Space Plane Assent

[Clipperride]

I've been turning my hand to Space Plane's with some very mixed results. It strikes me that there are two philosophy's

Shuttle - enough thrust to blast in to space and enough wing to land and recover the ship.

White Knight - Taking it steady through the dense lower atmosphere making the most of the free oxygen and wing lift then accelerating.

My first somewhat successful attempt uses the brute force method, getting as hot on assent as reentry. It seems a little too much like a rocket that you can steer home for my liking,, but I'm having trouble with the White Knight approach. Is it possible?

Another problem is centre of Mass being so far back, placing wings and wheels becomes an issue.

One last snag - I'd like to use Whiplash, Rapier and LV-N engines, but mounting them so the last two are in line with the CoM is an issue. Should I stick to just two kinds of engine?

All advice most welcome.

Edited August 26, 2015 by Clipperride
Mistakes are only obvious after you hit post

[tadswana]

Hey Clipperride!

I'm working on the same problem, trying to optimise refuelling runs from atmosphere. At moment I'm using the brute force method.

The White Knight method is appealing to me too, however I'm torn to whether the structural inefficiency of having the landing gear/aerodynamics to do it are worth the "free boost" you get from the lower atmosphere. For me it hasn't worked...

Let me know how you are going and post pics, I'll do the same.

[JTpopcorn]

Sadly, the white knight approach is much harder to engineer than a brute force method due to all the drag stuff. The general problem with a slow ssto ascent is that fuel is wasted in low atmo due to drag. I have only really gone for ssto's that are a mix, fast through the atmosphere but not crazily overpowered. I would post pics, but I dont have that save anymore.

[Pecan]

Rocket SSTOs are easy but not, of course, planes at all - requires more fuel per launch and is harder to land accurately.

'Shuttle' style orbiter/landers are about the hardest to build because of the unbalanced launch profile - not worth it for the ability to land where you want.

Pure apaceplanes are not too bad, once you get the ascent sorted, but they do need more design and flight effort than rockets on ascent.

The various 1.0.x versions changed things drastically from 0.90 and a fair amount amongst themselves so to an extent we're all still beginners with the air-breathing engines and spaceplanes.

That said, the broad outlines of flight to orbit are clear:

Phase 1: launch to 10km - start air-breathing and climb at the best rate the vehicle allows, just to get some useful altitude.

Phase 2: 10km to 20km - climb less and concentrate on building horizontal velocity, such that you reach around 1km/s - 1.5km/s or more.

Phase 3: Pitch-up to climb to the maximum altitude your air-breathing engines will allow while maintaining the highest horizontal velocity you can.

Phase 4: Switch to rockets when the air-breathers die and go for orbit.

[KerikBalm]

*Ascent, not Assent

Basically, climb 20-30 degrees until you reach 10km, then lower your nose to 15-20, and pick up horizontal speed.

When airbreathing engines cut out, burn LFO at the same 15-20 degree climb until your apoapsis is in space, follow prograde with your navball set to surface velocity to minimize drag..

[plotz]

Basically, KerikBalm is right, but as always, it highly depends on your craft.

Regarding the OP's questions:

- You can stick to two or more kinds of engines (or just use Rapiers for practice, though these still make your life too easy, imho). For highly efficient designs, I recently abandoned R.A.P.I.E.Rs altogether. For a 30t craft, two turbojets paired with two LV-Ns are always sufficient. You can make do with a single turbojet until around 27 tons (using high lift wings), though.

- My last two sentences from above also show the impact the engine layout has on the ascent profile: Two turbojets usually deliver a TWR that allows for a quick 20 degree climb. A single turbo is much slower but may be equally efficient (low thrust in low atmosphere = low fuel consumption + only a single engine + less weight) --> 7-12° climb angle.

- When dealing with moderate TWRs Profiles for ascent from my experience should always include a sea-level acceleration phase to at least 250m/s (for the ram-effect) and another acceleration phase at 10kms (Turbojet) or 12kms (Rapier). When parts start to overheat, do not adjust thrust but increase the angle of attack to climb more quickly.

- Small SSTOs with a Rapier or a Turbojet + a few of those small orange radial engines can be around 8tons and thus have tremendously high TWRs. Just lift off, at 250m/s pull up to 40° and reduce thrust until your acceleration is around 10m/s. When at 7500m, revert to full throttle, slowly reduce AoA until you hit 1300 (Turbojet) or 1400 m/s (Rapier) and climb out at the edge of overheating.

