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juvilado

Hopeless with SSTO spaceplane, give advices please!

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Hi, being playing since... well i dont remember, probably 4 years or so. 

I've done many many of the things in KSP that can be done, but SSTO spaceplanes are  ALWAYS a headache for me. For each time i try to build a new one (each new version of KSP, each time i retake the game since a long time) i need too many time to build a very crude SSTO (just LKO), and i find it very difficult to do it. And SSTO to Minmus for me is still undone, thats what i was aiming for this time, but can barely get a SSTO,

So i would really appreciate ALL the advices no matter if they are not very important, for there is not any real SSTO guide for 1.1.3 as far ive seen.

Thanks

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Well it would help to know where you struggle the most.  First off, drag is killer to space planes, so keep all radially mounted parts to a minimum.  Mass is your next enemy.  Only carry as much engine as you need and no more.  Lift is next, you want to be flying as near to prograde as possible.  The more aoa the more drag.  However, too much wing adds to drag so don't over kill it.  You should also be adding some incidence to the wing to improve its lift, as well as help fine tune col.  Last is fuel.  Best method I've found is jet and nuke combo to keep oxidizer to a minimum or none at all.  Granted I just started messing around with rapiers, but my current project only used the mk2-mk1 and a mk2-dual mk1.  So not a whole lot of oxidizer.  Beyond that, it depends on where you struggle.  Good luck!!!

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Hmmm. Well use rapier engines. They can function as both rocket and jet engines. As for a Minimus SSTO, 2 rapiers to one Nerva is a good setup.

A lot of people choose whiplash engines and this is a mistake. It only makes things more complicated since you need a rocket engine to get into orbit and de-orbit.

You also always need more LF than OX. Most of the fuel you use will be LF while ascending in the atmosphere and OX is always for orbital maneuvers. And let's say you want to land on another body, you are gonna need L-VN atomic rocket motors. These run on LF only so this makes you need even less OX.

Hope this helped.

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YZK8lQt.jpgTry building smaller space planes to start with.  As mentioned mass and drag are the two issues that make the biggest difference.  I rarely use anything other than Mk 2 parts for mine.  It's easy to get into a vicious circle of adding more engines and fuel to your designs.

If you don't mind your craft not being strictly SSTO, you might want to consider some liquid fuel drop tanks.  I often mount two tanks under the wings and use only that fuel whilst getting up to the altitude where you change to closed cycle with the Rapiers.  A nose cone on either end of the drop tank helps keep the drag down and it means your core vechile is full of LF and OX when you ditch the tanks and make the final push for orbit.

One other method I use (again it means it isn't a true SSTO vechile) is rocket assisted take off.  As the Rapiers work better once you get above ~400m/s, I will sometimes add a couple of small solid rocket boosters to really accelerate down the runway.  Then jettison them just before take off.  I always make sure I'm above 400m/s before pitching up to start climbing.

Hope that helps

PS added an image of one of my small craft with its rocket launch sledge.  It's (just) capable of getting to Mun orbit and back

Edited by Clipperride
Added picture

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My first space plane was a clone of this plane from Scott Manley's KSP Career Mode tutorial. It's a fairly early career mode plane, but still uses Ramjets to get up to 12 k. It required supersonic flight and high altitude flight researched.

I practiced on the "HR-71 Manley" many, many times. Blew up the cockpit on ascent many times due to overheating. Blew up the cockpit many more times on descent; I imagine the sight of a de-capitated space plane diving into the bay north of KSC would've been horrifying to watch. Also stranded the thing in orbit once, running out of oxidizer. Finally learned how to ascend and descend properly. After that, unlocking Aerospikes helped improve things, and finally unlocking Rapiers made the thing laughably easy to get into orbit and back.

The "HR-71" still flies about the same in 1.1.3 as it did in 1.0.5. Adding Ferram Aerospace Research made it easier to lift off and orbit, but much harder to land.

From there, almost any space plane I've tried used a similar ascent profile as that one. It becomes like falling off a bicycle; you don't really forget how.

