Author Topic: Overly aggressive destabilization in 109s while turning  (Read 1060 times)

Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« on: December 01, 2004, 11:56:10 AM »
Overly aggressive destabilization in 109s during turning... and, the lack of any destabilization at all with the P-47 and the P-51.
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Pyro or HT, how does stall limiter work?

The reason I'm asking this is that I've met a strange phenomenon while testing out sustained turn rates.


I've tested out a P-47D-11 against a Bf109G-6. The conditions are as follows:

* Full ammo load for both planes. The P-47 uses the "extra ammo" load of 3400 rounds. The 109 uses MK108 30mms.

* Fuel burn set to minimal

* No wind

* Climb to 10k, level out facing 360

* Decrease speed to 230mph TAS(all speeds hearby measured through E6B)

* Increase throttle to full military power(not using WEP). Upon reaching 250mph IAS, give 45~50 degrees bank(indicated by artificial horizon) and start a turn with full stick deflection.


The Stall limiter values are from 0.05 to 5. IIRC, this indicates the amount of "margin" the stick pull will be limited to, before the plane reaches an AoA which will induce a stall.

ie) Stall limiter value 1 = max joystick deflection will put the plane into an AoA 1 degrees short of stalling out.


The reason why the stall limiter was used for a turn test, was to minimize pilot errors or skill issues when comparing pure turn rates for planes.

The tester will go to full military power and enter a coordinated turn at a certain set bank angle with max stick deflection.

Since the Stall Limiter will mechanically prohibit an accelerated stall(only stalls induced from flying under stall speed is possible), one can continue this turn and wait until the speed stabilizes.

When the speed stabilizes, timing a full 360 turn will give you a value of a plane's turning ability when it enters a sustained turn with the tightest radius possible.

Although this figure is not the optimum turn rate, nor an absolute value - it does provide a useful info on how tight a plane can maintain its turn, and what speed a plane can fly at that kind of angles.


I've timed the P-47 with no problems at all. I've made only recordings so far, and didn't use a real stop-watch to time the full 360, but rough data set it out - the P-47 can sustain about 2Gs at 155~160mph TAS with a 45~50 degrees bank. With full flaps the P-47D-11 sustains about 1.7~1.8Gs at 130~135mph TAS at 45~50 degrees bank.

The problem is, this test is impossible with the Bf109. The Stall Limiter is the same - set 0.05 AoA before reaching stall. Starting at the same speed, full fuel load, same bank angle.

Pull a max deflection - the plane stalls out. It refuses to turn.

Either the stall limiter is broken and doesn't work only on the 109, or there is something wrong here(I think.. ).

So I tried other planes out, which I personally had some suspicions about, such as the C.205. Same thing. Can't turn. The system regulates reaching full stall AoA - yet it still stalls out.

The rough data I got, was that the 109G-6 can pull a 2.3G turn at 190mph - for 1 second. And then, it stalls out.

Well, it doesn't actually stall out - what happens is the plane wobbles uncontrollably at the roll and yaw axis. It starts a snaproll - and then the snaproll stops.

By this, I am guessing that the Bf109 starts a snaproll BEFORE the stall is reached. Continued stick deflection would make the plane tumble over, but the stall limiter halts the plane to its final limit - and the plane recovers. And then, as it recovers it snaprolls again.

Without the stall limiter, at that state the 109 would have flipped over as it met the stall AoA.

And this wobbling, you cannot 'ride this'.

Some planes will gently falter while stalling, which an ease of stick or change of aileron deflection would correct, so the plane would smoothly continue the turn. The 109 doesn't do that. It's more like 'turn-stop-turn-stop-turn-stop'.

This process repeats. Hence, the plane wobbles left and right before reaching actual accelerated stall status.

The 109 becomes controllable, at a 2G pull at about 190~200mph. That was the best I can do with my ability.

So basically, I think I was right. It's impossible to outturn a P-47 in a 109. At least, when it becomes a sustained, tight-turn contest, the 109G is about barely par with the P-47D-11. The 109 starts a destabilization serious enough to halt normal flight, before it reaches its critical AoA.

I was curious of why this such thing was happening. So I've tested a P-51 out. The P-51 may not have a torque as bad as a Bf109, but IIRC some people do quote that a sudden full throttle would flip the plane over(which I do think is an exaggeration).

