Issues with the Jas39 gripen flight model

Mirage 2000 has good low efficiency and then experiences massive drag penalty near its AoA limit. If you do max performance turn in Mirage 2000 you will lose speed at high rate.

New changes to Gripen do not alter drag factor in any noticeable way.

Gaijin’s aerodynamics are very strange.On the contrary, at 0.8M there should be the greatest lifting force

That is the chart for the Mirage 2000.

Current Gripen chart looks like this.

Here are some others for comparison.

180% last I checked, and it’s not feasible to say the Gripen should have 30% improved specific excess power over the F-16 when the aspect ratio is superior, thrust to weight significantly higher on the F-16.

i don’t think you mean x2.8? i thought it was double, as in “200% of” or “100% more/better”.
so did you misinterpret me or did i have the wrong number?

This has been discussed at length. my main arguments for higher for gripen in short:

  1. Because of comparatively 2/3 the mass it needs 2/3 the lift converted into right angle acceleration for any given radius turn at a given speed. this means a lower AoA needed and thus less drag.

  2. The canards move whereas the F-16 LERX does not and can thus optimise their angle at any given moment for what is needed to produce a better end result in a turn than the LERX can (JAS39 even has several other vortex generating things the F-16 does not have, like dog toothed wings, small strakes and a TINY LERX). this is mostly noticeable at higher AoA and a sustained turn is usually around 15deg AoA which is enough for canard vs LERX to make a noticeable difference.

  3. depending on AoA JAS39 does not need to angle trailing edge Elevons to pitch as it just puts the canards in neutral, so less drag is induced.


So, after this update the gripen sustained turn rate got reduced.
I did 2 quick tests at similar speeds as before (sorry but don’t have the time today to edit the video and put the local host beside it):
720kph, 21.2 deg/sec test:
385kph, 19.6 deg/sec test:

sorry also for the poor quality but after alpha strike fps are shit on macOS (btw @Metrallaroja or @Gunjob any idea if the devs are aware of this?)

The turn rate at 720kph was now reduced to 21.2 deg/sec which is only 0.2 sec more than the very upper end of what the devs set themselves as the range for the gripen at this speeds.

The polar curve on the other end has still a completely wrong pattern.
I just needed to reduce e_0 to calibrate it to new reference 720kph test and the 380kph test still falls exactly on the function (it’s slightly lower because the thrust interpolation underestimates thrust by about 100~150kgf as I took 400kph as baseline speed before but didn’t feel like doing a whole new interpolation for such a small difference)
A is 720kph test, F is 385kph test.


Real aerodynamics has left the chat

+100% = 200%.

Don’t forget that the percentage change in wing loading dwarfs the percentage change in thrust.

He said “nearly double” iirc, which explains where the 180% came from.

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It was never in that chat.

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You do realise there has never been realistic aerodynamics in this game? Pretty much every propeller aircraft in the game can rip its own wings off with just gravity if given enough altitude. That doesn’t really happen in real life. Instead they enter compressibility where the control surfaces stop working effectively. A lot of the time pilots were able to recover in these situations, when they descend to denser air and drag increases to slow them down. Some planes were infamous for being unrecoverable, such as the P-38 prior to having dive flaps fitted, but it wasn’t a death sentence in most ww2 planes.

If there is no real aerodynamics here, then there is no point in discussing anything at all. The developer is out of touch with reality and does as he wants, and not as the laws of aerodynamics dictate.

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its almost like a virtual world can’t fully simulate reality

You tell em sister!!

Yes, errors will always be unavoidable.But what I see on the charts is completely divorced from reality
And this applies not only to grippen, but to all aircraft in general

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You realize that the game by and large claims to be realistic and is trying to duplicate real world flight performance to a large extent?

Wings ripping instead of planes entering irrecoverable compression is a design decision done for the benefit of Air RB players.

If they wanted to really embrace realism then you would have to pre-trim your airplane for dive recovery.

You are not providing any insight that I don’t already know.

@Metrallaroja @Gunjob Clearly the performance is still above that which the devs claimed… is it still going to be adjusted further? Seems it’s another case of MiG-29 FM changes where I had to push for them to finally correct the high alpha behavior over the course of several reports and months of waiting.

Additionally, it doesn’t seem they’ve touched the SEP… so should Gio go ahead with his report?

edit. Why was this flagged as ‘off topic’?

The only reason SEP is high is because low speed sustained turn rate is high.

Was the same with the old MiG-29 flight model, it completely over performed in rate below 500kph, that’s why it could “pull longer” before running out of energy.
Rate and SEP are directly related, not disconnected

This was the only planned changed.


0.2 can be just a test error, I dont see it enough to forward it.


“dwarfs” is a bit of a hyperbole.
that and it’s REALLY hard to calculate as JAS39 has what effectively results in dynamic wing loading owing to the movable canards.
the main issue is if the wing area should include the area of the canards or not.
i have seen three numbers floating around for JAS39 regarding wing area. 25m^2, 28m^2 and 30m^2
if we use those numbers at gross weight (8.700kg) we get 348, 311 and 290 respectively.
(F-16 has 429)
if we look at the ratios of wing loading to T/W at gross weight by doing (T/W)/Wing Loading we get:
F-16: 0.26%
JAS39: 0.27% , 0.30% and 0.33% respectively

so depending on what number is used JAS39 is either: about the same, a tenth better or two tenths better. (in this very specific area)
But this is sort of a derivative of my point with point nr1 in my post as wing loading depends on weight.

and i just want to add:
Thanks to @Gunjob and @Metrallaroja for engaging with us and giving insights and answers where they can :) Great job guys!