Thanks to the internet, I found some info on the Fox experiment, using vertical stabilizers above and below the thrust line, to show the effects of helical propwash, known as the propeller slip-stream.These experiments must be at least 40 or more years old, but I do remember them."Regarding nose-left-with-power, the following are commonly muttered... "P-Factor". "Torque".UGH. Time for "myth busters". Not P-Factor nor Torque cause the nose to go left. Long ago Duke Fox exploded this myth, but it won't go away...The reason the nose goes left when applying power at slow speeds is because the prop is causing a vortex spinning (as you look at the front of the plane) *counter* clockwise (ie the same direction the prop is spinning), and because of the slow speeds the vortex is still spinning as it hits the vertical tail (located mostly above the thrustline of the engine).Now, think about it... The vortex hits only the left side of the vertical stabilizer, pushing the tail to the Left (looking at the front of the plane) or the right (looking forward from the back of the plane. If you are the pilot, the nose goes left.Duke Fox did an experiment with an airplane that had a conventional vertical stab (nose left w/power) then on the *same airplane* moved the vertical stab BELOW the thrustline (guess what!) the nose now moved RIGHT with power (at slow speed).At cruising speed the airflow behind the prop is aligned with the ambient air at approximately four (4) feet aft of the prop. So, no "induced yaw".Northrop experience with contra-rotating props showed near-zero "induced yaw".Oh yeah I'm prepared for a s**tstorm of protest on this one...Paul P.Northrop Grumman (retired)US Navy (aviator, retired)C-182, Colt ownerThe above = "relevant" although I'm the first to admit "expert in nothing".

>If MSFS has never modeled the "spiral slipstream" (helical>propwash), and only P-factor, then some designer has the terms>messed up! :D >Larry,take your favorite prop for a ride (the SF260 will do the job, but you could as well use RealAir's Spit either ported to fsx or in fs9...)...Now, from real life you know that slipstream/helical effects will affect you the moment you make considerable power adjustments even at cruise. Have you noticed that as soon as your spitfire, for instance, is flying level, making (even unrealisticaly abrupt!) power changes doesn't show any hint of a yaw moment? Why? Because in MSFS only p-factor plays it's role, and in order to pump it in while airborne you'll have to use high AoA and slow speeds... Propwash effects on the tail surfaces are also missing, but I believe these only have to do with the eficiency of the surfaces increasing as the airflow increases/decreases, not in the helical effect sense...In ELITE, unless you're flying a twin, specially if the SenecaV with counter-rotating props, you'll have to use your right foot all the way down the takeof run and initial climbout... Ah! XPlane (we both use it, from time to time ;-) ) these effects are IMHO erroneously concentrated on a roll moment - completely unrealistic as far as I'm concerned... Not to talk about the fact that the the ball in the turn coordinator doesn't behave anywhere near reallity... It appears that this "magic" ball hasn't been correctly implemented on anything I've tried so far other than ELITE, ALSIM or CondorSoaring :-)

>take your favorite prop for a ride (the SF260 will do the job,>but you could as well use RealAir's Spit either ported to fsx>or in fs9...)...>>Now, from real life you know that slipstream/helical effects>will affect you the moment you make considerable power>adjustments even at cruise. Have you noticed that as soon as>your spitfire, for instance, is flying level, making (even>unrealisticaly abrupt!) power changes doesn't show any hint of>a yaw moment? Why? Because in MSFS only p-factor plays it's>role, and in order to pump it in while airborne you'll have to>use high AoA and slow speeds... >I don't think we're going to agree here. Taking a Van's RV for instance; on the takeoff roll, you get that pushing back in the seat effect, and need some good right foot on the rudder to maintain runway centerline.The engine mount is canted to the right, and many, especially the new models have the vertical stabilizer mounted with a slight offset. Both are done, to correct for slip-stream in cruise. In addition, you might still need a hand adjustable trim tab or wedge on the rudder, to keep the "ball" centered in cruise.At cruise speeds. I don't feel that power adjustments have anywhere near the effect for requiring rudder, as the takeoff roll does.I did experiment with the new FSX modeled RealAir SF260, as a ported model of the Spit wouldn't do much justice for FSX anyway. BTW, RealAir is working on a revised Spitfire for FSX!At cruise speed, the SF260 did in fact, yaw to the left when adding more power. It also does well in pitch with power adjustments and trim left as is. As to MSFS simulating airflow over the tail surfaces such as the elevator, it does just fine in flight. It's when still on the ground, that these effects were removed in newer versions.I'll stick to my original thinking, that CFS2, as well as MSFS around that time, was quite effective in simulating slip-stream. And it still does today, but not as well. If it didn't, how can you account for the left drift on the takeoff roll?L.Adamson

>>>>I don't believe msfs ever modelled helical effects. It is>>limited to p-factor (which some aircraft designers tend to>>exagerate in order to give some hint of helical effect ...).>>>>>>>If MSFS has never modeled the "spiral slipstream" (helical>propwash), and only P-factor, then some designer has the terms>messed up! :D >........>L.Adamson Yes, prop helical effect was modeled until FS9. P-Factor wasn't. I had to set rudder trim a bit to the right to keep the ball centered in an SEL climb. Incidentally, P-Factor also applies to Yaw, not just prop AoA. But, the later is more obvious, one doesn't generally yaw by 15 degrees. Except in a slip. MS appears to have gotten the P-Factor working in FS9 and FSX, but killed the helical effect. As you say, the later is considerably more important. I wonder if they even know the differences in these effects. Ron

