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theskyisthelimit

XP11 beta, full throttle down runway in GA single prop immediate left hard turning? Realistic?

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I know people had commented on weathervaning issues with xp11 beta.. i'm not sure this is the same thing, but for some reason with any single prop aircraft i load up, weather carenado or the default cessna.. if i sit on the runway (any runway) and apply full throttle... the plane immediately starts a left turn.. within 2 seconds.. i had limited time with lessons and not with a cessna but i dont recall this ever being the case.. i know some rudder was needed but not the degree things seem to be here..

 

I've done the data output to see that the rudder is centered and no control surfaces are moving and also disconnected all joysticks to rule them out (ch yoke and pedals)..

 

Is this still a bug..?

 

Thanks in advance

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I've noticed that too it's like the ground friction and wind aren't meshing properly.It's like the weight on wheels isn't being figured properly so the aircraft blows around like a kite.

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I've noticed that too it's like the ground friction and wind aren't meshing properly.It's like the weight on wheels isn't being figured properly so the aircraft blows around like a kite.

Ah that makes sense.. i wonder if there is a hack to correct it for now.. someone posted up a modified vertical stabilizer airfoil file before (for the default cessna anyway) meant to fix light winds and weathervaning.. but it has no effect on this situation.

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I know people had commented on weathervaning issues with xp11 beta.. i'm not sure this is the same thing, but for some reason with any single prop aircraft i load up, weather carenado or the default cessna.. if i sit on the runway (any runway) and apply full throttle... the plane immediately starts a left turn.. within 2 seconds.. i had limited time with lessons and not with a cessna but i dont recall this ever being the case.. i know some rudder was needed but not the degree things seem to be here..

 

 

I actually have no memory of this ever not being the case. Whenever I start up a vehicle in Xplane I expect it to pull sharply to the left.

 

I was one of the first people to grab Xplane10, and I remember it through all those years, so I thought nothing about it when it occurred in Xplane11 as well.

 

I'm not even sure Xplane considers this a bug?

 

Betcha The UninstallerTM could answer this.  :smile:

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I actually have no memory of this ever not being the case. Whenever I start up a vehicle in Xplane I expect it to pull sharply to the left.

 

I was one of the first people to grab Xplane10, and I remember it through all those years, so I thought nothing about it when it occurred in Xplane11 as well.

 

I'm not even sure Xplane considers this a bug?

 

Betcha The UninstallerTM could answer this.  :smile:

Well that's unfortunate and I don't think p3d behaves like this. You would think there would be a fix by now then. It certainly isn't realistic (?)

 

This isn't enough to make me abandon xp11 though :)

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Well that's unfortunate and I don't think p3d behaves like this. You would think there would be a fix by now then. It certainly isn't realistic (?)

 

This isn't enough to make me abandon xp11 though :)

 

I think Jcomm, also known as The Uninstallertm  when he's wearing his cape, has been chasing that torque issue for years.

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Someone called me :-)

 

Yes, me, Larry Adamson, and Murmur and many others, but it was thanks to Murmur that finally the culprit was found in a double calculation of prop torque, and fixed somewhere along the XP10 track...

 

But probably due to the adjustments Austin is doing to his calculations of interaction of propwash with aircraft surfaces, maybe something has changed again ? 

 

I really can't tell because I don't have XP11 installed :-/ 

 

Anyway, as a passenger, I've flown in some GAs, from Cessnas to Pipers, going through Mooneys, Beechcraft, Extra, Pitts, Auster,... and the left turning tendency is always there, specially as you start the takeoff run, and specially if you firewall the throttle more abruptly. A DR-400 pilot used to start the takoff run with full right pedal to counter the left turning tendencies, even with starboard winds!

 

I think it is right, although I don't know if it's magnitude might have increased in the latest XP11 betas ?

 

ELITE ( all versions up to v9 I am beta testing ) was probably one of the serious flight simulators I used, and it models this tendency very markedly. But it's the same in well designed prop aircraft with non-counter-rotating props, specially small / medium GA in MSFS, AEFS, DCS, IL2, FG, ...

 

There is a very interesting training video for the TBM 750 in youtube you can watch showing the effect on a Pt-6 - powered single turboprop.

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Posts like this make me laugh and frown at the same time. No scientific evidence, just claims. And the best: It´s not like this in P3D, so it must be wrong!! What?? ROFLMAO. FSX can not even model a sustained sideslip (unless the flightmodel is hacked by talented designers, I hear) - so it´s hardly the authority here.

