SSTO Orange Tank Orbital Refuel-er?

[Claw]

Three words: Kerbal Joint Reinforcement.

Never have I had a problem with a serially staged rocket since installing that.

I haven't tried that yet, although the OP was wanting a space plane and not a serial rocket. Any experience using it on planes?

[Claw]

I'll race you to it

Tonight's efforts: Jackal II. My second iterations and it's not quite done yet, but here's a picture of it in orbit on it's second flight. First flight was aborted when Jeb discovered that nobody set up action groups and flameout sent it out of control. Although Jeb was able to shut down the engines manually and recover the craft, so at least it's stable at high altitude.

Needs some RCS thrusters (it has the fuel) and it wasn't the best ascent, but it's in orbit with a bit over 2/3 of an orange tank left. 76t on the ground and 50t in orbit with 24t of payload. So only about 31% payload at the moment. Need to fix the CG too.

Time to start work on the Jackal III.

Anyway, I'm not sure if this thread has been hijacked by now, but here's one example of how to get it done.

Edited January 31, 2014 by Claw

[Claw]

m4rt1n, the ammount of fuel you want to lift is a challenge for SSTOs. Record weight I've seen an SSTO lift was 40 tons, but it was using some totally unrealistic techniques (it had the wings copied so it was really two wings for the size of 1 and had an over 8-1 intake engine ratio, using B9). Sans rediculous techniques, best payload I've ever seen was 15 tons.

Now, I've tried without air hogging and wing clipping to deliver one of my standard fuel cans (standard docking port and 1.25-2.5m adapter OR Sr. docking port, large RCS tank, orange tank, same docking port setup on other end). I can put that in orbit without asparagus, as the whole thing, including rednezvous/docking upper stage, weighs less than 50 tons, which is starting to push my limits of single layer parallel staging.

Wait, I missed this before. Did you say you can put a large RCS tank and orange tank with Sr docking ports in orbit with only 50tons? Or was that 50t of payload?

[Captain Sierra]

Wait, I missed this before. Did you say you can put a large RCS tank and orange tank with Sr docking ports in orbit with only 50tons? Or was that 50t of payload?

No, it itself is a 40 ton payload. I can put that in orbit with about 150 ton lifter (which is probably an underestimate on the lifter since that would give me a 25% payload fraction on a standard rocket, making me a heavy lift god).

With a spaceplane, you could probably do it for 100-125 tons. Now, for a rocket SSTO (rocket with turbojet boosters), I've seen someone lift an orange tank with a 25 ton lifter (swear to God, I've seen it done). That's a 144% payload fraction, 12 times as good as modern rockets.

[m4rt14n]

Dang you beat me...

here's my futile attempt, still havent got it to orbit yet..

(I used your stacking ramjet inlet... )

[Captain Sierra]

First off, why are you using standard jet engines? They suck past 10km. Trade those out for turbojets.

In your initial ascent, climb harder. Climb 45 degrees off the runway to 10km. Level out to 25 degrees. Once you hit 20 km, your prograde indicator should be showing less than five degrees of climb. Air hog ascent profile 101: once at 20km, slowly climb and build speed until you get into the mid 30km range and 2000m/s It will take almost nothing with rockets to get you to orbit from that.

[m4rt14n]

First off, why are you using standard jet engines? They suck past 10km.

Ugh.... yea I keep on putting jet instead of turbojets...

DOh...

[Mobjack]

Here is a ship I used in a SSTO challenge. It uses 8 RAPIER engines, 16 intakes and is able to lift 12 tons of fuel into orbit.

Scaling this up, it would take about 20 to 24 RAPIER engines to get an full orange tank up into orbit with a two intakes per engine setup.

My initial goal was to get a full orange tank up with a design that doesn't use massive air hogging, but it is really impractical to do. My lifter can take up 3 FL-800 tanks into orbit while still looking good, and I was happy with that in the end.

