My first SSTO. Can you tell me what I need to do for it to . . .work? :D

[TomDRV]

Here's the craft file and a screen.

https://www.dropbox.com/s/ejw4glvqw3svyi1/SSTO - Starshot.craft?dl=0

Do I have enough intakes and wings? How do I know the ratio of rocket fuel to liquid fuel I should have?

Or it could just be my flying?

 

 

thanks

[Vanamonde]

That looks reasonable to me, though I have only ever been able to make 2 of these that worked, myself. And yes, the ascent profile seems to be more critical than the design.

[Rune]

Hum. Yeah, eyeballing it, it seems reasonable. TWR and aerodynamics are the main thing in a SSTO (TWR around 0,5, no open nodes because they are draggy), the rest follows once you nail those (you should en up somewhere between 25 and 50% payload mass in LKO), but of course flying it right is crucial... and easy.

Just make sure you accelerate past supersonic speeds (>400m/s) low in the atmosphere (under 2,000m), then just let the plane continue in a straight line: kerbin will curve under you, and the RAPIERs will keep accelerating, until you get to around 20kms and 1,200m/s, and from there a short rocket burn will get you suborbital.

 

Rune. But experimentation is the best way to learn!

 

[TomDRV]

14 hours ago, Rune said:

Hum. Yeah, eyeballing it, it seems reasonable. TWR and aerodynamics are the main thing in a SSTO (TWR around 0,5, no open nodes because they are draggy), the rest follows once you nail those (you should en up somewhere between 25 and 50% payload mass in LKO), but of course flying it right is crucial... and easy.

Just make sure you accelerate past supersonic speeds (>400m/s) low in the atmosphere (under 2,000m), then just let the plane continue in a straight line: kerbin will curve under you, and the RAPIERs will keep accelerating, until you get to around 20kms and 1,200m/s, and from there a short rocket burn will get you suborbital.

 

Rune. But experimentation is the best way to learn!

 

I did it! Thank you!

 

It was all in the flight profile like you said, I think I was climbing WAYYY too quickly.

Now I think I only have a few teething  problems.

I have my COL behind the COM, like everyone says for stability, but this causes my nose to keep dropping. Is there someway I can stop this? Trim my control surfaces or something?

And air intake, I only have 4 for 12 RAPIERs . . . I feel like i should have more?

thanks again!

[Thor Wotansen]

If it's current, use the RCS Build Aid mod.  It shows you the COM of your craft both fueled and unfueld at the same time.  With most SSTOs the COM will change as you burn fuel.

[AeroGav]

The main thing is to wait until you've hit max speed on the air breathing engines before switching to closed cycle mode.   You should be going at 1400m/s or more before staging.   If you climbed too steep your jets may flame out from getting too high before hitting your top speed.    This is why i like to disable the "auto switching" mode.   Just go Prograde until it starts to come back down again, and when it starts descending pitch the nose up a couple of degrees above prograde to stop the descent from getting too fast.  Use an action group to trigger the mode switch so it happens when you want it to.

 

Other thing,  some craft don't go supersonic at sea level and prefer to get up into thinner air first.    So it's ok to climb fairly steeply at first,  then level off to accelerate > 440m/s,  then climb and level off again for your 20km speedrun.

 

Golden rule, don't pitch more than 5 degrees away from Prograde as drag gets to be horrendous,  and keep your corrections gentle.   Try to plan ahead.

 

Video of me doing most of the above on a feasability test of the "single tank to tylo" challenge - using a mk3 liquid tank

edit - craft file link for the brave https://www.dropbox.com/s/gwusik0pe47jzje/TYLO SPACE.sfs?dl=0

Edited April 2, 2018 by AeroGav

[AeroGav]

On 01/04/2018 at 12:31 PM, TomDRV said:

 

https://www.dropbox.com/s/ejw4glvqw3svyi1/SSTO - Starshot.craft?dl=0

 

 

 

thanks

I had a quick play with your craft.        

Major Problem detected -   You have an open 3.75m node on the back of your fuselage.  That is huge source of drag and contributes to needing so many engines.

Major Problem detected - RCS build aid says that after using up your fuel, the craft becomes tail heavy (unstable).   Fewer engines or moving some  forward would help.