- When acceleration comes to a halt with turbojets, additionally switch on your LV-N or LF-O engines until flameout. For Rapiers, switch to closed cycle as soon as you begin to lose speed.

Hope this helps. If you need any example craft designs for ascent profiles, just write me a PM. I have some simple ones in my crate .

Edited August 26, 2015 by plotz

[KerikBalm]

Yea, it depends on the craft, I have craft where you can basically take off, pitch to 20 degrees at full throttle, and not do anything until your apoapsis is above 70km (if automatic switching is turned on).

With a proper craft, its really not hard.

[Geschosskopf]

I've been turning my hand to Space Plane's with some very mixed results. It strikes me that there are two philosophy's

Shuttle - enough thrust to blast in to space and enough wing to land and recover the ship.

White Knight - Taking it steady through the dense lower atmosphere making the most of the free oxygen and wing lift then accelerating.

Well, technically, both of these are multi-stage vehicles, not SSTOs. The "White Knight" is complicated by the severe difficulties of keeping 2 vehicles in existence simultaneously, let alone controlling them both. Is this what you really want to do or are you trying to do an SSTO?

Assuming you reall want a multi-stage spaceplane...... If you're not concerned with keeping the "White Knight" in existence, then that method is kinda easy to do. You build a small spaceplane "upper stage" that's all rocket, and carry it to high altidude with a large "lower stage" that's all jet. I find this rather easier than trying to build a shuttle, due to the asymmetric lift/drag/thrust inherent in shuttle designs.

OTOH, if you want an SSTO, then you have to do a lot of compromises. You need both jets and rockets in the same vehicle, fuel for both, fuel for both, both having enough TWR to do their jobs before they run out of fuel, and enough wing to land safely at the end. While the general parameters of such a spaceplane are fairly tight, you do have some wiggle room within them that will give the ship somewhat different performance in the various regimes of the ascent. This means your ascent must be tailored to suit the plane.

[Val]

Well, technically, both of these are multi-stage vehicles, not SSTOs.

...

SSTOs were not mentioned in OP. He said space planes. And both the options he mentioned are space planes, but not SSTOs.

I've been turning my hand to Space Plane's with some very mixed results. It strikes me that there are two philosophy's

Shuttle - enough thrust to blast in to space and enough wing to land and recover the ship.

White Knight - Taking it steady through the dense lower atmosphere making the most of the free oxygen and wing lift then accelerating.

As others have already mentioned there's a 3rd option in KSP. The Single Stage (to Orbit) Space Plane.

I've never tried the White Knight approach, and only tried the Shuttle approach before KSP 1.0. Since KSP 1.0.4 I've pretty much exclusively done space planes. All but one was Single Stage.

I also prefer a different Ascent Profile, than the posters above me. I build up speed to 1000-1100 m/s between 9 and 10 km, and pitch up 20 degrees from there, while there's still lots of Air breathing thrust. This allows me to gain lots of vertical speed and push the AP above 30 km, before engaging closed cycle engines/mode at around 20 km.

This Ascent Profile requires a very low drag builds, but is very efficient. (My entry is the top Single stage in the Air-breathing category of Stock Payload Fraction Challenge: 1.0.4 Edition)

[Clipperride]

What am I trying to achieve? Just a working knowledge of getting winged craft of various kinds into LKO and beyond (fuel willing). As a noob, I've only played with the new KSP flight rules. I guess that's good in a way as I'm not confusing myself with how things used to be done. I now carefully check the date of any information about Space Plane's (which to me includes "all of the above" from STTO through drop tanks and booster rockets to a drone carrier ship)

My first attempt is a bit of a brute that breaks loads of good design rules I've discovered in these forums. I was caught in the "not enough fuel - then too little thrust, then not enough fuel" loop. After about 20 iterations I got a little vexed and just bolted on loads of extra fuel, 2 whiplash, 4 Rapier, 2 LVNs and two small SRBs to get to 300+ m/s as soon after take off as possible. It works but gave an inelligent solution.

That said, it allowed me to practice ascents which led to needing less fuel + ox. I then flew the same ascent to see how much more fuel I could save lifting a lighter starting load. Keeping the design the same for consistent results, I removed over 900 fuel and 1500 Ox and still got into orbit and back.