If you really want to take up an orange tank up, then use normal rockets and staging and save yourself the headache. If you want the challenge of getting an orange tank up SSTO, first try with half a tank which will be a big enough challenge in itself. Then realize that a full orange tank lifter will have to be twice as big.

Edited January 31, 2014 by Mobjack

[m4rt14n]

I got close to 60% fuel and 35% oxidizer up into LKO with this behemoth finally... It did go into a tailspin (flamed out) cos I wasnt watching at 35km and I circularized too much (apo went up to 185km).

I think if I tinker a bit and fix the ascent it should have close to sending 50% fuel&oxidizer of a orange tank.

Not sure if it's possible without massing intakes though....

Edit: Here's final version. Oxidizer still less than fuel (not 1:1), but good enough I guess..

Edited January 31, 2014 by m4rt14n
add picture

[Captain Sierra]

My latest, the flying flapjack.

This girl is designed to put 6 tons in orbit. The latest iteration has a 3-1 intake ratio and is powered by 4 turbojets and 2 RAPIERs. For finishing circularization and orbital maneuvering, she's equipped with a single nuclear engine in the rear. Fully refuled, she could likely go to Duna on that nuke, perhaps with a small lander or with a satellite. I'll have to test that sometime when I finish the design. Right now, it's giving me large ammounts of lag even at 116 parts, which is really wierd and should not be happening.

[capi3101]

My own attempt did not go well. No screenies, pretty much the design I proposed earlier. She flew, but the pitch authority on the thing was practically non-existent; never did get it to go above 20 degrees and if I let off the S-key she'd immediately head for the horizon.

Lawn dart behavior, right? The CoL is too far back?

Like I said, I have no screenies of it; I'll see if I can get the .craft file up at least later this morning.

[Claw]

With a spaceplane, you could probably do it for 100-125 tons. Now, for a rocket SSTO (rocket with turbojet boosters), I've seen someone lift an orange tank with a 25 ton lifter (swear to God, I've seen it done). That's a 144% payload fraction, 12 times as good as modern rockets.

I'm going to try to do it for less. I'm shooting for 40% payload but we'll see. I haven't really messed with space planes this big yet so it's been fun learning.

I don't think you can have 144% payload fraction right? Unless I've been calculating wrong. 60%+ is still pretty awesome. I think you've also given me another challenge to check out after this.

[Claw]

Here is a ship I used in a SSTO challenge. It uses 8 RAPIER engines, 16 intakes and is able to lift 12 tons of fuel into orbit.

Scaling this up, it would take about 20 to 24 RAPIER engines to get an full orange tank up into orbit with a two intakes per engine setup.

My initial goal was to get a full orange tank up with a design that doesn't use massive air hogging, but it is really impractical to do. My lifter can take up 3 FL-800 tanks into orbit while still looking good, and I was happy with that in the end.

If you really want to take up an orange tank up, then use normal rockets and staging and save yourself the headache. If you want the challenge of getting an orange tank up SSTO, first try with half a tank which will be a big enough challenge in itself. Then realize that a full orange tank lifter will have to be twice as big.

Sweet, this looks cool. Kinda like a space plane glider.

I've heard a lot about "air hogging" but I've not actually seen anyone say how many intakes are required for "air hogging." I try to keep my intakes at 3 per engine, so I'm not sure if that qualifies. Other than that, I don't think I do anything that takes advantage of KSP bugs (like infiniglide). I actually don't mind part stacking either, but I don't do it myself.

As far as using normal rocket staging / headaches, that's the fun part! It would probably have been a while before I tried to get 36t of fuel into space with a space plane except someone asked.

[capi3101]

Here's the Auk VI craft file. Wasn't shooting for an orange tank with it, just half of one. Jets on #1, Rockets on #2, Intakes on #3-6, Solar Panels on #9, the back gear on #0.

