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Is it just me, or are space-planes insanely hard?


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Hey folks,

               I've been playing KSP since 1.2.2 and I've managed to get rocket launching pretty much sorted (stock game, no mods, except AFPW, to get my Saitek HOTAS to work properly), but man, I appear to be utterly useless at space-plane design/flight. I've designed a number of regular planes, which all fly just fine (I do have some experience in full size and model aircraft), but for the life of me, I simply *cannot* get any of my space-plane designs (SSTO specifically) into orbit successfully. I can get them *close*....and I mean *really* close, but I just always end up running out of rocket fuel.

I've watched countless YT videos from guys who seem to just point the thing at the sky and blast off into orbit with no drama whatsoever, but my designs all seem to just barely struggle to the upper atmosphere, then invariably fall *just* short of making it into a stable orbit. The closest I've managed to get is an AP of about 72k, but didn't have enough fuel left to circularise. IIRC I managed to get to about 12 or 13K PE before it ran dry.

One thing that most of the videos I've seen have in common is the ability to accelerate at the mid-flight stage to well in excess of 400 to 500m/s, but no matter what I do, I can't seem to get much beyond the 300m/s mark. I've tried adding more and various engines, but I either end up running out of fuel too fast, or being too heavy to climb steep enough to make it out of the thicker part of the atmosphere in time.

I've managed to find a couple of *really* good posts in the tutorials section for how to get rockets to launch with the most efficient profile, but there doesn't seem to be anything like that for space-planes/SSTO. Can someone point me to anything like that? Or perhaps share their 'hot tips' on space-plane design, so I can try to work out where I'm going wrong?

I'd rather not just download someone's craft file and go fly. I'm rather enjoying the challenge of building/flying stuff by having to do the trial and error process myself, but I've run out of ideas for SSTO.

Cheers,

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Thanks for the pictures.

First of all, mk2 fuselages are arguably bugged right now, they produce 4 times as much drag as a mk1 without actually holding any more fuel.

It would be much easier if you started off with a mk1 fuselage design,  just use an inline cockpit and put it a few modules back from the front so it doesn't get affected by the heat of high speed flight.  Inline cockpits are vastly less susceptible to heating - an inline mk1 will be less prone to blowing up the mk3 cockpit because it has to go at the front !

Second,   engines are heavy.  Rapiers are 2 tons each, Whiplashes weigh 1.8 tons, Aerospikes 1 ton.   Your vessel probably weighs 30 tons,  but is carrying 10 tons of engines.   Allowing for the structure and cockpit, cargo, it must have a fuel fraction under 40%?  That is why fuel runs out before orbit.

If you can reduce drag, you won't need as much engine.   Looking at your ship, i'd try to replace as many mk2 parts with mk1 fuel tanks as possible - if you insist on keeping it a mk2,  use them only for carrying kerbals and cargo.  Try to put nearly all your fuel in mk1 parts instead.  Also I'd recommend an inline cockpit even if you stay as a mk2.  Those rapiers can get up to 1600 air breathing in level flight at 22km - but if your cockpit is right at the front it will melt.

Profile - 

Untitled_zpspctazepz.png

A good flight profile reduces the need for lots of engines.   Jet engines behave a lot like ramjets in this game, they produce more thrust at supersonic speeds.    But,  the air down low is really thick and draggy, which makes getting supersonic difficult, also the transonic region (mach 0.9 to mach 1.2) as more drag even than supersonic flight.     On the other hand, if you climb too high without speeding up, the air gets too thin for your wings.  You end up pulling the nose more than 5 degrees above prograde , which makes for high drag.

Spoiler

 

Subsonic climb - Keep speed below 240 m/s as this marks the start of the high-drag transonic region.   Keep the nose less than 5 degrees above prograde.    At lower altitudes, you may in fact use nose angle just 2 or 3 degrees above prograde, if your craft has a good amount of lift.

Transonic Acceleration - When it becomes impossible to prevent airspeed exceeding 240 m/s without pulling the nose more than 5 degrees over prograde  , then it is time to go supersonic.   Reduce the amount of nose-up input so you are flying with the nose less than 3 degrees above prograde.  If you're over 5km, toggle the nukes on until over 440m/s.