 

I tested with no wind and the default Cessna. Output flight control deflections to screen. At full throttle and very low speed I need ca. 0.2 out of a total of 1.0 rudder deflection. In other words, for the mathematically challenged: I only apply one fifth or 20% out of the total available deflection. This is in XP11pb8.

 

My conclusion: This feels right, if not even a bit weak, but my 220h of SEL are in F33 Bonanzas, and they have a stronger engine.

 

My advice: Calibrate your devices properly. Check that you don´t have ANY wind (many users set a strong wind at 30.000 feet or so - and forget that it will propagate unabated all the way to the surface).

 

Jan

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. And the best: It´s not like this in P3D, so it must be wrong!! What?? ROFLMAO.

 

Jan

:LMAO: :LMAO:

 

Some right rudder is required is what i have noticed in XP10 / 11, and if there is a X-wind component hitting the stab on the left and then the right rudder needs to more input.  Also comes down to the modeling of the aircraft , tire friction modeling may also be playing up here you know what happens when you have bald tires

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Perhaps we should start a P3D Anonymous class, to help bring those folks up to speed.  For people to claim that the reactions and effects in XP on aircraft are incorrect because they didn't act that way in P3D, doesn't make it so.  If anyone has noticed, Austin has put a lot of work into the physics of the aircraft, and some may argue that it's a little too much, but overall, it's more accurate than FSX and P3D.  I switched from P3D to XP because of the realism, both in environment and in flight models.  I suppose if you set up P3D's aircraft to a hard level, you would get some of what LR did for XP, but with XP, out of the box, the aircraft handle realistically, so it's a challenge.  I expect the aircraft to act erratic every time I fly now and am prepared because I have started to learn the behaviors of all forces acting on the aircraft, and while it is more challenging, I still have fun and learn something along the way.

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Forget XP or P3D, see real life discussions...

 

I think a lot of us here understand the physics involved.  The question is, does X-Plane 11 get it right?  Will a Cessna 172 really shoot off the left side of the runway during the take-off roll without a sufficient amount of right rudder?

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I think a lot of us here understand the physics involved.  The question is, does X-Plane 11 get it right?  Will a Cessna 172 really shoot off the left side of the runway during the take-off roll without a sufficient amount of right rudder?

 

That was basically what i was after.. some real world parallels from pilots (hopefully).. I wasnt trying to battle the merits of P3D vs XP :)  And for the record, I always set realism to the max in P3D and i'm aware of the pfactor and the standard left turning tendency.. i was just trying to gauge if maybe there was a bug here that made it worse than it should be.

 

In fact, digging around i see there may have been a "double" pfactor bug back in XP10, which i thought maybe followed through somehow (I think it was corrected back then though).

 

I recognize the need for right rudder on take off etc.. no questions there.. just the "force" of the left turn if you throttle to full and go right away (instant left turn here).. obviously the better approach is the slow ramp up, 25% then 50% then full while applying the right rudder (but again how much right rudder).

 

My ch yoke/pedals are calibrated and i've tried it without them connected, same issue, so its not the controllers.   

It probably is as it should be, I was just seeking verification.. and those youtube links are good references in general.

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Using 0% control response for yaw might improve things. It's in "Joystick"->"Control Sensitivity"

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Posts like this make me laugh and frown at the same time. No scientific evidence, just claims. And the best: It´s not like this in P3D, so it must be wrong!! What?? ROFLMAO. FSX can not even model a sustained sideslip (unless the flightmodel is hacked by talented designers, I hear) - so it´s hardly the authority here.

 

As an authority here, bearing in mind, I'm not a commercial aircraft pilot like Janov,........ I do have the time in lot's of small single engine aircraft, ranging from the Cessna's, Pipers, to the Pitts, Marchetti SF260, Super Stearmans, many high powered experimental class, and backseat in a P-51D mustang.

 

In reality, thanks to third party intervention over the years, FSX (and I'll assume P3D, as I don't own it), became very capable of producing the effects of left drift, & side slip. Every time I tried a new model for MSFS, even before FSX, these forces are the first thing I tried. I'm the same way with X-Plane. For many years, I complained about X-Plane over doing some of these forces. It's well known, about my feelings on this subject.

