Su-25 doubling as an UAV?

[Pirimeister]

I was playing the Su25 quick mission and something very strange happened:

 

I pointed the plane up, with maximum thrust engaged and ejected and the plane, suprisingly, kept on climbing until going below min. speed and then strated diving. Only instead of crashing down (it was high enough when ejected, obviously), it picked up speed and after a while restarted climbing, this time reaching a higher altitude! And it went on and on like that for more than 30 minutes.

 

I left it like that while I went for dinner, and when I returned the plane was flying a straight course at what I suppose it's his max. operating altitude.

 

Now, I know FC has and advanced flight model, but surely, this has to be some kind of bug, right?

 

Cheers!

[NEODARK]

loose altitude = gain speed = gain altitude = loose speed, etc...

[mikoyan]

that is the ghost pilot uuuuuhhhhhhhhhhhhh:holloween: :holloween: :P

[nscode]

Normal airplane behavior :)

[GGTharos]

You left the plane, it went up, stalled, nose dropped, it sped up, and pulled up (TRIM, remember?) and then performed this again and again until it stabilized at an altitude and speed where it was flying 'trimmed' so the nose was not pitching up or down.

[Pirimeister]

OK, assuming it's normal behaviour, I have to ask -and please, bear with me:

 

would this happen in real life? I mean, the plane is subjected to other forces that must surely destabilize it enough to break this perfect flight path... even the weakest crosswind will throw it off that course.

 

cheers!

[504 Wolverine]

OK, assuming it's normal behaviour, I have to ask -and please, bear with me:

 

would this happen in real life? I mean, the plane is subjected to other forces that must surely destabilize it enough to break this perfect flight path... even the weakest crosswind will throw it off that course.

 

cheers!

Well IIRC a MiG-23 flew from Poland to Holland with no pilot after he ejected on take-off. It crashed after running out of fuel.

[GGTharos]

OK, assuming it's normal behaviour, I have to ask -and please, bear with me:

 

would this happen in real life? I mean, the plane is subjected to other forces that must surely destabilize it enough to break this perfect flight path... even the weakest crosswind will throw it off that course.

 

cheers!

 

Off course, sure, but off course doesn't translate to a spiral of doom. Some aircraft are pretty unstable, others are pretty stable (the Su-25 is one of those)

[Force_Feedback]

There was some Harrier that had a birdstrike, engine stalled, the pilot ejected, but the rocket from the ejection seat cleared the engine fan, engine spooled up and the harrier flew for half an hour before running out of fuel. This all happened over Germany in the 1980-ies.

 

Of, fighters were sent to intercept it, as it was heading to the eastern border, they were stunned to see the Harrier fly nice and level without a pilot in the pit. :P

[Pirimeister]

well, I'm conviced by the quality of the arguments you have out forward, gentleman!:thumbup:

[nscode]

Oh, and, you should, if you can, try to direct it to crash in an unpopulated area :)

[Weta43]

Also read in an article about the development of the Su-27 one of the prototype Su-27 was out on a test flight - pilot got into a spin, had been told that the plane would be unrecoverable & to eject if it happened, so he did, whereupon the plane recovered & flew off into the distance on its own.

[nscode]

That's why we love our Galeb. Got in a spin... no prob.. just let go of the stick and you're good :)

[Force_Feedback]

That's why we love our Galeb. Got in a spin... no prob.. just let go of the stick and you're good :)

 

Same with the flanker, I know that su-27 prototype didn't crash, but just recovered because the pilot let go of the controls, saving the plane. Maybe that was another test.

 

There was also an incident with a Yak-36M, the pilot forgot to turn off the automatic ejection system (later they installed an automatic disabler when the jet transitioned from hover flight), was ejected, but, the jet was on autopilot, and landed some time later in a field. The engine was still running, but, by the time the recovery crew were on the scene, the farmer already removed the clock and the HSI :P

 

A similar incident was with the Delta Dart, landing in a snowy field without a pilot and with very little damage.

