I can't make a spaceplane for my life

[MrAnonymous]

I've always had problems on making space planes. Does anyone have any suggestions?? Anything would help.

[Claw]

Well, what part are you having difficulty with?

This might be a good place to start if you are having a hard time understanding Center of Mass / Center of Lift relationships.

http://forum.kerbalspaceprogram.com/threads/65638-Basic-Airplane-Space-Plane-Aero-Tutorial

And that tutorial goes along with this other article. Which is well written by Keptin.

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

They aren't space planes, but it's a stepping stone if you don't understand the basics of aero. If you already understand all of that, let me know and I'm sure I can find more bits that discuss further details.

Also, are you using FAR? (It's a mod.)

[Kasuha]

And what exactly your problem is? How far did you get? Can you build a plane that can fly in atmosphere?

[MrAnonymous]

Well, what part are you having difficulty with?

This might be a good place to start if you are having a hard time understanding Center of Mass / Center of Lift relationships.

http://forum.kerbalspaceprogram.com/threads/65638-Basic-Airplane-Space-Plane-Aero-Tutorial

And that tutorial goes along with this other article. Which is well written by Keptin.

http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures

They aren't space planes, but it's a stepping stone if you don't understand the basics of aero. If you already understand all of that, let me know and I'm sure I can find more bits that discuss further details.

Also, are you using FAR? (It's a mod.)

I just downloaded FAR today

[MrAnonymous]

And what exactly your problem is? How far did you get? Can you build a plane that can fly in atmosphere?

I can fly in atmosphere just fine. I just cant get to space. Im not really good at balancing the "jet" fuel with the rocket fuel. That and also it takes me forever to get to space. I probably just don't know the ascent methods for space planes. I think sometimes I just make my plane too heavy for the amount of thrust is has. Also where exactly is the center of mass supposed to be? Is it supposed to be right in the middle of the plane or where the wings are or does it matter? I already know about the COL being behind the COM though.

[Northstar1989]

I can fly in atmosphere just fine. I just cant get to space. Im not really good at balancing the "jet" fuel with the rocket fuel. That and also it takes me forever to get to space. I probably just don't know the ascent methods for space planes. I think sometimes I just make my plane too heavy for the amount of thrust is has. Also where exactly is the center of mass supposed to be? Is it supposed to be right in the middle of the plane or where the wings are or does it matter? I already know about the COL being behind the COM though.

Screenshots would help a lot in identifying where there's room for improvement.

For reference, here's an all-stock spaceplane that I built explicitly to demonstrate building technqiues to a new player earlier. It's capable of getting to Minmus, landing, and returning on a single tank of fuel:

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As for your Center of Mass, ideally it will be in the center of the spaceplane- but there is a LOT of room for flexibility. The more important factor is where your Center of Lift is relative to your Center of Mass- ideally it should be behind your Center of Mass, so your spaceplane will stabilize towards the horizon in powered flight.

Regards,

Northstar

[Claw]

I can fly in atmosphere just fine. I just cant get to space. Im not really good at balancing the "jet" fuel with the rocket fuel. That and also it takes me forever to get to space. I probably just don't know the ascent methods for space planes. I think sometimes I just make my plane too heavy for the amount of thrust is has. Also where exactly is the center of mass supposed to be? Is it supposed to be right in the middle of the plane or where the wings are or does it matter? I already know about the COL being behind the COM though.

The location of the CoM doesn't strictly matter. You are already aware that the CoL needs to be behind the CoM, but make sure it's not too far back. Basically you'll want to build the craft and let the CoM be where it wants to be. Then design your CoL/CoT around that location, plus placing any RCS (if using it) in a relatively symmetric distribution around the CoM location. Balanced RCS makes orbital maneuvering a little easier, although SAS helps balance it for you.

FAR introduces a whole lot more considerations for airplanes over stock aerodynamics. With FAR, you also need to consider supersonic and hypersonic drag and CoL movement. I can't speak very well to all the FAR considerations because I don't use it.

[phoenix_ca]

FAR introduces a whole lot more considerations for airplanes over stock aerodynamics. With FAR, you also need to consider supersonic and hypersonic drag and CoL movement. I can't speak very well to all the FAR considerations because I don't use it.

To say nothing of mach tuck. -.- I recently put together a plane that takes a nosedive whenever it goes through transonic speeds. The simulator pointed toward the problem; I should've trusted it. *grumblemuttermutter*

[Kasuha]

I can fly in atmosphere just fine. I just cant get to space. Im not really good at balancing the "jet" fuel with the rocket fuel. That and also it takes me forever to get to space. I probably just don't know the ascent methods for space planes. I think sometimes I just make my plane too heavy for the amount of thrust is has. Also where exactly is the center of mass supposed to be? Is it supposed to be right in the middle of the plane or where the wings are or does it matter? I already know about the COL being behind the COM though.

There are two "extremes" how a spaceplane can get to orbit:

- burst out of the atmosphere as soon as possible, then use a lot of rocket power to circularize

- reach orbital speed still in atmosphere using turbojets (at 35-40 km altitude), coast to apoapsis and circularize

The first approach needs a lot of jet power but relatively small amount of jet fuel. You need to use the rocket still in atmosphere, the rocket engine you use needs to be strong and you need a lot of fuel because you'll need around 1500 m/s dv from it in a short time span. Usually you need two RAM intakes per jet but it may be possible with one. 13 tons of plane per engine or less.

