Help with SSTOs

[angeldust]

Hello everybody,

 

I have stopped playing KSP for a long time and now have started again, specially, because I wanted to try out reentry and all that awesome stuff since 1.1.

 

Now I'm trying to build an SSTO, but I can't do it! I don't know why all my designs are flawed, but I seem to be unable to build an efficient SSTO, which reaches Orbit and has some delta-v left over for maneuvering.

I don't know if it is the design that is flawed, or if I am flying it completly wrong. 

 

Can someone help me to figure it out? I uploaded my most recent attempt and would love some feedback on where you think I could optimize the craft, or some pointers on how to fly that thing efficiently.

Here is the craft file: https://www.dropbox.com/s/8x7cpvq4zxc4ccp/KSSShuttle.craft?dl=0

Thank you ever so much!

 

Angeldust

[AeroGav]

Hi Angeldust,

first things you really want to get rid of those fuel ducts.  They generate insane amounts of drag (possibly bugged) and are no longer necessary as of 1.2, since all engines drain from all tanks evenly now.

The engine selection is also not optimal, if you just want a low orbit taxi, then RAPIER only, if you want to go further, then a combo of RAPIERs and NERVs will take you where you need to be.

I'd loose that pointy cockpit and replace with inline too.  Won't matter too much on a whiplash design since you won't be going very fast down low, but on a rapier ship you'll be limited by overheating.    Any rapier design that can get through the sound barrier should be capable of about 1500 m/s at 21km.  Or more.

Finally, I don't know how long mk2 fuselages have been gimped, but their drag is really terrible at the moment.    To make something halfway competitive/useful out of a mk2,  you need to angle the wings up about 5 degrees or so and fly with zero body aoa or very close to it.

Feel free to have a look at some of my craft.   This is a 6 seater mk2, very similar to yours.   Angled wings , generous wing area, lack of ducts and struts, cones on the back of engines, mean it only needs one rapier and 2 nukes.  Oxidizer is optional and possibly harmful.

https://kerbalx.com/AeroGav/ASES-SP2-Xkos-Dual-Nukes

Then there's this mark 3, that can go to, and land on Duna, 

https://kerbalx.com/AeroGav/Wyvern-Offroad

Then there's a mk3 with cargo ramp.  The ramp adds some drag so it's not as good as the wyvern, but still interplanetary.

https://kerbalx.com/AeroGav/C7-Galaxian

 

Lift/drag ratio is king i've decided.   Means you don't need as many engines to accelerate, which allows the payload and fuel fractions to increase.

 

EDIT - BTW I did get your SSTO to orbit first try.  Had about 300 oxidizer left, however the cockpit nearly exploded from heat.    Inline cockpits only i say.   And we only got about 1150 airbreathing on the whiplashes.

I'm not sure what you must be doing to not reach orbit,     You need to level off at high altitude and get as much air breathing speed as possible,  then start the rocket engines.  Once the rockets are lit, I just kept the nose 5-10 degrees above prograde till our AP is heading over 65km, then shut down and coast to the circularisation burn.   On your ship i had to kill the engines a few seconds early because the cockpit was yellow hot.

I must admit, i was impressed with the power of this ship  compared with mine.  You were hypersonic  a few minutes after engine start - but overall time to orbit wasn't much shorter than mine, especially when you're having to cut power to not melt the cockpit.

Edited December 5, 2016 by AeroGav

[foamyesque]

I believe you actually tend to get better payload fractions for LKO hops out of higher TWR/TDR layouts, because they get you to a higher top speed, at a higher altitude, more quickly.

[AeroGav]

1 hour ago, foamyesque said:

I believe you actually tend to get better payload fractions for LKO hops out of higher TWR/TDR layouts, because they get you to a higher top speed, at a higher altitude, more quickly.

This is one instance where more engines could have helped.   Though i think you can put this down mostly to incorrect technique. 

(it's the Xkos i linked in the above post, i wanted to check it again and make sure i was actually referring him to an airworthy ship)

 

[bewing]

12 hours ago, angeldust said:

Now I'm trying to build an SSTO, but I can't do it! I don't know why all my designs are flawed, but I seem to be unable to build an efficient SSTO, which reaches Orbit and has some delta-v left over for maneuvering.

I don't know if it is the design that is flawed, or if I am flying it completly wrong. 

 

First, your difficulty really is in flying it efficiently. The design is basically OK. You have twice as many jet engines as you really need. Four times as many air intakes as you really need.

That gap in your nacelles is a horrible drag inducing thing -- don't do that!

As Aerogav said -- you don't need the fuel ducts anymore. (The drag bug he talked about got fixed in 1.2.0, but it doesn't matter if you don't need them anyway.)

And it could do with a little more main wing area. And those Basic Swept Wings that you are using for horizontal stabilizers are the very worst type of wings in the game -- very heavy for their size.

 

So: I got rid of the fuel ducts. Stuck your nacelles back together again. Got rid of the 2 ramp intakes. Replaced them with NCS adapters (a little more LF, a little less drag). And that's it.

First try (badly flown):

Edited December 6, 2016 by bewing

[bewing]

Just for fun, here's a sleekified version of your plane, done my way. 735 lf + 600 ox in a 71x70 orbit.

http://pastebin.com/raw/KBNrUkYd

Yes, it has practically no control surfaces. It flies well enough for all practical purposes. And I should probably have turned off the steering on the rear wheels. And I may have accidentally deleted a couple of your RCS ports.

 

[angeldust]

Thank you all for your help!!

I am working on the designs with the tips you gave me and I think I can do it. I think the biggest problem was too much jet engines and the MK2 parts... working on an MK3 design... but I find the MK3 Parts sooooooooo ugly...