Jet liners?

[MillionS]

I’ve been trying to make a passenger jet but ot never takes off. Anyone, help?

[Gargamel]

Some pics of your craft would help. 

But there are a couple common reasons for not being able to take off.

If your Center of Lift is too far behind your Center of Mass, your plane will want to fly perfectly straight, but will be harder to maneuver.   So moving your CoL right behind the CoM, will enable your control surfaces to control the vessel better.   There is a happy medium for this arrangement, and each craft is different.  Also be aware, as your fuel burns, your CoM will shift, and if it moves too far, your craft might become too stable, or completely unstable.  So in the SPH, you can drain the tanks like it would in flight, and observe the changes in CoM. 

Now while this has some affect on taking off, the second reason is far more impacting.

Your rear landing gear have to act as a fulcrum while on the ground.   The amount of force that your control surfaces can create is limited at slower speeds, which is what you usually encounter during take off.   So, if your rear gear is located far behind the CoM, then your have to exert a large amount of force to lift the nose up.  When this happens, it will just look like the plane is struggling to nose up, and you usually end up running of the end, when the tail can drop and you can gain altitude.  The KSP runway is actually good for this, as the ground drops away fairly quickly.   If you move the landing gear farther forward, so they sit just behind the CoM, it will take far less effort to raise your nose.  But now, you have to be aware that your tail will drop as you pull back, so you have to be gentle on the pull back, until the plane can lift itself up and clear the ground.    If you look at most modern airliners, you'll notice the main landing gear are positioned with a large portion of the plane behind them.

 

And moved to Gameplay Q's. 

 

[MillionS]

On 2/27/2019 at 1:15 PM, Gargamel said:

Some pics of your craft would help. 

But there are a couple common reasons for not being able to take off.

If your Center of Lift is too far behind your Center of Mass, your plane will want to fly perfectly straight, but will be harder to maneuver.   So moving your CoL right behind the CoM, will enable your control surfaces to control the vessel better.   There is a happy medium for this arrangement, and each craft is different.  Also be aware, as your fuel burns, your CoM will shift, and if it moves too far, your craft might become too stable, or completely unstable.  So in the SPH, you can drain the tanks like it would in flight, and observe the changes in CoM. 

Now while this has some affect on taking off, the second reason is far more impacting.

Your rear landing gear have to act as a fulcrum while on the ground.   The amount of force that your control surfaces can create is limited at slower speeds, which is what you usually encounter during take off.   So, if your rear gear is located far behind the CoM, then your have to exert a large amount of force to lift the nose up.  When this happens, it will just look like the plane is struggling to nose up, and you usually end up running of the end, when the tail can drop and you can gain altitude.  The KSP runway is actually good for this, as the ground drops away fairly quickly.   If you move the landing gear farther forward, so they sit just behind the CoM, it will take far less effort to raise your nose.  But now, you have to be aware that your tail will drop as you pull back, so you have to be gentle on the pull back, until the plane can lift itself up and clear the ground.    If you look at most modern airliners, you'll notice the main landing gear are positioned with a large portion of the plane behind them.

 

And moved to Gameplay Q's. 

 

Thank you i will try some of your recomedations