Nose down AB and do not acelerate?????

[Davee]

The delta wing is a big airbrake when you are at very high AoA, it is not unreal to me.

 

Of course!

We are talking about recovery acceleration, yes?

[Azrayen]

What i wanted to demonstrate was the excessive drag

Sure :)

 

stall means you don't have enough air pressure under the wings to lift you up, in a condition like that it's so strange to not having thrust.

Nope. ~75 % of the lift of a wing comes from the depression ABOVE the wing, not from the surpression under it.

In a typical stall, the airflow doesn't "stick" anymore to the UPPER surface of the wing (due to AoA > max(CL)), and this is why you "fall" : because you lost the depression above the wing. Not because you lack surpression below it.

And there is no issue re: lack of thrust. Do not confuse lack of acceleration and lack of thrust.

 

Anyway if the thrust/weight ratio of those two planes (su27-m2kc) is so similar i don't expect a so evident difference at low/stall speeds, because much more at those speed the aerodynamics and the control surfaces (slats elevators) have a minor importance on the drag factors, and the behaviour should be more influenced just by the weight, and thrust.

I beg to differ. Wings aren't the same, and this plays quite a role.

[hellking]

I just wanted to stop by to say that I have been experiencing similar unrealistic behavior (I was too lazy to create a thread for it but when I saw it I said aha!).

 

When the AoA is very high, speed is very low(<50 knots), afterburner on, and plane facing horizontally, the plane does not accelerate (not even a bit). This is against the physics laws since at low speeds there is no drag and afterburner should nudge the plane in the direction plane is facing (horizontal direction).. The only way to get the speed up seems to be to face the plane down and reduce AoA.

[myHelljumper]

When your speed is that low (holy cow low) you AoA is so high that your drag and your weight can't be overcome by your engine, again I don't see any problems here.

Edited April 19, 2017 by myHelljumper

[impeller]

Nose down AB and do not acelerate?????

 

You're not in stall, because the FBW prevent you from it.

Just release the stick and the plane will accelerate, no need to go inverted.

You can also "unload" the plane to ease the speed recovery (push the stick to 0G, but be careful not to push into the ground).

 

There is an AoA where the FPM is at its down limit and no longer represent the true flight path.

 

As a matter of fact, with fuel below 5000kg the Su 27 will often have a thrust to weight ratio greater than that of the Mirage 2000.

 

Good video that will give an idea of how quick the M2000 can decelerate:

 

When the FPM is stuck on the pitot tube, AoA > 16°

 

Last question: what is your real world aeronautical experience ?

 

 

 

4:30 in this video seems quite familiar, right guys?

Control speed and alt, you fly the plane. The plane doesn't fly you

 

 

Skickat från min iPhone med Tapatalk

Edited April 19, 2017 by impeller

[Conroy]

Yes, definitely a very good video.

M-2000C FM is almost perfect i think, but i agree there's still somenthing strange. I can confirm this myself too:

[OnlyforDCS]

Hi guys, I'm keeping an eye on this and will be looking into it. I believe there to be an issue in too severe of a drag build up both pitch rate derivative coefficients and in alpha rate derivative coefficients at mid to high angles of attack that is causing it. It's fairly complex and need to be graceful how I solve it but just wanted to chime in that I'm on the case :)

 

Good to know. :thumbup:

[lemoen]

Yes, definitely a very good video.

M-2000C FM is almost perfect i think, but i agree there's still somenthing strange. I can confirm this myself too:

 

Not sure what you're trying to show. The indicated airspeed is the speed of the air moving past the pitot tube, *parallel to the pitot tube*. In these cases the aircraft may well be accelerating, but not in that direction, maybe towards the nadir if you're level but has zero speed.

 

I would still however expect to regain airspeed about as fast as on takeoff, with the burner on and the nose and wings level, at very low airspeed, faster with the nose down.

[myHelljumper]

I would still however expect to regain airspeed about as fast as on takeoff, with the burner on and the nose and wings level, at very low airspeed, faster with the nose down.

 

I do not agree, on the runway you don't have to overcome all your aircraft weight and the huge drag from the high AoA. When you are taking off you only have to overcome friction from the wheels and the minimum drag of ~0° AoA.

 

Maybe you should gain speed but sure not about as fast as if you were taking off.

 

Edit : Just watch the video guys, same conditions, same behavior....

Edited April 19, 2017 by myHelljumper

[gavagai]

Hi guys, I'm keeping an eye on this and will be looking into it. I believe there to be an issue in too severe of a drag build up both pitch rate derivative coefficients and in alpha rate derivative coefficients at mid to high angles of attack that is causing it. It's fairly complex and need to be graceful how I solve it but just wanted to chime in that I'm on the case :)

 

Good news. Thank you.:)

[lemoen]

Hmmm. So, with the wings level and nose level, at low airspeed, the plane is going towards the nadir right? Mostly in the same direction as gravity. There is massive drag because the airflow is seeing the planform. Add burner now, that force is towards the nose of the plane. At least at low airspeeds you should expect to see an acceleration in that direction. You don't have to overcome weight or drag to gain airspeed, in this case. Same for nose down attitude.

