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oldflyguy

Exciting take off runs...

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CDNCAVOK,

I have a set of MKB rudder pedals , they are way more accurate and programmable than the Saiteks , CH products and thrustmaster I have used in the past.

They have not however saved me from doing an awful lot of lawn mowing and major structural landscaping at some of the airports I fly from with the TBM.

There are times in the TBM  when I think I've fired up Colin Macrea's Dirt Rally and am practising my drifts , hand brake turns ,obstacle jumps and skid control .

Comparisons can be invidious , but I have no trouble controlling the STMA  PC 12 on take off or landing , using the same software and hardware setup.

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If you're managing to do a 180 skid (handbrake turn) in the TBM, then your landing and taxi skills need some very serious practise.  

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I''ll see if I can capture this on video otherwise it just seems like I'm blowing smoke .

I'll do my own checking but, is there a way to simultaneously show the control inputs on the same video , similar to  fps in the top left corner ? 

  I've seen the reports of difficult ground handling of other aircraft in Xplane but never really took an interest because I had not experienced them . The TBM presents some interesting  challenges in that department.

 I'm  curious to know Goran,  if there are lines of code  in the TBM program that determine ground handling behaviour as speed increases ?

  If not , then our concerns regarding these observations can be laid to rest.

I should emphasise there are zero problems for me below around 40 knots . In fact at this speed or below the handling is excellent with the throttle in taxi  mode.

If I had to summarise , as the speed builds up to around 50 knots on take off , flaps as stipulated in the manual,  the rudder/ front wheel  response becomes more sensitive than I have experienced in other aircraft at the same speed  .  Then at a certain point an oscillation begins that amplifies as speed builds up , regardless of how small the correction(s)

I accept that practice on my part is necessary  ,  and I also accept that it may be in the Laminar code as others have stipulated,  or that my configs may be  awry . 

 

 

 

Edited by fireone
word change

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I have no doubt that you're telling the truth.  So no need to prove anything.  I'm just trying to imagine what kind of control inputs you must be putting in, to manage the moves you mentioned.  

There is a selection in the data output section that will show control surface inputs.  I would actually be very interested to see what you're doing in that regard.

I can tell you the ground handling is being overridden with code, but Saso is the authority on that.  Ironically, I think it's the low speed taxi ground handling that is being overridden.  

It's widely known that X-Planes ground handling needs some tweaking, so maybe this is what you're experiencing at higher speeds.  

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Thanks for the reply ,  Goran.

Once the oscillation starts,  it amplifies  , its as if there is a resonant frequency .

  The times I have made 180 degree + turns is when I have reduced speed , aborted the take off , and the plane has managed to stay upright on its undercarriage. 

It doesn't happen on every takeoff. When the aircraft is well aligned on the centreline and only miniscule corrections are made with rudder on the take off run all is well. Applying power slowly or more swiftly appears to make little difference .

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The oscillations ( when they happen ) occur between 50 to 90 knots ,  at 90 -95 knots I rotate , with flap on take off setting . The instant the front wheel is off the ground all is stable.

I'm flying CAVOK until I get a better feel for the aircraft and its systems. 

ATM trims for rudder are via the MFG software .  Aileron and pitch via Joystick trim wheels.

I''ll double check keyboard assignments , in cockpit settings and any other variables that may  influence rudder /front wheel/trim position and report back.

 

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I've done 6 take-offs and landings and have found a major improvement with the following:

Following the instructions in the downloadable Socata  POH   page 4.4.47   2014 edition .

There is copyright so can't cut and paste.

And using the default Laminar keyboard settings for aileron , rudder and pitch settings made for much finer , much better control  of all the  trims

Previously I was using scroll wheels on the joystick/throttle  for trim control .

In particular trim for rudder is 2/3 of the way from the midpoint to the green marker in CAVOK conditions .

Thanks to Goran for making me think about this more deeply.

 

Edited by fireone
added word
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One thought I would like to share with you guys.

X-Plane 11 is known for it's disastrous ground handling, at least in GA which is what I fly exclusively. My second favorite plane is the default Baron which is as terrible as the TBM in crosswinds either landing or taking off . I've ruined many nice flight in this situation, but I found out a great improvement.

