SSTO Under Construction, layout & appearance feedback

[AeroGav]

So,   I got thinking about making something that could do the job of Matt Lowne's old ship,  Argus, in 2018.        Requirement is 4 seats,  4k delta V in orbit,  and at least a CRG-25 bay.

The adapters either end of the cargo bay add waay more LFO tankage than i'd want (looks to be enough to add about 3-4 mach numbers to something this size),  so i'll scale up to a CRG-50 right away and see where that gets us.

The delta wing  makes it look like it's doing 0.5C while parked, unfortunately the CoL is WAAY too far back.      Yes, I accidentally clicked away, and lost, the front section, but it didn't move it forward much and unless i give it canards like Dumbo's ears we'll still be too far back.    I really  want the CoM to be in the middle of the cargo bay so it handles the same laden or not - and fuel needs to be distributed either side of our CoM too.     I tend to build lower powered designs that compensate with low drag.  But it will only have low drag if prograde hold keeps us within a degree or so of prograde throughout the the mission.

One other problem with this sleek wing - I need to find a place to put on 2 RAPIERs and 4 NERVs.      Once I add incidence to the wing,  there won't be any place i can attach these to the body and not have the efflux impinge on a wing surface - unless i put all the engines at the back - which will put our dry CoM way behind the cargo bay.

Anyway, I digress.  Subject for tonight,   Rhinoplasty. 

This reminds me of Sesame Street character,  can't remember the name.      Quack !

Ramp intakes,  sloping inward.  Hungry for Krill....

Ramp intakes sloping out.        Pointy.      Looks like i used some old parts off a Colonial Viper.

 Edit - craft name will change, don't worry.   The pre-alpha had the cabins between the panther engines and rear tri couplers,  it looked a bit medicinal,  you could say.

[qzgy]

I wonder if you've considered podding the rapiers and NERV's some how above and below the wing each 2x radially symmetric. Doesn't have to be a lot above or below, just enough not to clip the wing I guess.

I would also think about flipping the wing the other way around maybe to get more of the lifting surface closer to the COM. Would disturb the COM though I guess.....

 

[Kerbolitto]

What about something like that ?

You could get your 4 Nukes in 2 pods (those near the cargo bay on this pic), bursting above and below the main wing, and 2 Rapiers externally on wingtips (above forward landing gear) this makes things very easy to balance CoM.

Edited July 10, 2018 by Kerbolitto

[Rune]

I know you like your BigS wings, but here's a radical tought: liquid fuel fuselages+normal wing sections can offer the same dry-wet mass ratio, with much more freedom in design, and a better final look. BigS wings weren't made to look good when stacked, after all, and though they seem to be free fuel tanks at first glance, they have a mass ratio significantly worse than other tanks, meaning if yoy can get by with less wings, they can be an actual downside.

 

Rune. Also, you can balance the engines at the back by having the lighter cockpit on the front much farther from the CoM.

Edited July 13, 2018 by Rune

[FleshJeb]

That nose needs to go. I think I'd run the main central stack to an aerodynamic point, and then surface attach the cockpit, etc and clip them in.

I didn't know what the Argus looked like, so here it is: 

Spoiler

I experimented with ptiched up delta with a 10 deg dihedral recently to deal with the engine clipping problem. It worked pretty well, and the fuel balance was fine. It should clear your 3.75m stack. The nukes are still a problem.

https://kerbalx.com/FleshJeb/GavDelta

[AeroGav]

I haven't been playing so much KSP recently,  and the cut n paste nightmare of sharing crafts and pics is something i've been putting off.

But I finally got the craft flying.      

Sadly it's not quite as sexy in the metal as its shadow appears.   Though it does look quite sleek when viewed from behind as you're flying it.

First few flights revealed undesirable handling characteristics,  CG was too far aft,  making it capable of acrobatics but hard to control precisely.   Also,   the Panthers were slightly above CoM and RAPIERs a bit below it.   On takeoff,  it would fly ok, but as it accelerated, Panthers were first to get the RAM air boost and by 249 m/s it was flying at -5 AoA hands off.   If you fought past this, then the RAPIERs would get going and start pitching you up again.      Not good.   You need an airplane that does prograde when you set it to prograde hold, or your drag will be high.

Had to put both types of engines on separate stages then tweak with RCS build aid , then do the same for the NERVs.   Each time i move one set of engines, it effects the CoM so the first group of engines need redoing.   After several rounds of tweaking though,   such forces become negligible.

So I made an orbit shot.     First thing,  we have far too much oxidizer capacity.    These adapters are the lowest drag way to taper down from a mk3 cargo bay, so i suppose i just live with it.  Maybe you could have a chemical lander in the cargo bay and use these tanks to refuel it.   For now i just adjusted them down to 1/4 capacity.

Next 3 panther is too much for 2 rapier.       Initial subsonic climb was conducted with a TWR of about 0.55,  same as an F-105E  fighter bomber :

Levels off to go transonic at 6.6km,  3 min 40 sec after engine start.   TWR is 1.0 (like an F-15) at this point,  increasing to 1.15  (Eurofighter Typhoon,  F-22 Raptor) with nukes on.   It only needed 30 seconds to accelerate from 260 m/s to 440 m/s, that's hot !