--

Edited by Gordon Fecyk
grammar fix

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Ok, so there are few things. First - design things. Like ForScience6686  stated, minimize the drag by avoiding any sticking out parts. Make sure the wings are not eagle-like, but arrow like. A good wing - is delta wing, some like seen on F22 or T50, gives good balance of low drag and good lift. Wings do produce drag, so they are good but you require them less. Make sure wings are not angled, as they can cause flip. For easy take offs, shift the rear wheels more in fuselage and front wheels out, so that plane nose up when sitting. Regarding CoM/CoL, its important to have CoL behind and nearly outside of CoM ball,  because you aim at stability rather than maneuverability.

Depending on what engine you use.. you can go both whipsplash/nerv (W/N) combo or rapier, but this will impact your ascend profile (later). Generally, rapier are easier for lighter planes (because they weight less than W/N), whipsplash/nerv bring fuel advantages however once you make it in orbit. If you go with W/N, the good balance is 2/1. Have KER installed and make sure that Nerv stage gives at least 0.45 TWR in space, or nerv will fail to get you into orbit.

Then, and very important, ascend profile. Again have KER installed for info, as having apoapsis, time to apoapsis and vertical speed values is very good. The general idea is that vertical speed is very important, because when you climb to upper atmosphere layers, airbreathing will flame out and at this point you must be sure to have enough vertical speed to reach LKO, because this is where your rocket engines become efficient. If you are around 35 km and you have vertical speed of 300-400m/s, then you are good. Likewise, horizontal speed is important (but less) and should not fall behind (typically) 1250 - and should constantly keep climbing, even at price of starting rocket engine. A good factor is "time to apoapsis" - it should never go less than 20 seconds until you reach 70 km LKO. If you are say, at 40km and see "time to apoapsis" fall less than 30 seconds, you can abort because your profile failed to achieve vertical momentum.

And always remember - air intakes also create drag! Once your air-breathing engines go flame out, remember to immediately close all intakes. This also means - avoid any course corrections when accelerating. Once you are accelerating, the course should be locked with SAS on stability until you leave atmosphere.

Now to profiles. With W/N you have a different ascend profile than with rapier. This is because Rapier in air-breathing mode gives a good push at altitude and its closed cycle is quite powerful. To the contrast - Nerv is very pathetic in thrust at low altitude and still bad in LKO (which also means you can engage Nerv before Whipsplash flames out, in fact - you should, once you notice regular speed, on top of navball, to start to decline); and Whipsplash flames out earlier. But both are more energy efficient than Rapier.

Means: with Rapier you should directly climb to reach 8-11km and then aim at 10-15 degrees, set SAS to stability, hit max throttle and ... leave controls alone. You will start climbing to upper atmosphere. You will reach high speed in air-breath mode - which will help you get pretty high up. And once they flame out - switch to closed cycle, close intakes and watch for apoapsis and time to apoapsis. Former should constantly increase, while later should not get near 20 seconds until its 50km or so. Once you see time to apoapsis to start increasing, you can pitch somewhat downwards - back into prograde (if you set SAS to stability, it will automatically graciously pitch upwards in upper atmosphere) and keep it inside 20 seconds until your apoasis reaches 70 km, then set strict prograde on horizon and circularize.

With W/N, the vertical speed is most important.. Ideally, you should lift off, aim at 25-30 degrees, full throttle, set SAS to stability and burn, burn, burn. Around 22km the Whipsplash should flame out, but you should have 1250+m/s speed and 300+ m/s vertical speed. If you failed - abort attempt. When notice Whipslash starting to slow down (typically around 18km), activate nerv! Its weak, but efficient and will compensate. When Whipsplash flames out - close intakes. Then its the same as above about keeping time to apoapsis within 20 seconds, when you notice it to increase - pitching nose down to invest in circular burn=horizontal speed. If time to apoapsis falls less than 20 seconds and you are less than 60km, that means your vertical speed was too low. You need to get that from Whipsplashes when still below 17 km, as - as mentioned many times - LVN's impulse is pathetic and should be seen as a "complimentary" (in contrast to "standalone") engine when still not in LKO.

http://imgur.com/a/HGuHR

My 2 cents...

