Su-25t won't dive

[FlyToRainbowRay]

Hey, I have been having some problems flying the Su-25t. Every now and then the plane can't dive. When this happens I can turn left, right and up just fine but the stick won't go forward unless I trim it forward. And even after trimming is forward it usually gets screwed up again and I can't dive anymore. Also, after using the autopilot and then turning it off my plane often banks hard on the x axis and I have to trim it. Is this normal? I've never had any problems like this flying the A-10C. Oh, and I use a keyboard. Any help would be nice.

[Mohamengina]

Oh, and I use a keyboard. Any help would be nice.

 

 

You what?

 

Sounds like your issue could be mach tuck. How fast are you going when you try to pitch down?

[EtherealN]

Track files are always the best way to get a proper analysis of a problem, btw. Just save track after flight and upload here on the forum. :)

[mjolner]

Sounds like you have some kind of control assignment conflict. Make sure you are not activating the stick to trimmer function. Even better play it safe and delete all assignment for trimmer and control axis and start fresh. Do you have an old stick with pots or something newer with hall effect sensors?

[Boberro]

 

You what?

 

On the contrary of common stereotypes keyboard is handy. If you don't fly n close formations you don't have to get joy for successful mission accomplishments.... and that all without bigger decrease of comfort.

[Mohamengina]

On the contrary of common stereotypes keyboard is handy. If you don't fly n close formations you don't have to get joy for successful mission accomplishments.... and that all without bigger decrease of comfort.

 

What?

 

I'm just surprised you haven't invested in a joystick considering how much benefit you would get out of having one.

[Cedaway]

FlyToRainbowRay: Welcome to this forum.

[EtherealN]

Guys, let's not discuss the virtues of having a stick (which I agree with), but rather see if we can help this user? :)

[159th_Viper]

Disengaging the autopilot retains the stick setting at time of disengaging. Therefore necessary to trim back to level, coordinated flight. In addition, remember the difference between disengaging autopilot properly (LAlt-9) as opposed to merely hitting the 'A' button.

 

To avoid any issues, engage emergency levelling mode (LAlt-3) and once stabilised, disengage (LAlt-9).

[maturin]

I don't think this is an autopilot issue, but a speed issue. Tends to happen at level flight or at a slight dive.

 

It happens to me occasionally, always when I start an attack run without bleeding off my speed (usually around 500kmh but sometimes a little less). The autopilot has crashed me numerous times, so I am very careful with it now.

 

Bottoming out the throttle allows the nose to drift down to the point where I can use the down elevator again, but its usually too late for my Vikhrs.

"At high speeds the Grach-T likes to , counter intuitively, loose lift and pitch authority. I don't have figures to hand but I recognise it instantly. It can be very dangerous in a dive for example, when you pull the stick back you can get a nasty surprise. So If you've trimmed in a high speed dive and next thing you begin to slow down coming off the attack, the nose just loves to Jump back up again."

-quote from someone in the other thread

Edited August 10, 2012 by maturin

[HiJack]

I definetly think this is an autopilot issue. Viper is on the ball :D

[GGTharos]

It doesn't lose lift. It suffers from compression effects over the control surfaces, control reversal, and possibly a movement of the center of lift behind the CG. Standard stuff for aircraft that aren't built to fly at trans/supersonic speeds when they try to go faster than what they were designed to.

 

"At high speeds the Grach-T likes to , counter intuitively, loose lift and pitch authority. I don't have figures to hand but I recognise it instantly. It can be very dangerous in a dive for example, when you pull the stick back you can get a nasty surprise. So If you've trimmed in a high speed dive and next thing you begin to slow down coming off the attack, the nose just loves to Jump back up again."

-quote from someone in the other thread

[159th_Viper]

I routinely RTB at 1000km/h or thereabouts with no ill-effects so it's definitely not a speed issue.

[Dr_Arrow]

It doesn't lose lift. It suffers from compression effects over the control surfaces, control reversal, and possibly a movement of the center of lift behind the CG. Standard stuff for aircraft that aren't built to fly at trans/supersonic speeds when they try to go faster than what they were designed to.

 

That's correct, it is especially dangerous at low level when pilot isn't prepared, but it is modeled very well.

[maturin]

I routinely RTB at 1000km/h or thereabouts with no ill-effects so it's definitely not a speed issue.

How do you manage a thousand? I usually get the shakes at 800 or lower.

