How to ssto an orange tank?

[Stocchinet]

I like to build ssto, i like planes and designing spaceplane it's one of my favourite thing to do in ksp, i always used them for crew tranport and never messed with cargo bays or any payload whatsoever, everything was fine, but thigs have changed....

Finally i attemped to build an orange tank lifter for low cost refueling purposes in LKO. It doesen't work. I tried everything.  

This is my first attempt, flies like a charm, but after dumping the cargo the com shifts dramatically to the rear of the craft,reentry and landing becomes impossible, flipping like a mad horse, if you know what i mean.

So after some tweaking i realized that all the solutions i came with was slowly shaping my craft like a skylon, with the engine in the middle of the craft for balancing purpose, maybe real life engineers know what they're doing 

Now the COM stays in spot after the release of the cargo and burning all the remaining fuel, problem solved

But it won't fly.

I put canards to balance COL, they are useless, i put fins for the same purpose, they are useless, i put more engines they are useless, the thing cant climb, it can pitch properly but once reach 5km it start to fall down, so i tought : "i have not enough lifting area", then i put bigger wing and control surfaces but the result is the same, I don't think it'a a Twr problem, this big guy can reach 1.0 twr shotly after takeoff, so what am i missing?

Can someone give me some advice? What i need to make this thing to fly properly? As i said i never had problems with smaller craft but this, this is driving me crazy. 

I humbly ask for help from the ssto maestros, pretty please

A litte disclaimer: i alwais aim for a pointy and semi-realistic design, so no pancake style craft or any kind of absurd contraption please (don't mind all the horrible struts in the pics i dont care about hiding them while in prototipe state)

 

Edited May 7, 2016 by Stocchinet
cleaning

[AeroGav]

I've never built anything that big so you have my sympathies.   I worry about maintaining sufficient structural rigidity without resorting to draggy struts.  Ditto getting fuel from the mess of wet wings it's going to need, to all the NERV engines.

Yes, the stock canards are too small for a ship like this.   I'd probably try stacking a load of them vertically as well as behind each other.  At least type 3 fuselages are tall enough to mount multiple copies on top of one another.   Or a small wing at the front, with the biggest elevons you can find hanging off the back.

Quote

the thing cant climb, it can pitch properly but once reach 5km it start to fall down, so i tought : "i have not enough lifting area", then i put bigger wing and control surfaces but the result is the same, I don't think it'a a Twr problem, this big idiot can reach 1.0 twr shotly after takeoff, so what am i missing?

 

Can you be more specific? What happens at 5km?  Do you run out of pitch authority, and the nose starts dropping?   Or do you end up in a nose-high position, 10 degrees or more off the prograde, but unable to get sufficient lift?  Or in a nose high position, but with more drag than the engines can cope with,  start loosing speed even in level flight, and eventually stall?

[msasterisk]

In my experience, a plane that can lift a Jumbo off the ground falls apart under its own weight, requiring roughly 100 struts to hold it together. I might be doing something wrong...

[Stocchinet]

1 hour ago, AeroGav said:

Can you be more specific? What happens at 5km?  Do you run out of pitch authority, and the nose starts dropping?   Or do you end up in a nose-high position, 10 degrees or more off the prograde, but unable to get sufficient lift?  Or in a nose high position, but with more drag than the engines can cope with,  start loosing speed even in level flight, and eventually stall?

I have to pitch 20° with the nose to get the prograde vector to stay to 10°, if i pitch only 10° i start to go down, but reached that altitude the craft can't build up speed and i loose pitch autority

[AeroGav]

Sounds like not enough wing then, since if the difference between where the nose is pointed and prograde is getting that large , drag is bad. You shouldn't need that much AoA so low in the atmosphere !  I'd personally say you need less engine too, but that's just a personal preference.   The ship you posted in the picture seems to have a tail that's way too small given how nose heavy it is.

Have you tried opening the debug menu (alt-f12) and going to the physics>aero tab and checking the "display aero data GUI" box? Really useful info for troubleshooting spaceplane performance.  Particularly,  look at Angle of Attack (AoA),  Lift Drag Ratio,  Total Drag and Total thrust.

Edited May 7, 2016 by AeroGav

[regex]

Quote

How to ssto an orange tank?

