calling any pro* kerbal space program player. I have a question [details inside]

[Flixxbeatz]

*by "pro", I mean someone who has already launched a spaceplane into orbit and landed them safely back to kerbin.

emphasis on "landed" since almost all of the spaceplanes I've launched in orbit entered a "death stall" at around 12km-20km altitude upon returning to kerbin without any reason at all.

Tried other wing configurations, to no avail (delta, typical). Followed the CoG, and CoL guides. Still none. I've seen people do it successfully in any wing configuration and of any size (compact to fortress style) and I'm like sitting here "HOW"?

So here's the question(s).

-Do all spaceplanes launched into orbit around kerbin enter a death stall upon re-entering?

-If not, how can I prevent it from happening?

reference video:

Edited February 7, 2015 by Flixxbeatz
added vid in case

[Superfluous J]

You may want to change your subject to something more like "Help! My spaceplane is stalling on re-entry and I can't stop it!" so people who know about spaceplanes know you need help with them.

I can't help as I've never entered atmo with a plane (well, other than the below. It didn't stall but it came close).

[capi3101]

Well...let's start with the basics. What kind of aero are you using: stock, NEAR or FAR? The answer you seek may be different depending on what you use. Also, which mods do you use. All relevant mods here - any plane parts mods, whether or not you use RCS Build Aid, etc.

Me, I use stock aero. And I use RCS Build Aid and Nav Utilities; those are the only relevant mods I use. And I successfully land on the runway quite often.

And the problem you're having - the craft tumbles out of control upon re-entry - is one I used to have. From the look of your craft, I can see two issues:

A) Your CoM is shifting aft of your CoL late in the flight due to burning fuel. Had a RAPIER-powered cargo plane with that exact same problem; once the oxidizer was gone, the plane was unstable. RCS Build Aid would help you out tremendously here (it'll show you where the CoM will wind up once the plane is out of fuel, and let you know EXACTLY where the CoM will be at that point.

You haven't got nearly enough lift for the mass of your craft. Ideally, you want the sum of the lift coefficients of all lift-generating parts to be roughly equal to the take-off-mass of your craft. From the parts I'm seeing, you've got enough lift for about a five tonne plane - and it weighs quite a good deal more than that, I'd wager. You've got more thrust than you need, which is why it makes orbit in the first place.

You also might want to not fire up the engines until you're subsonic (below 400 m/s), and then don't fire them up past 2/3 throttle. That does help you maintain some control as you get further down into the soup. Of course, if the CoM has shifted that much, you're going to be in trouble no matter what.

Going to point you out to my general advice for new spaceplane users. Keptin's guide is good for the basics; DocMoriarty's guide is good for the specifics (even if you're not trying to build transporter spaceplanes - and the principles it contains are still sound, despite the guide being slightly out of date (0.24.2)).

Edited February 6, 2015 by capi3101

[Starwhip]

Shifting Center of Mass is your problem. Drain all your fuel in the Spaceplane Hangar. If your Center of Mass drifts behind the Center of Lift, your plane will stall.

[Alshain]

Take the intake off the front, keep your intakes close to the center of mass or behind it. You have a long body with a great source of drag right at the tip, recipe for disaster.

Edited February 6, 2015 by Alshain

[GoSlash27]

I'll tell you exactly what the problem is:

1) You have an unbalanced design, but your canards are masking it.

Your spaceplane should be balanced both with control surfaces attached and removed. That means you build the plane balanced with no control surfaces, then you add the control surfaces in such a way that they remain balanced.

2) You have an intake in the nose.

At high speed, intakes are the draggiest part of the plane. Flying a plane in this condition is like launching an arrow backwards; it wants to fly any way except nose first.

If you fix these, your problem should go away.

Best,

-Slashy

[Sirrobert]

Please remember to use discriptive titles. It'll get you help much faster than 'please help'

If your title contains the exact subject that you need help with, the people that know about that subject will see it and know that you need them. As it is now, it's vague and those people may skip it, because it doesn't ask for them (and alot of people check in, see that it's not for them, and leave). Noone gets any further like that

[Pecan]

...So here's the question(s).

-Do all spaceplanes launched into orbit around kerbin enter a death stall upon re-entering?

-If not, how can I prevent it from happening?

To answer your specific questions:

-No, otherwise no-one would ever use them.

-By i) designing a 'plane that flies well in atmosphere, ii) has it's centres of lift and drag behind that of mass at all times, iii) also happens to make it to orbit and back.

IE: - Build a plane first, make it spaceworthy second, because atmosphere's the difficult bit.

[Yakky]

Shifting Center of Mass is your problem. Drain all your fuel in the Spaceplane Hangar. If your Center of Mass drifts behind the Center of Lift, your plane will stall.

I cannot quite tell from the video if this is applicable to your plane or not, but: Remember that if you have fuel tanks connected in series, the fuel will drain from the farthest tanks first. In many configurations, and it looks like maybe in yours, the farthest tank is in front and will thus drain mass out of the nose first. This means when you re-enter with a small amount of fuel left over, that fuel is usually toward the back of the spaceplane where it may be pulling your center of mass farther aft than you want. Sometimes you can solve this problem by simply transferring the leftover fuel toward the front-most tank before re-entering the atmosphere.

BTW you can also use this trick deliberately, by reserving some fuel to use as ballast during re-entry and pumping it around to wherever balances out the spacecraft. I will sometimes deliberately put a small fuel tank at the very front of the craft so I can pump whatever leftover fuel I have as far forward as possible to help manage my center of gravity.

[EtherDragon]

Have you tried closing your air intakes during reentry?

[Flixxbeatz]

Have you tried closing your air intakes during reentry?

Done. They're even binded.

[Whirligig Girl]

Simple asnwer seems to be evident in the lack of fuel in the plane shown in the video. The center of mass has moved behind the center of lift, so the plane is no longer stable.

[Flixxbeatz]

Okay. Did everything you guys said, and ended up with this thing:

Gotta land it few orbits later. Thanks alot pro ksp-ers!

Now to become a pro myself...

[panzer1b]

Two major causes that ive used to have problems with on my SSTOs (and SSTOs are the primary craft i make any fly). One is intakes in front. All of your high-drag junk such as intakes should be well behind ur CoG. The other primary issue ive had is fuel draining asymmetrically. Many of my designs even to this day (due to aesthetic reasons) have fuel flow in such a way that they become unstable if the fuel isnt manually moved to the front tanks as im trying to reenter. They are stable fully dry, and fully fueled, but there is a problem i have where the front tank drains 1st, and needs tyo be refilled when reentering to keep the tanks behind CoG from sending you flipping all over.

If these 2 arent an issue, there may be 1 more problem: lack of RCS/SAS control authority. I generally have a rule, of roughly 2 medium sized reaction wheels for every 10 tons. That and plenty of control surfaces. In general, while this one hasnt been too big of an issue for me due to my requirement for plenty of torque on any vessel, some of my "more conventional" craft have had problems with this, when i tried to cut everything for pure dV, guess sacrificing too many reaction wheels and removing all RCS systems, wasnt exactly very good.