Spaceplane troubles

[Neodyme]

Ok so I been trying for days to make a decent looking functional space plane, to no avail. Ive got it to where I hit 17km, but at that stage, it ALWAYS loses control, as in I cant pitch down or even hold my current pitch even with rcs on, as such I always end up flipping out and losing control.

Now I dont have ASAS but I do have the avionics package, as I find it easier easier during the ascent wheni dont have to keep toggling sas. But wheni flip out, the AP cant even maintain itself, and I end up spinning wildly also. If need be ill find a place to upload the file to look at, but from this info, any suggestions I could try to stabilize above 17km?

[Marcvs101]

I had a similar problem caused by fuel mass shifting from tanks on the front to the ones in the back. Try shifting that weight on the nose while in flight (basically transfer fuel to the front)

Try having the center of lift a bit behind the center of mass, and watch out when adding canards to the front: atleast from my experience the craft undergoes tumbling and becomes impossible to recover.

[Tex_NL]

There are several reasons you might loose control. One of them Marcvs already mentioned; shifting CoG. This can be prevented by both design and/or running fuel lines. Another reason can be an asymmetric flame-out but since you mention problems with pitch I too tend to a fuel imbalance problem.

If you can provide us with SPH pictures showing both CoG and CoL (preferably from multiple angles) I am sure we can find the root of your troubles.

[Neodyme]

Cool thanks ill try out the suggestions, if it works ill post pics in spess, if it dont ill post the cog col pics.

Just wasted 2 more hours of my life today when I tried to dock my two super solar blocks onto my station, alighning them perfectly to a point that it just slotted in. Ofc no magnetism cuz I then realised I forgot to add docking ports to the hub Q.Q

[Neodyme]

Ok I fixed (sorta) the whole spinning out of control, but now I run out of fuel before establishing an orbit, much less reaching my station. Should I add another compartment of fuel perhaps? (the fuel I run out of is Oxidizer, if only there was a vanilla oxidizer canister lol)

http://i974.photobucket.com/albums/ae221/Comet92/Spaceplane_zpse68849c5.png

[CalculusWarrior]

Yeah, spaceplanes are hard. I suggest spending as much time as you can in the atmosphere, and save your oxidizer for when you'll really need it (circularizing your burn). While still in the atmosphere, concentrate on getting your speed up to as close to orbital velocity as you can. I've found that around 20 km, you can get around 1.2 km/s of speed, while orbital velocity is about 2.2km/s. Whether you have this >1km/s of delta-v depends on your aircraft. However, if you find yourself lacking in delta-v, I suggest going higher. Simply strap on more air intakes, and try for a higher orbit, keeping an eye on your intake air by right-clicking the resources tab to keep it up. When you reach ~1.7 km/s or higher, that would be a good time to light the main engine and circularize your orbit. The less time spent burning your main engine, the better, as it leaves you with more fuel for exoatmospheric maneuvering.

[Neodyme]

Cool thanks. I watched a tutorial somewhere about the climb. Like start at 45 degrees until about 10-15km, then level out a bit and pick up speed in the atmosphere. Is that a godo starting point, or should I try to climb faster, shallower? etc

[Tex_NL]

Yes it is. Get to 10 km quickly then reduce climbing rate to pick up speed. Looking at your plane it should be able to go 1000+ m/s at 20km with relative ease

To make it a bit easier you could loose the radial intakes and replace the 2 cones on the rocket pods with 2 ram scoops. This ensures more available air at high speed/altitude, saves weight and reduces drag. You could also loose 2 or 3 out of the 4 RCS tanks to safe even more weight.

[falofonos]

If you're using turbojets then the 10 to 15km altitude is best of gaining serious speed. Lower than 10km and there's too much drag effect, higher and you will start getting flame outs.

With the current drag model, the more parts you have on your plane, the lower your atmospheric top speed will be, so try keeping the part count as low as possible.

Either isolate the jet engines from the rocket propellant tanks with non-fuel bypass connectors or use fuel pipes to reverse the drain of your rocket engine tanks to leave yourself with a reserve in proportion to the oxidiser.

I set an action group hotkey to shut off all the jets and close intakes, using this will reduce the minimal drag and the uneven flameouts before you switch to your rocket engines.

May be worth setting up a few for intakes so you can close them for the climb to 10km to reduce drag as well then open them up when you're starting to lose intake air higher up.

Mechjeb ascent data tells me that almost 30% of my deltaV is spent on overcoming drag in the atmosphere, so anything to reduce drag for the first 10km altitude will pay off in your climb to orbit.

[Neodyme]

How many intakes should I have?

and the reason I have those two cones is symmetry and also I have 1 Aviation Package on one of them <.< dunno where else to put it. I guess I could hide it somewhere where it wont matter? (I like the current cockpit, hate the tube one lol)

[Neodyme]

Ok I got it into space, mildly easily, however I run out of fuel to attain orbit, I tried 2 other variants adding additional fuel but it did not work, as it adds mass ofc, so any suggestions how to attain orbit?

I also have to use mono fuel to keep me straight as it still likes flipping out and stuff, so if this czn also be corrected thatd helpa lot too

[Vanamonde]

Rather than adding rocket fuel, try increasing the speed you attain in the jet phase of the flight with more engines and or intakes. The same amount of rocket fuel may then be enough to circularize.

