My newbish spaceplane efforts: suggestions for improvement?

[Mister Spock]

Thanks for the link. That's a beautiful plane! I've been using the nacelles for engines, but hadn't thought of putting ramscoops in the front half. Thanks for the suggestion.

Incidentally, I have trouble getting the nacelles to "look" right on the (or under) the wing. They seem to attach in only one place, and they almost hover over the wing. It's the same almost cosmetic issue I have with control surfaces, which hover a couple inches above the wing. But I'll keep at it.

[Wanderfound]

Thanks for the link. That's a beautiful plane! I've been using the nacelles for engines, but hadn't thought of putting ramscoops in the front half. Thanks for the suggestion.

Incidentally, I have trouble getting the nacelles to "look" right on the (or under) the wing. They seem to attach in only one place, and they almost hover over the wing. It's the same almost cosmetic issue I have with control surfaces, which hover a couple inches above the wing. But I'll keep at it.

If you're attaching directly to wings, you could use pylons. Or, if they're close to centreline, attach them to the fuselage instead. Turn off angle snap and use the rotation controls and you should be able to get them where you want them. Be careful of off-centre thrust, though.

[Wanderfound]

The other option is to build the wings around the engines, as the D7 does it: http://forum.kerbalspaceprogram.com/threads/88628-Kerbodyne-D7-Heavy-X5-a-heavy-lift-SSTO-spaceplane

[allmhuran]

There is a ram-scoop attacher part, BTW: the nacelles. It's what they're made for; intake on front, engine on back. You don't need five hundred ramscoops to go to space.

Yep, intakes on the front of nacelles look pretty sweet and I will use these as the body to which an air intake is attached if I'm going for aesthetics. I'm not sure how well they scale with airspeed, I know someone did an analysis a while ago and RAM air intakes are a very clear winner in terms of efficiency, so using the nacelles might make things a bit more difficult.

If you want to efficiently lift silly things with spaceplanes then air hogging is pretty much required. But if you just want a functional SSTO then it's certainly not a necessity.

One tip if you do throw on a bunch of RAM air intakes: set up an action group or two to toggle subsets of them on and off. You don't need them all open at low altitude, they'll just be adding drag. Open up groups of them as you ascend for ultimate efficiency!

[Wanderfound]

If you want to efficiently lift silly things with spaceplanes then air hogging is pretty much required. But if you just want a functional SSTO then it's certainly not a necessity.

It depends in part on your definitions of "airhogging", "efficient" and "silly"; you can get a 100+ ton payload up with something that still looks like a real plane. I generally limit myself to one airscoop/nacelle combo per engine (not as limiting as it sounds, as I usually shut down as many engines as possible and concentrate the air once I'm at 30,000m; this gives the D7's pair of turbos eight ram/nacelle combos to draw on), and make up the slack with radials if necessary.

But yes, there is a performance tradeoff for aesthetics and realism. I'm happy to pay it; not everyone is, and that's all cool. One of the greatest strengths of KSP is its open sandbox nature. Everybody gets to play the game that they want to play, not the game that some marketing wanker thinks you should play.

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The other reason for setting your intakes to a few action groups is that this allows you to use them as air brakes during reentry. Open intakes to slow down, close intakes to speed up. They have a dramatic influence on drag.

[Hodo]

Double post.

If you want to efficiently lift silly things with spaceplanes then air hogging is pretty much required. But if you just want a functional SSTO then it's certainly not a necessity.

One tip if you do throw on a bunch of RAM air intakes: set up an action group or two to toggle subsets of them on and off. You don't need them all open at low altitude, they'll just be adding drag. Open up groups of them as you ascend for ultimate efficiency!

I call shenanigans on that.

You can use a 1:1 ratio if you built the craft correctly or better. I have a SSTO space plane right now that hauls 40 tons into orbit and it has a 1:1 ratio of intake to air breather engines.

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There are 4 intakes on the wings, and 4 under the wings, for a total of 8. There are 4 RAPIERs and 1 SABRE-M which is a 2.5m RAPIER, and has 4 times the power and air requirements.