I notice there is some variation in peoples preferred ascent (easy mispell to make with that one ) profiles, so I've built a little 4 engine test plane to play about with engines and flight paths. I guess its mainly a matter of style and actual goals with no "best" way. I'm on my very first Science game, with almost all the tech tree unlocked. My "house rules" are, budget no object and I can revert a flight but not reload a quick save. Although, after having to drive a top heavy Munar rover over 20km, I relaxed that rule a little!

I do love a game that involves a stack of notes on paper next to the computer

[Clipperride]

Tadswana - here (hopefully) is an album showing first my test plane and then the Brute that I made out of frustration!

http://imgur.com/a/PAYNC

PS the 1st picture is the result of a poor take off (the crew survived) and the last is an "explosive" separation.

"Flight - we definitely heard some sort of knocking sound on staging and the radar's gone bezerk"

Edited August 26, 2015 by Clipperride

[Pecan]

...I notice there is some variation in peoples preferred ascent...

...I also prefer a different Ascent Profile, than the posters above me...

My advice is usually "this is the easy or straightforward way". When it differs from Val there are probably one or two reasons i) he's tried way more than I have, ii) I didn't even know that!

It is safe to assume my guidelines will not be as good (although, I hope, generally easier to abide by).

[Clipperride]

I don't have any Mods installed,, so simply go by the numbers available in the stock game. My first test setup had 2 Rapier engines and could just get into an ~80x80km orbit with enough fuel/ox remaining to drop that orbit back below 20km to glide into land.

Noticing the thrust of the rapiers is pretty pitiful at take off, I bolted on 2 structural pylons to the back and added 2 whiplash engines to accelerate quickly and climb to 10,000m. The result was almost exactly the same fuel/ox remaining once in orbit. I'm guessing the saving made using more efficient engines at low altitude is equaled by the cost of the extra weight.

[Alshain]

Has anyone built a true SSTO spaceplane. I can't seem to find an ascent that works at all. I can build an SSTO jet assisted rocket with wings that looks like a plane, but does anyone have a plane with sea level TWR <1 that reaches orbit? Because, if not, there seems to be no point to spaceplanes in this game anymore, aside from shuttles. I just can't find a way and still have any fuel once I get to suborbital speeds.

[panzer1b]

Has anyone built a true SSTO spaceplane. I can't seem to find an ascent that works at all. I can build an SSTO jet assisted rocket with wings that looks like a plane, but does anyone have a plane with sea level TWR <1 that reaches orbit? Because, if not, there seems to be no point to spaceplanes in this game anymore, aside from shuttles. I just can't find a way and still have any fuel once I get to suborbital speeds.

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This was my attempt at a truly slow ascent, 30 bloody tons lifted by a SINGLE RAPIER! Do not believe anyone that a rapier cannot lift 30 tons, provided its low drag and has enough wings on it. Also, it was my 1st post 1.0 SSTO style craft that is 100% legit. The only non stock things are fuel switching mod (so those stupid FLT-100s can have 100 LF instead of all that worthless OXY), and i also used ALOT of part clippoing to achieve said looks, there are 2 bombs in the bomb bay, with at least 20 FLT-100s sideways stacked in teh center, all in that short bay, yes clippiung can be considered cheaty by some, but ive goven up caring about clipping since my designs process is: [1looks, 2armor, 3weapons, 4make it fly, 5give it the range i desire by spamming fuel tanks somewhere where they can fit in].

ANyways, if anyone is interested in slow and low accel approach, most excessively bad TWR craft will work like this:

1 Get off the runway alive, and build speed to ~300m/s.

2 Climb to ~5-7 km, making sure to not drop speed too much or you will never be able to recover it (regardles sif its a jet or a rapier, the faster you go the more thrust you get at a given altitude).

3 Level out so that your craft is just keeping altitude and boost up to at a minimum of 450m/s (if you can get through the transsonic region and get to 500+m/s, a single rapier will push 50 tons easily), this also means if your craft refuses to pass the transsonic, you need to dive somewhat and loose altitude to break through, or worst case, light the rocket engine for a temporary boost, it is better to eat more fuel to break through faster then spend 10 minutes trying to burn through to mach 2.

4 Gain altitude till you are near 10-15km and level out (this depends on your build, the less draggy you are, the lower you can start to gain speed, you will gain it faster and use less total fuel, but if you are more draggy then higher is always better).

