FAR again. Wings area over mass

[cicatrix]

I'm trying to find a way to get a good lift area/mass relation with FAR. So far I'm only guided by FAR configuration menu where I watch that 'all figures must be green' without any real knowledge what figure means what and how should I proceed.

The question I have is rather simple - by knowing atmo ISP/Thrust of an engine and ship's mass, how should I determine what wing area should be necessary to lift that thing? I tried 'the bigger wings the better' approach, but faced stability issues. My planes just don't fly. They go along the runway then pitch up very sharply and then the wings usually get torn off.

I do not have a joystick and so FAR I couldn't make a plane less responsive to WASD. Even the shortest key press is too much, as it appears. And also, I read in some tutorials that CoL should be slightly behind CoM, but wouldn't this make the plane pitch down?

And again, I watched real planes as they take off and they had flaps/elevons/whatever they call it on their wings pointed DOWN, not up - what's that? Some KSP peculiarity or there's some theory behind it? It sounds logical if CoL is really behind CoM but to produce good lever effect, CoL should be much farther than 'slightly behind' CoM.

I'm frustrated to a point of removing FAR right now (Not that frustrated of course, but I'm close).

[Taki117]

I'm trying to find a way to get a good lift area/mass relation with FAR. So far I'm only guided by FAR configuration menu where I watch that 'all figures must be green' without any real knowledge what figure means what and how should I proceed.

The question I have is rather simple - by knowing atmo ISP/Thrust of an engine and ship's mass, how should I determine what wing area should be necessary to lift that thing? I tried 'the bigger wings the better' approach, but faced stability issues. My planes just don't fly. They go along the runway then pitch up very sharply and then the wings usually get torn off.

I do not have a joystick and so FAR I couldn't make a plane less responsive to WASD. Even the shortest key press is too much, as it appears. And also, I read in some tutorials that CoL should be slightly behind CoM, but wouldn't this make the plane pitch down?

And again, I watched real planes as they take off and they had flaps/elevons/whatever they call it on their wings pointed DOWN, not up - what's that? Some KSP peculiarity or there's some theory behind it? It sounds logical if CoL is really behind CoM but to produce good lever effect, CoL should be much farther than 'slightly behind' CoM.

I'm frustrated to a point of removing FAR right now (Not that frustrated of course, but I'm close).

Alright, I'm going to try and tackle this one. A picture would really help.

It sounds like you don't have enough forward pitch authority, basically you are trying to pitch your entire aircraft with just your rear control surfaces. I suspect this is why you get going at a good speed (Probably about mach .5 on the runway) and when you pitch up your wings get torn off due to a rapid change in angle of attack resulting in a large dynamic pressure on the bottom of your wings.

As far as making aircraft less repsonsive if you hit CAPS LOCK it will turn on fine tune mode, which will dampen keyboard inputs.

For the CoL being behind CoL that relationship really doesn't matter too much as long as they are not too far apart. While it's generally not a good idea to have the CoM behind the CoL it is acceptable within certain margins.

Real aircraft have flaps that change the wing shape and increase lift, allowing them to take off at lower speeds.

Now, while this tutorial isn't optimized for far, the basic principles are there. I suggest giving it a read and seeing what you can come up with. Also, start small, don't try to build a big interplanetary SSTO or cargo hauler your first go round.

[cicatrix]

Pic it is:

It won't take off till the end of the runway, then it pitches up sharply (if I hold 'S') and loses stability

If I don't touch anything it just splashes down into the sea.

And all my planes tend to point its nose down (no level flight).

[Jovus]

Sounds more like a landing gear problem than a pitch authority problem. Place your rear landing gear further forward, because what's probably happening is that when you try to pitch up with that gear on the runway, you're fighting against a strong lever arm due to gear placement and the plane doesn't lift. Then, when you go off the end, the runway is removed from underneath, and your violent pitching up causes the plane to tear itself apart.

As an aside, the plane you have now is going to want to yaw all over the place in the air, and it's only going to get worse as you go faster. You need one or more of: bigger rudders, more rudders, rudders further back.