And that is just one of my .24.2 space plane SSTO.

I currently have 9 that are working and working on a new one almost every day.

Edited August 4, 2014 by sal_vager

[Laie]

I kinda wish there were a ram-intake-attacher part.

Like the cubic octagonal strut? Oh, wait...

A further question: I find myself using the little cube struts to attach ram scoops. And I've used a plate, or a long thin stick, to attach the rear landing gear. Are these sort of kludges unusual?

I've done similar, and have seen it in other peoples screenshots as well. Behind-the-rear-wheels (a.k.a. tailstrike preventatives) appear to be all the rage.

Along the same lines, my small control surfaces seem to hover about six inches over the wing. They work; they just look strange.

Turn OFF angle snap when attaching control surfaces; they may still attach a bit high or low, but not by as much, and careful mousing will let you get it just right.

[allmhuran]

I call shenanigans on that. You can use a 1:1 ratio if you built the craft correctly or better.

Do they all use mod parts like this one? You can't post a modded craft, or a craft that uses modded physics, and assume the capabilities are directly comparable. People have put 3+ kiloton payloads into orbit using rockets even before the SLS parts came out, because mods.

I currently have 9 that are working and working on a new one almost every day.

How much fuel are you using to do it? Edit: NVM, I see you are using FAR, so you are indeed using different parts and different physics. You might as well be playing a different game. No comparisons at all can be made here.

Edited August 4, 2014 by allmhuran

[Mister Spock]

I made more progress yesterday. First I tried a twin-hulled P-38 style fuselage, with lots of struts, but I didn't put enough ramscoops on it; I'll revisit that today.

I had more success just designing a simple aircraft just to practice getting to orbit and home safely. I *almost* got this one into orbit, but I ran out of oxidizer and had to return home. (Pics below.) I put the fuel tanks along the centerline, with the outer ones feeding the inner one, and lots of ramscoops. I wish there were some visual guide to drag in the SPH; I suspect I had too much drag up front and not enough in back, and too much drag altogether at lower altitudes. I might try disabling a couple ramscoops at lower altitudes, as one of you guys suggested.

Not sure of the optimal angle of ascent from KSC. Again, I think drag was slowing me down. I only just managed to reach takeoff speed, and my prograde vector was always below my nose.

Here it is on the factory floor.

Also, I had lots of trouble on re-entry: I basically lost control over the aircraft. Should I be trying to re-enter on a shallow glide path? As it was, I basically shut off my engines until I could get enough air intake, as I'd almost run out of oxidizer, and by the time I had air, I was already tumbling toward Kerbin. I gather that some people regard it as an abomination to include chutes on aircraft, but I try not to "revert" my designs, so I want to recover something. This is, incidentally, the main reason I keep designing aircraft with ugly unmanned pods instead of elegant cockpits.

[Hodo]

Do they all use mod parts like this one? You can't post a modded craft, or a craft that uses modded physics, and assume the capabilities are directly comparable. People have put 3+ kiloton payloads into orbit using rockets even before the SLS parts came out, because mods.

How much fuel are you using to do it? Edit: NVM, I see you are using FAR, so you are indeed using different parts and different physics. You might as well be playing a different game. No comparisons at all can be made here.

Yes I use FAR, and yes I use parts packs, because the stock parts are hideous. Many of those parts I use are heavier, and provide less power then the stock parts. Like the B9 cockpit on that craft I posted, it weighs more then the 3 kerbal capsule, currently it comes in at 3.9 tons. Stock wings are overpowered, and provide way more lift then something there size should. The stock jet engines, are so overpowered that you can not find a real life counterpart in any part in world history. There is no turbojet engine that weighs in at 1 ton that creates 150kn of thrust and is only 1.25m by .5m.

And because you have most likely never bothered to even research FAR, you probably don't know that it nerfs ALL air breathing engines. It reduces their power to 50% of stock so you can't take a turbojet to Duna. And it fixes the infiniglide and krakken drive systems so they don't work.

I also use DRE, Deadly Re-Entry, does that make the game easier also?

