Creating the most efficient SSTOs

[Shaun]

Hi guys! It's been a while since I posted anything on the forums. Since 1.0, building SSTOs has became considerably harder. That being said, I manage to get SSTOs with payloads of up to 20T into LKO, but not much further or heavier. I just have a few questions regarding SSTOs in 1.0.5, so I can make myself a whole range of successful SSTOs with fuel to spare.

1. How many intakes (and which ones) do I need per RAPIER? I'm aware of how much better RAPIERS are now compared to the Whiplash, but my knowledge of how airflow into engines is limited, I just know air-hogging doesn't work anymore.

2. Do wings create drag, or just weight? Is it more important now to have big wings to get low Angles of Attack? How much lift/tonne?

3. What parts make the best nose-cones in terms of drag?

4. Is it better to use adapters rather than placing engines on mini box struts and clipping a nice nose-cone to the front?

5. Say I've added tanks to the side of the craft, if I clip them into the main fuselage slightly, will this decrease their drag at all?

6. RCS or Vernors? Vernors are heavy but don't need RCS supply, but do they have lower drag? I tend not to use either unless docking is required.

7. What is the best ascent profile for SSTOs with low TWRs? What do I do if I can't get speed past 320m/s or so without a moderate dive?

8. What parts should be avoided at all costs, because they have high mass, drag or bad benefits.

9. What parts are physic-less? Lights? I'd still like to light up my craft without suffering too much penalty.

10. Do objects placed inside cargo bays or clipped into fuselages suffer from drag?

Thanks in advance  

 

[Starhawk]

1. Still collating, but 1 shock cone can feed 2 rapiers.
2. Yes, but only when the angle of incidence attack is non-zero.  Yes, you want big wings for low AoA's.  Stalling is definitely a thing now.  I was using about .25 lift per tonne in the previous version.  That doesn't seem like quite enough now.  Maybe something like .3 or .33.
3. Tail Connector A and shock cone intakes make some of the best nose cones.
4. I'm not sure what you mean by adapters.  Best practice is generally to use lowest part count - 'Drag is King'
5. No.
6. Vernors only for heavy craft or special purposes.  Otherwise RCS.  Use the place-anywhere units for low drag.
7. Flatten out to start your speed run somewhere around 15-18 km.   You want to maximize the speed you can get from air-breathing engines without exploding any bits of your craft.  Dive deeper, reduce mass, or add engine.
8. Fuel ducts and struts.  There are others.
9. Not sure anymore.  PhysicsSignificance = 1 now means that parts add their mass and drag to their parent part to prevent asymmetric drag, but they are no longer physicless.
10. Not inside a cargo bay, they should be properly occluded.  Clipped into the fuselage doesn't help, they still suffer full drag.

Hope this helps.  I could be wrong.

Happy landings!

Edited December 22, 2015 by Starhawk

[Val]

Great stuff @Starhawk, except this part. 

33 minutes ago, Starhawk said:

2. Yes, but only when the angle of incidence is non-zero.

Angle of Incidence doesn't affect drag of the wing. It changes drag off the fuselage.

@Shaun

Wings and Fuselages create no lift and little drag when they have no Angle of Attack.

Wings create lots of lift and a little drag when they have small Angle of Attack.

Fuselages creates lots of drag and a little lift, if it has small Angle of Attack.

This is why you give wings Angle of Incidence, so the wing can have Angle of Attack without the fuselage having it. Thus avoiding lots of drag from the fuselage.

 

Edited December 22, 2015 by Val
Clarification

[Starhawk]

5 minutes ago, Val said:

Great stuff @Starhawk, except this part. 

Angle of Incidence doesn't affect drag of the wing. It changes drag off the fuselage.

Wings and Fuselages create no lift and little drag when they have no Angle of Attack.

Wings create lots of lift and a little drag when they have small Angle of Attack.

Fuselages creates lots of drag and a little lift, if it has small Angle of Attack.

This is why you give wings Angle of Incidence, so the wing can have Angle of Attack without the fuselage having it. Thus avoiding lots of drag from the fuselage.

Very sorry.  I meant to say angle of attack rather than angle of incidence.  Thanks Val!

Happy landings!