Finally, I know from experience that at high altitude and speed rear delta designs like that are going to want to pitch up away from prograde; you probably want to place another pair of canards on the nose for the pitch authority to fight that tendency (and then move other things around to compensate for the change in CoL).

[Taki117]

Pic it is:

http://i.imgur.com/pZDxl4o.jpg

It won't take off till the end of the runway, then it pitches up sharply (if I hold 'S') and loses stability

If I don't touch anything it just splashes down into the sea.

And all my planes tend to point its nose down (no level flight).

Thanks for the pic, that really helps. Your CoM/CoL relationship si too far off, slide your rear wings forward a bit to get them closer. You also have way too much yaw authority (Which is probably why it appears that your CoL is off center, which will cause roll issues) I would use the AV-R8 winglets as rudders personally. I would also break up that one large control surface in the rear of your aircraft into two smaller ones. One set of elevons (That control both pitch and roll) and another set of elevators (that control just pitch) I also agree with Jvus in that your pitching problems sound more like misplaced landing gear than control authority issues. The wheel of the gear should be just behind the CoM, if your aircraft wants to pitch tail up on the runway as soon as it loads move them back just a bit, if you cant get off the runway with them moved back consider adding a tail wheel or tail strike (an I-Beam or Girder under the tail of your aircraft)

[sdj64]

If your plane has too much pitch-up, right-click on the control surface and turn down the "Control Deflection" a bit. Default is 20 but I've never had a FAR plane with any control surface higher than 10. I'm probably doing something wrong here too but that's how I fixed it. You want it to be low enough that it doesn't rip itself to shreds or wobble greatly with maximum deflection.

The two posts above me say you have too little, then too much vertical rudders. You should probably just get rid of the two side fins, they're too close to your COM. Or at least move them back more. The middle one looks good, but could use a larger control surface if you decide to get rid of the side ones. COL is also a little far back from the COM.

[NathanKell]

The question is not simply "how much wing do I need to lift this." The question is, "for a given velocity and density, how much wing do I need for level flight with a sane AoA" For instance, at Mach 4, you don't need very much wing area. At 100m/s, you need lots (or you must fly at like 15 degrees AoA).

The window you have open tells you. input speed and density and temperature, and it will report how high an AoA you need for level flight. If it's more than say 10 degrees at takeoff speed (0.3 Mach, say) and density (1.2), then you need more wing.

[Hodo]

Pic it is:

http://i.imgur.com/pZDxl4o.jpg

It won't take off till the end of the runway, then it pitches up sharply (if I hold 'S') and loses stability

If I don't touch anything it just splashes down into the sea.

And all my planes tend to point its nose down (no level flight).

Ok simple answer to your first question about Flaps.

Flaps are the things that go on the trailing edge of the wings. They are generally inline or near the CoL for the craft, this is to keep them from acting like a leaver and tilting the nose down, this way they create a longer wing area which generates more lift at lower speeds.

The Ailerons and Elevators are different all together. Ailerons are the things at the ends of the wings that control the roll of the craft. Elevators are the things at the end of the aircraft that control pitch. The rudder controls yaw and canards control nose pitch and sometimes roll.

The biggest thing to look at in FAR with designing an aircraft is to look at the CoL vs CoM. If the CoL is to far behind the CoM the craft will act nose heavy, if it is to close it will be "twitchy". And if it is infront the craft will be uncontrollable in game.

Landing gear placement is the next big thing. You want your rear most gear near your CoL point this is the point of rotation for the aircraft. This way when you take off you rotate around that point. If that is to far back then you could place them just behind your CoM.

The problem I see with that craft isnt you need more rudders or larger tail planes, it is you dont have enough real stability in the yaw catagory. It isn't bad the craft is otherwise pretty good. The tool you displayed is set at altitude of sea level and .35 mach which is about take off speed or landing speed. Which means your craft will have a very minor yaw issue at low speeds and low altitudes.

The only otherthing I see wrong with it is your CoL is way to far behind your CoM. You should have it a fair bit closer.

About like that.