Artificial feel in the F-5 (and other jets)

[nairb121]

Aircraft with hydraulically boosted flight controls are generally equipped with artificial feel, to give the pilot some feedback on their control inputs. I'm trying to get realistic behavior from my force feedback stick, but I'm having a hard time finding any specific info. I'm mostly wondering whether the feel system accounts for airspeed (increasing stick forces as the aircraft accelerates), or if it's just a static spring system. Does this vary between aircraft? Or between hydraulic and FBW? If there are any solid sources anyone can recommend for more info on this, I'd really appreciate it.

[=475FG= Dawger]

2 hours ago, nairb121 said:

Aircraft with hydraulically boosted flight controls are generally equipped with artificial feel, to give the pilot some feedback on their control inputs. I'm trying to get realistic behavior from my force feedback stick, but I'm having a hard time finding any specific info. I'm mostly wondering whether the feel system accounts for airspeed (increasing stick forces as the aircraft accelerates), or if it's just a static spring system. Does this vary between aircraft? Or between hydraulic and FBW? If there are any solid sources anyone can recommend for more info on this, I'd really appreciate it.

Artificial feel systems try to replicate aerodynamic forces present on un-boosted controls.

There are a few different varieties. Due to the age of the F-5, I would guess a spring/bobweight system is installed but that is just an educated guess.

[ViFF]

I use the MS SW FF2 and it is very good with the F-5E.

ED has implemented the artificial feel system for the pitch and roll control systems. With the MS SW FF2 you can feel the left and right movement of the control stick being limited by the real life spring mechanism installed in the F-5E for the pilot to feel and avoid excessive roll rates. At the half-way throw of the stick left/right you'll experience what feels like a "bump" with higher return to center force from that point to the edge of the throw.  Trim is also modelled and will move the center of the stick accordingly. Otherwise, the return to center force is constant like in most aircraft with hydraulic boosted flight controls.

Check out the DCS F-5E manual chapter 6.10  its explained in some detail.

from the manual:

The stability augmenter system (SAS) controls the horizontal tail and rudder to automatically damp out pitch and yaw oscillations and also provides manual rudder trim. The CADC controls gear ratio in the dampers during deflection of the control surfaces depending on a signal provided by an airspeed sensor, thus facilitating aircraft piloting throughout the entire aircraft speed range.

So from the perspective of the pilot, the force you feel on the stick is constant. The above concept and the trim effects are modelled well on the MS SW FF2 stick.

Cheers!

 

Edited July 12, 2022 by ViFF
further detail

[Mr_sukebe]

1 hour ago, ViFF said:

I use the MS SW FF2 and it is very good with the F-5E.

ED has implemented the artificial feel system for the pitch and roll control systems. With the MS SW FF2 you can feel the left and right movement of the control stick being limited by the real life spring mechanism installed in the F-5E for the pilot to feel and avoid excessive roll rates. At the half-way throw of the stick left/right you'll experience what feels like a "bump" with higher return to center force from that point to the edge of the throw.  Trim is also modelled and will move the center of the stick accordingly. Otherwise, the return to center force is constant like in most aircraft with hydraulic boosted flight controls.

Check out the DCS F-5E manual chapter 6.10  its explained in some detail.

from the manual:

The stability augmenter system (SAS) controls the horizontal tail and rudder to automatically damp out pitch and yaw oscillations and also provides manual rudder trim. The CADC controls gear ratio in the dampers during deflection of the control surfaces depending on a signal provided by an airspeed sensor, thus facilitating aircraft piloting throughout the entire aircraft speed range.

So from the perspective of the pilot, the force you feel on the stick is constant. The above concept and the trim effects are modelled well on the MS SW FF2 stick.

Cheers!

 

 

When you say it feels artificial, is that because you recently flew an F5 for real?

Edited July 12, 2022 by Mr_sukebe

[nairb121]

23 minutes ago, Mr_sukebe said:

When you say it feels artificial, is that because you recently flew an F5 for real?

Aircraft with hydraulic boosted controls don't give the pilot direct feedback from the control surfaces, like mechanical linkages would. They generally include some system to simulate that "feel", referred to as "artificial feel". Without that feedback, it's difficult to accurately control the inputs you're making. So really, using FFB in DCS is artificial artificial feel.

1 hour ago, ViFF said:

ED has implemented the artificial feel system for the pitch and roll control systems.

Unfortunately, my stick (Brunner CLS-E) doesn't support the DirectInput force feedback API (maybe it's time for me to pester them about it again), so I can't easily use ED's implementation. I'm mostly restricted to a force vs. deflection curve, with an additional multiplier based on airspeed. There are a few other variables, but I'm mostly trying to figure out how to dial in the airspeed multiplier curve.

15 hours ago, =475FG= Dawger said:

Due to the age of the F-5, I would guess a spring/bobweight system is installed but that is just an educated guess.

