So the new Drain Valve produces thrust ... and is quite broken.

[lajoswinkler]

2 hours ago, Starman4308 said:

1) Other than the intake air thing which is clearly the result of a typo, it can't really be considered cheating due to the rubbish Isp of the drain valve. Possibly funny if you set the drain rate crazily high and flip your rocket that way, but you'll use up tremendous amounts of fuel that way. The unlimited drain rate is funny, but hardly OP except in extremely narrow circumstances where even Sepratrons wouldn't give you enough TWR, and you don't mind blowing all your fuel in less than a second.

2) Substantially simpler and less prone to impinge on the tank is... symmetrical vents.

3) I play RO. With RTGs that decay. Please don't lump everybody together.

Dude, you can enter orbit with those things. It's safe to say it's preposterously overpowered.

I can put four Mainsails in a symmetrical fashion on a tank, too. It doesn't make them a good choice of fuel drains.

Not lumping, just showing some funny double standards that keep creeping on the forum.

[Zeiss Ikon]

5 hours ago, Lisias said:

anyway, there's always the old and faithful Tac Fuel Balance for this function, if you prefer resources (including ore) to just vanish from the tank.

There's also Ship Manifest, that lets you dump both resources and waste products (it's set up for use with a life support mod like TAC LS).  No thrust from Ship Manifest dumping, say, Jet Fuel; the drains are just abstracted away.

[Arugela]

Is the, "bug," in anyway proportional to the air intake(s), or just the tank size?

Edited February 16, 2020 by Arugela

[Xurkitree]

Quick note: The reason I ran a test while overclocking the drain valve was to show that ISP could be affected by drain rate - my initial assumption was that it was not affected by drain rate and any loss was due to gravity.

[Starman4308]

4 hours ago, lajoswinkler said:

Dude, you can enter orbit with those things. It's safe to say it's preposterously overpowered.

I can put four Mainsails in a symmetrical fashion on a tank, too. It doesn't make them a good choice of fuel drains.

Not lumping, just showing some funny double standards that keep creeping on the forum.

Please read and comprehend my posts. I have at no point stated that drain valves operating on intake air is a good thing; on the contrary, I have repeatedly expressed that it is a bug and needs to be fixed.

Other than that bug, though, I don't see any huge issues. The drain-valves-to-orbit thing has clearly been primarily a result of intake air shenanigans that were unintentional on Squad's part from the start.

[Superfluous J]

Disclaimer: I've not tried this - or even loaded 1.9 - myself. I'm going by what people are saying.

From what I can tell there are two actual bugs. Intake Air has a typo so it can be vented when it shouldn't, and the cap on how quickly you can vent (and therefore the thrust you get) is not present when using the KAL9000 part.

Seems like two minor oversights. Or as software professionals refer to it, a release.

[Kerbart]

5 hours ago, lajoswinkler said:

I can put four Mainsails in a symmetrical fashion on a tank, too. It doesn't make them a good choice of fuel drains.

I dunno. You'll drain any tank in seconds with that. Sounds pretty good to me.

[έķ νίĻĻάίή]

On 2/15/2020 at 7:25 AM, Xurkitree said:

When I attached just 2 to a Kerbodyne large tank, it shot up in the air, and built up massive acceleration towards the end

Ooh boy Danny2462 is gonna go crazy on this one

[Starman4308]

14 hours ago, Xurkitree said:

Quick note: The reason I ran a test while overclocking the drain valve was to show that ISP could be affected by drain rate - my initial assumption was that it was not affected by drain rate and any loss was due to gravity.

I'm actually wondering if what you're seeing is actually just a numerical error caused by discrete time steps.

Let's say you have a rocket engine with an exhaust velocity of 3000 m/s and a full:empty ratio of 2:1. You get 2,079 m/s out of that.

Now, let's say you have a mass driver that accelerates half of your ship to 3000 m/s. You impart -3000 m/s to that chunk, and since the masses are equal, you impart +3000 m/s to your ship. You've ejected the same mass out of your ship at the same relative velocity... but gained nearly 50% more dV.

All else equal, throwing large chunks of mass out the back is preferable to a steady stream, because with a rocket, some of your impulse is "wasted" on the propellant about to go through the nozzle, whereas with a mass driver, that comes out all at once.

How this applies to drain valves with crazy drain rates? Well, if you drain your entire tank in a half-second and you have the default 0.04 sec/tick, you are throwing the mass of your tank out the back in 12.5 discrete chunks like a mass driver rather than in a steady stream. There's a substantial time discretization error that becomes worse the faster you drain your tanks.

[Ericwi]

Will it be fixed or will it be a feature?

 

[Starman4308]

On 2/16/2020 at 3:05 PM, Ericwi said:

Will it be fixed or will it be a feature?

 

The intake air drain error has indeed been fixed in 1.9.1. I'm unsure about the KAL issue, but that's a very niche thing in any event.