 

And it's a dive issue as much as a speed issue.

 

Autopilot can't explain it when the loss of down elevator is only for the duration of the fast dive, and after using the Alt-3, Alt-9 disengage method.

[Ironhand]

I routinely RTB at 1000km/h or thereabouts....

 

IAS or TAS? :)

 

 

Rich

[RIPTIDE]

Vipers right. We recently had a screenshot battle (where I beat him with my Su-25A).

 

[Exorcet]

How do you manage a thousand? I usually get the shakes at 800 or lower.

You could cheat and raise the ambient temperature to max to increase the speed of sound, then dive from high altitude to overcome the loss of engine thrust.

[159th_Viper]

Vipers right. We recently had a screenshot battle (where I beat him with my Su-25A).

 

 

Aye - I didn't have GG and his Budgie on my A$$ - would have been faster had that been the case :P

 

You could cheat....

 

No need for that - she does it all by herself the Toadie does.

 

IAS or TAS?

 

IAS :)

[GGTharos]

The more relevant question is 'what was the mach number' ... the compression effect problem, which last I checked (although I checked long ago) was modeled for the Su-25A/T, depends on the mach number.

[FlyToRainbowRay]

Disengaging the autopilot retains the stick setting at time of disengaging. Therefore necessary to trim back to level, coordinated flight. In addition, remember the difference between disengaging autopilot properly (LAlt-9) as opposed to merely hitting the 'A' button.

 

To avoid any issues, engage emergency levelling mode (LAlt-3) and once stabilised, disengage (LAlt-9).

 

This was definitely the problem. I just flew a campaign mission and the plane would often roll to one side or not dive if I just hit the "a" button after engaging the autopilot, but making sure I hit Lalt-9 after engaging the autopilot kept things stable. Thanks.

[159th_Viper]

How do you manage a thousand? I usually get the shakes at 800 or lower.

 

And it's a dive issue as much as a speed issue.

 

Autopilot can't explain it when the loss of down elevator is only for the duration of the fast dive, and after using the Alt-3, Alt-9 disengage method.

 

Here's a quick track where I sustain 1030km/h IAS at ground level, with 1070km/h IAS (1120km/h on externals) obtained in a shallow dive. Also low-level valley flying at 950km/h IAS to 1030km/h IAS with no noticeable control-issues, albeit with the shakes.

 

Track: Toadie.trk

 

If you do still experience control-issues kindly post a track - that is the only way we can begin to investigate issues.

 

 

This was definitely the problem. I just flew a campaign mission and the plane would often roll to one side or not dive if I just hit the "a" button after engaging the autopilot, but making sure I hit Lalt-9 after engaging the autopilot kept things stable. Thanks.

 

Excellent - glad you got it sorted :)

[Ironhand]

I don't think this is an autopilot issue, but a speed issue. Tends to happen at level flight or at a slight dive.

 

It happens to me occasionally, always when I start an attack run without bleeding off my speed (usually around 500kmh but sometimes a little less). The autopilot has crashed me numerous times, so I am very careful with it now.

 

Bottoming out the throttle allows the nose to drift down to the point where I can use the down elevator again, but its usually too late for my Vikhrs.

Are you by any chance lowering or raising flaps, when this happens? You'll get a pitch up during those periods that, at the right speeds, could cause issues.

 

Just made a few high speed runs myself at about 800 ft ASL with an IAS of 1020kph and was surprised at the amount of nose up trim required for level flight. I wonder if that somehow plays into your issue.

 

And at those speeds bad things can happen, if you jerk the stick :) :

 

 

 

 

 

Rich

Edited August 10, 2012 by Ironhand

[RIPTIDE]

It doesn't lose lift. It suffers from compression effects over the control surfaces, control reversal, and possibly a movement of the center of lift behind the CG. Standard stuff for aircraft that aren't built to fly at trans/supersonic speeds when they try to go faster than what they were designed to.

I thought those compression effects were manifested as loss of lift? At least on the other part of the wing? :dunno:

[RIPTIDE]

A

 

Just made a few high speed runs myself at about 800 ft ASL with an IAS of 1020kph and was surprised at the amount of nose up trim required for level flight.

Rich

Yeah. Last time I was that fast was making the Su-25A run. Dropping down from 1000hph fast in a climb or turn meant LOTS of nose down trim and then nose up trim... nasty business.