SSTO help to minumus/mun... Fuel/thrust balance?

[Arugela]

Not sure if that is the problem. But I have an SSTO I keep trying to add range too to be able to refuel and get to miniumus and if possible the mun.

I started with this:

https://www.dropbox.com/s/jsq3j61h4aixuku/IDGAD Starfighter.craft?dl=0 <- This should be generally correct. I might have made some aerodynamic improvements which should be in the next file.

A 36 ton little MK2 plane. I can get into orbit and back down if I used nukes on the way up. I wanted to use only the Rocket fuel to get orbit then pure Liquid fuel for additional travel. Hence the nightmare begins. I have made many mining craft and have never had problems. I can't figure out what I am doing wrong. Not sure if I knew what I was doing right before either. But I always managed at least minimus!

This is the craft now!

https://www.dropbox.com/s/be3uax5v721p4gu/IDGAD Starfighter 1_4.craft?dl=0

About 135 tons of fun apparently. But the fun isn't on minimus.... Or the mun.

I also have problems with the landing gear. I'm trying to keep them balanced but the speed this gets sometimes on teh runway messed it up. If I try to make it lift higher it has issues with swerving all over the place.

Is MK2 designed not to be able to get to the mun or minimus now without refueling? I'm using nukes/Rapiers/whiplashes to get enough thrust.

Should I change out a bunch of the Rocket fuel for liquid fuel and not worry about if I"m using the nukes to orbit? I need to figure out the max delta V I need for the larger thrust also. I have no idea what it needs to deal with landings and other things in the solar system.

 

BTW, I'm currently using 3 nukes with 3 rapiers and 3 whiplash engines. Still can't find the sweet spot.

And as far as I can tell, besides too many engines/fuel, I have bear minimum of everything else. Even possibly the air intakes. I have around 5-6 tons of stuff for mining. The rest is plane, fuel, and engines. Maybe I just need to add one more 400lf fuel tank to the cargo or something. I just can't figure out what it is missing. I've explored a bunch of different engine configurations but can't get it to work. Basically everything between the first vessel/picture and this last one. All the fuel/engine combos I could think of or until I got tired of them more specifically.

Edit: Replaced some of the Rocket fuel for Liquid fuel and it is doing better now. It was an engine efficiency thing. At least for now.

Edited October 4, 2016 by Arugela

[Val]

10 hours ago, Arugela said:

That is a great looking craft. Nicely done.

I'm not at KSP computer, but based on the pictures, it has the following issues, in my opinion:

• It has more wing area than it needs. (Not critical, but does hurt performance a little)
• 4-ported RCS. Very draggy and low temp resistance. Both hurt ascent because it limits speed in lower atmos.
• Way too much engine for it's mass. When you have that high TWR you're often forced to climb so steeply, to avoid overheating, that you end up above airbreathing altitudes long before the airbreathing engines have reached their optimum speed.
  You want to reach 20 km at around 1250 m/s and no more than 15° pitch. Otherwise the potential of the airbreathing engines are lost to gravity losses instead of giving you horizontal speed. Which is what you really need to achieve orbit.

 

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I also have problems with the landing gear. I'm trying to keep them balanced but the speed this gets sometimes on teh runway messed it up. If I try to make it lift higher it has issues with swerving all over the place.

Placement of landing gear is just as important for stability on the runway, as CoM/CoL placement is for stability in the air. When you have landing gear with nose gear, then the main load bearing landing gear should be right behind CoM, just like CoL.

 

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Is MK2 designed not to be able to get to the mun or minimus now without refueling? I'm using nukes/Rapiers/whiplashes to get enough thrust.

Depends on what you mean by "get to"? Making a Single Stage spaceplane that can land on Minmus is doable. Landing on Mun a bit harder. Taking off and getting back to Kerbin without refueling, very hard.

Below is a 38t craft with 2x RAPIERs and 2x Nukes. Gets to 80 km equatorial orbit with roughly 1900 m/s dV left. That should be enough to get to Minmus and land there.

If you replace one or both of the passenger cabins with mining gear, maybe it'll do what you're looking for. (craft file)

If you want some inspiration on how to pack mining equipment, there's some inspiration here.

(Sorry. No craft file)

[Arugela]

I did it originally with the fuel cels but I wasn't mining enough to use them from what I could tell. Do you worry about time when you refuel? And how long does it take you when you use the small ISRU? I have gotten from 45 days down to 14 days in my current setup on the runway. currently I can't get the 14 days back and it seems to run at about 35 days.... I use a big drill though because the small ones took so long. I haven't found a way to make those small ones work efficiently. Although I would use them if it didn't take 99 days to mine with them.

Edit: 45 days was back when the design had only 6 engines or so total and less fuel. It is now a bit bigger.

Maybe I should strip off the whiplash engines too... And I totally forgot those inline air intakes existed... I'll have to try them.

Edited October 4, 2016 by Arugela

[Val]

8 minutes ago, Arugela said:

And how long does it take you when you use the small ISRU?

I had 2 large fuel cells, 3 RTGs, 9600 EC battery, 4 small drills, and a small ISRU. Took around 11 days to refuel 4581 liquid fuel and 759 oxidizer with a 5 star engineer (Sandbox game)

[DrLicor]

@Val, haha I knew you are quite OP in these things and almost couldn't resist to tag you here, but I didn't knew if you were pleased with it if I did.  

[Arugela]

I have discovered a new thing!! MEXICAN JUMPING PLANE!!!

Take it out on the runway and watch it go!!! ><

Does Mexican jumping plane qualify as a glitch or a feature? Does it count as a new form of propulsion?!

Maybe I should put up a challenge to see how many places people can get Mexican jumping plane to and have it dance! 8) With modifications allowed to get it there(assuming it still dances)

It does this without the engines going. I just put them on to see the movement was present.

