Noob Spaceplane Questions!

[Tazin]

So after rocketing for a few months, i set out to try spaceplanes. I managed to build a SSTO mk2 with 2 whips and 2 rapiers. I attached a small satellite on top for a contract and it delivered fine. I ran a rescue mission on kerbin orbit and managed it fine.

But i tried to add a cargo bay with science and a cockpit with parachutes to my satellite, making it a basic lander for Mun, and ran short of orbit. This is my basic manouver, any help is apreciated:

-start both whips and rapiers, take off and climb at 30 or 40 degrees, to 10.000m

-level and break sound barrier, keep going up to 1000ms

-climb again at 20 degrees until engines run out of air, turn off whips and switch raps, keep going until i hit 75km apo

-circularize and drop payload.

-sometimes i drop payload and circularize just that, letting the plane fall back into atmosphere.

I added more fuel, switched engines, and played around, but it seems i cant get into orbit with a lander using the mk2 4 engine format. My lander currently uses the bigger 1.25m tank, so i guess it weighs around 6 or 7 tons.

A couple other spaceplane questions:

-what do engine precooler and engine nacelle do?

-i feel like i am designing blind on the SPH. I use KER for rocket design, and consider it essential. But i have no similar tool for spaceplanes. What do you guys recommend?

-I realize it is not really efficient, but is it possible to design a spaceplane that will do more than a SSTO? like a plane that will go to Duna and return on a single stage? or maybe just land on the moon and return?

-I'm still playing 1.0.2, should i upgrade before toying with planes? i understand the aero model is the big change in the upgrade.

thanks in advance for sharing the wisdom!

[SalehRam]

I'm not an expert, but I will tell you my experience:

• I never liked (or managed to like) to work with RAPIERS, I prefer to use Whips and climb fast like a crazy rocket (their thrust will get my AP to 75k while I am still below 20,000m sometimes if I do my ascending right), then use Swivels when I get out of atmosphere and make my orbit.
  
• Because of the previous point, my "SSTO's" are not actually SSTOs, they are 2 or 3 stages space planes... basically, for engines, if I used 4 Whips, I tend to connect 2 of them directly to a fuel tank, then I put 2 Swivels, and a stack decoupler after them, then the 2 remaining Whips, this way, I can get rid of 2 jet engines when I want to, to switch to rocket mode... while keeping 2 jet engine for atmosphere burn when I get back.
  
• For information on designs in SPH, KER will work, I only care about TWR from KER info, and basically, if you are on spaceplanes, 1.0+ TWR is good, for the planes I design in the previous point, I put TWR to 1.5, and that will be enough to put my plane on 75k with just Whips engines thrust, then, in space, I just monitor the levels of liquid fuel and I would know by then if I failed the ascend or I did it well... in SPH also, make sure your CoM does not get far away from CoL... you need to see all the possibilities of your plane by manually changing the fuel levels and see how the 2 variables move, then adjust your wings and fuel tanks locations until you get the perfect balance.
  
• Designing a space plane that can go planets is possible, however it will NOT go there without a stop to refuel in LKO, so a refueling station will be needed for that.
  
• Engine pre-cooler, and nacell I believe I red about them that they should have something to do with preventing engines from overheating quickly, but I did not see any effects for them (or maybe the effect was there but I did not notice it) they do provide air intake as well, and they have 40 units of liquid fuel, however, I use them as radial mounts for engines and intakes.
  

To get around with your issue with the lander and the SSTO, try the staged approach as I mentioned, unless you make a stage to drop 2-4 engines something can ruin a space plane

[selfish_meme]

RCSBuildAid set to engine, red circle is dry mass, important to design plane to be balanced when full and empty.

IntakeBuildAid balances intakes for performance and stop asymmetrical flameouts.

These days spaceplanes are a matter of maximising your in atmosphere speed. Two whips to a swivel, or a Rapier to 15t. One intake only per engine. Get your speed to max possible by 17km, as close to 1350 m/s as possible. Then switch when acceleration tails off and pitch up a bit for orbit, not too high or you lose effiiency through cosine loss.

Rapiers don't hit max thrust till over 400 m/s so you want to hit that as early as possible.

[Red Iron Crown]

A couple other spaceplane questions:

-what do engine precooler and engine nacelle do?

They are combined intake and fuel tank parts. I rarely use them but others seem to like them.

-i feel like i am designing blind on the SPH. I use KER for rocket design, and consider it essential. But i have no similar tool for spaceplanes. What do you guys recommend?

KER is all I use for data (though I use RCS Build Aid and Intake Build Aid as selfish_meme does for convenience). I've found spaceplanes to require many more test flights and trial and error than rockets. You don't need a ton of thrust for the air-breathing mode, I've made planes work that had a TWR of less than 0.5 at 0 speed/0 altitude.

-I realize it is not really efficient, but is it possible to design a spaceplane that will do more than a SSTO? like a plane that will go to Duna and return on a single stage? or maybe just land on the moon and return?

It is possible.

