Help with Larger SSTO Engine Design/Implementation [STOCK]

[Zerik0]

I have been playing KSP for a while, and after mastering a lot of the community techniques to build rockets I set out to conquer space planes. I can now develop light space planes easily, but I have found that larger SSTOs really give me trouble. With that in mind, I have designed the following stock airframe utilizing the Mk3 size components.

Craft file: http://drive.google.com/uc?export=download&id=0B7woBToR2eXwSTk4MFc5QU5FRlU

Screenshot (with stats): http://drive.google.com/uc?export=download&id=0B7woBToR2eXwSUlVNWVfdTNrRVE

Design Goals:

• Stable/Controllable Flight
  
• Robust lifting capability (size: 3 unit cargo bay)
  
• Docking Capability
  
• SSTO (optional: rendezvous, refill, travel to other bodies).
  
• Safe return/landing
  

What I've got so far:

• The principal flight surface is a delta wing configuration to maximize lifting surface and place the center of lift as far back as possible.
  
• RCS and monopropellant with a large capacity for loitering in orbit (may be overkill, but it also puts more weight in the front).
  
• Winglets, canards and rear flight control surfaces are large enough to provide fairly robust flight control. After throwing 3x LV-T30 engines on the back to test take off without a load I was able to easily control take off utilizing around 2/3 of the runway.
  
• A controlled glide into the ocean was manageable enough to allow the crew cabin to survive sea surface impact at a descent rate of roughly 25 m/s with a forward speed of around 60 m/s.
  

Really, I will take any sort of advice, but I'm principally concerned with techniques for mounting stock engines in such a way that I have enough thrust and fuel to fly a typical SSTO ascent plan to orbit, dock or deliver payload and return for a safe landing.

Things I'm okay with:

• Intake stacking (but not throwing them everywhere... I can do that ) with drag and weight ratios in mind. Typically Ramjet Air Intakes > Circular Intakes > MG-350.
  
• Maintaining aesthetics without going overboard with flight surfaces, struts, fuel pump lines, etc.
  

Things I'm not okay with:

• Debug menu (infinite fuel, clipping allowed)
  
• Physics engine exploits (basically no crazy contraptions)
  

Things I don't know:

• Pretty much anything new with the Beta (root tool, etc). Still learning the changes and deciphering patch notes.
  
• The newer techniques from the last 6 months or so.
  
• How to build a large SSTO and properly fuel it to get to space.
  

I'm learning, but after several failed attempts I'm stumped. Any and all assistance will be much appreciated. Don't forget, I'm open to any recommendation on the design- not just the engine/fuel/intake implementation!

Update: my attempts earlier today were not fruitful. I was successful in adding five turbo jets and intakes that could reach 40k at around 2 km/s, but after attempting to mount two nuclear engines it fell apart from there. My first inclination is to make the craft a horizontally and vertically symmetrical as I possibly can. Thoughts?

Edited March 16, 2015 by Zerik0
Spelling/grammar corrections and update.

[Taki117]

You're aircraft is awful short, and a delta wing configuration isn't going to work too well for this. You should probably use a more conventional wing set up.

[Zerik0]

You're aircraft is awful short, and a delta wing configuration isn't going to work too well for this. You should probably use a more conventional wing set up.

The main problem I had with a conventional wing design of that size was getting the center of lift to stay sufficiently far enough back behind the center of mass.

It seemed like the obvious answer was to fly a delta wing so that I could have the majority of the lift surfaces as far back as possible.

Of course, my big issue so far has been having to adapt real life designs to the stock physics engine for atmospheric flight. Do you have any examples?

Edited March 15, 2015 by Zerik0
Spelling.

[GoSlash27]

Zerik0,

The principles are the same for Mk3 spaceplanes as they are for Mk2, but the techniques have to be adapted because Mk3 airframes are too big for the available components.

For example, your delta wings. Deltas are the most convenient for large structures, but they're also the least efficient part for the job. The most efficient parts are strakes, structural d, and swept (in that order), but using them results in floppy wings and high part counts. Refer to this chart for wing panel performance by type: http://forum.kerbalspaceprogram.com/threads/105090-KSP-90-Spaceplane-wing-comparo

I have run 1.0 lift coefficient per tonne of spaceplane previously with good results, but lately I've upped that. Now I'm running about 1.5. This cuts down on the induced drag,loss of intake air, and loss of horizontal thrust in the 32-36km region.

A Mk3 spaceplane will still be using turbojet/ OMS rocket combos for maximum efficiency, but it will require multiple engines and multiple intakes to feed them. You will need to design and build to minimize asymmetric air starvation to keep this from ruining your day. Lots of tutorials out there on this subject.

Intakes, like wings, are not all created equal. http://forum.kerbalspaceprogram.com/threads/106114-Stock-KSP-90-intake-comparo-for-SSTO-turbojets

Generally, one turbojet per 15 tonnes and .015 m^2 of intake area per engine are recommended, but I've been pushing those boundaries lately. My most efficient designs are using 1 engine per 18 tonnes with .01m^2 of intake per tonne. This gives you just enough turbojet to make 70km apoapsis on jet thrust if you nurse it, with a tiny rocket boost to circularize.

