X-Plane vs. FSX

[N1G 88]

So just for the record here, going back to previous versions of XP, how long has this slipstream inaccuracy existed? If this is true, and the behaviour you are seeing is dead wrong, and we have active developers, why then has this not been addressed?1. They are not experiencing the same thing you are.2. They believe the models behave accurately3. They are aware of it but for some reason have not corrected it, or it is hardcoded and cannot be change, or it is too much work and not enough people have complained4. The original developer is not there anymore and the new developers do not know how.5. Correcting it would not increase sales.6. The developers including Austin, like the way it behaves and will leave it as is.Hmmm, interesting why this has not been corrected or even been mentioned by the developers as an issue. (Maybe the have talked about it but I am not sure).Bob

Edited January 16, 2012 by N1G

[60North 120]

I mostly make jet's so I'm not expert on the prop model.However, you are making a whole lot of assumptions and base a lot of conclusions on them.Thats not how it works. X-Plane is a scientific sim so DOCUMENT your claims;1. Document the real effect in question.2. Document this effect is not present in XP.At this point I can't see you have done any of those, so you don't have a case.I'm not saying you are wrong but, but just throwing a few claims out there isn't good enough - sorry.M

[jcomm 5,924]

Hi M,referring to the bank instead of yaw subject, I can't really give you much data, although you can extract it from the various output forms XPlane allows us to use, anyway, this is a simple basic feature that we learn from RL experience flying prop aircraft. Austin, being a RL pilot as well, and having flown prop aircraft knows about it for sure. He certainly knows that when, say on a P180, his Cirrus, a C172, etc... he throttles up on takeoff/climb power, the yaw will be practicaly the ONLY effect he will feel from the slipstream of the prop on the tail fin/rudder. Rudder input is used to counteract and on some airplanes it can even become tiresome - say a Rallye or a Robin, where you have to keep quite a good amount of right foot to counter slipstream yaw effects.Xplane's prop airplanes bank instead. The worst part of this problem is that, when cruising, straight and level, bank tendency opposite prop rotation is present as well, and if you reduce power you'll get a right bank tendency (for a clockwise rotating prop as seen from the cockpit).This is also present on twins, unless you make them counter-rotating.For a scientific statement I could use fancy mathematics, with rotationals, to formalize the concept of slipstream, or a softer approach. Google for "prop slipstream". i.e.:http://en.wikipedia....iral_slipstreamAnother good (rather scientific) source of information is http://www.av8n.com/how/detailed here http://www.av8n.com/...elical-propwashBut then, there is something here too:http://www.av8n.com/...-propeller-dragUps! Hum! Ouch! BFC!Soooooo.... maybe I should really try to play around with asymmetric incidence on x-plane.... :sad:Regarding weather modelling and the fact that Xplane's atmosphere is allways an ISA one, with fixed temperature and pressure lapse rates, also RL flying experience talks for itself, but I can understand xplane's simplification. Anyway, when we say that "Going from High to Low, Watch Out Bellow" is satisfied on the pressure side by almost all flight simulators, so that when you travel using QNH and transit from a higher pressure region to a lower pression one, your airplane will be commanded (if flying on AP) to descend, unless you take the correct regional QNH settings. Flying on QNE the same applies.Unfortunately, no simulator, at least that I know, will model the temperature side of the sentence. If you fly from a region where you have a given pressure (p1) at surface and say, at 3000' AGL (p2), and arrive at another, colder, region, with the exact same pressure at ground level (p1) (you can even consider that the two regions have more or less the same altitude relative to mean sea level), the pressure level (p2) that you were intercepting at 3000' will now be lower, because the air is denser there.On both situations, flying an aircraft from high to low, relative to pressure or temperature, will represent danger o CFIT. For those who fly on mountains it is typical to say - mountains look higher in the Winter...MSFS includes the opportunity of defining temperature layers, allowing even for inversions, even if it doesn't really make any big use of it, yet there is no way to define pressure layers... XPlane not even allows to define temperature layers, and it would be great specially when using RW meteo data.

I mostly make jet's so I'm not expert on the prop model.However, you are making a whole lot of assumptions and base a lot of conclusions on them.Thats not how it works. X-Plane is a scientific sim so DOCUMENT your claims;1. Document the real effect in question.2. Document this effect is not present in XP.At this point I can't see you have done any of those, so you don't have a case.I'm not saying you are wrong but, but just throwing a few claims out there isn't good enough - sorry.M

Edited January 17, 2012 by jcomm

[Pascal_LSGC 298]

The worst part of this problem is that, when cruising, straight and level, bank tendency opposite prop rotation is present as well, and if you reduce power you'll get a right bank tendency (for a clockwise rotating prop as seen from the cockpit).

First, I'm not a rw pilot.Do you mean that torque caused by props has no effect at all in real life ! ??I can understand its compensated for a defined amount of power and airspeed. But then, when you reduce power, you should feel the counter effect !

