Trims and Forcefeedback
 

I am not sure if this has already been answered, but I have a question about the trim functions in BOB.

Currently in IL2, trims affect your virtual stick and the flight surfaces - they don't move your force feedback stick - the stick only gets stiff/sloppy according to airspeed. As I understand it, real life trims physically move your stick.

Will this kind of trimming be implemented in BOB?

Also, is there a chance that DT can implement this feature to IL2 in the future?

Thanks.

Just to be clear, when you trim a real aircraft, you usually put it in the attitude you want and then trim until pressure is taken off the stick/pedals. That's what makes trimming a real aircraft easier than trimming a virtual aircraft.

As to how it is implemented on IL-2, I can't answer that. I have never fond FFB to work well in any sim and have given up on it until someone comes up with a good solution.

Splitter

Right, my understanding is that when the pressure is taken off, the stick stays at the same place, not returning to the center - this is not the behavior on IL2 with force feedback sticks, the stick returns to center regardless of the trim settings.

Seems you're right. And it would prevent the trim-on-an-axis-cheat (which I use as well :cool:)

It's a bit less of an issue now that DT has implemented structural damage by G force at 4.10. Turning faster than spec should theoretically penalize your performance.

Theoretically, yes.

One of the things FF in IL2 doesn't do but FSX does is oscillation and/or gust feedback into the stick. I hated it in FSX, until I just got the insight that it is realistic. I'm unaware of any rudder FF systems (anyway my MS FF2 doesn't have it).

Gust feedback through the controls (in turbulence, I assume)? I can't really recall noticing that all that much (I've been flying since 1974). What I have noticed about IL2 and turbulence is that it seems to blow the tail about changing the dirction the nose is pointed (weathervaning) rather than moving the aircraft vertically/laterally with less direction variation that I'm used to in RL.

I'm not sure if stick position after trim is a big deal for me.

Great, what do you fly btw? is there any difference in feel between purely mechanical and servo-boosted/hydraulic controls, besides the forces?

I think this is a well known fact nowadays and various sims feature it. Helicopter trim mechanisms are different but the example that readily pops to mind is Black Shark, where you trim by setting the stick where you want it (ie, selecting an attitude for the aircraft) and pressing the trim button. This sets the default stick position to where it was when you pressed the trim button, which effectively lets you fly without applying constant pressure.

If you have a force feedback stick, its position matches the position of the in-game/virtual stick. If you don't have one though, it still works this way by defaulting the centered position of your spring-loaded stick to the off-center position of the virtual one.

I think the difference lies in the fact that in the helicopter the trim mechanism applies force to the collective to keep it at a certain position, which then transfers to the stick through the linkages.

In an aircraft however, trim moves the trim tabs which then move the control surface through aerodynamic interaction and then that movement is transferred to the stick through the control linkages.

In the end the result is pretty much similar, it's just the "how" that changes.

Also, the trim oscillations you guys mentioned are interesting. I don't have any real flying experience, just comparing my sims and FSX which i fly on a friend's PC when i visit him. Since most 3rd party payware aircraft for FSX are so much more detailed than the stock models but also feature a lot of differences between them in modelling (depending on developer), i can't be sure how pronounced the effect should be.

However, it's interesting that in certain airframes it's more apparent than in others. So, i might trim nose down for cruise after i reach my selected altitude, but after a while the aircraft still wants to climb because it has picked up speed as a result my down-trimming, which necessitates further nose down trim on my part to keep it level. However, if i dial in the necessary trim in one motion, the resulting down pitch from climb to cruise is so big that i can't pick up speed fast enough to keep it level. This forces me to trim in "stages", dialing in a bit of trim to zero the vertical speed indicator and adjusting as necessary a few more times until it settles in.

To make all this easier to manage, i stopped thinking of trim as a way to keep my nose at a certain angle to the horizon and also stopped thinking that nose up=climb all the time. In fact, there are cases where you can be nose up and descending, or cruising level at a certain altitude and yet have a nose down attitude.

This nose down attitude is more pronounced on aircraft that cruise "on the step" as the saying goes: it's better to climb at X+500 feet of altitude and descent to your chosen X altitude, trimming as you go, than climb to X altitude and level off straight away.
In FSX i've seen it on a B17 and a Boeing Stratocruiser (both 3rd party payware aircraft). This is also evident in IL2, anyone who flies the Fw190 knows that it can cruise faster this way at the same power settings.

In the end, what makes the difference in the whole process is the airspeed you maintain and the power you run your engines at.

Wing design and angle in relation to the fuselage all have a factor in this, but generally speaking i've found that the best way to think of trim is that it tells the aircraft to maintain a certain airspeed. If the aircraft can maintain this airspeed at the power settings it's currently running, then it will fly level. If it can't reach that airspeed it will nose down to achieve it. Finally, if it exceeds this airspeed with the chosen power settings it will climb to bleed off some airspeed and reach that value.

It's almost like the opposite of a car: when going uphill you apply more throttle than when going downhill.
In an aircraft where you can move in 3 dimensions, the reverse thing happens: apply enough throttle and the aircraft will make its own imaginary "hill" to climb.

Anyway, i'll leave this here since my excitement about the mechanical intricacies of aircraft is already getting my side-tracked from the topic into analogies and trim mentality discussions :-P

I think that since various modern sims have a more true to life representation of the transfer of aerodynamic forces from the control surfaces to the stick (DCS, RoF, FSX, etc), it will probably be something that SoW has paid attention to as well.

