Every spaceplane I've made crashes

[Artelusify]

This is me every time I make a spaceplane:

Are there any guides on how to make one...?

I understand the basics, wings, engines, put the landing gear shortly after the wings, put the wings near the back. But I still don\'t seem to get it

For example, I made this plane and it\'s so hard to fly every time I take off.

What I (thought) I did:

• Put the wings before the center of mass

• Put lifters in the front, angle them

• Angle the wings up so the plane is more stable

• Landing gears after the area of lift so the plane takes off easily

But it still doesn\'t work

[xclusiv8]

You can take a look at some of mine. They are all stable and flyable without the SAS. =)

http://dl.dropbox.com/u/11003858/KSP/X-Planes.rar

[vexx32]

First, remove the canard on the front of the aircraft.

Second, have your sings horizontal, and attach control surfaces to them. You\'ll find them in the controls tab with RCS and SAS modules. There are small and large variants. For those wings, use the large ones. If they attach at the wrong angle (you want them in line with the wings), use WASDQE to rotate them until they\'re attaching properly.

Then, to give you a bit more control, you want to add a tail fin; it should be in the structural and aerodynamics tab. Looks like a small version of the big wings you already have on there. Add it at the back, in the centre. Attach a small control surface to that, again in line with the tail fin itself.

Basically, always have plenty of control surfaces, have a rudder and avoid canards; they don\'t help a lot. You can use them, but it won\'t do alone.

Also, using the inline cockpit and attaching a nosecone base and the Avionics Module will help with any difficulty in controlling; it\'s like ASAS for planes.

[Temstar]

You\'ve been given bad advices bro

• Put the wings before the center of mass

Right, that\'s bad. The idea of a balanced plane is to have the center of lift right on the center of mass. Center of mass is pretty easy to understand, center of lift is the sum of lift from all your wings and control surfaces. For example most planes have a center of mass towards the rear of the plane because all the heavy stuff like engines, fuel and fat sections of the fuselage is at the back. That means when you add wings to the aircraft you got to add it so there\'s more lift at the rear at the plane then front. Hence why delta wing aircraft have the main wing at the back and the smaller canards at the front.

The best way to tell if your center of lift is exactly where your center of mass is is to fly straight and level with no control input. If they are matched then you nose will neither pitch up or down.

The tricky part is shifting center of mass - remember as you use up your fuel gradually the nose of your plane become lighter than your rear. You need to counter this with trim and clever engineering. In KSP one way is to make your nose a bit heavier so at take off the tendency is to pitch down slightly. Counter this with trim and half way through your flight the center of mass will be exactly on center of lift. Towards the end if your flight your rear will be heavier again so you have to counter by trim in the other direction.

• Put lifters in the front, angle them

Those are called canards. You use them if you need lift at the front of the plane. They improve the plane\'s maneuverability by giving you two separate set of horizontal control surfaces. Delta wing aircraft have a problem getting their nose up at take off and the canard is there to help with that by providing lift at the front of the plane. Don\'t angle them, see below for why.

• Angle the wings up so the plane is more stable

Don\'t do that, use vertical stabilizer for this. V-tail is used in real life by things like F-22 but they make the control much more complicated because when you move their control surfaces they introduce both yaw and pitch force rather than one or the other. If you want only yaw or only pitch you need a very complex control system (usually fly-by-wire) which can cancel yaw/pitch of one tail with the other. I personally doubt KSP can do this properly. So stick to either completely horizontal or completely vertical surfaces. Remember, you MUST have at least one vertical control surface on your plane or it\'s going to be unstable since it has no control over yaw forces.

• Landing gears after the area of lift so the plane takes off easily

Wrong again, basically if you put landing gear behind the main wing you ensure your plane will never be able to nose up at take off unless you have canards and said canards are generating so much lift they can lift 50% of the weight of the plane by themselves. That\'s a hard ask for canards considering their size compared to the main wings. Remember when a plane nose up at take off they do around the wheels of the main landing gears. So the more aft the main landing gears are the more weight the plane have to lift before the plane nose up. Imagine it this way: if the main gears are exactly at the center of mass of the plane and we retract the nose landing gear then the plane will be on a precarious balance like a seesaw. It will only require a tiny bit of force to tip the nose (or the tail) of the plane up. Conversely the further away the main landing gears are from the center of the mass the harder it becomes to tilt the heavier half of the plane up.

Whoever gave you those advices are off the mark four for four

[Waslop]

It might be worth noting that on some of my more flip prone designs, they seem to behaved much much better once I cut down the thrust (not very kerbal I know) and avoided steep climbs. I think the back end tries to overtake the front at the slightest bit of pitch if you\'re not careful.

[vexx32]

If that\'s happening, you should add more wings at the front or move the wings forwards a bit.

[theflyingfish]

Often, planes will flip because both standard jet engines are thrust vectoring. When you make a turn, the engine will try to push the end of the plane around. They make the plane more manueverable and controllable at low speeds or high altitudes (Flight envelopes with low dynamic pressures, where control surfaces are less useful), but often the off-center thrust of a vectored engine will tend to overcome the aerodynamic stability of the wings and cause a backwards flip. To fix this, either config edit out the vectoring, use an ASAS or Flight Stability module, add more wings in the back to increase aerodynamic stability, or place the engines on pylons at the middle of the craft, near the CoG.