[LAdamson 240]

First, I'm not a rw pilot.Do you mean that torque caused by props has no effect at all in real life ! ??I can understand its compensated for a defined amount of power and airspeed. But then, when you reduce power, you should feel the counter effect !

On my Van's RV (which Gorem doesn't care to hear about, although it has much to do with real life flight)..............Torque and most likely P-factor is evident sometimes on the takeoff roll, and very noticeable on a touch and go. It's because the power to weight ratio is much more than a Cessna 172, and the wings are short. During these moments, I'm using right aileron to offset it. The effect only last's a few seconds though. Rest of the climbout will be right rudder, with less being used as airspeed increases. For the initial takeoff, lot's of right rudder is required in the RV6. In cruise, it's fixed tab rudder trim only, with aileron trim (which I have) for fuel and passenger balance.L.Adamson

[GoranM 3,764]

LarryI never said I don't like hearing much about it, I said we've heard ENOUGH about it. Imagine everyone in avsim mentioned what aircraft they flew in the real world...in every single post they made...and then they made reference to that aircraft in every example about flight models. No one doubts your knowledge in the aviation world, but is it really necessary to mention the Vans in every single post you make?I mean, in over 90% of your posts, you have "In my Vans RV6..." or "On my Vans RV6 that I fly..." or "My Vans RV6 has..." or "When I fly my Vans RV6 in the mountains..."I don't mean any disrespect, but I get it. You're A pilot. But you're not THE pilot. And now we have all been made aware that your wife is a pilot with 114 hours in your Vans.You don't need to mention what you fly. Even my daughter knows what you fly. She reads some of these posts (she fell in love with aircraft when I took her to the airport when she was 3) and she keeps asking me, "What's a "Vans"??"BTW, my name is Goran. not Gorem.

[h2egc 31]

Now, back to our regularly scheduled programing!(I don't have my DC-3 yet :( )

[GoranM 3,764]

Now, back to our regularly scheduled programing!(I don't have my DC-3 yet :( )

God, I hope not. It's not even done yet.

[h2egc 31]

God, I hope not. It's not even done yet.

Yeah, Yeah... the waiting is the HARD part. :( Edited January 17, 2012 by h2egc

[jcomm 5,924]

Good to read!I never flew a real Van's RV, although there is at least one here in Portugal :-) Anyway, your post is rather important because it states that different aircraft, specially depending on their mass/wingspan. Even on a rather powerful light aircraft, where the torque should be a lot more noticeable, the bank is small compared to the yaw resulting from the prop slipstream acting on the tail fin/rudder.On bigger prop aircraft, like for instance the BEa ATP, operated in Portugal, Azores islands, by SATA, there is s noticeable (requiring ailleron trim input) right bank when power is reduced from cruise, because the aircraft is designed to be balanced for cruise flight.So, every aircraft is an aircraft, but I believe the torque effect on xplane is somehow too intense.And we're just talking about prop aircraft now - as a glider pilot in RL, and having flown the AS-K21, the way the default glider in xplane feels, not being that bad isn't good either... But that's theme for yet another thread :-) Ah! Goran , tell your daughter about the AS-K21 and... I'd really love my daughters have felt in love for aviation that easily... Or my ex-wife ... You're a lucky guy Goran!

A real life Cessna 172 isn't jumpy. It's rather sedate, and lackluster. That's the problem; as some of the challenging feel of some X-Plane models shouldn't be present at all. That's why I'd get annoyed and quit after five minutes. Things are changing though. I could almost say that some X-Plane models are becoming more like my favorite add-ons for FSX................but that would probably just irritate a few developers... :(

Edited January 17, 2012 by jcomm

[LAdamson 240]

LarryI never said I don't like hearing much about it, I said we've heard ENOUGH about it. Imagine everyone in avsim mentioned what aircraft they flew in the real world...in every single post they made...and then they made reference to that aircraft in every example about flight models. No one doubts your knowledge in the aviation world, but is it really necessary to mention the Vans in every single post you make?I mean, in over 90% of your posts, you have "In my Vans RV6..." or "On my Vans RV6 that I fly..." or "My Vans RV6 has..." or "When I fly my Vans RV6 in the mountains..."I don't mean any disrespect, but I get it. You're A pilot. But you're not THE pilot. And now we have all been made aware that your wife is a pilot with 114 hours in your Vans.You don't need to mention what you fly. Even my daughter knows what you fly. She reads some of these posts (she fell in love with aircraft when I took her to the airport when she was 3) and she keeps asking me, "What's a "Vans"??"BTW, my name is Goran. not Gorem.

