Anatoli-Kagari9

It's P-Factor Lixma, imo overdone in it's effects...

It's a "generalized" form of P-Factor. P-Factor is due to asymmetric lift / thrust due to the difference in prop blade relative AoA between the two ( left / right ) sectors of the imaginary circle created by the prop rotation, and differs, of course, depending on it being CW or CCW... particularly felt in taildraggers. This is present at any flight situation actually, whenever the relative wind is not aligned with the prop rotation axis, so the generalized case doesn't limit to the left / right sectors, but to any possible opposing sectors of the imaginary circle. A prop aircraft flying level in a sideslip will create P-Factor. Combinations of sideslip and "longitudinal AoA" will create even more interesting / complex variations on P-Factor. DCS Flight dynamics model does account for these effects, although I always tended to feel that it's somehow overdone... Now, in a stopped / "braked" prop, the kind of situation that easily becomes possible ( contrarily to real life ) with DCS prop warbirds, each blade is at it's own, fixed, angle to the relative wind, thus creating it's own lift not in phase with the other 3 ( there are 4 in this case ). If you think about it, starting at one of the blades, and admiting the huge prop in front of the P51d could actually play such a role, as DCS's flight dynamics model of that aircraft assumes to be possible, you'll find the reason for the swirl :-) Pick a pencil and a paper and try it :-) Ah! And there's yet another "asymmetry" in the P51... Even assuming your aileron and rudder trim tabs are set to neutral, the tail fin is canted 2º to port-side... There being enough stream / dynamic pressure, this will induce a sideslip, even without thrust... P.S.: Hey !!! You're a Lucky Guy living where you live! I want to go there soaring !!!!!!!

P-Factor has nothing to do with gyroscopic effects. Simply think of each stopped blade as a wing, generating lift ( and drag ) and try to figure out why that "swirling" movement is there... Is it right ? I don't think so - I think it's overdone.

It's supposed to be due to "P-Factor" from the stopped blades.

I tended to think like that, but, it's IAS that dictates the "stiffeness" / "efficiency", and at same IAS you should get the same feel...

If you: 1) Lock the tailwheel after rolling along the runways for a few feet / meter to make sure it aligns with the longitudinal axis; 2) You slowly advance the throttle to no more than 1,2 ATA; You will not need toe brakes - just rudder.

With less than 80% fuel, and a long runways and no bomb, I tended to use 1,2 ATA and flaps retracted. Trim at 1,5 nose heavy...

Yes, only in this case with that option set at neutral, zero ground adjustable trim tab, the ailerons still deflect, and even more weird - they only deflect a fixed amount, irrespective of dynamic pressure...

Of the 4 modules ( ww2 ) it is the most controverse for my liking...

Yep, I knew about that lua "trick" - I actually was the first to suggest, long ago here at the forums, for it to be used with the Fw-190 for rudder trimming :-) And yes, I was aware it was "frozen" some versions ago. None of the "editable" tab settings produce effects now.

And… it doesn't result from trimming ( even if the fixed aileron trim tabs were being set away from their neutral position ) because the diamond would then start moving with increasing dynamic pressure ( q )… which is NOT the case. It looks like a bug in the FM specification, or some "hidden" scripted feature ( ? )

Ok, thx for the feedback eekz!

If you fly 109s, you're on the Dark Side !

Happy Year Burning Skies Team!!! and thx a LOT for making your server available! One question: when I fly Axis, and shoot down a P51d or Spit, the message on the screen always says " Bf 109 dmaged / destroyed " ?

Well, just tested and there's something strange indeed… Created a quick mission based on the default "free fligth over Caucasus" where I start at 23000' and from there I enter a highspeed dive. The diamond never moves, stays at that slightly right position from the origin, so, should it be default aileron trim, it would start moving with increasing "q". The OP made an interesting observation! Bug ? Scripted effect ?

EDITED after testing it myself… Good Observation Lixma 06! 1) Are you sure your controls aren't playing tricks ? Nope ! Tested it too in my rig and it's the same... 2) Maybe the model was developed with a starboard roll trim set by default ? Doesn't look like so… because I tested in a dive and at increasing "q" the "diamond" never moves… Strange ?

They're actually trim tabs, ground adjustable. Don't have the links to the various sources, and the DCS manual "obliterates" it in the blue prints, but that's what they actually are, and were used to...

