Author Topic: Overly aggressive destabilization in 109s while turning  (Read 1054 times)

Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #15 on: December 02, 2004, 03:28:54 PM »
Quote
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.


 Urchin, what were your power settings during your testings?

 At least, according to my experience it is impossible to get a 109 under 180mph in a coordinated turn that does not lose or gain altitude, with full military power settings.

 In other words, when a 109 enters a turn with full throttle, it can't turn tight enough to bleed E to go under 180mph in the first place. The turn will be halted by the 180~200mph "barrier" like you've noticed. Any attempt to ease or stop the destabilization will result in a less elevator input and/or some counter aileron input - which, will keep the speed at the 180~200 mark.

 Now, technically, there are other methods of bleeding E. The most common combat practice is to go in a high yoyo - pitch the plane up slightly during a turn so the speed bleeds under 200 without much stick pull, and then roll during the stall-out to tighten turn. Or, you can just throttle down, which will kill your turning speed. Another method is to give lots of rudder with a slight stick pull.

 However, aside those methods, at least in my case I can never get a 109 to turn flat and lose E at the same time.


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"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.


 I understand Hitech... er, I think I do, that is. Please correct me if I'm wrong:

 So, essentially, what you're saying is;


1) In some cases like slatted planes or the Macchis, AoA set for the stall limiter will not be an actual representation of the plane's real "limits".

2) So, when the stall limiter is set to 0.05, and when you give max stick deflection with the 109, this plane isn't actually stalling before its max limit is reached.

3) The real limits of those planes, are not the "0.05 before stall" as set by the SL. For these planes, the actual point they destabilize so that they cannot continue the turn, is the real limits.

4) So, the 109s are correctly stalling out at the AoA they are set at. It's just that this AoA does not match the stall limiter AoA.

 Am I correct so far?

 ....

 
 Clearly, while you said that the stall limiter is not an accurate representation for the "edge of the envelope", some planes can handle it with no problem.

 The P-47s or P-51s have no problems in max stick deflection when the margin for the SL is set to 0.05 - despite whatever limitations you said it has.

 The stall limiter won't effect a FM parameter of a plane itself, so if a P47 or a P51 can handle that max stick deflection with 0.05 SL settings, then in their case there is no problem. Those planes really can handle that kind of turn.

 Am I correct on this?

 In that case, how about if I do this?

 I will progressively increase the stall limiter margin in 109s, until I get a point where the 109 too, will not stall with max stick deflection with SL turned on.

  And then, I will compare that 109 turn performance, with the turn performance of a P-47 or a P-51 using 0.05 minimum settings.

 Will this one be an acceptable test?

Offline hitech

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Overly aggressive destabilization in 109s while turning
« Reply #16 on: December 02, 2004, 03:34:15 PM »
I belive that would work kewassa.

But I find it simplar to just fly the plane low over the water so you have a nice flat frame of reference then just find the max sustained turn rate by hand and stop watch.

HiTech

Offline Furball

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Overly aggressive destabilization in 109s while turning
« Reply #17 on: December 02, 2004, 04:27:17 PM »
anyone noticed the complete lateral instability (think that is the right term?) on the spit 14?

makes it very hard to aim.
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Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #18 on: December 02, 2004, 04:46:55 PM »
The Spit14 is indeed quite a bit unstable when turning to left. However, I've noticed no such significant destabiliztion when turning right.


 As a matter of fact, most planes have some kind of noticeable difference between turning left and right.

 For example the Ki-84.., in constant left hand turns it can beat a P-38L fairly easy. In a right hand turn, I'd say the chance drops a lot lower - relatively much more unstable when doing right hand turns.

Offline Kweassa

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Overly aggressive destabilization in 109s while turning
« Reply #19 on: December 03, 2004, 02:19:50 PM »
Question..

 How do I calculate turn rate with speed and G data?

 For instance, a plane at 150mph TAS is pulling 2Gs. What's this plane's turn rate in xx degrees per second?

Offline hitech

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Overly aggressive destabilization in 109s while turning
« Reply #20 on: December 03, 2004, 03:52:32 PM »
V = Speed In Fps I.E MPH * 1.4666
G = Total G load

BankAngle = ACOS(1/G)

CircleRadius = (V*V) / (32.2 * tan(BankAngle))

CircleCircum. = 2 *3.14159 *  Radius


TimeAroundCircle = CircleCircum/V

DegPerSec = 360/TimeAroundCircle



HiTech