>>>>MS appears to have gotten the P-Factor working in FS9 and FSX, but killed the helical effect. As you say, the later is considerably more important.I wonder if they even know the differences in these effects.<<<

Wow.Of course the "flight model is flawed," and it will always be. There is no comparsion, obviously, between flying a real 182 and Flight Simulator. There is simply no way to model flight on a PC with a high level of realism, the developers do the best they can with a lot of compromises. As I have stated, this is why I prefer to fly the add on especially payware a/c, because they are so much better than the default planes, because the developers can put so much more time into modeling the airplane, rather than having to also model the whole world around it. I think given the limitations of the hardware they have always done a wonderful job.As far as realsim in simulator, it takes the mechanized full motion ones for the "real flight model." Years ago, I got some time in a Flight Safety, Inc DC-9 simulator, and crashed. When you crash one of those, you know it! :D

I'm a little confused, if there is lift on the elevator, but not the horizontal stabilizer, does that mean lift is less than it should be, so we are overcompensating by adding more elevator than we should be?Are you saying lift on the horizontal stabilizer should come alive BEFORE the wing produces lift? It would seem to me they would both produce lift at the same time, or is it airfoil/aoa that is at issue here, iow, the HS has a different airfoil/aoa so produces lift earlier than the wing? I guess I always assumed that the tail got extra lift first because a. the tail is lighter b. because the elevator activates the tail first.Are you saying that FS ignores airflow over the horizontal stabilizer and then switches on its affect when the wing is producing lift? Why?I assume this is not an issue for all moving tailplanes, i.e. piper cherokee, F100 super sabre, etc.?Thomas[a href=http://www.flyingscool.com] http://www.flyingscool.com/images/Signature.jpg [/a]I like using VC's :-)N15802 KASH '73 Piper Cherokee Challenger 180

So is that why they took it out, because it caused ground loops too easily?Seems like they could still leave it in with a switch and allow developers to turn it on if they want it.Thomas[a href=http://www.flyingscool.com] http://www.flyingscool.com/images/Signature.jpg [/a]I like using VC's :-)N15802 KASH '73 Piper Cherokee Challenger 180

>I'm a little confused, if there is lift on the elevator, but>not the horizontal stabilizer, does that mean lift is less>than it should be, so we are overcompensating by adding more>elevator than we should be? Technically, Lift, whether for the wing or the horiz stabilizer is a 'slope', and considered a 'Stability Derivative'. The FS Horiz Stab only displays the effect of its Lift if the stab is set at an angle. It's effect on stabilizing Pitch is set in TBL 473: Pitch Moment vs AoA. Which is a direct effect of that 'lift'. Actually, an aerodynamic surface with flaps, elevator, rudder, etc. should be considered as one unit, with the control devices modifying the 'Lift' and drag. For example, adding flaps in FS simply moves the Lift Curve up. The elevator changes the lift of the H. Stab >Are you saying lift on the horizontal stabilizer should come>alive BEFORE the wing produces lift? It would seem to me they>would both produce lift at the same time, .... Right, if there were no prop wash. Prop wash should affect the horiz stab + elevator combination. Since AoA is high when the tail wheel is on the ground, the Horiz Stab should come up when the engine is gunned. Even with the elevator neutral. I don't know if MSFS taildraggers ever did that, even when the prop wash effects were active. The prop blast might even bring the tail up before a taildragger is moving at 1 kt. Same goes for the rudder, one can steer rapidly by pushing down a rudder pedal and gunning the engine for a second. I don't think I've made this clear in Aired.ini. The original discoveries referred to 'prop on rudder' and 'prop on elevator'. There are two for each surface, one changed the effect on how much the prop blast increased elevator and rudder control, the other affected how much the blast increased the pitch and yaw damping. The latter two are dependent on the total vertical and horizontal stabilizer surfaces. That is, they include the control surfaces. The numerical values are not well understood, though I did add likely formulas in the Info. Regardless they have been adjusted experimentally, starting from the default values. At least when they had an effect. :)> or is it airfoil/aoa>that is at issue here, iow, the HS has a different airfoil/aoa>so produces lift earlier than the wing? I guess I always>assumed that the tail got extra lift first because a. the tail>is lighter b. because the elevator activates the tail first. The wing normally has camber, and generates lift at zero AoA. The wing's Lift Curve is set in TBL 403. The horiz stab may or many not have camber. As far as FS goes, it doesn't and any zero AoA lift is set in the 'horiz stab deflection' line in aircraft.cfg. However, that value really is not the physical angle of the Horiz Stab. Downwash from the wing changes the angle the air flows over the horiz stab. If it is really at zero incidence, it sees a negative AoA as far as the air flowing over it goes. Thus, the appropriate defection to set for MSFS is negative (or, the direction that forces the tail down). OTOH, if the real tail has camber, than that negative value would decrease, perhaps to zero or a small positive value. I don't worry about tail camber and downwash, I just set the horiz stab deflection so the tail lift is -5% to -10% of the wing lift at cruise speeds. That is the range real AC fly at. Herve' Sors AFSD displays Wing, Tail, and Elevator Lift, so I can use it to set the H.S. deflection. Pitch stability is also improved with negative tail lift, in fact, that's the main reason an AC is trimmed for a down force on the tail.>Are you saying that FS ignores airflow over the horizontal>stabilizer and then switches on its affect when the wing is>producing lift? Why? As far as I can see, the increase in air flow over the tail due to the prop is no longer modeled in MSFS. However, other effects are certainly modeled, though not necessarily directly. As I mentioned above, the effect of the H.S. on pitch stability is set in 'Cm_alpha'. While the vertical tail affects Yaw Moments and Side Forces. There is only one 'area' in the MSFS model. That of the wing. All other effects of surface areas are set by their effects, not directly by the areas. This is the standard approach to flight models which are based on aerodynamic parameters, rather than those which try to model the flight dynamics starting with the various areas (such as X-Plane). >I assume this is not an issue for all moving tailplanes, i.e.>piper cherokee, F100 super sabre, etc.?>Thomas>N15802 KASH '73 Piper Cherokee Challenger 180 In those cases I set Cl_dh equal to Cl_de (H.S. and Elevator are equal). I put a couple of hundred hours on a Cherokee 140 near 40 years ago. I didn't pay much attention to the 'stabilator' etc. at that time. Other than to check that it was still attached in my preflight inspection.Ron