Supersonic Climb - Once over 440m/s, turn the nukes off and pitch up again so the nose is 5 degrees above prograde.   Aim to level off at the acceleration altitude.

Speed Run - Accelerate in level flight to the highest practical top speed.     RAPIERs act like ramjets in many ways, producing more power as you get faster, but even so they do peak at mach 3.75 (1150 m/s) and after that thrust gets weaker the faster you go. The decline is quite slow out to mach 4.3 (1350 m/s) but becomes more rapid after that.   Which altitude for the speed run?  I prefer to fly higher, where drag and heat are less, but no more than 22km, as above that thrust falls faster than drag, so getting higher actually reduces top speed.   When is it time to quit and switch to rocket mode?     I tend to fly with the Aero Data GUI enabled (press alt-f12, physics tab, tick enable aero data gui).   When drag exceeds 75% or more of total thrust, it's time to switch.  

Climb to Orbit - Now that the rocket engines are active, just maintain a nose angle of 5 degrees above prograde.  This gives best lift:drag ratio in supersonic flight and will give lowest total drag.     Flying straight into prograde means zero lift so you spend longer in the atmosphere, meaning more drag  overall despite the slight reduction at first.     

 

Here's my latest mk2 -

https://kerbalx.com/AeroGav/Penta-Shuttle

screenshot87_zpsbalryzhq.png

20170313092644_1_zpsya90offw.jpg

It's a not as nice looking as yours though :-(.

    1 Rapier at the back of the fuselage is enough to get it to 1400 or so air breathing.   But not enough to get through sound barrier, so it has 2 Panthers for an extra boost low down.  Once the Rapier is on song, it doesn't need them.   There's also 2 NERVs which can boost it to orbit all by themselves, and use up the considerable liquid fuel capacity of the wings.   As you can see, it can reach minmus very easily.

    

Edited by AeroGav
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2 hours ago, MrBonk said:

Thanks everyone for the input. I've tried to refine a couple of my more 'promising' designs, using the suggestions regarding drag reduction. I've also been experimenting with different intakes/positions, and had some surprising results.

Anyway, following the design hints and launch profile advice, I've managed to get 2 of these into *very* low orbit, with enough fuel to spare to deorbit and then fly the remaining distance back to the KSC, so I'm really happy with that result :D

It's interesting to see just where some of the drag is being generated in these designs. Even the 'joints' between wing panels etc, which is something I hadn't originally considered might be an issue.

I used this design HERE, which performed quite well and was able to punch through the 300m/s mark with ease, even in a 45deg climb! I only just made it to orbit with this though, and only *just* had enough fuel to deorbit.

The final revision of this is HERE, and had 2 of the Whiplash jets swapped out for a pair of RAPIERs, which made all the difference once I switched them to closed mode for the rocket boost portion. Both designs used a pair of Aerospike engines for the rockets. The final result HERE.

So at least I'm finally on the right track. Thanks everyone :cool:

Other unexpected causes of drag are cargo-bay contents. The shielding model is a bit obtuse, and sometimes things that you think are in it turn out not to be. Always worth having aero debugging on so you can right click and see the drag from specific parts.

Regarding your design;
- There's no good reason not to be using 4x Rapiers here. In fact I think you'll be able to do without the aerospikes if you do. The Whiplashes are only better for starting thrust, but they fizzle at lower altitudes and slower speeds. Rapiers will breathe air higher and faster than any other engine :) 
- Personally I'd move the cargo bay back. You have a lot of heavy engines at the rear and no forward fuel tank with which to counterbalance them. Most delta designs benefit from a tank right behind the cockpit, or even at the nose, as this will let you pump fuel around to balance the plane better on re-entry.
- A 45 degree climb is madness, but it emphasises the point that you don't need the low-end grunt of Whiplashes at all. Consider them the diesel engines of the jet world. 
- For flight profiles, below 10km, fly how you like, but at 10km, you want your prograde to be around 5-10 degrees above the horizon, as this will give you lots of time on efficient air-breathing thrust. Steeper ascents eject you into the high atmosphere too fast to have gotten proper speed up. Rapiers should carry you over 1400m/s, and even upwards 1500 with a good design and canny piloting.