Basically, I don't think there's any reason a P-47 or a P-51 would be considered a plane with weak torque, although their heavy weight may mean it is effected less.

So I tried various planes out.


*Bf109F-4
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 160mph TAS, 2.5G

*Bf109G-10
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 162mph TAS, 2.1G

*C.205
- stalls before reaching stall AoA, due to extreme destabilization
- sustained turn with tightest radius around 169mph TAS, 2.3G

*F4U-1
- can maintain max stick deflection
- slight wobbling but controllable
- sustained turn with tightest radius around 160mph TAS, 2.2G
- sustained turn with tightest radius and full flaps around 125mph TAS, 2.0G

*Fw190A-8
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 189mph TAS, 2.0G

*Fw190D-9
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 200mph TAS, 1.9G

*Ki-84-Ia
- can maintain max stick deflection
- slight wobbling but controllable
- sustained turn with tightest radius around 154mph TAS, 2.8G
- sustained turn with tightest radius and full flaps around 117mph TAS, 2.2G

*La-7
- stalls before reaching stall AoA, due to moderate destabilization
- sustained turn with tightest radius around 168mph TAS, 2.3G

*N1K2-J
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 158mph TAS, 2.5G
- sustained turn with tightest radius and full flaps around 134mph TAS, 2.5G

*P-38L
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 178mph TAS, 2.4G
- sustained turn with tightest radius and full flaps around 122mph TAS, 2G

*P-47D-11
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 157mph TAS, 2G
- sustained turn with tightest radius and full flaps around 133mph TAS, 1.7G

* P-51D
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 175mph TAS, 2.3G
- sustained turn with tightest radius and full flaps around 125mph TAS, 1.9G

* Spit14
- turned to its right due to different prop rotation
- can maintain max stick deflection
- no wobbling at all
- sustained turn with tightest radius around 158mph TAS, 2.4G
- sustained turn with tightest radius and full flaps around 129mph TAS, 2G


The list is puzzling at best.

If high torque is causing such destabilization, then how does one explain the stability of the P-47 or the P-51 when it is 0.05 degrees before reaching stall AoA?

One clue may be that the planes with slats - all 109s and all Las - cannot reach its maximum AoA during a forced turn with no alt-loss.

If the slat is supposed to stabilize a plane at low speeds, now I'd really hate to think how bad the 109 would be without slats. If it can't reach its data-fed maximum AoA even with the slats.. then how worse is it gonna be without them!
« Last Edit: December 01, 2004, 09:04:27 PM by Kweassa »

Offline hitech

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Overly aggressive destabilization in 109s while turning
« Reply #1 on: December 01, 2004, 12:04:23 PM »
Slats would mess with the stall limiter. It is not ment to be used with such a tight degree .

HiTech

Offline Urchin

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Overly aggressive destabilization in 109s while turning
« Reply #2 on: December 01, 2004, 12:28:59 PM »
That is an interesting test.  

How are slats supposed to work?  I was under the impression they altered the air flow around the wing, in effect adding wing area in the same way certain styles of flaps do.  

Why would the stall limiter not work on planes with slats?

Offline 1K3

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Overly aggressive destabilization in 109s while turning
« Reply #3 on: December 01, 2004, 03:42:16 PM »
Slats on each 109F,Gs are independednt right? I notice (in AH2) that if u pull tghe stick hard @ lo speeds (-200 mph), the "torque" would take over and cause the plane to "flip a little bit" to the right and the slats would not (always) come out evenly.

(ps, just an "educated guess")

(edit) btw, is 109's stick ctrl almost the same like from MiG-15? I heard that MiG-15 (or maybe 109) had short throw sticks, maybe that's what is causing the 109 not to ctrl well at lo speeds.

