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

[airlinejets 709]

 

 

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.

[LAdamson 240]

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.

[Longranger 148]

 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..

[jime59 58]

Torque.   :wink:

 

 

Jim

[Mountain Man 142]

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.

[LAdamson 240]

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.

[theskyisthelimit 48]

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

[jcomm 5,925]

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 ?

[HiFlyer 9,358]

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..

[Janov 2,383]

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

[Jimm 437]

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

 

 

There's no denying the video, but to add to the strange behavior of this aircraft at present, I will compensate for the drift with right rudder, but then after making a turn in either direction, the drift subsides and then after making another turn, I find that the drift compensation switches sides...very odd.  After runway entry and just as I increase the throttle, then it's never the same which side the drift occurs, sometimes left, sometimes right...even more odd.

[Longranger 148]

There's no denying the video, but to add to the strange behavior of this aircraft at present, I will compensate for the drift with right rudder, but then after making a turn in either direction,

Well, as Janov already said. Nothing strange in this behaviour. And while your plane is really slow the rudder won´t have any effect, you will try to overcompensate. You need some speed till the rudder really works. If you try to control with the rudder till it really works you won´t reach a stable situation. Either you overcompensate and your speed still increases: You go to the right. If you don't compensate enough the airflow on your rudder, decreses-> The effectiveness of your rudder decreases...If you stand the rudder has no effect if you don´t have nosewheel control. If you are really slow it has some effect, The faster you go the better your rudder works.

[Paraffin 2,197]

There's no denying the video, but to add to the strange behavior of this aircraft at present, I will compensate for the drift with right rudder, but then after making a turn in either direction, the drift subsides and then after making another turn, I find that the drift compensation switches sides...very odd.  After runway entry and just as I increase the throttle, then it's never the same which side the drift occurs, sometimes left, sometimes right...even more odd.

 

Do you have any wind enabled? Whatever the torque/propwash effects are, the current weathervaning weirdness might be affecting drift to different sides.

 

A 90 degree crosswind of just 5 kts from the right will make the default Cessna turn to the right when brakes are released at engine idle, completely counteracting torque/propwash effects. That's a pretty big effect from just a 5 kt wind! And of course if winds are stronger the effect is stronger.

 

If you're using XEnviro you won't even know what the current winds are, or from what direction, unless you're near a windsock.

[Jimm 437]

Well, as Janov already said. Nothing strange in this behaviour. And while your plane is really slow the rudder won´t have any effect, you will try to overcompensate. You need some speed till the rudder really works. If you try to control with the rudder till it really works you won´t reach a stable situation. Either you overcompensate and your speed still increases: You go to the right. If you don't compensate enough the airflow on your rudder, decreses-> The effectiveness of your rudder decreases...If you stand the rudder has no effect if you don´t have nosewheel control. If you are really slow it has some effect, The faster you go the better your rudder works.

Apologies, I never specified my groundspeed but in general, I keep my speed at a rate that I can maintain control so let's say just under 15.  Since the C172 is idling at around 800rpm, my throttle will stay around 1200-1500 during taxi.  Windspeed I don't keep track of right now, since I'm using XP's default weather (no XEnviro or any other add-on), but there is wind.  I can see how the wind's groundspeed could affect the aircraft and I assumed as much, but horse is a hard one to wrangle.  I'm not really complaining, getting used to it actually.  Murmur's fix does help a bit too.

[Mountain Man 142]

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..

 

Thank you for the explanation!  You've greatly improved my take-offs.  No longer do I careen back and forth down the runway.