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34 minutes ago, eddiew said:

There's no good reason not to be using 4x Rapiers here. The Whiplashes are only better for starting thrust, but they fizzle at lower altitudes and slower speeds. Rapiers will breathe air higher and faster than any other engine

One whiplash and two rapiers will get him through the sound barrier as easily as four rapiers, but the 2R 1W config is a bit lighter.   Both will max out at similar speed if he does the speedrun in horizontal filght, because that is limited by either the cockpit melting down , or the engine hitting diminishing returns on the thrust curve hard

400px-CR-7_R.A.P.I.E.R._Engine_velocity_

You can see that past mach 4.5 (1350 m/s thrust starts to decline fast, it really falls off the earth at mach 5.5 (1650m/s).   Adding more rapiers at this point costs you more delta v in extra weight than it gains you in airbreathing speed.  Unless he's reaching his airbreathing top speed in a climb, and going well under 1300 m/s when the engines run out of air, in which case even more TWR might help.   Before anyone says it,  i know that levelling off for speed run takes longer,  which is valid if the mission is well within the dV of your craft - not the case here though.

Quote

In fact I think you'll be able to do without the aerospikes if you do.

I wish i could disagree, because they are such awesome and under used chemical engines.  They have Vacuum ISP 10% better than the Rapier, and weigh half as much.  But...  you're right.   Two Rapiers give 360kn thrust in closed cycle mode - which is a TWR exceeding 1.  My mk2 spaceplanes have less than 60kn drag in the upper atmosphere, with the wings producing enough lift to keep us up.  Assuming his is twice as draggy,  that's still thrust:drag ratio of 3 to 1 with two Rapiers.    Save the two tons then and leave them home.  The extra 2 tons of dry mass won't make up for their 10% better ISP.

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Yes! I've managed to get a hot-rod MK1 ssto design sorted to the point where I can get to the Mun with fuel to spare.  Oddly enough, having a shielded docking port right on the front seems to work quite well, even though it looks ugly as sin. 2 rapiers and a single nuke, and only liquid fuel. I'll upload and post some pix when I get home from work tonight ☺️

dU1PxIF.png

 

The cockpit gets a bit warm on ascent, but nothing to really worry about....unless you're sitting in it, I suppose :)

6fXG3a4.png

 

J1gm5TY.png

Edited by MrBonk
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Welcome to the forums!

Can you show us (a screenshot of) one of your ships? It's possible to have problems in the design or the flight profile or both, and a screenshot could help to identify the former. You can upload to an image hosting site like Imgur and then paste the URL into the forum.

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RCS Build aid....red dry center of mass, yellow wet center of mass, blue center of lift adn line of action. red center of thrust and line of action. Red and yellow as close as possible.  Blue slightly behind and in line with COM's, red perfectly in line with COM's.  Read landing gear somewhat behind COM's.  Front landing gear reasonably far in front of COM's. One set control surfaces set pitch only, authority limiter set 30-50%, main wing control surface, set pitch&roll low authority, outer wing surface control surface set roll only low%CA, vertical stabilizer set Yaw only, 30-50% CA.

Take your airbreather at sub 300m/s, keep your drag low up to the point thrust starts to drop below 70%. hammer it.  just below cutout bring it in to a shallow dive.  Getting velocity up to near its max. as it nears its thermal max speed at about 80-90% max thrust altitude, pull back up and in the transition to flame out power up the non-airbreather.  This is the beginning of a normal but flat rocket profile. 45deg, then gravity turn.  The trip back down is worse... if you aren't correctly balanced dry you just flop about and crash. have a chute :P

I suck at it but i can fly them, The combo of panthers and nukes is good for stock. Also adding drop tanks and drop SRB's can really get a lower tech craft up to orbit well.

You can make an orbiter with 13 or so part count. or 300+

zqsfHyL.png

Edited by Bornholio
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Agree with all the above, and especially eddiew. You may be trying to climb too fast, also. Spaceplanes take a good long time to get to orbit, and rushing the process costs you fuel.