What about Remote Tech 2?

Tac Life Support?

If you want to nit pick about things perhaps you should do some reading first.

And people, or just Wackjob have put 3+kiloton payloads into orbit using only stock parts, and the famed broken asparagus launch system.

[Wanderfound]

How to fly a spaceplane to orbit:

1) Get to 20,000m however you like. Around a 45 degree climb is probably most fuel efficient, but jet engines use so little fuel that it doesn't matter much. If the plane has enough power, I usually climb at 75 degrees or so just to get it done quickly.

2) When you get to 20,000m, level off and build some speed. You want to pile on as much horizontal velocity as possible while you make a slow ascent to 30,000m. Keep your angle of attack (the angle between where your nose is pointing and the direction in which the plane is actually moving, shown by the prograde marker when in surface mode) and climb rate low; by the time you hit 30,000m, they should both be around 10 or so. A low angle of attack reduces drag and helps your intakes work better. The low angle makes you climb slower, but that's okay; you need that time to get up to speed. As you go faster, the angle of attack required to maintain a given climb rate reduces, but as you go higher, the thinner air means that the angle of attack required to maintain a given climb rate increases. If you do it right, these two factors will roughly balance each other out and you should gain the necessary speed and altitude in a single smooth climb. However, a plane with some aerodynamic or piloting flaws may need to bounce up and down between 20,000 and 30,000m a couple of times while building speed before the final push.

3) Somewhere between 20,000m and 35,000m (exactly when depends on both plane and piloting), you'll start to run short of air. Don't switch to rockets immediately. If you've got multiple engines going, shut some down to concentrate the available oxygen into the ones you keep running. If you've already shut down as many as you can, throttle back a bit. You can dramatically increase your jet-only altitude by doing this, and once you get up to serious height the thin atmosphere means that you only need a tiny amount of thrust to accelerate.

4) Keep this going for as long as your plane and your patience can tolerate. A well-built and -flown plane should be able to get over Mach 4.5 and 30,000m in a single attempt on jets alone. Once you've wrung as much speed and altitude out of the jets as possible (you want at least Mach 4 and 30,000m), force the nose up to 45 degrees and light the rockets. If you have both jets and rockets, don't shut down the jets immediately; the thrust of the rockets will drive a ram-air effect that kicks the jets back into life for a while. Keep the rockets burning until your apoapsis exceeds 70,000m, then shut off and coast until it's time to circularise. Point prograde and close your intakes while coasting to minimise drag.

A good plane and pilot should be able to get the apoapsis to 70,000m with less than a minute of rocket power. Done properly, it requires very little fuel. But if you try to brute-force it from lower speeds and altitudes, the atmospheric drag is going to drain your oxidiser tanks before you get anywhere near orbit.

[Wanderfound]

And, yeah: as shallow as possible on reentry. Keep your nose a bit above the horizon the whole way down. Don't dive.

[allmhuran]

You've got all your drag (intakes) ahead of the CoM and your lift is still ahead of the CoM. About 5 people have advised you to make sure both of those are behind the CoM, so... not sure if trolling at this point.

[Mister Spock]

Don't worry, allmhuran, I'm not trolling -- just trying to learn from my mistakes, and I appreciate the time you and others have taken to help me.

You're certainly right about my center of drag; that's why I wrote in my previous post that "I suspect I had too much drag up front and not enough in back." As I mentioned, I wasn't sure, because there's no visual indicator of center of drag in the SPH. I gather, then, that the all-important factor is where the air intakes are? In any case, I do intend to move some of them aft. That's why I'm posting here -- to learn from my errors.

I didn't think my center of lift was ahead of CoM; they seem to be in the same spot to me. But yes, CoM should be slightly ahead of CoL, so I'll try moving the CoM forward a tad. For what it's worth, the plane seemed well-balanced when I flew it; it responded well to input. The main issue seemed to be drag, and my piloting skill.

Wanderfound, thanks for the helpful tips on getting to orbit. I hadn't realized that I should flatten out at around 20,000 meters. I'll try that and your other suggestions.

