Help with spaceplane. :(

[Vanamonde]

Yeah, yeah. I know I post a thread like this every few months, but I *STILL* can't make an SSTO plane that works. Here's my latest failure:

Now my question is, is it failing to reach orbit because of the way I built it or because of the way I'm flying it?

Craft file:

http://www./view/rfyj7wgmxfrnffh/XSP-32.craft

Edited November 29, 2013 by Vanamonde

[EtherDragon]

It's hard to tell without some sort of reference to how you are flying it. Any way you could you-tube a launch with it?

[UmbralRaptor]

My immediate in-SPH question: why are the jets on 2 different action groups, and why is there no action group to toggle the intakes?

edit: okay, the other engine action group is for landing. But now I'm curious as to the very large amount of rocket fuel tankage. (Enough for an LV-T30 to power SSTO by itself, if it didn't have to carry so much other stuff!)

Edited November 28, 2013 by UmbralRaptor

[Vanamonde]

It's hard to tell without some sort of reference to how you are flying it.

If somebody else can get that craft file into orbit, the design isn't the problem and therefore I am flying it wrong.

Action 1 fires all the jets for maximal power on ascent, and action 3 starts up only the lower 2 jets because it doesn't need as much power to land and therefore can benefit from the slight nose-up torque of having the upper engine off. So during a flight the action groups are called upon 1, 2, then 3.

What's the benefit to closing some of the intakes? It's got more than enough jet fuel, so the extra drag of leaving them open doesn't hurt at low altitudes, and you want them all open at high altitudes, right?

[UmbralRaptor]

What's the benefit to closing some of the intakes? It's got more than enough jet fuel, so the extra drag of leaving them open doesn't hurt at low altitudes, and you want them all open at high altitudes, right?

As designed, this seems like the sort of craft where you can't/don't run the jets into a 75 x 30 km orbit, so the drag of open intakes hurts somewhat on the later portions of ascent.

That said, I'm still not thrilled by the huge amounts of rocket fuel it's lugging around, or that it's using an LV-T45. (The TVC tends not to activate if you're using action groups without staging, and is not all that necessary, given control surfaces and pod torque)

[The Destroyer]

I've made a few of these myself, I'll take a peak tommorow.

[Murph]

Try the Aeris 4A tutorial mission on the wiki:

http://wiki.kerbalspaceprogram.com/wiki/Tutorial:Aeris_4A_mission

Just load the stock Aeris 4A, and replace the supplied LV-T30 with the Toroidal Aerospike for the sake of sanity (it's difficult to avoid leaving the LV-T30 on the runway when you rotate during your takeoff). Launch, and follow the detailed step by step instructions.

Once you can happily get the Aeris 4A into a 100x100 orbit, you should be in a much better position to figure out what you're doing wrong in terms of design, and/or piloting for your own plane. It's pretty much the best of the stock aircraft, the only major flaw is the LV-T30 hanging off the back of it. With a few tweaks, it can be a really good 100km spaceplane (it's basically ok as-is, the tweaks take it from ok to good), and gives you a baseline to compare against.

[UmbralRaptor]

Hm. Almost got it into orbit (80 x 15 km), trying a revised design...

And it works:

Changes:

Replaced Mk1 cockpit with Mk2 (-0.25 t, improved stability)

Added another intake (+ .01 t, partially undoes that stability)

Removed FL-R25 RCS tank (-0.55 t)

Removed 8 RCS quads (-0.4 t)

Replaced LV-T45 with LV-T30 (-0.25 t)

Net savings: 1.44 tonnes (~6% ), 10 parts.

Unfortunately, it now has some instability issues (in-atmo at high speeds), and will pitch up while firing rockets.

I'm not entirely thrilled about the I-beams running along this thing's spine, but ditching them would require greater changed. (I was surprised by the strut running from the aft beam to the rocket engine...)

It's pretty much the best of the stock aircraft, the only major flaw is the LV-T30 hanging off the back of it.

And the dynamic instability (the thing is notably tail-heavy). And the lack of air intakes. Vanamonde mostly successfully avoided both flaws.

[Hodo]

Looks like you have some CoT vs CoM problems.

With that engine mounted on the top it will move your CoM up slightly but your CoT will change drastically when you switch to rockets. This is why you are pitching up.

