Issues with the JAS 39 Gripen flight model

[Mytho-GR1]

@Giovanex05 was making some good points and wasn’t hostile but what a shame

[FeetPics]

@MiG_23M

Funny that, the people saying I’m biased didn’t or couldn’t report the issue. Glad you’re working on it… let us know if there are any death threats or associated things like I got.

What’s funny is the second I make a post that shows how the Gripen FM stacks up against other planes and why it matters…it gets immediately flagged and hidden within 5 minutes.

Still no death threats yet though…

[Mytho-GR1]

Interesting its back up

And you stuff is nothing new its just graphs you made complaining how op the Gripen is

You know when the Eurofighter comes it would be the same situation as they only US thing that rivals it in flight performance is the F22

[CorporalApollo]

Thank you for your work and attempts to make the thread civil, Going well so far.

@Giovanex05

Also I think the extra 1.3 deg/sec baseline it has at 700kph can be already reported

I’m sure I read of several people who tested the sustained after the nerf and claimed it performed to the ∼20-21° gaijin claimed, didn’t you also do this @MiG_23M ? I had no idea about this discrepancy (neither did the biggest Gripen haters out there during the last thread it seems). Did it accidentally get an extra sustained degree/s ‘buff’ during the engine patch maybe?

Anyways @Giovanex05, you seem like you know what you’re talking about, this is a complex matter still and admittedly I’ll have to take a look at your math again when it’s not 1am and I’m half-awake before I can make any informed comments on it, but regarding this:

@Giovanex05

The reason why I idid all this crap math up there is that lifting line theory does a good job at approximating the polar diagram with steady and non compressible flow, but at higher AoAs the flow is more and more unsteady and at very high AoAs upper flow even starts detaching from the wing (which causes the lift coefficient to start actually decreasing all the way to 0 while the drag coefficient increases (that’s why aircraft will stall at high AoAs and also why Cobras aren’t useful in 99% of the situations).

Isn’t this exactly what the delta-canard excels at? Making the flow more steady at very high AoA, and delaying the detaching from the wing, increasing lift? I think this is relevant if we’re using non canard-delta (different aerodynamic configurations) as reference for calculations? What’s your take on the whole canard-thing? Thank you :)

[Mytho-GR1]

@FeetPics

The Gripen in-game already matches Eurofighter performance numbers from what I have seen

It doesn’t its below them

[CorporalApollo]

I think the best way to go about this thread is to avoid/ignore non-productive comments and stay focused on the people actually providing meaningful input on the Gripen FM - goes both ways

[Mytho-GR1]

Fair enough i shall wait for what @Giovanex05 has to say as i find it interesting

[SlowHandClap]

@Giovanex05

Doing a sustained turn test at 700kph and 50% fuel we find that currently the sustained turn rate is ~22.3 degrees per seconds at that speed, at least 1.3 deg/sec higher than what it should be, but this is far from what makes the gripen such a good fighter, especially it does not explain why it loses much less energy than any other aircraft when tightening down a turn.

Your test was at 700 kph, which is the bottom of that range.

[FeetPics]

@Giovanex05

The reason why I idid all this crap math up there is that lifting line theory does a good job at approximating the polar diagram with steady and non compressible flow, but at higher AoAs the flow is more and more unsteady and at very high AoAs upper flow even starts detaching from the wing (which causes the lift coefficient to start actually decreasing all the way to 0 while the drag coefficient increases (that’s why aircraft will stall at high AoAs and also why Cobras aren’t useful in 99% of the situations).

I have friend who made flight model analysis tool. I have the polar plots and the CL/CD plot for the Gripen if you want it for your bug report.

[MiG_23M]

@CorporalApollo

I’m sure I read of several people who tested the sustained after the nerf and claimed it performed to the ∼20-21° gaijin claimed, didn’t you also do this @MiG_23M ?

I tested prior to the drag change for sure, however I have been absent and haven’t made any reports in some time.

@SlowHandClap

Your test was at 700 kph, which is the bottom of that range.

So, 2.3 deg/s higher than expected?

[Giovanex05]

@CorporalApollo

Anyways @Giovanex05, you seem like you know what you’re talking about, this is a complex matter still and admittedly I’ll have to take a look at your math again when it’s not 1am and I’m half-awake before I can make any informed comments on it, but regarding this:

Before we go further, i like to point that while I do have education on how to math like this (currently studying mechanical engineering), i’m not studying aerospace/aerodynamics so there may be stuff that I am missing on where and how certain formulas to approximate stuff can be applied.