(again, just an" educated guess")

I also think that 109s have improved in the game ( AH2). I noticed the improvem,ent with the roll rate @ lo to medium speeds. The revised roll rate gibes me some chance in this "game" to turn with spits for quite awhile ("expert" spit flyers = impossible) and kill/maim lalas, yaks, and yank irons:D
« Last Edit: December 01, 2004, 04:49:07 PM by 1K3 »

Offline DoctorYO

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Overly aggressive destabilization in 109s while turning
« Reply #4 on: December 01, 2004, 03:58:47 PM »
IMO 109's and most planes in general have taken a huge hit in stability under high to medium g loads.. and high AOA's

with exception to planes that can deploy flaps at high speeds..  (american iron)

granted im not claiming conspiracy like the other luftwabbles just seems funny the amount of violent stall i get in the 109 190(expected in 190) and alot of other planes when compared to the docile charateristics of the american Iron set..  (note i like the 109 and p47, p51 etc.. but the 109 seems to be taking a large hit..) (i can understand the g10 floundering but the 109f does the same thing except with a tighter turn radii..)

maybe its me..  never flew the real thing..  but from what i read on the subject something seems alittle out of whack...  

IMO the american iron should gain advantage at high speeds no doubt about that but at speeds under 200 the luftwabbles (especially 109f) should be able to eat a mustang or my beloved d11's lunch.....  as of current without the stall effects/reduced effects its the other way around due to snap stalls instability etc of the german plane set..

Kindly take a look at it...


DoctorYO

Offline StarOfAfrica2

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Overly aggressive destabilization in 109s while turning
« Reply #5 on: December 01, 2004, 04:06:30 PM »
This has been talked to death in at least 2 different threads.  Not only do the tests I did bear out 100% what you found Kweassa, they reduced my favorite rides to BnZ planes.  I'm glad someone else out there doesnt think I'm crazy.  Well, at least not about this.

Heres one thread............

http://www.hitechcreations.com/forums/showthread.php?s=&threadid=133497

Heres the other thread.........

http://www.hitechcreations.com/forums/showthread.php?s=&threadid=133921

The problem has been at least mentioned in several more, but these threads hold the most discussion on the subject.
« Last Edit: December 01, 2004, 04:13:08 PM by StarOfAfrica2 »

Offline leitwolf

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Overly aggressive destabilization in 109s while turning
« Reply #6 on: December 01, 2004, 07:58:43 PM »
Out of curiosity, did you turn off Combat Trim?
I think your tests are useful but the results will be skewed when flying with CT as it introduces destabilizing effects on some planes when riding on the edge.
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Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #7 on: December 01, 2004, 09:04:06 PM »
Quote
Out of curiosity, did you turn off Combat Trim?
I think your tests are useful but the results will be skewed when flying with CT as it introduces destabilizing effects on some planes when riding on the edge.


 The combat trim becomes a destabilizing factor at low speeds because it trims the elevator continuously upwards. However the roll & yaw axis is hardly effected by CT - it is actually more stable with CT.

 In something like extreme low speed, vertical maneuvering, the CT adjusts the elevators assuming that the plane is flying level - which leads to excessive elevator input which might stall the plane out.

 However in this case the stick pull is "mechanically" limited in the first place by the stall limiter mechanism so it won't be of any importance whether it is used or not.

 Oh.. and I did leave the CT off :) I went into sustained turn by first locking the bank angle with the stick, and then adjusting the aileron and yaw trims to achieve a sustained turn with no alt loss with a stickpull only.

Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #8 on: December 01, 2004, 09:08:00 PM »
Quote
This has been talked to death in at least 2 different threads. Not only do the tests I did bear out 100% what you found Kweassa, they reduced my favorite rides to BnZ planes. I'm glad someone else out there doesnt think I'm crazy. Well, at least not about this.


 Indeed :)

 But the difference is that I tried to devise a test method for it :D

 I don't know if the current method is right or wrong so suggestions on new or fixed test parameters would be welcome.

Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #9 on: December 01, 2004, 09:37:47 PM »
Quote
Slats would mess with the stall limiter. It is not ment to be used with such a tight degree .


 What does the "it" in "it is not meant to be..." refer to? Is the stall limiter not supposed to be used in such tight degree, or is the slats not to be used in such tight degree? :confused:

 In whatever the case this is all very confusing. Like Urchin asks I don't understand how slats would mess up the stall limiter. Aren't the slats a device which is supposed to be help to a plane specifically in such tight situations?

 My understanding of how slats work is superficial at best, but IIRC it alters, or "gathers" airflow to flow over the wing when stall is imminent. It wouldn't raise or lower the stall speed or have any effect on the stall AoA itself, but it would help control the stall motion so it is limited docile and gradual.

