• 0
Tassyr

SSTO's still escape me

Question

Okay, I admit it took me a long time before all the atmosphere rebalance, but I used to have a functional, even simple, SSTO spaceplane that could get to orbit, dock with a station, unload cargo/crew, return and land more or less safely. 

The atmosphere changes hit and suddenly I can't even get off the -ground.- Every spaceplane I design seems to hit a max altitude of 3km and then gives me the middle finger and sulks until I land it again. 

I'm seriously missing my old SSTOs. Is there -anyone- who can tell me what I'm supposed to be doing now? 

My old pattern was "45 degree burn to 15km, 15 degree level there while acceleratint to mach 2, 45 degree angle until lack of air cuts the engines, switch RAPIERs to rocket, and bam. I'd have an Apoapsis where I wanted it and be ready to circularize." But now I'm STUCK. I can't seem to design ships with enough liquidfuel to get anywhere -near- where I need the rockets.

http://i.imgur.com/R6gwiRY.png

That's my current design. 

What on earth am I doing wrong? 

Edited by Tassyr

Share this post


Link to post
Share on other sites

21 answers to this question

Recommended Posts

  • 1

I posted some ascent profile tips and example spaceplanes here.

Hope that can be of use to you.

Edited by Val

Share this post


Link to post
Share on other sites
  • 0

Well, if you need more LF, fill the wings and put on some fuel lines. Also, it's best not to 45 degree early acsent any more. After takeoff, right click one engine and check the thrust level. If it is rapidly increasing, you may have a bit more room to pitch up. If the accelaration is slow, or it's slowly losin thrust,  pitch down. Do this until you hit 10km, pitch level, speed up, and SPACE!

Share this post


Link to post
Share on other sites
  • 0
9 minutes ago, SpaceplaneAddict said:

Well, if you need more LF, fill the wings and put on some fuel lines. Also, it's best not to 45 degree early acsent any more. After takeoff, right click one engine and check the thrust level. If it is rapidly increasing, you may have a bit more room to pitch up. If the accelaration is slow, or it's slowly losin thrust,  pitch down. Do this until you hit 10km, pitch level, speed up, and SPACE!

I'll give it a try. Got anywhere I can look for a 'good example' spaceplane? I mean with the changes, and all.. 

Share this post


Link to post
Share on other sites
  • 0

This was my first working SSTO in 1.0.5.  I don't know if it will help, but this is the best picture I could find showing all it's parts.

KS1TJWC.jpg

All the round tanks are rocket fuel, and the extra liquid fuel is in the Big-S strakes, which I used as wings.  This has 2 rapiers and 1 whiplash. 

 

Share this post


Link to post
Share on other sites
  • 0
1 minute ago, Just Jim said:

This was my first working SSTO in 1.0.5.  I don't know if it will help, but this is the best picture I could find showing all it's parts.

All the round tanks are rocket fuel, and the extra liquid fuel is in the Big-S strakes, which I used as wings.  This has 2 rapiers and 1 whiplash. 

 

What the heck are the airbrakes for?

Share this post


Link to post
Share on other sites
  • 0
36 minutes ago, SpaceplaneAddict said:

Well, if you need more LF, fill the wings and put on some fuel lines. Also, it's best not to 45 degree early acsent any more. After takeoff, right click one engine and check the thrust level. If it is rapidly increasing, you may have a bit more room to pitch up. If the accelaration is slow, or it's slowly losin thrust,  pitch down. Do this until you hit 10km, pitch level, speed up, and SPACE!

Tried, failed several times. Here's my problem: Accelerate on relatively low pitch to 10km (Speed: 300m/sec surf.) 

Pitch up! (Speed drops to nothing)

Use up all fuel, even switch to rocket mode; apoapsis 18km. 

Splashdown and kill all crew.

Share this post


Link to post
Share on other sites
  • 0

Make sure you have enough engine power.  Air-breathing engines get more and more thrust as they go faster (up to a certain point, which is the speed limit of the engine).  If you're underpowered, you get caught in a vicious loop where you don't have enough engine power because you're not going fast enough because you' don't have enough engine power.

Whereas if you have enough power, then you go screaming off the runway like a bat out of hell and your acceleration just gets higher and higher as you go faster.

A suggestion:  Start small.  Build a really little plane, like a Mk1 inline cockpit with a shock cone on the front and a Whiplash or Rapier on the back.  Try that and see what "good" looks like.  Then gradually scale up with bigger designs.

TL;DR:  MOAR ENGINES. :)

 

Share this post


Link to post
Share on other sites
  • 0

Well, I made a little dink engine ship that DID get to orbit, but couldn't -make- orbit. I really wish there was some sort of official guide.

