Space plane help

[Nightwraith]

So today I've been working on building a ssto space plane. The ultimate goal is to have something that can take some payload, whatever can fit in the 6m long S2 cargo bay from B9, to other planets. Speaking of, using B9 and FAR. That's it.

As of right now, I cannot get anything off the runway.

I started off with a much more complex design, and have distilled it down to this.

If I can get it to go straight down the runway without it veering off, it just nosedives into the ground, well before I ever get to the water. I can't imagine I need more lift. And those two turbojets have me well above 120m/s at that point.

I can make a viable plane with the smaller parts, but they obviously have their limitations. Any ideas?

Edited November 4, 2013 by Nightwraith

[Grover]

turn on the centre of mass display and centre of lift, those buttons in the bottom left, the centre of lift (blue widget) should be sensibly oriented (all arrows should be along the aircraft axes) and situated just a little behind and above the centre of mass (black and yellow ball), but not outside the ball

you can move parts around to move the different centres, try angling the wings upwards (SHIFT - Q/E) to raise the centre of lift, and bear in mind, your centre of mass may move as fuel is used, depending on your construction

[Vanamonde]

Have you tried building small planes to work out the principles? Among other things you'd learn that way is that placing the landing gear all the way at the back like that causes it to act like a fulcrum, with the length of the plane acting as a lever to hold the nose down. That's a problem, because the game's current aerodynamic system is as placeholder, so KSP wing parts generate zero lift at zero angle of attack. Which I suspect is why you're finding that this plane acts like it's glued to the runway. Check out some of the plane-building tutorial threads.

[Cruzan]

Hey Nightwraith,

So on first glance, it looks like your front nose gear is mounted higher up than your rear landing gears. This will make your plane be pitched nose down on the runway, making it extremely difficult to liftoff! You can try mounting the front gear lower, if possible to fit the aesthetics, or mount the rear landing gears a little higher. Just be careful of the ground clearance for the tail of your plane if you mount those rear gears higher.

Another option, would be to give the wings a slight angle to begin with. You can try mounting the wings by using the Shift + WASD keys to pitch the wings upward slightly (1 to 2 clicks).

It might also help to place canards toward the front of your plane, again if it will fit into your design aesthetics . Canards in front of the CoM help a lot for getting more pitch authority! *Highly Recommended*

The two basic things your plane needs to liftoff the runway are:

1. Speed

2. Angle of attack (positive!)

You've got speed covered it sounds like, just work on the angle of attack and you'll be golden!

Good luck!

[Hodo]

To add to what Cruzan said, I also noticed your engines are set lower than your center of mass (CoM), if you get this thing airborne it will flip nose up as soon as you apply to much power.

The other thing I noticed is your center of lift, CoL, looks like it would be in front of your CoM. Again if you get this thing airborne it will do crazy things and be a complete pain to control.

But I am not familiar at all with the stock KSP (lack of) aerodynamics. I would suggest downloading the FAR mod it will help give you a bit more design control over your aircraft, and if you have any idea how a plane is actually built or works you will have pretty good success with space planes.

[Vanamonde]

your engines are set lower than your center of mass... if you get this thing airborne it will flip nose up as soon as you apply to much power.

On a ship that big the effect shouldn't be very strong, and can actually be beneficial because it helps to counter-act the slight nose-heaviness recommended for stability.

[Mmmmyum]

He's using FAR... I'd say that your center of lift is way behind your center of mass, thus your wings are just trying to shove the rear of the craft up and the nose down.

Also I find with bigger planes it's easier just to have "bicycle" gear and let the reaction wheels get your craft balanced for takeoff, as it doesn't jitter as much as more traditional tricycle gear

Edited November 3, 2013 by Mmmmyum

[Nightwraith]

Thanks for the tips guys, I'll give it a shot this afternoon when I get some time.

[MatzahMan]

The nuke engine on the back probably pushes the CoG back(those are heavy), so putting a LV-T45/30 might be better. Also the nuke engine may not provide enough thrust to get into orbit, another reason for trying the LV-T45/30

[Nightwraith]

The nuke engine on the back probably pushes the CoG back(those are heavy), so putting a LV-T45/30 might be better. Also the nuke engine may not provide enough thrust to get into orbit, another reason for trying the LV-T45/30

I ran into that very problem today. Added a lot to the design.....and two more nukes. I'm out of time to play for now, but I've gotten this thing to 20k meters screaming along around 1500m/s without the rocket engines. I haven't yet fired up all 3 nukes at the same time, it might not be enough...I may be better served by one LVT-45 - but I would like to be able to take this thing to Duna.

Pretty happy with it right now, you guys were a lot of help. I changed the AoA of the high elevator in the rear to tweak the natural lift/dive. Canards help too.

Getting past the 13-15k barrier is rough. Need to stop climbing around 10k to pick up speed else there just isnt enough lift.