Edited by Kerbal101

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@Kerbal101, I don't think intakes being closed currently has any effect.  But I've heard that it should eventually make it's way back in to the game.  I think ascent profiles have a bit more flexibility than you stated.  I think it has more to do with the specific craft and the mass you're working with.  What really matters is how easily you can get over the mach barrier.  If you find you can't make it at low altitudes, try a slow climb to thinner air before you start your speed run.  I would also advise that you should be flying as close to prograde as possible during this run to reduce drag and maximize acceleration.  But I would not wait for your acceleration to decline before switching modes or lighting the rockets.  I often light my nukes at 20km as they are producing near full power by this height.

I agree with col/com.  Control inputs are exaggerated at very high speeds, and that can lead to loss of control.  For in flight checks, I like to mount a part in the craft right at col, and since the camera focuses at com, you can zoom in and visually check that your com is correct before reentry.  As for the wings, I'm not quite understanding what you're saying.  Incidence is good for better lift performance.  And I often rotate the wing tips up, mainly for aesthetics, but control issues can become prevalent, but usually only in the roll axis.

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10 hours ago, juvilado said:

2ups9qo.png

Finally was able to build one this time! Thanks fir all the tips

Admit: it takes good 20 minutes to reach the orbit? :)

If you want to reach the orbit in a reasonable timeframe, you need a third type of engine. Anything with moderately high thrust and moderately good ISp, though thrust trumps ISp here - Reliant, Aerospike, closed-cycle Rapier, even Poodle will do in a pinch - I even made one that used SRB for that purpose (don't take THAT as an advice, it's not really a good idea!) - you activate this 'intermediate' engine when your jets lose thrust, and keep it running until your apoapsis is right (or you run out of oxidizer; you really don't need much of it). That way the lengthiest part of the journey - when Nukes struggle against atmospheric resistance trying to build up the missing 1000m/s - is shortened immensely, plus you gain enough horizontal speed that waning lift from wings ceases to be a problem as gravity drag is reduced to zilch.

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3 hours ago, Sharpy said:

Admit: it takes good 20 minutes to reach the orbit? :)

If you want to reach the orbit in a reasonable timeframe, you need a third type of engine. Anything with moderately high thrust and moderately good ISp, though thrust trumps ISp here - Reliant, Aerospike, closed-cycle Rapier, even Poodle will do in a pinch - I even made one that used SRB for that purpose (don't take THAT as an advice, it's not really a good idea!) - you activate this 'intermediate' engine when your jets lose thrust, and keep it running until your apoapsis is right (or you run out of oxidizer; you really don't need much of it). That way the lengthiest part of the journey - when Nukes struggle against atmospheric resistance trying to build up the missing 1000m/s - is shortened immensely, plus you gain enough horizontal speed that waning lift from wings ceases to be a problem as gravity drag is reduced to zilch.

Well not 20... it takes 10. I tried adding a LV engine but it weights too much! All in all this way i get 3.5K dV (according to KER) once in LKO, is not bad at all.

The bad part is it is unmaneuvable during the reentry, i think because CoM has moved behind CoL. Ill work on that...

Edited by juvilado

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13 minutes ago, juvilado said:

Well not 20... it takes 10. I tried adding a LV engine but it weights too much! All in all this way i get 3.5K dV (according to KER) once in LKO, is not bad at all.

Yes, it's a pretty good number. But you are not losing much by adding the mass of the third engine and its fuel. The climb on LV-N is very long and as result takes a lot of fuel. You're saving a lot of fuel by reducing the climb time. Of course you're losing most of these savings with the added mass, but whether you save more or lose more is a matter of good engineering.

