Pulling G

[pandoraefretum]

Forgive my ignorance; I love the L-39 module... but I am still puzzled:

 

I know what G force is and what AoA is and I know what a high speed stall is...

BUT when I pull back on the stick above 50% my L-39 loses it....

it flies ugly.. a wing stalls the craft is buffeted about.

 

In short, it can't take much strain. I can't for the life of me pull 6G

yet I know that's possible in an L-39

 

Is this how it's supposed to be ? everyone else happy ?

[flying rabbit]

Im glad you made this thread. The L39 should resist +8/-2 G and I never managed to get to 6G without getting instable.

 

If you compare this to the SU25T it can easily pull 9-10G without an comparable stall. Im no specialist in aerodynamics, but why is the SU25 so much more stable than the L39?

[RAZBAM_ELMO]

Do you have a file track? What was your speed at the time and how quickly did you pull the stick back? What were external stores at the time and how much on board fuel did you have?

[gospadin]

This is a sustained 6.5G turn:

 

 

Remember that G forces are a function of both speed and AoA. You don't need maximum stick pullback for more Gs, you likely need more airspeed. Try starting a dive to get as close to mach 0.9+ as possible, THEN apply stick input to the limit of roll stability.

 

You'll shed airspeed, but should be able to hit maximum turning Gs that way.

[frumpy]

If you put a L-39C in a 800 km/h dive, you can easily pull 10g.

 

As for pulling the Gs in a loop... I am not sure about this one

(don't remember where I read it): I believe you can pull max. G

depending on the speed... take the speed, subtract 100 km/h

and divide it by 100. So you enter a loop at 700 km/h and can pull

6g... 600 km/h 5g... and so on during the loop.

 

What I would fall in love with is an AOA readout... <3

[Flamin_Squirrel]

What gospadin said.

 

Understanding corner/manoeuvre speed is key. Above corner speed you'll be G limited (rip winds off/black out before you stall); below you're aerodynamically limited (you'll stall before you reach G limit).

 

The following image may help. Max turn performance is shown by the upper red line. Hopefully you can see this planes turn rate increases with speed up to its corner speed of 260mph above which it is G limited.

 

[gospadin]

The following image may help.

 

...

 

What aircraft is that graph for?

[pandoraefretum]

Pulling G

 

Okay I got into a 800 kph dive and sustained a 6+ G turn for a while.

Not happening by chance. Plus I was amazed at how little speed I bled.

 

Then I went up again.... started pulling & even got to 8G but went out of control after that.

 

But flying normally there's a ceiling of 4-5G.

 

Something not right in my opinion.

[Flamin_Squirrel]

What aircraft is that graph for?

 

Not sure, I just goggled turn performance. Probably a war bird of some type.

 

Okay I got into a 800 kph dive and sustained a 6+ G turn for a while.

Not happening by chance. Plus I was amazed at how little speed I bled.

 

Then I went up again.... started pulling & even got to 8G but went out of control after that.

 

But flying normally there's a ceiling of 4-5G.

 

Something not right in my opinion.

 

That's not a ceiling, you're flying to slow.

[pandoraefretum]

Ok let's forget about G

Just fly at 400, 500, 600 kph whatever you like

(Bank, or not) then Pull the stick towards you and the aircraft goes out of control

[Flamin_Squirrel]

Well, yes, it will.

 

Even flying fast, as soon as you begin a max performance turn you'll bleed energy until you're below corner speed at which point you're no longer G limited and are susceptible to stalling.

 

The L39 is a simple aircraft and won't fly itself; if you stall and drop a wing it's because you let it.

[FSKRipper]

Ok let's forget about G

Just fly at 400, 500, 600 kph whatever you like

(Bank, or not) then Pull the stick towards you and the aircraft goes out of control

 

You could try this with the FW-190 and see what will happen :music_whistling:

 

As Flamin Squirrel said, if you bleed all your energy the plane stalls faster then you can say "eject". If you think your problems are related to a FM issue it would be better to attach a track. It would it make easier for us to understand your issue...

[pandoraefretum]

One more try at explaining myself,

 

It's simple : I takeoff in L-39C quickstart takeoff will do...

Get her lean & clean to 600 kph low, say 1,000 ft and bank nearly 90 deg

I pull 20% back on my joystick... she turns

I pull 30% she turns tighter

I pull 40% I can hear and feel a little turbulence above the wings

I pull 45% and she spins, stalls, rocks, buffets does anything but fly

 

No other craft does this in DCS... maybe an Su27 in S mode pulling throttle 85% back ?