Edited October 4, 2016 by Arugela

[Aegolius13]

I've been working on an extreme range SSTO lately.  What I've found is that, to maximize range in space, the plane has to be just, barely, capable of getting to orbit.  It it performs well in atmosphere, then it's carrying too much dead weight for space.  So you want just enough wing to fly, just enough control authority to stay straight and pitch up slightly, just enough nuke power to get you from jet shutoff to orbit, etc. 

For example, my plane can barely take off by hitting the end of the runway.  Then I have to climb subsonic at like 5-10 degrees until reaching 4000 meters or so, then level off to hit the Rapier sweet spot.  I also take the bare minimum oxidizer, and plan to run my Rapiers in rocket mode for only the bare minimum kick to allow my nukes to get me the rest of the way to orbit.  So what I would try is iteratively removing engines and rocket fuel until you can just barely make it to orbit. 

It also looks like you have way more nacelles than you need, and way more air intakes.  Those are probably adding drag and making your engines work harder.    I would not be surprised if one shock cone could feed all the engines you need, but two would be plenty.  If you need two Mk 1 nacelles per side, I'd suggesting looking at Mk 2 nacelles with the bicoupler instead.   

As far as landing gear, have you tried rotating them straight down using "absolute" mode?  That usually fixes my issues.  But with a 136 ton ship, you may just be overstressing them.  Hopefully an engine diet will help with this too. 

Here's a pic of my non-ISRU unmanned variant.  Has almost 5,000 delta-v left after reaching LKO.  

 

 

And here's an ISRU variant I worked on.  Capable of getting to Minmus with 1,500  delta-v to spare.  (I just forgot the ore tank).  

[AeroGav]

What the OP is trying to do is very, very hard.    In fact, he's inspired me to take another crack at this, but if it is possible to fly from the surface of Kerbin to Minmus with a full ISRU setup, without refuelling and without leaving anything behind, I think margins will be so tight then the amount of loose change in Jeb's pocket could be the difference between success and failure.

The closest I ever came was with this mk2 cargo Spaceplane.   It has two panthers, two NERV and one RAPIER.    The Panthers are switched into Afterburner mode when the time comes to penetrate the sound barrier.  At mach 2.5,  I jettison them.

https://kerbalx.com/AeroGav/PENTA-STAR

Here it is packing a minimalist ISRU kit -

Made it to Minmus with about 400dV left.

Eight big S wings and three Vernier lift engines make for a really safe and comfortable landing speed on Duna.

The two Panther engines are in a watery grave somewhere on Kerbin,  but the single Rapier and two nukes are easily enough to orbit from the surface of Laythe, thanks to the lower gravity, orbital velocity and thicker upper atmosphere.    

The upcoming 1.2 patch means Penta Star no longer requires a fuel balancer mod to fly, so I think it's time to revisit her.

EDIT - here is mk2 https://kerbalx.com/AeroGav/PENTA-STAR-REDUX

If you can't get a full SSTO to do all this, I think dumping some of your airbreathing engines/boosters/external tanks is a good approach.  Panthers and Whiplash are less than a third of the cost of a RAPIER and about one tenth the cost of a nuke.   For less than the cost of your first career mode rocket to make orbit,  you can fly all over Duna and Laythe and visit most of the moons along the way.   

Alternatively, you could refuel in orbit but that means two flights and a VERY time consuming low orbit rendezvous and dock maneuver.  To me that's like pulling teeth, I'd give anything to avoid it.

Back to the OP question.

I'd agree with most of the advice here.   Minimise radially attached stuff, frontal area, bare minimum of engines.  I do differ on what has been said about wings.

As you make wings smaller, you have to use a higher angle of attack - ie. have the nose pointing up above the prograde marker at a sharper angle - in order to get enough lift.   Beyond a certain point, drag increases exponentially.   You get lowest drag below 3 degrees under 160 m/s (ok, you don't  spend enough time here to warrant optimising a spaceplane for this),  4 degrees when supersonic 10-20km,  and about 5 degrees when you've exceeded the max speed/altitude capability of your jets and are flying on nukes alone.

The downside to adding extra wings, is that Big-S delta wings aren't as mass efficient as mk1 fuselage liquid fuel tanks, from a pure fuel tanking point of view - 

Empty, a mark 1 fuselage tank only weighs 0.25 ton, yet it can hold 2 tons (400 units) of LF.    A big S wing   weights twice as much, at 0.5tons empty, but can only hold 1.5 tons' worth (300 units).   So, with larger wings, you might reach orbit with more fuel remaining due to lower drag/needing fewer nuke engines.    However, because the empty mass of your craft is higher, you will use more fuel getting from low orbit up to minmus.

I still prefer larger wings for Duna landing scenarios however.

Large wings - two big S deltas plus strakes on a 20 ton mark 1 (excuse the clipping of a RAPIER inside a NERV, this was a Duna and back challenge..) 

35km up,   mach 5.3 (1711m/s).    Only need 5 degrees AoA to make enough lift to fly.  Lift drag ratio 2.7.  Total Drag 16.3kn,   Thrust (one NERV only) is 60kn  so we are going to space today.

36 tons with one big S delta - looks to be about 15 degree AoA to fly at 28km and mach 4.59.    This means more drag and if you're only on one nuke, that might cancel out all available thrust.  Of course, he has 4 engines burning, and 480kn thrust available so it matters less, however whilst you gain in having less dry mass of wing to lift to minmus, you loose in terms of having extra engine/oxidizer mass to lug around.

 

Edited October 5, 2016 by AeroGav

[Aegolius13]

2 hours ago, AeroGav said:

I do differ on what has been said about wings.

As you make wings smaller, you have to use a higher angle of attack - ie. have the nose pointing up above the prograde marker at a sharper angle - in order to get enough lift.   Beyond a certain point, drag increases exponentially.   You get lowest drag below 3 degrees under 160 m/s (ok, you don't  spend enough time here to warrant optimising a spaceplane for this),  4 degrees when supersonic 10-20km,  and about 5 degrees when you've exceeded the max speed/altitude capability of your jets and are flying on nukes alone.