If you are using rocket engines the problem becomes twice as bad, because the default rocket engines are often very, very, VERY heavy, and the increased inertia of a 2.5 weight rocket engine will often overcome the aerodynamic stability of many planes as well.

This is why most successful KSP designs have large delta wings located as far rearward as possible, to keep the engine weight and thrust vectoring under control.

With your craft, I propose Four solutions:

1. Make the wings flat and move them as far back as possible. While with larger craft I will sometimes give the wings a slight dihedral (upward angle) to stabilize the roll axis by moving the CoG below the wings, on small craft it is unnecessary, and can make it want to pitch up. Moving the wings back will help keep the engine flip under control. Also, by making the wings flat, you can...

2. Mount the gear on the wings. This will remove the unnecessary pylons, and if you place the front gear on the fuselage, will give the plane a nose-up attitude on the ground that will reduce your takeoff length and speed, and help your ground manuevering.

3. Adding a Vertical Stabilizer will increase the lateral stabilily of the craft. Don\'t put a control surface on it. Rudders are only needed on large planes and only make small ones twitchy.

4. Take the canard off of the cockpit and put it on the side of the fuselage. And don\'t use those canards, use the regular ones.

[Twinky827]

OR, you could do what I do... add so many control surfaces that your plane flips at the slightest touch of the wheel... I\'m an expierienced pilot (FSX for 6 years!)

[Xivios]

Center of lift directly on center of mass probably works well in KSP, but it\'s not entirely ideal, or rather, it\'s unrealistically ideal. Center of lift behind center of mass makes a plane more stable, tends to pitch down, helps prevent stall and makes the plane easier to recover if it does stall. I don\'t know if KSP can model a stall yet though, but if the aerodynamics get overhauled it might be worth a consideration. At any case, if pinning down the exact center of mass is a pain, then center of mass ahead of center of lift is the next best thing. This means wings far back. But it does make a plane harder to take off.

Rudders would be a good idea in theory, but right now it\'s probably one of the only solidly bad pieces of advice Temstar has given you, the rest is pretty solid.

The reason is this. KSP couples ALL control surfaces together - there is no difference to KSP between an aileron, a rudder, or an elevator, if the control surface can at all affect an axis it will try to.

This creates a VERY BAD relationship between the ailerons and the rudder.

The rudder usually sits on the rear of the vertical stab, or is the vertical stab if you use an all-moving tail. The end effect is the same.

Imagine the plane now, as a series of levers around the center of gravity. The rudder is way out at the back, and has a long lever along the yaw axis, giving it great yaw authority. This is exactly what you want, right? Well, usually.

Imagine the ailerons now, way out on the ends of the wings, same deal, long lever along the roll axis.

But the rudder, it still has a little leverage on the roll axis too, doesn\'t it? But not much, it sits just above the fuselage, which puts it just above the roll axis. So it can affect roll, but only a little bit.

Well, KSP sees that it can affect roll, and will treat it as an aileron when you try to roll.

So you roll right, perhaps, and what happens? Right aileron goes up, right wing drops, left aileron goes down, left wings rises, all good, but the rudder, trying to roll the plane to the right by pushing over the fuselage, deflects left...fuselage swings left.

So here you are, trying to roll right, probably with the intention of turning right, and the aircraft is trying to turn left. This is called Adverse Yaw. It\'s a minor issue, in the real world, the Wright brothers ran into it, that the rudder is supposed to correct, but in KSP, it makes it worse, to an insane degree.

Odd thing though, that with such a simple aero model to begin with, adverse yaw is pretty minor anyways, and the rudder is that much less important! So skip it, because it will only make your life difficult in the meantime.

[Naiba]

I\'ve been working on a line of training jets that are pretty easy to learn to fly with, some pretty safe low-speed aircraft you can get to know what you\'re doing with before becoming a test pilot for crazily unstable designs.

*On a side note, with enough control surfaces, a lot of thrust and a few wings for lift, and some fairly reasonable balance, ASAS can fly pretty much anything in a straight line if you can point it in the right direction to begin with. I mean crazily un-flyable designs. (good luck on the landing \'tho).

[Guest JDB]

I find starting off small and working up works well. If you make a craft and can get it to fly level using trim, you can look at the angle of the control surfaces while it flies, re-enter the hanger and adjust them by sticking them back on and using the Shift+ WASDQE keys to make the changes permanent. Get what I mean? In the screenshot below, the control surfaces on the back have been angled up slightly. Without using trim, the nose would always dip down but now the plane flies true.

[Twinky827]

2 of you forgot tails... Those tings are HARD to fly..

[vexx32]

Aye, a tail is often quite necessary. For large planes, you\'re going to want a wide tailplane with two rudder surfaces. For small, you only need a single central rudder. However, you\'re going to need a LOT of ailerons/elevators in order to control just about anything as well.