[Pecan]

19 hours ago, Shaun said:

 I just have a few questions regarding SSTOs in 1.0.5

1. None.  Don't use rapiers.
2. Both.  Don't use wings.
3. Protective Rocket Nose Mk7 is about your only choice.
4. It's just counterproductive to add all those parts.
5. No.
6. Neither.  Fine control like that's only needed for docking - your payload can do that.
7. Normal rocket ascent, you'll probably even have a better orbit at the end of it.  Redesign your rocket.
8. Mk3 spaceplane anything mostly, except the passenger module.  Cargo/storage bays and claws are kraken-bait.
9. Like Starhawk, I don't know any more but assume nothing is truely insignificant now.
10. Yes, because 8 above, even though they shouldn't.

Following these guidelines you'll be able to design the most efficient SSTOs possibly, delivering more tons to orbit than parts needed to build them.
Or you could build spaceplanes, but since you said SSTO I assumed you meant rockets, as they're so much easier.
[A bit less tongue-in-cheek - what exactly is your measure of 'efficient'.  You say 'fuel to spare' but that's neither here nor there.  Do you want lowest dV to orbit, lowest cost/t of payload to orbit, infinite-range with ISRU, etc?]

[GoSlash27]

1) 1 precooler per RAPIER.

6) RCS, but use the linear RCS wherever possible, not the quads.

8) Boarding ladders. Especially the retractable ones. Avoid them at all costs!

Best,

-Slashy

[AeroGav]

On 22/12/2015 at 2:04 AM, Val said:

Great stuff @Starhawk, except this part. 

Angle of Incidence doesn't affect drag of the wing. It changes drag off the fuselage.

@Shaun

Wings and Fuselages create no lift and little drag when they have no Angle of Attack.

Wings create lots of lift and a little drag when they have small Angle of Attack.

Fuselages creates lots of drag and a little lift, if it has small Angle of Attack.

This is why you give wings Angle of Incidence, so the wing can have Angle of Attack without the fuselage having it. Thus avoiding lots of drag from the fuselage.

 

I've done a few designs with angle of incidence on the wings, usually 2 degrees.   I've noticed though when accelerating through mach 1,  significant   red drag  arrows coming off the engine nacelles of my LVN nukes, even though i set Prograde on SAS when accelerating through the sound barrier.  These nacelles should be at zero AoA with prograde set, but still make drag here.

I'm just having second thoughts about the practice of attaching wings with incidence, since it complicates construction and can make for a nasty tendency to pitch up at the stall  in canard designs.   I guess it depends on your flight profile.   I tend to stay rather slow until high up,  transition supersonic 10-16km and stay below mach 3 till at least 18km,   generally the only time i can see red lines appearing on the aerodynamic forces debug screen is when i'm going through the sound barrier.   The rest of the time I'm at too low a dynamic pressure to get much drag, also my craft have large wings and tend to run at low AoA anyway.

[Val]

1 hour ago, AeroGav said:

I've done a few designs with angle of incidence on the wings, usually 2 degrees.   I've noticed though when accelerating through mach 1,  significant   red drag  arrows coming off the engine nacelles of my LVN nukes, even though i set Prograde on SAS when accelerating through the sound barrier.  These nacelles should be at zero AoA with prograde set, but still make drag here.

I'm just having second thoughts about the practice of attaching wings with incidence, since it complicates construction and can make for a nasty tendency to pitch up at the stall  in canard designs.   I guess it depends on your flight profile.   I tend to stay rather slow until high up,  transition supersonic 10-16km and stay below mach 3 till at least 18km,   generally the only time i can see red lines appearing on the aerodynamic forces debug screen is when i'm going through the sound barrier.   The rest of the time I'm at too low a dynamic pressure to get much drag, also my craft have large wings and tend to run at low AoA anyway.

I generally have 1-2° less or no incidence on canards/elevators, but not always. I've never noticed any bad stall behaviors. But you are right that it complicates construction.

My ascent profiles are much more aggresive than yours. Generally they go something like this.

• 450 m/s at sea level.
• 8-900 m/s at 5 km.
• 11-1200 m/s at 10 km.
• 14-1600 m/s at 22 km.

