Tips/advice for building spaceplanes

[RocketScientistsSon]

So I have been playing KSP since about September last year and I am finally understanding the basic of building a rocket. Because I have been so focused on building and understanding rockets I have entirely neglected space planes. That is all about to change. Once I get the jet fuel parts unlocked I plan on trying my hand and building a plane.

So I have come to you all. The KSP community for any overarching tips and advice when it comes to building a spaceplane. I plan on starting small, namely building a plane that can get off the ground, and working up to successfully controlling said plane in the air and finally to getting one in orbit.

thanks,

[panzer1b]

1st things 1st, make sure its aerodynamically sound as a normal jet (for a beginner to SSTO/spaceplanes its best to start with a working jet and convert it into a SSTO instead of starting with space mode and make it work in atmo.

For a beginner spaceplane i strongly recommend the RAPIER engine. While it is inferior to the turbojet in general (and has rather poor range, u need nukes for laythe expeditions ect), it is the EASIEST method to begin learning how spaceplanes work, and its not that bad of an engine provided you want to just get into orbit and do some docking or rendezvous whatnot (i use it alot for combat SSTOs due to teh ability to accelerate in space very well).

You need to make sure ur center of gravity NEVER goes behind you center of lift at all times (or you get a plane that will do everything its capable of to flip backwards and fly backwards). Usually you want the CoL behind CoG by a little (and preferably mount fuel tanks so that CoG doesnt change too much, say a center mounting).

Intakes, make sure you have intakes. Ive found for efficiency you want approximately 0.01 intake/ton of craft. While many say its per engine, from experience, ive found that you need less intakes regardless of number of engines when you have less mass to obtain an equal AP on pure jet mode. so a 10 ton vehicle will most likely have 10 RAM intakes, others work, but are inferior in terms ofintake area/mass, so they add alot more dead weight one in space (ofc if you just want LKO/docking, this doesnt matter at all, but for say duna, laythe, ect, you need to use as much low mass as possible).

Make sure its able to take off, this means ADD WINGS! Wingless SSTOs arent going to be efficient in teh slightest. Im not the best person to ask what the best lift/mass is (as i tend to use very subpar lift rating and above average TWR). One craft i had recently has a TWR of about 2-5 depending on fuel loading, and has around 20 tons of mass (18 without ordinance), and has approx 9 lift rating total (less then .5 lift / ton, which i know isnt very efficient), but i did that as i couldnt clip 500 wings together and make it look right, i lie my stubby wings.

Anyways, all you really need over a normal jet is LFO storage, and RCS (optional unless you plan to dock to stuff)

[capi3101]

Here's a link to my general advice for spaceplane noobs - http://forum.kerbalspaceprogram.com/threads/100334-SSTO-Why-u-no-fly?p=1546536&viewfull=1#post1546536

Keptin's Basic Aircraft Design - Explained Simply, With Pictures is something I'd consider an absolute must read for anybody wanting to get started with planes.

Mod-wise, you might want to consider RCS Build Aid; it has a nice feature that shows just how much your CoM will shift in flight - which is one of many problems that usually squash the dreams of aspiring spaceplane enthusiasts. Not essential, but certainly handy if you're not adverse to mods; think of it as the KER of spaceplanes.

Edited December 15, 2014 by capi3101

[Geschosskopf]

So I have come to you all. The KSP community for any overarching tips and advice when it comes to building a spaceplane. I plan on starting small, namely building a plane that can get off the ground, and working up to successfully controlling said plane in the air and finally to getting one in orbit.

#1 Tip:

Build so that CoM moves as little as possible as you consume fuel and/or drop payloads. Your life will be SO much easier for that, not only for flying in the air but also for docking in space.

Concentrating on this will give you a plane that is easy to fly and will fly well in all regimes (launch, space, landing). However, you often won't get something that looks much like your typical hypersonic jet design here on Earth.

[RexKramer]

My advice is start small. And don't worry if you don't make orbit on your first try.

With spaceplanes, every change you make to one part potentially affects how you need to place other parts. That's one reason to start small. Large planes have lots of parts, making changes becomes tedious quickly.