Educated guess or not, this is really helpful, since it at least gives me a starting point for looking into these systems. It looks to me like (at least for longitudinal controls) it's generally expected that stick force will be proportional to g. I might have to do some math at some point, but I think this should at least get me headed in the right direction.

[ViFF]

2 hours ago, Mr_sukebe said:

When you say it feels artificial, is that because you recently flew an F5 for real?

 

Nice try. I did not write "it feels artificial"  I wrote "ED has implemented the artificial feel system for the pitch and roll control systems [in their simulation of the F-5E flight control systems]. I am quoting from the DCS F-5E manual on page 104. It would do you well to read the manual. Perhaps it would also help your reading comprehension skills and avoid misquoting people.

 

[Mr_sukebe]

4 minutes ago, ViFF said:

Nice try. I did not write "it feels artificial"  I wrote "ED has implemented the artificial feel system for the pitch and roll control systems [in their simulation of the F-5E flight control systems]. I am quoting from the DCS F-5E manual on page 104. It would do you well to read the manual. Perhaps it would also help your reading comprehension skills and avoid misquoting people.

 

When you’ve finished getting on your high horse, talking about “the artificial feel system” without stating whether that’s a quote from ED material or just some made up bs makes the attempt to correct my comment appear as it is, ie a bit pants.

If you want to avoid potential misinterpretation, be specific.

[=475FG= Dawger]

4 hours ago, nairb121 said:

Educated guess or not, this is really helpful, since it at least gives me a starting point for looking into these systems. It looks to me like (at least for longitudinal controls) it's generally expected that stick force will be proportional to g. I might have to do some math at some point, but I think this should at least get me headed in the right direction.

Artificial feel systems make stick force proportional to airspeed, simulating the effect of aerodynamic forces on the control surfaces.

G forces are not involved since no artificial feel is required for G forces in the real thing. 

And I am not sure what you mean when you say "longitudinal controls". For clarity, the longitudinal axis is roll, lateral axis is pitch. 

[nairb121]

48 minutes ago, =475FG= Dawger said:

5 hours ago, nairb121 said:

stick force will be proportional to g

G forces are not involved since no artificial feel is required for G forces in the real thing. 

 

I might not have worded this as clearly as possible. Most sources I've found seem to indicate "constant stick force per g".

I ended up finding this patent, U.S. Patent #2661169, relating to early artificial feel systems (in this case, actually granted to Northrop Co.).

Relevant quotes:

 

nullIt also included this figure, showing stick force vs. deflection at various airspeeds:

Although the aircraft configuration is different, and the mechanism had likely changed by the time the F-5 was designed, it seems reasonable to me that the overall design philosophy (i.e. constant force per g) would be maintained.

1 hour ago, =475FG= Dawger said:

And I am not sure what you mean when you say "longitudinal controls". For clarity, the longitudinal axis is roll, lateral axis is pitch.

I was unclear here as well, I meant fore-and-aft stick movement, i.e. pitch.

[=475FG= Dawger]

27 minutes ago, nairb121 said:

I might not have worded this as clearly as possible. Most sources I've found seem to indicate "constant stick force per g".

I ended up finding this patent, U.S. Patent #2661169, relating to early artificial feel systems (in this case, actually granted to Northrop Co.).

Relevant quotes:

 

nullIt also included this figure, showing stick force vs. deflection at various airspeeds:

Although the aircraft configuration is different, and the mechanism had likely changed by the time the F-5 was designed, it seems reasonable to me that the overall design philosophy (i.e. constant force per g) would be maintained.

I was unclear here as well, I meant fore-and-aft stick movement, i.e. pitch.

I understand what they were driving at as it relates to CG position. The apparent forces on the elevator change significantly with CG position and they were trying to replicate that with the artificial feel system so that for each given airspeed the force required for X g-force would always be ~ Y.

When the CG is pushed to the aft limit, elevator forces get very light and when the center of pressure and center of gravity get close together, the dynamic stability gets very interesting to say the least.

In DCS, I don't think you really need to worry too much about this part of the artificial feel system. I haven't noticed noticeable CG changes with loading in DCS leading me to believe the CG for DCS modules really doesn't move much, certainly not to the edges of the envelope.

I think if you modeled stick forces proportional to airspeed, you will be in the ballpark.

[nairb121]

16 hours ago, =475FG= Dawger said:

In DCS, I don't think you really need to worry too much about this part of the artificial feel system.

Yeah, I definitely agree with you here. I get confused enough with the airspeed/stick pull/g relationship, CG stuff isn't something I have any desire to worry about. It wouldn't surprise me either if DCS inputs already accounted for that anyway.

[=475FG= Dawger]

30 minutes ago, nairb121 said:

Yeah, I definitely agree with you here. I get confused enough with the airspeed/stick pull/g relationship, CG stuff isn't something I have any desire to worry about. It wouldn't surprise me either if DCS inputs already accounted for that anyway.

I am pretty sure its accounted for by not really moving the center of gravity or center of pressure.