Up to date Shock-cone VS pre-cooler for cargo SSTO

[wild_dog]

I've been using info from the forum to build a big cargo SSTO, specifically from Here on air intakes and Here on Shock-cone VS precooler drag and airsupply.
Based on the second mainly, I have chose to go with a pre-cooler and radial adjustable ramp intake per whiplash and 1 pre-cooler per rapier topped by a type b tail cone instead of 1 shock cone per 4 whiplashes/rapiers.
This has lead me to building the following plane:

It has a MK3 small cargo bay with science, a large reaction wheel and extra X200-8 tank, 1 MK3 small cargo bay with a convertotron 125, 2 large drills, 4 fuel cell arrays and 1 large heat radiator, a MK3 crew cabin,  a long MK3 rocket fuel fuselage, a long MK3 cargo bay, and the rest are MK2 liquid fuel fuselages and adapters with full liquid fuel and oxidizer.

The ultimate purpose of this craft is to be the 1 stop shop for everything I might want to do. It should be able to land on minmus, refuel by mining, and then get to about anywhere in the solar system. All the while it should be able to carry cargo the size/weigh of a Rockomax Jumbo-64 Fuel Tank, or about 40/45 tones, to all the science that would not need a permanent station or orbit such as asteroid spotting, the cargo is for carrying that. And it should be able to do so carrying up to 20 kerbals, be they for tourism or for a massive training mission to get everyone to level 5. And all of this on the same single mission.

However, I am struggling to get this thing into a 100KM orbit with enough delta-V to reach minmus even without cargo.

I realized the posts I referenced were 2 years old, and came across a newer post claiming the shock cone now has a much lower drag than any other nosecone.

My question is, is this true and are these posts I found outdated, or am I missing something else entirely?
What am I doing wrong?

Bewing has mentioned that it is way oversized for a space plane, and I agree to an extend.
I have a much smaller space plane for small trips and fun, so for just having a functioning space plane it is way oversize.
But for all the purposes I mentioned I don't think it is.
I'll be tinkering with the design in a bit.

 

EDIT:

So, I got the plane to minmus with a mock cargo of 44 tones and the 16 kerbal passenger cabin still attached. Flight path is tricky, since I was struggling to get the plane over 900 m/s at 21 km. But using an ascend profile based on accelerating and rapid climbing I could still reach orbit. I'm not sure if that is because my engines are oxygen deprived or for other reasons, but it worked.

Based on bewing's advice I swapped out the all the pre-coolers and radial intakes for shock cones. Following AeroGav's advice I ended up replacing my front wingets with the big-s tail fins, added big-s delta wings with control surfaces to the tail section, and completely reworking the wings switching out the MK2 for 2.5m and using only big-s wings and strakes and slightly slanting these. I also replaced the rapiers with aero spikes but maintained the overall number of engines. The aerospikes weigh only half as much and had an ISP of 340 in stead of 305 in vacuum without any (closed cycle) thrust loss. RAPIERS might be good for small planes but as soon as you go into over 8 engines it might be worth while to look into ditching them for straight up whiplashes and aero spikes. I further managed to squeeze the contents of the science cargo bay in with the contents of the refueling and refinery cargo bay, saving me a cargo bay. I could add one or two more 2.5m fuel tanks to increase he amount of delta-V once out of atmo, but I spent enough time on this already.

Overall, I am quite happy with the end result:

There is one strange thing however, the lift of the front Big-S tail fins is uneven.
It's not that big of a deal, the craft still flies, but it annoys my sense of perfection, or that might just be my OCD

.

Edited September 24, 2018 by wild_dog
Spaceplane improved, minmus reached.

[bewing]

Well, I think the thing you are missing is that the drag on the precoolers/shock cones is completely negligible compared to the enormous drag on the rest of your craft. So you are optimizing the wrong thing.

MK2 parts especially have enormous drag compared to what they accomplish.

The art of building an SSTO spaceplane is a very complex one -- so I can't really list all the rules of thumb here. But no matter what you are trying to accomplish with this monster, it's about 4 times bigger than it needs to be. So the two rules I think you need to apply a bit more are: 1) throw away every part you can to reduce drag, and 2) throw away every engine that you can get away with throwing away while still  making it to orbit. Then repeat.

 

[Gordon Fecyk]

Ya bewing is right, that design looks rather overkill.

Here's a much simpler design:

https://kerbalx.com/gordonf/Fat-Star-3

Even this space plane is complicated to fly for folks unfamiliar with space planes. If you're using it with the stock game, fill up all of the Big-S wings with liquid fuel, as it was originally designed for Ferram Aerospace but can fly in stock as well as long as you fill it right up. It can take a Jumbo-64 to low Kerbin orbit, but if you use that Jumbo-64 as well you can get to Minmus. I have a variant design with ISRU, large solar panels and radiators here somewhere...

