Vtol Landing

[erkha343]

So, I'm making a Duna mission, and one of the stages is supposed to be a vtol, since it's too long to do a vertical landing, it flies good, but as you burn fuel, the com starts to shift, and it just plummets nose first into the ground.

I've changed the thrust vectoring to 8, but that didn't help much, any ideas?

[ThePsuedoMonkey]

Easiest way would be to trade that tank for a pair of smaller ones and have them equidistant from the CoM, that way draining them doesn't effect the CoM.

[sal_vager]

Maybe swap the tank and the hitchhiker container, so the fuel is more central?

Ideally you want the fuel tank in the center of the crafts mass so as it gets lighter the CoM doesn't move, much like how real aircraft have fuel in their wings, close to their center of gravity and lift

You'll probably have to move the engines a bit as well, so there is equal thrust front and rear.

[SkyRender]

A proper VTOL in KSP needs centrally located fuel, or equal and isolated fuel at either end. You can do the latter fairly easily: just use the next size of tank down and put one at either end. Getting the game to drain them evenly can be a bit of a pain, however... I think there's a mod that forces it to do so on KerbalSpacePort.

[erkha343]

Updated version of the craft, this works for a while longer, but when there's about 1/4 of fuel remaining it will nosedive and crash.

Now, we COULD send this to Duna and hope it works and doesn't need more than 3/4 of the fuel to land, unless someone has an idea on how to fix this?

Also, maybe the low density and lower gravity allows for lower thrust and maybe it will work until all the fuel is used, but we can't know until we test this on Duna...

Edited May 5, 2013 by erkha343

[astropapi1]

Put that SAS at the back of the lander. That'll take the CoM backwards a bit and let you use more fuel before it nosedives.

[Catullus]

Put another command pot at the back so it's perfectly symmetric? Then you can use it as a passenger shuttle too.

[ThatBum]

This mod has a hitchhiker module that's also a command pod, so you don't even need the 3 man capsule at the front.

[Sathurn]

Try this

Put the fuel tanks together with the COG right between them, or use a bigger single tank (still with the COG in the middle of the tank).

[erkha343]

Put that SAS at the back of the lander. That'll take the CoM backwards a bit and let you use more fuel before it nosedives.

This sounds like it might help a bit.

Put another command pot at the back so it's perfectly symmetric? Then you can use it as a passenger shuttle too.

i've thought of that, but I have saved that as a last resort

This mod has a hitchhiker module that's also a command pod, so you don't even need the 3 man capsule at the front.

This might be the solution, It'd look a bit weird but whatever, works for me.

[CalculusWarrior]

Instead of trying to do a VTOL (which leads to madness, trust me) maybe try replacing the drogue parachutes with the full-sized ones. Then you will slow down reasonably quickly, and can do a short burn of the engines to prevent yourself from crashing.

Also, you could launch it vertically on a rocket, I don't see why not; I'm thinking something like the X-37, where it's launched vertically, lands horizontally. You have all that RCS fuel, why not use some of it to dock to a transfer stage in Kerbin orbit then fly to Duna?

Hope this helps!

[erkha343]

Instead of trying to do a VTOL (which leads to madness, trust me) maybe try replacing the drogue parachutes with the full-sized ones. Then you will slow down reasonably quickly, and can do a short burn of the engines to prevent yourself from crashing.

Also, you could launch it vertically on a rocket, I don't see why not; I'm thinking something like the X-37, where it's launched vertically, lands horizontally. You have all that RCS fuel, why not use some of it to dock to a transfer stage in Kerbin orbit then fly to Duna?

Hope this helps!

Well the plan is to assemble the vtol in LKO with a transfer stage and a 2 man lander, the vtol is just supposed to land and stay in Duna, Maybe a better placement of normal chutes and the engines will be enough.

[CalculusWarrior]

Yeah, I find that the normal chutes do a fair job at slowing you down, but their main advantage is that they will work to keep your vessel upright and fairly level.