Baron allows me to set an axis for the Tiller and I happen to have a spare axis in my HOTAS for that. With that set the rudder pedal acts just the vertical primary aerodynamic control excluding the front wheel. It's way less sensitive to inputs and makes life way easier.

Unfortunately I couldn't set the tiller for TBM like that but IMO is a good suggestion for future updates

Cheers

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One further  change I've made is to set the sensitivity of the  3 axis ,rudder ,pitch ,roll  all the way to the left in the Laminar joystick setup . Much better handling in the take off run.

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The ground handling issue is solved for me :

1) The POH recommendation : apply brakes , increase torque and release brakes when in torque range 40 - 60 % .

2 ) In  the Laminar control sensitivity window,  I  moved all three control response sliders all the way to the left.

3) Moved the stability augmentation slider for yaw to the 50% mark.

 

The default position for control response is at the 50 % position .

The fine print describes this as giving finer adjustment when the joystick /rudder is in the center position.

Whereas in the leftward position , control response is linear .  I interpret this leftward position to mean if I move my rudder a small amount it will  make a small correction of the rudder on the plane., not some value calculated by an algorithm when the slider is to the right.

Whatever it means , I now look on  take offs and landings as a far smoother ,enjoyable ,predictable event.

 

 

Edited by fireone
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I share the same opinion as others on this thread that the ground modeling of X-Plane is affecting stability on the takeoff run. I am familiar with my all-time favorite single engine turbine, the Pilatus PC-12, and own this for XP as well. I don't have the same issues with this model but that doesn't mean that the TBM is bad, or the PC-12 is "correct". I just went out and did some touch and go's with the TBM using the latest patch and the first run down the runway wasn't bad at all. I veered a little at first but was able to stay very near centerline the rest of the takeoff run. Cleaning up the airplane for the T/G can be a little nerve racking but nothing practice with this type won't cure. I also setup buttons on my throttle (right hand) to handle raising and lowering gear and flaps. That keeps my hands on the controls and eyes up to maintain that centerline for the re-application of takeoff power.

In previous releases, I did slide my yaw sensitivity control all the way to 100% because the veering effect was much more pronounced in prior versions. I find smoothly and slowly applying takeoff thrust helps. I think I also read somewhere to place rudder trim between the white mark and green mark on the scale to compensate torque. From there, any veering tendencies I attribute to my own X52 hardware setup. I am a RW Cessna 172 G1000 pilot and agree with others stating the "seat of the pants" feeling. You don't get that an any desktop simulator so you tend to tune your reflexes based on what you see only. I think the TBM may be too precise a model (a good thing) for X-Plane's ineffective ground modeling because handling all other aspects of flight phases are just fine. Overall, love this airplane!

Practice more! :)

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GreenDot , the written word sometimes comes across as lecturing and  disrespectful  . There are some  points in your description that merit analysis and there is no disrespect intended.

1) There is no yaw sensitvity  control.

There is a yaw control response slider inside the control sensitivity window . The control sensitivity window includes stability augmentation settings.

When the mouse hovers over the sliders it explains what the sliders purpose is. If you moved your slider to the 100% position , you have gone in completely the opposite position IMO  to create a more realistic yaw response . In my trials the 0% control response  position  for yaw and 50 % stability augmentation for yaw generates a very stable response on the ground and in flight.

2) If Laminar's code is responsible for yaw response problems all aircraft would suffer the same problem but they don't , as you say the Pilatus is stable. . But that is what the slider in the control sensitivity window  are for, to account for differences in aircraft.

3) There are detailed instructions in the official POH ,freely available online , on how to conduct the take off .

If you do experiment with  the yaw response and augmentation , would you be able to let us know if you see a difference , because as is so often stated everybody's experience is different and it may well be that I am talking out of my hat.

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I think the issue is sensitivity. Pedals are extremely sensitive in this model. For example pedals in the the new JRollons SF260 Marchetti are not as sensitive and to me 'feel' natural. Same with the Kodiak. My take on it is the TBM900 is simulated accurately and correctly, it's just that there's a sensitivity issue that is not accounted for as we all have different hardware.

 

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