How to make an SSTO?

[JebKeb]

In my career world, I'm trying to make an SSTO for refuelling and passenger services. I've been trying to make an SSTO for a while, and the present design just doesn't work. It runs out of fuel FAR too early. Here it is.

So, can anyone give me any methods of building one or some maths to find out the delta-V savings if with wings?

Thanks, 

JebKeb

[bewing]

Well, it's certainly pretty -- but I'm thinking you have too much airbreathing engine, too much wing, you need nice canards, you should get rid of the ailerons, and there has been a bug with those fuel ducts and struts creating an insane amount of drag.

(And I'd get rid of most of those RCS ports -- one vernor should be enough.)

Oh, and you should move the front wheel back past the nose section -- and maybe even cheat a little and clip it into the fuselage a bit to reduce its drag.

Edited May 1, 2016 by bewing

[AeroGav]

4 Airbreathing engines is too much on something this size as Bewing says.  Whiplash and RAPIER motors are heavy, about 2 tons each, that's a large increase in the dry weight that the closed cycle part has to accelerate to orbital velocity.

Also if you check the config file, thrust falls off a cliff on the airbreathing motors over a certain speed/altitude.   RAPIER does max thrust at mach 3.7, 80% of max at mach 4.5, then falls to 0 thrust by mach 6, so you can see why it's pointless carrying extra RAPIER to orbit in an effort to get more airbreathing speed.

Concur with RCS too.   Reaction wheels are better for spaceplanes since drag is more important than weight.

Wings, I actually prefer large ones also.   They add some extra mass but compared to all those engines you're carrying it's negligible.  The benefit is more efficient flight at high altitude, meaning you can get enough lift without having to much over 5 degrees Angle of Attack.      However, I'd recommend basing it on the "Big S" shuttle delta wing pieces instead,  they have the same mass/lift ratio as standard wing parts but also have considerable liquid fuel capacity.  Essentially that's free tank dry mass right there.   Only drawback is closed cycle engines won't pull from them automatically, you need to use fuel ducts or a mod like GPO Speed Fuel Pump.

Finally, those closed cycle engines look like Swivels.     Again, too much engine if you ask me.  A pair of Terriers would offer sufficient thrust, have better vacuum ISP and are lighter.  Airplanes need less TWR than rockets. But then if you are building an "oxidizer using" spaceplane, why carry two engines into space, when one RAPIER can do the job of both ?

I tend to build oxidizer-less ships however.    For something in the 30/40 ton class, I'd probably use two NERVs, one RAPIER and optionally a pair of Panthers as disposable boosters to make the subsonic climb quicker and more fuel efficient.

There is a distinction between Spaceplane and SSTO.   Pure SSTO is 100% re-usable but it is hard to make anything that can reach Minmus  pure stock without mods on the current KSP version.    In my opinion dropping Panthers and Whiplashes on the way up is acceptable because they are cheap - about 2000 credits each - so you're recovering over 80% of the cost of the vessel.    If you're dropping RAPIERs or NERVs back into the atmosphere at 6000 each, then the economics look questionable.

Here's a 2 NERV . 1 Whiplash SSTO I made -

It did reach orbit with 1000dv left when flown up empty (nothing in the two cargo bays).   I do wonder if it's got enough wing area for high altitude flight when heavily loaded however,  also whether it'd struggle to get through sound barrier with more onboard?

Above pic is a quick and dirty stage-discarding Whiplash-NERV vehicle I built.   The back end comes off, intentionally.   2800dV in orbit means it has the potential to take you places.

https://kerbalx.com/AeroGav/whippynerv

 

[Pecan]

Single Stage To Orbit.  Nope, still can't see anything in those words that says "wings".
Wings don't have much to do with getting To Orbit with a Single Stage and nothing to do with saving deltaV.
Wings will make it harder to get to orbit because they add mass and drag.

On the other hand - they let you use air-breathing engines which are much more efficient than rocket engines.  It is so hard to work out the deltaV required to fly through an atmosphere, because so much depends on the detailed ascent profile at each point, and air-breathing engines are comparatively so efficient, that deltaV isn't even something you should worry about for that part of the flight.

[Kosmo-not]

Have you tried a rocket design?

[AeroGav]

Just to revisit this, yesterday BeWing sent me one of his Single Stage to Minmus spaceplanes -

Which I couldn't resist tinkering with...

and again...

...and then Bewing folded some of my modifications in when he reworked his SSTO -

Quote

holds 2 more tourists, and I ended with 1328 fuel in orbit.

He keeps his designs lean and mean, and has worked out a flight profile where you set pitch to 5deg on takeoff, lock SAS and then more or less go hands off.   My version has a bit better hand flying characteristics but I wish I could work out how to make something that flies to space on autopilot !  And yes, Bewing's  that ship would do everything the OP needs too, holds the same amount of Kerbals.

Love modifying other people's ships, it's great when you're out of ideas.   Last night's experiences has me rethinking some of my advice earlier in the thread

1) engine shedding - only worth 10% more delta V it seems , perhaps not all it's cracked up to be

2) avoid mark 2 fuselages unless you specifically need their cargo bay.  They are so draggy compared to type 1.Of course, I had to have the last word on BeWing's ship.  Thought i'd ruin it with a pair of giant Boeing wings.

Spoiler

 

 

 

Edited May 2, 2016 by AeroGav

[Guest]

Do you want to make an SSTO or a speisplain?  SSTOs are simple with KSP's payload fraction, just need a large enough rocket for your payload.  I've sent 90+ ton interplanetary ships to orbit on a single stage no problem.

Speisplains are pretty easy too unless you're using jet engines, in which case you need more rocket fuel.  RAPIERs make short work of the atmosphere though; I've got a design for a dual RAPIER 4-Kerbal Mk2 crew shuttle that'll handle most LKO operations handily.  No pictures, unfortunately but there's a craft file lying around somewhere.