I would start by trying to move that top engine downwards into the body of the ship or move another rocket engine up to it so you keep your current CoT.

[bsalis]

Again Vanamonde!

Anyhows, I took a different approach to other helpful peeps here and just flew your bird as-is (well, I just changed the Action Groups so I could close the intakes). Guess what, works just fine. Did a full orbit and landed back at the KSC runway. It's terrible, granted, but make no mistake, it is a fully K-prize capable SSTO Spaceplane. Only "trick" was that I used up almost all the jet fuel to cut down on mass during ascent. Had 14 units per tank before switching to the rocket motor.

Orbit!

Overshot, and needed to glide back.

[Murph]

It's pretty much the best of the stock aircraft, the only major flaw is the LV-T30 hanging off the back of it.

And the dynamic instability (the thing is notably tail-heavy). And the lack of air intakes. Vanamonde mostly successfully avoided both flaws.

To be honest, I don't see either of those flaws in the Aeris 4A. If you keep the nose within about 30-45º of the prograde vector, with SAS enabled, it handles ok, so the instability doesn't make it unfit for purpose (successfully doing a round trip from KSC to 100km circular, and back). The instability only really bites if you let it get out of the envelope in the first place, although I do prefer it with bigger canards on the nose, and a few other tweaks. Intakes? It's got more than enough to get past 20,000m, then more than enough rocket fuel to hit 100km orbit from there, de-orbit, and have a bit of fuel left for some atmospheric powered flight back to KSC.

[Col_Jessep]

I made a couple of adjustments but tried to keep the spirit alive:

Javascript is disabled. View full album

https://dl.dropboxusercontent.com/u/2449177/Kerbal%20Space%20Program/XSP-32%20A.craft

I'm not happy with her yet although I got her into space alright. She still flies like a brick and landing is no fun. She buckles and kicks. I think she could use more lift. If you want I can polish her up a bit more.

PS: Are you okay with part glitching? I can probably hide a lot 'under the hood' and make her look nice and clean.

Edited November 28, 2013 by Col_Jessep

[Col_Jessep]

Well, I was bored and started working on an improved version. I tried to keep the visual theme you were going for but one thing lead to another and she became a Big Girl.

She still needs some balancing and I have to check if and how much the center of weight will move back after you have used up all the rocket fuel. But I think I'm close.

[Nao]

I had no problems getting this nice craft into orbit.

Used flight profile was:

-ascent vertically until 10km

-turn with moderate speed to attitude 20 deg. (so that you don't get below 4.00 units of airflow on each of the intakes)

-accelerate at attitude between 20 and 15 deg keeping intake air above 2.00 U

-above 20km attitude should be 10-15 deg (with velocity vector at around 2-5 deg)

At this point its important to note that one jet engine needs 3,4 air to operate, since we have 3 intakes, each intake needs to produce at least 1.13 U for the engine to operate at full power.

For SSTO's it is also important to maintain vertical velocity while accelerating so keeping velocity vector of around 3-5 deg is very important

-at 25km with forward speed of 1500m/s, vertical speed of 100m/s and intake air of 1.5U per intake we can engage rocket motor.

-start throttling down before 1.2 intake air. We need 0.8 air for 2/3 thrust and 0.4 air for 1/3 thrust.

-below 1/3 thrust shut off jet engines, throttle to maximum and increase attitude to gain vertical velocity (around 20deg shoud do fine, we need more of it if our target orbit is low)

-coast, circularize and wave to the space station crew since we have no docking port .

In my test flight i had 2t of rocket fuel left (500m/s dV) in 74x74 orbit, with 292/450 of liquid fuel for the jet engines.

Edited November 28, 2013 by Nao

[Smidge204]

I also had minimal difficulty getting it into orbit, with fuel remaining! No modifications to the craft.

Lift off the runway and climb as steep as you can without letting your velocity decrease - starts at ~15deg off the runway and gradually you can get to ~40deg. By that time you should be around 20km and need to start leveling off to pick up speed without running out of air. You might even want to let off on the throttle a little bit since you have plenty of thrust but don't want to run low on air, or your engines will start to flame out and you'll go into a spin.

I managed ~1600m/s and ~22km before deciding to nose up and activate the rocket.

Once the rocket is on, nose up to gain more altitude and be ready to turn off the jets. Once one of the jets flames out immediately disable all of them and work to recover from the (hopefully minor) spin. I ended up flying about 50 degrees sideways but recovered easily.

