Nose Dive

[locustgate]

So my first space plane that I was able to get off the ground, along with the crew surviving, didn't have enough to get into orbit. The problem was during the descent the plane seemed to just lock into a nose dive. If I disable the sas and pull up it only moves up a couple of degrees and then bounces back. If I reactivate the engine it starts into a spin or just speeds up the descent. I try to pull up until I hit 600m then deploy the emergency shoots.

The Plane: http://imgur.com/ZroVQmN,gYHo20R,qfTIFAv

Edited January 2, 2015 by locustgate

[CalMacDa]

It's probably too heavy and doesn't have enough lift. Try adding canards. Send pic of plane please

[Anquietas314]

Going by your screenshots, your center of mass is shifting forward as fuel drains. To fix that without really changing the design (disclaimer: use with caution), use the offset gizmo to slide the wings forward until the center of lift is just in front of the center of mass. Normally that's a bad idea, because in most planes the fuel drain causes the CoM to shift backwards or stay put. I have a few designs where the reverse is true, and I think your particular design falls into that category. Be careful not to move the parts between the two wing pieces on each side though - that might shift the center of mass further forward which is not what you want.

EDIT: Also, the above may only apply to stock aero. FAR/NEAR's model may be more or less forgiving, or exactly the same...

Edited January 2, 2015 by armagheddonsgw

[Torquemadus]

Using tweakables in the Spaceplane hangar, you can remove fuel from the plane's tanks to simulate how the plane's centre of mass moves relative to the centre of lift as fuel drains from the plane.

During descent, the plane is probably low on fuel, so the centre of mass will have shifted. If the plane is severely nose heavy, then it will be very difficult to keep the nose up. The plane's centre of lift is also it's centre of drag, so if the plane's centre of mass moves behind the centre of lift, the plane will try to "weather vane" backwards.

If the plane isn't too badly unbalanced, it might be able to compensate with reaction wheels and control surfaces. If you suddenly loose control, it might be because the centre of mass moved past a point of no return, or it might be because the plane exhausted it's batteries trying to compensate.

Planning how to manage changes in centre of mass can be difficult, as the plane needs to be just as flyable at takeoff as it is at landing.

[locustgate]

Going by your screenshots, your center of mass is shifting forward as fuel drains. To fix that without really changing the design (disclaimer: use with caution), use the offset gizmo to slide the wings forward until the center of lift is just in front of the center of mass. Normally that's a bad idea, because in most planes the fuel drain causes the CoM to shift backwards or stay put. I have a few designs where the reverse is true, and I think your particular design falls into that category. Be careful not to move the parts between the two wing pieces on each side though - that might shift the center of mass further forward which is not what you want.

EDIT: Also, the above may only apply to stock aero. FAR/NEAR's model may be more or less forgiving, or exactly the same...

I was able to pull up after a 5km warm up.

EDIT: And able to land.

Edited January 2, 2015 by locustgate

[Anquietas314]

I was able to pull up after a 5km warm up.

If you were falling for those 5km, it's probably just that the atmosphere became thicker, giving your plane's control surfaces the extra force needed to pull up.