Departure tendencies

[Yo-Yo]

I assumed this was because of where the engines are positioned (almost analogous to the deep stall issue with T-Tail configurations) where the engines are in the path of chaotic airflow after the wings are stalled. The -1 has charts on where airflow will disturb the engines based on AoA and Mach number. Is engine airflow disturbance modeled in DCS?

 

you will be surprised but - yes it is!

 

I am not sure that it is in the current beta... try to stall the aircraft with engines at max ... take a look at the ITT.

[Headspace]

you will be surprised but - yes it is!

 

I am not sure that it is in the current beta... try to stall the aircraft with engines at max ... take a look at the ITT.

That's really impressive. Thanks for the tip, I'll give it a shot in the open beta.

[BlueRidgeDx]

...try to stall the aircraft with engines at max ... take a look at the ITT.

 

I briefly worked for an airline that lost a CRJ due to a high-altitude upset that resulted in a dual-flameout. For those who aren't aware, the CRJ has the same basic engine as the A-10.

 

After stalling at FL410, the airplane experienced pitch and roll oscillations that resulted in high pitch attitude (~30 degrees), high alpha (~30 degrees), low airspeed (75KIAS), and high power setting (98% N1).

 

The net result of this was a dual-flameout and subsequent "core lock" of the engines. Core lock is when the N2/HPT spool is physically prevented from rotating due to physical contact between rotating and stationary parts caused by rapid differential cooling experienced during engine failure/shutdown at high thrust or ITT/EGT.

 

During the upset, the engines suffered N1 rollback and stagnation, followed by flameout. Because of the extremely low airspeed, the #2 engine ITT spiked above 1250*C. The engine was so hot, that the HPT blades melted and lost 80% of their surface area. The molten metal actually flowed aft into the LPT section where it resolidified into long strands.

 

So yeah, heed those Dash-1 warnings concerning engine disturbance and flameout susceptibility regions. It will ruin your day.

 

You can read about the accident here:

 

http://www.ntsb.gov/events/2005/pinnacle/exhibits/default.htm

[Laud]

I'm by far not so deep into aerodynamics as you guys are, but I got to mention, that I think I already managed (accidently) to stall one engine in the DCS:A-10. I was operating the TAD and didn't observe my attitude a while too long when I noticed, that I was about to hit the ground. I made a sudden heavy pull on the stick and the AC got into some strange movements (can't say which kind of stall/spin it was...). After having it recovered I noticed one of my engines loosing RPM, ending up flamed out. Impressive!

[Yo-Yo]

I'm by far not so deep into aerodynamics as you guys are, but I got to mention, that I think I already managed (accidently) to stall one engine in the DCS:A-10. I was operating the TAD and didn't observe my attitude a while too long when I noticed, that I was about to hit the ground. I made a sudden heavy pull on the stick and the AC got into some strange movements (can't say which kind of stall/spin it was...). After having it recovered I noticed one of my engines loosing RPM, ending up flamed out. Impressive!

 

Do you want core-lock as a desert? :)

 

It was a good idea... we always can add more friction to the shaft if you mistreat your engines.

[Geskes]

I also had a wing departure! It was slightly damaged and when I made a high-G pull out of a dive, half my wing departed from the rest of the airplane :)

[mattag08]

I briefly worked for an airline that lost a CRJ due to a high-altitude upset that resulted in a dual-flameout.

Worked for Pinnacle huh? That accident is pretty famous. In fact, AOPA just had it in their most recent "NTSB Debriefer" column. My favorite part is where the angle of attack reached 29 degrees...who taught them how to fly an airplane?

[sobek]

It was a good idea... we always can add more friction to the shaft if you mistreat your engines.

 

While at the subject of engines and friction, can something be done about the fan rundown time after engine shutdown? The friction seems pretty high even in the low rpm regime of the fan, resulting in a very unnatural looking rapid and too constant deceleration to stop. Shouldn't deceleration decrease as rpm decreases?

 

Just nitpicking, btw. ;)

[Druid_]

If there's a good wind blowing from the right direction they shouldn't run down completely. Conversely a tailwind will cause the run down time to decrease (then rotate in the opp direction).

[Sid6dot7]

The friction seems pretty high even in the low rpm regime of the fan, resulting in a very unnatural looking rapid and too constant deceleration to stop. Shouldn't deceleration decrease as rpm decreases?

 

High friction and/or a rotor with low mass/inertia looks like what I observed. Especially at unsteady or turbulent wind conditions, the fan reacts far too sensible to wind speed changes, when the engine is cold.

 

Maybe WIP, but it catched my eye.

Edited November 4, 2010 by Sid6dot7

[Yo-Yo]

While at the subject of engines and friction, can something be done about the fan rundown time after engine shutdown? The friction seems pretty high even in the low rpm regime of the fan, resulting in a very unnatural looking rapid and too constant deceleration to stop. Shouldn't deceleration decrease as rpm decreases?

