What is the limiting factor in your SSTOs?

[PanzerAce]

1 hour ago, nosirrbro said:

For whatever reason, the style of SSTO I make never has a high enough TWR. They have lots of fuel, but often just re-enter the atmosphere (Or possibly never even left it) before I can use it all up and get to orbit.

In my experience, that means you're treating it too much like a rocket and leaving the atmo as soon as possible. I find that I get the most delta out of a SSTO spaceplane if I leave the atmosphere as late as possible, and build as much horizontal speed as possible before switching to closed cycle. In fact, if you ever have to thrust anywhere OTHER than straight pro-grade, you're not going fast enough.

[nosirrbro]

34 minutes ago, PanzerAce said:

In my experience, that means you're treating it too much like a rocket and leaving the atmo as soon as possible. I find that I get the most delta out of a SSTO spaceplane if I leave the atmosphere as late as possible, and build as much horizontal speed as possible before switching to closed cycle. In fact, if you ever have to thrust anywhere OTHER than straight pro-grade, you're not going fast enough.

No, not even close. What is happening to me in these cases is that after a long period of getting lots of horizontal speed and maintaining altitude, I eventually begin to try to ascend, but in these cases I never even last long enough for my horizontal speed to even have effect as im not getting anywhere close to orbital speeds.

However, this is still just the most limiting, the vast majority of my SSTOs dont have much of a limiting factor, beyond that I never build them with enough payload capability but all that does it require more trips.

[PanzerAce]

3 hours ago, nosirrbro said:

No, not even close. What is happening to me in these cases is that after a long period of getting lots of horizontal speed and maintaining altitude, I eventually begin to try to ascend, but in these cases I never even last long enough for my horizontal speed to even have effect as im not getting anywhere close to orbital speeds.

However, this is still just the most limiting, the vast majority of my SSTOs dont have much of a limiting factor, beyond that I never build them with enough payload capability but all that does it require more trips.

What's your flight profile like? To give you an idea, my most successful SSTO launches consist of full throttle, and locking my AoA at ~15-20 degrees above the horizon (depends on the size of the SSTO, basically as low as possible such that I *just* avoid overheat induced kabooms). That usually gets me an Apo of ~45km when I have to switch to rockets at ~22km. At that point, you've got so little air resistance that I find it's easiest to just lock your craft pointing prograde when thrusting.

 

Do you have pictures of your SSTO? My most recent one is this guy:

 but I've also built a larger Mk2 sized one recently with essentially the same flight profile, but twin Rapiers, Big-S wings, etc to give me way more delta in orbit.

[Raideur Ng]

Control and stability. Having incredibly efficient payloads to orbit and insane lifting is great and all, but if one false move results in RUD, then it's not a functional system. An SSTO that is highly forgiving of mistakes and still allows easy access to orbit (and if no mistakes were made, a very high orbit) is preferable for me. This little guy doesn't have great lift capacity, nor can it travel the solar system, and it can probably be carried in some of these monster machines, but it is an absolute joy to fly from start to finish, it never tries to !@#$ you at any point during the entire profile, including re-entry, which is more than I can say for most other SSTOs... That was the HARDEST thing to design, reliability.

http://www.filedropper.com/showdownload.php/lightlifter

[GoSlash27]

There is no limiting factor that keeps my SSTOs from achieving orbit, but there is a size limit to how big I build them.

They can be a PITA to land when they're too large due to the slow handling response.

Best,
-Slashy

 

 

[PhylumCnidaria]

I've had trouble getting to orbit, but now I can get nearly anything to orbit.

The only problem now is barely any fuel to get to minmus and mine there.

[BloodDusk]

If it's for small payloads. It goes too fast. Some planes I made can easily fly as fast as 1 Km/s under 5 Km high. As for the bigger ones, they lack power to even lift themselves off the ground.

[KerikBalm]

the slowness of my computer is the limiting factor

[nosirrbro]

12 hours ago, PanzerAce said:

What's your flight profile like? To give you an idea, my most successful SSTO launches consist of full throttle, and locking my AoA at ~15-20 degrees above the horizon (depends on the size of the SSTO, basically as low as possible such that I *just* avoid overheat induced kabooms). That usually gets me an Apo of ~45km when I have to switch to rockets at ~22km. At that point, you've got so little air resistance that I find it's easiest to just lock your craft pointing prograde when thrusting.

 

Do you have pictures of your SSTO? My most recent one is this guy:

 but I've also built a larger Mk2 sized one recently with essentially the same flight profile, but twin Rapiers, Big-S wings, etc to give me way more delta in orbit.

I usually keep around 5-10 degrees profile in the jet engines to get the most velocity out of them as possible since they are so damned efficient, then once they begin to flame out I do a hard turn upward to 75-85 degrees with my rocket engines to get me into the vacuum where they are most efficient, but at that point I often fall out of the sky as my craft is too heavy for the engines without any lift from the wings

 

3 hours ago, KerikBalm said:

the slowness of my computer is the limiting factor

True that.

Luckily I tend to build lower part count SSTOs so this isn't too much of a problem, but im always at least getting the yellow mission time level of lag, often red.

[Evanitis]

8 minutes ago, nosirrbro said:

I do a hard turn upward to 75-85 degrees with my rocket engines to get me into the vacuum where they are most efficient, but at that point I often fall out of the sky as my craft is too heavy for the engines without any lift from the wings

The fuel you save by pitching up so hard to reach vacuum sooner is a lot less than the speed you lose by the quick AoA change and pushing your wide profile into the airflow (and eliminating wing lift). That ascent can work for very high (vauum) TWR craft (like around TWR-3), but a less powerful one will just fall on the ground. Try pitching up very slowly - just keep the nose really close to the prograde marker, only until 30-40° It might get you an extra few hundred m/s of dV you need for orbit.