No Goran, my wife is not a pilot....P.S. ---- show your daughter what a Van's is. It's a preferred airplane for F16, F18, Airbus 380, Boeing 737,747, 757,767,777, Cessna Citation.........pilots when they're not flying for business hours. These are just examples of pilots who I personally know, or are on our RV forums. The Airbus 380 pilot, had his RV parked next to the 380 at Oshkosh.BTW--- didn't you make a Dutchess for XP? I hear about it constantly! I don't know much about it though, and my wife doesn't either.One other thing, I've flown many airplanes besides the RV. It just happened that I built and own one. And it's much more fun to fly than most GA aircraft.L.Adamson

[GoranM 3,764]

No Goran, my wife is not a pilot....

Remember this...http://forum.avsim.n...84#entry2209584Or a direct quote...

I think he needs a ride in a real plane. At least in calm conditions. BTW--- I'm showing this thread to my wife. She has 114 hrs. in our RV6. She's often made the comment while flying over the Great Salt Lake, or the farm lands of southern Idaho.............that it seems as if we're standing still. And yet we're at approx 200 mph, and perhaps 2500 - 4000' agl. And then of course, I have to say............that some simmers just don't believe it....

Either she is a pilot or she isn't a pilot. One of those is a lie. (sorry, I call it how I see it)

And then of course, I have to say............that some simmers just don't believe it....P.S. ---- show your daughter what a Van's is. It's a preferred airplane for F16, F18, Airbus 380, Boeing 737,747, 757,767,777, Cessna Citation.........pilots when they're not flying for business hours. These are just examples of pilots who I personally know, or are on our RV forums. The Airbus 380 pilot, had his RV parked next to the 380 at Oshkosh."

I don't have a problem with you or anyone else flying a Vans. But you mention it like it's the king or queen of all aircraft. It's like watching the same episode of a tv show every single day, twice a day.

BTW--- didn't you make a Dutchess for XP? I hear about it constantly! I don't know much about it though, and my wife doesn't either.One other thing, I've flown many airplanes besides the RV. It just happened that I built and own one. And it's much more fun to fly than most GA aircraft.L.Adamson

Yeah. And I mentioned it in the avsim forums maybe half a dozen times. I certainly don't reference it nearly as much as you reference the Vans RV6.

[60North 120]

Hi M,referring to the bank instead of yaw subject, I can't really give you much data, although you can extract it from the various output forms XPlane allows us to use, anyway, this is a simple basic feature that we learn from RL experience flying prop aircraft. Austin, being a RL pilot as well, and having flown prop aircraft knows about it for sure. He certainly knows that when, say on a P180, his Cirrus, a C172, etc... he throttles up on takeoff/climb power, the yaw will be practicaly the ONLY effect he will feel from the slipstream of the prop on the tail fin/rudder. Rudder input is used to counteract and on some airplanes it can even become tiresome - say a Rallye or a Robin, where you have to keep quite a good amount of right foot to counter slipstream yaw effects.Xplane's prop airplanes bank instead. The worst part of this problem is that, when cruising, straight and level, bank tendency opposite prop rotation is present as well, and if you reduce power you'll get a right bank tendency (for a clockwise rotating prop as seen from the cockpit).

jcomm,Not 100% sure I understand you right but..AFAIK, X-Plane models BOTH propwash and P-factor. Attach a shot of the propwash over the tail causing yaw.(static on runway, purple lines, from lelf to right hitting the rudder). On my XP Archer (which I also fly in real) you have togive significant right rudder, especially at low airspeed+full power (like takeoff). So to me that seems realistic.With regard to P-factor, as your links say, it will at an AoA (climb+cruise) give you a left BANK which X-Plane also does well atleast on my Archer. (it is trimmed so there is no bank in cruise)This being said, I can PROVE that the propwash is a bit weak in X-Plane. I suspect this is intentional(!) because of the ground model. Long story, but if it was100% realistic, most prop aircraft would end up in the ditch on takeoff because of gear friction/computationalcreep issues.The other thing is offcourse that real aircraft have buildt in trim tabs, offset stabilizer, canted engines etc that the XP designer mightnot be aware of and the aircraft will not behave correct in this regard.M Edited January 17, 2012 by MortenM

[LAdamson 240]

From my iPhone.......She does have 114 hrs in our RV6A. That's 114 hrs in the right seat. I'd say that, that's enough experience to make the comment she did, about perception of speed. Did I ever say she was the pilot and I was the passenger? Of course not.

[GoranM 3,764]

LarryShe has 114 hrs. in our RV6. She's often made the comment while flying over the Great Salt Lake, or the farm lands of southern dahoWhen someone says something like this, in this kind of context, I would take it to mean she has flying hours in the pilots seat. If I went by your context, well, I have over 200 hours in a Boeing 747-400, roughly 50 hours in a 737NG and about 6 in a Dash 8Perhaps if you said she has 114 hours as a passenger, it would be clearer. I don't think ANYONE could interpret your statement as your wife having 114 hours as a passenger.(read it a few times)