## Saab 37 Viggen

Questions and discussion about creating aircraft. Flight dynamics, 3d models, cockpits, systems, animation, textures.

### Re: Saab 37 Viggen Development

I just did some tests in Siberia at almost 40000 ft altitude.

At AC set at 16 degreesC, there will be full frost on the glass, both inside and outside, when outside temp is -56.5.
At AC set at 20 degreesC, the frost will go to 0.85 approx.

The problem is not that the AC cannot warm the cockpit faster than it cools down from outside temp., its that the dewpoint and temp outside will form frost with my calculations. The inside frost is also not simulated so good, due to I really don't know how to simulate the inside dewpoint so well.

The glass temperature is done via glass-temperature-index which I think is a standard way of calculating that. Its already at 0.75 which I think is rather high for a cockpit glass, that's probably only single layer.

So there must be something off with the way I do frost/fog, if the glass is not supposed to frost up in those conditions, I guess I just know too little about how frost forms, I did several assumptions when making that.

If your interested, this is my code for fog/frost on outside the glass, its run every 1.5 seconds:

Code: Select all
` var fogNormOutside = clamp((tempOutsideDew-tempGlass)*0.05, 0, 1); var rain = getprop("/environment/rain-norm");  if (rain == nil) {    rain = 0;  }  var frostSpeedOutside = clamp(-tempGlass, -60, 60)/600 + (tempGlass<0?(fogNormOutside/50 + rain/50):0);  frostNormOutside = clamp(frostNormOutside + frostSpeedOutside, 0, 1);  # recalc fogging from frost levels, frost will lower the fogging as some of that frost probably is formed from fog.  fogNormOutside = clamp(fogNormOutside - frostNormOutside / 4, 0, 1);`
Last edited by Necolatis on Sat Sep 22, 2018 1:51 am, edited 1 time in total.
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Necolatis

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### Re: Saab 37 Viggen Development

Does the temperature determination include friction heating?

In the pilot interview linked from the wiki

http://www.milavia.net/specials/iv_viggen/

this seems to be a major factor - and it sounds like this would actually de-frost things.

You can actually feel the temperature rising in the cockpit from the friction between the aircraft and the air. I once put my hand at the fuselage next to the throttle and could feel the heat!
Thorsten

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### Re: Saab 37 Viggen Development

No, it only gets heated by air-conditioning, pilot body and hot-air-on-windshield.

I think I will add that, thanks.

Edit: I found something called the ram rise formula which tell how much the incoming air will heat up from hitting fuselage, depending on true airspeed, its rather much.
Last edited by Necolatis on Tue Jan 24, 2017 11:34 pm, edited 1 time in total.
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### Re: Saab 37 Viggen Development

Just to be clear - I would think that there's always some amount of frost at that altitude (a real fighter jet pilot might correct me on that one...). My 'problem', if you like, is that I felt it is too much, to the degree that it was impairing my ability to fly. And I suspect that the designers would not let happen in reality with A/C to full warm.
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### Re: Saab 37 Viggen Development

Thorsten

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### Re: Saab 37 Viggen Development

Nice we got another article on the main FG website, I hoped more articles about progress of new FG version or scenery, but this perfect aircraft also rise to the occasion

Catalanoic

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### Re: Saab 37 Viggen Development

I hoped more articles about progress of new FG version

That might be depressing at the moment. I can't recall seeing 'doesn't compile' or 'segfault after commit XY' or 'compilation broken on Windows again' and similar quite so frequently since I monitor the list.
Thorsten

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### Re: Saab 37 Viggen Development

Thorsten wrote in Fri Jan 20, 2017 3:46 pm:Smile - you're on FG:

Wow, nice article too, great!
"Airplane travel is nature's way of making you look like your passport photo."
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Necolatis

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### Re: Saab 37 Viggen Development

Rework of how cockpit A/P controls work. Also A/T no longer will engage afterburner.
Split landing up into 4 modes. To use this, be sure to have the landing runway selected in the route-manager.
"Airplane travel is nature's way of making you look like your passport photo."
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Necolatis

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### Re: Saab 37 Viggen Development

Tutorial 3 & 4 is on Youtube now.

"Airplane travel is nature's way of making you look like your passport photo."
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Necolatis

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### Re: Saab 37 Viggen Development

Great work.
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### Re: Saab 37 Viggen Development

Great Job!

I flew test flights with Viggen. There is strange behavior on emptying fuel tanks.
Generally: Left and Right Fuselage Minor Tank is not used same time.

First is emptyed Drop tank - this is OK.
(Droptank jettysoned after emptying.)
Second the "Left Fuselage Minor Tank" is emptied to dry.
Meanwhile almost all other tanks is emptied but one.
The "Right Fuselage Minor Tank" is not used and stay 100% full until the "Fuselage Forward Tank" is empty.
After than it start emptying.
Fuselage Main Tank is last one.

Parameters:
"Refuel: Long distance"
FG16.4/17.1.1
AJ37/AJS37/JA37

It seems to me that FFT is routed to RFMT by mistake.

Krsta
krstev .. secar.cz
krsta

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### Re: Saab 37 Viggen Development

krsta wrote in Tue Feb 28, 2017 1:20 pm:The "Right Fuselage Minor Tank" is not used and stay 100% full until the "Fuselage Forward Tank" is empty.

They are both used, you just wont notice it, since fuel from Left Fuselage Minor Tank flows to Fuselage Forward Tank, then from there to Right Fuselage Minor Tank, and from there to Fuselage Main Tank.
So Right Fuselage Minor Tank will appear full, but fuel is flowing through it all the time.
Its a strange setup, but is how the manual explains it.

krsta wrote in Tue Feb 28, 2017 1:20 pm:Fuselage Main Tank is last one.

Fuselage Main Tank is a collector tank. This is the only fuel tank that the engine can take fuel from. If it didn't empty last the engine would maybe be starved even though there is still fuel. (which can happen, depending on how you fly, see last conditions in this post.)

krsta wrote in Tue Feb 28, 2017 1:20 pm:It seems to me that FFT is routed to RFMT by mistake.

No mistake there, its how it works.

Also flow from those 3 tanks stops when any of these conditions are met:
- pitch higher than 60 deg or lower than 30 deg
- roll right higher than 50 deg or roll left higher than 40 deg
"Airplane travel is nature's way of making you look like your passport photo."
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Necolatis

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### Re: Saab 37 Viggen Development

As there are no speed breaks: how do you actually slow down this bird? Narrow turns do the trick, but that is not ideal while approaching an airport. Any tips?
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### Re: Saab 37 Viggen Development

At least in earlier versions you could hit the "delete" key to activate the reverse thrust. It's also a way to back up.

https://youtu.be/RSgUTHEm8xo?t=32s
Lydiot

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