Thing is, making proof-of-concept SSTO for sport is all fun and good, but to make SSTOs actually useful in the game - you need to make them do their work in a reasonable timeframe. So, now that you got it to orbit, your second goal is to reduce time to orbit. Once you have that, you start working on payload mass / leftover range (which are roughly the same thing, lose payload, add fuel.).

 

Edited by Sharpy

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3 hours ago, juvilado said:

The bad part is it is unmaneuvable during the reentry, i think because CoM has moved behind CoL. Ill work on that...

If you're not adverse to mods, try installing RCS Build Aid - it has a "dry center of mass" marker that can show you where the CoM winds up when your tanks are dry. Easy way to verify if that's happening to you or not. Alternatively, you can stay stock by draining all your fuel tanks by hand in the SPH and doing it that way. Make sure to refill the tanks before you try to fly, of course...

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49 minutes ago, capi3101 said:

If you're not adverse to mods, try installing RCS Build Aid - it has a "dry center of mass" marker that can show you where the CoM winds up when your tanks are dry. Easy way to verify if that's happening to you or not. Alternatively, you can stay stock by draining all your fuel tanks by hand in the SPH and doing it that way. Make sure to refill the tanks before you try to fly, of course...

Well I recently uninstalled the mode because I found it useless i'm going to reinstall it right now

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On 17/9/2016 at 10:52 PM, juvilado said:

Hi, being playing since... well i dont remember, probably 4 years or so. 

I've done many many of the things in KSP that can be done, but SSTO spaceplanes are  ALWAYS a headache for me. For each time i try to build a new one (each new version of KSP, each time i retake the game since a long time) i need too many time to build a very crude SSTO (just LKO), and i find it very difficult to do it. And SSTO to Minmus for me is still undone, thats what i was aiming for this time, but can barely get a SSTO,

So i would really appreciate ALL the advices no matter if they are not very important, for there is not any real SSTO guide for 1.1.3 as far ive seen.

Thanks

SSTOer to the rescue! Let this be a mini-guide to all things SSTO:

First, rocketry is all about ratios. Thrust-to-weight and mass ratio, mostly, and we all know those two well and how they play with each other (high TWR means a lot of engine weight, so for the same payload, a lower mass ratio and thus less dV, for example).

Well, SSTOing is even more so, since there are more ratios involved, and with airbreathing SSTOs, even more so. But there is a great thing about that: once you have a working design, you can extract the ratios from it, and be damn confident that if you build something exactly twice as big, with twice the thrust, twice the payload, and so on, it'll behave just the same. Science is great, ain't it?

So, just what are good ratios, anyhow? Well, I, like many others, have my rules of thumb. First, I use one RAPIER for each five metric tons of payload, more or less (there are other engines, yes, but they are worse for SSTOing, no exceptions). Note that "payload" is anything other than engines, fuel tanks, and wings, so all cockpits and payload bays and landing gear and such count towards that. I then aim to get around 0,5 TWR on the runway using RAPIERs, but with all the fuel I can carry. I put about 400 units of extra liquid fuel per RAPIER to make the climb on airbreathing mode and then, it's all about aerodynamics and mass distribution, and also make it as pretty as I can manage.

Aerodynamics are relatively simple, just make it pointy, leave no open nodes (they are great sources of drag), and make it fly stable-ish. Mass distribution takes much more, because you have to make sure that your plane is just as stable when full as it is when empty, but that it still has enough control authority to reenter at a high AoA and thus brake slowly. Just exactly where you place your fuel tanks is key, and a very good rule of thumb is "symetrically around the CoM, preferably right on top of it".

With all that taken care of, there is still the task of flying the thing, which is anything but straightforward, but perhaps that would better be a topic for another time.

 

Rune. Helpful so far, at least?

