Su27 inverted depart is realistic?

[theropod]

:) EDIT:

 

One issue is that most of us don't fly with a split throttle. If we did, controlling taxi speeds would be much easier and I wonder if you could actually perform the cobra turn--or a reasonable facsimile. Just thinking out loud because I've read that differential thrust is used during the cobra to control any yaw.

 

Looking forward to viewing your track.

 

thank for your interest ironhand:)

as you say this manouevre can be only perform with split throttle. i tried different combinations but no way to perform it without split throttle.

if your timing is good you dont enter spin with using opposite thrust.

 

Edit:before 1.2.14 patch this manouevre cannot be performed even with split throttle. i guess they improved asc.

before that patch ,asc worked only for disable the limiter of pitch rotation but now, it disables all rotations. that is good improvement:)

those are my other tests if you want to check:

_LastMissionTrack1.trk

_LastMissionTrack3.trk

Edited January 6, 2015 by theropod

[Ironhand]

...

if your timing is good you dont enter spin with using opposite thrust.

those are my other tests if you want to check:

I'd love to take a look at them. It'll be until tomorrow morning before I can get to them, though.

[OB1]

What is considered the critical AoA on the 27 ?

[Darkwolf]

I did several cobra with entry speed IAS330 and exit speed as low as IAS230. No issue at all :D

[Ironhand]

What is considered the critical AoA on the 27 ?

I keep seeing 31* cited in references and that's what it appears to be in the sim. I say "appears" because I haven't actually magnified the gauge at that point to double check as I'm usually too busy falling out of the sky. But I'm certain that in the sim it's very very close to that, if not that exactly.

[GGTharos]

That may well be. I'm just saying their definition smells, and I wouldn't want to use it. And given that published stall speeds tend to be curves, well ... you know :)

 

I think we might be talking past each other in regards to stalls and level flight. We both agree that, once stalled, there is no such thing as level flight. But, again, that's not what the article quote seems to be saying. They specify stall speed as one criterion. I take that to mean the published stall speed for the aircraft. Nothing more. Nothing less. If they don't, then I'd have to agree with you. We know that you can fly at slower speeds without stalling and maintain level flight and much higher speeds and still stall. Everything hinges on pushing past the critical AoA at whatever airspeed that occurs.

[OB1]

I keep seeing 31* cited in references and that's what it appears to be in the sim. I say "appears" because I haven't actually magnified the gauge at that point to double check as I'm usually too busy falling out of the sky. But I'm certain that in the sim it's very very close to that, if not that exactly.

 

Interesting, currently the way its modeled you can maintain level flight with AoA around 40-45 and sometimes cresting ~48 deg at approx ~130km/h That seem about right to you ?

[GGTharos]

LERX can increase the AoA.

 

You probably can't really maneuver at those AoA's though, so it's not a very controllable state. Note the AoA at which you start getting wing-rock. Above this you should quickly reach a stall.

 

Notice that the limit is 24 AoA (which you can pull through, but the system tries to discourage you). With that in mind, 40-45 might seem a bit much, but that's hard to tell.

 

In the F-15, the aircraft is considered to have good characteristics up to 20 degress AoA, after which stability is reduced until the stall ... but you can probably push it up to 30-35 deg AoA under the right circumstances.

Edited January 6, 2015 by GGTharos

[Ironhand]

Interesting, currently the way its modeled you can maintain level flight with AoA around 40-45 and sometimes cresting ~48 deg at approx ~130km/h That seem about right to you ?

Really? Can you post a track? I haven't been able to accomplish that. Or, actually, I haven't truly tried. Just assumed it wouldn't work.

 

And, no, that doesn't seem right, although I suppose it might be. Lift drastically reduces as you pass 31*. Granted, some engine thrust, with that nose high attitude, would factor into the lift component but...

 

We are talking AoA and not pitch angle, right?

[GGTharos]

Good question: Can you even read 45 AoA on this gauge?

 

http://upload.wikimedia.org/wikipedia/commons/4/44/Cockpit_of_Sukhoi_Su-27_%282%29.jpg

[Ironhand]

Good question: Can you even read 45 AoA on this gauge?

 

http://upload.wikimedia.org/wikipedia/commons/4/44/Cockpit_of_Sukhoi_Su-27_%282%29.jpg

I know. I'm at work but have the manual on my HD here (how's that for dedication to a sim?). I just checked. Our AoA indicator pegs at 38* assuming that what's in the manual is identical to what's in our cockpit.

[OB1]

TacView can :)

 

At the risk of showing how crap my flying is... Have not flown the 27 for a while but achieve some results, you can see when I push it too hard nearing AoA of 50 and above is where it wants to fall out of sky. Someone with more flight experience should beable to keep it consistent between 40 and 45.

