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View Full Version : flatspins, and other wing's autorotation based phenomenes



Graf_Solingen
11-15-2004, 03:08 AM
Hello
In real world, when speed drops down below critical value, aircraft can start spinning, becouse of so called 'wing autorotation phenomen'.
In order to recover , pilot needs to reduce power, push the stick, and after second or two use rudder, opposite to spinning direction. In old il-2 sturmovik, we had many diffrent kinds of 'spinns', modelled near perfectly. Near all 2ww warbirds, in case of stall were entering spinn or flatspin. Only one known exception is Yak-7, that plane was unable to perform spinn. Why ? Saying very ,very simply , becouse of its wing's profile, wing's shape and point of mass balance. In FB/PF in case of dynamic stall, all what we need to do in order to recover from 'spinn' is move joystic to neutral position.

I would like to know , why did You decide to make that 'part' of simulation so simplified, comparing to first il-2 sturmovik?

Graf_Solingen
11-15-2004, 03:08 AM
Hello
In real world, when speed drops down below critical value, aircraft can start spinning, becouse of so called 'wing autorotation phenomen'.
In order to recover , pilot needs to reduce power, push the stick, and after second or two use rudder, opposite to spinning direction. In old il-2 sturmovik, we had many diffrent kinds of 'spinns', modelled near perfectly. Near all 2ww warbirds, in case of stall were entering spinn or flatspin. Only one known exception is Yak-7, that plane was unable to perform spinn. Why ? Saying very ,very simply , becouse of its wing's profile, wing's shape and point of mass balance. In FB/PF in case of dynamic stall, all what we need to do in order to recover from 'spinn' is move joystic to neutral position.

I would like to know , why did You decide to make that 'part' of simulation so simplified, comparing to first il-2 sturmovik?

Kwiatos
11-15-2004, 03:44 AM
....and in old Il2 was possible to make inverted spin. I cant repeat it in FB/PF http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif

julien673
11-15-2004, 04:57 AM
Arcade market http://forums.ubi.com/images/smilies/10.gif

lindyman
11-15-2004, 06:09 AM
I agree with the conclusion (although not at all with the reasoning behind it.) Early stages of stall are well modeled, but when you get to the late stages of the stall, the planes behave rather oddly, to say the least, as if some invicible force grabs the plane by the nose and twists it (and before someone jumps in and tells me how a plane enters a spin, I know this well and have experienced it first hand on a number of different aircraft.)

A small correction (beside the point of the problem.) At the first signs of a spin (actually, the first signs of a flick, i.e. the dropping of a wing,) apply full rudder in the opposite direction, and neutralize the stick. Chances are very good that you'll stop the spin at its incipient stage, i.e. before it gets to autorotation (most aircraft require a couple of revolutions to get into stable autorotation.) The theory applies to real world aerobatics, and the method described works very well in PF, even with its odd behaviour.
_
/Bjorn.

Graf_Solingen
11-15-2004, 07:36 AM
Lift force lose never happens at the same moment on both wings, always one wing loses lift force(stalls) faster than the second, becouse of diffrent airflow speeds ( during turn for example), or proppeler torque. As i said one wing loses lift force, and drop down. It causes increment of relative AoA angle on that wing. Drag is a function of AoA, so drag factor of that wing also gets bigger very faset... and it casuses rotation. As you said it takes a moment before airplane will get stable autorotation

by the way , i cant find my technical english dictonary http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif so forgive me, not really correct terminology. i promise , i ll describe it again when i ll find that **** dictonary http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

swingman
11-15-2004, 04:47 PM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Graf_Solingen:

by the way , i cant find my technical english dictonary http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif so forgive me, not really correct terminology. i promise , i ll describe it again when i ll find that **** dictonary http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif <HR></BLOCKQUOTE>

Don't worry. I think posters with a genuine first hand knowledge of both the English language and english aviation terminology, are quite a minority on these boards. Those who have some knowledge of aerodynamics understand more or less what you mean, and those who don't, would probablt not understand regardless of language http://forums.ubi.com/groupee_common/emoticons/icon_wink.gif
_
/Bjorn.

effte
11-16-2004, 01:56 AM
Spin is a very complex phenomenon. Spin modes can't fully be predicted outside of flight testing, even with state-of-the-art technology. I think we will have to be content with a reasonably accurate model of spins in a PC simulation.

The main shortcoming is that every stall leads to wing drop. This is not the case out in the real world. There is also some way to go to the 'reasonably accurate', as far as spins go.

While most of these fighters probably were able to enter a spin, most of them likely had benign handling even in this part of the envelope. You want the pilots to be able to use the entire envelope. They won't do that if they are worrying about spinning while in combat. Further, you really don't want losses due to the relatively inexperienced pilots which saw combat duty in these crates augering in after spinning on final.