@CorporalApollo

Isn’t this exactly what the delta-canard excels at? Making the flow more steady at very high AoA, and delaying the detaching from the wing, increasing lift? I think this is relevant if we’re using non canard-delta (different aerodynamic configurations) as reference for calculations? What’s your take on the whole canard-thing? Thank you :)

All moving certainly do have a benefit at lower speeds together with the unstable configuration, but they can’t outright prevent unsteady flow and flow separation, so the polar of a delta canard fighter, while better in the low speed department than a ”conventional” configuration, is it impossible for it to be literally equal to what is basically an ideal perfectly steady flown that never detaches.

The reference of the calculation is not a delta wing, but an ideal elliptical wing as it present a perfectly even lift distribution (which again is the best case possible as with the flown assumptions before), and then e_0 simply scales that efficiency back to another wing (that’s why the 700kph test calibration was important, there’s no other way to find the current e_0 the gripen has in game).

In shorter terms, the calculation I did should proove that the gripen in game follows that approximated curve that assumes what is basically an ideal flown. Now we need to see how much is it overperforming, as the real gripen curve will certainly be below current levels, but will most likely be above the ones of the MiG-29 or the F-16.

[Giovanex05]

@SlowHandClap

Your test was at 700 kph, which is the bottom of that range.

Since that STR value is higher than what was reported by devs it is still too high. The reason i picked 700kph is that this was (and is) not the absolute best rate speed (wanted to have some margin) and there’s no risk to get close to transonic regime where i have no idea if Lifting line theory works.
Thinking back thought i could have done 750-800kph and be fine… current function I did in topic predicts 760-790kph as peak rate speed, it would be cool to find out if it is true.

@FeetPics

I have friend who made flight model analysis tool. I have the polar plots and the CL/CD plot for the Gripen if you want it for your bug report.

That would be very welcome indeed, if his Cl/Cd plot matches mine we would have a really solid base. Obviously need to know also how he did the testing (or datamine if it extrapolated them from there)

[FeetPics]

@Giovanex05

That would be very welcome indeed, if his Cl/Cd plot matches mine we would have a really solid base. Obviously need to know also how he did the testing (or datamine if it extrapolated them from there)

I will DM them to you.

[SlowHandClap]

@MiG_23M

So, 2.3 deg/s higher than expected?

The image used in your bug report shows that 20-21 isn’t the peak though afaik, and we don’t know if that was at 700 or 900kph.

[Metrallaroja]

@Giovanex05

• Around 20-21 deg/sec sustained turn at: sea level, speed: 700-900kph and 50% fuel
• Engine thrust curve should be somewhat accurate

Doing a sustained turn test at 700kph and 50% fuel we find that currently the sustained turn rate is ~22.3 degrees per seconds at that speed, at least 1.3 deg/sec higher than what it should be, but this is far from what makes the gripen such a good fighter, especially it does not explain why it loses much less energy than any other aircraft when tightening down a turn.

Thanks, I asked several times for this to be tested and none did but kept arguing.
Can you also do a vid at 900kph or 800kph?

[Malekitth]

R-73 still gets flared in rear aspect >%50 of the time <1KM VS afterburning gripen

[Metrallaroja]

Also, please dont fake flag posts just because you dont agree with them.
You are just wasting time of the forum moderators and making the forum a worse place to discuss.

[SlowHandClap]

@Metrallaroja

Thanks, I asked several times for this to be tested and none did but kept arguing.

You’re more than welcome to test yourself.

@Malekitth

R-73 still gets flared in rear aspect >%50 of the time <1KM VS afterburning gripen

I’m not having any problems with R-73s. Any reason you’re launching from within 1km? Depending on your airspeed that’s potentially inside the minimum engagement range.

edit: unhiding my posts after mig23m flag abuse.

[Necronomica]

@Giovanex05

If this calculation was done to approximate what the real life gripen would look like I think we would not be able to get further than ~5 degrees AoA analytically (basically untill canards start moving extensively) as to simulate actual canard and wing interaction i think you need to do a CFD or a straight up wind tunnel.
(Idk thought, i am studying mechanical engineering so maybe some way exists that allows to approximate that analytically for steady flow)

https://sci-hub.ru/https://arc.aiaa.org/doi/abs/10.2514/6.1991-3195
here is some information from the pre production trials if you are interested :)

and here is some general comparisons to generic delta canard configurations and their relative performances :)

ADA063819.pdf

[Necronomica]

i think you are talking about different things here, you are saying lift, he is saying lift-coefficient.

you are both correct in your statements just talking about different things and interpreting each other to mean the wrong thing.