SSTO Help

[Mk3 Maniac]

Dear Everyone,

I have created this beast, big ,slightly excessive this craft could use some improvement.

The unnecessary oxidizer tanks are there to make the craft stable when taking off by moving oxidizer towards the back while leaving the front empty, so it can be stable when drained of fuel and filled with fuel.

I haven't tested it yet, but I hope for good advice from the KSP community. So what Improvements can I make to improve the range and maneuverability.

This craft "should" be Laythe Capable

Here is a picture 

Sincerely Mk3 Maniac

Edited May 9, 2017 by Mk3 Maniac
Not Specific

[bewing]

Maneuverability??!? You're nuts! You can only maneuver something that large in your dreams. But the very large distance between your CoM and CoL is going to make this thing extra stable and hard to turn.

To increase range, you need to reduce mass, mostly -- without giving up any fuel. Depending on the number of rapiers that you are feeding, you may be able to halve the number of air intakes and get rid of the MK2 bicouplers.

[Spricigo]

3 hours ago, Mk3 Maniac said:

The unnecessary oxidizer tanks are to help maintain stability when drained of fuel.

Well,  you noticed that mistake.  Yet you did it anyway. The first improvement I propose it's to get rid of this unnecessary oxidizer. 

Something important, if we are to help you,  is to know what the purpose of the plane is.  Without knowing the purpose it's hard to give food advice.  That said:

Try to balance the craft so  the CoM stay around the geometrical center.  If possible CoM ahead of GC because it makes easier to design a aerodynamic stable plane (as in don't flip when slight off prograde).  Place the fuel tanks and cargo bays in such way that the CoM don't shift to much (ideally not at all)  when you burn fuel or delivery the cargo.  Engines may be moved to shorter lateral stacks further ahead to help with CoM but it also may cause drag. 

You want to avoid drag as much as possible, unfortunately everything causes drag.  Thus don't bring anything you don't need,  if you bring don't expose to airflow if you don't need to,  if you ou expose to airflow make it count.  Do you really need the rearmost landing gears, the cockpit or all the intakes? The ship is built to allow minimal fuselage exposure to airflow (wing incidence) ? Do you 'closed' all nodes with matching nosecones or other pointed part?  The control surfaces are limited(both in authority and surface area) to not change the direction more than necessary?  (in this regard a SSTO spaceplane follow a pretty straight trajectory with very gentle changes of direction.  Some behemoths can be kept under control with close to no control surfaces.

Well,  that's general advice. For more specifics I'm waiting for more images,  maybe a craft file but,  most of all,  a defined purpose. 

[Wanderfound]

Minimise number of engines, minimise number of intakes, minimise drag, eliminate any unnecessary mass.

Replace the cockpit with a proper Mk3 one; your current setup looks aerodynamic, but isn't.

For intakes, one shock cone can feed three RAPIERs or Whiplashes. Anything surface-mounted that can be moved into a cargo bay should be. Cap any open node with a nosecone, and minimise the total number of stacks.

Wings should have enough lift and incidence to allow a decent climb rate with the nose on the horizon at 10,000m/1,000m/s.

Ditch any excess mass. No more battery than necessary, no more solar than necessary, no more monoprop than necessary. You want enough jet thrust to reach takeoff speed and crack transonic, but no more.

Balance your fuel load right. If it's a non-nuclear ship, you want enough extra LF to cover the jet ascent, but no more. If it's a nuke ship, you want enough oxidiser to lift the apoapsis, but no more.

As a demonstration:

6,500m/s, ISRU equipped, four crew and a full science kit, seaplane.

It ain't the size of the plane, it what you do with it. Streamline and optimise and you'll get much more performance.

Edited May 9, 2017 by Wanderfound

[AeroGav]

11 hours ago, Mk3 Maniac said:

Dear Everyone,

I have created this beast, big ,slightly excessive this craft could use some improvement.

The unnecessary oxidizer tanks are to help maintain stability when drained of fuel.

I haven't tested it yet, but I hope for good advice from the KSP community. So what Improvements can I make to improve the range and maneuverability.

The main problem  i see is that all your engines are at the back of the ship.    There is only a very light cockpit up front,  so it becomes tail heavy when empty (unstable).

This is despite you moving the CoL very far behind the fully loaded CoM, and carrying around extra fuel as "ballast".

The CoL being so far behind CoM  when loaded down must make it hard to takeoff, and you probably have a lot of drag from the control surfaces in flight.

Try to find a way of getting some engines mounted further forward, especially the super-heavy nukes.   Rapiers can sit a little further back,  panthers or whiplash are lighter and can go furthest aft.

Also, from a handling viewpoint, i tend to fit larger wings to my spaceplanes and try to minimise fuselage fuel tanks. I prefer to carry my fuel in big S strakes where possible, though you'd need a crazy number of them on a ship this size unless using tweakscale.  The reason for this is that they have less drag per unit of fuel carried than other tanks,  and the lift they generate brings you into thinner air more quickly which lowers drag from non-wing parts of the aircraft.        Cylindrical tanks have better fuel per dry mass but most of your fuel is used just getting to space, so i think the drag consideration is more important.

 

[Hodo]

There are several ways to approach your design.  

For me I look at it from the limited picture you show, and I can see the CoL is quite a bit back from the CoM, causing the craft to be nose heavy or overally stable.   

If you were running in FAR this craft would never pitch up and actually not fly at all.    

But to help that craft I would reduce its size, the scale of that craft is a bit too beefy to be "maneuverable".

No matter what it will handle like the Exon Valdez.   The suggestions of increasing the wing size is a good one.  And one I would say myself.  But wings are ultimately dead weight in space.   Same for intakes and air breathing engines.  

I would find a way to move your CoL closer to your CoM, I would then increase the amount of lift the craft generates at low speeds.  This will help with landing and take off speeds.   The sooner the craft is off the ground and above 10km the  less fuel it will use getting to space.

 

After that I would work on figuring out the optimal flight profile for it.  This is the hard part.  Not every craft flies the same.  

No jets and works just fine.   I have even upscaled it and made it able to haul a 20t cargo to orbit.

[Mk3 Maniac]

I did not specify what I meant by using the oxidizer tanks, the oxidizer is for keeping the craft stable during normal flight, I have edited my question to represent this.

   I have edited the ship a bit, here is the result. I simply removed some intakes.

 

Edited May 9, 2017 by Mk3 Maniac

[Spricigo]

1 hour ago, Mk3 Maniac said:

I did not specify what I meant by using the oxidizer tanks, the oxidizer is for keeping the craft stable during normal flight, I have edited my question to represent this.

Which is worse than we supposed (stable at normal flight unstable at reentry) Get rid of those empty tanks and fix the cause of instability. 

Since I can't see,  I will try to guess,  but you have 20t of engine in the rear and 1t of cockpit in the front? There is no way to have a good balance without adding a lot of deadweight.  With the increased weight you need more wings for lift and control surfaces for control,  but that add drag so you need more engines.  And the cycle start over. 

Define a purpose,  build the vessel and then remove.  Remove weight,  remove drag,  remove power.  And keep removing until you can't remove anymore.  When you become proficient you'll not put so much unnecessary things to start with and find more to remove. 

Another point: looks like you decided big=cool.  If that's your opinion no one can say it's wrong.  But different approach can also be cool,  look at something build by,  for example,  Wanderfound or AeroGav. Their vessels may not 'fit your style' but certainly there is lot to learn from how these guys design spaceplanes.