Graf_Solingen
11-16-2004, 03:25 AM
Yes , it requires most complex math for description, between all subsonic aerodynamic's phenomenas. Descriptions of spinn contains 3 differential equations of aircraft's balance, one for each of axis. Two of them we can simplificate by linking them , and it is ( x,y axis) so called first equation of autorotation, and 3rd ( equation of vertical axis) is called Second equation of autorotation.
dynamics of spinn doesnt require enormous mathematic, all differential equations used for math description of that phenomena ,base on XVIII th century's math. I remember i created a MathCad template with full deterministical model of spinn during my studies (i am chemistry engineer http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif, however i had parts of aerodynamics). If somebody would like to see it , i can put it on web , i think

Effte said it is unpredictable phenomena - i would say it diffrent - we can easy create 100% acurate model of IDEAL spinn, but not model of spin for example bf-109, there are too much elements with unknown influence for spinn dynamics. Example? A MG 'bubbles' with ammo magazines can cause aerodynamical shadow, and change spinn characteristics. its unestimated and unpredictable by maths method , we can only test it on model or in real. http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif Actually in 1943 in Rechlin germans were working on that problem, heinrich beauvise was a test pilot, or rather spinmaster http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

TX-EcoDragon
11-18-2004, 12:02 AM
<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Kwiatos:
....and in old Il2 was possible to make inverted spin. I cant repeat it in FB/PF http://forums.ubi.com/groupee_common/emoticons/icon_frown.gif <HR></BLOCKQUOTE>

Inverted spins worked in AEP pretty well, but in PF they are. . umm .. "porked. . . the 190 A5 seems to sorta manage them, but for now it's an area that needs a little work.

<BLOCKQUOTE class="ip-ubbcode-quote"><font size="-1">quote:</font><HR>Originally posted by Lindyman: I agree with the conclusion (although not at all with the reasoning behind it.) Early stages of stall are well modeled, but when you get to the late stages of the stall, the planes behave rather oddly, to say the least, as if some invicible force grabs the plane by the nose and twists it
<HR></BLOCKQUOTE>

Yeah, I first saw this when testing the Ta-152 a few patches ago, it would exit the spin, and enter what looks like a spiral, except unlike a spiral the control surfaces were not "flying" so the aircraft would remain in this spiral as if in an unrecoverable spin yet not appearing to be above critical angle of attack. I have found this in many more aircraft in PF, and find it pretty annoying (I have kept AEP Isntalled as such), but I know it doesn't need to stay that way as it wasn't that way before.

Graf_Solingen
11-18-2004, 03:08 AM
Yes , i got it many times in ta-152 , and sometimes in D-9
I loved to 'play' with spins in old sturmovik, i remember i was able to perform anykind of spin, including flat like table spin, and next recover in desired moment ( in case of flatspin, secret of recover was in correct enter that spin - full left rudder and max rpm , when u wanted recover , power to 0 , opposite ruder...and sometimes u could recover sometimes no lol)
I was trying to 'investigate spins' in case of ta152. In my opinion that kind of spin is "triggered event", independent of players inputs and partialy from flight model. Why do i think so ? With my mate, we started that kind of spin at high alt, after several tries of recover , unsuccesful of course, i asked him to cut off one of my wings with mk108 http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif. Of course he turned me serveral times into fireball, before he did it correctly, ...and nothing changed in dynamisc of spin, plane was spinning the same, but in fact had only one wing.

TX-EcoDragon
11-18-2004, 12:26 PM
Yes, it almost seems like a scripted event, and that is why there is a tangible dissconnect between the expected and observed transition out of the spin. I hate to have that s-word associated with this sim, as I have never seen any indication that it was in the past, I can't imagien what the reason for it would be. IMHO a few patch versions ago spin dynamics were at their paramount for this sim series (with the exception perhaps of the P-39, which did not behave as it did earlier on back when it reward the actual recovery technique over the usual one).

Graf_Solingen
11-18-2004, 02:08 PM
Oh yes, i remember Cobra in early il-2sturmovik releases.
If u started loop at too low speed You could be near sure that it ends with inverted flatspin.
As far i remember minimal speed was about 450 km/h
And it was 100% acurate moddeling of Cobra FM , according to Pokryshkin words, and other opinions about P39 and its mass distribution problems ( poin of mass balance near in the same place with point of geometrical center of aircraft).

In my opinion, opinion of 2% of players, who would like to see so complex and detailed aircrafts FM is not important comparing to 98% who wants only new planes, nice gfx, 30mm cannons and more powerfull engines.
I dont see also any reasons for simplification of FM or replacing it with scripted elements, except marketing reasons.
Game will get easier for typical 14 yrs boy who doesnt know anything about aerodynamics, physics and other usally neccesery things in sims. Easier means that game wont get opinion on gamers portals "totally unplayable, for maniacs only, couldnt even take off , but i thought i was good in sims" (lol i saw that kind of opinions about old sturmovik), and it means more kids will buy this game. And of course they will be happy and proud , becouse sims are also called 'elite' of games , so they must be **** good...
And that my opinion isnt anything offensive , its only pure fact - game producers dont make games for 'idea of realistic sim' only for money

Kwiatos
11-18-2004, 02:16 PM
hmm i suppose i know you from somewhere Graf_Solingen

BTW minimal speed to enter loop for Cobra in old IL2 was close to FB/AEP version http://forums.ubi.com/groupee_common/emoticons/icon_smile.gif

Graf_Solingen
11-18-2004, 02:24 PM
Are you talking about version patched with first or second patch ?
I remeber that there were only 3 models of 109 and one FW-190, maybe 3 migs, and planes were behaving much diffrent than after latest patch.