Big S wings do negate some of the weight penalty for adding more wings.  But... they still add drag.  Lots of drag.  So while more wings will help you keep your nose on prograde and reduce body drag, you're paying for it with more wing drag (plus some extra mass).  Huge wings may also get floppy, or require strut reinforcement.  

 

2 hours ago, AeroGav said:

36 tons with one big S delta - looks to be about 15 degree AoA to fly at 28km and mach 4.59.    This means more drag and if you're only on one nuke, that might cancel out all available thrust.  

Keep in mind I was not pitching up anywhere near that far while the Rapiers were in jet mode - with a little wing incidence built in, prograde was just a few pixels below the dot.  To build up maximum possible speed by the time the Rapiers cut out, the underpowered plane has to go nearly horizontal (with more powerful jets, I could have been pitching up further while climbing which would put my prograde higher).  Then the plan is to turn on the rocket Rapiers (nukes are already on), grab some quick altitude by pitching up,  and then ride the nukes the rest of the way.  I could keep flying at prograde here, but if I did, my nukes would not be able to keep apo in front of me once the Rapiers give out.  Yeah, this causes the plane to stick out fairly far from prograde, but I think it's a sacrifice worth making.  And at least air is a lot thinner up at this stage.  

2 hours ago, AeroGav said:

Of course, he has 4 engines burning, and 480kn thrust available so it matters less, however whilst you gain in having less dry mass of wing to lift to minmus, you loose in terms of having extra engine/oxidizer mass to lug around.

But the important part, I think, is that you're only lugging the oxidizer up to this point - then it's gone, and will not hinder you in spaceflight.  And the work to bring the oxidizer this far up was done with comparatively cheap jet thrust.  With more wing, you've got them for the duration.  And I would not say it's carrying extra engine - I needed every bit of that Rapier jet thrust to get this thing up to 20km and 1300m/s.  Even if you never needed to turn on rocket mode, I would still use Rapiers as my jet of choice - their high speed/altitude performance is much better than the Whiplash, for only .2 tons extra weight and a small ISP penalty.  

Put another way, for this project atmospheric efficiency was not very high on my priority list.  The design process was more like, "can I still get this to orbit with more LF, and less of anything that's not LF?"  But again, that's to maximize space range to the utmost limit.  For craft that are designed to stay closer to Kerbin, I would probably emphasize atmospheric performance more heavily, such as with more wing, or a Panther/Whiplash to help get it off the ground and supersonic.  

Not saying a wingier approach can't work - I haven't tried it myself.  But it is possible to get good space performance from a wing-lite design.  

And no doubt, for landing on Duna, the more wing, the better.  

22 hours ago, Arugela said:

I can get into orbit and back down if I used nukes on the way up. I wanted to use only the Rocket fuel to get orbit then pure Liquid fuel for additional travel.

One other thing - sounds like you may be heading this way already, but there is absolutely nothing wrong with using your nukes to help you to orbit.  You're carrying them anyway, so it's like free TWR.  Plus even at 20km altitude or so (which is when I usually start them), their ISP is much better than rockets.  Plus, with a rocket powered ascent you may end up with more oxidizer than you need.  But with nukes, you'll want all the LF anyway so there's no chance of dead weight.  

I would love to be able to ditch oxidizer entirely, and just transition from jets to nukes.  Unfortunately this does not seem feasible with most designs on Kerbin, but you can ride your nukes hard and only bring a small amount of oxidizer for your Rapiers (often less than the capacity you have anyway in bicouplers and adapters).  And on Laythe, it is quite feasible to go LF only.  

[AeroGav]

11 hours ago, Aegolius13 said:

jets to nukes.  Unfortunately this does not seem feasible with most designs on Kerbin, but you can ride your nukes hard and only bring a small amount of oxidizer for your Rapiers (often less than the capacity you have anyway in bicouplers and adapters).  And on Laythe, it is quite feasible to go LF only.  

That's what I do with pretty much all of my Spaceplanes these days, no oxidizer.   Nukes give almost their Vacuum ISP rating from 10km upwards.   My 2 Nuke / 1 RAPIER SSTO designs climb subsonic to 10km then need a short burst from the nukes in a shallow dive to get through the sound barrier.

I start them up again when the jets can no longer push me higher from their power alone.

This approach requires good aerodynamic efficiency - ie. plenty of wing area so you can fly these high altitudes with no more than 5 degrees AoA, which keeps drag low at very high altitude.   It seems there is two ways to get to space then -

- my approach, lots of wing for low drag at extreme altitudes, and not much engine (nukes only)

- your approach, small wing, very high thrust weight ratio

With the Penta Star cargo plane i linked,  filling the oxidizer tanks doesn't seem to help me reach orbit with any more delta V vs just leaving them empty. [edit ]

PS - if you want to try an oxidizer-free spaceplane,  you can try this simple design i put together quickly.

https://kerbalx.com/AeroGav/WhippyNerv-II

It was designed in the KSP 1.2 Preview,  which has the enormous advantage that fuel drains from all tanks evenly with rocket engines as well as jets.    If you're playing on live you'd need a fuel balancer mod to get the fuel from the wings to the nuke engine and not have uneven tank emptying mess with the CG.

I've only flown it to orbit but it looks like it should have enough fuel to get to Duna and back.

Quote

 

Edit - I've reworked my Penta Star freighter for KSP 1.2 .   Swapped the Panthers for Whiplash (negligible cost difference in the disposable jet).   Negligibly increased fuel burn below 10km and we reach a higher speed before calling the nukes in, and do so more quickly.    Also I filled up such oxidizer tanks as we have and set the single RAPIER to auto switch.   That way we extract every last little bit of thrust it can provide in air breathing mode up to 29km, before a short lived burst from the oxidizer in the mk2 to m1 adapters at the nose and tail of the ship boosts us to mach 5.5.   

