Fly by wire simulation

[Django]

What will "fly by wire simulation" mean in this project, i.e. how deeply will the Mirage 2000C fly by wire system be represented?

 

I'm coming from a mostly FSX simming background where you often come across developers advertising simulations of Airbus or other fly by wire aeroplanes. In fact I can think of only one Airbus A320 project that is actually modelling the fly by wire system - i.e. movements of my my flight controls are actually monitored by a module in the sim.

[Manuel_108]

The Mirage has FBW?

[Random]

The Mirage has FBW?

 

Yup IIRC.

 

Would be nice if it could be simulated!

[Zeus67]

We will try. No promises thought. It depends on what is possible.

Edited September 10, 2015 by Zeus67

[XeNoise]

I ask myself what would fly by wire mean for a simulation, since our inputs are anyways digital. What would be the main differences?

[Jumbik]

I ask myself what would fly by wire mean for a simulation, since our inputs are anyways digital. What would be the main differences?

 

It would mean that they would have to program a computer which would be analyzing the flight parametres and change the inputs to prevent hostile behaviour. Then analyze players inputs, compare them to the flight characteristics, modify the inputs a little bit... etc. etc. all this at least 50 times per second.

[Manuel_108]

It would mean that they would have to program a computer which would be analyzing the flight parametres and change the inputs to prevent hostile behaviour. Then analyze players inputs, compare them to the flight characteristics, modify the inputs a little bit... etc. etc. all this at least 50 times per second.

 

Another developer is doing exactly that for a quite well known civil airliner :music_whistling:

In that respect, without simulating the FBW, the DCS Mirage module would be incomplete then and should not be an official "DCS: Mirage" module as the FBW system arguably plays a huge part of the simulation of flying.

[Jumbik]

Another developer is doing exactly that for a quite well known civil airliner :music_whistling:

In that respect, without simulating the FBW, the DCS Mirage module would be incomplete then and should not be an official "DCS: Mirage" module as the FBW system arguably plays a huge part of the simulation of flying.

 

That depends ... did ED/Belsimtek program the FBW for Su-27 the way they should have? Does anybody know? It's the only airplane in DCS that should have a working FBW already. Razbam could base their programing on that.

[Zeus67]

Hmm. No, we are not.

FBW is more than just controlling the surfaces. FBW is really a set of rules that the aircraft must follow in order to maintain controlled flight.

 

Basically these rules work like this;

"If the pilot wants to do this and the sensors report these conditions, then override the pilot and do something else, but if the sensors report these other conditions, allow the pilot to do this up to a limit, and finally if the sensors are within parameters then allow the pilot to do what he wants."

[Mobius_cz]

Another developer is doing exactly that for a quite well known civil airliner :music_whistling:

In that respect, without simulating the FBW, the DCS Mirage module would be incomplete then and should not be an official "DCS: Mirage" module as the FBW system arguably plays a huge part of the simulation of flying.

 

I will consider you are really know what is Fly by Wire (FBW) system is and why it is used. For the others as far as i know the FBW system is used because you can build naturally unstable aircraft and it can still fly very well or even fly at all. If Razbam will use real performance data for they AFM or any simulation data you will notice even from the first view that Mirage 2000 can't be stable plane at all. And without any system (or solution) to compensate this it shouldn't be flying even in a PC game at all. The last point is only my personal feeling about this and i really doubt i will recognize if it is FBW solution or not.

[Moos_tachu]

To clarify:

 

With traditional controls:

Your input on the HOTAS means "I want a 10° angle on my control surfaces" (just an example).

The output you get from the aircraft is a 10° angle on your control surfaces.

The consequence is a pitch up attitude, and depending on speed/altitude/etc., the result might be a more or less 10° AOA.

 

With FBW controls:

Your input on the HOTAS means "I want a 10° AOA".

The output you get from the aircraft is a 10° AOA.

To achieve this, the flight computers will command whatever angle of the control surfaces is required to get a 10° AOA, taking into account the speed/altitude/etc.

And while doing that, they obviously filter any inputs which would result in going out of the desired aircraft flight enveloppe.

 

Very simplified and not really accurate, as classic FBW systems would pilot in G rather than AOA...

But otherwise it would take several pages to explain FBW :)

Edited September 16, 2015 by Moos_tachu

[Zeus67]

To clarify:

 

With traditional controls:

Your input on the HOTAS means "I want a 10° angle on my control surfaces" (just an example).

The output you get from the aircraft is a 10° angle on your control surfaces.

The consequence is a pitch up attitude, and depending on speed/altitude/etc., the result might be a more or less 10° AOA.

 

With FBW controls:

Your input on the HOTAS means "I want a 10° AOA".

The output you get from the aircraft is a 10° AOA.

To achieve this, the flight computers will command whatever angle of the control surfaces is required to get a 10° AOA, taking into account the speed/altitude/etc.

