I hate spaceplanes

[paleorob]

Okay, new save just for SSTO aircraft. I am determined to crack this nut. Advice so far: less jet fuel, turbojet in line with CoM, different tail than the tripod, and more lift/control surfaces (but no canards). My latest design: SSTO Mk. 1

2 909s, one on either side of fuselage for more circularization ability and thrust vectoring. Avionics package hidden inside fuselage, 4 intakes on each nacelle (8:1 ratio overall) linked to action groups. Nose up, tail down for takeoff plus RCS for on-orbit and high-altitude maneuvers. Let's fly.

The profile will really depend on your specific plane's capabilities, but the general trend is this:

0> Before launch, close most of your intakes.

Okay, done.

1> Climb at a 45-degree angle until you reach 12km altitude.

Tried - couldn't climb at anything greater than a 25 degree angle. That barely got me to 10km.

2> Pitch down to a ~10-degree angle, open all of the intakes, and start accelerating.

Got an additional 30 m/s out of this. Leveling out and climbing back to 10km was a pain.

3> Watch your airspeed. At first you'll start gaining speed quickly, but eventually the acceleration will drop off to where you're only gaining a fraction of a m/s at a time. This means you're too low for your speed, so pitch up to gain some altitude.

See above.

4> At each altitude, level off to gain speed again. Go back to #3 until you're almost out of intake air.

Lots of air but running out of jet fuel. Still ~230 m/s velocity.

5> Once your air is about to run out (~0.01 per intake), pitch back up to 45 degrees, turn on your rockets, turn off your turbojets, and close most (or even all) of your intakes again. This NEEDS to be done at a high altitude (>25km) to prevent your wings and intakes from destabilizing you.

Unable to reach 25km (or even 15km) on jet alone. I kicked in the rockets and started climbing. Jet engine ran out of gas so I closed the intakes and powered through on the rockets. Apoapsis was around 81km.

6> You will be going to space today.

Yes, barely...but no orbiting for me. Pics:

Struggling through 10km and running low on gas.

Out of jet fuel. Pushing apoapsis out of the atmosphere in hopes of being able to circularize then.

Completely out of gas.

Jeb, you're an idiot.

A> You need more intakes than engines (I have a 7:1 ratio on my own plane, and I'd consider 4:1 to be the practical minimum)

Using clipping I always have at least a 4:1 ratio for supposed SSTO craft.

B> You need to have ASAS or Avionics on as much as possible, with enough control surfaces (both horizontal and vertical) to offset any roll/pitch/yaw you don't want

I always fly with avionics. I just usually bury it with clipping someplace.

Back to the drawing board.

[Devo]

My shuttle takes off and lands fine. Sure it's totally unrealistic and has more fuel than you will ever need, but you did say take off and land

This puppy takes off either wheels or VTOl and lands the same.

[Spatzimaus]

Tried - couldn't climb at anything greater than a 25 degree angle. That barely got me to 10km.

Then you're carrying way too much weight, or you have too few turbojets. Looking at your plane, you've got WAY too much fuel for a 1-engine plane. With two turbojets on a plane that size, your speed will basically hold steady during a 45-degree ascent.

Got an additional 30 m/s out of this. Leveling out and climbing back to 10km was a pain.

I guess I wasn't clear. I didn't mean pitch to a DOWNWARD 10-degree angle, I meant pitch from +45 down to +10. You should never need to go downward; the point of the shallow angle is to give you time to gain velocity and intake air while slowly increasing the terminal velocity. Terminal velocity increases as you go up, but there's no point in going up so quickly that you don't push that limit as you go.

The idea is that you level off at ~12k, then accelerate to 350m/s, then ascend to 15k, then accelerate to 600, then ascend to 19k, then accelerate to 900, and so on. Like I said before, once you're more familiar with a design you can get a better idea of what angle gives the optimum ascent, but this sort of profile works just fine.

Lots of air but running out of jet fuel. Still ~230 m/s velocity.

This goes back to my first comment: you've got way too much weight for a 1-engine plane, by a factor of 3 or so. Right now, nearly your entire engine power is just being used to offset drag, and that wastes a tremendous amount of fuel. Add a second jet engine, and remove one of the fuel tanks, and you'll do much better.

This isn't like normal rockets, where you can just go bigger. Smaller is often better, since your primary opponent is drag. Once we get a better friction model then that might change, but for now you'll need to tone it down a bit.

Unable to reach 25km (or even 15km) on jet alone.

If you've designed well, you shouldn't fire a rocket until you're above 1200m/s, and at 22km or higher. Below that and you're just wasting a tremendous amount of fuel offsetting drag and gravity.

[Scottiths]

The plane you mention that flys fine till you fire up the aerospike sounds like the CoT is off for the rocket. Try taking off the air breathing engines (note where the COM was) and see where your Center of Thrust is without them. If is slightly above or below where the CoM was with the jets on then you need to move the rocket in line.