9 hours ago, Sharpy said:

Admit: it takes good 20 minutes to reach the orbit? :)

If you want to reach the orbit in a reasonable timeframe, you need a third type of engine. Anything with moderately high thrust and moderately good ISp, though thrust trumps ISp here - Reliant, Aerospike, closed-cycle Rapier, even Poodle will do in a pinch - I even made one that used SRB for that purpose (don't take THAT as an advice, it's not really a good idea!) - you activate this 'intermediate' engine when your jets lose thrust, and keep it running until your apoapsis is right (or you run out of oxidizer; you really don't need much of it). That way the lengthiest part of the journey - when Nukes struggle against atmospheric resistance trying to build up the missing 1000m/s - is shortened immensely, plus you gain enough horizontal speed that waning lift from wings ceases to be a problem as gravity drag is reduced to zilch.

That is bad advice, sorry. Use RAPIERs, like any good SSTO will always do. RAPIERs get to orbit the highest payload fraction, period. Mostly because they have the highest cutoff speed, but also because they have a way more than decent TWR on rocket mode, and thus you have the absolutely minimum engine mass in orbit. You can then talk about high-efficiency engines for in-space travel, but then you should go straight to nukes or ions, and count them and their fuel as payload, because we are talking about something other than SSTOing anyway.

 

Rune. For proof of my assertions, I refer to the payload ratio challenge.

Edited by Rune

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57 minutes ago, Rune said:

That is bad advice, sorry. Use RAPIERs, like any good SSTO will always do. RAPIERs get to orbit the highest payload fraction, period.

Oh, Rapiers with their dual mode serve both as jets and as the intermediate engines, and don't weigh all that much, which makes them a good choice - if you have them unlocked. Still, that's for playing stock and sticking for moderately sized spaceplanes. If you go with something larger, like MK3, they stop scaling up that well - you quickly run into sticking 8, 10 or more them onto your plane to get a reasonable TWR, and you're running into problems of framerate, construction durability, spacing this all reasonably, your spaceplane becoming a monstrosity with rear packed with so many rapiers it starts to look silly.

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1 hour ago, Sharpy said:

Oh, Rapiers with their dual mode serve both as jets and as the intermediate engines, and don't weigh all that much, which makes them a good choice - if you have them unlocked. Still, that's for playing stock and sticking for moderately sized spaceplanes. If you go with something larger, like MK3, they stop scaling up that well - you quickly run into sticking 8, 10 or more them onto your plane to get a reasonable TWR, and you're running into problems of framerate, construction durability, spacing this all reasonably, your spaceplane becoming a monstrosity with rear packed with so many rapiers it starts to look silly.

Let me quote myself here:

2 hours ago, Rune said:

First, rocketry is all about ratios. Thrust-to-weight and mass ratio, mostly, and we all know those two well and how they play with each other (high TWR means a lot of engine weight, so for the same payload, a lower mass ratio and thus less dV, for example).

Well, SSTOing is even more so, since there are more ratios involved, and with airbreathing SSTOs, even more so. But there is a great thing about that: once you have a working design, you can extract the ratios from it, and be damn confident that if you build something exactly twice as big, with twice the thrust, twice the payload, and so on, it'll behave just the same. Science is great, ain't it?

That is, like, the first thing I said. If something works good at1x, it will work just as well at 8x. As proof, I offer my Claymore, which does actually better than my average design (>45mT to orbit in the payload bay), mostly because of some stuff like the cockpit, RCS system, undercarriage, that sort of thing kind of gets lost in the rounding, while you are doing the mass budget in such big birds.

http://imgur.com/59Du952

And of course, it could just as well have twice the engine pods and a bay twice as long. It would also get a very slightly better payload ratio. Granted, at some point it's a bit harder to build bigger things, structurally speaking... but frankly, I doubt you really need a bigger SSTO than what you can build in KSP in an average computer, with a bit of thought (and lots of practice!).

 

Rune. It's also easier to tailor your TWR to the perfect number when adding an extra engine is closer to 10% more thrust, rather than, say, 50%.

Edited by Rune

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6 hours ago, Sharpy said:

you quickly run into sticking 8, 10 or more them onto your plane to get a reasonable TWR, and you're running into problems of framerate, construction durability, spacing this all reasonably, your spaceplane becoming a monstrosity with rear packed with so many rapiers it starts to look silly.