And while doing that, they obviously filter any inputs which would result in going out of the desired aircraft flight enveloppe.

 

Very simplified and not really accurate, as classic FBW systems would pilot in G rather than AOA...

But otherwise it would take several pages to explain FBW :)

 

With FBW

"I want 10° AOA"

FBW System: 10° AOA will generate 9Gs acceleration, this profile only provides for 6Gs max. 4°AOA will generate 6Gs.

FBW Reply: You get 4°AOA and don't bother bending the HOTAS stick because that's all you will get.

[Essah]

Su-27 has FBW simulated. that's what the S key overrides allowing you execute Pugachev's Cobra. If it's 100% accurately simulated is another question but there is something, If there weren't, flying it would be like flying with the S key override enabled all the time... try that for a minute :P

[Yeoman Scrap]

Moos_tachu had enough sense to not lay down a wall of text. I do not :music_whistling:

 

A Flight Control System (FCS) does so much more than just "You only get 4° AOA". A limiter and a scheduler are part of the system, but it does so much more.

 

N.B. The following is pretty general, but the only aircraft I truly understand is the Hornet, so I'll draw my examples from it. It's FCS laws are a bit squiffy (like everything Navy), but the principle is the same.

 

Fly-by-wire, at its heart, disconnects the control stick from the control surfaces. Control stick inputs are run through the mission computer (MC1, assuming we haven't failed anything). The mission computer takes a holistic look at the aircraft -airspeed, altitude, mode selector, gear position, flap switch, Mach No., loading, AoA, pointing vector, INS gyros, fuel load, C of G, stick deflection and hundred other things- and then proceeds to interpret the pilot's inputs, and make them reality.

 

In the most basic case, the pilot has centred the stick. In the Hornet (other A/C are a bit different), MC1 takes this as an instruction to "maintain 1G". To do this, it makes dozens of little measurements and adjustments every second to all the flight control surfaces.

If it feels a little reduction in G, it checks the stick position. If I haven't commanded nose down, it then checks all the little factors (mainly airspeed) and uses that to schedule a specific (and very small) Both Stabilators Up command, which brings us back to 1G.

If it registers a little left roll on the laser gyro, it checks the stick. If I haven't commanded a little left roll, it checks all the sensors, and then schedules a specific combo of Right Aileron, Left Aileron, Left Fin, Right Fin, Left Differential TEF, Right Differential TEF, Left Differential LEF, Right Differential LEF, Left Stabilator, and Right Stabilator to put the wings level. That's a total of ten different control surfaces for the FCS to call on to correct a little roll.

 

The beauty, and the importance, of a modern FCS is in all those control surfaces it can call upon. In a Cessna, I move the flaps with the flap switch. I move the ailerons with left and right yoke, the elevators with up and down yoke. The rudder pedals are connected solely to the rudder. In a fighter aircraft, all those control surfaces are available to me regardless of input I am commanding, and the FCS uses them to make the plane's behaviour a perfect representation of what I want.

 

Let's try a more complicated example. I hear "TwoBreakRight!" over the radio, so I mash the stick right and push for MAX AB. The FCS notes my request for maximum right roll, looks at the sensors, and then moves all 10 control surfaces. What results is pure longitudinal axis roll. The FCS uses the control surfaces to cancel the adverse yaw, and to max out roll rate (the Hornet can roll way, way too fast if you ask it to). When I get to my 87°ish, I haul the stick from full right to full back. The FCS sees this, and cancels the roll, again using all the control surfaces to prevent adverse yaw. It then pushes the stabilators up, and we start to pitch in a circle. When we hit +7.5Gs, the FCS notes the limit, and stops commanding more Stabilator up. While this is happening, the engines have kicked into Min AB, and the igniters are firing. When both engines light into AB (2 seconds from MIL), the FCS opens the gate, and the ABs crank out to MAX (with the nozzles moving appropriately). It also plays with the other controls to keep the turn coordinated. Now that I'm established in a max-rate turn, speed begins to come off. As I bleed speed, the FCS calls on more Stab Up (the Hornet has a lot of stab). With more Stabilator comes a higher angle of attack, so the FCS begins to drop collective LEF and TEF (including the ailerons, which function like flaps here). This will continue until we've got max maneuvering collective controls. Above 22° AoA, the stick force will kick in, as the FCS politely asks if I actually want to be doing what I'm doing. With 35 pounds of force, I can continue to command full aft stick. At 35° AoA, we'll have maximum lift, and the departure tone will sound. The Hornet can go farther than this (55° AoA steady flight is possible, LEREXs are basically black magic), but we rarely want this. When I release the stick (manoeuvre complete, or I've Gloc'd (again)), the FCS pushes nose down until we get below 22° AoA, at which point it goes hunting for 1G again.