The steepest part is between 10 and 20 km where pitch will be 8 to 15° depending on thermal tolerance. Steepest with low tolerance.

I'm very strict about avoiding low thermal tolerance parts and stuff that could create drag and putting it in bays, but I also want my designs to look plausible and cool. That complicates construction, too.

And that's what I love about this game.

[fourfa]

8 hours ago, AeroGav said:

 I've noticed though when accelerating through mach 1,  significant   red drag  arrows coming off the engine nacelles of my LVN nukes, even though i set Prograde on SAS when accelerating through the sound barrier.

Probably a dumb question... but don't exterior nacelles always have drag?  Have you compared to the same craft with no incidence?  I'd suspect the nacelle drag is there no matter what the incidence on the wings

[AeroGav]

2 hours ago, fourfa said:

Probably a dumb question... but don't exterior nacelles always have drag?  Have you compared to the same craft with no incidence?  I'd suspect the nacelle drag is there no matter what the incidence on the wings

That was kind of my point,   looking at the red arrows, my main sources of drag were from 

1) the canards, holding the nose up

2) nacelles and their unavoidable drag

...in my low dynamic pressure flight profile in an aircraft with low wing loading.

It should be possible to work around the pitch up issues you get when combining canards with wing incidence, by applying slightly more incidence to lift/control surfaces at the front of the aircraft than the rear, what way the front end looses lift first and will start to pitch down at the stall i guess.

As regards nacelle drag, everyone's heard about the "put tailcones on engines with rear attach nodes, then offset them so the engines can still make thrust" trick  by now i take it?

Canard drag is a tricky one.   Fitting more/larger control surfaces means less deflection needed to maintain level flight, therefore lower drag , but will make it prone to stalling/snapping its wings off if you pull too hard.   With stock Aero, i've found better results using the "Advanced Canard" part, which has a maximum deflection of just 10 degrees compared with 30 on most control surfaces.   However , it's tiny and weak so you'll need to find a way to mount multiple copies and clip them into each other in order to get enough pitch control.

  

 

[Temstar]

With a medium-high TWR craft, you can in fact support at least 3.5 Rapier per shock cone:

This craft was 135 tons on take off, so just 19.29 tons per Rapier.

[g00bd0g]

How do you add 1-2 degrees incidence to wings? I thought angle snap was 5 degrees?

[Edax]

5 hours ago, g00bd0g said:

How do you add 1-2 degrees incidence to wings? I thought angle snap was 5 degrees?

Toggle the angle snap off.

[g00bd0g]

3 hours ago, Edax said:

Toggle the angle snap off.

How?

[Wanderfound]

12 minutes ago, g00bd0g said:

How?

Look down the bottom left when you're in the SPH/VAB; there's a symbol that will be a hexagon if angle snap is on, a circle if it isn't. Clicking that will toggle between on and off.

[Val]

12 hours ago, g00bd0g said:

How do you add 1-2 degrees incidence to wings? I thought angle snap was 5 degrees?

I use Part Angle Display.

You can change snap angles with it.

[g00bd0g]

On 12/27/2015 at 0:11 AM, Wanderfound said:

Look down the bottom left when you're in the SPH/VAB; there's a symbol that will be a hexagon if angle snap is on, a circle if it isn't. Clicking that will toggle between on and off.

Not sure this provides sub 5 degree rotations.

 

On 12/27/2015 at 3:54 AM, Val said:

I use Part Angle Display.

You can change snap angles with it.

Thanks, just what I needed. Maybe... can't decide if this is a "physics changing" mod as it allows you to build stuff you couldn't in stock KSP

[Wanderfound]

3 hours ago, g00bd0g said:

Not sure this provides sub 5 degree rotations.

It does, but you need to use the rotation tool and the mouse, not just rotate it with the keyboard.

[Kerbal101]

I strongly suggest you to install Kerbal Engineer Redux mod.

Its a statistic-pure mod and also allows you to show heating, ascend/descent, orbital time, thrust-to-weight, total vehicle weight and much more.

Aside from giving your vital information, it does not change anything. Its real real shame stock KSP lacks this.