-I'm still playing 1.0.2, should i upgrade before toying with planes? i understand the aero model is the big change in the upgrade.

You should. 1.0.4 has reduced drag compared to 1.0.2, spaceplanes are a bit easier to build and can carry more useful payload than in 1.0.2.

[capi3101]

My designs tend to go either Whiplash/rocket or RAPIER; I don't generally put both on the same plane. 13 tonnes per engine if you go with RAPIERs, 15 tonnes per Whiplash. For the rocket phase, I'd recommend you plan for 1800 m/s of delta-V; that should be sufficient to get you into orbit, let you fiddle around a bit (say if you wanted to send the plane on to some kind of orbital rendezvous), and de-orbit. If you don't want to add fuel, go for a higher efficiency engine; Thuds work okay. I've also had luck with Aerospikes if you can handle their lack of gimbal.

Your ascent profile is sound, and the mods I would suggest have already been suggested to you - RCS Build Aid to let you see how your CoM is going to shift in flight (thereby letting you know if your plane is going to become more stable or more maneuverable as you go), and Intake Build Aid to easily side-step a known bug in how Intake Air is distributed to air-breathing engines thereby vastly improving their performance. If you only got one of these two, go with RCS Build Aid; it's really the KER of spaceplanes.

Of course, there's always the option of updating your aero model from stock to FAR. That's a whole other experience there, but FAR does give you a whole slew of data about your planes - the challenge being learning how to interpret that data, find potential problems and correct them.

Trying to think if there's any other mods I use for planes...I do use B9 Procedural Wings just because I like being able to make precise tweaks to my plane parts, but I wouldn't consider it an essential mod.

[ajburges]

In general rocket design on paper I like to visualize each stage as 3 components: engine mass, tank mass (fuel multiplied by 1+ dry ratio), and payload (everything else). This allows you to place bounds to find optimal layout for desired characteristics in a formulaic manner using the rocket equation and force equation. Expanding range is a manner of selecting a higher dV. Expanding mission is a matter of increasing payload mass. Creating a plane to go beyond LKO is a simple matter of dV. The approaches tend to be either a light payload and a nuke, orbital refuel, or a stop to mine at Minmus. I am working to develop a Duna capable rocket plane with mining equipment for my exploration of Duna. Once it's to orbit it won't need any support vessels; Duna SSTO gives enough dV for transfer, and the ore tank can hold enough to refine to reach Minmus after launch or Kerbin for return burn.

For design in SPH, I need to play with staging to change between aerobic and anaerobic values; KER does not understand mode changes in its calculations. I seek approximate a takeoff dV of 1600 m/s and .7 TWR with just rockets and determine desired LF surplus for aerobic operation empirically. In actual ascent, flight rocket dV and TWR is actually a touch higher after you burn jet fuel getting there.

The precooler like parts mix an intake and tank. For their mass penalty they really only offer 2 advantages: they can be stacked for aerodynamic occlusion and they can soak a lot of heat (useful to keep intakes in front of it from exploding).

For ascending the first 10 km of Kerbin, focus on keeping a speed of 250-270 m/s at full throttle. The faster you go, the more thrust you have, and you can maintain a better climb rate. Climbing faster will cause you to lose less fuel. My current Mk3 SSTO can no longer maintain that speed on jets alone with a full load from the combination of drag changes, (shielded) docking port installation on the nose, and additional airbrakes I added. It winds up being more efficient to tap the rockets to keep the speed above 250 on a more aggressive acent with the jets laboring to keep as much of that precious energy as possible. At angels 10 the rockets are used to boost me to 500 m/s and the jets can then get me to 1 km/s on their own. A few hundred rocket dV saved me from a more massive and complex redesign!

[Tazin]

Thanks for all the input guys. I read a few tutorials and videos, of people reaching 2000ms of speed and still going on jet power at 27km altitude, one guy stated the idea was to get as much of the circularization done on jet engines because of their extra efficiency. But later i read this is no longer possible after 1.0, since now there is a hard cap of 22km after wich jet engines will simply not work anymore. Is this true? i have not been able to go past 1500ms at around 20km, and that is with insane jet TWR of 3.0 at 0/0 . . .

Also, what would you recommend for more realistic spaceplane design: FAR, 1.0.4, or both?

[SalehRam]

Thanks for all the input guys. I read a few tutorials and videos, of people reaching 2000ms of speed and still going on jet power at 27km altitude, one guy stated the idea was to get as much of the circularization done on jet engines because of their extra efficiency. But later i read this is no longer possible after 1.0, since now there is a hard cap of 22km after wich jet engines will simply not work anymore. Is this true? i have not been able to go past 1500ms at around 20km, and that is with insane jet TWR of 3.0 at 0/0 . . .

Also, what would you recommend for more realistic spaceplane design: FAR, 1.0.4, or both?

At 22,000m jet engines have no use due to very low air compared to what is required by the engine to work, however, if you switch to rocket mode while your AP is still not high enough, then your ascend will not go well...