 

All those little bits and pieces let Fly-By-Wire aircraft pull unbelievable manoeuvres. It also lets a designer build aircraft without having to worry about inherent stability (can use control canards, for example). A well built FCS can make those hundreds of little stabilizing corrections every minute without fatiguing, allowing for these sorts of unconventional layouts.

 

I feel obliged to delve into all this because the Mirage 2000 is a non-traditional layout (although not inherently unstable). Part of what makes or breaks strange beasts such as the tailless delta Mirage is the FCS logic. Tailless delta aircraft have their strengths (lift!), and their weaknesses (low stab authority). A well designed FCS minimizes the weaknesses, and optimizes the strengths. I do not know enough about the Mirage 2000C's Flight Control System to even come close to passing judgement, but it would be lovely to see it well modelled.

[WildBillKelsoe]

to my understanding FBW maintains performance within acceptable envelope limitations. The best way to learn about FBW is reading A320 FBW modes of operation. For example Alpha Protect.

[Azrayen]

to my understanding FBW maintains performance within acceptable envelope limitations. The best way to learn about FBW is reading A320 FBW modes of operation. For example Alpha Protect.

 

You're right, but the protections (against getting out of the safe/proven/tested flight enveloppe) really are just a part of the FBW.

[Rotorhead]

Hi!

 

This is pretty old and well-known video, and of completely unrelated aircraft to boot, but it demonstrates what FBW can do prety nicely IMO. Look at the tail control surfaces every time she lifts off the deck:

 

 

Of course it's not the pilot pitching *down* on takeoff. The FBW system simply concludes that it's the best way of maintaining takeoff pitch in this unusual VTOL configuration. Also note how the control surfaces (and even the nozzle) work to cancel out any unwanted roll or yaw. Again, this is uncommanded by the pilot, he simply tells the plane to fly straight by holding the stick still, and the computer takes care of the rest.

[XeNoise]

It would mean that they would have to program a computer which would be analyzing the flight parametres and change the inputs to prevent hostile behaviour. Then analyze players inputs, compare them to the flight characteristics, modify the inputs a little bit... etc. etc. all this at least 50 times per second.

 

Sounds like a lot of work for the cpu, if not scripted well. Thanks a lot for claryfing.

[Azrayen]

Sounds like a lot of work for the cpu, if not scripted well. Thanks a lot for claryfing.

No worries. On the real aircraft, this is done with old technology chips (and militarized ones, so not the top-of-the-art from the times).

[Justin Case]

Nice first post Yeoman!

[Nerd1000]

No worries. On the real aircraft, this is done with old technology chips (and militarized ones, so not the top-of-the-art from the times).

 

I doubt that the devs would write an entire CPU emulator- they already have access to a real CPU that is far more capable, to wit the one running the game. All they need to do is write appropriate control code in the FM. The player isn't going to know the difference so long as the plane flies correctly.

[=4c=Nikola]

I doubt that the devs would write an entire CPU emulator- they already have access to a real CPU that is far more capable, to wit the one running the game. All they need to do is write appropriate control code in the FM. The player isn't going to know the difference so long as the plane flies correctly.

 

No one said they will make CPU emulator. The point is if an old chip can handle FBW instruction, then i5/i7 should not have a problem.

[Stealth_HR]

Technically, even getting a CPU like that working right isn't resource-intensive. A 300 MHz Pentium could emulate an entire Commodore 64 with its 1 MHz MOS 6510 and the video, sound, PLAs, CIAs and everything else. Even if they go down that route it would be a drop in the ocean. :D

[OnlyforDCS]

Thank you CptSmiley for another quick clarification. I was most gratified to learn that the M2000C is already flying without any scripted behavior and will be pre-purchasing as a result.

 

One suggestion though, PM Wags or one of the moderators to get the "3rd party developer" tag added to your forum nickname. :thumbup:

[Manuel_108]

Hey guys! I'm the flight model/dynamics coder for the M2000C...see my post here:

 

http://forums.eagle.ru/showpost.php?p=2477968&postcount=7

 

The FCS is coming along nicely and will be modeled with all available data and information. It took quite some time relearning my knowledge of control theory, filters, and controllers but it's looking really good right now. Trying to fly without the FCS takes quite a bit of stick work and discipline, especially at very low and high speeds as the FCS severely limits the control authority at very high speeds to make sure you can't rip the thing in half! Without the FCS, at very low speeds you are constantly making full throw adjustments to maintain a somewhat steady flight as you can't think or move as fast as the FCS can.

 

If we go by the Cooper-Harper Rating Scale...my initial estimate is that without FCS the rating would be about a 7-10 depending on the current task, speed, etc. With the FCS, it easily becomes 1-2. With that kind of control flying through valleys, low alt passes, turning combat, etc. at very high speed is an absolute joy. The craft just goes where you want it, when you want it and you get pin-point accuracy.

 

Hope that answers all the questions :)

 

Alright you convinced me! Preordered.