[paleorob]

I cracked the nut with a super idiotic-looking craft I named The Wandering Albatross.

Space + fuel left? Could this be the one?

ORBIT!

I may even be able to deorbit with the fuel onboard.

Glamor shot. This thing sure is stupid looking. But it kind of works. Now to try and incorporate everything I missed from what y'all have said.

[Torham234]

Congrats. I think the wandering albatros has got a bit too much wing, but if it flies, now you have a working prototype to iterate on. I think the reason that you couldn't pitch up with the previous model is that the control surfaces couldn't keep you pointed upwards. If your nose goes down in high altitude no matter how hard you pitch, there are usually 2 remedies.

- more speed. This one is difficult, since you would need more engines, and that would mean more weight and that means more fuel and rinse and repeat.

- more control surfaces at the front. I see you don't actually have any control surface in the front half of the aircraft.

This is my lightweight SSTO . I have the rotating canards at the very tip to help me pitch in high altitude ( the satellite at the front is the payload, disregard that)

And this is my regular jet. Notice you can mount the winglets on the front of the wings as well, and they work just fine. The game automatically inverts the function so they pitch in the appropriate direction.

[foamyesque]

Y'want a simple, functional, light SSTO craft?

Here.

No intake spam. No gigantic wings. No clipping shenanigans. Flies fine without MechJeb.

[RoboRay]

Okay, new save just for SSTO aircraft. I am determined to crack this nut. Advice so far: less jet fuel, turbojet in line with CoM, different tail than the tripod, and more lift/control surfaces (but no canards). My latest design: SSTO Mk. 1

Great mission report. This thing is very close to working, and I see from your next post that you did get into orbit with another design. I'll make some suggestions on this one, anyway, since I like the design.

If your climb-rate is low, you're probably too heavy for your thrust and/or lift. More thrust isn't an option if you're sticking with a single jet engine (and I recommend that, for one-seat craft), so you can try adding some wing area. If your Center of Lift is well behind the Center of Mass, you can try adding some canards up front, too. They can be helpful, especially if your craft is otherwise very stable to fly.

Those two long 1.25m rocket tanks are really heavy. I bet that's the source of your insufficient thrust/lift. LV-909's are really efficient motors; they don't need a lot of fuel. Consider replacing those tanks with smaller rocket tanks. That would also move the drag from your intakes further back, which would add aerodynamic stability.

Learning to cut back on fuel to improve performance (which reduced fuel consumption enough to more than offset the lost fuel) has been one of my hardest lessons to learn. I'm still struggling with it a little, but I'm getting better, with smaller, lighter designs each time. Here's my current best performer, with two seats and weighing in at 12 tons wet...

About intakes... you don't need that many. Excess air beyond what your engine requires doesn't help you, and the extra drag is hurting you. I'd cut the clipped intakes out completely and put just one on each side, where you have them stacked. Those are probably enough (I've gotten planes with one intake per engine into orbit, you just burn more rocket fuel as you can't get as high on the jets). If that's not enough air to cruise at 20km+, then add a second pair back on.

Congrats on your success with the Albatross, though!

[Flixxbeatz]

Y'want a simple, functional, light SSTO craft?

Here.

-snip-

No intake spam. No gigantic wings. No clipping shenanigans. Flies fine without MechJeb.

Dude...

I made something similar like that before. And #7 happened.

Nobody's calling you a noobie. Spaceplanes are hard. I attempted, failed, and gave up on spaceplanes several times before I finally figured out the very narrow band of tolerances that will result in a working design. There's nothing wrong with going back to having fun with vertical rockets until you're ready to give the planes another try.

Then go tell that to some guy I saw here some time before the forum reset who said that vertical rockets are BORING, which basically tells that people who have made and successfully flown an SSTO spaceplane are cool and professional (spaceplanes are cool. that's an undeniable fact) and those who doesn't make (i.e, rocket people) aren't as cool as them.

[RoboRay]

If you're going to obsess over childish things that one egotistical "kewl kid" supposedly said, I think you're going to find much bitterness in life.

[Spatzimaus]

If you're going to obsess over childish things that one egotistical "kewl kid" supposedly said, I think you're going to find much bitterness in life.

No kidding. Besides, I'd bet that there's a lot of paraphrasing involved; it's not uncommon for people to say that rockets are EASIER, because they are. Rockets are inherently more forgiving of design flaws, because there are many less variables involved. You only need symmetry along the vertical axis, whereas with spaceplanes you need to balance the CoM, CoT, etc. in three dimensions. Rockets generally use a single set of fuel tanks (liquid+oxidizer) whereas spaceplanes need to have a separate oxidizer-less reservoir for the turbojets. And as we've discussed in this thread a few times, a rocket can always go bigger and come out ahead, whereas spaceplanes are often better if you make them smaller.