5 Maximize your speed without cooking your kerbals (as much as the kraken enjoys eating kerbals, deep fried kerbal doesnt really suit him very well), aim to be going at a minimum 1300m/s before you start to angle upwards, although the faster you go, trhe less dV you will need to eat in rocket mode (it is far better to spend an extra minute or two in atmo gaining speed slowly, then it is to use rockets to gain that speed).

6 Angle up slowly and try to get your trajectory to around a 20 degree angle when your jets/rapiers run out.

7 Engage rockets (if you have alot of thrust in rocket mode like LFO engines, just aim for prograde until your AP is whatever you desire it to be, if you have low thrust, aim at 30 degrees above horizon at all times until you are above 1900m/s after that prograde provided you are still gaining altitude at that point).

8 Point yourself prograde to cut down needless drag, burning occasionally if your desired AP drops below acceptable.

9 Do the usual stuff you do to circularize or attain orbit or whatever you fancy doing once out of atmo (go buy your kerbals some coffee).

This approach works for 90% of my very bad thrust SSTLs (single stage to laythe surface and back). It is highly recommended to have some oxy for a rapier if you have very bad TWR with the space engines (ions, nukes, ect), since oftentimes you cannot gain enough speed fast enough to punch out of atmo with these engines alone, and an extra 300 or so m/s after jets die goes a long way to keep you afloat until the speed rises to orbital velocities.

Edited August 27, 2015 by panzer1b

[Slam_Jones]

Has anyone built a true SSTO spaceplane. I can't seem to find an ascent that works at all. I can build an SSTO jet assisted rocket with wings that looks like a plane, but does anyone have a plane with sea level TWR <1 that reaches orbit? Because, if not, there seems to be no point to spaceplanes in this game anymore, aside from shuttles. I just can't find a way and still have any fuel once I get to suborbital speeds.

Indeed! This particular craft is able to SSTO, then proceed to do a Mun fly-by and return. It was built with space tourism in mind, and can carry 8 passengers and 2 crew (or 9 + 1 if I really want).

It usually takes off with approx 0.7 - 0.85 TWR, depending of the particular engine arrangement and fuel supply. My ascent probably isn't the most efficient, but it works for the designs I've built.

I'll usually keep an eye on my Thrust readout, and adjust my ascent so that it's consistently rising. If the thrust is not increasing, I'll angle down a degree or two til it begins slowly rising again. Biggest issue is often in the 200 - 350 m/s range, wherein there often isn't enough speed to keep the positive feedback loop going, resulting in decreasing thrust. Some spaceplanes need to do a shallow dive at the point to build speed past the barrier, then pitch up again.

Typically, I will never activate my LF+O engines unless I am at least 1100m/s (1300+ preferred, but not always possible) and 20km+ altitude.

My end goal for this was to be able to SSTO, then perform both a Mun and Minmus fly-by, and return to KSC. I can almost do it, but I'm usually just a few hundred m/s of dv short :\ Of course, I could dock and re-fuel in LKO, but that kinda takes some of the fun out of it.

Is it the easiest way to do it? Not really. But it's fun

So it's definitely possible, it's just much harder than it was. I used to be able to SSTO with nearly anything... not so much anymore

Edited August 27, 2015 by Slam_Jones

[Alshain]

Ok, my bad. I mean a useful plane. It needs to have a purpose beyond getting a pilot to orbit, such as cargo hauling or even a crew cabin.

[Slam_Jones]

Ok, my bad. I mean a useful plane. It needs to have a purpose beyond getting a pilot to orbit, such as cargo hauling or even a crew cabin.

Does getting 8 tourists (or crew, even) to orbit (and slightly beyond) count?

Used to be able to do cargo SSTO's in 0.90 which could build stations piece-by-piece... not so much anymore :\

The good old days.

Edited August 27, 2015 by Slam_Jones

[Starhawk]

Ok, my bad. I mean a useful plane. It needs to have a purpose beyond getting a pilot to orbit, such as cargo hauling or even a crew cabin.

Have you taken a look at the Stock Payload Fraction Challenge?

There are some pretty good cargo spaceplanes in there.

Happy landings!

[Alshain]

Does getting 8 tourists to orbit (and slightly beyond) count?