Above mach 5.5/33km drag is half what it is when first switching to closed cycle @ mach 4.5/28km.   I think that's because we are approaching orbital velocity, so the freefall effect is supporting most of our weight.   This in turn means  our wing lift takes us higher up, into thinner air, where drag is less. 

 

 

Edited October 5, 2016 by AeroGav

[AeroGav]

Returning to the subject of engines for a true Minmus SSTO -

Jet Engines

I's a balancing act , because the more of these you fit, the faster/higher you can go on jet power before having to call in the comparatively thirsty rockets.

RAPIER ISP (Airbreathing)   3200

NERV ISP 800

RAPIER ISP (Closed Cycle) 305 

The problem is each RAPIER is 2 tons.   That's  a LOT of mass that has to be boosted from 20km to orbit and then on to Minmus.   What's a good compromise ?

At the very least,  I think there should be enough jet power to reach mach 3.7.   As you are probably aware,  RAPIERs deliver more and more thrust in jet mode as you get faster, but there is a peak - mach 3.7.    After that, thrust declines even if you stay at the same altitude.   At mach 4.5 they loose 20% of their power compared with what they do at 3.7.  After that the decline steepens considerably, thrust falling to zero at mach 6.

To be honest, if mach 3.7 is your target you may find it hard to pass the sound barrier in the first place.   I have to climb above 10km, then set Prograde on the autopilot and temporarily activate the nukes, to accelerate from 0.86 to 1.3 mach on some of my designs.

Closed Cycle Power

I find that with my 35 ton mark 2 designs, there's about 75kn of drag  in the mach 4-5 speed range at 24-33km.

At some point,  the thrust output of your jet engines is going to decline so that it barely exceeds this.    If your jet engines have four times the ISP of your nukes, but 75% (or more ) of their power is just being used to stand still,  it's worth firing up the nukes -

Jet power 100kn (one Rapier) @ 3200isp

Nuke power (2 NERVS) 120kn @ 800isp

Drag 75kn

Excess power -  145kn

"gravity loss" - 34%

isp (averaged across all 3 engines) 1891 ISP

This is a better situation than having only the jet running @ 3200 ISP but loosing 75% of it to gravity.

Unfortunately as you get faster and higher,  the jet engine produces less and less till it flames out completely @ 29km.  Then you go through a tough patch where you have 120kn thrust @ 800 isp, with  75kn drag taking away more than half your gains.     However,  as you edge towards mach 5.5 and 33km the orbital freefall effect increasingly supports the craft's weight.  The wings are able to lift you higher and higher into thinner and thinner air without requiring excessive and draggy AoA to do so.   By this point your drag will be at least halved and things continue to get easier until your AP heads out of the atmosphere at around mach  6.6.

So, at this point,  you start asking if I really need  2 nukes.  They are even heavier than RAPIERs, at 3 tons each.   Our closed cycle propulsion system has two jobs to do -

1) boost your airbreathing speedrun 1250m/s to orbital velocity of about 2250 m/s (+1000 m/s speed increase)

2) lift the craft from LKO to Minmus and land on it(at least 1000 dv?)

If 1) is easier with more nukes, due to reduced need for oxidizer/less gravity loss,  2) is merely penalized by the weight.  On a low gravity body like minmus, one engine is more than enough!

Obviously, the problem with cutting down on nukes is that you will end up with less thrust than drag once the jet engines fade.  You will never be able to reach the magic 35km/mach 5.5 halfway point where drag starts falling rapidly.

To get around this, people switch their RAPIERs to close cycle mode and start burning oxidizer.

There's three problems with this -

1. The RAPIERs only give 305 ISP in Closed Cycle mode which is just awful.   
2. You no longer benefit from the residual jet thrust from 22-23km all the way up to 29km @ 3200 ISP
3. The vast increase in acceleration as you go from 60kn (or less) per engine to 180kn can cause you to go too fast too low and encounter excessive drag.  Or you try pulling up hard to get around this, and create lots of drag with high AoA/G forces as well as cosine losses from thrusting directly downwards against gravity.

As far as point 1) goes, the fuel and oxidizer burned as a result, will weigh more than a nuke engine.   But, as Aegolius13  points out, you're only lifting this mass to 35km,   not taking it to Minmus and back.   He further states that this oxidizer was lifted by "cheap" jet power, though I'd like to point out that an optimised design is probably already lifting as much weight to 20km as it can with jet engines, so this oxidizer does not come "free".  More oxidizer means bringing less LF for the Minmus insertion burn,  or tacking on another RAPIER engine (another 2 tons to carry up to Minmus and back).

To me, it seems there's an obvious solution to 2) and 3) -  don't switch all of your RAPIERs over to closed cycle !

Imagine a somewhat larger 70 ton Ship,   with 2 LV-N Nukes and 3 RAPIER - when the climb rate gets too sluggish, switch only the centreline RAPIER over to Closed Cycle.     You'll have 180kn from the Closed Cycle engine and 60kn each from the two nukes, plus whatever dregs of power the outboard RAPIERs can still manage in air breathing mode.   Since this craft is twice the size , drag will be double at 150kn - but we'll still have at least twice as much thrust as drag.

70 tons doesn't seem an unreasonable size given the weight of IRSU gear, and given the very low payload mass fraction possible to Minmus when fully SSTO.

[Arugela]

I have a version about 70 to 100 given the fuel. I think I will go all LF to see if it gets farther. 8) The extra weight being distributed might help. I've been using Rapiers with Whiplashes also. If you don't mind getting some of the speed at 15k instead of 20k the whiplashes could save a small amount of weight. They feel better on takeoff also.