Should mention that - I've got a set of gear aligned with the center of mass and another set further back to avoid tail strikes. So far the takeoff profile is 1) hit the brake, throttle up and fire up the jets, 2) close the intakes, 3) let off the brakes, 4) fold up the back gear at 80 m/s, 5) attempt to take off after 100 m/s. She will take off before hitting the end of the runway but the design is susceptible to tailstrike (as previously mentioned).

Issue: poor pitch authority. Rolls great, yaw is good, pitch sucks. This tends to come up a fair bit with some of my designs; some pointers would be appreciated.

And I don't want to hear anything about the intakes - I know it doesn't have enough.

[m4rt14n]

My own attempt did not go well. No screenies, pretty much the design I proposed earlier. She flew, but the pitch authority on the thing was practically non-existent; never did get it to go above 20 degrees and if I let off the S-key she'd immediately head for the horizon.

Lawn dart behavior, right? The CoL is too far back?

Like I said, I have no screenies of it; I'll see if I can get the .craft file up at least later this morning.

Most likely not enough wings. Is the AOA and prograde vector too far apart when climbing?

[Claw]

Edit: Here's final version. Oxidizer still less than fuel (not 1:1), but good enough I guess..

Martian, that looks great! Congradulations. I'm curious how much it weighs, because it looks like you did a better job of payload fraction than I did. It also looks like you have a lot less wing area that me. Looks good!

My latest, the flying flapjack.

This girl is designed to put 6 tons in orbit. The latest iteration has a 3-1 intake ratio and is powered by 4 turbojets and 2 RAPIERs. For finishing circularization and orbital maneuvering, she's equipped with a single nuclear engine in the rear. Fully refuled, she could likely go to Duna on that nuke, perhaps with a small lander or with a satellite. I'll have to test that sometime when I finish the design. Right now, it's giving me large ammounts of lag even at 116 parts, which is really wierd and should not be happening.

I like this too. This seems to be how I usually design, with the turtle back sandwich. I just like the way it looks. And I'm a fan of 3:1 intakes also, although my design above is ever so slightly below that. How much does it weigh on the runway?

[Claw]

My own attempt did not go well. No screenies, pretty much the design I proposed earlier. She flew, but the pitch authority on the thing was practically non-existent; never did get it to go above 20 degrees and if I let off the S-key she'd immediately head for the horizon.

Lawn dart behavior, right? The CoL is too far back?

Like I said, I have no screenies of it; I'll see if I can get the .craft file up at least later this morning.

Here's the Auk VI craft file. Wasn't shooting for an orange tank with it, just half of one. Jets on #1, Rockets on #2, Intakes on #3-6, Solar Panels on #9, the back gear on #0.

Should mention that - I've got a set of gear aligned with the center of mass and another set further back to avoid tail strikes. So far the takeoff profile is 1) hit the brake, throttle up and fire up the jets, 2) close the intakes, 3) let off the brakes, 4) fold up the back gear at 80 m/s, 5) attempt to take off after 100 m/s. She will take off before hitting the end of the runway but the design is susceptible to tailstrike (as previously mentioned).

Issue: poor pitch authority. Rolls great, yaw is good, pitch sucks. This tends to come up a fair bit with some of my designs; some pointers would be appreciated.

And I don't want to hear anything about the intakes - I know it doesn't have enough.

I don't have time to load it for a little while, but I'll see if I notice anything if someone doesn't beat me to it.

I find that poor pitch authority can generally be one of two things:

1) CoL is to far behind the CoM.

2) Not enough tail authority. I.e. Not enough tail section or not having the tail far enough back.

Also, like Martian said, it could also be that you don't have enough wing area to generate lift, or that you don't have enough thrust to push fast enough (and thereby you don't have enough lift). But I usually find this is apparent before I'm having pitch problems. If you have more than 10 degrees Angle of Attack at max speed at sea level, you're probably going to struggle at higher altitudes.

EDIT: Sorry for the stream of posts. I was going to do all these replies at once, but it was turning into a big mess.

