-it-all... We already have too many of them around these forums as it is

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10 minutes ago, Holton181 said:
41 minutes ago, QuiGon said:
 
Oh, alright then. I saw some posts of you in the Viggen forum, that sounded like you might know *a bit more* emoji846.png

I don't know what that might be, but I really hope this doesn't make me look like a self proclaimed know-it-all...

Not at all, don't worry. :smile:

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  • 2 weeks later...

The issue seem to be 2 folded, there is no indication within the zones because the throttle has no travel within the zones in DCS.
On the real throttle I would say, give or take, that Mil power has about 50% of the throttles range, including ground and flight idle and the 3 AB zones has the last 50% of the throttle range.
In DCS we have a very narrow range for all 3 stages and I would guess they are just stages.
And if they are stages in DCS the nozzle indicator show correctly for the throttle in DCS.
But it would be nice if the nozzle could be completely open in zone3.
Perhaps the engine is throttled ;)

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7 minutes ago, outbaxx said:

...there is no indication within the zones because the throttle has no travel within the zones in DCS. ...
 

The throttle does have movement inside the zones, but it's, as you noticed, not very much. But it's there and somewhat useful sometimes i find, although not often as the movement is so small.

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Anyone noticed if the nozzle position is absolutely fixed in each zone, or if it has a specific position that varies with Mach and altitude (but not with thrust lever setting)?

"Subsonic is below Mach 1, supersonic is up to Mach 5. Above Mach 5 is hypersonic. And reentry from space, well, that's like Mach a lot."

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The throttle does have movement inside the zones, but it's, as you noticed, not very much. But it's there and somewhat useful sometimes i find, although not often as the movement is so small.

I stand corrected , I’ve just tried it and I can see the throttle animation move when I move within the zones and the thrust varies with the movement.
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