 

Problem here, is that many non-pilots do not know, what their trying to reference. They have no real idea about the forces and reactions of real aircraft. And, FSX will add auto-rudder, if the box isn't unchecked, if you don't have rudder pedals, or a twist grip. IMO, twist grips never provide the right sensation of feel, anyway. Point is, numerous FSX models do provide the correct feel ( or close to it), and response. I say close to it, because I still see FSX & X-Plane models that tend to wander too much during the roll down the runway. The force is actually there, and we push the pedal against it. The force doesn't get all wishy-washy & cause wandering that needs constant right/left pedal to correct. It's more like riding the side of a gutter, or wake while water skiing. Just push against it.

 

P.S. ---- Lot's of X-Planes (especially some of the 3rd party addons) do fine, these days with left drift. IMO, it had better be there! But there has to be pedals or something to offset it. Otherwise, you'll end up in the weeds. Some models may do too much, or not enough. Same with products for MSFS,

I recognize the need for right rudder on take off etc.. no questions there.. just the "force" of the left turn if you throttle to full and go right away (instant left turn here).. obviously the better approach is the slow ramp up, 25% then 50% then full while applying the right rudder (but again how much right rudder).

I once sat in the back seat of a Piper Archer, for my daughters first flight lesson. On the way to the airport, I told her about left drift. Told her she'd end up running over the left side runway lights, if she didn't push right pedal. Of course, in reality, an instructor would be hitting right pedal, if she didn't. Planes certainly do vary. Much to do with engine size versus aircraft weight, size of the vertical stab/rudder, whether the engine & possibly the vertical stab is canted or not, etc. Expect it on the first part of the roll, especially if powered up quickly, and to stay there throughout the roll & initial takeoff. You'll still need rudder to maintain runway centerline. As airspeed picks up, the push needed on the rudder will diminish. Shouldn't be needing right aileron (see note). If so, the model or real thing, needs some re-rigging.................unless the pilot is just terrible with fuel, passenger, and cargo management.

 

note: a little bit of subconscious aileron may be needed for imbalance, in aircraft which don't have a form of aileron trim. Unfortunately, a desktop joystick/yoke centering spring is usually more than the real life force. Being an inflight perfectionist with my kitbuilt Van's RV, I did add aileron trim. Very nice!

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Expect it on the first part of the roll, especially if powered up quickly

Exactly my thought. I've come to the conclusion that many flight simmers just firewall the throttle and let it rip down the runway. Gradually increasing throttle while maintaining center line, works quite well in the aircrafts I use in X-Plane.

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Perhaps we should start a P3D Anonymous class, to help bring those folks up to speed.  For people to claim that the reactions and effects in XP on aircraft are incorrect because they didn't act that way in P3D, doesn't make it so.  If anyone has noticed, Austin has put a lot of work into the physics of the aircraft, and some may argue that it's a little too much, but overall, it's more accurate than FSX and P3D.  I switched from P3D to XP because of the realism, both in environment and in flight models.  I suppose if you set up P3D's aircraft to a hard level, you would get some of what LR did for XP, but with XP, out of the box, the aircraft handle realistically, so it's a challenge.  I expect the aircraft to act erratic every time I fly now and am prepared because I have started to learn the behaviors of all forces acting on the aircraft, and while it is more challenging, I still have fun and learn something along the way.

Many years ago, somewhere before MSFS's FSX, either version 8 or 9 of MSFS, Rob Young of RealAir simulations perfected the desktop simulator side slip.  It was the first time ever, that a sim pilot could fly a perfect slip right down to the landing, without the airplane wandering all over the place.  Of course, rudder pedals were a requirement.  Two of Rob's objectives were realism with slips & spins. He was a pioneer in the desktop sim world.  These days, I consider a number of X-Planes & FSX planes to be much the same, flight dynamics wise.  I enjoy sim flying both.  The benefit of higher frame rates also makes a difference for both sims, considering many simmers considered the fluid part, as a part of "feel".  I never considered X-Plane as having superior flight dynamics over some of the 3rd party entries for MSFS/FSX.  Still don't know if P3D is different, flight dynamics wise. May never know.

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 Will a Cessna 172 really shoot off the left side of the runway during the take-off roll without a sufficient amount of right rudder?

In Theory: Certainly.

 

If we imagine a pilot who goes to full power in a second it would mean tha6t the stabilizers and rudder don't have any effect, while the slipstream pushes with full power at the stabilizers. If the tail moves even slightly it would mean that the plane starts to turn, while the pilot can only try to stop with the wheels since the rudder doesn't have a significant effect to control thze direction.

 

But in reality: No one wants to torture an engine and you feel that the controls don't really have any control about the plane. So you increase the throttle slowly, the slipstream is much weaker but the plane starts to pick up speed.. You slowly feel that the controls gain authority. You increase the throttle but while the slipstream is stronger the stabilizers and rudder can work against it.