Edited January 31, 2014 by Claw

[m4rt14n]

Vessel mass 61 Tons on the runway. 6 Turbojets and 2 Rapiers. 1 Orange tank, and 4 jet fuel cannisters.

All in all 52 ram jet intakes so about 6,5:1 ratio per engine. Not sure if I could use less intakes, action grouping them together is really annoying by the way. I should really swap 2 jet fuel canisters with 2 regular rocket fuel ones to end up with more oxidizers.

P.S: God knows if I can land this though....

Edited January 31, 2014 by m4rt14n

[capi3101]

You can put your intakes on the sides like that? Whoa...I thought they had to face forwards. I also thought angled twin faintails were supposed to be bad.

AOA is generally about 15 degrees for my designs - that was true with the Auk IV, though, and that was the one I flew to the Mün and back.

Tail authority? Could be it - I'm still more apt to think it's CoL too far back.

[Captain Sierra]

You can put your intakes on the sides like that? Whoa...I thought they had to face forwards.

They are facing forwards.

I also thought angled twin faintails were supposed to be bad.

They used to be but with tweakable control surfaces, it's no longer a problem provided you set up your control surfaces realistically.

AOA is generally about 15 degrees for my designs - that was true with the Auk IV, though, and that was the one I flew to the Mün and back.

Solution: MOAR LIFT.

Tail authority? Could be it - I'm still more apt to think it's CoL too far back.

looking at the design, CoM is more likely to move backwards, not forwards.Based on the size, a bigger rudder is in order or else you're going into a flatspin right quick when the turbojets go.

[Captain Sierra]

I like this too. This seems to be how I usually design, with the turtle back sandwich. I just like the way it looks. And I'm a fan of 3:1 intakes also, although my design above is ever so slightly below that. How much does it weigh on the runway?

I don't remember. It actually was not what I was going for visually, but it works. payload comes out the belly and is strutted in. It made orbit on the first proofing payload of ~4.7 tons. Ultimate goal is a proofing payload of 6.

[capi3101]

They are facing forwards.

D'OH!! Missed that.

They used to be but with tweakable control surfaces, it's no longer a problem provided you set up your control surfaces realistically.

So is there a benefit to using an angled fantail?

Solution: MOAR LIFT.

Hmmm...I was going of off numerobis's formulas for generating how much lift I needed (3 tonnes lifted per Swept Wing/Delta Wing, 1 tonne per Wing Connector/Small Control Surface) with the design. How much more would you suggest? What guidelines do you use? Would there be a benefit to doubling up on the wings (i.e. extend all of the Swept Wings out further with another set of Swept Wings)?

looking at the design, CoM is more likely to move backwards, not forwards.Based on the size, a bigger rudder is in order or else you're going into a flatspin right quick when the turbojets go.

How much rudder would you suggest? I also use TAC balancer these days, so I can keep the fuel levels in the jet tanks balanced pretty well during the ascent. Not sure how it'll behave once the supplies (side tanks) are delivered. I've had luck with reducing throttle as the engines approach the point of flameout. There's actually been some discussion on that very subject in another thread this morning.

[Claw]

You can put your intakes on the sides like that? Whoa...I thought they had to face forwards.

Those are all attached to the fuselage using cubic struts. So you can't attach them directly, but you can attach struts then stick the intakes on those.

AOA is generally about 15 degrees for my designs - that was true with the Auk IV, though, and that was the one I flew to the Mün and back.

Guidelines are just that. I find for my designs, above 10 degrees AoA and I start running into problems. Those problems can be fixed by a lot of things. More intakes, more engines, more wings, more rocket fuel, etc... Just depends on what you want...

I also thought angled twin faintails were supposed to be bad.

So is there a benefit to using an angled fantail?

It also depends on how you fly. They aren't strictly "bad," but can introduce some unusual flight characteristics. Sort of like controlling yaw with canards. You can do it, but it has other side effects.