Minor Problem detected - the MK2 bi coupler on the side pods have open nodes on one of the  1.25m mounts.  Put a cone on or use a single mount part

Minor Problem detected - mk2 fuselage parts have crummy fuel to drag ratio.   Best for drag are 2.5m tanks

https://www.dropbox.com/s/t9ymj2ehv8u3j8v/SSTO - Starshot.craft?dl=0

My version of your craft  uses 5 rapiers and 4 panthers.  Mode switch on action group 1.   It needs more work , because i got to space with 5000 oxidizer left but only half as much liquid fuel, so the tanks need adjusting (but also my profile was imperfect and ended up diving down to 13km when trying to level off for the 20km speedrun).

 

[TomDRV]

18 hours ago, AeroGav said:

I had a quick play with your craft.        

Major Problem detected -   You have an open 3.75m node on the back of your fuselage.  That is huge source of drag and contributes to needing so many engines.

Major Problem detected - RCS build aid says that after using up your fuel, the craft becomes tail heavy (unstable).   Fewer engines or moving some  forward would help.

Minor Problem detected - the MK2 bi coupler on the side pods have open nodes on one of the  1.25m mounts.  Put a cone on or use a single mount part

Minor Problem detected - mk2 fuselage parts have crummy fuel to drag ratio.   Best for drag are 2.5m tanks

https://www.dropbox.com/s/t9ymj2ehv8u3j8v/SSTO - Starshot.craft?dl=0

My version of your craft  uses 5 rapiers and 4 panthers.  Mode switch on action group 1.   It needs more work , because i got to space with 5000 oxidizer left but only half as much liquid fuel, so the tanks need adjusting (but also my profile was imperfect and ended up diving down to 13km when trying to level off for the 20km speedrun).

 

thanks again!

the last problem I'm having is it just won't pull up off the runway. I feel like I don't have enough wings? I think my gear is far enough forward. But the takeoff speed is ridiculous right now.

[Thor Wotansen]

5 hours ago, TomDRV said:

thanks again!

the last problem I'm having is it just won't pull up off the runway. I feel like I don't have enough wings? I think my gear is far enough forward. But the takeoff speed is ridiculous right now.

Put your main gear right behind your COM at the farthest back it goes.  Another thing that helps is to have th front gear a little longer, so that the plane has a slight nose up attitude at rest.

[Freds]

I dont have too much to add to what is already been told above, but here is 2 pictures of a cargo ssto , inspired in the skylon project.

40T to orbit.

It flies very nice when loaded, but, it needs very careful piloting when it comes back into the atmosphere unloaded.

I used it 2 ou 3 times, but because i need spaceplanes that can reach 700km, i switched to spaceplane with droptank design.

Spoiler

 

 

 

[FleshJeb]

On 4/2/2018 at 4:29 AM, TomDRV said:

And air intake, I only have 4 for 12 RAPIERs . . . I feel like i should have more?

The Precoolers are also intakes. The general rule of thumb is one Shock Cone per four Rapiers. Each Precooler should be able to feed about three Rapiers.

https://wiki.kerbalspaceprogram.com/wiki/Parts#Air_intakes

If you're into mods, Kerbal Engineer Redux has a display option for Intake Air (Demand/Supply).

EDIT: My personal rule is always listen to Gav, he knows what he's doing.

Edited April 3, 2018 by FleshJeb

[AeroGav]

4 minutes ago, FleshJeb said:

The Precoolers are also intakes. The general rule of thumb is one Shock Cone per four Rapiers. Each Precooler should be able to feed about three Rapiers.

https://wiki.kerbalspaceprogram.com/wiki/Parts#Air_intakes

If you're into mods, Kerbal Engineer Redux has a display option for Intake Air (Demand/Supply).

Although,  worrying about the drag created by pre-coolers or shock cones when you've got a mk3 fuselage of that length, which will be running at at least 5 degrees angle of attack because the wings aren't angled up with respect to the fuselage, is a bit like worrying about spilling a teaspoonful of Gin on the Titanic.   

[FleshJeb]

1 hour ago, AeroGav said:

Although,  worrying about the drag created by pre-coolers or shock cones when you've got a mk3 fuselage of that length, which will be running at at least 5 degrees angle of attack because the wings aren't angled up with respect to the fuselage, is a bit like worrying about spilling a teaspoonful of Gin on the Titanic.   

For sure. I'm just letting him know what he can get away with.

Hey, what's your favorite rear-node cone for Rapiers? I've been using the 0.625 pointy cone, even though I know it's not ideal.

[AeroGav]

1 hour ago, FleshJeb said:

 

Hey, what's your favorite rear-node cone for Rapiers? I've been using the 0.625 pointy cone, even though I know it's not ideal.

