Problems With Heavy SSTO

[Werty]

I'm triying to make this thing fli to deliber a payload up to 200.000m but i habe problems with the lift that i'm not capable of solving that's why i need your help. It seems not to create drag and if i achive the drag necessary then the central mass overpass the center of lift so i need more knowledge that maybe you have.

If you need the ship file make me Know

Edited November 20, 2014 by Werty
fixed the images

[Pecan]

Drag is not necessary to fly, although it's rather helpful when you want to slow down.

In the SPH the Centre of Lift (CoL) should be just behind the Centre of Mass (CoM) for balance and controlability and the Centre of Thrust (CoT), actually axis of thrust should be in-line with the CoM, otherwise the engines will always tend to rotate the whole ship.

What is not shown is the Centre of Drag, which will dictate the orientation the plane naturally wants to adopt. Air intakes create a lot of drag and yours are all right at the front of the plane, meaning it will want to fly 'backwards' all the time (which won't work, needless to say). You need to make sure those drag-inducing parts are behind the CoM so the plane wants to point in the right direction.

[Werty]

OK the CoT is not aligned so i will correct it.

and i will change the intakes but it will make the CoM aproach to the CoL so i will be unestable. I will make a new design trying to solve the problems.

thanks for helping

[capi3101]

I assume you're using NEAR or FAR? If you are, I'm of no help. If not, I can tell you right off the bat that you're definitely well short of what you need pretty much in every department...

What's the payload and how massive is that plane as is?

[Werty]

I'm not usig any aerodynamics mod

the payload is 13.8 T

the plane full without cargo 88 T

you think i have not enought engine-power?

[Oafman]

You have very little, in terms of lift surfaces, considering the mass. I would say that is a more urgent issue than thrust.

Do you have KER or MJ to give atmospheric TWR figures?

[Werty]

i use MJ

i start redesing all the ship i'm balancing it trying to put the engines close to the center of the lift so the DCoM don't get behind the CoL.

i will put the redesing here so you will se the improvement

but is triky to desing somethin that delibers 13 T in orbit

[capi3101]

I'm not usig any aerodynamics mod

the payload is 13.8 T

the plane full without cargo 88 T

you think i have not enought engine-power?

Right. Okay...I won't give you my full spaceplane newb advice, but I will go ahead and point you to DocMoriarty's KSP Space Plane Construction and Operation Guide. It's slightly out of date (by slightly I mean it was designed for 0.24.2 and he hasn't yet updated it for the changes in 0.25), but so far the only thing I've seen that's major is that the new Wing Connectors are functionally equivalent to Delta Wings. Shock Cone Intakes are equivalent to 1.2 Ram Intakes and 4 of the new Structural Intakes are roughly equivalent to a single Shock Cone Intake. Big focus on transporter spaceplanes there. I think the guide comes with the planes he designed in 0.24.2; they probably aren't directly useable in 0.25 but they could give you a few ideas at least. And I know there's at least one there that can handle thirteen tonnes.

If you want my full array of advice for stock aero spaceplanes, it's here. I'll mention that a good payload fraction for planning a transporter spaceplane is about 25%.

For the record: engine power = more than enough, lift generation = nowhere close to enough. And the plane is a bit heavy for the job.

[GoSlash27]

I had a really hard time trying to decode what you meant by "no drag", so please bear with me if I've gotten it wrong.

Are you saying that it becomes dynamically unstable at high speed and wants to flip backwards?

If so, the problem is that your intakes are too far forward.

Contrary to popular belief, not all parts have equal drag in KSP. Balancing slow planes is just a matter of getting the CoL correct in relation to the CoM, but at high speed it's more important to have the low drag parts in front and high drag parts in back.

Intakes have extremely high drag, so they need to be in the back.

Also, wings are extremely low drag, but they must necessarily be close to the middle for the plane to fly. It is important that your center of lift not be above or below your center of mass so that it doesn't cause a torque moment at high speed.

Best,

-Slashy

Edited November 20, 2014 by GoSlash27