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jjgp101

Tendence to go to the left while T/O run

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As soon as start the run for T/O the aircraft has a great tendency to go to the left and in a few seconds if I don't make any action it is out of the runway.

 

No brakes.... no automatic pilot ....ailerons, rudder, etc etc centered .... condition levers, prop levers and power levers both equal ....... fuel tanks also equal ......  no wind at the airport .... all indicators for both engines equal ......

 

I don't find anything that justify that tendency .... can you help me to solution this issue please ?

 

I use  Prepar3D v3.0 and don't have this problem with any other aircraft

 

 

 

Regards

 

J J Gómez Prieto

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Hi JJ...

 

I don't have the plane - but - most propeller planes pull to the left on a takeoff run... If modeled correctly - you should be riding your right rudder pedal all the way down the runway and throughout the initial climb until you reduce power for cruise... The more powerful the engine the greater the turning force... Planes with larger engines/forces at play usually have rudder trim to reduce this effect... The turning tendencies are caused by Torque, P-Factor, Spiraling Slipstream, and Gyroscopic Precession (just look up the terms for more info in any basic flight manual)... That said - I can't vouch for the accuracy of the Carenado model...

 

Regards,
Scott

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Go into your P3D realism settings and reduce the P-Factor slider.

 

The way FSX/P3D models P-factor is incorrect. Yes due to the torque of the engines the airplane will pull slightly to the left during the take-off roll so unlike jets a technique in the King Airs is to line up 5 degrees right of centerline. However, there should be no P-factor during the take-off roll, P-factor is caused by the change in relative wind through the prop disc. During the take-off roll there is no P-factor as the relative wind is entering the prop disc evenly. P-factor comes into play on rotation as the downward stroke of the prop has a greater angle of attack then the upward stroke. In a clockwise rotating prop (such as on the King Airs) this causes a left turning tendency and is also responsible for the #1 engine being the critical engine for VMCA.

 

Spiraling slipstream, is not modeled in FSX/P3D and has no major effect on a twin like the King Air since our engines are not fuselage mounted. 

 

Under FSX/P3D all of these left turning tendencies, most noticeable on Single Engine Propeller airplanes is modeled under P-Factor. While it is about right for the Default Cessna 172 it becomes woefully inaccurate in twins. i.e. a Piper Seminole with its counter-rotating props still exhibit left turning tendencies. So depending on what you are flying you will need to adjust the P-Factor setting. I keep mine around 50% as a good-enough setting for most aircraft. Your mileage may vary. 

 

The other issue with FSX, not sure about P3D is weathervaning. Due to poor FDE coding many third party aircraft exhibit a heavy pull into the wind during take-off and landing. I have noticed this anomaly on the C90GTx and unfortunately there is no fix that I am aware of other then good crosswind take-off and landing technique.  

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Thanks Scott and Ken for your answer .... I have tested them but I have got nothing.

 

Nevertheless I have observed two strange things in the aircraft.cfg

 

A)

 

[GeneralEngineData]

Engine.0 = 6.4, -4.8, 0

Engine.1 = 6.4,  8.3, -0.2

 

Usually the lateral position is the same for both engines,  one positive and the other negative.

Also vertical position of the engines use to be equal for both

 

B)

 

[propeller]

..............................

..............................

propeller.0= 2.5, -1.7, -0.3
propeller.1= 2.5, -1.8, -0.1

 

Same explanation for lateral and vertical positions ...... more ... in this case both lateral positions are negative ..... ??????

 

I am sure that Carenado knows very well what and how they have to design an aircraft, but for me in this moment is not very understandable 

 

I have tested some provisional changes in the engines lateral position  and I have found that with same values ( one negative and one positive ) for both engines the tendency changes and became right instead left and with the follow lines the left/right tendency is near cero ...... but I think I have not to change what Carenado has built .... what is your opinión about ?

 

Engine.0 = 6.4, -4.8, 0

Engine.1 = 6.4,  8.3, -0.2

 

Sorry for the " tostón " (pure spanish .... hi ) and thanks for your help.

 

J J Gómez prieto 

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Same as what I have...

 

Engine.0 = 6.4, -4.8, 0                       
Engine.1 = 6.4,  8.3, -0.2 
 
 
propeller.0= 2.5, -1.7, -0.3
propeller.1= 2.5, -1.8, -0.1
 
 
Looks to me like they are trying to put the thrust location on the right downward stroke of the propeller. 
 
Since these are swept turbofan propellers maybe this was the best way to simulate the thrust off the propeller disc. But, it is interesting they did that and offset the propeller as well.  
 
 
Their regular C90B used the following:
 
Engine.0 = 8, -6.7, -0.5
Engine.1 = 8,  6.7, -0.5
 
no propeller offset.

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Correct Ken .... well .... let's see what happend with my test offset and continue testing this wonderful but a little difficult to understand aircraft ...... not to have a good tutorial for it make things run very slow .... the procedures are well but I thing is not enough nowadays.

 

 

Thanks Ken

J J Gómez Prieto

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I use FSX-SE and bought the C90GTX a few weeks ago and I have experienced the same issue with this aircraft turning left during takeoff run. In FSX the P-factor and all other controls are set to easy, but the aircraft is obviously not responding to these settings. In my experience from real life flying, the left turn during takeoff is way too much. I am looking forward if someone has a solution to this issue.

 

Regards

 

Erik Bentsen

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