I had a nice experience with FAR in 0.90, but since 1.0 came and now on 1.0.4, I am getting some challenge with the stock aero, which I think is not bad at all compared to how it was before 1.0...

FAR will give you more realism for sure, but I'd say try both setups and see what fits you.

[Sharpy]

At 22,000m jet engines have no use due to very low air compared to what is required by the engine to work, however, if you switch to rocket mode while your AP is still not high enough, then your ascend will not go well...

.

That's not true. Well, half the time.

There are two schools of climbing to the orbit. A fish jump, and an arduous climb.

Fish jump is getting your apoapsis above the atmosphere and then using strong (and heavy and wasteful!) engines to quickly raise your periapsis - circularize, before you fall down. Rapiers, Swivels, Aerospikes even a Poodle, a Mainsail or a goddamned Rhino, all kinds of moderate-to-high thrust engines that can get you into a circular orbit in matter of two-three minutes before you lose your periapsis hard won with excessive power of jets. If you don't, you can still struggle through a significant radial component of your thrust but you're wasting lots and lots of fuel. So, one fast thrust, and if you're not in orbit, you're falling.

Then there's "Arduous climb" - you use the Nukes, LV-N. They definitely don't have enough thrust to get you into orbit in matter of 2-3 minutes, but they can keep burning for good half a hour. Plus they run on the same fuel as jets, and they are very efficient for space travel. But again, their poor thrust may be a significant roadblock.

In short: Using your jets, you reach your 1100m/s or so, climbing to some 20-22km, at a quite shallow angle, like 10 degrees. Then, when jets start losing to thinning air and drag, you fire the nukes, and keep burning. You need to gain another 1100m/s all the while flying through the air, climbing really slowly as your speed gets you more lift and less gravity drag vs thinning air, and eventually you reach the orbital speed while still embedded deeply in the atmosphere (some 35-40km) but it means your apoapsis is already in space and you're somewhere near the periapsis. Just burn a little against the air drag and you'll eventually reach the orbit and maybe 50m/s short of circularizing above 70km.

In that case a fifteen-minute climb is really not unheard of, and again, as you're fighting the drag, you may find yourself not gaining speed fast enough to get there before you run out of fuel.

Recently, I found a hybrid approach to work well. The two nukes were unable to overcome the drag of 25km, but of couldn't sustain a periapsis of 35km (never mind 70!), I added a single Aerospike and a rather small LF+Ox tank. It would push the plane from 1100 to 1600m/s and lift it to a 35km apoapsis. From there the nukes alone could keep it going, steadily raising the apoapsis and speed.

[SalehRam]

That's not true. Well, half the time.

There are two schools of climbing to the orbit. A fish jump, and an arduous climb.

Fish jump is getting your apoapsis above the atmosphere and then using strong (and heavy and wasteful!) engines to quickly raise your periapsis - circularize, before you fall down. Rapiers, Swivels, Aerospikes even a Poodle, a Mainsail or a goddamned Rhino, all kinds of moderate-to-high thrust engines that can get you into a circular orbit in matter of two-three minutes before you lose your periapsis hard won with excessive power of jets. If you don't, you can still struggle through a significant radial component of your thrust but you're wasting lots and lots of fuel. So, one fast thrust, and if you're not in orbit, you're falling.

Then there's "Arduous climb" - you use the Nukes, LV-N. They definitely don't have enough thrust to get you into orbit in matter of 2-3 minutes, but they can keep burning for good half a hour. Plus they run on the same fuel as jets, and they are very efficient for space travel. But again, their poor thrust may be a significant roadblock.

In short: Using your jets, you reach your 1100m/s or so, climbing to some 20-22km, at a quite shallow angle, like 10 degrees. Then, when jets start losing to thinning air and drag, you fire the nukes, and keep burning. You need to gain another 1100m/s all the while flying through the air, climbing really slowly as your speed gets you more lift and less gravity drag vs thinning air, and eventually you reach the orbital speed while still embedded deeply in the atmosphere (some 35-40km) but it means your apoapsis is already in space and you're somewhere near the periapsis. Just burn a little against the air drag and you'll eventually reach the orbit and maybe 50m/s short of circularizing above 70km.

In that case a fifteen-minute climb is really not unheard of, and again, as you're fighting the drag, you may find yourself not gaining speed fast enough to get there before you run out of fuel.

Recently, I found a hybrid approach to work well. The two nukes were unable to overcome the drag of 25km, but of couldn't sustain a periapsis of 35km (never mind 70!), I added a single Aerospike and a rather small LF+Ox tank. It would push the plane from 1100 to 1600m/s and lift it to a 35km apoapsis. From there the nukes alone could keep it going, steadily raising the apoapsis and speed.

Recently I was using fish jump without knowing its name then ... I found out this method by accident when I was messing around in sandbox, I thought to go crazy on Whips and created a plane, their thrust did put my AP at 75k while still below 22,000m, so when I got there I activated 2 Swivels and I got my orbit done.

[Sharpy]

on a separate note, I'm now really, really tempted to make a tiny SSTO using arduous climb profile with ion engines.