Edit: If this is true this is probably not new to people. But I think I found(or refound) something possibly interesting. The altitude ideal for the engine of jets seems to possibly be related to their ideal angle. Rapiers are 20k and you put them at 20degrees. Whiplashes are 15k and are better at 15k max. ETC.

Edited October 5, 2016 by Arugela

[AeroGav]

1 hour ago, Arugela said:

I have a version about 70 to 100 given the fuel. I think I will go all LF to see if it gets farther. 8) The extra weight being distributed might help. I've been using Rapiers with Whiplashes also. If you don't mind getting some of the speed at 15k instead of 20k the whiplashes could save a small amount of weight. They feel better on takeoff also.

 

I think the main advantage of Whiplash engines is their stronger thrust at low speed means you don't need as many of them to have a ship that can cross the sound barrier.

For example, you might need three RAPIERs to be able to go Supersonic (6 tons of engines) but you might get away with just 2 Whiplashes (3.6 tons of engines).    However, the RAPIERs will take you to Mach 3.7 and 20km on jet power alone.   The Whiplashes would only get you mach 3 and 15km.

Also, the RAPIERs have their closed cycle mode which means you could possibly reduce the number of nuke engines if you use oxidizer to boost yourself to 35km .

Quote

Edit: If this is true this is probably not new to people. But I think I found(or refound) something possibly interesting. The altitude ideal for the engine of jets seems to possibly be related to their ideal angle. Rapiers are 20k and you put them at 20degrees. Whiplashes are 15k and are better at 15k max. ETC.

Not sure what you  mean by  "ideal angle" ?

Climbing angle?

That depends on the thrust - weight ratio of your plane, not engine type.       It also changes a lot throughout the ascent.  Starts steep-ish,   slows right down nearer 10km as the air gets thin and I approach the limits of what I can go to subsonic.     I go into a shallow dive while accelerating through the transonic region.    Then as the engines get a boost from being supersonic, the climb angle can get quite steep again, like it was just after takeoff, before levelling off as we approach our air-breathing max altitude.   On a long range SSTO  your climb rate is never going to exceed 20 degrees and mostly be 10 or less...

As for my attempt on this "challenge",  this is what I have come up with so far.     I've cracked the most important problem, which is to think of a good name for a mining / fuel refining ship.    What could possibly go wrong ?

Three Rapiers, two nukes, the plan is to switch only the middle RAPIER to closed cycle and leave the outer two to run in air breathing mode until flameout.

It has the large converter but only the small drill (since on Duna and further afield, mining rate is limited by solar power and the little converter is horribly wasteful on electricity),   and two mk2 cargo bays to house the drill, solar panels, radiators and ore tank.  There is room in the cargo bay for a probe with the orbital survey scanner.     There is one cockpit and a crew cabin - the idea being it's got room for two crew (a pilot and an engineer) and each of them get their own private compartment (the mk1 crew cabins).

Problems 

1. Centre of lift too far forward.   I can't shift the main Big S wing cluster further back because they are attached to the NERV engine pods.   I can't move the NERVs any further back because that shifts the CG too far aft (edit - I just realised it's not a general purpose freighter and it's not essential to have the CG right in the middle of the cargo bays)

2.  Too much LF/Ox tankage forward of CG, not enough aft.  This means the CG shifts aft as the LF/O drains,  and I don't build planes with bad handling qualities !  The problem is that the fuselage adapters fore and aft of the ISRU converter are the lowest drag parts available,  I don't want to swap to something draggier in order to reduce the size of the fwd tanks.   And I don't want to increase the size of the aft tanks because we already have more LF/O capacity than I'm happy with. 

[Arugela]

Made it too Minimus. Might be able to do the moon also if I don't try to do a polar orbit.

https://www.dropbox.com/s/66sffvq8kfq3ggq/IDGAD Starfighter 1_7.craft?dl=0

Just have to add a coms and look for any stray weight to be safe. and fix the wheels and other small things. The weight is a little close to the COL though and want's to tilt up at the end of the flight to orbit. I need to find a way to move the COM forward more. Like putting the cargo bay where the docking port is for instance...

 

BTW, the Mexican jumping plane is a glitched version where on the runway it bounces around like a Mexican jumping bean. That was the challenge I was talking about. It was more a joke than anything. The point was to get the glitched plane to places and watch it dance. The glitch seemed to have something to do with some strut alignment after I moved some stuff around. No idea how to reproduce it. The download I put up with that post has the version with the glitch. Assuming it works for anyone but me.

Made this to minimus also:

IDGAD Starfighter 2.1 <- 97 tons 150 parts

Added a crew cabin for 6 crew and mining equipment plus science and coms. It has a fixed scanner in the bay so you can scan planets. I had to drop the probe for weight. So it is now the probe! 8)

On the way to Duna as we speak.

Edit: Would have made it to duna(was beginning reentry) but whenever I quicksave or go back to the KSP and go back to a ship it blows itself up... Have to start over from kerbin now. That is rather annoying when you are not doing a vehicle with direct flight...

 

BTW, what was everyone elses hypothetical max deltav for their vessels. Mine is 6 rapiers and 6 nukes for 4200-4400ish DeltaV. I'm curious how it changes as you get different numbers of engines. And everyone using some number of rapiers and nukes together. Obviously mine is not the cheapest either. My latest version cost 765k(I added more science and stuff). I always seem to build them expensive...

Edited October 6, 2016 by Arugela

[Arugela]

I have gotten it to the Mun with almost 600 LF left over! 8) I finally refined the mining gears electricity. Dropped it to 52 empty weight from 53ish and added 400 more LF.