 

Just nitpicking, btw. ;)

 

If somebody knows the exact fan spool-down time we can tweak it.

Concerning fan windmilling due to the wind I can not promise anything because thermodynamics model can not accept low dynamic pressures :)

[leafer]

:thumbup:

[aaron886]

Worked for Pinnacle huh? That accident is pretty famous. In fact, AOPA just had it in their most recent "NTSB Debriefer" column. My favorite part is where the angle of attack reached 29 degrees...who taught them how to fly an airplane?

 

Nasty, eh. A little options-limited in that scenario, but that kind of reaction seems to be a recurring theme with over-worked regional pilots. :no_sad:

[BlueRidgeDx]

Not to get too side tracked, but despite their situation, they actually had quite a few options.

 

I'm not one to pass judgement, especially on "teh internets", but those two guys made a LOT of REALLY bad decisions. It's very sad, because they certainly didn't go flying that night with the intention of getting killed.

 

The best we can do is learn from their mistakes. I learned a lot about the airplane that I didn't know from that accident, and even more about the human factors that precipitated it.

[FlandersRevenge]

What exactly does a flameout mean? The engine shuts off?

[Sid6dot7]

Flame out is an unstable condition, which is resulting in an extinguished combustion chamber flame.

Obviously without the flame, one of the most important parts of the thermodynamic process (creating a large temperature gradient in the combustor) is broken and the whole gas generator can't provide any thrust.

 

In short: Yes, the engine shuts off.

 

There are varied operation conditions causing a flame out, but in most cases the flame can be reignited somehow, if the gas generator didn't take damage.

Edited November 17, 2010 by Sid6dot7
spelling ;P

[Tango]

I have to correct something: there is no such thing as a tip stall. All that happens is the ailerons become ineffective, and this is usually alleviated by the wing tip design/wing twist/other aerodynamic things including strakes and vortex generators to help prevent the boundary flow breaking up.

 

The reason you use rudder in a stall is because yaw (and subsequently, side-slip) is the make or break point in whether the aircraft will drop a wing/spin.

 

If the aircraft is perfectly balanced through the stall, all that will occur is a high rate of descent followed by a nose-down reaction (either gentle or violent - depends on the aircraft and C of G position).

 

The reason for the wing drop is simple aerodynamics: it stopped creating lift before the other wing.

 

Application of rudder in the opposite direction to the turn should prevent entry into a spin. Idle power, center the controls, counter any spin with rudder (opposite direction if inverted!), then recover from the dive.

 

If aileron input appears to help, the reason is due to induced yaw by upwards aileron and dihedral effect (the A-10 has a small amount of dihedral which aids with static spiral stability, that meaning when you enter a roll, the aircraft will want to roll back towards wings level, and requires a little bit of "hold off" aileron input in a turn in order to hold a constant roll angle). As already mentioned however, aileron input at the stall is not advised.

 

Out of interest, has anyone managed to spin the A-10 yet?

 

Best regards,

Tango.

Edited November 18, 2010 by Tango

[Sid6dot7]

Out of interest, has anyone managed to spin the A-10 yet?

 

No continous ones.

Maximum were 4 not controllabe spins so far, when I tried "tail slide"/"hammerhead"-ish maneuvers. Had several engine hickups/stalls, sometimes flame outs in one engine, but no real self sustaining spins. :joystick:

 

But great flight model, especially the engine model so far. Even it's WIP yet. :thumbup:

[BlueRidgeDx]

I haven't tried it myself yet, but you should be able to spin the A-10 provided full rudder is maintained above stall AOA. Below stall AOA, sustained rudder application will lead to a sideslip departure and a Post Stall Gyration (PSG), but no spin.

 

Full aileron input, or crossed controls held after the stall break will also result in a PSG. Roll authority is maintained into the stall. Using the ailerons while stalled increases sideslip and reduces aileron effectiveness.

 

Failing those conditions, in a 1g stall, the airplane will simply enter a high sink-rate with reduced elevator effectiveness and some airframe buffet.

 

In an accelerated stall, there is airframe buffet, a slight rolling moment, and a loss of elevator authority that can be observed as a G-break.

 

In Beta 1 and 2, I usually got snap-rolls when flying in the chopped-tone. The rolling motion should be far less aggressive. I was never able to achieve a wings-level, high sinkrate, stalled condition.

 

As I mentioned, things could be different in B3.

[Tango]

I haven't paid much attention to stall characteristics in this build, but I have already found that it doesn't roll as much.

 

I'm disadvantaged in flying more advanced maneuvers as I have no rudder pedals to do things properly. At the moment I'm just flying with a constantly neutral rudder. :helpsmilie:

 

Best regards,

Tango.

[pyates2104]

This behavior seems to be similar to the coordinated side slip, doesn't it?

 

What reason would cause departure?

 

Had to reply to this one after a long absence. With no power at 35 knots, you would expect a lot more of a descent rate than 1300 fpm + you are below stall speed at 35 knots and you will depart (you"ll stop flying) I think it depends on your definition of departure.