I bet 90% of DCS L-39C Pilots have noticed how intolerant to high G the DCS model is

I know the shape of the wing cannot generate that much lift... but I feel it behaves a little oddly as it starts to fail.

[cardboard_man]

Try that in any of the ww2 birds you will have the same problem, probably even more pronounced. The only planes that don't do that at all, at least in my experience are the ones that still have SFM's ( Su-33, Mig-29).

 

To me it just sounds like you are trying to pull to hard. So As FSKRipper said if you think i am wrong or something is wrong with the flight model upload a track so we can see what is happening and what you are doing.

[fjacobsen]

That's simply called accelerated stall.

[NeilWillis]

Try not pulling the stick back beyond the point that the aircraft starts to complain that you're pulling the stick back too far.

 

Accelerated stalls actually exist. They happen when you pull back on the stick too far.

[WinterH]

I don't own L-39 but, WW2 modules and F-86 do nasty stuff at speeds below their comfort zones when you pull the stick too much.

[pandoraefretum]

Yes, thx for understanding now

 

high speed stall, or accelerated stall is what I am talking about...

BUT I am getting it with only / barely 50% deflection of my joystick... (in the Albatros)

 

Perhaps in Tune-Axis I should flatten out the Y axis ? maybe a little ?

[Dr_Arrow]

Yes, thx for understanding now

 

high speed stall, or accelerated stall is what I am talking about...

BUT I am getting it with only / barely 50% deflection of my joystick... (in the Albatros)

 

Perhaps in Tune-Axis I should flatten out the Y axis ? maybe a little ?

 

The real L-39 has very sensitive elevator at high speeds, it is even not recommended to use the trim above 700 km/h IAS as it can cause very abrupt response of the aircraft. So if you pull stick to 50% at such high speed abruptly to achieve some Gs you are in for trouble. In real life however, forces acting on the elevator won't allow you to jerk the stick like at home.

[flying rabbit]

Why can you pull the stick on the su25 like a maniac without such behaviour?

[Flamin_Squirrel]

Probably because it's a completely different aircraft.

[Ramsay]

In real life however, forces acting on the elevator won't allow you to jerk the stick like at home.

 

Probably because it's a completely different aircraft.

I thought it was usual for ED and 3rd party developers to model increased control forces by reducing joystick responsiveness and maximum deflection to reflect what a real pilot can pull on the flight stick/rudder.

 

Certainly the DCS L-39 seems to enter an accelerated stall easier than I would have expected but I'm not overly concerned ATM, as I expect ED will continue tweaking the flight model/control response until it's closer to what I'd expect (they usually get pretty damn close 18 months after the first beta).

[Flamin_Squirrel]

Certainly the DCS L-39 seems to enter an accelerated stall easier than I would have expected but I'm not overly concerned ATM, as I expect ED will continue tweaking the flight model/control response until it's closer to what I'd expect (they usually get pretty damn close 18 months after the first beta).

 

What you expect the flight model to be like and what the aircraft actually flys like may not be the same.

 

Yes the L-39 stalls out quickly easier than any other jet, but it is the only jet has straight wings and is significantly lighter than any other jet also.

[WildBillKelsoe]

Im glad you made this thread. The L39 should resist +8/-2 G and I never managed to get to 6G without getting instable.

 

If you compare this to the SU25T it can easily pull 9-10G without an comparable stall. Im no specialist in aerodynamics, but why is the SU25 so much more stable than the L39?

 

 

powerplant issue?

 

 

Sent from my iPhone using Tapatalk

[gospadin]

I thought it was usual for ED and 3rd party developers to model increased control forces by reducing joystick responsiveness and maximum deflection to reflect what a real pilot can pull on the flight stick/rudder.

 

Certainly the DCS L-39 seems to enter an accelerated stall easier than I would have expected but I'm not overly concerned ATM, as I expect ED will continue tweaking the flight model/control response until it's closer to what I'd expect (they usually get pretty damn close 18 months after the first beta).

 

This would be interesting.

 

Instead of the joystick representing deflection of the stick, you'd model the joystick to represent force applied to the stick, where 1.0 = maximum force a trained pilot could exert.

 

This would then be translated to an actual stick deflection, based on current aerodynamic loading, hydraulic state, aircraft damage, etc.

 

Neat idea!

--gos