IDGAD Starfighter 2.2

Action Groups:

Abort: Empty Ore Tank

1. Toggle 6x Nuclear engines

2. Toggle 6x Rapier engines

3. Switch mode 6x Rapier engines

4. Toggle 2x(middle) Nuclear/Rapier engines

5. Extend/Retract Drill

6. Toggle Drill/Fuel Cell

7. Toggle Smalle ISRU LF+OX

8. Toggle Smalle ISRU LF

9. Toggle Smalle ISRU OX

0. Toggle Smalle ISRU MONO

The ladder on this is messed up. It really needs help so it is actually usable in space. I can't figure out for the life of me how to make sure the kerbals can get off of it and onto the ship while climbing it.... Any help would be appreciated.

Edited October 9, 2016 by Arugela

[Aegolius13]

2 hours ago, Arugela said:

The ladder on this is messed up. It really needs help so it is actually usable in space. I can't figure out for the life of me how to make sure the kerbals can get off of it and onto the ship while climbing it.... Any help would be appreciated

Ladders are trouble.  In this situation, I would just skip the ladder and have your kerbal jetpack or manually climb onto the plane (if you go up to the edge of the ship, it may prompt you to hit F to have the Kerbal climb).  You can also retract your landing gear so the kerbal has less distance to climb.  

[Arugela]

Same shortcuts as the previous version. Just used the autostruts and rigid connections to get rid of the normal struts to reduce weight. I increased the weight a bit by adding some generators in which I can remove or reduce in numbers if struts are needed. But I just got into orbit with 4066 LF left over. This came out to  2580ish Delta V. Or did they just reduce the gravity amount and the forumula? I used 72.43-20.33=52.1... Ln(72.43/52.1)*9.81*800=2585.56778 DeltaV? This is in the new 1.2 release. I still have to test reentry at normal and high speeds to see if I need to add some struts which may reduce this delta V alot. And I'm not sure if I want one of the new science storage bays for research or not.

So, is the new gravity the 9.806... in the release info and does it affect the delta V formula? Edit: I entered it in and it only changes it to 2584.xx. But should it still be used over 9.81 now in DeltaV calculations?

Craft:

https://www.dropbox.com/s/4emzdl283motgd3/IDGAD Starfighter 2_5 Autostrut.craft?dl=0 <-Reuploaded with fuel changes and fuel lines removed.

Pics:

Edit: I need to make adjustments so it can hold it's nose up during reentry again... Makes it hard to slow down without flying all over the place. Not enough forward weight or I need to take advantage of the fuel system and use the rear fuel up first. Or both..

Just finished a new version where I removed the struts and the fuel lines. I didn't realize the new version adds auto connection fully for fuel now. Saved another ton on the craft and I'm at under 51 tons empty. I made it to orbit with 4600 LF this time! 2900+ Dv. And another for 4800LF and I could have gotten 5000 potentially. that is 3k-3.2k DeltaV after orbit! Just have to finish working on balance for reentry.

Anyone know how to balance a plane to keep a planes nose upwards(Radial) during reentry? I keep designing the plane randomly to do it well but I don't know how I do it. And I keep having difficulty getting it to do it fully again.

Edit: NVM, I reverted back to the above version and ripped out the fuel lines. I need to quit changing the weight distribution and wing surfaces so much.

I need to try a straight shot to duna now!

Out of curiosity, how were people figuring out their drag?

Edited October 12, 2016 by Arugela

[AeroGav]

6 hours ago, Arugela said:

 

Edit: I need to make adjustments so it can hold it's nose up during reentry again... Makes it hard to slow down without flying all over the place. Not enough forward weight Just have to finish working on balance for reentry.

Anyone know how to balance a plane to keep a planes nose upwards(Radial) during reentry?

I balance my plane with empty fuel tanks first.   To achieve balance, the only things you can really move around are the engines, mining gear, and cockpit.

The obvious place for engines is at the back  , but even on a low thrust-weight ratio design there is far more engine weight than the cockpit and mining stuff can balance out, even if you shove the payload and crew area as far forward as possible.    Balancing engine weight with fuel tanks looks good in the SPH but once it burns off you'll be in trouble, though i suppose you can work around this by locking the forward tanks and only using their contents for exo-atmospheric flight.   You can always stop at a moon to refill the fwd tanks before attempting re-entry on a place with an atmosphere.

Once I have achieved balance with an empty ship i then start adding fuel tanks fore and aft with the aim of keeping CG in the same place when loaded.

In practical terms, what this means for you, is moving those wing mounted engine pods further forward, closer to the CG.     Unfortunately that means shortening the nacelles, which cuts your fuel capacity.   I suppose it must be harder to achieve perfect balance when you've got a very brawny high powered design.

ps.  yes removing them fuel lines massively reduces drag.   I think each fuel line has more drag than the cockpit !

Edited October 12, 2016 by AeroGav

[AeroGav]

On 05/10/2016 at 6:22 PM, AeroGav said:

 

 

Ok, my take on this is finally done.  It's probably the most complex thing I've built, getting the balance right on such a large ship with so many fuel tanks was a pain.  The final ship - 

It has the planetary survey scanner as well as the narrowband one and the one you use from the ground, though to be honest I don't care too much about finding the best ore concentration - tanks fill quite fast at 1000-10,000 time acceleration regardless !  Accommodating these bulky antennas meant two long mk2 cargo bays in addition to the 2.5m converter.    Also,  so as to avoid the "spam in a can" accusation, I've included a mk2 crew cabin to give the crew somewhere to sleep (mission to Eeloo could be 40 years, after all).     I had a bit of an issue with pitch instability at high altitude, eventually resolved by adding 5 degrees incidence to the front wing and then rebalancing everything.  That way the front wing gains lift more slowly than the rest of the ship with increasing pitch,  so it resists being pitched to extreme angles.   

I was pleasantly surprised by the stability, flying almost the whole way to orbit with pitch trim alone, no SAS.  Agility is not so good, it's very hard to get the nose to pitch up to more than 8 degrees above prograde.    Also as you can see, it takes a loonng time to get up to orbit.    Even so, thrust was double our drag rating throughout the ascent, so combined with the ship's stability it was an easy ascent - it never threatened to get stagnate,  and didn't try to flip out.