From there it's basically point straight up to gain altitude. You'll lose a bit of horizontal velocity this way but once your Ap is over 75km you're basically home free. Cut the rocket engine and coast up (I aimed for 80km knowing that I'd be losing speed and altitude on the way up.)

When you're about 40 seconds away from Ap, thrust horizontally to start circularizing your orbit. Your AP will move forward and up, so I cut the engines and coasted up some more, trying to stay near Ap.

Even managed to deorbit and land back at KSC... though not in one piece. (Overshooting KSC by ~1/4 of an orbit did not do my fuel reserves any favors!)

=Smidge=

[Vanamonde]

I am confused. I thought the trick was to keep the engines running at altitude by spamming intakes, and while closing some would decrease drag, won't it also cause the jets to flame-out sooner? What fraction need to be closed, and why doesn't this cause earlier engine shutdowns?

trying a revised design...

What did you do to my baby?! You can't see out of that cockpit, and there's no plausible way for the nose intake to duct air to the engines. I like to keep at least a certain degree of realism. And it needs the RCS system because, if I can get it to work, I will later want to be able to dock it to things, and I'd rather not take those off, balance it, put them back on, and re-balance it.

I'm not entirely thrilled about the I-beams running along this thing's spine

But they make building/altering wings so much easier because it can be shoulder mounted without fiddling around with shift-WASD while moving wing parts. Also, the central fuselage can be altered or even removed without disturbing the wings. What is the nature of your objection? I agree that there's a weight penalty involved.

Looks like you have some CoT vs CoM problems.

Actually, no, it flies beautifully in plane mode. It requires a very light hand on the controls, but is stable and has a nice glide ratio after the rocket fuel is spent. That's mainly why I'm reluctant to make big changes to the configuration.

Again Vanamonde!... It's terrible

I apologized already! Yes, you fixed that previous one for me: the one that was the size of Nebraska. Aren't you at least pleased that this one is so much smaller?

landing is no fun. She buckles and kicks.

Are you talking about the bounce after touchdown? Because other than that I've found it to be pretty easy to land, even on fairly rough ground. I haven't tried it on the runway, though.

PS: Are you okay with part glitching?

No, feels like cheating to me, but thanks anyway.

I had no problems getting this nice craft into orbit...

I also had minimal difficulty getting it into orbit

Now you, you guys I like.

All kidding aside, I very much appreciate the time all of you folks spent testing my ship and giving feedback. I will try various permutations of these suggestions.

[Cruzan]

I am confused. I thought the trick was to keep the engines running at altitude by spamming intakes, and while closing some would decrease drag, won't it also cause the jets to flame-out sooner? What fraction need to be closed, and why doesn't this cause earlier engine shutdowns?

Basically you just want to close most of your intakes when you're in low atmosphere (<10km) to reduce drag, then open all of them once you need the extra air. You'll close them again once you switch to rocket engines. Also being able to close them helps for making re-entry much more smooth

I'm d/ling now so I'll give her a whirl. Sounds like others have got it working as-is though so it might be user error

UPDATE:

Works great! It's a little wobbly for my tastes, but that just makes it more engaging to fly

Tons of fuel to spare as well.

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Try out the previously posted flight profiles and if you still need help let us know!

Edited November 28, 2013 by Cruzan

[Sirine]

There are 3 categories of space-plane.

A) Major in rocket fuel. They fly well in space, mostly consist of LV-N engines. Keep the atmospheric part-count down, it is a dead weight in space.

Major in atmospheric flight. Small and light. They fly well in atmosphere. Need little thrust to get to LKO, as little as RCS gas is enough to bring it to LKO. or mostly Rockomax engines (30Kns little engines). And don't go out of Kerbin SOI. Landing to Minmus at most.

C) Both of A+B. And the space plane get large and heavy. They can go to Duna, land and back to Kerbin.

@Vanamonde in which categories, are you looking for?

[Vanamonde]

I was going for a fast climb to set a fairly high apoapsis on jets (hence 3 engines), and then circularize with the rocket. I may have over-endowed the rocket part.

I'm trying these suggestions, but finding it a real struggle to maintain the plane's balance.

[Col_Jessep]

I was going for a fast climb to set a fairly high apoapsis on jets (hence 3 engines), and then circularize with the rocket.