There isn't a great benefit to using a fan tail that I would say "ah haa, use it here!" But I like the way they look from time to time. Also, if you angle them they give you a little bit of lift at the expense of some lost rudder authority/directional stability.

Hmmm...I was going of off numerobis's formulas for generating how much lift I needed (3 tonnes lifted per Swept Wing/Delta Wing, 1 tonne per Wing Connector/Small Control Surface) with the design. How much more would you suggest? What guidelines do you use? Would there be a benefit to doubling up on the wings (i.e. extend all of the Swept Wings out further with another set of Swept Wings)?

His numbers are good if you use them all. i.e. your Auk VI design does not appear to have 37 intakes on it. Less intakes means you need more engines or more wing area. It's a trade off. Personally I use 12t per engine, decrease the number of intakes, and bump up wing area slightly as the weight gets heavier. You can also stack wings if you don't want a huge wingspan.

[Claw]

My own attempt did not go well. No screenies, pretty much the design I proposed earlier. She flew, but the pitch authority on the thing was practically non-existent; never did get it to go above 20 degrees and if I let off the S-key she'd immediately head for the horizon.

Lawn dart behavior, right? The CoL is too far back?

Like I said, I have no screenies of it; I'll see if I can get the .craft file up at least later this morning.

Here's the Auk VI craft file. Wasn't shooting for an orange tank with it, just half of one. Jets on #1, Rockets on #2, Intakes on #3-6, Solar Panels on #9, the back gear on #0.

Should mention that - I've got a set of gear aligned with the center of mass and another set further back to avoid tail strikes. So far the takeoff profile is 1) hit the brake, throttle up and fire up the jets, 2) close the intakes, 3) let off the brakes, 4) fold up the back gear at 80 m/s, 5) attempt to take off after 100 m/s. She will take off before hitting the end of the runway but the design is susceptible to tailstrike (as previously mentioned).

Issue: poor pitch authority. Rolls great, yaw is good, pitch sucks. This tends to come up a fair bit with some of my designs; some pointers would be appreciated.

And I don't want to hear anything about the intakes - I know it doesn't have enough.

I tried to modify your AUK VI, but for some reason my KSP does not like symmetry on your aircraft. The wings get all messed up. Did you use any mods to build it?

Anyway, I would say you are right on with your assessment. Your CoL is way to far back compared to your CoM. It's causing your pitch trim to run at 7-8 notches at sea level which means you'll have a heck of a time up above 15km. That's why when you let go of "S" it drops. You can actually overcome this with certain flying techniques too, but it's probably easier to adjust your CoL. Also, with such a long plane you might need a little more pitch authority via control surfaces or a reaction wheel. I would actually recommend adding one more reaction wheel, but you can do it either way.

I can offer a few other tips too if you want them, but I hate telling people how to design unless they want it.

EDIT: By the way, I think you have plenty of intakes. Although I'm not sure why they are on different action groups.

[capi3101]

No mods were used for construction; they're all stock parts. I'm running KER, KAC, TAC, Crew Manifest, Protractor, Docking Alignment, and one of the Texture Reduction packs. And the TARDIS mod. Mostly piloting mods - I don't know why it would be messing up.

Tips are welcome; I'm golden with rockets but at best I'm an amateur with spaceplanes.

Intakes on different action groups...well, it occurred to me that an intake adds drag when it's opened, and if you go open thirty of 'em all up at the same time that's a lot of drag all at once suddenly placed on your craft. I don't know what kind of effect that has on flight characteristics; my understanding up to this point has been that it would cause me to lose velocity and therefore lift. Plus you don't need all that air all at once from my observation - you're generally okay with 0.05 to 0.07 units of IntakeAir per engine at full throttle. It lets me be more gradual about it. I dunno - could be a holdover from rocketry (rockets = stages, spaceplanes = intake events, that sort of thinking).