The above pic is with 3 all Rapier still in airbreathing mode and the 2 nukes active.  We have 231 thrust and 121 drag,  so shortly after i kick the centreline Rapier over to closed cycle mode taking our total up to about 350.

On Minmus -

One of my requirements was that it could still land like an airplane on Duna.  This seemed like a tall order for a heavy ship, but we made it.  The gear can in fact survive horizontal velocity of 100m/s,   and landing slower than 70 m/s can be a bad idea - it means not having enough lift to arrest a high rate of descent that can result from flying towards rising ground, and that will cause breakup. 

unsuccessful landing attempt - i missed the crest of this hill, floated over the next valley with speed decaying through 55m/s then blundered into the next bit of rising ground without enough lift to flare.  Kerbals lived but it ripped the wings and engines off.

Will share this on KerbalX soon,   after I get my Duna landing video uploaded.

https://kerbalx.com/AeroGav/Nostromo

Edit - second landing attempt (first success!)

 

Edited October 12, 2016 by AeroGav

[Arugela]

I took some stuff I saw on the Whiplash and Nostromo and make FrankenSTO! Still working out the kinks. Lost a little DeltaV. But it looks like a duck now!! >< (It is a bit hard to fly without blowing up atm also. If you are not careful.)

Craft:

FrankenSTO <- AKA Space Duck!! (Have to fix the mining equipment still. It's missing an ore container and needs new cooling.) Reuploaded! Still needs help with tipping at high altitudes.

Pics:

 

Edited October 12, 2016 by Arugela

[AeroGav]

It does look nice.

I have three times as much wing, you have double the number of engines.

Yours flies like a supermaneuverable fighter plane - you can basically point the nose in any direction you want, regardless of whether the plane can actually go there.   I stalled and crashed on takeoff first time because I wasn't expecting it,  then later got up to mach 4 and started overheating, tapped the UP key a little too long and ripped the wings off !

I like how you've managed to keep the engines - of which you have a large number - at the back which is best for aesthetic purposes.  Yet still it has a decent balance, from what i can see.

I had to shove mine right at the front, which looks dorky, and then attach wings outside of them to avoid the jet blast, which looks more dorky.

I'll have a look at custom wing designs,  see if i can make a "tunnel" through which the jet wash can flow.

[Arugela]

When I take off I let it take off without pulling up. And I always fly with SAS.(Mostly because I use linux and the position of the Super key is different and I never got in the habit of using anything that uses it.) Then I pull up by tapping a little. I had to do this with all previous version. I think if you wait until it's getting air graphics it's more maneuverable and doesn't flip up. You have to do very small maneuvers. No more than 5 degrees max. 10 under good conditions. which, from what I can tell is fast in decent air resistance. As far as I can tell! ><

This is how I started making all my planes form when I got the game in 0.9xx. I have no idea why but I habitually make them like this every plane even when I try to deviate... I can't get myself to do other things with planes. Even if it looks very different when I start. lol

Edit: This duck version has odd problems with deviating to one side... I wonder if it's from the SAS/torque being to forward of if I have something balanced wrong. Maybe I should move the Drone core back so it's balanced along the neck. That or it needs bigger nose wings... Which would require me to have to rebalance weight potentially. 8\ Maybe I can get lucky and fix it with fuel balancing.

The forward engines have a lot of advantage though. I have to do a lot of work to get the COL behind the COM sufficiently or at all sometimes. I have to move my weight around carefully and do some funky stuff with my tailfins and other rear aerosurfaces because of it.

My first big SSTO back in .9 was basically a missile. IT has small wings that were in a 8 or 6 symetry around teh plane in the rear. But I had to put alot of fuel(among other things) in small stacked space. It flew really well on Duna. It could infini glide at almost any altitude. 8) I basically stacked everything into the shape I wanted. I've managed to almost not stack anything now. Which is miraculous if you know what type of craft I used to make before 1.0. (air hog with over 1k+ air intakes and 250+ engines. Up to 300 or even 500 Plus engines for large scale Ion thrust before nukes were LF only.)

And I've found there are some odd ways to avoid jet blast. The wings and other surfaces don't seem to take damage everywhere. so you can possibly get them in spots you would think would get damage but don't. My rear tailfins have problems with this on and off. Certain engines seem to almost never damage wings also.. Like the Rapier and other jets. Or it's very difficult to. Usually my nirvs do the damage first.

Edited October 12, 2016 by Arugela

[AeroGav]

7 minutes ago, Arugela said:

 

Edit: This duck version has odd problems with deviating to one side... I wonder if it's from the SAS/torque being to forward of if I have something balanced wrong. maybe I should move the Drone core back so it's balanced along the neck.

I think it might lack yaw stability,  those shuttle tail fins are canted to a near horizontal angle which makes them more like tailplanes.

Also I think those small delta sections that make up the lower part of its cruciform tail have acquired a rotation angle you probably didn't intend, from being attached to a curved surface.   They are angled downwards causing them to constantly give an up elevator input, which i think makes it unstable in pitch.  

I went a bit far messing with your design and ended up making it rather sluggish to the controls.  Flew it to orbit with SAS off below 30km and got this result.  

Oh i also did some experimentation with an engine tunnel to tidy up the appearance of my designs

Now looks like an Avro Vulcan !

[Arugela]

I found a fun new tailfin configuration. >< Lost all angling on takeoff though. And it needs to loose a little weight also! Turn on no joint cheats or it blows up on the runway.(You can turn it off after it loads.)