With smaller planes, you can very quickly see how different parts produce different results. And it can be simpler to adjust the locations of your COM and COL- center of mass and center of lift. Their relationship is critical to a plane which flies well.

Although air-hogging may benefit you eventually, I don't recommend immediately jumping to put 10 intakes on a plane with one engine. One or two intakes for your first single engine jet should be plenty. Again, keep it simple at first.

If your goal is to reach orbit, you will need to make a plane fly really high and really fast before switching to a rocket. You'll probably want to reach 30,000 meters if possible, and speeds of over 1800 m/s. If you can reach those goals, one or two tiny 48-7S engines and a little rocket fuel should be enough to get to orbit. By the way, that is absolutely possible without air hogging. It's a little easier with 2 intakes per engine however.

I normally try to get to about 42,000 meters at 2300 m/s on jets, at that point a little nudge from a rocket gets me to orbit.

Anyway, my advice is start small. Once you get to orbit, you can start scaling things up if needed.

[Kesa]

It's a good idea to start small.

About the Center Of Mass/Lift/Trust

(1) COL very close to COM, so that the plane don't flipp up (COL too forward) or down (COL to backward), COL slightly behing COM so the plane naturally stabilize toward velocity.

(2) COT toward COM, quite obvious for simple plane, nearly impossible for stock assymetric shuttle

(3a) Constant COM : the COM of you fuel tank must be the same that the COM of your whole craft, so that (1) and (2) stay true over time. This can be useful.

(3b) Symetric fuel flow : if you are having several tanks, you don't want the fuel in front of the craft to be depleted before the one at the back. Three ways: building sideway, balancing fuel preferably not manually, and the stock way (my favourite).

For how many wings, fuel and TWR, it's alot of guess and trial, but you can start with TWR > 1.2, and enough fuel to take off before the end of the runway.

Also position at least 3 landing gear, and preferably 2 or more in the back, since they will likely be the last to take of and the first to touch down, and not too far behind COM, so your craft can steer up (and take off).

Lastely, some advice for high altitude :

(1) Have alot of intakes. It's try and guess, but an equivalent of 10 ram air intakes per engines is not too much

(2) basic jet die quickly upon speed and altitude. They can only build altitude, but no velocity, so go almost straight upward if you want to use them for ssto

(3) Advance jets : climb slow (~50-100m/s vertically), you will need horizontal speed to feed your air intakes and fight gravity. You should have burning aerodynamic effect.

(4) Throttle back when cutoff to reactivate engines and get the most of them.

(5) multiple engines : (4) is vital. Also shutdown some engines before throttling down, external first (those that makes more spins upon assymetrical cutoff).

(5b) neat trick : Orient your engines so that they do not push completly forward, but slightly toward COM.

Edited December 16, 2014 by Kesa
added stuff

[Vanamonde]

How to make a spaceplane:

Build, test, revise.

Repeat 10,000 times.

Seriously, it's a matter of patience and tinkering with balance until it flies well enough.

[LethalDose]

I would recommend Tip #0: Get FAR.

If you're going to be doing much of anything with aircraft in KSP, I'm solidly of the opinion that you should this mod installed. FAR allows planes that look like planes to fly like planes. You don't have to unlearn everything about aircraft you've learned your whole life just by seeing what planes look like.

It does a lot of other stuff too, but improved (read as "not idiotic") aerodynamics is it's primary purpose. If you want to get into the derivatives and coefficient graphs, super, but you don't have to.

[Northstar1989]

@RocketScientistsSon

This is probably going to run completely contrary to what you'll hear ANYONE else tell you, but since you're just starting out, start with the mods FAR and MechJeb2 installed:

http://forum.kerbalspaceprogram.com/threads/20451-0-90-Ferram-Aerospace-Research-v0-14-5-12-16-14

http://forum.kerbalspaceprogram.com/threads/12384-PART-0-90-Anatid-Robotics-MuMech-MechJeb-Autopilot-v2-4-1

This is for two VERY good reasons for each:

- You'll thank yourself later if you play with FAR now. The devs have officially confirmed that they will be overhauling the aerodynamics system before KSP reaches version 1.0 and if you get used to more realistic aerodynamics now, you'll have less adapting to do when Squad introduces their own improved aerodynamics model (though I doubt it will be quite as comprehensive as FAR, you'll have a *MUCH* easier time adapting from FAR than from the stock model if Squad does even a teardrops' worth of respect to how aerodynamics work in real life...)