[AeroGav]

In answer to your original question, the Pre-Cooler is outstanding at low speed and good enough at high speed to feed a single RAPIER all the way to mach 6.     The Shock Cone is outstanding at high speed (one can feed many) and ok at low speed (enough for one engine).    A combo of a single shock cone and single pre cooler could feed 6-8 engines across the speed range i'd bet.   However,  i always find i've got enough 1.25m nodes to cap off at the front that I'm running more intakes per engine than that.    Intake drag is pretty minor compared to fuselage drag now.

 

Re:  Your ship

1.   The best LF/Oxidizer tanks on a capacity/drag basis are the 2.5m ones.     Mk2 tanks are the worst, swap them all for Rockomax tanks then see if you can get away with less engines - exchange the quad mounts for triples.

2.   Engines are heavy.  RAPIERS 2 tons each,  they are hurting your Delta V massively.    A reasonably slick ship should be able to do fine with 30 tons per jet engine.         Or,  try one panther and one RAPIER per 50-60 tons.    The hard bit is getting past mach 1.  The Panthers can help there and are very light, by the time they quit at mach 3,  the RAPIERs will be going ramjet mode crazy.    If you can bust mach 1 you can bust 1400 m/s in level flight at 21km.     More RAPIERs than that doesn't get much more air breathing speed as their thrust falls off rapidly after mach 4.5,  it just kills your delta V with dry mass.     

3.  If you can angle your wings up where they attach the fuselage,  you can make sufficient lift with the airplane flying on prograde hold.   This keeps the fuselage angle to the airflow minimal and really cuts down on drag, which means less engines still.

4.  Wings that don't have fuel in them are a waste.      I only use non fuel wing parts if i need to change the position of CoL  without adding fuel to that part of the ship.

As for how efficient you can go,  well,  i did build this, which can orbit an orange tank.   The minimalist fuselage makes little drag on prograde, but the wings still make plenty of lift, so it doesn't need oxidizer and can get to space with the feeble thrust of a few nervs.     Those nervs in turn, sip fuel and get all they need from the wing tanks.

https://kerbalx.com/AeroGav/Andromeda

That said,  cargo bays add huge drag and have quite a bit of mass even when empty.   This thing will never be as efficient as a dedicated crew/science mk1 fuselage explorer ship.

[wild_dog]

On ‎9‎/‎21‎/‎2018 at 9:55 PM, AeroGav said:

In answer to your original question, the Pre-Cooler is outstanding at low speed and good enough at high speed to feed a single RAPIER all the way to mach 6.     The Shock Cone is outstanding at high speed (one can feed many) and ok at low speed (enough for one engine).    A combo of a single shock cone and single pre cooler could feed 6-8 engines across the speed range i'd bet.   However,  i always find i've got enough 1.25m nodes to cap off at the front that I'm running more intakes per engine than that.    Intake drag is pretty minor compared to fuselage drag now.

 

Re:  Your ship

1.   The best LF/Oxidizer tanks on a capacity/drag basis are the 2.5m ones.     Mk2 tanks are the worst, swap them all for Rockomax tanks then see if you can get away with less engines - exchange the quad mounts for triples.

2.   Engines are heavy.  RAPIERS 2 tons each,  they are hurting your Delta V massively.    A reasonably slick ship should be able to do fine with 30 tons per jet engine.         Or,  try one panther and one RAPIER per 50-60 tons.    The hard bit is getting past mach 1.  The Panthers can help there and are very light, by the time they quit at mach 3,  the RAPIERs will be going ramjet mode crazy.    If you can bust mach 1 you can bust 1400 m/s in level flight at 21km.     More RAPIERs than that doesn't get much more air breathing speed as their thrust falls off rapidly after mach 4.5,  it just kills your delta V with dry mass.     

3.  If you can angle your wings up where they attach the fuselage,  you can make sufficient lift with the airplane flying on prograde hold.   This keeps the fuselage angle to the airflow minimal and really cuts down on drag, which means less engines still.

4.  Wings that don't have fuel in them are a waste.      I only use non fuel wing parts if i need to change the position of CoL  without adding fuel to that part of the ship.

As for how efficient you can go,  well,  i did build this, which can orbit an orange tank.   The minimalist fuselage makes little drag on prograde, but the wings still make plenty of lift, so it doesn't need oxidizer and can get to space with the feeble thrust of a few nervs.     Those nervs in turn, sip fuel and get all they need from the wing tanks.

https://kerbalx.com/AeroGav/Andromeda

That said,  cargo bays add huge drag and have quite a bit of mass even when empty.   This thing will never be as efficient as a dedicated crew/science mk1 fuselage explorer ship.

