Empress Neptune

I subtracted initial and final fuel, found the cost and divided by payload. As a sanity check, I did the same with the image you posted showing fuel and I got 156 funds per ton for 40 ton payload. I'm assuming this (fuel cost only) is how you calculated cost, as SSTO costs should be recoverable otherwise.

Horizontal speed is certainly the most important factor, but I find vertical speed to be beneficial as well. A pure horizontal launch will suffer from drag losses, which are noticeably below 30,000m. I like to get above that altitude as quickly as possible. Vertical speeds of 200-300 m/s make it pass by quickly without requiring an overly steep ascent. I don't know how well angled wings work in that situation because most of my focus with them was on low speed flight. I have a bit more testing to do before I figure out the real advantages and disadvantages, so feel free to correct me when I make a mistake. On cost, if I use the images from my album, I get a cost per ton around 120 funds/ton. I'm probably carrying more oxidizer, but it's cheaper than liquid fuel.

You can disable staging on decouplers, making them purely structural. That will keep your nose gear fixed to the craft but it will still look funny. The lack of large steerable gear is a problem with the current parts list, but there are a few work-arounds. You can offset the main gear into whatever it's attached to which will effectively make it shorter. Doing this also hides the gear fairing which is arguably a more realistic look. You can also use smaller gear instead of the Extra-Large gear for your mains, you will just need more of them. The XL gear has very high stress tolerance though, so using smaller gears will probably be heavier overall. The other downside with these two suggestions is that it lowers the height of the plane, which can make tailstrikes more likely. If you want to be able to steer yet still have nose level or nose up attitude, but don't necessarily need to do both at the same time, you can have two sets of nose gear. A tall set for runway takeoff and a Medium gear set for ground maneuvers. I've never tried this arrangement, but it should work on paper. When it comes to wing AoA relative to fuselage, I have not seen big benefits from that arrangement. I've actually seen it make things worse. That doesn't mean it's not a good design choice, but I'm not sure if it should be universal. I like to go prograde at times during ascent and keeping the wings level results in minimum drag when doing so.

Nice, once you have something works, fine tuning should get you the rest of the way. One idea that might help with the fuel drain issue is playing with the pylon decouplers, you can enable/disable fuel flow across it and play with staging to force draining from certain tanks while leaving others full. It depends on what you want to do besides optimizing payload carriage. My aircraft is overbuilt if you only care about payload fraction. I sacrificed some weight and drag to allow it to rotate before the end of the runway, maneuver easily in case of runway overshoot, and give it essentially unlimited g tolerance. Magzimum may have goals outside of raw payload fraction that would make more wing beneficial.

I have an album from a flight that lifted 85 tons to orbit. The takeoff speed is around 120 m/s. http://imgur.com/a/8RrV2 I've lifted more weight by putting the payload outside of the cargo bay and filling the bay with more fuel. I don't think it was 100 tons (payload was the largest fuel tank in the game and some additional fuel in the bay tanks), but it was probably close.

How much are you trying to lift? I find that 8 Big S wings are pretty capable for a ~250 ton takeoff weight. I prefer using Big S wings over the structural wings, even on small planes, since they carry fuel. So I would recommend sticking with them. They are also easier to work with structurally.

The biggest factor in landing difficulty is probably how slowly your plane can safely fly. What is your speed just as you cross over the runway? Adding more lifting surfaces will help you fly more slowly. Once you're on the ground, you want to make sure that your landing gear has proper traction settings. I turn off the automatic traction control and set the sliders to about 1 or 2. The rear wheels should have a higher setting than the front. Increasing the traction setting will allow the brakes to work better. You can then improve the braking even more by having your control surfaces produce downforce instead of lift. Not only does this increase brake effectiveness, but it creates drag to help slow you down. I tend to use deployed control surfaces instead of dedicated airbrakes when I can to save some weight. Just make sure that your plane doesn't flip over when doing this. Flipping can be a problem for very light aircraft with large control surfaces.

I don't think they're useless for return trips. I was curious about using the shield for SSTO reentry, so I put one on a craft returning from the edge of Kerbin SOI. Landing with the shield inflated wouldn't be possible, but I came up with two solutions that would allow me to remove the shield. The first was to break the reetrny into multiple phases by leaving the atmosphere after the initial reentry. This makes it easy to jettison the heat shield. You would only need to slow down to roughly LKO velocity before jettisoning, which should be survivable for most SSTO's. The second option was to jettison in the atmosphere after slowing down. This is actually what I did in my test flight. I just pitched up to about 90 AoA and jettisoned. It was not enough and the shield didn't fly off, so I had to oscillate pitch until the angle was enough to drag the shield off the nose, but it did work. Obviously, getting this to work the first time every time would be the goal. While it might take some work, I don't think it's impossible at all. A deflate option would certainly be useful though.

I experimented with this and came up with a pretty reliable way of recovering the carrier plane. It's not the simplest mission though. You would basically launch the plane out of the atmosphere and carry a payload with a very high TWR. The rocket payload would get to a high Apoapsis before getting out of active ship range thanks to its speed and that would give you enough time to fly the carrier back to KSC. Naturally it's better to turn around on takeoff and head west before turning again so that you will be heading east toward KSC when staging, but this makes it take even longer. I find SSTO's to be much better in general. I don't have any problem landing on KSC from orbit and the spaceplanes I use tend to have plenty of return fuel left over, so there isn't really a risk of crashing.