- FAR is actually the more intuitive aerodynamics model in many ways, when it comes to building planes. IF you know what a real life plane looks like, you can expect it to work in FAR. Many designs that would NEVER fly in real life WILL fly in stock aerodynamics, on the other hand (I've literally seen a flying box), and many things that fly GREAT in real life won't work nearly as well in Stock Aerodynamics (for instance, one key effect is that Center of Lift shifts backwards as you break Mach in real life or FAR- meaning that real/FAR hypersonic aircraft can be built a bit more tail-heavy than in stock KSP aerodynamics...)

- MechJeb2 provides the two EXTREMELY useful features for Spaceplanes. The first is an ASAS system, similar to the one now part of Stock KSP, except that it *ALSO* allows you to set a specific Angle of Attack relative to your prograde vector or the horizon when in Surface or SVel+ relative modes... This will also take a LOT of the human error out of flying your plane (pulling too hard back on the flight stick/ S-key when trying to gain altitude, for instance), which will not only save you enormous amounts of headache, it will make it easier to figure out which plane design really flies better, and just wasn't tested when you were having a really good or bad day in KSP...

- MechJeb2's second ENORMOUSLY helpful feature is the informational readouts. Specifically, the Kerbal Engineer Redux-derived data screen in the Spaceplane Hanger, and the Surface Info screen when flying. The SPH readouts were actually originally taken directly from KER, and provide you with important figures like how long your engines can burn in the atmosphere, and what your TWR is (it even adapts to Sea Level vs. Vacuum TWR if you are running RealFuels- where Thrust varies with altitude instead of Fuel Flow, like in real life!) The Surface Info screen, which is only available when flying/orbiting/landed and not in the VAB/SPH, will tell you a number of key pieces of info about your plane's situation: such as the climb or sink-rate (how fast you are gaining or losing altitude) much more precisely than the stock logarithmic altimeter, your precise heading and Pitch/Roll (which is EXTREMELY useful if you are near maximum cruising altitude, and know your plane starts to stall above a certain Angle of Attack), and just how far you actually are above the ground (rather than sea-level)- which is IMMENSELY helpful when you are landing a spaceplane and coming in low over the mountains west of the KSC...

You'll thank yourself (and me) later, if you install and get accustomed to these two mods now...

Regards,

Northstar

P.S. DON'T try to use MechJeb2's Spaceplane autopilot features to get to orbit or land. Not only are these particular autopilots virtually useless, and will crash you more often than get you where you want to go successfully- they're also going to rob you of a lot of the learning of actually FLYING your spaceplane to orbit.

P.P.S. Flying with an ASAS is still flying- you need to know what Angle of Attack to set, how much to throttle your engines and when to activate your rockets, etc. Sometimes, you will even have to deactivate the ASAS and fly 100% manually, because *no ASAS system is ever perfect*, and there will be times where you can do it better on your own (although at other times, ASAS will improve precision and reduce human error).

Edited December 19, 2014 by Northstar1989

[RocketScientistsSon]

Hey guys, just wanted to update since I found the time to play yesterday finally! I read some other threads on basics to aeroplane building...

I actually got a plane off the ground and made it to the island runway!!!

Then I crashed...whoops.

But even so! That was so exciting! I do have some more questions.

1. The plane didn't actually get off the ground until the runway ran out. I noticed that the stock wings didn't have any of the moving parts you typically find a plane (elevons, they are called?). Is this why my plane wouldn't take off? I also noticed the pitch was horrendous while flying.

2. Every time i tried to turn my plane left or right while leveled out it wanted to completely roll so the wings were vertical. Any help with that would be nice.

thanks guys

[Norpo]

...I do have some more questions.