Other than that, basic spaceplane construction techniques still apply. Intakes behind the center of mass, canards instead of elevators, lift/thrust/ mass all in line, yadayada. You just have to scale it and get a little creative.

HTHs,

-Slashy

[Zerik0]

Slashy,

Man, that is a comprehensive and supportive response! I have just begun to post in the forums (usually just a lurker), but I sincerely appreciate it!

Would you be willing to provide some examples of your pre- and post-efficiency-overhaul models? The move to less thrust/more lift/fewer intakes is interesting, and I would love to take a gander at what you've done so far. I have to admit that I usually have a much higher intake ratio to get the job done, but I had no idea that lift surface ratio would help so much at those higher altitudes.

My other issue is scaling up! It seems so easy to build and fly a spaceplane with Mk1 components when you only need one or two of everything in a nice, neat package. Mk2 gave me some problems, but it was a fairly simple adaptation of Mk1. Mk3 has been a beast to figure the things out that you pointed out. I'll try a little this afternoon to get something going.

Thank you much!

[GoSlash27]

Zerik0,

Not a problem. That's what we're here for

My older designs are kinda lost to the sands of time, but I think there's still some pics floating around.

This would be an example of an older typical Mk2 design. It could orbit cargo at about $43/ tonne.

These are examples of where I've gone since then. They are running about $27/ tonne. As you can see, they're really just bigger planes running on the same engine as before. re-tweaking the lift/weight allows me to run a little cleaner in the 32-36km range, so I can push more mass.

Reducing the intake area doesn't actually help any, but it's surprising how little intake area you can get by with.

Best,

-Slashy

Edited March 15, 2015 by GoSlash27

[Taki117]

The main problem I had with a conventional wing design of that size was getting the center of lift to stay sufficiently far enough back behind the center of mass.

It seemed like the obvious answer was to fly a delta wing so that I could have the majority of the lift surfaces as far back as possible.

Of course, my big issue so far has been having to adapt real life designs to the stock physics engine for atmospheric flight. Do you have any examples?

Why not swap the conventional design then. Have your large, main lifting surfaces at the rear, and use canards up front. This would solve the center of lift issue, while giving you enough lift up front. You might also think about lengthening the fulselage by adding a rocket fuel tank at the back.

[Zerik0]

Slashy,

Thanks for the update with the screen shots. MK3 level platforms seem pretty far out from my current skill in building yet, but this gives me a lot to work on towards that goal. Ultimately, I think without really gaming the system... the parts for space planes may not exist yet for a moderately informed individual such as myself to easily find success with that large of an SSTO lifting platform.

Why not swap the conventional design then. Have your large, main lifting surfaces at the rear, and use canards up front. This would solve the center of lift issue, while giving you enough lift up front. You might also think about lengthening the fulselage by adding a rocket fuel tank at the back.

I think I will go back and play around with it, but I was under the impression that my set up was fairly close to what you're suggesting. Do you have any examples?

Also, wouldn't adding another tank at the back exacerbate the CoM and CoL ratios?

[Taki117]

I think I will go back and play around with it, but I was under the impression that my set up was fairly close to what you're suggesting. Do you have any examples?

Also, wouldn't adding another tank at the back exacerbate the CoM and CoL ratios?

Not exactly. I'm suggesting, instead of a single delta wing, which puts all your control surfaces at the rear of your aircraft, have a single wing at the rear, with a set of canards up front, similar to this:

You don't have to put the tank at the back, that's just normally where I put them because that's where I think they should go. You can put it up front if you want, which would make your aircraft more stable. building a large delta-winged aircraft is hard, but it can be done.

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[GoSlash27]

Slashy,

Thanks for the update with the screen shots. MK3 level platforms seem pretty far out from my current skill in building yet, but this gives me a lot to work on towards that goal. Ultimately, I think without really gaming the system... the parts for space planes may not exist yet for a moderately informed individual such as myself to easily find success with that large of an SSTO lifting platform.

No problem.

Mk3 designs are kind of a pain because (as you said) the proper parts don't really exist yet. This will all change when 1.0 comes out. Then we'll all be back to square one.

Best,

-Slashy

[LordFjord]

Take a look at this thread.

Many big planes with lots of different engine setups.

For your plane, I would suggest to add some engine pods next to the cargo bay, maybe 2 rapiers on a MK2 bicoupler on each side. Probably will need more when you want to haul heavy cargo, but its a start. If you place the bicoupler vertically, then you can always extend it to the sides with another pair and stack them as much as needed. Just make sure that they are in line with your center of mass.

Happy building!

[Zerik0]

Thank you, everyone, for your help. I've got enough here that I can move forward with some design concepts. I hope this thread, in the future, provides good information to others as well.

Marking as "Answered!"