[Kerbal101]

On 12/26/2015 at 7:03 AM, Temstar said:

With a medium-high TWR craft, you can in fact support at least 3.5 Rapier per shock cone:

This craft was 135 tons on take off, so just 19.29 tons per Rapier.

Rapiers are by default inefficient on medium and bigger SSTO. They are very competitive for ascending, given the right strategy; but loose on ISP below 22k and in space, compared to specialized engines.
Their major advantage is to save weight, but when you need more than two (aircraft dry weight is more than 20-25t; typical rule is 1 air-breath engine per 10t weight), its much better to switch to J-X4 "Whipsplash".
Otherwise, in your typical SSTO orbiting, already 3x Rapiers will burn through more fuel than 2x Whipsplash + 1x T-1 Dart.
This is because their typical ISP is worse than both Whipsplash and Dart.

Edited January 18, 2016 by Kerbal101
Fixed using hints from Val (thank you Val!)

[Val]

46 minutes ago, Kerbal101 said:

Rapiers are super-inefficient on medium and bigger SSTO.
Their only advantage is to save weight, but when you need more than two (aircraft dry weight is more than 20-25t; typical rule is 1 air-breath engine per 10t weight), its much better to switch to J-X4 "Whipsplash".
Otherwise, in your typical SSTO orbiting, already 3x Rapiers will burn through more fuel than 2x Whipsplash + 1x T-1 Dart.
This is because their typical ISP is worse than both Whipsplash and Dart.

I don't agree with this. The RAPIER can be the most efficient air breathing engine, if you use it's high air breathing speed. It's ability to get you up to 1600 m/s will save more fuel for the whole launch, than using the higher Isp Whiplash to 1300 m/s, because those last 300 m/s delta V on rocket mode will kill all the savings of the Whiplash.

Of course, if you don't use the RAPIER to get the extra air breathing speed, either because of a less optimal ascent profile or because the craft can't take the thermal punishment, then you are right, that RAPIER is less efficient.

Edited January 18, 2016 by Val
Grammar

[Temstar]

How does one harden their spaceplane against high temperature anyway?

[Val]

4 minutes ago, Temstar said:

How does one harden their spaceplane against high temperature anyway?

Use a Shielded docking port or a small Heat Shield as nose cone.

[Kerbal101]

28 minutes ago, Val said:

I don't agree with this. The RAPIER can be the most efficient air breathing engine, if you use it's high air breathing speed. It's ability to get you up to 1600 m/s will save more fuel for the whole launch, than using the higher Isp Whiplash to 1300 m/s, because those last 300 m/s delta V on rocket mode will kill all the savings of the Whiplash.

Of course, if you don't use the RAPIER to get the extra air breathing speed, either because of a less optimal ascent profile or because the craft can't take the thermal punishment, then you are right, that RAPIER is less efficient.

From 35k to space - almost any rocket engine is more efficient than Rapier and Whiplash is more fuel efficient to get to 22K. The efficiency between 22K and 35K is defined by an AoA. Rapier can achieve the same efficiency by a bit steeper AoA..

To rephrase: getting to Orbit - Rapier can be just as efficient as a combo, given the right strategy. Its compact weight turns into huge plus for small SSTOs. But any operations within of "not getting to Orbit" - Rapier looses on ISP. The answer to the question lies within area of operation for the SSTO.
 

PS.
Your SSTOs are awesome!
 

25 minutes ago, Temstar said:

How does one harden their spaceplane against high temperature anyway?

Hide any part that can't take 2400K Tmax. Use the right descend strategy. Heatshield can be scaled down with Tweakscale, but usually not needed (thats no rule, YMMV).

[Temstar]

12 minutes ago, Kerbal101 said:

Hide any part that can't take 2400K Tmax. Use the right descend strategy. Heatshield can be scaled down with Tweakscale, but usually not needed (thats no rule, YMMV).

I mean for ascent. For reentry high alpha reentry solves almost all heat issues.

For ascent the part that get heated the most is the cockpit/nose cone. Problem is all nose cones and all cockpits only have 2000 degree heat tolerance, and I don' care for using shock cone as my nose. I suppose the shielded docking port is an option. Does the increased heat tolerance of the shielded docking port offset its increased drag?