>>>>Are you saying that FS ignores airflow over the horizontal stabilizer and then switches on its affect when the wing is producing lift? Why?<<<

>>>>As far as I can see, the increase in air flow over the tail due to the prop is no longer modeled in MSFS.<<<

Curiously, while I was browsing accross X-Plane.com I found the lattest additions to the upcoming 8.60 release:"Helo flight-model fixed: There was a problem with tail-rotor effectiveness in beta-7.Also, the propwash should be improved for airplanes and helos across the board... this will effect control effectiveness of prop airplanes on the ground as well, since the elevators and rudders are in propwash"So, again, while X-Plane evolves, MSFS steps-back....

>>>>>Are you saying that FS ignores airflow over the>horizontal stabilizer and then switches on its affect when the>wing is producing lift? Why?<<<<>>For a single engine aircraft with centerline thrust, airflow>from the prop has no effect on the horizontal>stabilizer. As far as the reason for that is concerned: I>have no idea at all why they did it that way Thomas. >Douglas Oops, and I said the tail should lift from the prop wash due to the horiz stab. In the simple case it should only lift if the stab is at an angle, or has camber. Since the prop blast is pretty much at the same AoA as the stabilizer is. However the prop blast is deflected by the ground, thus it would force the tail up some in a taildragger. Something I would not expect to be modeled. Nor is Ground Effect modeled for the H. Stab. Ron

Christian you hit on allot of things that's been talked about in these forums for years. We were hoping Aces would address these underlying elements in FSX but sadly that didn't happen. I have to disagree with you on the turn slip as others have pointed out, different planes respond uniquely in turns. A Cessna 152 (which I trained in) for example needs more rudder than a Warrier. "In real life, you can put on a toe brake, push the pedal forward, and pivot the plane around with the wheel not even moving."I think Bill Leaming (or someone on the FSX beta team I've talked to) wrote that they were trying to get Aces to do better concerning ground handling but it didn't happen for all axes in the final release of FSX. This defect has been known for some time in all versions of FS. "And although turbulence seems a little better, it's far from reality, and I'm just referencing the physical aspects (obviously not even most full motion sims can feel like a good gusty day). I've had a good wind shear make me lose 20 feet, or make my wing drop 25 degrees. I don't expect flight sim to ever match this aspect that closely, but in real life fighting wind kind of feels like riding out some big waves, and I think flight sim could do that."This should have been fixed and/or addressed in FSX, GREAT POINT. At this late stage of the game in FS development there's really no more excuses for Aces."And after flying all over my state, I can definitely say the terrain is far from 'as real as it gets'. Even Megascenery New York doesn't really look like Connecticut from the air. This isn't flight sim's fault- just something I have noticed."Who's fault is it then??? FSX's terrain/landclass is better in the US than FS9 but the rest of the world needs help. All this could have been addressed fully in FSX. I will say to get a better look to Flight Simulator we would need a new generation engine much like what we saw from FS98 to FS2000. This may happen for FS12.All in all post like this prove there was so much more that should have been done for FSX than what we got. To much underlying enhancements needed to be addressed. All Aces focused on was improving the look of this existing engine. There's a few bells and whistles here and there but for the work this community has to put in to convert to this new version, so much more should have been looked at (Bill Leaming who wonders why I continue to harp on this fact).

"Of course the "flight model is flawed," and it will always be."There's always room for improvement and the motion of turbulence can be simulated (the only thing that can never be simulated is the feeling of flight on the body)...