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[BigFatStupidHead]

Hey, that's awesome! How are you dealing with the underwater camera problem?

Not very well.

On the plus side, underwater rovers+ Mk1 Cockpit= actually looks pretty neat.

Also, the sub behaves weirdly in regard to depth. Your 'buoyancy' has relatively little effect on the water's surface, and it takes some time to sink fully, especially if you have a lot of bits that, well, float. As long as you're barely underneath the surface, you can actually go around quite well and the sub tends to stay mostly horizontal. Once you get down lower, though, it's sort of like breaking surface tension: suddenly the 'buoyancy' becomes far more responsive, and the sub tends to go vertical one way or another, and usually starts heading down. The fact that the force exerted by the 'balloons' increases as you get lower may be part of the cause of this. There's also the fact that those winglets in the back do generate lift and tend to point you in the direction of travel, something not always preferable. 

Oh, and if you roll enough you go forwards XD

In short:

Boating on surface: controllable just fine.
Subbing just under the surface: reasonably controllable.
Going at depth: Can be difficult to control.
Roving underwater: you have traction.

Hmm... Because buoyancy is a plugin, it could be added to all your sub parts to allow for uniform negative buoyancy across the sub; this -might- help with some control issues. And I wonder if a sub that is tall rather than wide would work better.

  How well do the jets work underwater? Snjo's Firespitter parts have props that can supply thrust based on atmosphere density, so these may give you a bit more bang for your fuel-budget.

Finally, how did you modify for negative buoyancy? I haven't dissected that mod in any way well enough to know if I could do it myself. Thanks!

[jocan2003]

This little link will give you the best terminal velocity at multiple athmospheric stage. This table reflect the most efficient grav/drag velocity.

Edit: Brain fart. http://wiki.kerbalspaceprogram.com/wiki/Kerbin#Atmosphere

[Girlinhat]

This little link will give you the best terminal velocity at multiple athmospheric stage. This table reflect the most efficient grav/drag velocity.

What link?

[Nao]

Submarines!

Awesome!
The old Hyperedit had "submarine" mode which zeroed buoyancy out. It was quite fun to swim around but the camera problems were a killer . Idk if the newer hyperedit has this option since it dropped a bunch of them some time ago. I think i have it uploaded somewhere, if you are interested i can finding and posting it. (most features still work on 0.19)

Why is a TWR of 2 ideal?

Maybe this little link can help you. It has a chart and not super hard math in it.

[ank]

Note that the equations in the link says that TWR=2 is only desirable when you are already at terminal velocity, a=0.

To actually use the equations we have to test a craft to find it's terminal velocity, or drag factor(either will do), next you will have to do a separate calculation for each moment of the flight, with the changing mass.

The calculations also simplify the drag coefficient to b, when it's really A*d (where A is the atmospheric pressure and d is the drag "number"(which again is simplified from a*d))
So this does not account for the fact that once you move fast enough to actually throttle down, the atmosphere is only 80% of ground level.

We'd need to throw at least 2 integrals on top of this, and plug in the rocket equation, to get the right answer.

Which is why the link does not give any usable calculations, because more maths is needed!



Also this "Y represents the required mass fraction of engines fuel and fuel tanks to reach mun orbit."
what the hell is a mass fraction of engines !?

[Twi]

Hey, that's awesome! How are you dealing with the underwater camera problem?

Not very well.

On the plus side, underwater rovers+ Mk1 Cockpit= actually looks pretty neat.

Also, the sub behaves weirdly in regard to depth. Your 'buoyancy' has relatively little effect on the water's surface, and it takes some time to sink fully, especially if you have a lot of bits that, well, float. As long as you're barely underneath the surface, you can actually go around quite well and the sub tends to stay mostly horizontal. Once you get down lower, though, it's sort of like breaking surface tension: suddenly the 'buoyancy' becomes far more responsive, and the sub tends to go vertical one way or another, and usually starts heading down. The fact that the force exerted by the 'balloons' increases as you get lower may be part of the cause of this. There's also the fact that those winglets in the back do generate lift and tend to point you in the direction of travel, something not always preferable. 

Oh, and if you roll enough you go forwards XD

In short:

Boating on surface: controllable just fine.
Subbing just under the surface: reasonably controllable.
Going at depth: Can be difficult to control.
Roving underwater: you have traction.

Hmm... Because buoyancy is a plugin, it could be added to all your sub parts to allow for uniform negative buoyancy across the sub; this -might- help with some control issues. And I wonder if a sub that is tall rather than wide would work better.

  How well do the jets work underwater? Snjo's Firespitter parts have props that can supply thrust based on atmosphere density, so these may give you a bit more bang for your fuel-budget.

Finally, how did you modify for negative buoyancy? I haven't dissected that mod in any way well enough to know if I could do it myself. Thanks!

1: That's what I did, as it happens. Well, at least all of the fuselages. And maybe.
2:  Just fine, really. I might try it though. It would remove the need for silly air intakes.
3. Well, the equation of buoyant force is the density of the fluid (which makes sense- it's easier to float in denser stuff, right?) times the volume displaced by the object times the acceleration of gravity. The Hooligan Labs airships have an (effective) volume stat used for calculating said buoyancy. Edit it to be negative and you have negative buoyancy. Surprisingly, it doesn't crash the game, although it certainly seems to confuse the GUI showing net force and would probably make altitude control mode fail horribly. Also, strangely, I'm not sure the exact stat matters that much, as long as its negative. I'm guessing water really is stupidly dense in KSP.

