How to design a spaceplane worth using?

[DukeDankins]

I can make a spaceplane that can get to orbit.
I can make a spaceplane that can carry a payload worth the effort.
I cannot do both.

Am using aerospike engines and whiplash engines, trying to get a double size mk2 cargo bay, 1 mk2 cockpit, 1 mk2 clampotron, and 1 mk2 crew cabin to 120km orbit.


Edit: Some lessons learned -
Intakes suck. Use as few as possible, preferably radial.
Wings are like bricks. Use as few and as small as possible.
Control surfaces are a drag. Replace as many as possible with reaction wheels.

Done all of that, reduced my profile as much as possible, and my smallest spaceplane can get to orbit, with no cargo in the bay. And even if that worked it would be too small to really be useful :/. Problem is that a useful cargo load is too heavy without adding so many wings and so many engines and so much fuel as to make an absurd amount of drag.

[Venusgate]

Engines are only about 15% of what makes a good spaceplane. Experiment with smallers drag cross-sections, different ascent profiles, different lift-mass-drag ratios. A good space plane may take 20 hours (from scratch) of testing and tweaking to get right.

Also, enjoy others' ideas:
https://www.youtube.com/results?sp=EgIIBQ%253D%253D&search_query=ksp+space+plane

[Chibbity]

Aerospikes are good because they are just as powerful in vacuum as out.

They are pretty heavy though, you may get better results with something like the Terrier which is light, but still powerful in vacuum.

Other things to focus on are high TWR for the Whiplashes as they like speed, a proper climbout angle of 5-10 degrees at Mach 3+, and reducing any drag you possibly can. More wing surface is good as well, but not too much of course. Mk2 parts in specific are a bit draggy, but if you want the cargo bay, it is what it is. Overcome it with more TWR.

[DukeDankins]

Originally posted by Chibbity:

Aerospikes are good because they are just as powerful in vacuum as out.

They are pretty heavy though, you may get better results with something like the Terrier which is light, but still powerful in vacuum.

Other things to focus on are high TWR for the Whiplashes as they like speed, a proper climbout angle of 5-10 degrees at Mach 3+, and reducing any drag you possibly can. More wing surface is good as well, but not too much of course. Mk2 parts in specific are a bit draggy, but if you want the cargo bay, it is what it is. Overcome it with more TWR.

Tried terriers, nuke engines, lv-45's, and even a cluster of the tiny rockomax engines. lv-45 isnt efficient enough and the others dont have the twr.
As for flight profile, I take off, level out till about 300 m/s then go to a 10 degree climb. Problem is the planes with a payload large enough to be useful dont really go up much, or gain much speed.

[maculator]

If you watch stuff while playing this is a interresting series:
https://www.youtube.com/watch?v=rzsAsfWyO7M&list=PLhvGL3FPEICeO0PqN90SxFps113QSOKra
He ONLY uses spaceplanes for his career mode.

[Chibbity]

Originally posted by Sir Derpykins:

Originally posted by Chibbity:

Aerospikes are good because they are just as powerful in vacuum as out.

They are pretty heavy though, you may get better results with something like the Terrier which is light, but still powerful in vacuum.

Other things to focus on are high TWR for the Whiplashes as they like speed, a proper climbout angle of 5-10 degrees at Mach 3+, and reducing any drag you possibly can. More wing surface is good as well, but not too much of course. Mk2 parts in specific are a bit draggy, but if you want the cargo bay, it is what it is. Overcome it with more TWR.

Tried terriers, nuke engines, lv-45's, and even a cluster of the tiny rockomax engines. lv-45 isnt efficient enough and the others dont have the twr.
As for flight profile, I take off, level out till about 300 m/s then go to a 10 degree climb. Problem is the planes with a payload large enough to be useful dont really go up much, or gain much speed.

A picture of your best design would help. Could maybe give more specific advice.

Sounds like you just need more engines to me. You really want to get those Whiplashes up to their ideal operating conditions. Ie. going really fast at 10k-ish.

Drop tanks can work well too, if you aren't trying for SSTO.

[DukeDankins]

Originally posted by Chibbity:

Originally posted by Sir Derpykins:

Tried terriers, nuke engines, lv-45's, and even a cluster of the tiny rockomax engines. lv-45 isnt efficient enough and the others dont have the twr.
As for flight profile, I take off, level out till about 300 m/s then go to a 10 degree climb. Problem is the planes with a payload large enough to be useful dont really go up much, or gain much speed.

A picture of your best design would help.

Sounds like you just need more engines to me. You really want to get those Whiplashes up to their ideal operating conditions. Ie. going really fast at 10k-ish.

Drop tanks can work well too, if you aren't trying for SSTO.

I'll be getting off for tonight pretty soon. I can take screenshots and upload them tomorrow. Adding more engines would seriously impact either twr inatmo or twr in space.

[maculator]

So I'm no expert, but I managed to get a SP working that can haul 10-12t into orbit, but I used rapiers. All the other engines didn't really work that good for me on such a small craft. Seemed to me that whiplashs for example are only usefull if you go big. And if you want to have some deltaV left in orbit you better accept the fact that this comes with a pretty low TWR. I guess I could fill the 12t I got left in my SP with a atomic engine and a bit fuel, that would take me places but would take its time.

[DarienKane]

My question is, What are you trying to do?

Different objectives mean different builds, a satellite laucher is not the same as a Mun Rover launch.

[musthavecake]

Use a ton of boosters/engines, weight will not be a problem just a few stability issues...

[munch15a]

I was thinking of doing a space plane to land and take off from eve I will use a rocket to get it to kerban orbit is this feasible ?

[andylaugel]

Originally posted by munch15a:

I was thinking of doing a space plane to land and take off from eve I will use a rocket to get it to kerban orbit is this feasible ?