But whether they are "insanely" hard depends on your definition of insane. :wink:

You absolutely have to be able to get to at least 800 m/s with your jet engines to make a workable spaceplane. And if you can double that with just your jet engines then you are in really good shape. But that's the key, to gain a lot of speed before you light the rockets. To break the sound barrier and gain that speed you need to really understand where the draggy bits of your plane are, and get rid of them if at all possible. SSTO spaceplanes take a lot of designing to make them super light, and unusually low in drag.

 

Edited by bewing
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As you've encountered, there's a drag-induced speedbump in the high transonic (i.e. about 300m/s). Drag reduces sharply once you get beyond this; if you can make it to 400m/s you'll be away to 1,000m/s+.

A well-built ship can usually punch through transonic while climbing, but even a marginal one can usually break the barrier if flown right. Basically: climb up to a few thousand metres, then level off (or even go into a shallow dive) while you accelerate up to 400m/s before resuming the climb. Don't pull up too steeply, or you'll drop back into subsonic.

The way to make this easier is basically more power or less drag. Your problem is much more likely to be excessive drag rather than insufficient power, though.

Keep the frontal area minimised; no more parallel stacks than necessary. Don't leave any blunt surfaces exposed; nosecones everywhere. Don't clutter up the surface of the ship with RCS tanks and solar panels and such; stick everything inside a cargo bay if you can. Make sure you've got enough wing to maintain level flight with no more than a few degrees of AoA. Building in a bit of wing incidence helps a great deal with this.

You want to extract as much speed and altitude from your jets as possible before lighting the rockets. Mach 3 and 25,000m as a minimum; Mach 5 and 30,000m if you can manage it.

Start with small and basic before you go big and complicated. Try this for a simple example ship:

 

 

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Please post a copy of the craft file.    A  design can look aerodynamic but due to the way the game calculates drag, some methods of attaching parts cause huge drag.

Are space planes insanely hard ?  Space is hard.   The SPH / VAB is hard to use, and poorly explained.   If you're building anything complex, it can be very frustrating until you know its quirks.

However,  I actually made my first orbit in a space plane, because i could not fly any of the stock rockets and the ones  i designed were even worse.      Gravity turns are very hard,  and are completely unfamiliar to anyone that's never played a space game.  Someone who is interested in aircraft / has flown a few flight sims will have learned a few of the principles of aerodynamics during their life,  but what about the aerodynamics of rockets?   What keeps the correct end pointing at space?  How do you stop it becoming flip happy when fuel burns off ?   How do you calculate TWR and delta V?  

I remember my first Kerbal aircraft.    It was a canard, and i thought, why not put the vertical stabilizer up front too?  Exit stage left.   Lesson learned.      The next one became pitch unstable at high speed because of body lift and fuel burning off.      I put the fuel tanks in the middle and two of my engines either side of the fuselage instead of all at the back...  and off it went.  2 rapiers and  1 nerv.  That first ssto even gave me a Munar flyby, once i figured out how to use the map screen..

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23 minutes ago, Wanderfound said:

Drag reduces sharply once you get beyond this; if you can make it to 400m/s you'll be away to 1,000m/s+

Along with this, the Rapier starts putting out WAY more thrust around 450/500 m/s.  So once you can get your plane there, you should be able to get up to well over 1,000 m/s, and well on your way to orbit.  

If your plane relies on Rapiers, sometimes you can get around that transonic hump by adding an engine that does better at lower speed, like the Whiplash or Panther.  Or even another Rapier to brute force it.  But like the other folks, I would suspect excess drag or an overaggressive ascent profile is to blame for your issue.   New plane builders (myself included) tend to design planes with a lot of... stuff sticking out of them, and make up for all the associated drag by adding more engines than are probably necessary. In those cases, just adding more engines can be a crutch at best, and counterproductive to your plane's effectiveness at worst.  

But yeah, a screenshot would help pinpoint your particular problem.

As far as ascent profile, like everything else, it depends.  The most efficiency-crazed spaceplane builders tend to build with just barely enough engine thrust to make it to orbit.  These kind of underpowered planes have to be flown very conservatively.  This often means climbing at subsonic speeds to where the air is a little thinner (maybe 5,000 meters), and then leveling off or even diving to break through that transonic barrier and into the Rapier sweet spot.  If you have a higher-powered plane (and there's nothing objectively wrong with that, it's down to personal preference and mission requirements), you can often skip that step and just continue a shallow climb as you go transonic.  

