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blue six
September 22nd, 2011, 12:32
I'm attempting to model in FSX the effect of a V stab installed at a fixed (non-zero) angle of incidence to the fuselage, as found on the Hawker Hurricane or Curtiss P-40 for example. I can't spot any entries in the CFG or .air file directly relating to this. The effect I'm looking for is a progressive variation in directional trim with changes in airspeed. If anyone out there has accomplished this or has any thoughts as to a solution, I'd much appreciate any guidance you could offer. Thanks.

blue six

Dev One
September 22nd, 2011, 23:57
'p_factor_on_yaw=1.0' in the .cfg appears to be the only variable associated with engine/prop torque effect. Its also associated with the prop rotation direction.
HTH
Keith

blue six
September 23rd, 2011, 11:47
Thanks Dev One, I'm not entirely sure that's what I'm after, but I'll give it a try. I was hoping to find a yaw-related entry in the .cfg or .air file that's strictly a function of airspeed, not thrust/torque. For example, in a dive at a fixed throttle setting, I'd like the yaw moment to build progressively, as airspeed rises.

blue six

Dev One
September 23rd, 2011, 23:51
There are possibly a couple of things you could experiment with in the .air file:
1206 Vertical stab efficiency factor
1536 Cn_dr Rudder control vs AoA
1544 Yaw derivatives.

Not tried any of the above with relation to your query, but I think if one has some rudder trim applied then 1536 might be the one to change.
You might also be able to find a rudder control vs mach or airspeed. [edit] After thought; this might be the one - Just found it 519 Rudder deflection factor vs Q!
HTH
Keith

bstolle
September 24th, 2011, 06:41
I have experienced the same problem with the Bf-109K and so far haven't found any solution.....still thinking about a solution....I'll let you know ASAP

fliger747
September 24th, 2011, 11:14
The incidence in the verticle stab is intended to somewhat compensate for the P-factor range. The Corsair amongst others had this feature. There is not a direct way to impliment this in FS, however one might be able to get a ballance by offseting the CG laterally and adjusting the rudder roll moment. Haven't tried this as yet though the F4U-1A FDE that I did for the A2A/Milviz one does use the correct real world rudder, aileron and pitch values for carrier takeoff.

Cheers: Tom

blue six
September 25th, 2011, 12:27
Thanks fliger747, bstolle and Dev One - you've all given me some interesting avenues to explore. I'll keep grinding away at it, and will update the forum if I can come up with a change or combination of changes that gives me a reasonable approximation of the effect of an offset fin, with no adverse consequences. Appreciate your time taken to respond.

blue six

fliger747
September 28th, 2011, 10:30
Just another thought: One can offset the thrust line slightly laterally, which would also have the same effect.

Cheers: T

blue six
September 30th, 2011, 18:19
Thanks fliger747, offsetting the thrust axis laterally sounds to be an easier proposition than moving the cg. I was hoping initially for a solution which would generate a yaw moment varying purely as a function of airspeed (squared), independent of power setting. That doesn't seem to be easily achievable within FSX. Looking into it further, the primary thinking behind the offset fin seems to have been compensating for slipstream effects, so perhaps it's not such a bad thing if thrust also has an influence. I'll give this latest suggestion a try, and let you know how it goes.

On a possibly related note, could you perhaps explain the influence of the "*!Propwash Related?" term in the Primary Aero section of the .air file? Would this be something I could use to my advantage in this endeavour?

Best wishes,

blue six

fliger747
September 30th, 2011, 19:08
The only other idea that comes to mind would to be to make a gauge to offset the rudder trim from the advertised value.

Cheers: T

Dev One
September 30th, 2011, 23:27
This entry can also be called 'downwash related' - if one refers to the Freimuth FS9 version. Only aircraft possibly uses any value other than '0' appears to be the Extra 300.
Keith

blue six
October 4th, 2011, 10:19
Thanks again, fliger747 and Dev One.

For fliger747, I think that's the best solution yet; something that will cause the rudder trim to take up a slightly non-streamlined neutral position, giving a built-in bias in yaw. I'm not sure exactly how to accomplish this, but will look into it further.

For Dev One, thanks. I have several payware WWII fighter add-on FSX aircraft that use 200,000 for this propwash or downwash related term - I'll try substituting different values here and see if I can detect any changes in handling in the sim.

blue six

Dev One
October 5th, 2011, 10:29
I've not tried any experiments for this question, but did notice yesterday when testing my current project that it still yaws to the right with power on or on the glide slope power off, & thats with a p factor on yaw of 0.5. So hope you have more luck!
Keith

blue six
November 29th, 2011, 10:07
Not a lot of progress to report, unfortunately. Offsetting the point of thrust application laterally didn't give me the effect I was hoping for. And radical changes to the "!propwash related?" term in the airfile seemed to indicate it has no effect on the yaw due to slipstream, but does affect the amount by which control surface effectiveness increases when they are subject to propwash.

Getting back to slipstream, here's the question perhaps I should have asked first: is there a way to adjust the strength of the slipstream effect in FSX, without tampering with engine or propeller parameters? It seems to me that the slipstream effect dies off very quickly as airspeed rises; as such, perhaps there's not much point in trying to simulate the effect of an offset fin, which would balance off yaw due to slipsteam, in the cruise condition. By the time you achieve cruise, yaw due to slipstream is basically undetectable (the FSX turn and bank indicator doesn't really help matters - the ball seems very underdamped).

Any thoughts on this? Is the slipstream effect "hard-wired" or can it be modulated without disturbing engine and prop characteristics, or tampering with yaw stability or MOI?

blue six

Dev One
November 29th, 2011, 11:04
I've been experimenting with getting yaw when airborne on a twin engined a/c ( as opposed to yaw during take-off with a tail dragger) & the only way I have so far been able to achieve the effect is to have 'hidden' some fuel in one of the wing tanks ( not much; 3 gallons US is sufficient) & this has a variable effect depending on engine power & airspeed - worth a try on your aircraft?

I wanted it so that the pilot has to use the rudder trim in S+L flight. It has a very noticable effect when changing from S+L power on flight to power off glide.

Keith

fliger747
November 30th, 2011, 00:44
Another way to do that is to (1) offset the CG to one side (2) offset the thrust line laterally.

T

Dev One
November 30th, 2011, 08:06
That sounds a better idea - it would stop the wing down tendency & possibly add less drag? Will try later on.
Keith