Edited August 4, 2014 by Mister Spock

[Wanderfound]

Your CoL is a whisker in front of your CoM. It's not surprising that it's responding well to inputs: that's what a forward CoL does. The further forward it is, the more agile the plane is; the further back, the more stable. The reason why you want CoL behind is that CoM is the inflection point where "agile" rapidly starts to become perpetually unstable.

When CoL is in front of CoM, any diversion from straight flight gets amplified in a positive feedback loop, and eventually the plane flips backwards. When CoL is behind CoM, any diversion gets gradually damped out and the nose returns to the prograde vector.

You got away with it for a bit because you only had CoL a tiny bit in front of CoM and the (unrealistically powerful) torque from the SAS was probably able to partially compensate. But you were riding it on the edge, so as soon as things got tricky the torque was overwhelmed.

[Mister Spock]

Thanks for the explanation. OK, back to the drawing board.

[GoSlash27]

Thanks for the explanation. OK, back to the drawing board.

Your CoL was also a hair below your CoM, which creates a torque moment when you encounter air at high velocity and low AoA. For best results, try to get the CoL directly behind the CoM.

-Slashy

[Mister Spock]

Thanks, Slashy. OK, I modified the design, and it worked much better. It had CoL in line with, and directly behind, the CoM. And I divided the ramscoops, two in front, two in back, feeding air to the single RAPIER, still mounted in the rear. Big success!

I took off with the front two ram scoops closed to reduce drag, and I achieved a faster takeoff speed, but I don't know if closing the front two was optimal. Once I was airborne, the nose wanted to go down a tad, with the CoM slightly ahead, but it was still a stable ride. I adopted a shallow angle of attack around 20,000 meters, and I climbed gradually and easily got over Mach 3. I opened the front ram scoops in the thinner air -- again, I'm not sure when is optimal. I got to orbit with just a few units of oxidizer to spare -- oxidizer, not fuel, was the only concern. Still, that tiny bit of oxidizer was enough to make it home. I burned a little retrograde to lower periapsis to around 40-45,000 meters (is burning retrograde still the right thing to do to de-orbit a spaceplane?), and then I tried Scott Manley's technique of doing slalom turns on the way down. I don't know if the slaloming helped, but for once, I kept control of the aircraft. With a shallow, slaloming descent, I never saw any re-entry effects at all! This is stock, not Deadly Re-entry, but it was still a new experience for me to re-enter without any red flames at all. That was great!

I descended smoothly to about 2,000 meters, and then...I realized I'd placed my solar panels in a stupid place, blocked by fuselage, and I ran out of power, lol. It would've been an easy landing if I coulda just gotten the landing gear down! Even as it was, I had hopes I might survive, but nope. I am trying not to "revert to launchpad," so it was a total loss, but these planes I'm building are relatively cheap, and I have 5 million roots in my career bank.

I'll post a pic after I tweak the design. It worked fine, but I obviously need to improve my power situation. Back to the drawing board *again.*

[Wanderfound]

Congratulations on launching your first SSTO spaceplane.

Don't feel bad about the panels; my first one hit the runway so hard on landing that pieces of the resulting debris made it to the ocean...

[GoSlash27]

Thanks, Slashy. OK, I modified the design, and it worked much better. It had CoL in line with, and directly behind, the CoM. And I divided the ramscoops, two in front, two in back, feeding air to the single RAPIER, still mounted in the rear. Big success!

I took off with the front two ram scoops closed to reduce drag, and I achieved a faster takeoff speed, but I don't know if closing the front two was optimal. Once I was airborne, the nose wanted to go down a tad, with the CoM slightly ahead, but it was still a stable ride. I adopted a shallow angle of attack around 20,000 meters, and I climbed gradually and easily got over Mach 3. I opened the front ram scoops in the thinner air -- again, I'm not sure when is optimal. I got to orbit with just a few units of oxidizer to spare -- oxidizer, not fuel, was the only concern. Still, that tiny bit of oxidizer was enough to make it home. I burned a little retrograde to lower periapsis to around 40-45,000 meters (is burning retrograde still the right thing to do to de-orbit a spaceplane?), and then I tried Scott Manley's technique of doing slalom turns on the way down. I don't know if the slaloming helped, but for once, I kept control of the aircraft. With a shallow, slaloming descent, I never saw any re-entry effects at all! This is stock, not Deadly Re-entry, but it was still a new experience for me to re-enter without any red flames at all. That was great!

