Space Plane runs out of Fuel before Orbit.

[Barujin]

I started playing Kerbal at version 0.2. I've been trying to get into orbit with a space plane after watching Scott Manley's YouTube video about them. He got into orbit with an optimized Aeries space plane with plenty of fuel to spare. I built a similar plane with twice the fuel, two aerospike rockets, four tanks of jet fuel, and four jet engines. I can get 1 Km/S of speed at 20 Km altitude, but the plane burns through its fuel before reaching 40 Km. What am I doing wrong? Did something in Kerbal change with a recent version or does the plane simply have too much weight? I thought everything would scale up just fine, but I guess it doesn't. I'll try building exactly the same plane that Scott Manley built and see if it works.

[Nibb31]

You mean 0.20 I suppose, because KSP 0.2 was at least 2 years ago.

SSTO is hard, and it's a good thing. IMO, it's still too easy.

[Mach56]

Try making your own plane, copying someone else w/o a craft file won't work to well. And SSTO are meant to be small.

[rodion_herrera]

Basing from what you said about your build, you are indeed overweight, and the culprits are the two extra jet engines. You can live with just two--the key is not the number of engines, but if they are still working ABOVE 22k meters. And to do that, you need extra intakes, and I mean LOTS of intakes. Read my blog on how I made my first successful SSTO-return-to-KSC-Runway flight last night in my Black Mamba (will share the .craft file soon, when I finish all the tweaks I need to do with it).

Additionally, you cannot open the extra intakes below 15-19k feet (depending on your v at that point), because they cause drag. Opening them up at higher altitudes (above 19k) will ensure that your jet engines are fed with air well, before they reach flameout. Thus you need to bind intake opening with Custom Action Keys, to activate them at the right time. You also need to bind your regular (default) intakes to action keys, because it helps to close all of them during re-entry.

Edited May 30, 2013 by rodion_herrera

[AnalogAddict]

http://forum.kerbalspaceprogram.com/showthread.php/30368-Laythe-Nuke-SP-SSTO-20-OK%21

Here is my space plane and a guide on how to get it to orbit. Maybe it will answer some questions for you.

Also, in your attempts, are you firing your aerospikes early? I see where can reach 1km/s @ 20km, which is normal, try pushing that up to 1.3~1.4km/s and nudge your altitude up to 24~26km and then fire those aerospikes while pitched towards the heavens. (45 degrees or such, maybe higher depending on if you're catching your apoapsis.)

Edited May 30, 2013 by AnalogAddict

[RoboRay]

I built a similar plane with twice the fuel, two aerospike rockets, four tanks of jet fuel, and four jet engines.

There's your problem.

Diminishing returns on added mass are huge. You don't get equal performance by doubling the fuel and engines, you get less. It's far easier to improve performance by removing mass (even fuel and engines) than by adding mass.

Even the stock version is oversized for a one-seat SSTO plane. A one-seater should come in under 10 tons. Even a two-seater is doable at 12 tons or less:

Every little bit of weight you can shave off by using fewer engines, smaller engines, and less fuel will make reaching orbit easier.

Edited May 30, 2013 by RoboRay

[Barujin]

Okay, being new to Kerbal, I hadn't tried actual rocketry yet. I just was really interrested in the whole space plane concept. I finally made a rocket with aerospikes and one striped tank for each one. The one without staging could not make it into orbit (without really smart maneuvers). Once I added ordinary staging, though, it worked perfectly. I realized that rocketry truely functions due to dropping the extra weight. If someone could get a huge amount of fuel up to 20Km safely and with little extra weight, then they could likely get into orbit and go to other planets. Otherwise, I just don't see space planes as realistic (take-off to landing). Tiny doesn't exactly get far out there.

[Snooze]

Tiny planes are fine. Like Scott Manley, I use a modified AERIS IV to put satellites in orbit. Recently I've started using them to trade out crew on my orbital fuel station.

OP, you can likely get what you've designed into orbit with fuel to spare. All you need to do is mind your throttle. Keep your resource window open and watch your fuel consumption versus speed gained. Don't light the aerospikes until you're above 22k meters and you've gotten all the speed you can out of your air-breathers. Then you light the spikes, assume 45 degrees nose up to grab altitude, once above 32k, level off and start gaining orbital speed.

