At the outset I should point out that I am not a FlightSim aircraft designer, I know nothing about the inner workings of FlightSim, my FD expertise is extremely basic (ie: of the sometimes hazardous "Trial & Error" variety) and my piloting skills are none too crash-hot either.
That said, I'll dive in at the Deep End and ask ....
Can anyone explain to me why FlightSim aircraft designers and/or their FD "experts" completely ignore the Lever Arm Principle when determining Lift/Side Force and Pitch/Yaw Moment parameters for Elevator, Horizontal Stabilizer and Rudder in Record 1101 of the .air file ?
I'm no aerodynamics expert either, but it is my understanding that [Lift/Side Force] multiplied by [the longitudinal distance from the FS Reference Position to the Point of Lift/Side Force] equals [Pitch/Yaw Moment].
Regards
David.
Tailplane Lift and Pitch Moments
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Garry Russell
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David,
I'm not entirely sure that is true in this case because I'm not sure quite how applicable that analogy is. In most non-aerodynamic lever cases, there is a very definite fixed pivot point. Someone told me, that to make an aircraft more manoevrable, it was desirable to minimise the distance between the C. of G. location and the tailplane - which if true - would suggest the lever principle wasnt quite appropriate.
In any ase, as Garry says, the way FDEs and the Microsoft flight mechanics 'engine' operate are some way apart from "real" physics, but, having known a fair few aeronautical engineers, I know that even in calculations for the "real world", the use of "fudge factors" is rife and quite accepted to acheive the desired result
As much as it pains me to say it, 'correct' FDEs are as much of an art form as they are a science in FS. And I still say that with a different joystick on a differently set up system, the same aircraft can still "feel" quite different.
There, that hasnt helped at all
Toby
I'm not entirely sure that is true in this case because I'm not sure quite how applicable that analogy is. In most non-aerodynamic lever cases, there is a very definite fixed pivot point. Someone told me, that to make an aircraft more manoevrable, it was desirable to minimise the distance between the C. of G. location and the tailplane - which if true - would suggest the lever principle wasnt quite appropriate.
In any ase, as Garry says, the way FDEs and the Microsoft flight mechanics 'engine' operate are some way apart from "real" physics, but, having known a fair few aeronautical engineers, I know that even in calculations for the "real world", the use of "fudge factors" is rife and quite accepted to acheive the desired result
As much as it pains me to say it, 'correct' FDEs are as much of an art form as they are a science in FS. And I still say that with a different joystick on a differently set up system, the same aircraft can still "feel" quite different.
There, that hasnt helped at all
Toby
tailplane
Hi,
There is a lever effect due to the tailplane incidence angle as when I find a plane with too much or too little trim movement between take-off/ landing and cruise pitch, I amend the angle of incidence by a degree or so to change the gap.
I guess one factor affecting the tailplane lever/ distance effect is the relative placement of the wing to the datum point. Since the stabiliser is there to balance the pitch effect of the wing lift, adjusting one must affect the other. :think:
I think Toby's right, we tweak the FDE files to get what we want but even with the additional cfg data in FS9 compared to previous versions, we don't always know exactly what we're doing.
Perhaps we really shouldn't worry about it
There is a lever effect due to the tailplane incidence angle as when I find a plane with too much or too little trim movement between take-off/ landing and cruise pitch, I amend the angle of incidence by a degree or so to change the gap.
I guess one factor affecting the tailplane lever/ distance effect is the relative placement of the wing to the datum point. Since the stabiliser is there to balance the pitch effect of the wing lift, adjusting one must affect the other. :think:
I think Toby's right, we tweak the FDE files to get what we want but even with the additional cfg data in FS9 compared to previous versions, we don't always know exactly what we're doing.
Perhaps we really shouldn't worry about it
Regards,
Degsy
Degsy
We don't - why do you think this?LoadMaster wrote:Can anyone explain to me why FlightSim aircraft designers and/or their FD "experts" completely ignore the Lever Arm Principle when determining Lift/Side Force and Pitch/Yaw Moment parameters for Elevator, Horizontal Stabilizer and Rudder in Record 1101 of the .air file ?
Well, I amLoadMaster wrote:I'm no aerodynamics expert either, but it is my understanding that [Lift/Side Force] multiplied by [the longitudinal distance from the FS Reference Position to the Point of Lift/Side Force] equals [Pitch/Yaw Moment].
and it isn't. The wing and tailplane each exert their very own pitching moments (even at zero lift and even in isolation). The overall aircraft pitching moment varies with the incidence of the wing or tailplane involved, and their position relative to the overall aircraft centre of pressure and is additional to the simple (tailplane lift x moment arm).Don't forget also that in addition to the derivatives which tend to move the aircraft (eg pitch rate due to elevator deflection), there are also major derivatives which tend to damp motion (eg pitch rate due to rate of pitch, roll rate due to rate of roll, etc).
Just increasing the tail moment arm will generally make the aircraft more stable in pitch and yaw, unless other changes (such as elevator/rudder area or gearing) are made at the same time.
This is as true in the real world as in flight sim.
Oh, and by the way, Garry is quite correct - FDEs ARE full of compromises because flight sim modelling operates on a pretty limited set of derivatives and other factors and much of the underlying MS model is 'fudged', to put it mildly. It has taken me quite a while to learn how to apply my decades of experience in real-world aerodynamics to the world of MS flight sim: I think it would be fair to say that a good set of working FS9 FDEs start out as engineering and end up as an artform!
Kevin