I recently modified a few SSTO's to work with 1.1.12 and also took the time to eliminate some of their undesirable quirks. I think now they are ready to be K-prize certified. The 85 ton payload S-840 https://kerbalx.com/EmpressNeptune/S-840B-HSSTO-PLUS And the slightly smaller 45 ton payload S-640 https://kerbalx.com/EmpressNeptune/S-640B-HSSTO More images on Kerbal X. They can both reliably hit KSC from orbit, and the S-840 has been to Mun orbit, though I never landed that mission as these spaceplanes are designed as lifters rather than long range transports. I'm currently testing a version of the 840 with nuclear engines. I've been able to get 36 tons to LKO with 3000 dv remaining. Edit: No luck on getting my video to record, so I made an album instead. S-840 taking 85 tons of bricks to orbit [imgur]8Rrv2[/imgur] It looks like that is not working either. So direct link: http://imgur.com/a/8RrV2

On the stability issue, keep in mind that it's not just the CoL/CoM relationship that matters. Your rudder deals with sideforce, not lift. The fuselage will produce its own sideforce just as it produces lift and drag. Sideforce ahead of the CoM will make the plane unstable while force behind the CoM will help stability. Fuselage aero forces in KSP can be be very large, so if your rudder is closer to the CoM than the nose, the nose sometimes wins and overpowers the rudder. To fix this, try moving the CoM and CoL forward together while keeping the tail where it is. Alternatively, you can move the tail backwards on a boom.

Your main landing gear is very far back. When you try to takeoff, you're rotating around the center of mass until you lift off. The landing gear creates a counter force against the rotation. The further back the landing gear, the stronger the resisting force. This is why real planes tend to have the landing gear near the center of mass. You can also try making the plane sit at an angle on its wheels. If you have enough wing and enough angle, the plane will lift off by itself at speed without any control inputs. The rest of the plane looks workable, but there are some things you might want to change. Adding more lift to the front (and bringing your CoL forward) might make it more agile. Moving your pitch controls to the front can also help with short takeoff because they will create lift instead of downforce. Your vertical stabilizer is very large and might create annoying roll when you try to command yaw. I would make it smaller, or use multiple shorter stabilizers if you really need the yaw stability.

True, lengthening the plane might be the better way to go, especially if it doesn't add much weight. Maybe the weight and AoA of the plane without the excess engines should be posted to make it clearer which is the best route to go down. Sorry about jumping to wave drag, but I saw that the goal for the plane was supersonic flight, so I thought it would be helpful to know. The area graph will be really important for this project. Thanks for the info on FAR. I want to try it eventually, but I don't feel like I've "finished" stock KSP yet.

There are some problems that make scaling slightly off from 1:1, but these shouldn't be deal breakers. My Mk3 planes use a lot of Mk2 parts because of the poor Mk3 fuel mass ratio. The advantage of the Mk3 is that they allow for more solid aircraft (less need for struts) and easier fuel management. I don't use Mk3 for much besides those two things. When it comes to wings I used the Big S wings as much as possible. I really think all wings should have fuel capacity as it's extremely common in real aircraft. The Big S wings also provide a good amount of lift even for large aircraft. My ~40 ton payload SSTO uses 4 of them, while my 85 ton payload lifter uses 8. My lighter SSTO's use 2 no matter how small. I only needed struts on my 85 ton SSTO and the performance hit was marginal. Without KER it was hard to reliably notice. I agree with most of what you said though. There are some things that you need to consider as you go larger that cost efficiency. If there is a hard limit that arises from these inefficiencies, you probably won't see it unless you build a truly enormous plane. This depends on your TWR mostly. If you can quickly rise vertically and transition to a low angle, that will be efficient. Fuel burnt on the runway and accelerating to climb speed doesn't really get you any closer to orbit. Also keep in mind that wings are dead weight at high altitude so they can hurt you as much as they help lower in the atmosphere. The biggest advantage from wings is probably better control on reentry and landing.

From the third image you posted showing FAR diagrams, you can see the effect of the many engines on your cross section. There is too much cross section in the middle of the plane. Your engines are giving you massive drag at high speed. You need better area ruling, this is a direct analogue to the classic F-102 Delta Dart problem: https://en.wikipedia.org/wiki/Convair_F-102_Delta_Dagger#Design_and_development The plane was not shaped properly and couldn't go supersonic. Ideally you want your green cross section curve to be smooth for supersonic flight. This should help you get past 310 m/s. Your nose also looks blunt. Could you try a thinner and pointier nose? With wings you want enough area to hit your best L/D at cruise speed, and as much aspect ratio as possible for efficiency across the board. However when you go supersonic, you are forced to limit your aspect ratio because of area ruling and shockwaves. If your goal is Mach 1, you will want moderate sweep and a mid-low aspect ratio probably between 3 and 4. Your current wingspan may be too much for the length of your aircraft as it is now. The shape look good, perhaps try clipping off the wingtips bit by bit until performance improves. If you do this while removing away engines, you shouldn't see too many negative effects. A final note, I've never used FAR, so I don't know how it works specifically. I'm generalizing based on real aircraft design.