Used to be able to do cargo SSTO's in 0.90... not so much anymore :\

That was a response to panzer, your post didn't show up till after I posted. I last did SSTO spaceplanes in 0.90 with FAR, but I'm about to give up on it now. I can't get up to speed above 12km, and getting up to speed below it has too much drag and eats too much fuel. The plane side of this game has definitely taken a turn for the worse I'm afraid.

[Slam_Jones]

That was a response to panzer, your post didn't show up till after I posted. I last did SSTO spaceplanes in 0.90 with FAR, but I'm about to give up on it now. I can't get up to speed above 12km, and getting up to speed below it has too much drag and eats too much fuel. The plane side of this game has definitely taken a turn for the worse I'm afraid.

Oops, me being awkward again... like seeing someone you think is waving at you, but they're waving at the person behind you...

The best I can offer is to try to level off in your planes "power band," a term I use to refer to the speed/altitude combo that provides the best boost before losing thrust. For mine, it's usually around 15-20km, during which I usually get from 600 - 1200 m/s, usually pitched at just about 5 degrees above horizon.

[Nich]

That was a response to panzer, your post didn't show up till after I posted. I last did SSTO spaceplanes in 0.90 with FAR, but I'm about to give up on it now. I can't get up to speed above 12km, and getting up to speed below it has too much drag and eats too much fuel. The plane side of this game has definitely taken a turn for the worse I'm afraid.

12km is the sweet spot for turbos and 15km for rapiers IMO

if your upset imagine how rocket people feel. Most are happy with 20% I feel SSTOs with less then 30% are pretty lackluster.

The great thing about KSP is you can always modify your files to give double thrust with double isp.

[Red Iron Crown]

Has anyone built a true SSTO spaceplane. I can't seem to find an ascent that works at all. I can build an SSTO jet assisted rocket with wings that looks like a plane, but does anyone have a plane with sea level TWR <1 that reaches orbit? Because, if not, there seems to be no point to spaceplanes in this game anymore, aside from shuttles. I just can't find a way and still have any fuel once I get to suborbital speeds.

I'll just leave this here (look at the TWR numbers during the ascent from Kerbin, and the considerable fuel payload in orbit):

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[ajburges]

That was a response to panzer, your post didn't show up till after I posted. I last did SSTO spaceplanes in 0.90 with FAR, but I'm about to give up on it now. I can't get up to speed above 12km, and getting up to speed below it has too much drag and eats too much fuel. The plane side of this game has definitely taken a turn for the worse I'm afraid.

There are plenty of resources for SSTO space planes now. Just limit your search to the past 2 months.

The challenge is that you only get about half orbital speed from jets. This means you don't want to spend much mass on them, but you still need the thrust to break the Mach barrier.

I find turbo jet SSTO designs easier to build and fly. They perform much better in the sub- and transonic range.

Assuming a relatively low drag craft, you want at least .6 "vaccum" takeoff TWR on jets. A more aggressive number to shoot for would be .8 TWR. Low TWR my need a little rocket/gravity assist to go supersonic, but the thrust curve will still give you 600 m/s supersonic acceleration and power through most the drag losses.

Once your jets stop accelerating you (near 19 km and 1.2 km/s) you will light rockets and pull up to establish a ballistic trajectory. The goal is to get an Ap of 50 km 30-120 s away. You want a rocket TWR of near unity to do this. Near 50 km burn until your Ap is at the desired orbit. You need roughly 1.6 km/s to orbit on rocket power.

My heavy lifters incorporate RAPIERs for efficiency, but the magic numbers are very similar. I have one heavy cargo SSTO that can take Orange tanks to orbit.

On RAPIERs: These either need discreet rockets, super streamlining, or over engineering to make Mach 1. That's why I consider them harder to work with. It is easy to get the impression that they can't go supersonic. OTOH, an overpowered RAPIER SSTO is a hoot. 2 crew SSTO + 650 m/s on 6 tons of fuel in 5 mins.

[Clipperride]

Some more great information thanks people.

My desire to try using Whiplash engines for the initial climb seems fruitless, unless I "cheat" and dump them at around 10km, with plenty of speed for the Rapier engines.

I solved the problem of having the CoM so far back, gear attachment became an issue, by simply switching to the inline cockpit (doh!)

One problem I sometimes have - deorbiting with little fuel and electricity, the plane can flip then go into a flat spin which is a real challenge to get out of. Is this a result of pilot error or having the CoM to near the centre of the vehicle?

At the moment, my space planes are only "recoverable" with a large clean up team with brooms!