[da_nang]

Spoiler: Second Populator arriving at Eve (click to show/hide)

I pulled a wonderful aerobrake maneuver that let me land with rocket fuel.

Spoiler: New rover at Colonial I-NA Munbase (click to show/hide)

[jocan2003]

This little link will give you the best terminal velocity at multiple athmospheric stage. This table reflect the most efficient grav/drag velocity.

What link?

Sorry had a brain fart... http://wiki.kerbalspaceprogram.com/wiki/Kerbin#Atmosphere

[Nao]

Note that the equations in the link says that TWR=2 is only desirable when you are already at terminal velocity, a=0.

To actually use the equations we have to test a craft to find it's terminal velocity, or drag factor(either will do), next you will have to do a separate calculation for each moment of the flight, with the changing mass.

The calculations also simplify the drag coefficient to b, when it's really A*d (where A is the atmospheric pressure and d is the drag "number"(which again is simplified from a*d))
So this does not account for the fact that once you move fast enough to actually throttle down, the atmosphere is only 80% of ground level.

We'd need to throw at least 2 integrals on top of this, and plug in the rocket equation, to get the right answer.

Which is why the link does not give any usable calculations, because more maths is needed!



Also this "Y represents the required mass fraction of engines fuel and fuel tanks to reach mun orbit."
what the hell is a mass fraction of engines !?

Yep, the calculations are simplified, but show why 2 and not infinity or 1 (that was my goal here). Getting better model will not give much better efficiency anyways due to part and control limitations. Mechjeb's ascent autopilot covers some of the advanced math, so it uses ~2,1 TWR on kerbin.

The fraction was used because i wanted the chart to be applicable to any ship. The Y axis effectively corresponds to launch mass needed to get specific cargo mass in orbit (1-(cargo_mass_[kg]/launch_mass_[kg]))*100% cargo mass being 1000kg in my trials.
I'm not really good at math nor english, so its probably not the proper way to show data, but im trying to get better as i go with this

[jocan2003]

As far as english goes you are handling yourself very well, much better than i do ( im french ).

[Twi]

SSTO's are hard :<

With this in mind, I'd like to show off one of my latest attempts! Well, one of my earlier things that I looked at and said 'hmm, maybe this could SSTO, y'know?"

So I brought up the Recettear! Being named after a game I desperately need to play (DX ), it is a two-man tailsitter VTOL spaceplane.

Unfortunately, I then realized something: It doesn't quite have enough TWR to get off the ground with jets alone. Needless to say, this is silly, so I strapped some SRBS to the side, instantly disqualifying it from being an SSTO. But hey. SRBs are cheap.

Spoiler: Takeoff roll! (click to show/hide)

It does a bit better once it's at altitude.

Spoiler: Go go gadget spaceplane! (click to show/hide)

THen the time came to transition from jets to rockets and things got... harrowing.

Spoiler: Control is hard, featuring pointing the wrong way (click to show/hide)

It didn't have enough delta-v to make a stable orbit...

Spoiler: Fun fact: the maneuver node does not result in a stable orbit. (click to show/hide)

On the plus side, awesome reentry pics were had.

Spoiler:  We didn't start the fire~ (click to show/hide)

Eventually, I went  in for a landing.

Spoiler: see above (click to show/hide)

And then the parachutes ripped the cockpit off. AGAIN.

RIP Jebediah Kerman #9261. Your temporary death was not in vain.

Spoiler: forgetting something? (click to show/hide)

On a side note, the unpiloted remains hit the ground softly-ish, but fell over and broke apart. Jeb's co-pilot would have survived, though.

[ank]

@Nao
Yeah your English is fine.

I see how the graph works now, and I can see your point that adding more engines after a certain point will just make the craft heavier.

The thing is that infinite boost at liftoff will still be optimal, IF you don't count the mass of the engines.(but we do)
What you should really take away from this is that you should never throttle down on a moon ascend(besides for steering purposes), but strapping on 5 more engines is not gonna make your ascend any more efficient.

[Sean Mirrsen]

Until after a point, perhaps. More engines will certainly reduce your gravity losses as you get out of the gravity well faster (without an atmosphere present), but yeah - extra mass reduces your Delta-V in space. You have to scale your design so that it has enough engines to lift off anywhere it is supposed to lift off as fast as possible, yet still not so many engines that it doesn't have enough delta-v to get anywhere.

[ank]

But extra engines will also add to the gravity loss, because they add mass.

What we need to do is find the Dv needed for a Mun ascend, plug it into the rocket equation, then use differential calculus to find the optimal engine weight.
Or you can just fucking take off from the Mun, without any maths, since it's so easy

Also remember that the TWR=2 has no relation to a Mun ascend, since there is no atmosphere, and the Mun only has about 0,165 G.

[Sean Mirrsen]

Yep. Though a Mun TWR of 2 is vastly different from a Kerbin TWR of 2, and taking off from the Mun with a Kerbin TWR of 2 is pretty damn efficient.