36 tons to orbit in one stage is simple, even in early-ish career mode.

[Crown]

2 minutes ago, regex said:

36 tons to orbit in one stage is simple, even in early-ish career mode.

Please enlight us with your knowledge

[regex]

Just now, Crown said:

Please enlight us with your knowledge

A Single Stage To Orbit vehicle just needs enough fuel and engines to reach @3.5km/s delta-V with a > 1 TWR on the pad, which is quite easy in KSP.

[Red Iron Crown]

Sidestepping the VTOL rocket vs HTOL spaceplane SSTO thing, it looks like the second plane doesn't have enough pitch authority. The gimbals on the engines are too close to the CoM to provide much, and the horizontal tail surfaces have only small trailing edge surfaces. I would suggest replacing the rear horizontal stabilizers with something larger, like the shuttle tail part, and possibly adding all-moving canards as well.

I would also suggest going supersonic while still at low altitude, to get the Rapiers into the meaty part of their thrust curves for the climb. A small bit of incidence on the main wing could also be helpful. Finally I would replace the front nosecone with an empty 1.25m fairing, as that has much better heat resistance for fast atmospheric flight.

[mk1980]

not sure what the purpose of the nuclear engines is. that plane would probably work better without them. rapiers are good enough to circularize and without the nukes, the back of the plane is a lot lighter, so chances are you'd get less flipping during reentry.

if you have fuel left after dropping the cargo, transfer it all to the frontmost tanks to get as much mass as you can as far forward as you can. 

also, such a large plane could probably use some more wing area.

if your plane can get a TWR of 1 shortly after liftoff it may have too many engines. i balance Rapier planes so they have just enough thrust to get through the sonic barrier. they don't have a lot of static thrust, but they sppol up and get A LOT more thrust once you're getting into high mach speeds. if it can break through the sound barrier. it can also get you to space.

if you can't climb, level out and try to accelerate to get more thrust first.even losing some altitude is fine. i have made planes that would barely climb at all, but if they can still accelerate and get to supersonic speeds in level flight, the design is still viable. ramjets and rapiers produce so much more thrust at higher speeds that climbing up becomes a non issue.

every engine beyond that point is dead weight that serves no purpose, basically. just means you need more deltaV in closed cycle mode later to push AP to orbit and circularize and you'll have more mass in the back half of the plane that will mess up your empty CoM <> CoL balance.

 

[Vanamonde]

This question about how to play the game has been moved to Gameplay Questions. 

[Stocchinet]

48 minutes ago, regex said:

36 tons to orbit in one stage is simple, even in early-ish career mode.

With a rocket ssto configuration i can't agree more with you, but my concern ragards ssto spaceplane with airbreathers, it's a little more tricky

27 minutes ago, Red Iron Crown said:

I would also suggest going supersonic while still at low altitude, to get the Rapiers into the meaty part of their thrust curves for the climb. A small bit of incidence on the main wing could also be helpful. Finally I would replace the front nosecone with an empty 1.25m fairing, as that has much better heat resistance for fast atmospheric flight.

The nose overheating always bugged me, i never thought to replace it with a fairing, also i'm working with the supersonic at low altitude thing, sometimes i'm to impatient to gain altitude, i have to re-learn everything i knew with smaller crafts, thanks for the tips

3 minutes ago, mk1980 said:

not sure what the purpose of the nuclear engines is. that plane would probably work better without them. rapiers are good enough to circularize and without the nukes, the back of the plane is a lot lighter, so chances are you'd get less flipping during reentry.

The nukes are for squeezing some more Dv to use in orbital rendezvous, the idea is to use rapiers until the circularization, i balance Lox to supply them until space, then i use all the remaining Lf  with the nukes, also they don't influence the Com a lot, the current iteration i'm working on it's even more balanced

12 minutes ago, mk1980 said:

if you can't climb, level out and try to accelerate to get more thrust first.even losing some altitude is fine. i have made planes that would barely climb at all, but if they can still accelerate and get to supersonic speeds in level flight, the design is still viable. ramjets and rapiers produce so much more thrust at higher speeds that climbing up becomes a non issue.

Ok i'll try it, i'm always worried to waste to much fuel in atmosphere during that phase, with smaller craft i usually zoom climb till 10km where i start the final run to orbital speed, thanks for the advice

15 minutes ago, mk1980 said:

f your plane can get a TWR of 1 shortly after liftoff it may have too many engines.