After Panther flameout,  we're down to the TWR of an F-105E again.         At 22km speedrun, the thin air drops our TWR to just 0.3  (twin engine jetliner at max takeoff power), so it took a further 7 and a half minutes to reach 1350 m/s.    With the nukes on ,  we're back up to F-105 TWR.      At 1600 m/s , we're turning into a Boeing again,  so it's time to hit close cycle mode - while the oxidizer lasts, our TWR is 1.7.   The Space Shuttle only had a TWR of 1.5 on liftoff, so this must give quite a kck.

Next iteration of the craft I replaced the tricoupler for a bicoupler on the back of the fuselage to drop us to two Panthers.   Yes, the tricoupler has the best ratio of engine nodes to drag, but sometimes you got to look at the bigger picture.    I wanted to try keeping the triple node and replacing its panthers with nukes.      Then either 2 panthers/2 rapiers either side of fuselage or  2 panth/2 rapier/2 more nerv on side pods.    The latter option meakes an even bigger mockery of our oxidizer capacity, it would probably have more delta v with none loaded at all.      Also,  having the heaviest, as opposed to the lightest engines at the back, means the side mount engines will need to go  a lot further forward which may result in a less sleek looking craft.

Finally,  I loaded the cargo bay with an FT800/spark probe (like on the Argus demo video) and 4 additional tanks of jet fuel.       

This version went transonic at 5km,  and needed 8  minutes to get to 360m/s.  TWR during transonic was only 0.5,   and that's with nukes on too.     But it actually has a smoother ride than the triple panther ,  not pitching itself up into zoom climbs when the engines go banzai, and bear in mind this is worst case scenario - it's fully loaded here.

Over 4k delta V in LKO,  with the probe onboard, 5 seats.   

Looks like it pretty much does what Matt Lowne's craft did, so I'm naming it the Agenor, who was the 3rd ruler of the ancient City of Argos after Argus    :-)

Available here -

https://kerbalx.com/AeroGav/Agenor

 

Working on a 3 nuke version right now,  might have more delta V due to lesser dry mass.

 

 

[AeroGav]

On 7/12/2018 at 6:53 PM, FleshJeb said:

 

I experimented with ptiched up delta with a 10 deg dihedral recently to deal with the engine clipping problem. It worked pretty well, and the fuel balance was fine. It should clear your 3.75m stack. The nukes are still a problem.

https://kerbalx.com/FleshJeb/GavDelta

 

I had a play with this and tried to make a Tylo capable vessel as you said you were planning.     The goal was "easy" flights to Tylo without complicated  Eve/Kerbin Flybys (I can't do those!).   It's not single stage but mostly re-usable - the two whiplash and single panther dropped are quite cheap.    There's two seats and a small IRSU for refuelling on the surface.

After the jets detach, the orbiter starts with 8177dV and 0.44 TWR,   but it reaches a TWR of 1.26 as the tanks empty.

Whiplash separation is cool and usually results in a nice explosion as they smack each other -

I was watching a video while flying this and cut engines a bit late, hence the 135km PE.   

>6600dV in this wonky orbit and space for two (romantically inclined?) Kerbals who don't mind spending quite a few years together.  Or who are just really really good at travel chess.

 

So,  you can probably reach Tylo with the thing, and probably land.    Getting off again however...       I  emptied fuel tanks till it's TWR reached 1,  at which point it's only got 1833 dV - not enough to complete orbit, especially with the losses its gonna have at that TWR.     So,  you might be able to land on TYlo then smash yourself into atoms at sub orbital velocity.

If Tylo is possible at all (Without a fooking big rocket,  or a large space plane carrying a tiny  staged, disposable lander),  i suspect some chemical fuel is needed.

Maybe take out the centreline nuke for a chem engine and swap some tankage over to LFO.    Then you are trading interplanetary delta V for more short term thrust..   the question is,  can you make this chem engine last long enough to do any good, without swapping so much tankage over to Ox that your delta V goes into the toilet.

Atm this design  is good at bringing a fantastic portion of its original fuel reserves to tylo orbit, but it doesn't do much good as you plummet to the rocky surface.

Another option is to dump the IRSU converter with a decoupler.  It's only 1000 kredits, but weighs 1.25 tons.    

The biggest challenge looks to be taking off from Tylo surface with enough fuel to get back to Kerbin.     You could leave some fuel in orbit before descent, but rendez-vous and docking are time consuming and require a lot of player skill.   You could land on Pol home for a final top off before going home, but that's not an option if you ditched the converter.

Maybe i could take advantage of the fact this thing has 5 RTGs (for the IRSU) and fit a ion engine, will save a bit on the transfer burns (admittedly, the lion's share of the burn is in the tylo descent and ascent, which must be at high TWR.   That is why one does not simply walk into Tylo!)

 

 

Use at own risk !

https://kerbalx.com/AeroGav/GavDelta-Tylo2

 

 

 

 

Edited July 24, 2018 by AeroGav