Share this post


Link to post
Share on other sites
  • 0
2 hours ago, Tassyr said:

What the heck are the airbrakes for?

For landing:

oOJEhA1.jpg

vG7mouU.jpg

5dqJQfZ.jpg

iNlow9Z.jpg

Share this post


Link to post
Share on other sites
  • 0
2 hours ago, Tassyr said:

Tried, failed several times. Here's my problem: Accelerate on relatively low pitch to 10km (Speed: 300m/sec surf.) 

Pitch up! (Speed drops to nothing)

Don't pitch up... the rapiers have a terrible TWR until you've exceeded mach 1... you were trying to ascend at 45 degrees earlier... what is relatively low pitch? 15 degrees?

Why would you pitch up when you're only at 300m/s? why would you pitch up when you're only at 10km... it seems like you are flying your ascent profile very very wrong.

If you are not over 500 m/s by 10km... something is wrong... you should have built up more speed before getting that high. I see you are using modded parts, so I can't exactly comment on your design over all... but if those are stadard intakes... you shouldn't be using circular intakes, use the shock cones (circular intakes don't do well at high speed and altitude)... but with all those precoolers which are intakes, that shouldn't be a problem (maybe switch out some of them for LF or LFO tanks).. if you run out of LF... are you using the internal wing fuel tanks?

I have no idea what you have on your rear node... it seems like your plane may lack sufficient airbreathing thrust... consider another rapier...

1SP1bqP.png

If you can't break mach 1, the rapier is going to be performing worse than the panther or turboramjet...

Share this post


Link to post
Share on other sites
  • 0
3 hours ago, Tassyr said:

Tried, failed several times. Here's my problem: Accelerate on relatively low pitch to 10km (Speed: 300m/sec surf.) 

Pitch up! (Speed drops to nothing)

Use up all fuel, even switch to rocket mode; apoapsis 18km. 

Splashdown and kill all crew.

Don't pitch up aggressively.  SSTO spaceplanes can eat away at your kinetic energy and fuel reserves if you don't fly them carefully.  If you use a joystick, apply gentle backpressure on the stick to pitch up gently.  If you don't use a joystick, use the trim function (ALT-W,A,S,D,Q,E, and ALT-X to reset to zero) or tap the pitch back, experiment with Precision Mode (CAPSLOCK).  Not only do full control surface deflections increase drag (just like airbrakes), you have an aircraft that is flying very fast with momentum; so if you change the attitude, the craft won't shift it's momentum instantaneously.  If you pitch up abruptly, now you're changing the airflow from impacting the nose head-on, to now impacting the belly of the plane, changing the entire underside into one massive draggy airbrake.

- If you're not accelerating fast enough, your TWR is too low and you're expending too much fuel while you try to speed up.  Add more thrust.
- If your velocity vector (little airplane symbol on your navball) hangs out below your nose watermark (center of the navball), you don't have enough lift for how much weight your spaceplane has.  You keep your nose high to maintain a constant flight path, meaning a portion of your engine thrust is being used for lift.  The underside is now producing excess drag, and your engines aren't thrusting in-line with your flight path.  Not efficient at all, add more lift-producing surfaces.
- If you need to constantly have "pitch up" input to prevent the nose from sinking, your Center-of-Lift (CoL) is too far behind your Center-of-Mass (CoM).  Your tail control surfaces (or forward canards) are now deflecting into the airstream just to keep your nose up, producing excess drag.  Readjust your design so the CoL is just slightly behind CoM.
- Drain your fuel tanks in the SPH while you have the CoL and CoM markers enabled.  Watch how far the CoM drifts forward or back.  This is important.  Just because your craft flies good with full tanks, doesn't mean it'll fly right at the end of the mission when you're trying to land.  Mount the majority of your expendables (fuel, monopropellant, cargo/payload) as close or as evenly-placed in front and behind the CoM as possible.  This will keep the Center-of-Mass from drifting throughout the flight.
- Main landing gear placement is one of the most overlooked design features on spaceplanes/aircraft.  It should be just aft of the CoM so that the craft can rotate during takeoff.  Too far back and the plane won't be able to takeoff until it shoots off the end of the runway; too far forward and the craft will tip back on it's tail.  (This is another reason why you don't want the CoM to drift during flight as fuel is spent)

Edited by Raptor9
Typo

Share this post


Link to post
Share on other sites
  • 0

That aircraft you built looks like it should make orbit or come close, though I'd personally change it up a bit.

As others have said, RAPIER motors deliver 5x their static thrust at mach 3.7 (1100 M/S) .    Which isn't to say you want to be going that fast below 20km or you'll burn up or waste fuel fighting drag, however you want to do the last bit of your climb at that speed when the air is getting very thin, to keep decent airbreathing power going as long as possible.