Thx for the video grafspee… It's interesting to notice: .) not even 1,2 is used for takeoff power, while in DCS most "pilots" slam the throttle or use 1,4... Most of the time I see it at maybe 1,1 ATA in the video.. .) SLIGHT rudder input. Maybe there was some significant starboard wind component, but the amount of rudder used to correct for the drift is minimal, maybe due to the conservative ATA used ? So, after watching the video I am even less surprised that with toe brakes only, aileron ( at near rotation speed and after airborne ) and correct pitch, the real thing can probably also be made to takeoff without rudder input. @msalama : yes there are also ground adjustable elevator trim tabs on left and right elevators. You can easily glimpse it in RW footage but even on ED's Web page for the Bf109 K-4 here: https://www.digitalcombatsimulator.com/en/products/planes/kurfurst/index.php for example on the third photo from the left in the first row...

Because otherwise we would probably be given the chance to also set the ground adjustable elevator trim tab that exists in the 109.

SORRY! Double post :-/

If you look carefully he maintains 1,2 ATA until around 150km/h, which means that enough propwash has already developed, by that time, for the rudder trim tab to start doing it's job. Since a few versions ago the 109, as well as the 190 if I'm not wrong ( ? ) also allow for the setting of their ground trim tabs for rudder and aileron - we don't know if the video was recorded when this additional aid was already available, and that ground adjustable trim tab set considerably starboard ? P.S.: Yet, I actually can't observe any rudder deflection even eventually induced by that rudder trim tab ... The only thing that the DCS 109 does not have, probably due to a limitation in it's core FDM, is the chance for multiple ( more than two ) control compensators contributing to a control surface. Probably a maximum of two are allowed, and since in the 109 and the 190 there are actually 3 "pitch control contributors" - elevator, stabilator and elevator trim tab - only the first two can work. In another combat flight simulator that allows for all of the three, we have a fixed, set by the developers and not adjustable by the user, elevator trim tab, and as power is added during takeoff, one can see the elevator deflect ( down ) compensating for the pitching up tendencies of the K-4 with a filled MW50 tank ( although the weight of the MW50 tank is probably also well compensated by the heavier engine ? ). Overall, I don't say DCS is perfect, of course it isn't for sure, but it is a very close approximation in many levels to the possible PC-based modelling of a prop aircraft, given the limitations imposed by a combat simulation game. Some years ago I discussed in a thread started by me the fact that there was a weird effect noticeable on the P51d when taking off with the first point of flaps, full power and a good deal of crosswind. Instead of turning upwind the aircraft, at the beginning of the takeoff run, showed a tendency to yaw downwind, and the downwind wing a slight tendency to want to come up, resulting in the virtual pilot having to use at that phase rudder into and aileron away from the wind ?????? How was such effect possible ? I found out later, and even sent Yo-Yo the document with the mathematical development, the "proof of concept", from an aerodynamics text book. The reason was, just as Yo-Yo pointed out on that thread, the fact that indeed the deflected propwash acting over the root of the downwind wing, and the downwind tail surfaces was enough to cause the additional lift, and associated drag as well as the asymmetric hit of tail surfaces, and the resulting downwind moments at that initial phase of the takeoff run... So, I tend to accept, with due imitations of course, most of the outcomes I get from DCS aircraft I own ( only those by ED/Belsimtek, until the Christen becomes available :-) )

Rudder wasn't used, but toe brakes - right toe brakes - were... That explains why it worked, I guess ? Actually, I have to say that DCS WW2 modules are the only reproductions of prop aircraft where I can feel the need to apply rudder, inflight, without having to look at the turn coordinator. In combat the need for rudder input differs from module to module, but when required, you feel it naturally, and not by "being told".... In other games, sometimes a whole lot of sideslip is being indicated by the turn coordinator, but without looking at it I wouldn't tell from the feedback of my virtual aircraft.

I'm with you! Wish you All a Very Happy 2019!

A friend who just installed DCS 2.5.4 beta and the K-4 is trying to run DCS but whenever he tries to start a mission the HD use grows to 100% and mission never starts. He can access the configuration menus, and even managed to activate the Bf109 k-4, but he is also receiving a popup screen saying: Authorization cancelled Multiplayer will not be available The following DLCs are not authorized and will be disabled: Bf 109 K-4 Any suggestions welcome!

Ordered !!! :-)