Anyway, once you're in that 450m/s plus sweet spot, you have one main objective: get your airspeed as fast as possible by the time your jet engines cut out.  It is horizontal speed, not vertical speed or altitude, that's most important for getting you to orbit.  And since jets are around 10x as efficient as rocket engines, the more speed you can gain on your jets the better your plane will work.  So while it's tempting to pitch way up and use your newfound engine power to climb, that's going to leave some of that all-important horizontal speed on the table.  This is basically the same reason you want to finish nearly horizonal after a rocket gravity turn.

So, you want to finish your jet ascent at a shallow rate of climb that will maximize your horizontal speed.  5-10 degrees is a good starting point.  If your plane is very powerful or has parts with low heat tolerance, you may run into thermal trouble.  If possible, you'll want to heat-proof your plane as much as possible so you can go super-fast.  But if you're still having heat problems, try doing the mid-stage of your climb a bit steeper.  You'll probably still want to level off by the time you hit 15-20km altitude, to wring every possible bit of speed out of those jets.

 

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Thanks everyone for the input. I've tried to refine a couple of my more 'promising' designs, using the suggestions regarding drag reduction. I've also been experimenting with different intakes/positions, and had some surprising results.

Anyway, following the design hints and launch profile advice, I've managed to get 2 of these into *very* low orbit, with enough fuel to spare to deorbit and then fly the remaining distance back to the KSC, so I'm really happy with that result :D

It's interesting to see just where some of the drag is being generated in these designs. Even the 'joints' between wing panels etc, which is something I hadn't originally considered might be an issue.

I used this design HERE, which performed quite well and was able to punch through the 300m/s mark with ease, even in a 45deg climb! I only just made it to orbit with this though, and only *just* had enough fuel to deorbit.

The final revision of this is HERE, and had 2 of the Whiplash jets swapped out for a pair of RAPIERs, which made all the difference once I switched them to closed mode for the rocket boost portion. Both designs used a pair of Aerospike engines for the rockets. The final result HERE.

So at least I'm finally on the right track. Thanks everyone :cool:

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Wow...so much great info here! Now I can't wait to get home from work to try more designs out :)

I didn't realise the MK2 parts were so draggy. I originally only used them because I wanted the cargo bay size for doing the "rescue Bob and his wreck from orbit" contracts, but they also *looked* like they should be less draggy than the other bits. I'm very keen to try an all MK1 design now with an inline cockpit, so that's gonna be my first job this evening. 

I knew I had too much engine when I realised I could go supersonic in such a steep climb, but I ran out of time last night to try anything else before I had to get some sleep.  This working-for-a-living thing is seriously interfering with my gaming time these days!

Thanks again for all the effort for such detailed replies. This is exactly what I needed to get me going in the right direction (pun may or may not have been intended there lol)

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4 hours ago, MrBonk said:

didn't realise the MK2 parts were so draggy. I originally only used them because I wanted the cargo bay size for doing the "rescue Bob and his wreck from orbit" contracts, but they also *looked* like they should be less draggy than the other bits. I'm very keen to try an all MK1 design now with an inline cockpit, so that's gonna be my first job this evening. 

 

I have just started playing the Ferrram Aerospace again, which accurately simulates wave drag.  In Ferram,  mk2 parts are as fast as they look,   and your ship wiould greatly outperform mine :-).    It's still in beta though, and not for the fainthearted.   Landing speeds are waay higher too. 

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Even in stock aero, Mk2 ships aren't overly draggy if you build and fly them right.

The key is that you need to keep that broad, flat fuselage aligned with the wind as much as possible. Hence, wing incidence:

angle_of_incidence.jpg

With a bit of that, you can climb to altitude while keeping your nose on prograde the whole time.

jHc6r9R.jpg

 

NOYwtKP.jpg

Edited by Wanderfound
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Well, what a difference it makes when you're armed with some useful information :)

I got home this evening and jumped straight into the SPH to make my test MK1 design. I slapped THIS thing together in a big hurry, just so I could launch it and see what would happen. LOL! Into orbit on my first try, with *loads* of fuel (comparatively speaking) to spare. I didn't even bother trying to tidy up the gaps between any of the parts. Just lumped it together and blasted off :D. I *did* think I was gonna melt it on the way up though :0.0:.

