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Old 02-25-2019, 12:22 PM   #1
DD_Fenrir
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Default Yo-Yo: What causes Pitch Up at lowering IAS

Hi Yo-yo.

Hope you can clarify this question; what aerodynamically is happening in the Spitfire to cause the aircraft to become tail heavy as IAS drops?

This behaviour is counter to how most aircraft behave, i.e. in they get nose heavy as airspeed drops.

Please note, that I am in no way challenging the FM, I am more than happy that this is what should be happening, just curious as to what the CP is doing in relation to the CG and what makes the Spitfire fairly unique in this regard.

Thanks!
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Old 02-25-2019, 05:16 PM   #2
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Quote:
Originally Posted by DD_Fenrir View Post
Hi Yo-yo.

Hope you can clarify this question; what aerodynamically is happening in the Spitfire to cause the aircraft to become tail heavy as IAS drops?

This behaviour is counter to how most aircraft behave, i.e. in they get nose heavy as airspeed drops.

Please note, that I am in no way challenging the FM, I am more than happy that this is what should be happening, just curious as to what the CP is doing in relation to the CG and what makes the Spitfire fairly unique in this regard.

Thanks!
I do not understand completely what you mean. What conditions? Power-on, gliding?
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-25-2019, 07:33 PM   #3
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Clean aircraft, power on steady climb with airspeed dropping, the aircraft becomes tail heavy as ias drops through 180mph.
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Old 02-25-2019, 08:22 PM   #4
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Yes, its absolutely distinctive for props, especially with low stability margin. prop destabilising effect.The more AoA is the more is the propeller lift, thus nose-up moment, so the plane getting additional instability.

109K behaves the same way.

The clear sign of it is reverse trim position of the stick vs IAS. Try to glide at different speed and watch the trim position, then try to climb and watch the same.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-26-2019, 10:00 AM   #5
DD_Fenrir
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Ahh, that makes sense, particularly for aircraft with neutral stability, thanks Yo-Yo.

I had assumed it was something to do with differing rates of lift loss between the wings and the horizontal tailplane, had not even thought about prop effects.

On a separate note, I have noticed almost every Spitfire in air-to-air shots when trimmed for cruise has the elevator always slightly depressed. Indeed this great video of a Mk.V flying over Malta shows over the tail shots and the elevator barely even reaches datum with the chord line of the horizontal stabiliser through a aerobatic routine:

https://www.youtube.com/watch?v=3sk7fGHPXdk

I would have assumed that some sort of engineering could have been accomplished so that the elevator trim 0 position for cruise would have matched the horizontal stab datum. Is this not important for trim drag?
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Old 02-26-2019, 12:03 PM   #6
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Quote:
Originally Posted by DD_Fenrir View Post
Ahh, that makes sense, particularly for aircraft with neutral stability, thanks Yo-Yo.

I had assumed it was something to do with differing rates of lift loss between the wings and the horizontal tailplane, had not even thought about prop effects.

On a separate note, I have noticed almost every Spitfire in air-to-air shots when trimmed for cruise has the elevator always slightly depressed. Indeed this great video of a Mk.V flying over Malta shows over the tail shots and the elevator barely even reaches datum with the chord line of the horizontal stabiliser through a aerobatic routine:

https://www.youtube.com/watch?v=3sk7fGHPXdk

I would have assumed that some sort of engineering could have been accomplished so that the elevator trim 0 position for cruise would have matched the horizontal stab datum. Is this not important for trim drag?
Do you take in account wing downwash stream?

And, by the way, different stability margin (or different neutral point) is possible for high and low CL regions.
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-27-2019, 05:52 PM   #7
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I got question about elevator control linked with stick in cocpit and joystick position.



Without FF joystick i noticed that if joystick is in center (neutral), stick in cocpit is in center ( control zone window) but elevator surface (steer surface) is little in down position ( behind center axis) which casue to fly Spitfire more level. It looks that stick in cocpit in neutral casue elevator surface little down postion. No need full trim nose down to level flight. Much easier to fly without constant push stick to level flight.





If i turn ON Force Feedback on stick i noticed that joystick is in neutral ( center), stick in cocpit is little aft postion ( below center in control zone window with axis) and elevator surface is in neutral (center) position. Plane now need full trim nose down to fly more level flight but still required constant push stick - not possible to trim for level flight.






Whats is reason of these? In real Spitfire stick in neutral casue elevator in little down position?

Last edited by Kwiatek; 02-27-2019 at 05:56 PM.
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Old 02-27-2019, 08:42 PM   #8
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What type of FF stick do you have?
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Ніщо так сильно не ранить мозок, як уламки скла від розбитих рожевих окулярів
There is nothing so hurtful for the brain as splinters of broken rose-coloured spectacles.
Ничто так сильно не ранит мозг, как осколки стекла от разбитых розовых очков (С) Me
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Old 02-27-2019, 09:58 PM   #9
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Saitek Evo Force.


In other warbirds everything is ok - joystick neutral, stick in cocpit neutral, elevator neutral. Only Spitfire is different.
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Old 02-28-2019, 10:45 AM   #10
Malexx
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Default same too

Well, here its the same. Flying with MSFFB2 and 20cm Extension.
Even with full trimm i have to push the stick forward for levelflight.
With more Speed it gets better, but neutral Position is a no go with the spitfire.
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