Strange issues on space plane takeoff

[Shivershorts]

I haven't played Kerbal for a few months and recently jumped back on. Suddenly I was having issues with a space plane that used to fly just fine (it flew fine even after the aerodynamic changes of 1.0 release). As soon as I get enough velocity to get the proper lift for takeoff, the nose immediately starts pitching up and the whole plane flips over and crashes.

Here's the space plane, very basic:

And here's what happens as soon as it gets off the ground:

I tried building some other very basic models with varying part placement but they all do the same thing. I just can't fly planes at all.

I uploaded the save, craft file, direct x info and output log here: https://www./folder/v2el3d896678g/Kerbal_troubleshoot

Running Kerbal version 1.0.4.861

[diomedea]

Here are the reasons (IMHO) why your craft isn't behaving:

1. Your plane has the Center of Mass (CoM) exactly where the Center of Lift (CoL) is, that means it has no dynamic stability of its own (the effect of forces from the lifting/control surfaces is stabilizing if they act rear of the CoM):

2. Stabilizers (the horizontal control surfaces controlling pitch) are very close to the CoM, their effect to control pitch is minimum (torque = force * distance). It is effectively not enough to keep a desired pitch while aerodynamic forces make the plane change attitude.

3. Lift from the wings is high enough to make the plane climb even at low speed. The more it accelerates, the greater the lift: when the plane gains speed the effect is to increase the torque they exert. As the wings CoL is forward of the CoM, that effect is destabilizing and will soon be greater than the amount from those tiny stabilizers.

So, to correct that:

- move stabilizers to the tail;

- if the above isn't enough to make the CoL enough to the rear of the CoM, move the wings towards the tail a bit too.

[Shivershorts]

Wow thanks! I thought there's a problem and it turns out it's just me! Maybe there should be a tutorial for building functioning and stable space planes. Thanks again for the information, very helpful.

[SAI Peregrinus]

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

There's a good tutorial. Note that most of what it says about FAR now applies to stock, though the new FAR does it even better.