 

With the nose up however, then yes, the engine must overcome gravity too and it doesn't provide as much thrust at low airspeed as it does at higher airspeed (everything else being equal).

 

Anyhow, you'll still be heading towards the ground in all these cases.

[p1t1o]

Hmmm. So, with the wings level and nose level, at low airspeed, the plane is going towards the nadir right? Mostly in the same direction as gravity. There is massive drag because the airflow is seeing the planform. Add burner now, that force is towards the nose of the plane. At least at low airspeeds you should expect to see an acceleration in that direction. You don't have to overcome weight or drag to gain airspeed, in this case. Same for nose down attitude.

 

With the nose up however, then yes, the engine must overcome gravity too and it doesn't provide as much thrust at low airspeed as it does at higher airspeed (everything else being equal).

 

Anyhow, you'll still be heading towards the ground in all these cases.

 

Possibility of reduced thrust due to non-optimal airflow into intakes?

[myHelljumper]

Possibility of reduced thrust due to non-optimal airflow into intakes?

 

Yes, something that does not happen while taking off.

[lemoen]

I'm not arguing the FM is wrong, btw. Just that I agree on some of the previous posts' points. The implementation details of all these things IS the Flight Model and we're discussing that. I'm just curious to see what comes out. I fly this module the most of all.

[myHelljumper]

I'm not arguing the FM is wrong, btw. Just that I agree on some of the previous posts' points. The implementation details of all these things IS the Flight Model and we're discussing that. I'm just curious to see what comes out. I fly this module the most of all.

 

Me too, but I'm on the other side :D.

 

It's nice to have a clean discussion for once :).

 

As we aren't Mirage pilots maybe the better thing to do is to wait for Cpt Smiley to do his magic and see the results ;).

[hellking]

When your speed is that low (holy cow low) you AoA is so high that your drag and your weight can't be overcome by your engine, again I don't see any problems here.

 

Drag is in vertical direction (plane is literally falling like a brick), but the force from afterburner is in horizontal direction. I don't see why it doesn't accelerate in horizontal direction because of a drag in vertical direction. But don't get me wrong: here I am not expecting the plane to stop moving down and recover. It should still move down but with increasing horizontal speed.

[gavagai]

Drag is in vertical direction (plane is literally falling like a brick), but the force from afterburner is in horizontal direction. I don't see why it doesn't accelerate in horizontal direction because of a drag in vertical direction. But don't get me wrong: here I am not expecting the plane to stop moving down and recover. It should still move down but with increasing horizontal speed.

 

That sounds like a deep stall to me. In the F-16 you can't AB your way out of it, either. You have to disengage the FBW AoA safety and rock the plane out of it.

 

That said, my suspicion is that something is awry with the M2000 induced drag at medium AoA, as Cptn Smiley already hinted.

[sleat]

You can be in a dive but with 90° AoA you won't accelerate....

 

A track recording of being in a dive at 90° alpha in full burner and not accelerating would certainly be amusing to watch. Your velocity vector would be coming right out of the belly. Sounds even better than my 2 second disintegration. My alpha was 180 easy!

Edited April 20, 2017 by sleat
typo!

[Zodiac]

+1

[Dugong]

Has there been any progress on this? It's been 2 months since CptSmiley acknowledged this as a bug but it's still a problem in 1.5.

 

Has it been fixed in 2.0/2.1?

[Esac_mirmidon]

Wait for incoming updates.

[zero]

Tested again:

 

30° dive, Full AB, 150 knots, AOA 18°, and 1.6 G

 

In this attitude the aircraft loss speed.

 

At AoA 18 - the vortex generated lift (delta wing) burst.

Way to high AoA.

And only 1.6 G. Falling like a brick.

 

I am not sure how well the pitot probe is simulated. But at this angle the total pressure will be too low. (could be compensated by computers I do not know of) - giving a false indicated airspeed.

 

Agree that there something not correct simulated in this regime. But certainly not as much as some claim to be.

[myHelljumper]

I am not sure how well the pitot probe is simulated. But at this angle the total pressure will be too low. (could be compensated by computers I do not know of) - giving a false indicated airspeed.

 

IIRC the Mirage have CAS (Corrected airspeed) not IAS (indicated airspeed) so it might be corrected with the AoA.

[Azrayen]

Zero, IMO there is really no point further discussing the matter at hand until...

Wait for incoming updates.

 

I don't mean to be mean ;)

It's just that I fail to see the point to continue to elaborate complex theories based on the current DCS FM that the dev himself acknowledged (twice alrealdy at least) to be incorrect in the high AoA regime... Kinda feel like beating an already (very) dead horse. :D

 

Regards

[Esac_mirmidon]

Exact.