 With 0.05 stall limiter on the plane would stop just short of stall. I can understand the fact that some planes, in this tight situation may or may not be more stable than others.

 But what I don't understand is why a plane equipped with a device which is supposed to prevent violent destabilization, in fact destabilizes in a most violent manner, among all planes.

 Also, what I don't understand is why a P-47 or a P-51 would be so different from a 109. I've tested the Spit9 out, and even the Spit9 usually encounters a slight "shake" (the turn motion is uninterrupted) during the sustained stick pull - once or twice in a 360 turn.

 The P-47 and P-51 is flat-out, no-torque machine. Its characteristics are almost like the P-38L. It flies like an  "easy mode" plane in that these planes encounter none of the problems other planes suffer.
 
 I don't know if the stall limiter is not supposed to work with slats, but that doesn't change the end result at all.

 The 109s are outturned by both P-47s and P-51s at all speeds - even when contesting planes enter the tightest sustained turn possible at very low speeds.

 So if this is really supposed to be like this, then I'll stop commenting anything on this subject in the future - I'll take it as an AH reality and just accept the fact the P-51s and P-47s and a truckload of planes which I thought the 109 would outturn, turn better than the 109s.

 So that's probably what I want to ask.. is it supposed to be like this? Am I doing something wrong? What kind of test should I do to confirm this, if the current test method is wrong? :confused:

Offline StarOfAfrica2

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Overly aggressive destabilization in 109s while turning
« Reply #10 on: December 01, 2004, 10:07:11 PM »
It's not supposed to be like this.  The slats accomplish exactly the opposite of their intended function in the AH Flight Model.  I hope your pleas do not fall on deaf ears, as I would dearly love to see the 109s return to their former place in the lineup of good "all around" planes.  As it is, we are left with a better turning FW that suffers control problems at 400mph and doesnt quite have the guns.

I know they have alot of stuff on the plate right now.  Pyro's last "news" post said as much, and I'm sure as they update planes they can look at the Flight Models, although from the way the 109 changed in AHII, I'm afraid the changes have already been made to it.  I'd be happy enough if someone "official" would at least come out and say "Yes its supposed to be this way and we arent changing it", or even "There may be a problem and we will be happy to look into it but we are a little busy with blah blah right now".  Just an acknowledgment.  Ah well.

Offline Urchin

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Overly aggressive destabilization in 109s while turning
« Reply #11 on: December 02, 2004, 06:29:25 AM »
I am pretty sure the 109s have fairly high wingloading, but it has been a while since I actually looked at the numbers I've got for them and worked it out.  

I flew the G-2 a little last night, I did notice some instability at ~180-200 mph, but it went away once my speed dropped below that mark.  The slats didn't pop open though, at least not when the plane was getting unstable.  

I'll film a few sorties and look at the planes behaviour... I'll be able to tell if it is markedly different from AH1 behaviour or not.

Offline hitech

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Overly aggressive destabilization in 109s while turning
« Reply #12 on: December 02, 2004, 09:21:52 AM »
"It" refers to stall limiter. Slats work fine, the stall limiter is not designed to be used as you are trying to use it. It is only designed to lessen the effects of ham fisted pilots.

As to why slats effect the stall limiter, they do because they change things in the wing (lift/drag/cm/cp) that the stall limiter does not take into account.


HiTech

Offline Karnak

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Overly aggressive destabilization in 109s while turning
« Reply #13 on: December 02, 2004, 11:28:11 AM »
HiTech,

What about the C.205 in his tests?  It doesn't have slats and still stalled out even with the stall limiter on.
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Offline hitech

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Overly aggressive destabilization in 109s while turning
« Reply #14 on: December 02, 2004, 12:09:50 PM »
Like I said Karnak. The stall limiter is not a precise thing, it realy is only designed to limit the ham fisted pilots, not to ride the edge.

When keweassa changed the stall limit AOA to close to the stall edged, all bets are off how the stall limiter will function. Things like CG,CM,CP are not taken into acount in the stalll limiter,  so how it functions on different planes realy close to the edge is nothing im realy conserned about.


HiTech