But how do you really recognize the amount of rudder control? You don't really look at your feet. Instead you look at the runway aqnd don't really care as long as thew controls don't grow to big. 

If you drive your care you look at the street, not at you steering wheel tio control your direction. And you don't thiunk about if it is the sidewind, the runway, torque or slipstream that tries to interfere, you simply push against it.

 

And if we now look at X-Plane 11 pb8:

I use it as a game and give full throttle and you go haywire, as you could expect accoring to the theory.

But if I slowly increase the throttle you more or less stay on course, while the plane picks up speed. While you don´t feel the controls or the engine you see that the controls are working and increase the throttle, while you try to stay in the correct direction but now you don't have any problems to maintain the control. The rudder is more than enough to stabilize the plane.

 

Is it correct? How shall I know?

Is it plausible? Yes..

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I've come to the conclusion that many flight simmers just firewall the throttle and let it rip down the runway. Gradually increasing throttle while maintaining center line, works quite well in the aircrafts I use in X-Plane.

 

Hmmm... apparently I've been doing it wrong.

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I don't jam the throttle, but I don't take too long either.  It's that one Mississippi count, or a bit more. That's a second or so.  A few years back, a friend made a comment, that I was taking a bit longer on getting to full throttle with his Van's RV9A.  My RV was the 6 model, with 20 more HP, a shorter low aspect ratio wing, and a shorter vertical stab/rudder tail assembly.  Van's actually increased the vertical tail height of the 6, but we think it lost a bit of speed as well as looks.  The original was like the earlier model P51D's.   My 6, wanted to head left with a lot more force, than his 9. Quite noticeable. My airplane also exhibited more torque roll  on the ground, if I quickly added power for a touch & go.  Both airplanes did not require right aileron as soon as the wheels left the ground, even though my left wheel pushed down hard, until normal airspeed for rotation was obtained.  If, I needed to quickly increase power, because of a runway bounce on landing, the immediate thought had to be hard right rudder. If not, the plane will pull hard to the left, and want to roll from a combination of yaw coupling & torque. Just think rudder, and not aileron.

The P51's would just simply roll over on their back, in these aborted landing situations, if applying power too quickly. There were specific rules, as to the amount of power being applied in go-arounds.

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Here are two quick and dirty videos (apologies, they are crude but i think the point is made).. i disabled the rudder/yoke before doing these.. i did notice that for some reason 0.159 0.159 shows in the output for rudder deflection, yet in video 1 you really cant see any..

Both of these done on a Clean install of PB8.. Wind is Zero

First one, just sitting on the runway at KSEA (sloped maybe?) it starts to turn left before adding throttle.

Second one.. line up and give almost half throttle and you can see it swings left quickly, very quickly in my opinion



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Austin is also fine tuning the propwash effects including slpistream asymmetric hit on different surfaces, fuselage inteference, etc... Maybe we may see some quirks while things are being adjusted ?

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Here are two quick and dirty videos (apologies, they are crude but i think the point is made).. i disabled the rudder/yoke before doing these.. i did notice that for some reason 0.159 0.159 shows in the output for rudder deflection, yet in video 1 you really cant see any..

 

Both of these done on a Clean install of PB8.. Wind is Zero

 

First one, just sitting on the runway at KSEA (sloped maybe?) it starts to turn left before adding throttle.

 

Second one.. line up and give almost half throttle and you can see it swings left quickly, very quickly in my opinion

 

Yup, looks about like what I see as well. In fact it's best to hit the throttle and get the heck off the ground after releasing the brake or your plane will head for the buildings. Again, this didn't bother me at all because I'm accustomed to this in Xplane and just consider it one of those things..

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Both of your videos show totally normal behaviour.

 

In the first video - your engine is running at idle. So its not "before adding throttle". The propeller is already putting out thrust and slipstream. While the plane creeps forward, the slipstream pushes on the vertical stabilizer and the plane turns left as a result.

 

The same effect can be seen in the second video, at a greater magnitude.

 

You are not countering slipstream and torque effects with rudder/nosewheel - therefore the plane will turn to the left. I am not sure what you are trying to show with these videos? That X-Plane aerodynamics are realistic? Well, it´s working! :smile:

 

There is a known shortcoming in X-Planes ground friction model, and it occurs when speeds are slower than 2 kts, approximately. At these slow speeds the tire slip under a sideforce is larger than it should be - there is currently no fix for this possible, due to computational creep in calculating friction forces.

 

Jan

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