Meh, it's all design challenge. And the nice thing about rapiers is that you don't have to up the part count with fuel lines to keep things running properly, which gives you some breathing room if your computer is a bit... venerable. My current workhorse is a refinement of this Archon (which I think looks pretty decent and not at all silly) and runs with no framerate issues on your average digital toaster.

Edited by Jarin

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6 hours ago, Rune said:

Let me quote myself here:

That is, like, the first thing I said. If something works good at1x, it will work just as well at 8x. As proof, I offer my Claymore, which does actually better than my average design (>45mT to orbit in the payload bay)

[...]

Granted, at some point it's a bit harder to build bigger things, structurally speaking... but frankly, I doubt you really need a bigger SSTO than what you can build in KSP in an average computer, with a bit of thought (and lots of practice!).

Oh, I call BS. that's still pretty moderately sized. Upscale that 8x, volume-wise. Not payload mass-wise. Say, my recent payload, packed as tightly as possible. Orange tank for comparison.

aw7Yc2g.png

i8mW59Q.png

Mere 19 tons.

Suggest a nice spaceplane to take it into LKO.

Edited by Sharpy

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Someone around here has a nice Y-hull design that has a wide faring-covered payload area between the engine nacelles. Or tweakscale the cargobay  wide enough to fit.

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2 hours ago, Jarin said:

Someone around here has a nice Y-hull design that has a wide faring-covered payload area between the engine nacelles. Or tweakscale the cargobay  wide enough to fit.

And how many Rapiers to carry that tweakscaled cargo bay?

Alternatively, how many struts keeping that Y-hull structurally stable?

Edited by Sharpy

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7 hours ago, Jarin said:

Meh, it's all design challenge. And the nice thing about rapiers is that you don't have to up the part count with fuel lines to keep things running properly, which gives you some breathing room if your computer is a bit... venerable. My current workhorse is a refinement of this Archon (which I think looks pretty decent and not at all silly) and runs with no framerate issues on your average digital toaster.

Archon looks good

Anyway with tweak scale you can make the plane twice big except for cockpit maybe, so you are getting double payload capacity isnt it? Ill try that

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7 hours ago, Sharpy said:

Suggest a nice spaceplane to take it into LKO.

Well... you asked for it :wink::

K9UFpJJ.png

Not that I couldn't fit that payload in the last SSTO's bay, but just in case.

 

Rune. When a bay is not enough, there are always payload fairings.

Edited by Rune

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8 minutes ago, Rune said:

Well... you asked for it :wink::

Not that I couldn't fit that payload in the last SSTO's bay, but just in case.

 

Rune. When a bay is not enough, there are always payload fairings.

I don't quite see the Rapiers from this perspective. But I see three engines in the staging list. Two Rapiers and one LV-N or two LV-Ns and one Rapier?

1 hour ago, juvilado said:

Archon looks good

Anyway with tweak scale you can make the plane twice big except for cockpit maybe, so you are getting double payload capacity isnt it? Ill try that

Square-Cube law kicks in.

For 2x the wing length you're getting 4x the wing area and 8x the wing mass. Also, AFAIR Tweakscale doesn't make joints stronger, so you're getting into a strut hell.

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3 hours ago, Sharpy said:

I don't quite see the Rapiers from this perspective. But I see three engines in the staging list. Two Rapiers and one LV-N or two LV-Ns and one Rapier?

Square-Cube law kicks in.

For 2x the wing length you're getting 4x the wing area and 8x the wing mass. Also, AFAIR Tweakscale doesn't make joints stronger, so you're getting into a strut hell.

Yes, im having to use struts...

Uff, im having trouble with the HUGE spaceplane....

Edited by juvilado

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Yes, closing intakes make sense. It tested it in 1.1.3 and they (seem to) produce drag. "Seem" because I have not tested that extensively but I noticed dV to improve when closing them. Need to retest this though.

I agree about complexity of ascend profiles. IMHO this is because like rocket engines. each of air-breathing engines has two thrust ratios but in atmosphere:
One - at normal speeds. Two - at "optimal" speeds. Means two completely different TWRs depending on speed for each air-breather.