That's a design choice drived by impatience 

[regex]

10 minutes ago, Stocchinet said:

With a rocket ssto configuration i can't agree more with you, but my concern ragards ssto spaceplane with airbreathers, it's a little more tricky

Ah, well, when I see a thread asking about SSTO vehicles I don't automatically assume someone wants to talk about SpeiSplains To Orbit.

[mk1980]

oh i wouldn't worry too much about fuel for rendezvous. chances are that 6 tons of extra fuel would give you similar (maybe even more?) deltaV than adding 2 nukes just for the docking. if your target station is in a high orbit, you'd probably be better off using a tug to move the tank to the station. if it's just in a 120 km orbit or something, you'll need maybe 150 deltaV for rendezvous & docking, not enough to warrant an additional set of engines.

also, as a random note - if you only wanr the fuel and don't really need the orange tank, it may be smarter to build the plane around mk3 fuel tanks. you need a long cargo bay for the tank, which adds 4.5 tons of weight in addition to the ~4.5 tons emtpy weight of the tank. you could instead use 1 long and 1 short mk3 tank and just transfer the fuel after docking to the station/ship. you'd save a few tons of dead weight.

[Stocchinet]

3 minutes ago, regex said:

Ah, well, when I see a thread asking about SSTO vehicles I don't automatically assume someone wants to talk about SpeiSplains To Orbit.

Hehe my fault with the title, I thought that my screenshots were quite explanatory

[Jarin]

Ah, Regex being pedantic, I'm shocked.

 

I second the "more wing lift, and fly level to build speed" suggestions.

[Stocchinet]

1 hour ago, mk1980 said:

also, as a random note - if you only wanr the fuel and don't really need the orange tank, it may be smarter to build the plane around mk3 fuel tanks. you need a long cargo bay for the tank, which adds 4.5 tons of weight in addition to the ~4.5 tons emtpy weight of the tank. you could instead use 1 long and 1 short mk3 tank and just transfer the fuel after docking to the station/ship. you'd save a few tons of dead weight.

Oh that's a nice one, but i like the cargo bay more cause i can configure the payload for any need, maybe i'll build 2 separate versions, one tanker and one cargo

Also i'm having great results with all the tips you guys gave me, thanks, i'll post soon the results

Edited May 7, 2016 by Stocchinet

[mk1980]

your request inspired me to play around in sandbox and make a monstrous fuel tanker - just to see if it works. 

i've uploaded some images in the "waht did you do in KSP today" thread over at the steam KSP forum, here's a link in case you're curious.

http://steamcommunity.com/app/220200/discussions/0/864973123555815074/#c364040961440819685

 

[AeroGav]

2 hours ago, mk1980 said:

not sure what the purpose of the nuclear engines is. that plane would probably work better without them. rapiers are good enough to circularize and without the nukes, the back of the plane is a lot lighter, so chances are you'd get less flipping during reentry.

I've had very good results with a Whiplash/NERV single stage to minmus/almost duna return ship , so my next project is going to be a heavy lifting cargo mk3 using this combo.     The low thrust and weight of the NERVs is not so much of a problem - build your ship for low drag in high altitude flight, have one NERV for every 15-20 tons launch weight and one Whiplash per 30T and it performs pretty well.     The main issue with NERV is that they don't drain evenly stage by stage like jet engines or rapiers in closed cycle,  they have all the annoying behaviour of standard rocket engines in that they only take fuel from tanks in the same stack  as them and don't drain evenly, pulling from the front tanks first, leading to a fuel imbalance.    Try to fight this with fuel ducts and you run into drag issues.   Obviously, this is only a real problem if you're forbidding yourself all mods, for whatever reason.

[mk1980]

ok i guess it makes sense in that combo. but not really my idea of what spaceplanes are for. i made some rapier+nuke spaceplanes and the biggest one had a bit more than 4k deltaV left in LKO. tried to land it on duna, but failed miserably since i totally overestimated the lift you could get from that thin atmosphere. with a set of parachutes it would have worked i think. i made a falry reliable one that can make a roundtrip to the mun or minmus with 4 passengers and science equipment etc., but by the time you have the tech for doing such a trip in an SSTO, you might as well setup refuelling stations everywhere and use dedicated spaceships for the transfers.

in practice, i only really use planes as supply/crew transport to get stuff to LKO cheaply. i can't help but feel that i'm doing it wrong when i make a plane that hauls all the dead weight (wings & jet engines) over to another planet. i usually just launch my exploration vessels conventionally strapped between some rockets (or at the top) and use planes to refuel spaceships in orbit and get crew and tourists up (and down).