[M5000]

How many intakes should I have?

I've found that a good, safe number of RAM AIR intakes should be about 3 for each engine, maybe 2.5 (say if you have a two engine craft with 5 intakes). I know it's possible with less intakes, but a good number is 3 per engine and will give you a pretty good heads up.

[Eric S]

I've found that a good, safe number of RAM AIR intakes should be about 3 for each engine, maybe 2.5 (say if you have a two engine craft with 5 intakes). I know it's possible with less intakes, but a good number is 3 per engine and will give you a pretty good heads up.

I thought I might be overdoing the air intakes at 5 per engine. Good to know.

[M5000]

I thought I might be overdoing the air intakes at 5 per engine. Good to know.

Good lord.. Yeah at that point, you're actually probably making your engines work harder than they need to due to the drag of the intakes...

[Neodyme]

Ok cool. When you say RAM intakes, does that also include Radial? as I don't fancy creating like 15 engine nacelles haha >.<

[Eric S]

Good lord.. Yeah at that point, you're actually probably making your engines work harder than they need to due to the drag of the intakes...

Yeah, my first hint that I had overdone it was even though I was opening the 10 in pairs, the last 4 wound up getting opened at almost the same time because the atmosphere was fading so fast.

[Neodyme]

Ok, so I reduced it from about 30 (I ahve 5 jet engines) to 20 and I get maybe 1km higher before any issues. When I had 30ish, I was able to get to low orbit (but ran out of Liquid fuel before I hit orbit regrettably) but for some reason (and I can't figure out for the life of my why) I keep spinning out of control. It seems to be between 15-20km, dunno if its my speed, or there lack of for the drag at that altitude, or what. everything is symmetrical.

Ive uploaded my craft, If someone wants to take a look at It, see where Im going wrong thatd be appreciated. Its running the laser, fuel distribution and BS9 aerospace mods I believe.

heres the craft: http://www./?36pisw8vjj9ti9e

[bsalis]

Ok, so I had a look at your original picture...

as such I always end up flipping out and losing control.

I would say your center of drag (COD) is too high. Ram scoops are not very good either. If you do use them, then don't have them all on top like that, put some on the underside to balance the COD, ideally behind the COM too. The other reason it's pulling up would be the COM is moving backwards as the jet fuel drains from the front tank. So perhaps move the COL back a bit... or disable the front jet tank for initial flight.

And I have more advise...

* Nosecones and other pretties add dry mass and reduce performance.

* You only need one ASAS. It's more dead weight having three!

* You have more RCS fuel than you need. More dead weight!

* I think proportionally, you have more thrust than needed, in both Jet and Rocket power. (ie. possibly want to add more fuel)

* Mebe want some more control surfaces (especially if you add more fuel and more lifting surfaces)

* You have a lot of jet fuel in proportion to rocket fuel. That's fine if your going for a high altitude screamer. However to do that you need a lot more air intakes.

* No need for so many RCS ports. If done right you will not need it to pitch up, or just a regular fitout will be enough.

* Control surfaces work better the further they are away from the COM. You have quite a few near it... on angles.

* No need for dual fuel lines... one is all you need.

[Neodyme]

Hmm thanks for the help, but that image is actually an old overwritten design, I should update pics, but regardless the advise will help the new design,.

Regarding the intakes, how do I add more ram intakes without creating more engines etc, or is there no way?

[PolecatEZ]

Hmm thanks for the help, but that image is actually an old overwritten design, I should update pics, but regardless the advise will help the new design,.

Regarding the intakes, how do I add more ram intakes without creating more engines etc, or is there no way?

You can do that in a few ways, all of them seem a little cheatish but work well:

1 - Non-cheat: Use nacelles on your wings with a ram intake in front. This gets a bit bulky after a while.

2 - Clipping some (my method): Use a tiny lattice connector (forget what its called) in front of the intake, pull another on top of it and attach it.

3 - No clipping, but tacky: Use those same tiny lattice connectors, line them along your wings, and just put the intakes there one-by-one.

4 - Clipping a lot: Just stack the intakes one on top of another in the same place as you already have them -or- just put them anywhere clipped between everything. The game doesn't care where they are, just what direction they're pointed in.

Now go forth and ram that air!

[bsalis]

1 - Non-cheat: Use nacelles on your wings with a ram intake in front. This gets a bit bulky after a while.

If you design the craft to use many small tanks, you can fit quite a lot of intakes. For example, I call this a boxkite style design...

So that is 12 intakes for 5 engines. Could probably have 16 using those bi-adapter thingies. Having two mount points like that also lets you spread out the engine mass too.

[Neodyme]

Ok cool thanks, I didn't think about the bi coupler. Would 10 intakes be suitable (minimally) for 5 jet engines you think?

Also whats that rod looking thing on top at the back? 0.o

[K^2]

2:1 tends to be a good ratio, yes. Gets you to about 20-21km on full throttle. (Depending on speed.) You can get higher if you cut throttle and fire up the rockets.

Also, I'd practice with smaller SSTOs first.

[bsalis]

Also whats that rod looking thing on top at the back? 0.o

Landing gear...

2:1 tends to be a good ratio...

Yeah. Agree. But some people go nuts and put 5:1 or more. I suspect Squad will do something about that one day.