 

On ‎9‎/‎21‎/‎2018 at 3:36 AM, Gordon Fecyk said:

Ya bewing is right, that design looks rather overkill.

Here's a much simpler design:

https://kerbalx.com/gordonf/Fat-Star-3

Even this space plane is complicated to fly for folks unfamiliar with space planes. If you're using it with the stock game, fill up all of the Big-S wings with liquid fuel, as it was originally designed for Ferram Aerospace but can fly in stock as well as long as you fill it right up. It can take a Jumbo-64 to low Kerbin orbit, but if you use that Jumbo-64 as well you can get to Minmus. I have a variant design with ISRU, large solar panels and radiators here somewhere...

Thank you guys for the feedback. I worked them into the new design and got to minmus (see OP edit).

[AeroGav]

On 9/20/2018 at 9:37 PM, wild_dog said:

 

So, I got the plane to minmus with a mock cargo of 44 tones and the 16 kerbal passenger cabin still attached. Flight path is tricky, since I was struggling to get the plane over 900 m/s at 21 km. But using an ascend profile based on accelerating and rapid climbing I could still reach orbit. I'm not sure if that is because my engines are oxygen deprived or for other reasons, but it worked.

Based on bewing's advice I swapped out the all the pre-coolers and radial intakes for shock cones. Following AeroGav's advice I ended up replacing my front wingets with the big-s tail fins, added big-s delta wings with control surfaces to the tail section, and completely reworking the wings switching out the MK2 for 2.5m and using only big-s wings and strakes and slightly slanting these. I also replaced the rapiers with aero spikes but maintained the overall number of engines. The aerospikes weigh only half as much and had an ISP of 340 in stead of 305 in vacuum without any (closed cycle) thrust loss. RAPIERS might be good for small planes but as soon as you go into over 8 engines it might be worth while to look into ditching them for straight up whiplashes and aero spikes. I further managed to squeeze the contents of the science cargo bay in with the contents of the refueling and refinery cargo bay, saving me a cargo bay. I could add one or two more 2.5m fuel tanks to increase he amount of delta-V once out of atmo, but I spent enough time on this already.

Overall, I am quite happy with the end result:

Good to see you've had success.     The Whiplash engine hits peak thrust at mach 3 (about 900 m/s)   and declines to about half that by mach 4.5.    Rapier Peaks at Mach 3.7 and is still giving 80% of peak power at mach 4.5,  then it quickly falls off the boil.           The Whiplash's altitude characteristics are also less good.   Speedrun altitude on Whiplashes is about 17km vs 21km for RAPIER.    I'd have thought you should be able to get close to 1100 m/s on Whiplash ,  was that in level flight?   

Once the Aerospikes kick on, I'd say just maintain a pitch angle such that the nose is not more than 5 degrees above Prograde,  as drag builds rapidly after that.

As you can see I'm a fan of  combining RAPIERs and Panthers, but the differences aren't that large i suppose.   Also Whiplash make blue flames which look cool.

Oh yes, the good old days of fretting over how much oxidizer to bring.   Not enough, won't make orbit.  Too much,  it becomes dead weight for the NERVs to drag around.   I think that's one reason why I nearly always go pure LF these days.    One fuel gauge,  you've either got gas or you haven't,  simples.

So, looks like you got -   4 nerv  (12t),  8 darts (8t) and 12 Whips (22t) - for  a total engine mass just under 42t.

I'd probably swap the mounts to triples and try with 

6 nerv, 6 rapier,  6 panther ,  for a total engine mass of 36t.   Rotate the Rapier mount 90 degree sideways so the inboard motor is inline with CoM and the outers are above and below, then set an action group so you can switch the inboard to close cycle  while the outers stay AB,  or vice cersa.  If you want to share the craft file i'll have a play with it.

As you can see, with SSTOs efficiency seems to trump "moar boosters",  though i did attempt to build something different today and just "go big", trying to get as many Kerbals in orbit as possible while keeping part count down.      So,   the rocket engine is a Rhino our jets are Goliaths.    Actually that wasn't enough jet, so i stuck on 4 whiplashes (wasn't going to be easy finding space for another pair of Goliaths).      OVer 400 tons gross, more than half of it fuel (despite the apparently small size of the tanks compared to fuselage),     I had to deal with unfamiliar problems, namely wings snapping off due to insufficient strutting.

[ajburges]

Protip: even if you follow a LF only design paradigm, use the "not enough" oxidizer for some more kick at the start of anerobic flight.

Adapters typically have oxidizer capacity and not using it messes with dry mass ratio. Since you have Rapier engines (and said adapters) regardless, having a little oxidizer makes for a nice little nitro that boosts the efficiency of your least efficient flight phase.