In real world, there’s also the “backside of the power curve”. That is, under a certain speed (usually 1.3 times the power off stall speed), fly slower requires more power, until power on stall is reached.

I understand that recreate correct trim behaviour is not easy in a sim.
For example, attitude should change noticeably with flaps extension, with nose going down for a steeper glide path.
For trimming, I believe that the best solution would be to link it to speed, making the plane seeking to keep it, descending, climbing or maintaining speed with power variations without any other control input. That speed should appear as momentary text with power setting.
Something like:
Power: 75%
Trim speed 220 km/h.
The beauty of this solution would be that you’ll end up to use realistically the trim to obtain the speed you want: best climb angle speed, best rate of climb speed, best endurance cruise, best range cruise, all of these speed being listed in any aircraft pilot’s manual.

Perhaps we should suggest this solution for Team Daidalos’ consideration...

Trim can vary by weight, but much more significantly by CG and speed. For best speed you want to be loaded at the aft limit because the stabilizer produces less downforce* at that loading than at the forward limit (the stab always produces downforce in a normally loaded conventional aircraft). Some aircraft can behave oddly concerning trim, for example the 190 which has a single trim setting (based on a given CG) for all speeds above 260mph. Some aircraft nose up sharply when flaps are lowered - some don't. That would be a function of the stabilizer size and distance from the wing and the type of flaps. This, of course, affects trim changes during flap operation. IL2 handles aircraft trim alright in a generic sort of way but my feeling flying the different aircraft is they all seem to be variations of a single flight model. I'm sure that's rather unavoidable. Rather than scoping in on the intricacies of trim I would go after much bigger fish by, first and way-up-front-and-foremost, coming up with a halfway realistic stall. The current IL2 stall makes the plane feel like the CG jumps toward the tail about eight feet during stall making spins universally almost inevitable and difficult (if not impossible) to recover from, regardless of real world performance.




*lift and downforce are drag and the more downforce a stab applies, due to the CG moving forward, the more drag it has and the more weight the wing has to carry - more lift - more drag. A typical figure for stab downforce carried by the wing is 10%. (This is why canards are more efficient - no downforce.)

This is true in theory, but at the price of a reduced stability. P51 emptied rear tank before attempting any aerobatic manoeuvre.

This is true for the immediate reaction of plane (more common in high wing design). Fact remains that you must re-trim – PRESTO – nose down and maintain a steeper glide.

For me it is a very interesting subject because I am in the process of designing my own stick with force feed back .

I successfully ,so far, am receiving the X and Y componant from IL2 .(I did not check if it is proportional to air speed or to the square of it)
(I for now , as a test ,am ONLY modulating the intensity of an LED (PWM) with this signal)

It is now left to me the enjoying work to drive the Stick.
I can do it anyway that would be the closest to reality
As it is some 35 years that I have n' t used a real stick I have forgotten what it is like and am open to any suggestion.....
It would be interesting to get the designing team of BOB to answer this question
I have asked if BOB will handle FFB like IL2 but have RX no answer so far
I must be swamped by the COLOUR of the EXHAUST gas FLAMES actual topic

Looking forward to a continued interest in THIS topic

g b

Again, different aircraft behave ... differently. The flaps by themselves cause a severe nose down force that is countered by the downwash behind the wing (created by the flaps) landing on the stab. The size of the stab and its position in the downwash are major factors in trim settings. I've flown planes that I've trimmed in the downwind leg and not had to retrim before touchdown. As the planes slowed on base and final rather than retrim noseup I simply fed the flaps down and maintained neutral trim. Not all planes are like this.

ha - my first response got caught in the quote ...

The P51 was just an example. Stability is reduced while the cg goes aft and, beyond aft limit, we cannot talk anymore of reducing stability but of increasing instability. All of this to say that playing with cg for obtaining more speed is something acceptable for racing, but I doubt it can be a wise choice – or a realistic one – in an operational plane loaded for war.






You’re right, different planes behave differently, and I also flew with planes that showed pitch-up at flaps lowering. But generally speaking, the effect of flaps in landing position is to generate more drag than lift and – again, generally speaking – planes steepen their approach with flaps down.

Returning on topic, trim is presently simulated with moderate realism, and this is perfectly understandable and acceptable. Any attempt to simulate it with force feedback should try to simulate stick force variation with trim changes. It's no easy task, and I sincerely wish good look to anyone attempting it!

I'm looking at building another stick from scratch and the thought I had on trim was to have a means of rotating the pot or hall sensor body so that the center point could be moved in game so setting trim via the hardware rather than software. This may give a more realistic solution? But obviously no good if you are using a bought stick unless you can modify it in some way although I think at least one stick, not sure which one, has trim wheels but again don't know if they control trim via hardware or software.

moved from wrong place

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For me it is a very interesting subject because I am in the process of designing my own stick with force feed back .

I successfully ,so far, am receiving the X and Y componant from IL2 .(I did not check if it is proportional to air speed or to the square of it)
(I for now , as a test ,am ONLY modulating the intensity of an LED (PWM) with this signal)

It is now left to me the enjoying work to drive the Stick.
I can do it anyway that would be the closest to reality
As it is some 35 years that I have n' t used a real stick I have forgotten what it is like and am open to any suggestion.....
It would be interesting to get the designing team of BOB to answer this question
I have asked if BOB will handle FFB like IL2 but have RX no answer so far
I must be swamped by the COLOUR of the EXHAUST gas FLAMES actual topic

Looking forward to a continued interest in THIS topic

g b