The second approach needs less jet power but comparatively more jet fuel (it's still less than rocket fuel needed for the same dv). It takes long. Circularizing then takes almost no effort. Three RAM intakes per jet are good idea. One turbojet per 13-15 tons of plane.

Regarding fuel, get some extra liquid fuel and make sure the jet can steal it from the rocket if necessary.

[Heagar]

Your goal have to be to reach an altitude above 30 km (in standard KSP) - under FAR it will be much lower - to be under the weakesed possible amospheric pressue to gain the most speed for an orbital injection. There are several possibilitys to archive that:

• To have an intake spam to ensure that there is enough air intake to operate the jets even at low speeds at an higher altitude.
  
• To be fast enough even with the least ammount of intakes (two per engine) to sustain a considerable ammount of intake air (Can work up to 37 km with a speed of 2400 m/s in standard KSP). For that your TWR (for the jets) should be good enough to archieve that. To be on the save side, you can install three intakes per enginge.
  
• To climb (as Kahuha already mentioned) as fast as possible to be able to use rocket engines within a space where they can operate with the highest ammount of ISP possible. That is mostly a waste of fuel, because you have to build up the needed speed only with rocket engines. Witch means, you are using a great ammount of liquid fuel and oxediser only to achieve orbital speed.
  
• 
  

Witch soloution you choose depends on the mission profile you are working with:

• The most possible load into LKO: May be the intake spam. Because you save the rocket fuel for maybe refuelling a space station/tanker of some kind.
  
• To go fast into LKO for a quick interception or an "inspector plane" of some kind: It may be the fast climb method.
  
• But: To go to distant planets/moons you need a well balanced ship for saving the fuel for an trans xxx injection, landing at the destination and returning to home.
  
• 
  

One major fact you have to consider:

All parts in KSP have at least a drag of 0.2 points. Wich means, that a plane with more parts have an increased drag, forcing you to install more engines. That results in more fuel you need to operate them, more intakes (when opened, heavy drag) with an increased weight of the plane and - maybe - lower TWR.

The art of building a spaceplane is therefore to have an mission profile and building an plane especially for that task, maximising the chances for a succsessful mission. In short: Leave all parts behind you don't need for that paticular mission. Don't try to build a plane for all possibiltys that may occur.

And one thing more: Don't build only for the looks. Especially when it comes to the wings of your spaceplane. Because the kind of KSP wanting you to put it on your plane is the only direction in witch they will effectively produce lift, otherwise (attaching it in reverse e.g.) you have more weight and drag but not an increased lift (look at your CoL when attaching airfoils)! And some wings produce more lift that others at the same ammount of drag and/or weight, these you should prefer.

[lammatt]

enough lifting surface

wheels not too far from center of gravity

have enough fuel in the rocket stage (~1.5km/s at least)

[Hodo]

There is three styles of SSTOs you can build aside from the intake spam monstrosity.

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This one that I build when RAPIERs were new.

Notice there is no additional jet fuel onboard of the craft. And it has 2 intakes for the RAPIER in jet mode.

Then there is this, which does not have a Rapier or a nuke, but has 3 intakes per jet engine.

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And the Tail lander, which is MUCH more challenging to build and fly but no less interesting.

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Edited May 25, 2014 by Hodo

[DaMichel]

I can fly in atmosphere just fine. I just cant get to space. Im not really good at balancing the "jet" fuel with the rocket fuel. That and also it takes me forever to get to space. I probably just don't know the ascent methods for space planes. I think sometimes I just make my plane too heavy for the amount of thrust is has. Also where exactly is the center of mass supposed to be? Is it supposed to be right in the middle of the plane or where the wings are or does it matter? I already know about the COL being behind the COM though.

The further CoM and CoL are apart, the more steering authority you will need to keep the plane at a certain angle of attack. But other than CoM in front of CoL there is no strict rule. Since you are playing with FAR, keep in mind the the aerodynamic forces become distributed differently over your craft as you transition through transonic speeds. You'll have to familiarize yourself with the static analysis tool in order to see under what conditions your craft is (un)stable.

Getting into orbit with space planes takes longer than with rockets. Climbing up and accelerating can take a few minutes especially if your plane has low thrust. I usually climb steeply to 12 km and then level off at 20 km. With FAR you cannot get as high i guess. You might just manage to climb up to 30 km where the jet engines will run out of air. Two intakes are enough. I usually only look at the Mach number as far as speed is concerned. If you are above mach 4, that should be enough. Switch to rocket mode, nose up slightly and hope you don't run out of fuel

I suggest building something simple at first. A mk1 cockpit, a single long 1.25m tank, a RAPIER engine (they are pretty good actually, just not for IP traveling), delta wings and canards or a tailplane. Don't forget a vertical stabilizer. You'll need one with FAR.

(Edit: Hodo ninjad my post Very nice space planes. The first is about what i had in mind)

Balancing fuel can be a pain. But there are options. Add tanks symmetrically left/right/center. Use only few large tanks. Use tweakables: remove a bit of oxidizer for the time where you are flying through the atmosphere (just to save some weight). There is no extra extra jet fuel, it is all just liquid fuel. Try RCSBuildAid, it is an awesome plugin which can show you the dry and full CoM at the same time.

Example: Two large fuel tanks left/right, payload in the middle

Other example: Tanks aft and in front of payload. Such design has the advantage that you can pump fuel to the front/back in order to move the CoM.