Edited May 7, 2016 by mk1980

[AeroGav]

Well yes MK, I guess the application we are talking about here is an LKO only vehicle, though i think if you can solve fuel balancing issues the NERV makes sense here too, even on the boost to orbit the fuel it saves offsets the extra engine mass.    Me personally I do tend to use my spaceplanes further afield, it's kind of cool turning up in a huge ship that has "go anywhere" ability,  but I also hate doing orbital rendez vous.  Land on minmus flats, hook up to an irsu plane and get a fill with Kerbal attachment system, is stress free and doesn't involve watching two ships spin around a planet for an hour.  After that you can go to duna , laythe etc.      I know the most efficient setup would be to transfer the crew to an optimised vehicle for every leg of the journey, have spaceplanes on kerbin, duna and laythe to shuttle people to orbit and a series of planetary tugs inbetween, but that's too many docking manuvers for my taste plus it's an even more heavily built out set of space infrastructure.

Incidentally, this is my whiplash/nerv 5 kerbal/docking adapter ship..

and here it is landing on duna..

 

and minmus

https://kerbalx.com/AeroGav/Astrojet-Citation

The empty / full weights are 15t/30t.   I suppose you could make an interplanetary shuttle a bit lighter, though there is only one airbreathing engine in this design (1.8t) and most of the lifting surfaces do double duty as fuel tanks.

[Stocchinet]

That's a very cool spaceplane Aerogav, but regarding those big wings, they have a very little heat resistance, based on my experience they cook on reentry very easily, how do you deal with it?

 

Edited May 7, 2016 by Stocchinet

[bewing]

2 hours ago, Stocchinet said:

That's a very cool spaceplane Aerogav, but regarding those big wings, they have a very little heat resistance, based on my experience they cook on reentry very easily, how do you deal with it?

 

You come in very shallow, and bleed off all your speed in the stratosphere.

I liked your first plane much better. You can double canard control by putting a pair of canard wings in a shallow X. I think all you really needed to do was add another fuel tank in the front of your SSTO -- once you dump the orange tank, move all your remaining fuel into the front tank. That'll rebalance your CoM.

[AeroGav]

4 hours ago, Stocchinet said:

That's a very cool spaceplane Aerogav, but regarding those big wings, they have a very little heat resistance, based on my experience they cook on reentry very easily, how do you deal with it?

 

I just pitch up to 15 or 20 degrees angle of attack as soon as i dip below 70km and lower the landing gear.  Because the design has so much lift compared to its weight, it tends not to fall into the thick of it until most of the speed has bled off.  

Launching is harder actually, however these days I just raise pitch angle according to a mach number schedule that gives best l/d ratio and if temperatures start getting critical, throttle back a bit.  Again, thanks to all the lift, I only start overheating at mach 5 whilst heading upstairs quickly, so easing back on the power temporarily (until the air gets a bit thinner) doesn't seem to hurt delta v much.

The main reason for using the airliner wings was that they hold twice as much fuel as big S delta wings, which meant fewer ducts to keep the NERV engines fed.  Relying on fuselage tanks would give me CG issues.  Was trying to build something that would work without mods and not need you to pump fuel around while flying to orbit.

Edited May 8, 2016 by AeroGav

[Sereneti]

one question: Can i have the .craft file from the Topic

I need a large lifter, and have some ideas to improve the desing

(like: exchange the Y-mk2 to a mk2-mk1- adapter, and exchange the air-intakes to shoc-cones... -> decrease drag, decrease the air-intake a little bit)
(exchange the Nose-con to a shoc-cone intake-> increase air-intake, decrease drag)
(exchange the Nerv against a ramjet -> decrease weight , increase atmospheric trust)
(flip the MK2 parts about 90 degres. -> that give you a small wing-area)

Edited May 8, 2016 by Sereneti