SSTO tips

[mrmcp1]

Since the new areo update I know that there have been many changes to SSTO design. I am going to start trying to design a new RAPIER powered SSTO and have a few question. I have made SSTO's in the past so I do know the basics.

The Precooler: Should I use it and if so what do I connect to it (the intakes or the RAPIER engine)?

Intakes: Which one would be best to use: the ram intake or the shock cone intake? Also how many intakes per engine 1,2 or more?

For my assent profile would I be right in assuming that you should get to 10k s quickly as possible then try and gain speed then pitch up once my speed starts to decrease and go to closed cycle mode?

Thanks in advance for the help

Edited June 5, 2015 by mrmcp1
Question was answered

[Mastikator]

Put the preccooler behind your RAM intakes. They conduct heat well.

Big surface area = more heat radiation, so you want wings on those precoolers too.

As for assent profile, go in sandbox mode and play around.

Don't overdo the wings on SSTO Space planes though, they are good for gliding but slow you down too much.

[Feradose]

If you cant break the sound barrier, do a shallow dive and break it, then pull up again and continue climbing.

Precoolers are just good at radiating heat, not necessary but if you want to get fancy attaching it to hottest part is probably a good idea (do not attempt to attach precoolers to struts, elevons or landing gear).

Since new aero update, one intake seems to be enough for all my SSTOs, which ranges from 1 rapier to 4 turbojets, another reason to this is radial part drag.

Always try putting the cargo bay balanced beetween dryCoM and wetCoM if you cant get dryCoM and wetCoM on the same spot.

Avoid huge tailplanes if you want your SSTO to be stable in space or higher atmosphere, Ive made a lot of unstable, spinny craft because of this.

Also, try to minimize radial attaching because of the insane drag, inline planes perform better.

[n0xiety]

Use shock cones instead of ram intakes. They are less dragy. Also put a shock cone behind the rapier engine and clip it inside untill you can't see the white part of the shock cone. This will give you stability as well as less drag at the tail of plane and a bit more air but don't expect it to work like the ones that are looking directly front. Using this method i was able to create an ssto that goes 1550m/s at 30k height without loosing altitude. At that speed and height making orbit comes easy and don't use much fuel.

[capi3101]

* For RAPIERs, you want your total takeoff mass to be somewhere between 17-24 tonnes per engine; that'll give you between 0.55 and 0.75 TWR on the Runway, which is plenty.

* One Intake per engine is plenty at this point; I've got a couple of designs that made it to orbit with Circular Intakes.

* You won't be making it as high or as fast as you used to be able to do before switch-over in the pre-1.0 days; pack more rocket fuel. I'd say two FL-T800s worth per RAPIER at least, and then a little more if you want to come back down again.

* Any payload fractions you're used to won't be as high either; plan for 15% if you use planes to deliver probes and the like.

* You're going to have to do your speed-up lower and nowadays frictional heating is a thing. Level out to 10 degrees above the horizon at 10k and start speeding up. If you start seeing temperature markers on bits of your plane, steepen up not much past 20 degrees. At 20k, aim your nose up and keep going until your engine kicks over.

* Pre-coolers, if you use them, should be down by your engines.

Edited June 5, 2015 by capi3101

[mrmcp1]

Thanks for the help.

[herbal space program]

* For RAPIERs, you want your total takeoff mass to be somewhere between 17-24 tonnes per engine; that'll give you between 0.55 and 0.75 TWR on the Runway, which is plenty.

* One Intake per engine is plenty at this point; I've got a couple of designs that made it to orbit with Circular Intakes.

* You won't be making it as high or as fast as you used to be able to do before switch-over in the pre-1.0 days; pack more rocket fuel. I'd say two FL-T800s worth per RAPIER at least, and then a little more if you want to come back down again.

* Any payload fractions you're used to won't be as high either; plan for 15% if you use planes to deliver probes and the like.

* You're going to have to do your speed-up lower and nowadays frictional heating is a thing. Level out to 10 degrees above the horizon at 10k and start speeding up. If you start seeing temperature markers on bits of your plane, steepen up not much past 20 degrees. At 20k, aim your nose up and keep going until your engine kicks over.

* Pre-coolers, if you use them, should be down by your engines.

In every plane I've built so far in which I used only RAPIER engines at 15 tons/engine or less, I've either had big problems breaking the sound barrier or my engines have flamed out too low because I didn't have enough intakes. Balancing how much intake drag you can push through the SB against how much weight you have to ship in engines is the key consideration IMO. I'm finding that the sweet spot is around 12.5 tons/engine, with enough intake area to keep them burning up to 25km+. By using a nuke as an afterburner, I've been able to get to 28km at almost 1400 m/s, with maybe 150m/s climb at switchover. I've gotten to orbit with 23% of my initial takeoff weight on board in fuel that way. Using 4 RAPIERs plus one nuke, I just landed my most recent SSTO on the Mun last night. I'm not yet sure if I can do it with enough fuel to get back, but it's close. Anyway, I think more power than that is better in the new aero system. You really need those RAPIERs to be working at their peak on air at the high end, or you'll just have to burn through too much atmosphere on bipropellant at 305 ISP.

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Dang! I just landed it and fell only 65 m/s short of getting back into Kerbin's atmosphere! I've got to be able to squeeze that out somewhere...

Edited June 6, 2015 by herbal space program

[cybersol]

I fully agree herbal space program on the 12.5-13 tons per Rapier in stock. When I had about 15 tons per rapier, adding 15% more engines to get to 13 tons per engine actually REDUCED my total fuel use. I think capi might be talking about nuFAR where I think you are able to go to a higher tonnage per engine.

[capi3101]

I was, my bad (and my bad for not mentioning it!). The engine thrust levels are the same these days between FAR and stock aero so I made the (bad) assumption that you'd want similar TWRs; I didn't account for the differences in how drag is accounted for. Which is what FAR has always done, so I don't know why I didn't think about that before opening my trap...

[RuBisCO]

Put the preccooler behind your RAM intakes. They conduct heat well.

Big surface area = more heat radiation, so you want wings on those precoolers too.

As for assent profile, go in sandbox mode and play around.

Don't overdo the wings on SSTO Space planes though, they are good for gliding but slow you down too much.

I can attest to and verify this advice.