Edited February 13, 2016 by Evanitis

[nosirrbro]

Just now, Evanitis said:

The fuel you save by pitching up so hard to reach vacuum sooner is a lot less than the speed you lose by the quick AoA change and pushing your wide profile into the airflow. That ascent can work for very high (vauum) TWR craft (like around TWR-3), but a less powerful one will just fall on the ground. Try pitching up very slowly - just keep the nose really close to the prograde marker, only until 30-40° It might get you an extra few hundred m/s of dV you need for orbit.

Well, maybe 'hard' was a bit of a misnomer, I do pitch up slow, by hard I just meant changing it alot. Either way though whether or not I am going fast horizontally or am not, that wont change the fact that the plane never even gets to space as it isn't being slowed vertically which is where I am having TWR problems.

[Evanitis]

Either way, low TWR SSTOs shouldn't pitch up much, or at all. Nuke-planes traditionally go to orbit with a 10-15° AoA. My 'sane' planes aim for 30°, and I wouldn't shoot for more than 40° even with a wastefully overpowered craft.

Edited February 13, 2016 by Evanitis

[LABHOUSE]

Payloads move the centre of drag, causing me to take an inefficient accent profile, or lose the payload and launcher (that I reuse).

[numerobis]

Limiting factor is my patience: both in the SPH and in flight. Even with no lag it's several minutes of active work to fly a plane, whereas rockets fly up much faster and have better autopilots.

Edited February 13, 2016 by numerobis

[I_Killed_Jeb]

16 hours ago, PanzerAce said:

locking my AoA at ~15-20 degrees above the horizon

Not to be too pedantic but what you mean here is heading/attitude, not angle of attack. Angle of attack is the difference between the angle your noise is pointed at and the angle you are actually traveling. Seems at least a few posters are making that error here so thought I'd chime in.

[Vanamonde]

This poll is missing an important answer option: 

• My incompetence. 

[AbacusWizard]

10 minutes ago, Vanamonde said:

This poll is missing an important answer option: 

• My incompetence. 

Also:
   • Gravity.

[Gojira1000]

Pretty much just dV for Moho. And Tylo and Eve, but good luck with those two.

[PanzerAce]

6 hours ago, nosirrbro said:

Well, maybe 'hard' was a bit of a misnomer, I do pitch up slow, by hard I just meant changing it alot. Either way though whether or not I am going fast horizontally or am not, that wont change the fact that the plane never even gets to space as it isn't being slowed vertically which is where I am having TWR problems.

Sounds almost like you don't have enough thrust when in the atmosphere. If I go any less than 15 degrees above the horizon I'll get a heat induced explosion before I even hit 10km in altitude. You need to JUST thread the needle of getting your airspeed up, and now blowing up.

[Shania_L]

Well, for starters we'll go with lack of thrust,

then later we can add lack of control authority, lack of Dv, too slow, too low which generally ends up with designs getting too big and too heavy resulting in less control authority and eventually lower FPS.

After that you have the issue of too fast at low altitude, phantom rolls that trimming doesn't solve, excessive response to the tiniest of control inputs (on the same craft that had minimal response to full input earlier in the same flight) resulting in forwards or back flips, flame outs, rapid unplanned disassembly, flames, explosions and death.

Large pieces of flaming debris, toxic (and possibly radioactive) fuels and various parts of the crew falling from the sky, setting light to homes schools and vast tracts of pristine forest. Then over the next few years, countless deaths due to starvation as orphaned Kerbals attempt to grow food in irradiated soil, mutations from drinking poisoned water, visions of shattered lives as malnourished Kerblets wander across scorched and barren wasteland that used to be their homes ....

So essentially I don't build SSTO's because I am not a monster!!!

 

[Foxster]

If you want a less painful way to de-orbit an SSTO without burning up then...

You angle your airbrakes at 45° and then re-enter with a pitch of 45°. 

Get the airbrakes either side of the CoM and the craft will orientate itself for optimal air braking without you even having to maintain the pitch.  

This means you combine the drag of the lifting parts of the aircraft with the maximum drag of the airbrakes whilst hitting the atmosphere. The airbrakes also work at least 50% during landing. When undeployed, airbrakes have zero drag regardless of orientation so positioning them at 45° does not alter the aeordynamics when they aren't used.

You can get craft down this way you would really struggle with otherwise.  

Edited February 14, 2016 by Foxster

[regex]

19 hours ago, numerobis said:

Limiting factor is my patience: both in the SPH and in flight. Even with no lag it's several minutes of active work to fly a plane, whereas rockets fly up much faster and have better autopilots.

Why are you building airplanes then?  Vertical launch your SSTOs.

[Edax]

One of my limiting factor is aesthetics.  Often I can easily solve a problem by adding a part, but if doing so greatly damages the spaceplane's appearance, I'll leave it out and find some other way to tackle the problem.  Sometimes there is no other way, or it'll take me days to figure out a solution, leaving many of my designed abandoned for the next idea.  I have so many non-SSTO prototypes just sitting in the save file gathering digital-dust.  If it doesn't look cool, I'm not flying it!

Edited February 14, 2016 by Edax

[SingABrightSong]

Limiting factor? Landing them. Reentry is fine, but more often than not I'm still supersonic on approach to the runway. VSSTO landings are easier to pull off, but I'm not quite sure how to get them pointed at the Launchpad, or any other site for that matter.

[KerbonautInTraining]

I only have 1 successful SSTO design, a Mk1-size long range one. 4600 m/s left once in orbit.

The limiting factor for me is the LV-N's terrible TWR. It can go to and return from Duna but lifts off of Duna with a TWR of 0.9, luckily it has a VERY light wing loading.