Reall big/cargo SSTOs?

[Der Anfang]

How exactly do people build those huge clunky SSTOs also capable of carrying meaningful loads? I see a handful of people using the mark III parts, and everytime I attempt those they always fall apart on the runway, or veer off. The wheels and wings usually go first because parts simply aren't that rigid. I can manage smaller sstos just fine, though, even the mark II vessels are not a big issue for me, but I can only ever build sstos real light... up to 40 tonnes at most. Any bigger and they usually can't get into orbit or fall apart. Best I can deliver is maybe 1.5 tonnes, usually less.

How the heck do you build bigger sstos and especially how does one transport heavy payloads to lko?

[FlipNascar]

Well you can try by using struts. If it's falling apart on the runway, use struts. You don't need masses of them, but I always build first, and then strut the obvious (to me parts), and then load it onto the runway and see where it sags, and what sags. Then you strut that together and job done. If you had a picture, or an example craft I could take a peak and help if you like.

[KerikBalm]

Big like this:

[img]http://i.imgur.com/FOfPjuO.png[/img]

[img]http://i.imgur.com/bBoCaoc.png[/img]

[img]http://i.imgur.com/EZ6XwJt.png[/img]
(ok, that one involved docking something to it in orbit)

[img]http://i.imgur.com/kuZeQIo.png[/img]

Or merely big like this?
[img]http://i.imgur.com/Fvfy9vY.png[/img]

[img]http://i.imgur.com/QVI4EiZ.png[/img]

Or merely like this, where it doesn't even launch horizontally:
[img]http://i.imgur.com/m9kOsCx.png?1[/img]

[img]http://i.imgur.com/ak00vON.png[/img]

[img]http://i.imgur.com/jNYV7Xn.png[/img]

If all you want is 1 mk3 bay,
Vertical launch SSTOs (I made one yesterday for Laythe, no pictures yet) would be the easiest, but you'll have a lot of engines and not the best payload fraction.
You'd need about 16 rapiers for a mk3 bay, but you could get by with less if you replace some with turboramjets (higher static thrust) or panthers in afterburner mode (even more static thrust)

If you want to do horizontal launch, I find the biggest problem is collapsing when the craft loads on the runway... often it gets "dropped" enough to destroy it.
What you can do is in the vab move the craft so that its wheels are just 1 pixel above the ground. If your craft doesn't sit level on the ground (mine typically sit with the nose pointing up a little when wing incidence isn't used - typically because I have forwards and aft wings with engines mounted on the wings, and I don't want the exhaust of the forwards jets hitting the rear wing - also I don't want to have to deal with the offset thrust issues that can create) - then this may involve rotating the entire craft as well to get all wheels equidistant from the floor, just above the floor - do it that way and the "drop" on craft loading is very small.

On top of that, landing gear placement is very important, you don't want a long "tube" of heavy parts, with just support at the front and back.
Make sure your landing gear are very straight, landing gear that isn't vertical can cause all kinds of "disassembly" problems on take off.

While you want to minimize struts because of their drag, on a big craft you can throw several struts on it without killing its viability. As you see in my top images, I'm using struts to keep the payload in place, and also to keep the two halves of my craft together. It still manages ~35% payload fraction... so don't be afraid to add some struts.

[Der Anfang]

[quote name='FlipNascar']Well you can try by using struts. If it's falling apart on the runway, use struts. You don't need masses of them, but I always build first, and then strut the obvious (to me parts), and then load it onto the runway and see where it sags, and what sags. Then you strut that together and job done. If you had a picture, or an example craft I could take a peak and help if you like.[/QUOTE]

Well, here is an example of one of my many successful MK 2 crafts: [img]http://i.imgur.com/t2GZ7k1.png?1[/img]

And here is my typical always failing MK 3 designs: [img]http://i.imgur.com/c0CbkjM.png?1[/img]
Keep in mind that for the latter image used, I wasn't focused on creating an SSTO at all, but rather just to perform a suborbital test. It couldn't even take off without collapsing on itself. The previous design I had lost... it had 6 whiplash engines on those same wings and 3 aerospikes on the mount, but otherwise the design is simular to what I usually do. I can't ever get those off of the ground.

[KerikBalm]

There may be some clipping issues with the wings and the FL-T800 tanks, especially when they flex.
Also, thats a lot of mass at the back with no direct support underneath it, I'm guessing it fails at the back first.
Either strut up the wings, or add a centerline landing gear at the back.
You could also improve its tolerance by having your nosegear moved back to be attached to and under the very front of the forward fuel tank instead of the cockpit.

[Der Anfang]

Yeah, at that point I wasn't even concerned about the Fl-800 tanks, but you make a good point with those. I didn't think about the mass being an issue. (And yes, that is a very generic design, I know. Not very creative, lol). So, how can I counteract the clipping issue with the wings? Just strut it up?

Also, is the whole veering issue with my larger spaceplanes because of the heavy mass in the rear, or is that an issue? Edited November 23, 2015 by Der Anfang

[KerikBalm]

Well for the T800 tanks, you could try just using offset to get your wings a little lower

For the veering, my guess is that it is because of where you have your rear wheels mounted.
I strongly recommend having the wheels mounted directly underneath the weight they are supporting.
Put a wheel, or pair of wheels, directly on the fusalage at the back.

