2 Questions: SSTO spinning out of control; Block fuel passage?

[ISmokeThis]

Hey guys

I am currently faced with two dilemmas and I was hoping you guys could help out. Here they are:

1. Whenever my SSTO gets to around 20,000 m it begins to spin out of control. I added vertical wings to mitigate this, but even with several (and a very large one) the problem still occurs. The spinning can also be triggered when I turn off my jet engines and close air-intakes. What am I doing wrong?

2. Is there a way I can block fuel from transferring between two attached fuel tanks? My design has two fuel/oxygen tanks that are separate from the rocket thruster and, therefore, require fuel ducts. However, these tanks are also connected to pure liquid fuel tanks for the jet engines and so fuel transfers between them. With that, when my rocket thruster is in use, fuel from the pure liquid fuel tanks gets spent over the fuel/oxygen tanks.

Here are the pics of my design:

[DeMatt]

Hey guys

I am currently faced with two dilemmas and I was hoping you guys could help out. Here they are:

1. Whenever my SSTO gets to around 20,000 m it begins to spin out of control. I added vertical wings to mitigate this, but even with several (and a very large one) the problem still occurs. The spinning can also be triggered when I turn off my jet engines and close air-intakes. What am I doing wrong?

When a jet gets high enough, it starts running out of air. The way KSP allots intake air, is it starts by feeding each engine in sequence. So what's happening is this:

1. Feed far left engine: Okay!
   
2. Feed far right engine: Okay!
   
3. Feed inner left engine: Okay!
   
4. Feed inner right engine: Nope, I'm out, stop thrusting.

And then your plane spins because it's got two left engines and one right engine.

The typical solution is to A) monitor your intake air more carefully and switch (some) jets off before you actually run out, or add a jet on the centerline after you've added symmetrical jets. Last-placed jet engines get air last, and a failing centerline jet won't cause your plane to spin out of control.

2. Is there a way I can block fuel from transferring between two attached fuel tanks? My design has two fuel/oxygen tanks that are separate from the rocket thruster and, therefore, require fuel ducts. However, these tanks are also connected to pure liquid fuel tanks for the jet engines and so fuel transfers between them. With that, when my rocket thruster is in use, fuel from the pure liquid fuel tanks gets spent over the fuel/oxygen tanks.

My recommendation would be to swap out the inner two jet engines for rocket engines, then swap the centerline rocket for a jet. Put all the rocket fuel on the inner wing pods, switch the centerline tank out for jet fuel, and remove all the fuel ducts. Leave the air intakes as they are.

[ISmokeThis]

When a jet gets high enough, it starts running out of air. The way KSP allots intake air, is it starts by feeding each engine in sequence. So what's happening is this:

1. Feed far left engine: Okay!
   
2. Feed far right engine: Okay!
   
3. Feed inner left engine: Okay!
   
4. Feed inner right engine: Nope, I'm out, stop thrusting.

And then your plane spins because it's got two left engines and one right engine.

The typical solution is to A) monitor your intake air more carefully and switch (some) jets off before you actually run out, or add a jet on the centerline after you've added symmetrical jets. Last-placed jet engines get air last, and a failing centerline jet won't cause your plane to spin out of control.

My recommendation would be to swap out the inner two jet engines for rocket engines, then swap the centerline rocket for a jet. Put all the rocket fuel on the inner wing pods, switch the centerline tank out for jet fuel, and remove all the fuel ducts. Leave the air intakes as they are.

Thank you for that information. Especially about how KSP processes intake air. I am not too happy about this solution (although its probably all I can do) because I want my plane to be very fast when inside an atmosphere.

Edit: Actually, I'm still not quite sure I completely understand what you mean by the air intake sequence. Do you mean that once any one of the jet engines does not receive air, it first shuts off then then the rest all at once, or do they shut off in sequence? If the latter, I don't follow how you're solution does anything.

Edited January 10, 2014 by ISmokeThis

[ISmokeThis]

So, now I have a problem where the docking port attaches to the center fuel tank and so I don't think I will be able to transfer rocket fuel to the proper tanks unless I have a port for each of them. However, that just seems silly. I would have to dock one tank then undock and dock the other tank every time I fill up my ship. OMG this is a disaster.

[Kasuha]

So, now I have a problem where the docking port attaches to the center fuel tank and so I don't think I will be able to transfer rocket fuel to the proper tanks unless I have a port for each of them.

Instead of worrying, you can always make a test.

When you're docked, you can transfer between any two fuel tanks regardless of what's in between them. Actually that doesn't depending on whether you're docked or not. Docking is just a way how to make one large ship from two smaller.

Swapping the center rocket engine for jet engine is a good idea because high in the atmosphere you can fly on single jet and when it flameouts it will not put your plane to a spin.

You can, however, also keep your current design and fix the problem by adding more fuel pipes. There's a myth that fuel loops cause disasters, but when you know what you are doing, they can be very powerful.

Edited January 10, 2014 by Kasuha

[numerobis]

Thank you for that information. Especially about how KSP processes intake air. I am not too happy about this solution (although its probably all I can do) because I want my plane to be very fast when inside an atmosphere.

I suspect you can fly level around 28km altitude, one-third throttle, about 1400 m/s, and about a 20-degree pitch. From there, the single rocket engine will easily boost you up to orbit. If you want to go faster, add intakes.

Your payload is pretty light; you could easily leave two of your turbojet engines behind, which would save 10% of your mass. That means you can go slightly faster on the jets, and you don't need as much rocket fuel. I'd even fly it with just one turbojet, but that gets trickier.