I've seen a YouTube video of this. The spaceplane was enormous though, and mined for fuel once on Eve's surface.

[RoofCat]

1 Rapier for up to 20t launch mass if you are a good pilot and plane has good aerodynamics.
1 Rapier for ~15t launch mass if you are still learning the ascent and plane is less smooth.

Additional Nukes for travels to Duna, Laythe, Mun, Minmus, .... Eeloo with tricks... Moho with mining and tricks probably... Eve in old versions with old Rhino and landing on 5km mountain and mining...

Other engines kind of suck. One exception - you can do Darts on Eve at sea level, but the ascent profile is not very plane'ish anyway since you want to reach at least 5km asap and it is rather impossible to SSTO from Eve sea level. You will have to drop something there.

Whiplash can be used on Kerbin and Laythe too, but they won't be as good as Rapiers for the same airbreathing part and can not assist vacuum ever. So rather not.

For airbreathing mode launch on Kerbin you need up to 400 units (one MK1 2.25t tank) Lf for each Rapier engine on heaviest planes. For those with "15t" it can be less than 300 units. Since you will want to land too, 400 units is just fine in most cases.

Roughly twice as much Lf+Ox for closed cycle for each engine (one 4.5t tank) if you use Rapiers only for LKO. The rest - payload or more fuel for further targets like Mun, Duna, Laythe, Eve orbit, etc. You will need Nukes for those though.

If you use nukes for vacuum completely without closed cycle rapiers, you need roughly 1 nuke for each 2 rapiers. And rather "15t" case. "20t" will be really hard orbiting. You can start Nukes above 12..15km while rapiers are still running. 1 nuke for 3 rapiers for further travel should work too for experienced pilots, if you use some closed cycle Rapier assist for LKO anyway (between ~1500..2000m/s, the rest nukes). You could also try higher orbit and a lot of struggle, but it is not just struggle for you, but also a lot of fuel waste for nukes burning fuel at high angles to extend rise so you have enough time to reach orbital velocity.

MK2 are probably the worst for high delta v spaceplanes. MK1 are lighter and MK3 are while slightly heavier due to suboptimal tanks, also a lot more compact. Which kind of helps, probably due to surface drag having a lot to do with plane length.


As for ascent profile I'm pretty sure Matt Lowne on YT does them well. He may fast forward sometimes though. I guess not just him. Look for videos that aren't older than 1.5 years. There are basically 2 ascent versions everybody uses. Which also have been discussed here a few times.

In some cases only one will work. Rather the lower one, but it is also drag related, so no promise here.
1) reach Mach2 (700m/s) right above sea. Like 200m low can be just fine. Let planetary curvature add to the climb incrementally after reaching 500m/s or do adjustments with pitch. The target is to have 1400m/s+ flying at ~15° on heavy planes at 13ooo m and 1500+m/s on smaller ones. As much as possible, but not below that altitude or you will explode. After a few tests you will learn what to expect and how to adjust in advance.
2) Climb to 6500m first, level out (stay below 8000m), do the same you did in (1). You have less drag here. But also less thrust. And you have to change curve twice, which also wastes some fuel. And since you have much less room & time left to 13km, you also have to reach much higher velocity before starting climb. The target is still the same - high speed at 15° at 13km.

you will have just slightly more velocity at 20km due to climb angle and very high velocity already. At 23.. 26km switch to closed cycle on Rapier in case you use some. 23km will make your upper climb steeper, 26km shallower. Not a huge difference - it will delay the prograde angle falling by a degree or two. But since it is so far in advance, it may change 40km Ap into 50km one at that point.
On very light and powerful planes you can wait all the way to 29km where airbreathing will shut down completely - due to higher velocity to start with, your Ap and upper trajectory will be rather easy anyway.

I probably forgot quite a few things. But it's mostly about practice. A perfect Rapier plane can get up to 1/2 of launch mass as a payload to LKO. While slightly less - 0.4 is pretty common.
Or up to 6200m/s delta v left for further (Nuke) travel, while 5000..5500m/s are pretty common.

Best case scenario is delivering fuel. As MK3 cargo bays are quite heavy and don't do any good basically. Walls around walls. Carrying payload without cargo bays on the other hand can add drag and may be harder to design and balance. Best design may be to have payload on two docking ports in the middle of MK3 or 3.75m plane. Decouple and then dock the plane back in one. But you will need a script doing angle snap to dock back perfectly and I have yet to find a person who loves extra docking a lot.
And there are no f. docking ports for MK3 and 3.75m profiles, Squad! :(

But hey, you can build 2.5m sized plane too. Nothing wrong with rocket parts. Those are actually lighter for the same fuel amount and thus have best delta v. Except there are no f. stock Lf tanks in that size, Squad!

[AoD_lexandro]

@OP - Right away mate you have made the same mistake as everyone else when starting out on spaceplanes. Mk2 parts SUCK big time. A Mk2 fuel tank is the same as a standard FTO tank only with excessive drag and some body lift.

You can get three times the fuel load in the same area as a single Mk2 tank, just using standard FTO fuel tanks. And have much reduced drag factors meaning easier launches. In KSP you do not need body lift, and the wing shape has no bearing on the planes performance (ksp doesnt compute wing aspect at all).

So in essence you can just put on some wing bits to some FTO tanks, a cabin, some engines and et voila space plane made easy. Only use MK2 parts once you have a much better grasp of the mechanics and know how to counter the drag and wasted space.


Also as for intakes there is only two worth using. Either Shock cone intakes or Variable ramp intakes. Everything else is pointless drag and crap performance.

[Mightylink]

Like this?

http://steamcommunity.com/sharedfiles/filedetails/?id=887877699

[Phoenix]

Question to OP, how does your ascent profile look?