It takes a fair bit of practice as well as getting used to the... peculiarities of your design but once get the basics down it's all a matter of adjusting for your own plane.

[White Rider]

What's unrealistic about spaceplanes?

They are not commonplace on earth for the same reason they are not common here. They are hard to build.

You should look up Skylon Project.

[Tripod27]

You guys seem pretty good at this whole SSTO thing, and my only attempt so far hasn't gone so well

As you probably noticed, none of those pictures are in orbit. The plane itself flies amazingly well, with good stability and a great turning circle (especially considering it weighs 38 tons). The issue is that once I get it to about 23km up, the lower engine starts losing power, it's at 140kN compare to 220 on the top one and has half the electric charge, and it doesn't equal out until I nose down to a point where I start losing altitude. I started throwing on a ton of wings thinking it started nosing down because it didn't have enough lift in the thin air before I noticed the engine imbalance. I have an equal amount of intakes on the top and bottom so I have no idea what's going on. do the intakes get mapped to certain engines or does the angle of the intakes matter?

Edited May 31, 2013 by Tripod27

[rodion_herrera]

I have an equal amount of intakes on the top and bottom so I have no idea what's going on. do the intakes get mapped to certain engines or does the angle of the intakes matter?

You have to understand one thing--KSP doesn't care about intake angles or how many intakes are PER engine--all it cares about is that you have PLENTY (I believe you can even mount them in reverse to the direction of flight LOL) So yeah, you have to be creative in mounting them, but the key is really to carry a lot of intakes. My Black Mamba (you can find it in Spacecraft Exchange) has 14 intakes (7 pairs) but the placement doesn't make them seem obvious. You can live with 2 intakes up to around 16-18 km, then you have to open up (via action keys) the remaining intakes (in my case, the 12 other intakes) so that your intake value doesn't drop below 0.13 (dangerous, close to flame out!)

Now some might say "intake spammer!" or "that's cheating!" Well, this is how I see it--they are simply "constructs" of better, and more efficient intakes--like if I put 3 intakes together and treat them as "one" intake, its like saying I have a new intake (modded?) that is three times more efficient than the stock one, so it still makes sense.

Edited May 31, 2013 by rodion_herrera

[Tripod27]

Still odd that the bottom engine stalls out first, but whatever I guess, time to add more intakes

[RoboRay]

Tiny doesn't exactly get far out there.

On the contrary... a key principle of rocketry is that "tiny goes farther."

Once you're above 30km or so, the same rules apply to spaceplanes that apply to rockets.

Edited May 31, 2013 by RoboRay

[JebDynamics]

Intakes add a lot of drag. The design I've been using can get 3 tons of cargo to 80km easily, and up to 5 tons with careful flying ( it gets very front heavy making pitching up to escape the atmo difficult ).

It uses about 300 LF to get to 24km on jets, then around 1000-1200 LFO to get to orbit.

Pictured in orbit with cargo behind ( 4.5 ton spacelab )

[rodion_herrera]

Intakes add a lot of drag.

Which is precisely why you bind their open/close controls to a Custom Action Key (1...9 keys) so you can ONLY OPEN THEM above 18k meters by pressing the appropriate action key, and up there, where air is thin, drag is negligible, and your jet engines can enjoy more operation time.

[JebDynamics]

Which is precisely why you bind their open/close controls to a Custom Action Key (1...9 keys) so you can ONLY OPEN THEM above 18k meters by pressing the appropriate action key, and up there, where air is thin, drag is negligible, and your jet engines can enjoy more operation time.

I've been leaving them all open to simplify things for myself, but I'm sure there are still ways to optimize the ascent.

It is critical that you close the intakes when escaping the atmosphere, otherwise the drag will prevent an orbit.

Edited May 31, 2013 by JebDynamics
spelling

[rodion_herrera]

I've been leaving them all open to simplify things for myself, but I'm sure there are still ways to optimize the ascent.

It is critical that you close the intakes when escaping the atmosphere, otherwise the drag will prevent an orbit.

You close the intakes AFTER you attain more than 1,200 m/s with the jet engines, at an altitude of around 24,000 to 25,000 meters. This is why some people can't raise their rocket engine speeds high enough to attain insertion, because they haven't built up their jet speed.