So, after some tidy ups in the SPH and the addition of a small batt pack, so I don't run out of electrickery during re-entry, I had another crack at it to see if I could outdo my first launch. Pro Tip: Don't hit the runway lights at 120+m/s. Anyway, after some hasty repairs, I had another go and managed an even better orbit than before. Obligatory close-up glamour shot :wink:

I also *finally* managed to get reasonably close to the KSC after re-entry, which enabled me to actually finish the flight where all courteous pilots should :cool:

I'm now curious to find out if I could do away with the 3 tons of NERV completely, and just rely on the RAPIERs for the boost into orbit. So, that's what I'm gonna try right now!

 

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The gaps at the nacelles don't actually hurt anything, and are sometimes necessary to allow shrouds or fairings to detach properly. Sometimes it's even useful to spread them a bit further to widen your footprint.

And orange temp bars aren't anything to worry about. :) It's only the red ones with only a hair of space left that should get you worried.

 

 

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4 hours ago, MrBonk said:

. I didn't even bother trying to tidy up the gaps between any of the parts.

 

Stock drag model doesn't care.  It just sees a mk1 part with no radial bits hanging off and something pointy on the front.  It then applies drag according to mach number, aoa and air density.   BTW the rapiers and nukes have attach nodes on the back face, the game thinks this is a flat plate of drag like leaving the nose cone off the front of the cockpit, and applies drag accordingly.   Effectively you've got 3 cockpits with no nose cones on the front !This video shows me applying cones to those unwanted attach nodes -

Spoiler

 

 

.

.

 

Quote

 

I *did* think I was gonna melt it on the way up though :0.0:.


 

Adding more wing area will make it gain altitude faster, so heat is less intense.  If you use Big S wing parts, you get extra LF for the NERV.  In the video i linked above, you will also see that I build my vertical fins out of Big S strakes , for even more fuel.     Also, instead of a ramp intake, I'm a fan of using the engine precooler with an ncs adapter then a small nose cone in front, since that puts Val even further back from the hotness.   In fact since you are using two Rapiers, you will need 2 pre-coolers , so Val will be the 5th part in line :-).

Quote

I also *finally* managed to get reasonably close to the KSC after re-entry, which enabled me to actually finish the flight where all courteous pilots should :cool:

Good job.  I was worried that your plane would become unstable with empty fuel tanks, since you got 7 tons of engines at the back and only  1 ton of cockpit up front , i thought maybe the fuel was the only thing keeping it stable.  With mark 1 parts, you can afford to use parallel stacks to solve this problem (and forward swept wings),  so long as the extra stacks have pointy stuff at the beginning and end, the drag penalty vs keeping it long , thin and noodly is negligible.   

https://kerbalx.com/AeroGav/Auto-Ray  (about the lowest tech nuke ssto it is possible to make)

20170115222528_1_zpstxtxcqjl.jpg

Forward swept wings also works for moving the nukes closer to the front  . 

20161216174338_1_zpstbdmwv9i.jpg

Spoiler

I'm now curious to find out if I could do away with the 3 tons of NERV completely, and just rely on the RAPIERs for the boost into orbit. So, that's what I'm gonna try right now!

My rule of thumb is that a well streamlined ship, with decent wing area, sensibly flown (keep AoA moderate, preferably 5 degrees),  needs 60kn of thrust per 15 tons takeoff weight.

60kn is 1 terrier or 1 nuke.

The rapiers do 180kn each in closed cycle mode.

So , you certainly wouldn't notice the loss of thrust if you left it off.    In fact the simplest ssto of all would get rid of the side stacks and be powered by a single rapier.

But if you want to go beyond low kerbin orbit, remember the RAPIER burns 2.3 times as much fuel as the NERV for the same delta V.  Pretty soon the weight of oxidizer becomes greater than the mass you saved by not having a NERV.     As you can see in my video, I went with 1 rapier/2 nervs instead,  and made the climb to orbit (easily) without even bringing any oxidizer.

