RoboRay

Big connection nodes might make it rather hard to get payloads positioned in the cargo bays... they might be trying to snap to the lower of the two big overlapping nodes. I haven't had any structural issues with the current node size, though I do tend to add a few reinforcing struts out of habit from back before they made joints stronger.

That is not why you want the CoL behind the CoM, though I do see a lot of people trying to "teach" that here. The reason you want the CoL behind the CoM is for positive aerodynamic stability. Lift is a form of drag. When a solid object is moving through a fluid, it naturally rotates so that the drag is toward the back, behind the CoM. Right. That's negative stability and neutral stability, respectively. The effect I described above. The CoM is the pivot-point about which the plane rotates. Look at a weathervane... one end has high drag, the other end has low drag. The wind makes it rotate around the pivot-point (the pole) so that the high-drag end is downwind, behind the pole. It's the air flowing past your plane that makes it "flip-happy" or not based on the CoL/CoM relationship, not gravity pulling down on the plane. All of this is just a misunderstanding of the underlying principles. It's not about "balancing" your plane, it's about fluid dynamics pushing the high-drag end harder than the low-drag end, and the CoM is the point about which it forces rotation. If you make a plane too positively stable, by putting the CoL too far back, it can actually become impossible to turn no matter how much you pull on the controls... they simply cannot apply enough force to overcome the airflow trying to keep the CoL directly behind the CoM. That makes it pretty difficult to fly, since you can't steer. If you design a plane for neutral stability, it also becomes very difficult to fly... by being so easy to point it in any direction, it becomes very difficult to make it point in the direction you want it to actually go. The slightest disturbance and you're facing a different direction. That's great for fighters with flight-control computers, where the pilot is really just voting for what the controls should be doing and he's in the minority party, but not so great for anyone trying to just fly in a straight line by hand.

I'm afraid I'm just going to have to go with MarvinKitFox's assessment. Good luck everyone.

From above... "Your plane is like the arrow shot from a bow. If you try to throw an arrow sideways, what happens? The drag from the fins naturally turns the arrow so that the fins are behind the CoM. Lift is a form of drag, so the CoL also naturally "seeks" a position behind the CoM."

There are two unequal and opposing factors competing here that affect that. One, positive stability, is determined by how far the CoL is behind the CoM. Your plane is like the arrow shot from a bow. If you try to throw an arrow sideways, what happens? The drag from the fins naturally turns the arrow so that the fins are behind the CoM. Lift is a form of drag, so the CoL also naturally "seeks" a position behind the CoM. The further back the CoL, the more aggressively the airflow tries to hold it behind the CoM. If a plane has the CoL way back, the plane can become very difficult to turn, meaning you must apply a lot of force with the control surfaces. If you move the CoL closer to the CoM, you don't need to apply as much force to make it turn. However, that doesn't mean it's good to put the CoL right on top of the CoM. If you do that, the plane has neutral stability and has no preferred orientation in respect to the airflow. This makes it very hard to control because the nose will easily flip in any direction, even around backwards. Putting the CoL in front of the CoM would give negative stability, meaning the plane is always trying to turn around backwards and you will find it impossible to control. The other factor is that the further your surfaces are from the CoM, the more effective they are for that axis of control. Moving your elevators forward gave them less leverage, but the plane also became less positively stable because you moved the CoL forward closer to the CoM, making it require much less force to control pitch. So, the airflow applies leverage based on how far apart the CoL and CoM are, and the elevators apply leverage based on far apart they are from the CoM. Which one has greater effect depends on the design of the plane. In your particular design, the effect of moving the CoL forward helped you more than the effect of moving the elevators forward hurt you.

Have you read those references we gave you earlier yet? Because that should have told you that you're making a lot of incorrect assumptions and helped you understand why.

Not if the goal is to learn to build planes that don't need that crutch. But if you want to add extra mass, power consumption and most importantly, cost to the the design, feel free. Heck, with enough SAS you don't need any control surfaces or stabilizers at all.

Adding SAS modules is the last thing I would suggest to someone trying to learn to build planes. What that does is create a band-aid work-around so that they can ignore the problems of their design, rather than learning to build a design that actually works. Basically, he just needs to read a few of the many good references provided earlier and gain an understanding of the basic principles.

It will work in 0.24 whenever [PART, 0.24] appears in the subject line of this thread.

Editor? Hell, I used MS Paint!

CoM is actually about in the middle of the speed brake (which is why the speed brake is right there), but that's close enough for this discussion.

See? (sigh) Unlike pitch, having the surfaces forward or back from the CoM doesn't make them significantly less effective at roll control. It does have some controllability complications, but that's really getting into advanced topics.

Yes, but I didn't want to add that as it might confuse him further. Sticking to "one purpose per surface" is probably best for an elementary introduction.

The F-15 does not have only ailerons. It has ailerons on the wings. The horizontal tail-surfaces are all-moving "stabilators" that perform the elevator function of pitch-control. They tilt up and down to raise or lower the nose in flight. Here... I'll label all the F-15 flight control surfaces for you:

Imitation is the sincerest form of flattery.

It's coming right at us!

You mean like SmartASS in SURF mode?

You get lift from the whole wing. That doesn't have anything to do with the effectiveness of your flight controls. You have to put them in the right place for them to provide certain control axes.

Your wings are in near the center of the plane, meaning surfaces there will provide roughly zero pitch control. The center of mass is the pivot point about which your craft rotates. To move it in a certain direction, the surfaces need need to be well away from the center of mass. It's like rolling a heavy rock with a stick... the longer the stick, the more leverage you can apply by grabbing the stick at the far end. In the second version you showed, you've got some canards up front for pitch control, so that's helping. Honestly, though... Put this big giant plane back in the hangar and start over from scratch. Build something small, so it's easy to assemble, easy to design, and easy to fly. Walk, then run. Come back to big giant planes that really don't do anything the little planes can't do later, when you've mastered building the little planes.

Personally, I hate the B9 gray. Your current stock-alike look is great. Maybe a better solution would be for B9 to add a stock-alike option!

Oh, now that's interesting. I wouldn't call you dumb for it, though, as that's not really obvious that you must start with a command pod (or not use SelectRoot to change it).

Are you using the Fairing sections in the Aero page of the VAB? Or are you using the Fuselage sections in the Structural tab? Because Fairing sections eject, but Fuselage sections don't. Edit: Is there an echo in here? ...here? ...here?

Right about where the Kerbals are.

Even NASA had to go on EVA to retrieve film cassettes from the Apollo Service Module's SIM Bay cameras.

... Yes, the proportional differences between us and kerbals does give KSP cockpit design some very different requirements than in the real world. Kerbal giant foreheads are much harder to design around.