The flip side of this is that there are just a lot of things that rockets can do that spaceplanes can't, like travel to Duna and back without refueling. I wouldn't want to begin to launch a space station using a spaceplane, or launching a base to Laythe, or delivering a major fuel depot into orbit.. Heavy-lift rocketry is a lot of fun to develop, and it has a lot of the same issues that spaceplanes do.

But back to the original topic.

I cracked the nut with a super idiotic-looking craft I named The Wandering Albatross.

It looks fine from here, and it's obviously got all of the important things you need. Now that you have a working design, and the know-how to get it into a stable orbit, it's time for the FUN part: fine-tuning. You've got the functional core working, so start off by redesigning the wings to be a bit less obtrusive and/or stable. Because your later shots are so dark I can't tell where your RCS jets are placed, so you might be able to improve that as well. And your landing gear looks strangely placed, too, but if it works then it's not a high priority.

I've had at least three times in the past couple months where I was sure my spaceplane design was done, that I couldn't improve it any more. Each time, I turned out to be wrong; you can always find some way to make a small improvement. So you have that to look forward to...

[paleorob]

Because your later shots are so dark I can't tell where your RCS jets are placed, so you might be able to improve that as well. And your landing gear looks strangely placed, too, but if it works then it's not a high priority.

Wow, they are a lot darker on my work computer than at home. Hmm...

Anyway, about those RCS thrusters...yeah...I kind of forgot to strap them on so that is already part of the planned redesign. I'm not sure what I was thinking with the nose gear either...

[Warscribe]

Since i took my little dip at athmosphere spaceplanes (basically for retrieving Kerbals that landed off base) i had come to a conclusion

When this

Explodes on the runway

and this

gets me nearly anywhere on Kerbin

Something is seriously rigged.

[Spatzimaus]

Something is seriously rigged.

The Rutan Voyager looks a lot like your lower design, and it set the atmospheric endurance record. Your upper plane, on the other hand, looks extremely unstable; without seeing the exact positions of the center of mass and center of lift, I'd be extremely worried about the thing flipping over. Also, look carefully at the positions of your intakes, since they're the primary source of drag. The lower design has imany intakes behind the center of mass, while your more "normal" design has only the two intakes towards the front. (And what's with the solar panels on the top plane? What does it have that requires electricity?)

The simple fact is, those sorts of unconventional shapes ARE better, at least from the point of aerodynamics. It's just that in the real world you have to worry about things like pumping air to the engines, or transferring large amounts of fuel, and so making things as compact as possible is a good idea. In KSP, struts and fuel lines work just fine, and intakes can be anywhere on the craft, so it's not as limiting.

[Warscribe]

The upper plane was made as a relay station for remotetech (i think the blue remotetech probe body sticks out pretty well) because i was opting for really low KO remotetech satellites, its job was to fly to north, south and 3 other equatorial points 90° to each other and relaying signals through the satellite network to command station KSC. if you're interested, after throwing over the whole concept and starting from zero, this is the plane that actually made it. it did fly quite stable.

also, the upper plane (slightly modified, still unstable) with the indicators:

http://img.photobucket.com/albums/v699/BlackAnti/2013-04-21_00004_zps55650e88.jpg

Edited May 2, 2013 by Warscribe

[leax256]

spaceplanes, I hate, planes I love.

[foamyesque]

<snip pictures

I don't think I've mentioned this before, but I love how that plane looks and your use of the orange radials to eliminate the awkward lateral pods.

Dude...

I made something similar like that before. And #7 happened.

#7... running out of fuel to orbit? Shouldn't happen with the .craft file I provided. If it does, you're flying it wrong.

Oh, and there was someone talking about a 25 ton spaceplane...?

[Jean Deaux]

I haven't been able to fly or control one to save my life. Even tried attaching a joystick. They are way to unstable and jerky to fly for me, I've been sticking to rockets hopeing they get better. I scrape my engine off half the time just taking off from the runway. Someday... someday...

[RoboRay]

I haven't been able to fly or control one to save my life. Even tried attaching a joystick. They are way to unstable and jerky to fly for me, I've been sticking to rockets hopeing they get better. I scrape my engine off half the time just taking off from the runway. Someday... someday...

Try the Avionics Package. It solves the "jerky" controls and makes it a lot easier to get the nose up on the runway without a tailstrike.

I don't think I've mentioned this before, but I love how that plane looks and your use of the orange radials to eliminate the awkward lateral pods.

Heh, thanks. I mainly used them for their extremely low mass (combined, they are lighter than an LV-909 and have more thrust), which more than offsets their lower Isp. But they do permit a rather elegant design, if I do say so myself.

Edited May 3, 2013 by RoboRay