I'd always pick something whose attachment node is the same diameter as node of the engine i'm putting it on.    Last time I checked, shock cones were the lowest drag and they can take a bit of heat too, though they're not cheap or light (but then , neither are your engines).

I just had another go at making a cargo mk3.    I must say,  next to these chem fuel monsters, it looks so small you could almost describe it as cute and adorable.   Well apart from the radiation.      Part count is probably not all that much less though.   It's probably heavier than it looks too.

5 NERVs,  2 RAPIERs,  2 Panthers and no oxidizer.  Test payload was 18.5 tons.  I had a mad idea to try jet off to Moho in it,  then realised I forgot to add Kerbals and it has no probe core.

https://kerbalx.com/AeroGav/Andromeda

 

[Lego_Prodigy]

SSTOs can be either crazy hard and heavy, or pretty simple and somewhat lightweight. I will post one of my own SSTO designs here once I figure out how to post images that actually show up (imgur is not working, and I have downloaded KSP from squad)

[fourfa]

21 hours ago, FleshJeb said:

Hey, what's your favorite rear-node cone for Rapiers? I've been using the 0.625 pointy cone, even though I know it's not ideal.

If you don't mind someone other than AeroGav jumping in on that question - I just investigated this a few days ago in 1.4.2, wondering if there had been any small aero changes.

You'll have to zoom in to read the details from the Drag field.  This is a craft with seven different configurations of Rapier engines in a row.  Left to right: plain (no rear cone), shock cone, Type A cone, circular intake, plain blue dot cone, and small cone.  Data is pinned for both the cone and the engine it's attached to, so you can look at the total drag of the pair, not just the cone by itself.  (Mods are all visible at right, no parts or gameplay mods, mostly just visuals.)  In decreasing order of total engine+cone drag, it looks like this:

1. none =13.61
2. Advanced Nose Cone A = 4.72
3. Small nose cone = 4.36
4. Shock cone = 4.31
5. Circular intake: 4.31
6. Aerodynamic nose cone: 3.58

The plain old blue dot nose cone is light, cheap, tied for best temp rating at 2400K, and has the lowest combined drag.  On my test ships, the extra mass of the plain cones yields a higher top speed on jets and more dV remaining in orbit.  Will it do the same on all ships, or with other tailcones - highly dependent on your design and no way to know for sure without controlled tests.

Edited April 4, 2018 by fourfa

[AeroGav]

2 hours ago, fourfa said:

'll have to zoom in to read the details from the Drag field.  This is a craft with seven different configurations of Rapier engines in a row.  Left to right: plain (no rear cone), shock cone, Type A cone, circular intake, plain blue dot cone, and small cone.  Data is pinned for both the cone and the engine it's attached to, so you can look at the total drag of the pair, not just the cone by itself.  (Mods are all visible at right, no parts or gameplay mods, mostly just visuals.)  In decreasing order of total engine+cone drag, it looks like this:

1. none =13.61
2. Advanced Nose Cone A = 4.72
3. Small nose cone = 4.36
4. Shock cone = 4.31
5. Circular intake: 4.31
6. Aerodynamic nose cone: 3.58

The plain old blue dot nose cone is light, cheap, tied for best temp rating at 2400K, and has the lowest combined drag.  On my test ships, the extra mass of the plain cones yields a higher top speed on jets and more dV remaining in orbit.  Will it do the same on all ships, or with other tailcones - highly dependent on your design and no way to know for sure without controlled tests.

Nice - I can redesign some of my craft and replace the shock cones with lighter and more streamlined nose cones.   Its a bit annoying stuff like this changes back and forth with every game version though.    I noticed currently,  horrible drag from 2.5m fairings.   Actually, the fairing itself shows 0 drag, but the thing it is attached to gains an extra 180kn or so in drag at 380m/s and 7km.   

Another change I noticed is the mk3 engine mount has quite a lot of drag when mounted up front , even if you cone all its nodes.    Though at the back of the ship, it is still a pretty aero choice compared with every other method of mounting so many engines.

Edited April 4, 2018 by AeroGav

[FleshJeb]

@fourfa Great work! It might be worth trying that with the A10 Adapter + Small Nose Cone, and the NCS Adapter + Small Nose Cone. I will test values for 1.3.1, because I'm probably going to skip 1.4.x entirely.

Fourfa, @AeroGav I'm sure you''re both as tired as I am of having to play the click-pin game to see part drag. I want to have a per-part drag output similar to this:

https://krpc.github.io/krpc/python/api/space-center/parts.html#trees-of-parts

I just looked into it and KRPC is not currently able to access those part attributes. However, I've left a comment on the mod thread, and I'm hoping he's able to do it.