1. The plane didn't actually get off the ground until the runway ran out. I noticed that the stock wings didn't have any of the moving parts you typically find a plane (elevons, they are called?). Is this why my plane wouldn't take off? I also noticed the pitch was horrendous while flying.

2. Every time i tried to turn my plane left or right while leveled out it wanted to completely roll so the wings were vertical. Any help with that would be nice.

1. Elevons aren't on every wing, you'll want to add control surface parts to the wings. A large amount. You may also want to lower your front landing gear, so you start pitching up somewhat.

2. Completely normal, i'm pretty sure normal planes roll, then turn to the direction they want to go, so the center of lift is going the right way. Then, just roll the other way and be level again.

(hope this helps)

[capi3101]

Hey guys, just wanted to update since I found the time to play yesterday finally! I read some other threads on basics to aeroplane building...

I actually got a plane off the ground and made it to the island runway!!!

Then I crashed...whoops.

But even so! That was so exciting! I do have some more questions.

1. The plane didn't actually get off the ground until the runway ran out. I noticed that the stock wings didn't have any of the moving parts you typically find a plane (elevons, they are called?). Is this why my plane wouldn't take off? I also noticed the pitch was horrendous while flying.

2. Every time i tried to turn my plane left or right while leveled out it wanted to completely roll so the wings were vertical. Any help with that would be nice.

thanks guys

1. Well, it sounds like you didn't add any control surfaces to your craft; the stock wings don't include them (the only part that does at all is the Delta-Deluxe Winglet, and you won't want to be using that as a main wing body unless your plane is really, really light; as a control surface, I'll just say there are better options). The Elevon parts are the ones you want to add; I find Elevon 4 good for elevator controls and Elevon 3 makes a pretty good aileron. Standard Canard is a decent choice for a rudder. The AV-R8 winglet also works well as a rudder; never really have tried it for any of the other control surfaces but if your tech level's low you might give it a shot. KSP's stock aerodynamics also favors the use of canards up front to help out with pitch, but they aren't 100% necessary. The other thing you might be experiencing is having your rear gears too far back; you want them positioned so that they're slightly behind the CoM of the craft - too far forward and your plane will pop a wheelie before takeoff, too far back and your plane won't take off until it hits the end of the runway. Using the entire runway to takeoff isn't necessarily bad - you definitely avoid the risk of tail-strike entirely that way - but it is satisfying to see the thing take off much sooner.

2. Again, I'd have to see what kind of control surface you're using. But if you weren't using any control surfaces at all, I imagine that would have a lot to do with it. Not trying to be facetious here...

Edited December 19, 2014 by capi3101

[arise257]

1. Elevons aren't on every wing, you'll want to add control surface parts to the wings. A large amount. You may also want to lower your front landing gear, so you start pitching up somewhat.

2. Completely normal, i'm pretty sure normal planes roll, then turn to the direction they want to go, so the center of lift is going the right way. Then, just roll the other way and be level again.

(hope this helps)

There are a couple problems with the advice above:

1) You should add control surfaces to the backs of your wings, as many as it will hold across its length. "Lower your front landing gear" is a little confusing. It's easier to remember that the back gears should be mounted higher on the plane than the front gear(s). This causes the nose to be angled slightly toward the sky so that as you build speed on the runway, your plane will lift without even having to pitch up. If you mount all of your gears at the same height, you can either rotate the angle of attack on your wings upward to passively generate more lift (heavy crafts), or pitch up (hard) on the runway (light crafts).

2) This is isn't normal. If the plane is level and you just point the nose left or right, the entire plane should NOT begin to roll over. In my experience, this can be avoided by giving the plane a tail fin (or two) with a control surface. It will act as a rudder.

[RocketScientistsSon]

Thanks guys. I just read Keptin's basic intro to Airplanes. I probably should have done that before yesterday. It was really good. Very easy to understand albeit a lot of different concepts all at once.

Hopefully this weekend I can play some more and tinker with control surfaces and angle of incidence to get a better take off.