Launch Profile for spaceplanes

[Mustangrande]

So, now we have Horizontal takeoff capability and a spaceplane hangar. Has anyone come up with the optimal launch/climb profile to orbit for such a craft? (Or how to 'unstick' from the runway, for that matter? lol)

[vexx32]

Unsticking can be done by pitching forward until the rearmost wheels come off the runway, and then pulling back up.

As to optimal climb profile, there really isn\'t one at the moment. In the real world, having an angle of attack (angle to airflow direction relative to the plane, usually assumed to be just angle to horizontal) of over 16 degrees will stall the plane making it fall pretty quickly. In KSP, this mechanic is nonexistent, and wings continue to generate lots of lift at ridiculous angles. because of this, a good angle of attack simply depends on whether you\'re going for distance or height. if you want height, 60 degrees works well, but for distance, you might want around 30 degrees. An optimal one is actually much the same as a projectile -- 45 degrees.

[Mustangrande]

A projectile in a vacuum, of course. I think I\'m over-engineering the hell out of this spaceplane. So far, I haven\'t even come close to orbit.

[Vostok]

Everybody knows that the best way to unstick from the runway is to drop off the end of it, break something off the ship when you hit the ground and then drop off the cliff and just get enough airspeed after that not to land in the sea.

Ever since .15 the sea is full of broken spaceplane pieces.

[vexx32]

... OR you can attack some struts to prevent breakages when that happens. A lot of my planes tend to go off the end, so I\'ve learned to reinforce them for a bit of a knock.

[cardgame]

My planes can go off the end, but they always pull up in time without breaking anything...

[sneakeypete]

I\'m scratching my head about the best way to do this. get up to a really high altitude and use the high altitude engines? just get upto a medium altitude and hold it flat for speed? what is everybody doing?

[Temstar]

I use two turbojet engines to climb at 45 degrees. Then at somewhere between 8,000 to 9,000m I fire up my rocket engine and pitch up to about 60 degree to get up above the atmosphere as fast as possible. At 19,000m I switch off the jet engines and go purely on rocket. Then at about 40,000m I pitch down to pick up more horizontal speed.

The spaceplane I use is:

http://kerbalspaceprogram.com/forum/index.php?topic=12625.0

Surprisingly the weight penalty from bringing two deadweight jet engines from 19,000m to 70,000m is more than offset by the fuel saved in the first 19,000m, especially the first 8,000m where the plane uses pure jet power. I tried the same plane with two rocket engines and it can\'t even make orbit.

[Mustangrande]

I figured I\'d post back here with my solution to the unsticking problem; move your rear landing gear forward, so that they\'re closer to the point of balance. Then, use SAS to lift your nose slowly, and prevent a tailstrike. I\'ve found that this makes the difference between running off the pavement and taking off with a third to spare.

[Ed]

Also breaking at the start until your turbines spin up helps i can take off in stupidly short distances with my little jet plane. No Stol systems on it or anything.

Just going for deliberate short takeoffs i got off the ground before the end of the first white stripe.

[VincentLaw]

I figured I\'d post back here with my solution to the unsticking problem; move your rear landing gear forward, so that they\'re closer to the point of balance. Then, use SAS to lift your nose slowly, and prevent a tailstrike. I\'ve found that this makes the difference between running off the pavement and taking off with a third to spare.

This is correct. In real airplanes the main gear are close to the center of mass and hold around 90% of the weight of the airplane. So if you are 'stuck' it just means your landing gear are too far back so too much weight is on the nose gear. If the landing gear were placed too far back in real life, the airplane would also be stuck and unable to raise its nose for takeoff (This may also indicate you need more elevators). If you have a problem with tail strikes I recommend either putting the gear on pylons to make them longer or raising the tail up.

[RedDwarfIV]

My orbital spaceplane, the Vulcan, has an engine set-out comprising of two high-altitude jets, and two NERVA engines on either side. Of these, all the high altitude jets are on Tri-couplers, and two of the NERVAs take up the remaining spaces on the tri-couplers. The other two NERVAs sit on fuel pods positioned so they don\'t overbalance the craft.

I usually have it so that the NavCon highest efficiency marker [yellow circle] is at 45*. This ensures fast climb, whilst still using the wings for lift. However, it is not the most efficient flight profile.

[Bluejayek]

Everybody knows that the best way to unstick from the runway is to drop off the end of it, break something off the ship when you hit the ground and then drop off the cliff and just get enough airspeed after that not to land in the sea.

Ever since .15 the sea is full of broken spaceplane pieces.

The most amusing part about this is that the sea is full of floating broken spaceplane parts that are all made out of metal...

[Zephram Kerman]

The most amusing part about this is that the sea is full of floating broken spaceplane parts that are all made out of metal...

Makes you wonder about the (stuff we assumed was) water.

To avoid tailstrikes / sticking to the runway, I do two things:

1) tilt the tail upwards a couple of steps, and

2) put a fourth landing gear on it (just in case).

That way, I can rock forward and back to get unstuck, and nothing explodes (usually).

[Temstar]

2) put a fourth landing gear on it (just in case).

Delta wing aircraft tailstrike is a well known problem and a 4th tailwheel is actually quite a common solution. Here\'s a picture of Concorde with its tailwheel deployed.

[Mustangrande]

Delta wing aircraft tailstrike is a well known problem and a 4th tailwheel is actually quite a common solution. Here\'s a picture of Concorde with its tailwheel deployed.

And, as you can see, main gear well forward of the trailing edge, to provide a more balanced rotation.