What this means if you attach rapier, panther and whipsplash to long mk3 liquid fuel can (with KER):

1) TWR at regular speeds:

rapier: 0.18(!!)
panther (dry): 0.15
panther (wet): 0.23(!!)
whipsplash: 0.22

2) TWR at optimal speeds:

rapier: 0.79(!!)
panther (dry): 0.19
panther (wet): 0.39
whipsplash: 0.65(!!)

I think this is why:
Rapier is very bad for lift because it gives less TWR than Panther(!) (and burns fuel like whipsplash at same time) if it has not reached optimal speed. If Rapier reaches optimal speed - it gives best TWR.
Thus with Rapier you want to have acceptable TWR to start acceleration, then set to leave atmosphere at lower angle (because less of atmosphere = less drag, lower angle = faster acceleration = sooner optimal speed/best trust) and soon you reach best trust, after which the usual stuff with rocket engine or mode. But planes with lower total TWR, will reach a barrier of about 200-300m/s with this engine, when flying like this. For such planes other ascend profile can be used - acceleration in higher atmosphere - go straight to 8-11 km, point nose perfectly horizontally until accelerated to 900+m/s then point nose at 15-20 degrees (so both vertical and horizontal speed are not affected) and accelerate away.

This engine is exceptional for travel at very high speed(and altitude) or for leaving atmosphere. Because its optimal speed is very close to typical 2200m/s, its easier to leave Kerbin with it. Otherwise its inefficient. This partially includes its rocket mode, which ISP is horrid but thrust - ok, thus best used as orbit reach assist. :)

And its very unforgiving to planes with bad TWR: a) its has bad trust at regular speed b) it takes lot of time to reach its optimal speed, a plane with bad TWR will burn through lots of fuel or even fail to achieve it.

 

I find whipsplash to be very good. It has excellent TWR in both modes - can lift more mass upwards than Rapier. In optimal speed its thrust is close to Rapier, but because its still less and the fact it has no rocket properties - one needs to also package a rocket engine(weight) - which causes TWR to sink, especially on small planes. And one really needs sharper attack angle (higher vertical speed) with it so rocket engines have room to catch - because it will flameout sooner, lower and at lower speed than Rapier. Still it gives fuel economy to compensate fact it flames out soon. Thus, me calculates, its bad for SSTO on very small planes, but very good for bigger SSTO. Speaking of which, if plane has good TWR calculation and goes straight to orbit rather than flying around - Rapier would still be better than Whipsplash, in its air-mode that is.

 

And I am still unable to reach orbit with Panter. :) Great engine, but one thing ruins it - its optimal speed happens to early, thus it can't develop enough speed to reach optimal altitude for Nerv. 800m/s at 18km is still not enough for nerv. Should try it with aerospike "dart" though :) The profile is approx this: climb in dry mode to 6-8km, then in wet mode to 12-14km, then engage rocket engine and set higher angle slowly.

cfRWSSG.jpg

Btw I found out that acceptable TWR for craft to orbit to be at least 0.7. Its about 1 engine for 17 tonne of craft.
Ofc one can use more wings to help lift, but more wings -> more drag -> more required thrust -> (here we go again) more engines. So its investing in wings or in fuel in the end. And if its SSTO - fuel is better, because nothing worse than getting speed block due to drag at 15-28km+ point.

Edited by Kerbal101

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On 20/9/2016 at 0:56 PM, Sharpy said:

I don't quite see the Rapiers from this perspective. But I see three engines in the staging list. Two Rapiers and one LV-N or two LV-Ns and one Rapier?

Actually, three Vectors. That's a rocket, Jim. But also technically a SSTO spaceplane, using Vertical Takeoff and Horizontal Landing, like the acronyms on the name imply. For low mass, high volume payloads, they work great, since the payload can sit on top with a fairing, and a gliding runway recovery is relatively easy to nail.

 

Rune. There's more than one way to skin a cat.

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