Craft:

FrankenSTO: https://www.dropbox.com/s/czy4940ns3j0fen/IDGAD Starfighter 2_6 FrankenSTO.craft?dl=0

Normal: https://www.dropbox.com/s/n94iyl196ued6dn/IDGAD Starfighter 2_6 Autostrut.craft?dl=0

FrankenSTOPics:

Normal Version Pic:

 

I've been flying it a while. I think space duck(FrankenSTO) has hit the limits of what this design can do without adding engines... That or I need to dump some of the rocket fuel...

This new fin configuration has way too many control surfaces in the rear. It gets really unstable. Unless there is a way to balance with fuel. It might be to far gone though. 8)

Edit: this design just takes away all of the landing advantages and it adds base weight.

The curve in the lift on the old one was actually on purpose(sort of) it was because I was using it to pull the COL down to center between the COM and COT. It's more of a byprodcut of it. I just use SAS or trim. I was looking at changing some of the Little fuel tanks for the Wing with 100 fuel. It weighs the same base and lets me move the COL back a hair and add more lift. This assume it doesn't have enough drawbacks.. Not sure wether having more or less angle on those rear control surfaces is better. Edit: NVM, the wing strakes have twice the base weight. I miscalculated it. I'm sticking with the 2.5autostrut version atm... I haven't improved on it yet. And Space duck needs to be redesigned to heavily. 8)

So, did that tunnel design go well?

 

Edited October 13, 2016 by Arugela

[AeroGav]

5 hours ago, Arugela said:

I found a fun new tailfin configuration. >< Lost all angling on takeoff though. And it needs to loose a little weight also! :

Normal Version Pic:

 

 

So, did that tunnel design go well?

 

The tunnel design won't improve performance or structural rigidity (will probably make things worse!) but it gives me an option to improve the looks.

Quote

This new fin configuration has way too many control surfaces in the rear. It gets really unstable

The curve in the lift on the old one was actually on purpose(sort of) it was because I was using it to pull the COL down to center between the COM and COT. It's more of a byprodcut of it. I just use SAS or trim

One other thing I did to your "duck" design was limit the control authority of some of the surfaces.    I set the FAT outboard ailerons to like 40% authority so they deflect at a lesser angle and create less drag = adverse yaw , when used.   I also turned off a lot of the control axes : the wing trailing edge surfaces close to CG should not be trying to control pitch and yaw, though you could perhaps make a case for the inboard ailerons as they're so far back - likewise the canards should only be trying to do pitch etc.

I've never bothered trying to keep Centre of Lift in line with Centre of Thrust.  I can't see how it has any bearing on the handling.  Yes, you want CoT in line with CoM or it starts pitching up or down in response to power when the air gets too thin for the craft's natural stability to resist.   However, having CoL above the Centre of Mass is usually considered a good thing since it adds roll stability from the "pendulum" effect.  

Quote

Edit: this design just takes away all of the landing advantages and it adds base weight.

I'd just move those Y tails to above the fuselage and go back to your original landing gear config.  You can see from the picture how I modified your "duck" tail to get more yaw stability and more lift at the rear of the craft.

 

Quote

I was looking at changing some of the Little fuel tanks for the Wing with 100 fuel. It weighs the same base and lets me move the COL back a hair and add more lift. This assume it doesn't have enough drawbacks.. Not sure wether having more or less angle on those rear control surfaces is better. Edit: NVM, the wing strakes have twice the base weight

Re: Big S strakes -  these have the same lift rating : mass ratio as the other modular wing parts,  with no fuel in them they are no heavier than a combination of smaller strakes of the same lift rating.    The only drawback is they are not a regular polygon shape, making it difficult to integrate with other parts in a visually pleasing way.

The mark 0 fuel tanks add drag but no lift.  If you need more LF tankage I'd probably swap the mk2 rocket fuel fuselage section for a LF one. I think the obligatory LFO tankage forced upon you with the fuselage size adapters is more than you'll ever need.

Quote

 

I've been flying it a while. I think space duck(FrankenSTO) has hit the limits of what this design can do without adding engines... That or I need to dump some of the rocket fuel...

 

 

Honestly,  I think it has too many engines already !  If you take off and don't climb, it is able to brute-force through the sound barrier at sea level where the atmosphere is like treacle.  If you take off and climb out at a moderate angle, it will go through the sound barrier all by itself in a climb without firing up the nukes to assist.    Those Rapiers weigh 2 tons each,  once in orbit that extra mass reduces the amount of delta v you'll get from a given quantity of residual fuel.

One thing I did notice was I was getting worse Lift/Drag ratio on your design at supersonic speeds.

If you look at the AeroGUI,  my design had a lift/drag ratio of 2.435 to one. Yours was doing barely 1:1 from about mach 2 onwards, which means you need more heavy nuke engines to keep climbing once you're above jet altitude.

I'm not sure of the reason for this.  The fuselage diameter of both our craft is the same (2.5m widest point).   You have four 1.25m engine nacelles besides the main fuselage, as do I.  Engine nozzles are a very draggy way to end a stack, but thanks to your use of clipping you only have one more nozzle facing the wind than I do. 

Your design does have 25% more weight and 66% less wing than mine,  so at any particular mach number (mach 3 etc) it will either be at a lower altitude to get enough lift (resulting in more fuselage/nozzle drag) or higher angle of attack (more wing drag, more fuselage drag).  Is there any way you can add more wing area without spoiling her looks? 

I'd also probably loose the RCS ports or hide them in service bays.   Reaction wheels rock !

Since you are now using the big converter,  it has 10 times the Ore > fuel conversion efficiency as the little one.  This means you should take off with full ore tanks and convert that to fuel for the Duna/Minmus injection burn in low orbit. 

Finally,  I did make it to orbit with >3000LF on your duck, which  should be enough for a Minmus refuelling stop.  I'd be more concerned about it's ability to land safely on Duna.

ps. I wouldn't consider using Whiplash engines except as disposable boosters to be dropped at flameout altitude (they r quite cheap!).  This would dramatically cut down the number of rapier you need to haul around.