 

Now your first problem is not being able to get over 300 m/s.   These days KSP models the sound barrier, drag increases dramatically above 240 m/s, and especially over 280 m/s, then eases off a little bit at 400 m/s (mach 1.3 ) before heading up again.    Not all space planes can penetrate the sound barrier at sea level, drag just builds up quicker then RAPIER engine power.    Have you tried flying with F12 (aero forces display on) to show the nasty red drag arrows?

Try a subsonic climb to thinner air before going through the sound barrier - maybe 10km?   Push over into a shallow dive to accelerate through it.    

The next thing is, KSP now models lift induced drag.   The drag from wings and control surfaces is now dependent on the angle of attack - the angle they meet the airflow.    Optimal lift:drag ratio is at about 2 degrees subsonic,  5 degrees hypersonic - so your nose shouldn't be pointing too far away from the prograde marker.     If your AOA is below target, then you are going too fast and might be taking excessive drag, steepen the climb to slow down, if your AOA is too high, then you're too slow and should shallow out your ascent - or if unable to do so without burning up , you need more wing.

My profile is generally 

1. climb subsonic, staying below 240 and ideally at 2degrees AOA (hard to be that accurate, but that's the ideal).  As the air gets thinner, the airspeed needed to maintain optimal AOA will increase, till you start nearing the sound barrier.

2. I then start using more AOA to get as high as possible while avoiding the transonic region.  It's a compromise between  getting drag from excessive AOA and drag from encroaching sound barrier.

3. eventually you find yourself in "coffin corner" where you can't get sufficient lift without either excessive AOA or exceeding 280m/s, then i go prograde and try to accelerate to 400m/s.

4. if you make it while still being reasonably high up ( above 7km), you've probably got it made right now. Enjoy the rapidly increasing thrust from the RAPIER and zoom up.  Start pushing the nose down about halfway between your supersonic altitude and 20km however, so that you reach your 1100m/s optimial speed before the air gets too thin to accelerate.

5. switch to rocket mode once you can no longer climb to a significant degree while maintaining at least 800m/s.

6. in rocket mode, try to limit AOA to 5 degrees.   If you burn up , ideally add more wing, or try more pitch.

Share this post


Link to post
Share on other sites
  • 0

In terms of that airplane, and fuselage drag -

You have one Type II (main fuselage)  and two Type I (each nacelle) facing the wind.

Assuming you're not attaching junk radially (doesn't look like you are) the drag is going to come from the nose and tail of each of those fuselages.  

The very lowest drag thing you can put on those leading and trailing nodes is a tail cone, however the mk2 cockpit is not too far behind so we can let that pass.    

However, i'd get rid of the circular intakes at the front of the nacelles - intake mechanics have changed, and one pre-cooler on it's own can feed a single rapier - and replace with tail cones.      Did you know you can also attach tail cones to the back of RAPIERS and NERVS, then offset them forwards so only the very tip of the cone is visible deep inside the engine nozzle, and get the best of both worlds?

 

At the back of your main fuselage, i'd be tempted to put a NERV engine behind that Mark 2 to Mark 1 adapter, then clip a tailcone to the back of it and offset as described above.     You're paying a fair price in drag for having those nacelles you may as well mount a tailconed engine to each available point.

 

The NERV can be triggered to help boost through the sound barrier if above 9km (it's horribly inefficient below that, don't bother), and left on permanently above 22km.

Alternatively, remove those nacelles/sponsons altogether, and replace the type 2 to type 1 adapter with a dual engine mount.  Put a pair of pre-coolers, rapiers and tailcones behind that.

BTW I'd recommend TACfuelbalancer and ModularFuelTanks mods, saves on draggy fuel ducts and gives you flexibility about the mix of what you carry.

Share this post


Link to post
Share on other sites
  • 0

This is the only video i've made of KSP, me launching a 30 ton vehicle (carries 10 kerbals) with one RAPIER , two NERV and no oxidizer.  It does demonstrate some of the above principles but isn't an ideal vehicle by any stretch, it was an experimental low thrust machine.    As I mention in another thread,  the problem is this plane has too much wing to go fast at low level,   and at low speed the single RAPIER provides very little thrust, so it takes nearly 15 minutes to reach 10km and the sound barrier.    Up to that point , the one engine is only making slightly more thrust than i need to fly level, so a lot is wasted just staying airborne for a long time.    Above that, it does go quite well however...

 

 

 

Share this post


Link to post
Share on other sites
  • 0

Okay, I've been trying your tips but either a) I'm not meant to be a pilot or b ) (STUPID EMOTICON) KSP physics has just decided I'm supposed to be ground-bound. After nearly 12 straight hours of bashing into the water, overheating and exploding, or flipping around like a leaf, I'm -done.-

 

Is there a way to go back to 'Flight Physics that aren't meant to make it impossible to fly?' 

