Large Space Plane

[locustgate]

So I'm trying to make a space plane, never have been able to get them into orbit. My current plane when it hits the end of the runway it tries to do a donut, ending with it kissing the ground, which the ground doesn't like.

. If anyone knows how to upload a file tell me.

[Anquietas314]

You should make the Center of Mass(CoM) and Center of Lift(CoL) visible on the screenshot. Without them, it's harder to tell what the problem is. From your description, I would guess the CoL is too far forward - it should be just behind the CoM in a typical spaceplane design, but it depends on how fuel drainage affects mass distribution in your particular design.

[Pecan]

You can't upload .craft (or any other files) to the forum directly. Put it on dropbox or similar and post a link to it.

A photo of the 'plane showing the CoM, CoL and preferably the CoT would help us spot any problems but it doesn't seem to have many control-surfaces (eg; elevons).

What would help you most would be building something much smaller to start with, just to practice :-) Mk1 parts ftw, even a satellite-delivery SSTO.

[locustgate]

[Pecan]

CoT looks ok but the CoL is in front of the CoM, which will make the whole thing prone to doing a back-flip. This is accentuated by having the higher-drag parts like intakes ahead of the CoM; they should also be behind it, otherwise it all just wants to fly point backwards

[GoSlash27]

http://i.imgur.com/9nFCjg2.jpg

That balance is very bad.

You never want your center of lift ahead of your center of mass.

I can also see that you have nothing to keep your yaw (swiveling left and right) under control, so you'll want to see to that. Put some vertical tailplanes in the back so it'll want to point towards where it's flying.

Best,

-Slashy

[AlexanderB]

Not to mess with a pretty creative looking design, but:

-Take those R.A.P.I.E.R. engines off and put on some of those small orange 24-77's, it saves a lot of weight, and you already have turbojets which are way better than the rapiers.

- It has *no* vertical tail fin, add one (or two)

- Make sure the center of mass is in front of the center of lift with both empty and full tanks, but not too far ahead.

- Put the landing gear not too far behind the center of mass, so you can just flip the nose up on the runway, without having to rely on the little hop at the end to get you in the air. Add an extra wheel in the back (raised up a little) if the tail hits the ground. If I use the mk2 to 2x adapter, I like to stick it halfway between the engines.

- Add more control surfaces. Perhaps some canards too. If you add more to the wing, make sure the wheels are far enough forward for it to have enough leverage.

And an added trick, make sure you place x intakes, first jet engine, x intakes, second jet engine. If you don't, all the air will go to 1 of the 2 jets and you'll get asymetric flameout. 4 structural intakes per jet is plenty for the way I fly and doesn't look too overkill, but 5 might be okay too.

It may look a little boring, but this is pretty much how I built my spaceplanes for a while now:

It carries quite a load to orbit too: (the lander flew from kerbin orbit to minmus on its own)

And I also made a slightly longer version that has a couple of those passenger compartments and an inline docking port instead of a big cargo bay, works nice too.

[edit:] I see that your CoM is behind your CoL, its really important that you fix that..

Edited December 27, 2014 by AlexanderB

[locustgate]

Good news and bad news

Good: I got the CoL Behind CoM

Bad: I can't get it off the ground

[Moss]

Try placing the rear-most wheels as far forward as the centre of mass.

[Anquietas314]

Try placing the rear-most wheels as far forward as the centre of mass.

For safety, make sure it's slightly behind the center of mass. You really don't want to be landing empty and find you've got yourself a tail-scraper

[locustgate]

Try placing the rear-most wheels as far forward as the centre of mass.

Oooook? Not sure how that would solve lift off problems, and didn't do anything.

[Anquietas314]

Oooook? Not sure how that would solve lift off problems, and didn't do anything.

If the rear wheels are too far back, you can't get the leverage to pull up, which prevents you from lifting off. If it doesn't work with the rear wheels very close to the center of mass, you need more lift or less weight.

EDIT: You could need more thrust in that situation too, but going by your screenshots you have plenty engines

Edited December 28, 2014 by armagheddonsgw

[tibbe]

AlexanderB, what are the exact specs for that aircraft? I see almost no fuel.

[Anquietas314]

AlexanderB, what are the exact specs for that aircraft? I see almost no fuel.

Given turbojets can get you out of the atmosphere entirely on their own, I wouldn't expect it to need much fuel. The tiny rockomax radial engines are probably enough to raise periapsis to a circular orbit for next to nothing. I actually considered making a design like that in my 0.90 career save (but currently don't have access to necessary spaceplane parts or action groups )

[GoSlash27]

Locustgate,

You really want your center of lift just barely behind your center of mass. You also want to make sure it stays that way throughout the flight, so fuel tanks need to be in the center of mass.

Like this...

Best,

-Slashy

[AlexanderB]

AlexanderB, what are the exact specs for that aircraft? I see almost no fuel.

It doesn't need that much fuel, this much is just enough to reach 80x80 to 100x100 orbit depending on how much weight is in the cargo bay, and de-orbit afterwards. (Put your PE at 35-40 km above the KSC, and it will put you on a glide slope that takes you really close to the runway.) If you want to go further (say, to the mun or beyond) you need a LOT more fuel (fuel to get further, and fuel to drag all that fuel up to orbit.)

Forward tank is just liquid fuel, I use the turbojets to get to a 100x30-ish orbit (at about 2400 m/s @ 35 km) before they flame out, (mostly) coast to the AP, then use the 24-77's to circularise. It works so well because its a really low-mass design, adding more stuff quickly leads to adding more stuff.