Uri_ba's pit

Road to FCC, Part V – Deciding on a feature list

Well, now that we had covered the  bases and we can actually “talk” with the hardware, it’s time to start designing the User experience.  Or in other terms, I want to go from a “joystick” to a “product”.

in this post I’ll try and go over some of my ideas and howto overcome some of the difficulties involved.

Learning the “market”

First on my TODO list was actually understand what’s out there, what are the requirements, determine the gaps and finally decide if and how to address them.

So naturally I went to look at current Force-controllers. the two intimidates were the FCC3 with the cougar board and the FSSB-R3 with its fancy firmware with lots of features.

I’ve decided to look back and do some thinking. FCC is primarily for F-16 sims.. I.e BMS.

In the past, people had to do all sort of fancy things in order to get the curves and response right. BMS however, is doing it for you. all you need to do is provide a linear stick deflection from side to side and BMS does all the rest for you. which is great, that means I don’t need to worry about curves in the FW. what about other sims? well DCS you can program custom curves per aircraft, so no need to do anything there either. cool, straight out clean linear it it.

Going back to FSSB docs, they allow you to change sensitivity as well as force setting. to me to sounds a little redundant, as all FBW aircraft have different gains.for example takeoff&Landing, cruise and Air refuel. BMS does all of this in code, again, you just need linear deflection. so no need for sensitivity. but force calibration is a thing. some will have a mounted stick and would want a full strength stick. others will have it desktop mounted and would like a “lighter” stick. So force calibration is in.

Next on the bucket list.
F-16 has different force requirements for each axis. full deflection in pitch is not the same as full deflection in roll for example.

FSSB addressed this by allowing different settings for pitch and roll. But it made me think, if I’m going for F-16 why not just allow “F-16” limits. I went digging, as to my surprise, it seems that even in pitch, gains are different for pull up vs push over. so why should I bother with differential pitch and roll? I can just simulate whatever the FLCS does, it should be OK for “other sims” as well. if not, they can just disable it and build a curve.

F-16 is a special boy (FLCS rant)

Well FLCS we said, let’s dig into that too.

The F-16 FLCS had some variation over the lifespan of the airframe.

initially the stick was fixed in place, it was just like holding a metal rod. Pilots resented that, so in Block 10 a little movement was introduced to the stick, about 0.25″ each direction (which translates to about 6mm).

but that is only half of the equation.  behind the stick (or rather under it) sits the sensor unit.

before we go into the SSC gains, let’s talk about how the FLCS works.

In conventional aircraft, the amount of stick deflection will directly affect the Control surfaces deflection. the amount is fixed and the speed of the aircraft will affect the effectiveness of the controls.

As time progressed, hydrolic systems were introduced, and some control logic was added, thus allowing things like flaperons and rotating horizontal stabilizers to be introduced. but the pilot still needed to maintain control over the aircraft, make sure he does not put too sharp of an input into the controls, as the aircraft can exceed the structural limits in some cases.

The Introduction of the FBW system to the F-16 was a game changer. the pilot no longer was in control of the aircraft, the computer is. the pilot is just one of the inputs into the computer.

however, unlike “classic” controls, where the pilot commands Aerodynamic Surfaces to be actuated. in the F-16 pilot inputs a “maneuver request” to the FLCS.  In both axis, the inputs are rate driven. In Roll the pilot requests roll rate (in degrees per second up to 306 deg/s). In Pitch however,rate is requested in G (between +10 and -4).

FLCS variants

initial implementation was referred to as “Analog FLCS” as the pressure sensing gains were all Hardware driven (pre-amps, resistors etc.) which meant that whatever forces the SSC was initially designed for were there to stay. The Analog FLCS was calibrated so that the full pitch up command (+10G) required 180N (40.46 lbf / 18.35Kgf). full pitch down command (-4G) on the other hand required 80N (18 lbf / 8.15Kgf). full roll was also 80N.

With block 40/42 the “Digital FLCS” was introduced. unlike it’s predecessor, the electronics on it were programmable, and it was possible to change the gains from the device. According to HAF’s Dash1 manual in the block 52+, the current gains are 25lbf (111N / 11.34 Kgf) for full pitch up and full pitch down is 16lbf (71N / 7.25Kgf). While the full roll command is 17lbf (7.7 Kgf / 75.6N).

However, this was not the only change. along with the Digital FLCS another change was introduced, the sensor assembly under the stick was rotated 12 degrees clockwise, so that it will be easier for the pilot to produce clean pitch or roll commands.

Compiling a feature list

so from that we can create an initial baseline feature list.

  • Sensor rotation
  • FLCS emulation – to some extent, probably linked to selected force setting
  • Force sensitivity/calibration settings.
  • Some sort of user interface – preferably on stick controls

On the next “episode” I’ll try and go over the development of the “User interface”

Leave a Reply