Improve dynamic stability and dampening

[gilbertohasnofb]

These are excerpts from a discussion in the forum, from: https://forum.flightgear.org/viewtopic.php?f=49&t=30604

edroberts1943 writes:

I am new to FG and very impressed with the simulation. I have been flying the 172p which I have flown as an instrument rated pilot in real life.

In my set up, the 172 seems very unstable not representative of the inherent stability of a real 172. When I make a small correction on an approach, the simulated plane rocks and yaws about the longitudinal and vertical axies respectfully.

edroberts1943 writes:

I have the same experience with both the mouse and joystick. I have modified the OS mouse response and also modified the xml file for the joystick. I can make both require greater displacement for a given action but the inherent instability seems to still exist in the model. In civilian planes such as the 172, the plane is constructed with dihederal so that these are inherently stable. Not so for fighters.FG is still a remarkable simulation but I would like to get the 172 more stable so that I can practice instrument approaches with greater realism.

it0uchpods writes:

I have this problem with a lot of smaller planes.

D-EKEW writes:

If you want to try an aircraft that has a pitch force model: try the extra500. You can switch to a different pitch control mode where the joystick controls the force, not the position. This will give a bit more 'feel' to the simulation. The aircraft model is a bit more complicated (but the wiki pages are extensive) to fly and needs some practice.

This last comment seems particularly interesting IMO.

[gilbertohasnofb]

@wkitty42 thanks for replying back to that user, maybe you want to let him know about this newly opened issue

@onox @dany93 what do you guys think?

[Juanvvc]

I have had the same impression with the c172p since the first time I tested FlightGear: the real aircraft is much more stable than the simulation. Anyway, I also agree a bit with curt and the problem maybe not in FligthGear itself, but lacking a force-feedback joystick.

In a real aircraft you must apply a considerable amount of force to move the yoke. Since we can move a joystick in a PC without any apparent effort, there is a possibility experienced pilots think the simulation is not as stable as a real aircraft.

Anyway, checking what they have done in the extra500 to address this issue seems a wonderful idea.

[dany93]

Not disturbing for me. I have posted a response. Suggestions to "fiddle" with two FDM parameters.

@gilbertohasnofb, @Juanvvc , did you check that the extra500 (kind of) force-feedback gives an improvement?

[onox]

Anyway, checking what they have done in the extra500 to address this issue seems a wonderful idea.

I think this is what @Juanvvc is referring to: http://wiki.flightgear.org/Extra_EA-500/pitch_control

[dany93]

Yes, I've read this.

These assertions, used to justify the force control mode, seem wrong. Something that I don't understand?

Direct elevator control mode As the function of trim is to reduce the pilot force to zero, on most models trimming is completely useless.

The disadvantage is for joystick users: you will never be able to let go of the joystick as trimming reduces the pilot forces (which you don't feel), but does not change the position of the yoke (= the position of the joystick).

With the usual (direct) mode and a joystick, correct trimming enables you let go of the joystick (at neutral assuming it has springs) and have the aircraft fly horizontally, straight and levelled. No force exerted, with no strong tendency. Even if the trim does not change the position of your physical yoke or rudder pedals with no force applied, as it does in real world. In FG, possible on the three axes even if the real aircraft isn't provided of these trimmings.

Force elevator control mode You can use the elevator trim to reduce the force needed and thus get into a stable flight attitude with your joystick centered.

This is already true also with the usual (direct) mode.