[Weta43]

Perhaps a different flight - I'm sure I read that the initial development pre flight test calculations led the designers to believe that if the Su-27 prototype went into a spin it would be unrecoverable & that the test pilots were under instructions to eject if they entered one - which they did first time & the plane recovered of its own accord - which is maybe where the letting go of the stick came from.

[Kenan]

Hmm....

[JG27_Arklight]

If that happens, then it is a bug (that is, if the aircraft never crashes).

 

Eventually, the aircraft has to crash. Perpetual motion is not possible.

[Weta43]

when they run out of gas - they crash.

 

Can't find that story about ejecting again ....

[ARM505]

It's called a 'damped phugoid' if I remember correctly, ie the aircraft is dynamically stable, and oscillations about the lateral axis (in this case) and above and below the trimmed speed become smaller over time. The aircrafts static and dynamic stability all contribute to this behavior. Perfectly possible, until the aircraft runs out of fuel of course, or one of the oscillations brings it plummeting into the ground.

[JG27_Arklight]

It's called a 'damped phugoid' if I remember correctly, ie the aircraft is dynamically stable, and oscillations about the lateral axis (in this case) and above and below the trimmed speed become smaller over time. The aircrafts static and dynamic stability all contribute to this behavior. Perfectly possible, until the aircraft runs out of fuel of course, or one of the oscillations brings it plummeting into the ground.

 

 

It is impossible for an aircraft to remain dynamically stable forever (due to oscillations, as you stated), that's the issue.

 

The phugoid principle/mode (whatever, lol) analyzes potential vs kinetic energy (IIRC). I could be wrong though. I think it also states that an aircraft cannot remain stable forever, only for a certain period of time depending on various factors. :)

 

*EDIT* I did a quick internet search, but couldn't really find much info on "how long" an aircraft could remain stable (in general). Does anybody know of any good sources for information on this subject?

[Shaman]

Well IIRC a MiG-23 flew from Poland to Holland with no pilot after he ejected on take-off. It crashed after running out of fuel.

Lol, exactly. I just wanted to tell that story.

 

23 actually went into spin. Pilot ejected, and some sort of inertia and weigh shift got the plane out of spin, and then it trimmed itself. Shortly after another jet was sent to shoot down the empty plane but it didn't happen. Pilot who intercepted the plane was calling the ground control that the plane "is one of ours", but he was getting a reply "correct. plane is empty". Like I said he didn't shoot it down. Later he explained himself he couldn't find in the codebook what means "plane's empty" command. :doh:

 

As far I remember correctly, that MiG-23 when it fell from the sky killed a boy and his granddad who were sleppin in a barn :/

[ARM505]

It is impossible for an aircraft to remain dynamically stable forever (due to oscillations, as you stated), that's the issue.

 

The phugoid principle/mode (whatever, lol) analyzes potential vs kinetic energy (IIRC). I could be wrong though. I think it also states that an aircraft cannot remain stable forever, only for a certain period of time depending on various factors. :)

 

*EDIT* I did a quick internet search, but couldn't really find much info on "how long" an aircraft could remain stable (in general). Does anybody know of any good sources for information on this subject?

 

As far as my hazy ground school memory goes, dynamic or static stability is either positive, neutral, or negative. Without waffling on about the physics, an aircraft can certainly have positive dynamic stability (ie the oscillations reduce in amplitude over time). I've seen it happen in Cherokee's, Cessna's etc (despite the students best efforts to mis-trim the plane!). I haven't had a chance to do that experiment in a B737, I don't think the pax would be so happy with the ride, and the cabin crew would hate me for all the vomiting....Still, most planes are designed to be dynamically stable - I'm not so sure how keen the FAA/CAA would be to certify an aircraft in the public transport category that was dynamically unstable, or 'divergent'.

 

The Su25 seems to be a fairly benign sub-sonic design, so I reckon it could end up stabilised at it's trimmed speed, assuming it had enough altitude/time to play with, and the initial entry wasn't at wildly crazy pitch attitudes etc.

 

We'd need a real Su25 pilot to do a little hands on experiment for us though!