Tail wings.

[G'th]

So with b9 5.0 on its way, I've started getting REALLY into spaceplanes again (Even more so than usual), and I've started becoming curious about something.

And that is the tail wing. (I completely forget the technical term for it. The vertical wing part usually placed in the back) I've seen the typical design where you have one (with one rudder control) placed right in the middle of your plane and towards the back behind your main wings. But then I also see designs where you have two of them on the wing tips, either straight up or slanted outwards or inwards. Sometimes, I see two placed on either side of the plane's body, but still in the middle-back of the plane. Sometimes straight up, sometimes slanted. Sometimes I also see smaller wings placed at a slant, but without rudders.

What does placing tail wings like this affect? I know that slanting the wings themselves will affect the vertical location of your center of lift, but I haven't seen any obvious advantage to where you place them on your craft or whether or not having multiples really does anything for you aerodynamically. (Obviously having multiple rudders gives you stronger Yaw control)

[TechnicalK3rbal]

Are you talking about in FAR/NeAR or stock aerodynamics?

[Kasuha]

Vertical stabilizer/rudder is at the end of the plane usually to prevent flat spin or to help the plane to face forward - the surface is usually so small that it has negligible lift and cannot really be used for the plane to change direction, its main purpose is to stabilize. As such it is mostly irrelevant what exact geometry is used. Slanted/straight and one/two/more of them is mostly matter of personal taste and aesthetics.

[DocMoriarty]

Multiple rudders give you stronger yaw control and the farther away from CoM they are the better is their lever action which helps reduce their number eventually. And they are also used to fly a "coordinated" curve. Basically you "steer" with ailerons but thats only 1/3 of the truth since in a coordinated curve you also use pitch elevators and rudders to speed up the curve and to keep the ball of the turn indicator in the middle.

In KSP the number of rudders at least for space planes, as in planes going into space, depends mostly on how many you need to keep the plane stable and not breaking out left or right when the engines get deprived of oxygen at high altitudes short before you need to switch to rockets. Also helps to keep them big planes stable on runway before takeoff.

"Repoman" has 24 rudders.

[O-Doc]

In the real world, rudders are to prevent side-slip in a banking turn(some planes actually do use them to turn). As you roll, the nose wants to fall down because of the change in lift between the left and right wing. The rudder is to keep that nose up by offsetting the difference in lift.

The ideal location is always at the back in the center but other factors may lead the designer to put the rudder into a different configuration. These include, structural and material strength, airframe cost, drag, and desired aerodynamic performance/stability.

[cantab]

Indeed in stock KSP it's not much of an issue, unless you want to carry a payload that would physically collide with a vertical stabiliser in a certain place.

In FAR you might have issues if the airflow to the stabiliser is obstructed, but I'm not sure.

[RexKramer]

Traditional aircraft have a vertical stabilizer and a horizontal stabilizer.

The vertical stabilizer is to limit and control Yaw, or right-left motion. Attached to the vertical stabilizer is normally a Rudder, which is a movable control surface that can induce yaw, causing the nose to sweep right or left.

The Horizontal Stabilizer is used to limit and control Pitch, or up-down rotation. Attached to the horizontal stab is normally an Elevator, which is a moveable control surface, causing the nose to pitch up or down.

The stabilizing and control effects of a horizontal stabilizer and vertical stabilizer (with rudder and elevator surfaces) can be combined into two surfaces which form a 'V'. The two angled surfaces provide both pitch and yaw stability and control. The control surfaces attached to the 'V' shaped tail are sometimes called 'ruddervators' because they perform the function of both a rudder and elevator.

Real world examples of aircraft with this configuration include the Beechcraft V35 Bonanza, F117 Nighthawk, and several military UAVs.

The theoretical advantages are reduced drag from having only two stabilizer surfaces instead of three. Disadvantages would be added complexity, and added weight. The 'V' tail configuration is very uncommon, currently you are more likely to see it due to design considerations other than aerodynamic reasons. Keeping the tail out of the air behind engines, or reducing radar profiles are a couple of reasons a V tail might be handy.

In KSP, you have a lot of freedom to place control surfaces wherever you want. KSP aircraft react badly to having center of thrust not perfectly in line with center of mass, so I personally end up with at least one center-mounted engine usually. That makes it difficult to put the tail dead-center, so some creative placement of control surfaces is often in order.

[Hodo]

Traditional aircraft have a vertical stabilizer and a horizontal stabilizer.

The vertical stabilizer is to limit and control Yaw, or right-left motion. Attached to the vertical stabilizer is normally a Rudder, which is a movable control surface that can induce yaw, causing the nose to sweep right or left.

The Horizontal Stabilizer is used to limit and control Pitch, or up-down rotation. Attached to the horizontal stab is normally an Elevator, which is a moveable control surface, causing the nose to pitch up or down.

The stabilizing and control effects of a horizontal stabilizer and vertical stabilizer (with rudder and elevator surfaces) can be combined into two surfaces which form a 'V'. The two angled surfaces provide both pitch and yaw stability and control. The control surfaces attached to the 'V' shaped tail are sometimes called 'ruddervators' because they perform the function of both a rudder and elevator.

Real world examples of aircraft with this configuration include the Beechcraft V35 Bonanza, F117 Nighthawk, and several military UAVs.

The theoretical advantages are reduced drag from having only two stabilizer surfaces instead of three. Disadvantages would be added complexity, and added weight. The 'V' tail configuration is very uncommon, currently you are more likely to see it due to design considerations other than aerodynamic reasons. Keeping the tail out of the air behind engines, or reducing radar profiles are a couple of reasons a V tail might be handy.

In KSP, you have a lot of freedom to place control surfaces wherever you want. KSP aircraft react badly to having center of thrust not perfectly in line with center of mass, so I personally end up with at least one center-mounted engine usually. That makes it difficult to put the tail dead-center, so some creative placement of control surfaces is often in order.

Don't forget the best of the next gen fighter contest....

The YF-23...

I actually have built a new SSTO fighter that is pretty much following this design. It works better than expected.