Right now the wings flex under the unsupported center load, the flexing means that the wheels are no longer perpendicular to the runway, and it won't roll quite right.

If you remove the outer wheels, you'll have a narrow wheel base, which will require you to set it down better on landing, but its not too much of a problem, as you see in my picture from above:
[url]http://i.imgur.com/QVI4EiZ.png[/url]

You can also have outrigger wheels to help stabilize but not for much support... Important: disable breaks on outrigger wheels, otherwise if you set down without being level, it will exert significant yaw torque that will likely make things go very badly.

Or you could compromise - move the landing gear inward (but not all the way to the fusalage) so the flexing force is reduced, and strut up the wings.

You should really put the landing gear directly under the mass, as things get bigger, it avoids a lot of flexing related issues (and this is realistic... you can't scale things up 1:1... the often cited example is a spider/ant 100x its size wouldn't even be able to lift itself off the ground)

[eddiew]

If big SSTOs are your thing, I recommend a combination of Kerbal Joint Reinforcement, and Tweakscale. Keeps your parts down, your fps up, and removes saggy underbellies. Design for mk3 just like you would for mk2 and enjoy flying them :)

[IMG]http://i.imgur.com/Szk0vAC.jpg[/IMG]

The above can be achieved with 8x rapiers, 8x intakes, some quad adapters, a ton of struts, and a lot of regular sized wing pieces... but you end up with 50+ wing parts alone, probably 150 for the whole ship, and a very laggy ride all round. I see no reason not to just scale up the pieces to match the mk3 fuselages :)

[COLOR="silver"][SIZE=1]- - - Updated - - -[/SIZE][/COLOR]

[quote name='Der Anfang']Also, is the whole veering issue with my larger spaceplanes because of the heavy mass in the rear, or is that an issue?[/QUOTE]

In my experience, this is usually flexing somewhere in the plane. Sometimes it's the landing gear itself that's wobbling, but it might be whatever it's mounted to. As suggested above, KJR will remove a lot of this by simply stiffening up all connections ^^

[Val]

Veering on the runway is mostly caused by the main load bearing landing gear being too far from CoM. Just as having your CoL too far behind CoM is a bad idea, so is having the landing gear far away from CoM.

If you want inspiration for a working Mk3 design for KSP 1.0.5 you are welcome to study my SSTMun Z-1 Double-D

It'll bring 17 t payload to orbit around Mun or Minmus.

Edited March 2, 2016 by Val
Furum update formatting fubar

[Vegetal]

The gear placement is quite wrong from what I see, but they already told you that. One thing you have to understand, is that Mk3 planes will always be more fragile - you can land HARD a Mk2 plane, a Mk3 one you have to be careful or run the risk of splitting it in half.

Note: They say those FAT wings aren't good for reentry nowadays, and from their max temp, I believe it.

[A_name]

Didn’t have time to go through the whole thread so I don't know if all of this has been mentioned already, but here are some tips off the top of my head:

-Use struts, or better yet, install Kerbal Joint Reinforcement. Either of these options will go a long way in keeping your parts firmly together.

-Keep your designs simple. The fewer parts there are, the less likely it is that a joint between them will fail. If possible avoid building wings made out of a lot of parts. If possible, use one of the larger sets of wings (the Big-S delta wing or the Aeroplane wings) so that each of the wings is only 1 part. You can also install Tweakscale and use it to make other parts larger. The bottom line is reducing points of failure by reducing parts.

-Don’t put your landing gear on the wings as you will only be adding unnecessary stress/loads on them. Attach them to the fuselage and use the offset and rotate gizmos to move them to your desired position even if it’s under the wings; just make sure you initially attach to the fuselage and not the wings.

-Use the medium or large landing gears.

-Smooth piloting and patience are also key.

[Val]

In case you want something else to study or compare with, I made a new smaller variant of the one I posted above. I call it SSTO Z-2 High-Five

It'll bring an Orange tank (36 t) payload to LKO.

On 24/11/2015 at 1:28 AM, A_name said:

Didn't have time to go through the whole thread so I don't know if all of this has been mentioned already, but here are some tips off the top of my head:

-Use struts, or better yet, install Kerbal Joint Reinforcement. Either of these options will go a long way in keeping your parts firmly together.

-Keep your designs simple. The fewer parts there are, the less likely it is that a joint between them will fail. If possible avoid building wings made out of a lot of parts. If possible, use one of the larger sets of wings (the Big-S delta wing or the Aeroplane wings) so that each of the wings is only 1 part. You can also install Tweakscale and use it to make other parts larger. The bottom line is reducing points of failure by reducing parts.

-Don't put your landing gear on the wings as you will only be adding unnecessary stress/loads on them. Attach them to the fuselage and use the offset and rotate gizmos to move them to your desired position even if it's under the wings; just make sure you initially attach to the fuselage and not the wings.

-Use the medium or large landing gears.

-Smooth piloting and patience are also key.

In my experience the medium and large landing gear have very low brake torque. I usually up it to 18 or 24, from the default 12.

Lots of good advice, though I've never had problems with Mk3 breaking apart. I don't use Kerbal Joint Reinforcement and very rarely struts

Edited March 2, 2016 by Val
Forum update formatting fubar