Share this post


Link to post
Share on other sites
  • 0

Maybe if you provided more pictures, or a video, or a craft file, we could help.

Have you first tried with an SSTO that should work easily? (ie, one that someone else made).

At the moment, we have no idea what you are doing, but it was obvious in your first posts that your were doing something very wrong (ascending at 45 degrees.... pitching up at 10km and only 300 m/s... etc)

Share this post


Link to post
Share on other sites
  • 0

I have to agree with some of the others, I think the initial 45 degree ascent is what's doing you in.  I didn't think to mention, but the picture I posted earlier, that one I set to only about 20-25 degree ascent and then I just let it fly itself until she hits around 20,000-25,000 meters or so and runs out of air. She's so stable I can actually leave the room and make coffee while she's climbing.   At 20,000m she should be doing at least 1,200 m/s or so and look like she's bathed in flames.  When the air dies I close all intakes, toggle the whiplash off, switch the rapiers to rocket mode and very gently nose her up to about 45 degrees.  From there she practically circularizes her orbit on her own.

Once in orbit she'll have just enough oxidizer left to kill the orbit, but plenty of liquid to use the jets again when you get back into the atmosphere.

Edited by Just Jim
forgot a sentance

Share this post


Link to post
Share on other sites
  • 0
6 hours ago, KerikBalm said:

Maybe if you provided more pictures, or a video, or a craft file, we could help.

Have you first tried with an SSTO that should work easily? (ie, one that someone else made).

At the moment, we have no idea what you are doing, but it was obvious in your first posts that your were doing something very wrong (ascending at 45 degrees.... pitching up at 10km and only 300 m/s... etc)

 

1 hour ago, Just Jim said:

I have to agree with some of the others, I think the initial 45 degree ascent is what's doing you in.  I didn't think to mention, but the picture I posted earlier, that one I set to only about 20-25 degree ascent and then I just let it fly itself until she hits around 20,000-25,000 meters or so and runs out of air. She's so stable I can actually leave the room and make coffee while she's climbing.   At 20,000m she should be doing at least 1,200 m/s or so and look like she's bathed in flames.  When the air dies I close all intakes, toggle the whiplash off, switch the rapiers to rocket mode and very gently nose her up to about 45 degrees.  From there she practically circularizes her orbit on her own.

Once in orbit she'll have just enough oxidizer left to kill the orbit, but plenty of liquid to use the jets again when you get back into the atmosphere.

Okay, now that I'm home from work and not rocketing on rage here. I was trying a "start at 10 degrees," get to 1km/sec, slap it up to 30ish, maybe a bit higher to get apoapsis where you want it, then circularize. But I can't seem to make it WORK. 

I don't know how to get someone else's ship to be -recognized- by my game. I tried putting one in the folder and it doesn't list it. 

It doesn't help that I really am used to using Mechjeb for my flights, and this is really not something I can use Mechjeb for.

Share this post


Link to post
Share on other sites
  • 0

Try Pilot Assistant. It's like MechJEB, only for planes. Then when you find out what you are doing wrong, try for yourself. And you seem to be doing a lot wrong....

Your plane looks like it can make orbit, although not fully optimized. I guess it's all your ascent profile's fault.

Share this post


Link to post
Share on other sites
  • 0

You may need to adjust your plane.... it's hard for me to tell from the screenshots. or try designing a new one.  I can tell you is it took me several attempts with different designs before I came up with one that actually worked right. I have several comical screenshots of SSTO explosions either on or near the runway.

IMO, a working SSTO is by far the hardest thing to make in this game.

Share this post


Link to post
Share on other sites
  • 0

@Tassyr I'm working to publish a craft file download that is a pretty simple ascent profile to get to orbit.  As soon as I leave the runway, I put the nose on +15 degrees, and hold it there until my apoapsis reaches 75km, and then I cut the throttle and hold the nose prograde on the velocity vector to reduce drag as much as possible while I coast to space.  At apoapsis, I usually only need to burn for ~15 more seconds to circularize.  And there is still a little fuel in the tanks to push up to 100x100km orbit, and for retro-burn to reenter the atmo.  When I get it published on KerbalX, I'll let you know just in case you want to give it a go.

EDIT: Give this a go.  SR-19A 'Valkyrie' KerbalX Download

SR-19A%20Valkyrie%20Small_zpso4a8jvjz.pn

Edited by Raptor9
Added download link and image

Share this post


Link to post
Share on other sites
This thread is quite old. Please consider starting a new thread rather than reviving this one.

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.
Note: Your post will require moderator approval before it will be visible.

Guest
Answer this question...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.