I descended smoothly to about 2,000 meters, and then...I realized I'd placed my solar panels in a stupid place, blocked by fuselage, and I ran out of power, lol. It would've been an easy landing if I coulda just gotten the landing gear down! Even as it was, I had hopes I might survive, but nope. I am trying not to "revert to launchpad," so it was a total loss, but these planes I'm building are relatively cheap, and I have 5 million roots in my career bank.

I'll post a pic after I tweak the design. It worked fine, but I obviously need to improve my power situation. Back to the drawing board *again.*

For a "failure", this is an awfully good one! Way to go!

-Slashy

[allmhuran]

snip

Settle down mate, there's no need for this level of defensiveness. I'm not criticizing you for using FAR and mod parts. I'm saying no comparison can be made between what the OP is doing and what you are doing.

Meanwhile, whackjob has certainly not put 3kt into orbit using stock parts (most of whackjob's stuff is for show, not to be functional orbit capable vehicles), and I'm quite sure nobody else had either prior to the SLS parts and joint reinforcements.

Edited August 5, 2014 by allmhuran

[Mister Spock]

Woot, I was able to repeat my success, and this time land, thanks to the installation of a nuclear generator, better-placed solar panels, and a larger battery. Here's the plane in the hangar. How's that COM/COL look? I tried to keep COM at the same height as COL, and to keep COM slightly ahead of COL. The plane seemed stable in both my flights.

In flight, I paid particular attention to the drag numbers on the four ram scoops. Even though many parts in the assembly building carry a "drag" rating, only the ram scoops seem to generate a "drag" number dynamically during flight. The rear scoops usually showed a bit more drag than the front scoops, but not a lot. (In my earlier designs, the rear scoops were higher up, and they generated more drag, and I had trouble keeping the nose down. At first, I thought my nose-up trouble was because of mass imbalance, but it dawned on me that it was drag. I think.) Again, I'm playing stock; I gather FAR and NEAR improve on how drag works. Anyway, I was pleased that drag seemed pretty balanced throughout the flight.

I made orbit easily, with plenty of oxidizer to spare. Although fuel was a bit touch and go by the end. I did a few joy-ride orbits.

Nice circular orbit. More circular than some of my orbits obtained via rocketry, I'll tell ya!

Again I saw no re-entry effects on the way down. I did the Scott Manley slalom, which he says the actual space shuttle used to do. I still don't know if it helps, but it gives me something interesting to do on the way down. Unfortunately, I had no idea where KSC is. I haven't marked KSC on my map; I suppose I should drive a rover past the runway and plant a flag or something so that I can spot it on the "M" map while trying to land. So I just aimed to land on, you know, land.

Thanks again for all your help. Obviously I'm not done; my next goal is to design something that can carry a payload. (Accordingly, I may leave this thread "unanswered," although being new here, I'm not sure of the etiquette about that, since I've received so many helpful answers!) But I also need to earn some more science to buy the end of the tech tree, so I may spend some time with my fleet now approaching Duna before I return to the SPH.

[Wanderfound]

Yup, a flag or parked rover on each end of the runway works nicely as a navigation beacon. But without them: KSP is on the east coast of the continent that vaguely resembles Africa.

[allmhuran]

Looking good!

[Wanderfound]

Gotta say again, though: give FAR a try. If you don't like it, getting rid of it just takes a single click.

Incidentally, Mechjeb is very useful for flight data even if you never use the autopilots. Climb rate, angle of attack, total drag, air available/required, current thrust; you can have all of this data constantly available. And it isn't "cheating"; it's been a hundred years since anyone flew a plane without decent instrumentation.