Help-a-Whack: SSTO edition

[BubbaWilkins]

I'm curious to see this, as I have not yet managed to get a spaceplane of any real size to take off and make orbit.

[briansun1]

have the center of mass infront of the center of lift slightly

[StrandedonEarth]

Sounds like Whackjob is going for something on the scale of an Avengers-style HeliCarrier. Or is his creation going to make that seem puny by comparison?

I fear kerbquakes when (not if) that thing crashes!

[SuperBigD60]

I don't know about any general rules to really follow for building spaceplanes, as if you have a particular objective in mind you could probably make a plane to fulfill it.

I do know that once I started using FAR, it made designing planes a lot more intuitive. Harder to fly, mind you, but more realistic (ie more intuitive) to make work.

Just my musings, though.

[Dispatcher]

Wow! Whack is asking for advice, and I suspect he knows much more than he lets on. Nevertheless, here goes. First, please do not be offended when I suggest that you enjoy this pictorial tutorial on aerodynamics: http://forum.kerbalspaceprogram.com/threads/52080-Basic-Aircraft-Design-Explained-Simply-With-Pictures. You might find inspiration in the smallest (pun intended) of details. Next, again, don't feel bad when I suggest that you watch this 3 part series of Manley aerodynamics (Scott, that is):

. The above posts give very good advice. I'll just add that you might experiment with a variety of engines and see what results you like best.

Good luck!

[briansun1]

I fell that whackjob will need this...

[Sirine]

Thread 11 already provided the download link.

Seems that today I can play the invisible man. Im so unnoticeable...

[bsalis]

Oh boy, I don't know where to begin. Large SSTO Spaceplanes are just a pain. The game really needs to have big plane parts for big planes.

Anyhow, my only advice is you may want to look into using what I call a Boxkite style design (see old pic below). I think the design could scale up well. Note that there are two tank & engine clusters, one at the front and one at the back. This allows you to balance out the wet and dry mass. It's length means that the control surfaces are far from the CoM so you have good pitch authority.

[arq]

If you are willing to mod, Procedural Wings lets you make stock-balanced wings of any size. I use them on most all of my SSTOs, since the stock ones are so darn tiny and tough to build with.

[LordFjord]

Just bumped into this thread. Cant wait to see what Whackjob will throw at up.

Oh boy, I don't know where to begin. Large SSTO Spaceplanes are just a pain. The game really needs to have big plane parts for big planes.

Anyhow, my only advice is you may want to look into using what I call a Boxkite style design (see old pic below). I think the design could scale up well. Note that there are two tank & engine clusters, one at the front and one at the back. This allows you to balance out the wet and dry mass. It's length means that the control surfaces are far from the CoM so you have good pitch authority.

http://farm8.staticflickr.com/7285/8738327166_06e16caaa6_c.jpg

Nice SSTO there (honest opinion, I didn't go interplanetary with mine so far), however I see a few problems when you try to scale it up.

- fuel drainage and CoM: your CoM probably moves as you fly. SAS may be able to compensate for that on your plane, but when things get bigger, this is an issue

- landing gear: I guess you have some under the rear and front engines. could be an issue for heavier craft as it would snap the ship in half in the middle.

I am currently experimenting with my "huge" (for whack: "tiny") SSTO plane design of ~170 tons weight.

It is basically a huge Y-Wing-shaped craft. 2 Orange tanks as the Y-Wing Engines, from there built sideways, triple row of smaller tanks/engines with each wings attached and strutted.

The space between the engines makes a nice cargo hold.

The nice side-effect is, that the CoM almost never moves and keeps its relative position to the CoL, regardless if i empty the orange tanks or put some 40 ton cargo in the middle.

A bit similar to Whack's first pics of his plane.

The thing isn't perfect and finished yet, but it flies and behaves similar empty and loaded.

It still cant get to space, but I think I got the basic idea with the concept right, just need to find the right engine setup.

Currently 16 turbojets, 16 rapiers - this failed due to my bad atmosphere-space transition, some random spinning on engine flameouts, ... then rapiers started overheating and exploding. Note to self: Rapiers on quadcouplers get too hot to run beyond 50% thrust...

I'll post a pic of this horrible design later when @home - and maybe one of my working SSTO (70 tons and half the fuel left when in LKO)

[JumpsterG]

FIRST: Please get and use RCS Build Aid:

http://forum.kerbalspaceprogram.com/threads/35996-0-23-RCS-Build-Aid-v0-4-3-blizzy78-s-toolbar-support

It will display your dry center of mass in addition to your starting center of mass and helps IMMENSELY with making sure your center of mass doesn't end up somewhere you don't want after burning a lot of fuel. No parts or obnoxious elements, just a straight-up editor tool.

Just yesterday, I succeeded in designing and flying a stock SSTO spaceplane carrying 13 Kerbals (Mk2 cockpit + 3 hitchhikers). Takes off, lands softly (even fully laden), reaches orbit with 900 m/s dV, and has ejection parachutes to boot. I'm not at home, so I can't get the specs or screenshots for it, but I think it's dry mass is somewhere between 20-30 tons.

It's not so big (compared to other's designs), but I'm now scaling up 3x to a 37 Kerbal capacity (Mk2 + 9 hitchikers) and, surprisingly, I'm finding it's not that much harder to go bigger (with proper strutting; god help you if you don't strut well). The biggest problem I have found is that the number of wing pieces (total lift) required to takeoff and land gets ridiculous and it can be a struggle to find places to put them all without clipping or looking strange.

The best trick I have found so far is to extend the length of the plane by adding additional large fuel tanks at the back. Thanks to tweakables, you can adjust fuel load wherever you need to, so some tanks can be used just as structural elements. This gives you more room to attach wings and provides more flexibility for tweaking center of mass and center of lift, since parts and fuel can easily be moved more forward or backward over a wider area.

It's been said before, but I'll reiterate it: Putting your intakes at the back of the plane (behind center mass) helps maintain stability by a wide margin (inversely, having them up front will cause a tendency for the plane to want go backwards). This makes me want a fourth indicator in the editor: A center of drag indicator that shows the average of drag from all parts. Maybe I should throw that on the suggestions page...

Finally, I advise leveraging the massless-ness of the tiny cube struts when extending your landing gear below the plane. Since you will need some good clearance from the ground and will likely be using a lot of wheels, you need to avoid adding too much structural weight below the plane (this will cause center of mass not to line up with center of thrust, causing a nose-down force).

[Javster]

Thread 11 already provided the download link.

Seems that today I can play the invisible man. Im so unnoticeable...

Did someone say something?

[LordFjord]

Here's my 250 ton "Megamoth Mk IV" on a test flight with 15 tons of cargo (station science part). I was amazed that it indeed made it into orbit. It's far from finished, not very stable, it got into endless spins on reentry at ~10km altitude.

Anyway, here are some pics:

And from the back:

It is powered by 24 turbojets and 4 skippers, probably will need more and maybe a few nukes if i want to get it to mun. Currently 32 intakes, will need more of these as well.

The wheels could take a soft landing on flat terrain like around the space center.

Still in progress, but hey, it flies!

[Moar Boosters]

One thing I ran into: Wings of course have a direction of lift. I didn't think about that. Accounting for it will be... difficult. Not to mention the lander / wheel assemblies. That'll be annoying.

The easiest solution would be to just clad the outside with wingparts, like this thing I made.

This is the first of this design I've made. It takes off vertically but then turns sideways and builds up speed like a regular plane. It's around 300t but I don't think its anywhere near the limit. Shouldn't be to difficult to scale up to over 1000 tons. The only difficulty is the landing gear, or wheels if you're using them.