Simplify? It just takes ONE keypress to toggle a custom action.

[Tripod27]

You close the intakes AFTER you attain more than 1,200 m/s with the jet engines, at an altitude of around 24,000 to 25,000 meters. This is why some people can't raise their rocket engine speeds high enough to attain insertion, because they haven't built up their jet speed.

I had a speed of 1300 m/s at 26,000 and soon after I turned off my two jet engines and turned on my 3 nuclears I started losing speed and altitude

[JebDynamics]

You close the intakes AFTER you attain more than 1,200 m/s with the jet engines, at an altitude of around 24,000 to 25,000 meters. This is why some people can't raise their rocket engine speeds high enough to attain insertion, because they haven't built up their jet speed.

That is what I said, maybe I didn't make it clear enough. Intakes need to be closed when your are burning/coasting to apogee.

Simplify? It just takes ONE keypress to toggle a custom action.

I find it simpler to have one hotkey for all intakes on/off. I fly up to 24km as fast as possible without flame-out due to low airspeed.

[JebDynamics]

I had a speed of 1300 m/s at 26,000 and soon after I turned off my two jet engines and turned on my 3 nuclears I started losing speed and altitude

The nuclear engines have too little thrust I've found, I have much better luck with LV-T30's.

[rodion_herrera]

Aerospikes are the best rocket engines for spaceplanes.

[JebDynamics]

When burning from 24km:

LV-T30s give me 215kN of thrust at ~360isp and weigh 1.25t

Aerospikes give me 175kN of thrust at ~390isp and weigh 1.5t

Doesn't that give T30's the edge for this use? ( I'm still a little confused about comparing thrust/isp between engines )

Edited May 31, 2013 by JebDynamics
spelling

[Shrike42]

That is one heck of a plane, Tripod27. But yeah, the LV-Ns are not really much good in-atmosphere, and as a rule of thumb, you're only ever going to need 2 once you've gotten to orbit.

Depending on if you have a means to refuel once you're up there, you might keep one LV-N and swap out the other two for LV-T30's or something. Then shut down the T30s and go wherever your fancy takes you.

I now have an idea for an SSTO with one of the huge new docking ports at the back end, designed to be used with an LV-N on a fuel tank that you get into space on a rocket. Give your shuttle a long-range option, just because.

[Curs0r]

In the interest of the most conventional and sleek look for my SSTO I came up with this air hog, which I named the K-21 Munray (yes it took me 21 tries to get my ideal plane happening). The K-19 was probably my favorite but ended up being pretty gutless for Hohmann uses.

She is not as nimble as I'd like, and takes the entire run from that start of the runway to the edge of the water to lift off. She will make it to the surface of Minmus from the runway though.

I generally end up at a 212km orbit from takeoff with over 2/3 of the fuel remaining. I have a gas station parked in synchronous Kerbin orbit, and I managed Duna (using Ike to brake) off of 1 refuel.

Ike braking maneuver

I was bone dry for fuel, even RCS after pulling the deorbit burn. I have never been so glad to have pointed my craft at a perfectly flat area. At this point I would have been quite screwed in a conventional lander, but this is the very reason for using a space plane.

After pulling the standard speed-bleed seesawing for about 10 minutes, I set her down like a leaf in a very flat area.

[Tripod27]

That is one heck of a plane, Tripod27. But yeah, the LV-Ns are not really much good in-atmosphere, and as a rule of thumb, you're only ever going to need 2 once you've gotten to orbit.

Depending on if you have a means to refuel once you're up there, you might keep one LV-N and swap out the other two for LV-T30's or something. Then shut down the T30s and go wherever your fancy takes you.

I now have an idea for an SSTO with one of the huge new docking ports at the back end, designed to be used with an LV-N on a fuel tank that you get into space on a rocket. Give your shuttle a long-range option, just because.

Well the reason it's so huge is because I want to use it to get to Duna and back, and apparently 12.5 tons of rocket fuel is pretty heavy. I'm trying swapping one nuke for a t30 right now just for making orbit

At least with the engine swap it's slightly under 40 tons now >_<

Edited June 1, 2013 by Tripod27