Wanderfound

To make sure that your future interplanetary spaceplanes landing gear doesn't spontaneously explode (hey, it's KSP; spontaneous explosions happen all the time) as soon as it hits escape velocity, of course.

Screenshots. From the top and the side, in the SPH with CoM/CoL/CoT indicators turned on. We can't help you if we can't see what we're dealing with. F1 to take a screenshot, then chuck 'em on Dropbox or Photobucket or somesuch.

RAPIERs are almost as fuel efficient as turbojets while they're in air breathing mode. Don't let them switch to closed cycle until you want them to. Either turn off the auto mode switching (make an action group for it instead) or shut down the RAPIERs entirely after 25,000m and don't turn them back on until the turbojets start to die and you pull the nose up for the final burn. The trick to maximising your horizontal speed is to keep to low climb rates and minimal angles of attack until it's time for that final burn (when you pull the nose up to 45 degrees and start burning oxidiser). Get up into the low friction air over 20,000m and then level off to build speed before going higher. By the time you pass 30,000m your climb rate should be down to about 10m/s. Don't pull the nose up until you've extracted as much speed from the air-breathers as possible.

Screenshots. From the top and the side, in the SPH with CoM/CoL/CoT indicators turned on. We can't help you if we can't see what we're dealing with.

I know I'm harping on a bit here, but: wings. You can get 50 ton into orbit for less than √10,000 if you let the air do the lifting.

Or, alternatively: design your plane properly. Arrange your tanks and fuel lines right and the CoM will stay fairly stable no matter what stage of the flight you're at.

About √100,000. But as they're all spaceplanes, the only launch cost is the fuel bill, which is typically about √5,000.

Go to the Saves folder. In there, there will be another folder with the same name as your game save. Inside that will be a folder named "ships" (or "craft" or something; can't remember for certain). Inside that will be two folders: VAB and SPH. Put the .craft file in whichever of those is appropriate (SPH for planes, VAB for rockets). When you go to the appropriate building, the ship will be in the "load ship" list.

Yeah; thats a dodgy plane. Nothing should be flipping at those speeds and altitudes. Try to make something that looks a bit more like a real-world plane. They look like they do for a reason.

I admire your dedication. Here's a pretty screenshot for design inspiration:

If it's stalling at 180m/s, there's something seriously wrong with the design. Typical landing speeds are closer to 100m/s.

Give us some screenshots (preferably with the resources tab open) of it all going wrong? Are you using FAR or NEAR or stock aero? Pics (from directly above and directly from the side) of your spaceplane in the SPH with CoM/CoL/CoT indicators would also be helpful, especially if you do one set with tanks full and one set with tanks empty. The spaceplane in that video does look like it might tend to the unstable side, though; it's hard to get your balance right with such a short fuselage. If you'd like, I'll design you an SSTO spaceplane that's relatively easy to fly. A properly built ship shouldn't spin unless you deliberately provoke it to.

So you like Kurt all the time, then?

Not more, better. Eight turbojets are way more than you need. Swap some of 'em (use the four in the central bay if y'wanna maintain the aesthetics) for something that works in vacuum. As mentioned above, I'd suggest Aerospikes or RAPIERs.

Yah. Fast climb to 20,000m, slow climb to 30,000m/Mach 4, then pull the nose up and light the rockets.

It's a draw for me between Scott and Kurt. Scott is more informative, Kurt is funnier.

I don't think this is related to any changes; I could hit 2,200m/s and 30,000m + in a similar single-turbojet basic plane in 23.5. I circumnavigated Kerbin in that thing. IIRC, it only had a few radial intakes.

Hmmn... (yes, I have been spending a lot of time flying this plane lately, now that you mention it...) And just to prove that I do occasionally fly other things:

Nukes don't have enough thrust for getting to orbit, and air-breathing engines are largely ineffective over 30,000m; even if you can keep them running, their power decreases as you climb. Ditch the nukes (unless you feel you absolutely must have them for long-range interplanetary stuff) and swap out some of the turbojets for RAPIERs or Aerospikes.

You don't need more. All they're doing is adding to the drag and making it harder to keep the nose up. Ditch at least half.

When I: Try to use my mouse to alter the view angle to look at the back of something...and then remember that I'm not actually playing KSP at the time. Ditto for attempting to use the time acceleration controls to hurry up a real-life download.

OTOH, if your docking takes so long that this sort of orbital effect becomes an issue, you really need to polish up the speed of your docking. It should only take a minute or two.

Looking at the plane, adding to the valid points above re: air, CoT and excess weight: Almost all of your control surfaces are on the wing; the only surface I can see that's placed to control pitch is that tiny tailplane. Because the wing is close to CoM, it doesn't have a lot of leverage for pitch. Mid-plane control surfaces are primarily for roll; pitch is handled from the ends of the plane. You want to get some chunky horizontal control surfaces (best if they're all-moving; AV-R8’s or similar) mounted as far as possible from CoM. Elevators on the tail or canards on the nose (preferably both). Build a larger tailplane from wing pieces, put standard control surfaces on the back of it and AV-R8's on the tips. Then use the right-click tweakables to crank their control authority to maximum.

Eight turbos on four circulars are certainly underfed, but I was speaking in general, not specific; I hadn't seen the images. Regardless, forty eight ramscoops is extremely excessive and unrealistic unless you're dealing with a 200 ton vertical SSTO. If you're looking to maximise speed and altitude on a spaceplane, you want to be shutting down engines as you ascend to concentrate the remaining air. By the time I crack 25,000m, the RAPIERs are turned off and don't come back on until it's time to start burning oxidiser. My smaller planes generally have a single turbojet on the centreline that is their sole source of high-altitude thrust. The RAPIERs are only used for the initial climb to 20,000 and the final push to orbit. You just don't need a lot of thrust for high altitude level flight; two turbojets are enough to get my 100 ton spaceplane to Mach 4.5 at that altitude. The poster should also be shutting down engines as the air thins; the eight turbos may be handy for getting off the ground, but they just aren't that useful at altitude. Adding more intakes is usually a waste of time; keeping more engines running isn't going to make you significantly faster, because once you approach Mach 5, the turbojet thrust (which reduces greatly at these speeds, no matter how much air you feed them) begins to be outweighed by the intake drag. Hypersonic is rocket and scramjet territory.

Not so much. My big SSTO spaceplane (two turbojets, six RAPIERs) manages fine with 8 ram intakes, 8 nacelles and four radial intakes. And the radials are probably unnecessary overkill. So long as your engines don't choke below 30,000m (at low climb rate and angle of attack; if you're climbing steeply, they'll choke much earlier), you're all good.