advanced ssto payload plannimg

[jonatron5]

Ive finally gotten to the point where i consider myself gairly competent in ssto designs. Even chalking up a few interplanetary ones. However without a doubt what plagues me is using them as lift vehicles. To bring cargo to orbit.

The other day i finally got my first mk3 ssto out of design and i honestly think i way over built it compared to its cargo capcity.(specs to come soon)

Also im strugiling to get the craft ballanced both during launch and reentry as my cargobay is near the rear of the ship.

So while i do have a working solution im looking to make it even better.

[Starhawk]

One of the methods I've used is to balance the craft without payload, then add the payload and add a fuel tank at the other end to balance it out. By right clicking on a fuel tank you can turn off the flow for each type of fuel it contains. You accomplish this by clicking the small button to the right of the gauge in the info panel for the tank that pops up. You can do this in the VAB or in flight.

Once you release your payload, you pump the fuel out of the balance tank and into your normal fuel tanks. This is done by right-clicking on one of the tanks and then Alt+right click on the other tank. You can then use the buttons that appear to pump fuel.

Hope this helps.

Happy landings!

[DocMoriarty]

It's correct that you balance an empty transport space plane. But adding a tank for balancing it with payload is a huge waste of weight. Instead the plane is constructed in a way that the payload can be attached so that CoM doesn't move at all. The doc in my signature has a lot of examples of such transport planes. It's a tad outdated though since they use the old wings but with all changes to aerodynamics and drag anything built now will be obsolete.

[WhiteKnuckle]

While both of the above suggestions are valid, I'm firmly in Doc's camp. Your CoM should be in the dead center of your cargo bay, so no matter what you have or don't have in there your plane still flies like it should.

Bonus points if your fuel load is balanced around your CoM as well.

Starhawk's idea is also useful, but in general I try to only use that trick for fine tuning a design.

I will say the Mk3 parts are tough to make work for spaceplanes, especially in FAR. I've got one that works, but it's still shy of being able to take an orange tank to orbit which is what I designed it for

Edited February 14, 2015 by WhiteKnuckle

[Starhawk]

adding a tank for balancing it with payload is a huge waste of weight. Instead...

Quite right. However, I was trying to assist OP in adjusting an already existing design, rather than creating an entirely new one.

Happy landings!

[Pecan]

...Also im strugiling to get the craft ballanced both during launch and reentry as my cargobay is near the rear of the ship.

Avoid wings of any sort because they unbalance the rocket all the way. If you must have them, for FAR stability or similar, place them radially around the base of the rocket. If you want the aerodynamics and are not against mods Procedural Fairings makes much better cargo-bays than the stock ones.

Otherwise, SSTOs are as simple as any rocket - you just need a couple of 100m/s extra dV for de-orbit and landing if you add a couple of drogues. The Mk3 parts are currently ridiculously heavy though - use anything else in preference.

As Doc said though, all this is going to change a lot with the release of 1.0; probably to the extent that we'll all have to go back to school with all the parts rebalancing and changed aerodynamics.

[jonatron5]

I know 1.0 is going to nuke all my work with spaceplanes. But in the mean while im still fidiling with this thing.

I really like the idea of putting the center of mass dead center of the cargo bay. But i will have to do a complete redesign to manage that becuase my center of lift has to be there too.

Also a comment on these insanly heavy mk.3 parts, Is it normal to have like 8 jet engines to get the thing off the ground?

I really feel wastefull pitting all those engines on the thing but i consistantly land liquid fuel rich.

Away from my pc till monday ill give weight and effective payload then and you guys can tell me if im being horribly ineffecient or not

[Sampa]

I know 1.0 is going to nuke all my work with spaceplanes. But in the mean while im still fidiling with this thing.

I really like the idea of putting the center of mass dead center of the cargo bay. But i will have to do a complete redesign to manage that becuase my center of lift has to be there too.

Also a comment on these insanly heavy mk.3 parts, Is it normal to have like 8 jet engines to get the thing off the ground?

I really feel wastefull pitting all those engines on the thing but i consistantly land liquid fuel rich.

Away from my pc till monday ill give weight and effective payload then and you guys can tell me if im being horribly ineffecient or not

Though i like the idea of ssto s (even attempted building one, briefly), i find that they are not the greatest heavy lifters. Small satellites, maybe, but not heavy lifters. Passengers are more suited to ssto, and normal rockets for heavy lifting

[MarvinKitFox]

SSTO rocket will still outperform SSTO plane, for all but the very lightest of cargoes.

Easier to build, too.

Just not as pretty.

[Van Disaster]

Though i like the idea of ssto s (even attempted building one, briefly), i find that they are not the greatest heavy lifters. Small satellites, maybe, but not heavy lifters. Passengers are more suited to ssto, and normal rockets for heavy lifting

I've put 270t into orbit in a spaceplane, I think that counts as fairly heavy lift admittedly a) FAR, and making full use of the fact that to get to orbit on Kerbin you don't actually have to go that fast. Not stock, of course - stock's lack of suitable engines for large spaceplanes is a problem. I try and keep mods internally consistent performance-wise and usually sub-stock levels of effectiveness. The plane, fuelled with no cargo, weights 258t I think - that's quite a payload fraction.

Generally: split the fuel around the cargo bay so as you run out the CoM doesn't move. Balance engines at one end with the cockpit at the other ( might even blow a couple of tons on a structural fuselage piece to balance moments ), and don't move CoL too far away from CoM or you won't have any control authority.

Edited February 16, 2015 by Van Disaster