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On 22 March 2017 at 1:35 PM, Bornholio said:

RCS Build aid..... 

zqsfHyL.png

My god, I wish I'd known about this mod sooner! I've been manually emptying my tanks to check dry cg :o 

I'm normally not a fan of modding games, but it looks like there are some that are just must-haves for KSP. 

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1 minute ago, MrBonk said:

My god, I wish I'd known about this mod sooner! I've been manually emptying my tanks to check dry cg :o 

I'm normally not a fan of modding games, but it looks like there are some that are just must-haves for KSP. 

yeah, RCS build aid is on a lot of should be stock lists.

Correct CoL may be more what you want if its aero design focus. It provides useful graphs of things like AoA and Pitch Static stability.

RCS build aid is however critical if you're building large ships that need to dock as it shows torques and thrust effects and how off center they are by axis. Also I find all i need is the Wet/Dry CoM indicators to get a "good enough".

 

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10 minutes ago, MrBonk said:

My god, I wish I'd known about this mod sooner! I've been manually emptying my tanks to check dry cg :o 

I'm normally not a fan of modding games, but it looks like there are some that are just must-haves for KSP. 

Then I'll also shout out to CorrectCoL.  The blue indicator only takes account of parts with a lift rating, this one makes it more accurate by computing the effects of aero forces from non wing parts.

If you only  install two mods in KSP, get these two.  

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5 hours ago, AeroGav said:

BTW the rapiers and nukes have attach nodes on the back face, the game thinks this is a flat plate of drag like leaving the nose cone off the front of the cockpit, and applies drag accordingly.   Effectively you've got 3 cockpits with no nose cones!

LOL ok, so that's also not something I'd have expected. I mean, I realise the blunt engine exhausts will cause turbulence, but simply adding a cone and then moving it *away* from where the drag is actually being caused seems so daft :) 

Looks like I have even more performance gains to make tonight. 

And yes...I certainly got to orbit after ditching the NERV and rebalancing, but it was clearly way less efficient. Fun to try anyway :D 

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15 hours ago, Wanderfound said:

Even in stock aero, Mk2 ships aren't overly draggy if you build and fly them right.

The key is that you need to keep that broad, flat fuselage aligned with the wind as much as possible. Hence, wing incidence:

angle_of_incidence.jpg

With a bit of that, you can climb to altitude while keeping your nose on prograde the whole time.

NOYwtKP.jpg

But remember kids, if you're going to add incidence to your wings, add it to the strakes, elevons and canards as well.   Or Mr Flip gets happy.

Surfaces behind the CoM having less incidence than those in front moves your CoM forward, so you'll have to shift the wing further back to compensate.  But it increases stability the further the nose pitches up, because the wings at the front stall first.  In fact it can be difficult to pull more than  8 degrees of pitch  with this in place.

Surfaces at the front not having any incidence, but the main wing having it, is bad.   It is effectively a nose down  trim that makes the CoL marker in VAB look further forward than it really is.    When your AoA gets large , the main wing will stall while your canards are still unstalled and making lift.  Your craft will swap ends or get into an unrecoverable deep stall.

2 minutes ago, MrBonk said:

LOL ok, so that's also not something I'd have expected. I mean, I realise the blunt engine exhausts will cause turbulence, but simply adding a cone and then moving it *away* from where the drag is actually being caused seems so daft :) 

Looks like I have even more performance gains to make tonight. 

And yes...I certainly got to orbit after ditching the NERV and rebalancing, but it was clearly way less efficient. Fun to try anyway :D 

Yeah,I've started playing with Ferram Aerospace again and it makes the game reflect the laws of aerodynamics much more closely.   Silly tricks like this are irrelevant,  it actually rewards you for building sleek, graceful stuff.   I think when an engine is running the exhaust stream greatly reduces drag off the back of the aircraft, but yeah engine bells on non-running engines are draggy as heck.  I think when the shuttle was being transported on a plane they put covers on for that reason.

You could mimic that with decouplers + cones, but when you start the engine you'll get hit with drag that isn't there on a real running engine.

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