When you fly SSTOs you actually don't want to climb fast! You want to gain as much horizontal speed as possible and then 'sail' to your apoapsis on as little rocket fuel as possible. If you are seeing the airflow drop push down the nose! Once you have picked up enough speed you can start to climb again slowly. But as the air gets thinner you want to keep your nose mostly on the horizon until you switch to your rockets.

[Vanamonde]

A little background: I have tried many times to maximize horizontal speed before pitching up to transition from plane to rocket, and there are always control problems during the transition and often a profound loss of momentum as my direction of travel is forced up by control surfaces. But once while just derping around, I made an unmanned drone that achieved a 110,000m apoapsis simply by climbing 45 degrees on full throttle, and I was hoping to scale that idea up and add a rocket with which to circularize once I'd arced up to orbital height on momentum from the jets. Is that latter approach just impractical for a larger vehicle?

[Sirine]

I was going for a fast climb to set a fairly high apoapsis on jets (hence 3 engines), and then circularize with the rocket. I may have over-endowed the rocket part.

I'm trying these suggestions, but finding it a real struggle to maintain the plane's balance.

I will take it you choose option B.

So, below are for your consideration.

1) Light.

2) More lift, more wings.

3) Maximum 2 Turbo jet.

4) Little fuel for orbiting purposes.

5) Part count limit to 100.

6) Going really fast...MET 4~5 minutes, you should be orbiting.

7) Switch to rocket only at 30km.

8) Use Redial Intake 'Close' to cheat for the flame off issues. (optional)

9) 6~8 Air intake (RAM Air Intakes only) per turbo jet engines. (for you to climb to 30km, with > 2000m/s)

Example:-

The famous: FRANK-I (<---This plane can go over 2300m/s easily, just put some rocket engines 20 units of fuel is enough to bring it to LKO).

http://forum.kerbalspaceprogram.com/threads/50790-BSC-Ravenspear-Mk-1-This-time-for-real!?p=668836&viewfull=1#post668836

http://www./view/blfyvihdmvzy8y5/V1%20Craft.craft

Above both craft are LKO able, just need to add some thrust to let them orbit. Remember >2100m/s before switching to rocket engines.

[Cruzan]

A little background: I have tried many times to maximize horizontal speed before pitching up to transition from plane to rocket, and there are always control problems during the transition and often a profound loss of momentum as my direction of travel is forced up by control surfaces. But once while just derping around, I made an unmanned drone that achieved a 110,000m apoapsis simply by climbing 45 degrees on full throttle, and I was hoping to scale that idea up and add a rocket with which to circularize once I'd arced up to orbital height on momentum from the jets. Is that latter approach just impractical for a larger vehicle?

As long as you're okay with the efficiency loss, you can definitely design an SSTO to do this.

Design's like this:

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This one follows the exact profile you laid out, climbing at 45deg and transitioning from Jets to rockets at 18km. Info for the design can be found here: SSI Aeon (Not my design )

You just need high T/W and a decent amount of rocket fuel!

[Hodo]

As long as you're okay with the efficiency loss, you can definitely design an SSTO to do this.

Design's like this:

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This one follows the exact profile you laid out, climbing at 45deg and transitioning from Jets to rockets at 18km. Info for the design can be found here: SSI Aeon (Not my design )

You just need high T/W and a decent amount of rocket fuel!

I know most of my SSTOs can do this exact launch profile, it is not the most efficient use of them but it can be done. The trick is finding that right balance to get it right. In someways it is easier to do in the stock KSP then in some of the modded versions. In other ways it is harder.

And trust me we all started somewhere, here is my first successful SSTO.

The SP-301 "Orca", and I still use it today, granted it has had some improvements but it is the base for most of my SSTO designs now.

[Vanamonde]

I replaced one of the rocket fuel tanks with 2 structural fuselage pieces, so the shape and balance of the plane aren't affected but the weight is reduced, and replaced the gimbaled 200-thrust engine with the un-gimbaled 215-thrust, which is also lighter. Combining that with flying it right to the flameout point in level flight on the jets (c.1650m/s at 25,000), I was able to squeak it into orbit twice in a row. So there's still room for improvement in both the design and my flight profile, but it's improving.

(I haven't rejected the other suggestions helpfully offered here, but of the ones I've tried, the method above got the best results so far.)