SSTO Space Plane Problems

[I likeOxidizerrfuel]

I am having trouble keeping my SSTO stable in the Atmosphere. This is my first time building an SSTO space plane. I have to spend a lot of time in the Atmosphere. 

 

[Foxster]

I'm sorry to hear that. 

[Vanamonde]

Pics of the craft in question are necessary to diagnose the problem. Please provide some of those. 

Off the top of my head, I'd guess that the center of mass is changing as you burn fuel, but we'll have to see. 

Meanwhile, your thread has been moved to Gameplay Questions. 

[eddiew]

As Vanamonde says, we can't help without screenshots. Too many billions of configurations of spaceplanes that might maybe not be quite right yet still kind of fly to some degree.

General thoughts after seeing many many people asking why their planes fail:

- Instability happens because the CoM is too close to the CoL, sometimes happening as fuel drains. Some people seem to think the CoM and CoL should be aligned; no. No. That is exactly how to MAKE a plane unstable. You do it for fighter jets, not for anything you want to be able to take your hand off the stick.

- Some people seem to like to fly planes without a vertical tailfin... don't be doing that unless you want flat spins.

- If you're stuck in the atmosphere for a very long time, maybe you just don't have enough thrust and need more jet engines. Or maybe you need more lifting surfaces because you''re having to pull back 30 degrees to stay level. Again, pictures are vital to getting help with your specific plane.

- Delta wings with no canards. These planes are usually heavy at the back, then people put the control surfaces half a metre behind the CoM and wonder why they have no pitch control. Got to give them some leverage and have a good distance between the control surfaces and the CoM.

[IronMaiden]

51 minutes ago, eddiew said:

- Instability happens because the CoM is too close to the CoL, sometimes happening as fuel drains. Some people seem to think the CoM and CoL should be aligned; no. No. That is exactly how to MAKE a plane unstable. You do it for fighter jets, not for anything you want to be able to take your hand off the stick.

Good advice except for this. Spaceplanes are very sensitive to drag. The closer you can get your CoL to your CoM while maintaining stability the better. This requires less angle of attack and less wing area to remain at level flight, resulting in less drag. If you have your CoM in the center of your fuselage then there's no problem with having a CoL right on top of the CoM, the tail plane will easily dominate pitch torque. In fact, I prefer my space planes have a CoL in front of CoM at low angle of attack, that way it will naturally tend toward nose up and require less control surface deflection to stay at level flight.