Tacview-20150107-035640.txt.zip

[GGTharos]

It's not impossible to fly an aircraft above the critical AoA, but the aircraft is very ill-behaved at that point.

 

To my limited knowledge, what happens at Critical AoA:

 

Lift coeffient reaches its peak.

Roll damping drives to zero.

Pitch damping drives to zero.

 

 

Past the critical AoA:

 

Lift coefficient decreases rapidly - each degree of additional AoA eats a lot of CL.

Roll and Pitch damping are very poor (always driving towards zero), and this causes the aircraft instability.

CD becomes greater than CL, IIRC.

 

However, with those huge engines, you might be able to make up for enough of it to fly a light flanker at a steady 40AoA.

Edited January 6, 2015 by GGTharos

[Azrayen]

1. You try doing the Cobra under 400km/h and show us the trk.

(...)

Case closed.

May I re-open said case?

 

Attached below are:

- a short track where I execute 2 cobras with 300km/h IAS (first cobra without too much energy management leads to important altitude loss, 2nd one was better executed)

- 2 graphs from this flight's ACMI

 

Cheers

Az'

27_cobra_300kmh.trk

[Ironhand]

TacView can :)

 

At the risk of showing how crap my flying is... Have not flown the 27 for a while but achieve some results, you can see when I push it too hard nearing AoA of 50 and above is where it wants to fall out of sky. Someone with more flight experience should beable to keep it consistent between 40 and 45.

Just downloaded and installed Tacview at work. Nice flying! I did notice that in the first extended low speed, high AoA sequence, you didn't have the lift to maintain level flight but impressive nonetheless. Can't wait until the weekend when, hopefully, I'll have some time to experiment.

[OB1]

Just downloaded and installed Tacview at work. Nice flying! I did notice that in the first extended low speed, high AoA sequence, you didn't have the lift to maintain level flight but impressive nonetheless. Can't wait until the weekend when, hopefully, I'll have some time to experiment.

 

You wasted company time and bandwidth ! LOL where's your supervisor !

 

Yeah I am rusty. Its relatively hard and when your not smooth with throttle and pitch you start oscillating vertically as you can see, which tends to take most of your concentration and you loose track of altitude.

 

But to me it feels very stable and safe to fly, at no point does it feel it might suddenly loose control and fall out of the sky. It gives you plenty of notice when you're starting to loose it, at that point just put on the gas and you're good.

 

Credit to ED I think its a good start on the PFM.

Edited January 6, 2015 by OB1

[GGTharos]

Use the trim force, Luke ;)

[OB1]

Use the trim force, Luke ;)

 

Bwhaha !

[Ironhand]

... those are my other tests if you want to check:

VERY, VERY COOL! :) I suppose the question is: should there be enough rudder authority to make that happen? But a pleasure to watch just the same.

 

GG, have you watched his tracks?

 

EDIT:

You wasted company time and bandwidth ! LOL where's your supervisor !

 

...

He was in a meeting and we only had 5 customers all day. It was either this or play cards and I figured this would be more productive. :) Extremely cold out and the roads are slick with snow. So few visitors.

Edited January 7, 2015 by Ironhand

[GGTharos]

VERY, VERY COOL! :) I suppose the question is: should there be enough rudder authority to make that happen? But a pleasure to watch just the same.

 

If it looks like the rudder would be washed out it should have no effect, or negligible effect even at full deflection.

 

GG, have you watched his tracks?

 

Not yet, but I will have to :)

[Ironhand]

If it looks like the rudder would be washed out it should have no effect, or negligible effect even at full deflection.

That's my problem with what I'm seeing. I don't think there would be proper airflow to make it happen...certainly not with that much authority. I like what it enables you to do. Unfortunately I have my doubts that it should be happening. At the extreme AoA this is happening, nothing but dirty air should be passing over the rudders. Only my opinion of course.

[OB1]

That's my problem with what I'm seeing. I don't think there would be proper airflow to make it happen...certainly not with that much authority. I like what it enables you to do. Unfortunately I have my doubts that it should be happening. At the extreme AoA this is happening, nothing but dirty air should be passing over the rudders. Only my opinion of course.

 

Hang on, watch the track closer and as he said> I see no reason why this can't be. Its plausible.

 

He primarily used his engines to turn not his rudder.

[GGTharos]

The way to study this is to attempt to use rudders only, not engine, and see if they do anything at all - then we'll know :)

[OB1]

Well the answer is - yes you do loose rudder authority under X conditions, are those conditions correct ? I don't know but it seems about right.

[GGTharos]

If you're in a cobra you should have either no rudder authority of very negligible.