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Finally! Secrets of SSTO spaceplanes, unlocked!

ComradeGoat

By ComradeGoat
in KSP1 Discussion

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evilC

evilC

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Ah! Cunning. Thank you. Best I have so far is 6:1 (the one pictured above), which gets me to 28K. Not *quite* enough to get to orbit on just a NERVA afterwards

Then you are doing something wrong in the build or fly.

My plane lifts 30 tons with a 4:1 ratio and the thrust hits 50% at 30km, at which point I turn on the aerospikes.

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RoboRay

RoboRay

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Anyone can pick arbitrary numbers and say "that's the reasonable limit." Oddly, "the limit" usually aligns with whatever works best for them.

Me? I usually use two or three. I've used as much as five.

The non-abusive number, based on my knowledge of turbine engines, would probably be one.

Edited by RoboRay
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evilC

evilC

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Anyone can pick arbitrary numbers and say "that's the reasonable limit." Oddly, "the limit" usually aligns with whatever works best for them.

Me? I usually use two or three. I've used as much as five.

The non-abusive number, realistically, would probably be one.

More works much better. 4 seems reasonable - I could fit way more on and ride it full throttle to 50km on jets alone, but that seems like abuse to me.

With 4:1, you have to manage air and think about ascent profiles (Plus you need rockets to escape) etc - much more than that and the game becomes easy mode.

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RoboRay

RoboRay

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More works much better. 4 seems reasonable - I could fit way more on and ride it full throttle to 50km on jets alone, but that seems like abuse to me.

With 4:1, you have to manage air and think about ascent profiles (Plus you need rockets to escape) etc - much more than that and the game becomes easy mode.

Like I said, you're just picking arbitrary numbers for your "reasonable" limit. I find four intakes to be easy mode. Try one or two if you're concerned about "reasonable" realism.

This is a sandbox game. There's no justification in posting peanut gallery comments about how people should use "more reasonable" designs when they build things that are unrealistic, but neither does anyone need to be impressed by the accomplishments. If they're having fun doing things their way, and we're having fun doing things our ways, it's all good.

Edited by RoboRay
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SteevyT

SteevyT

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Nope, I mean 400km... or more.

See? No rockets:

-snip-

I'll have to see if I can repeat it, but I managed to hit a Kerbin escape on a single jet engine once. I'm pretty sure they've been rebalanced since then though.

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SkyRender

SkyRender

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I must be missing something with spaceplanes. Whenever I get up to about 15-20KM, even with ASAS and avionics both on, the plane starts pitching upward uncontrollably no matter where I tell the stupid thing to hold position. I cannot possibly get up to 1000m/s+ in a situation like that, because the damned thing is determined to push high above the horizon and rob itself of all intake air. What the hell am I missing here?

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Flixxbeatz

Flixxbeatz

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I consider Spaceplane building as a "skill check" part of the game, since it will test how much you've learned from countless hours of launching rockets, flying aircrafts, and designing spacecrafts.

"Never consider yourself as a professional KSPer if you haven't successfully sent a fully stock SSTO Spaceplane into orbit and landed it in one piece."

For those who say that spaceplanes are easy, it's because you are already a professional KSPer by my definitions and you've successfully done it many times already. :)

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RoboRay

RoboRay

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I must be missing something with spaceplanes. Whenever I get up to about 15-20KM, even with ASAS and avionics both on, the plane starts pitching upward uncontrollably no matter where I tell the stupid thing to hold position. I cannot possibly get up to 1000m/s+ in a situation like that, because the damned thing is determined to push high above the horizon and rob itself of all intake air. What the hell am I missing here?

Your craft is out of balance (it may have become out of balance in flight due to the Center of Mass shifting as fuel is burned off), is not positively stable and the air has become thin enough that the control surfaces are no longer able to counter the instability (make sure the Center of Lift is slightly behind the Center of Mass throughout all phases of the flight), or you have a thrust asymmetry issue (make sure the Center of Thrust vector is lin-line with the Center of Mass indicator).

Also, having ASAS and Avionics is pointless. Avionics is a weak ASAS, and is ignored if you turn on an actual ASAS. You probably want to leave off the ASAS and just use Avionics on a plane.

Planes are hard compared to rockets. Don't get discouraged and do keep experimenting. You'll get it.

Edited by RoboRay
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SkyRender

SkyRender

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@SkyRender: You have to account for the usage of fuel when balancing your center of lift/center of mass in the SPH. It will move backwards as you fly. Make sure it will still have the center of lift slightly behind center of mass even after it has burned fuel.

It must have to go about 6 billion miles behind the plane, then. I've tried it with the center of lift WELL behind the center of mass, and it still does the same "desperately trying to kiss the sky" maneuver the second I get above 17KM. Trying to add more lift just causes the plane to go completely nuts and refuse to lift off, since it would much rather perform somersaults over the runway and destroy itself.

Edited by SkyRender
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SkyRender

SkyRender

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No, you're putting it too far away. Put the CoL halfway in the back of the CoM.

Perhaps you could demonstrate with a screenshot of the proper center of mass to center of lift ratio? It seems like explanations are 100% insufficient here, seeing as every piece of advice I've tried following on it thus far has resulted in ever more elaborate pyrotechnics.

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RoboRay

RoboRay

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It varies with the craft design, really. But the absolutely gorgeous MS Paint work up there is a good starting point. I usually have mine a little further back with full fuel tanks, with the markers not quite touching.

Edited by RoboRay
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SalmonellaDingDong

SalmonellaDingDong

Posted
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Nowhere near enough lift for those GIGANTIC fuel tanks. No wonder it isn't working! You need a total redesign, although I'd like to give it a try. Please post the .craft file, and then design something that looks more like this:

Lls6yeY.png

or this

AKXLnTA.jpg

or this

jvrbYYL.jpg

Edited by SalmonellaDingDong
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RoboRay

RoboRay

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I've tried that. It doesn't help. At all.

shuttle.jpg

Here's the model I'm trying to get into orbit. Perhaps seeing it might help with providing some advice.

Ah, at last. Pictures are indeed worth a thousand words. :)

All those control surfaces longitudinally parallel to the CoM are actually doing nothing for your pitch control. The only effective elevator control you have is the two winglets on the jet engine nacelles, and they don't actually do much. You appear to have nearly no effective rudder control, either. And having all those lifting and control surfaces near the CoM actually makes the design less stable, not more.

Lengthen your design, more like a real aircraft, moving the control surfaces further aft. You can put a pair of canards up front, if you need them, but try to do without as they contribute to negative stability. Longer planes are inherently more stable than short ones. You can build short designs that work, but they are much harder. Start with longer designs.

Also, if you're just learning how to build SSTOs, I suggest skipping the passenger compartment. Smaller, lighter craft are far easier to design and fly.

Here's some pics of my first (working) SSTO experiments:

bX8WB.jpg

t8cVd.jpg

309Kt.jpg

bWfLy.jpg

More at http://imgur.com/a/hWYVx#0

This is my current two-seat ground-to-orbit taxi, which weighs in at half the size and mass of my earlier designs:

NtzPzzT.jpg

loAAomX.jpg

GtCq1iO.jpg

More at: http://imgur.com/a/z2gqN#0

Try to design craft that look more like real-world planes. That actually does help, as the same general rules apply.

Edited by RoboRay
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