I can get that done for the thermal info tonight. I'll do Temp/Max, and Skin Temp/Skin Max. I'll add the % of max as well. I'll edit this comment when I get it done.

reference: https://krpc.github.io/krpc/python/api/space-center/parts.html#SpaceCenter.Part.temperature

EDIT: Alpha code here. Steal at will: https://www.dropbox.com/s/wg0050ur5ab2d01/part_tree_temp.py?dl=0

Edited April 5, 2018 by FleshJeb

[fourfa]

10 minutes ago, FleshJeb said:

It might be worth trying that with the A10 Adapter + Small Nose Cone, and the NCS Adapter + Small Nose Cone.

Good idea, please share if you test it.  Personally I wasn't interested, as the extra part count of only a single part per engine was hard enough to swallow.

[AeroGav]

4 hours ago, AeroGav said:

Another change I noticed is the mk3 engine mount has quite a lot of drag when mounted up front , even if you cone all its nodes.    Though at the back of the ship, it is still a pretty aero choice compared with every other method of mounting so many engines.

Right guys, here's the data.

Pic 1 - Baseline scenerio

Both ends of the mk3 rocket fuel fuselage have mk3 engine mounts on them.   The bottom has 3 dart engines on its small nodes.    There's a 2.5m tricoupler on the big node, mounting a further 3 engines.    The top mount has a mk2 command pod on the big node, and another 3 dart engines on the small nodes which have been rotated 180 degrees (so  as to have the flamey bit pointing at ground) and then offset outwards (so the plume clears the fuselage).     

Note, in KSP min drag is at prograde/retrograde and then as you move away from that drag increases to a peak at 90 degrees, perpendicular to the airflow.    As far as it is concerned, nose cones mounted pointy end first are just the same as ones flipped 180 fat end forwards.

I am actually blown away that the front mount has so much more drag than the first.  Previously all my tests revealed that a part's position in the stack did not affect its drag, but now streamlining is more important up font after all.

Pic 2 -  With Fairing instead of Command Pod

 

Whilst the fairing itself registers zero drag , it has caused the parent part to gain a massive 400nm of extra drag.   This is despite the fact we're significantly higher up by the time we achieve 380 m/s velocity.    The fairing is lighter than the 3ton mk2 pod of course, but the extra drag means it takes longer to reach mach 1.17.     Seriously, this kind of rubbish breaks craft files.    Space planes designed in older KSP will not get supersonic and rockets will be likely to flip on launch.

Pic 3 - No top rockets

What if we leave the 3 small nodes unoccupied on our front mk3 mount?

The reduction in thrust means we're nearly at 10km by the time we hit 382m/s.     Despite the thinner air, drag is greatly increased on the front mount because of the open nodes.    Slightly off topic, but while i was there -

Spoiler

The mk3 to 2.5m adapter is still the drag champ.   That's great if you're actually going to use that oxidizer, but otherwise there is a dry mass tradeoff.

For getting down to 1.25m diameter,  the best options are a command pod or a c7 adapter.   Again, mass vs drag tradeoff vs whether the fuel or seats are needed.

A mk3 cockpit is noticeably  draggier than a mk3 adapter + c7 adapter combo, but better than a mk3 engine mount.  

 

And what about a good old fashioned nose cone?  The 2.5m protective rocket nose cone is still pretty sucky :

 

 

[FleshJeb]

@AeroGav Would you kindly start a "Aerodynamics Per Part" entry on the wiki? Barring that, maybe we need to add columns to all the part listings, showing the drag cubes.

Edited April 5, 2018 by FleshJeb
I have fat fingers.

[CWhizard]

It's overly complicated.  Try something simpler, like this. ---   

[FleshJeb]

On 4/4/2018 at 5:51 PM, fourfa said:

Good idea, please share if you test it.  Personally I wasn't interested, as the extra part count of only a single part per engine was hard enough to swallow.

More data, version 1.3.1. I tried normalizing it to your results, but the ratios didn't match up. I suggest we make sure we're close to zero AoA. I tried setting that up a few times, but I kept smacking it into the ocean. It was within a degree or two when I took the data. Still, the data shows that the blue dot cone is best.

1. Aerodynamic Nose Cone = 1.72
2. Shock Cone = 1.87
3. FL-A10 Adapter + Small Nose Cone = 2.14
4. NCS Adapter + Small Nose Cone = 3.40